CA2600740C

CA2600740C - Discharge pressure actuated pump

Info

Publication number: CA2600740C
Application number: CA2600740A
Authority: CA
Inventors: Grant Duncan
Original assignee: Suncor Energy Inc
Current assignee: Suncor Energy Inc
Priority date: 2006-09-11
Filing date: 2007-09-07
Publication date: 2014-01-28
Anticipated expiration: 2027-09-07
Also published as: CA2600740A1

Abstract

A pump has a pump barrel formed from a larger diameter section and a smaller diameter section. Each section has a biased piston moveable within the section and the pistons are connected together to form a variable volume chamber between the pistons. As the connected pistons move toward the larger diameter section, a volume of fluid is moved through an inlet valve into the variable volume chamber of increasing volume. When the pistons are moved toward the smaller diameter section, a differential volume of fluid is discharged from the variable volume chamber of decreasing volume through a discharge valve into a discharge conduit. The pistons are actuated to move within the pump barrel by application and release of pressure at a remote end of the discharge conduit.

Description

1 "DISCHARGE PRESSURE ACTUATED PUMP"

2

3 FIELD OF THE INVENTION

4 Embodiments of the invention are related to pumps and more particularly to single conduit pumps for use in locations remote from the pump's 6 discharge including being located in wellbores, the pumps being actuated 7 remotely such as by cycling pressure at the discharge of the pump.

Pumps are well known to move fluids from at least a first location to 11 a second location. A large number of pump configurations are known, each with 12 particular advantages and disadvantages and which may have been designed 13 for particular uses in a variety of fluid-moving industries.
14 It is well known to provide pumping apparatus situated in subterranean wellbores for pumping fluid therefrom to the surface.
16 Conventionally, a prime mover, such as an electric motor, has been located at 17 the pump or mechanically connected thereto so as to permit actuation of pumps, 18 such as a rod pump or progressive cavity pump, to lift liquids such as produced 19 fluids and accumulated fluids therefrom. In the case of wellbores, particularly those situated in remote locations, it is desirable to situate the pump within the 21 wellbore and to actuate the pump remotely. Typically, many of the pumps known 22 in the art require two conduits, one to provide a motive force to operate the 23 pump, such as in the case of hydraulic-actuated pumps, and the second to 24 permit production of the fluids to surface.

1 In the case of said wellbores, it is known to provide remotely 2 actuated pumps, such as those which are actuated by sonic or acoustic pressure 3 waves (US
Patent 4,295,799 to Bentley, US Patent 1,730,336 to Bellocq, US
4 Patents 2,444,912, 2,553,541, 2,553,042, 2,553,043, and 2,953,095, to Bodine Jr.) 6 Further it is known to provide remotely actuated pumps which are 7 actuated by alternately applying and releasing pressure at discharge of the 8 pump. One such pump is taught in US Patent 4,390,326 to Callicoate which 9 teaches an annular external piston and an internal piston movable in concentric annular and internal chambers. The internal chamber has an inlet end and an 11 outlet end fit with one-way valves. The internal piston divides an internal barrel 12 into a lower chamber and an upper chamber. The lower chamber has an inlet 13 valve and an outlet valve through which pumped fluid is transferred to the upper 14 chamber. The upper chamber has an outlet valve through which fluids are transferred into conduit thereabove. As the pump is stroked, fluid from below the 16 pump is sucked into the lower chamber on the upstroke. On the downstroke, the 17 fluid in the lower chamber is transferred to the upper chamber through the valve 18 positioned therebetween. On the next upstroke, while fluid is being drawn into 19 the lower chamber, the fluid in the upper chamber is transferred from the space above, through the upper chamber's outlet valve, while the external piston 21 causes the fluid in the space above to be pumped to surface. Pressure is applied 22 cyclically to the conduit causing the pistons to be moved downhole. An energy 23 storing means, such as a spring, returns the pistons uphole as the pressure is 24 relieved at the conduit discharge.

1 Remotely actuated pumps are particularly advantageous for use in 2 oil wells to produce hydrocarbons to surface and for deliquification of gas wells, 3 wherein the pump can be situated at or near the perforations, and can be 4 actuated to pump accumulated liquids such as water and condensate, to surface which, if left to accumulate in the conduit through which the gas is produced 6 causes backpressure on the formation which impedes gas flow and which may 7 eventually kill gas production.
8 In the case of deliquification of gas wells, conventionally beam 9 pumps or hydraulic pumps, including piston downhole pumps and jet pumps have been used, as have electric submersible pumps and progressive cavity 11 pumps however the cost of these pumps is relatively high. Regardless the use, 12 providing power for actuation of such pumps in remote locations, size of the 13 pumps and interference due to produced gas during use in deliquification have 14 typically been problematic.
Further, other technologies such as foam lift, gas lift and plunger lift 16 have been used to deliquify gas wells. In some of the known technologies, the 17 gas well must be shut-in for at least a period of time to permit sufficient energy to 18 be built up to lift the accumulated fluids which results in, at best, a cyclic 19 production of gas from the wellbore.
Clearly, there is interest in a large variety of fluid-moving industries 21 or technologies, including pumping apparatus, which have relatively low power 22 requirements, are capable of being remotely actuated and which have a 23 relatively high pumping efficiency. Of particular interest are pump apparatus for 24 use in producing fluids from wellbores, including but not limited to deliquifying of gas wells to improve and maintain production therefrom.

SUMMARY OF THE INVENTION
In accordance with one aspect of the invention there is provided a fluid apparatus including a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit. The first barrel section has a diameter greater than the second barrel section, the first and second barrel sections being fluidly connected therebetween. The apparatus includes a first piston housed in the first barrel section for axial movement therein and a second piston housed in the second barrel section for axial movement therein. The apparatus also includes connecting provisions between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position, the first and second pistons being spaced apart for forming a chamber of variable volume therebetween. The apparatus also includes biasing provisions for biasing the first and second pistons to the discharge position, an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber, and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit. The apparatus also includes a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit.
The bypass passageway forms a second chamber fluidly connected to the variable volume chamber, wherein the inlet check valve is positioned at the inlet end of the bypass passageway and the outlet check valve is positioned at the outlet end of the bypass passageway. When an actuating pressure sufficient to overcome the biasing provisions is applied to the second piston through the discharge conduit, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve into the variable volume chamber.
When the actuating pressure is released, the biasing provisions return the first and second pistons to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the outlet valve to the discharge conduit.
In accordance with another aspect of the invention there is provided a method for producing accumulated liquids from a gas well involving positioning a fluid apparatus in the wellbore and forming an annulus therebetween. The apparatus includes a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit. The first barrel section has a diameter greater than the second barrel section, the first and second barrel sections being fluidly connected therebetween. The apparatus also includes a first piston housed in the first barrel section for axial movement therein, a second piston housed in the second barrel section for axial movement therein, and a connector between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position. The first and second pistons are spaced apart for forming a chamber of variable volume therebetween. The first and second pistons are biased to the discharge position.
The apparatus also includes an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit. The apparatus also includes a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit. The bypass passageway forms a second chamber fluidly connected to the variable volume chamber, wherein the inlet check valve is positioned proximate the inlet end of the bypass passageway and the outlet check valve is positioned proximate the outlet end of the bypass passageway.
When an actuating pressure, sufficient to overcome a biasing force, is applied to the second piston through the discharge conduit, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve and the bypass passageway into the variable volume chamber. When the actuating pressure is released, the first and second pistons are biased to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the bypass passageway to the discharge conduit. The method also involves producing gas to surface through the annulus, with liquid accumulating in the wellbore adjacent the distal end of the conduit. The method also involves cyclically applying an actuating pressure at the discharge conduit such that when the force of the actuating pressure is greater than the force exerted by the biasing provisions and a force of pressure at the fluid source, the discharge valve operates to the closed position, the first and second pistons move to the inlet position, and the inlet valve operates to the open position for charging the accumulated fluids from the wellbore into the variable volume chamber. The method also involves releasing the actuating pressure so that the first and second pistons are biased to return to the discharge position, the inlet valve moving to the closed position, the discharge valve moving to the open position and pumping the differential volume from the variable volume chamber through the discharge valve to the discharge conduit.
In accordance with another aspect of the invention there is provided a fluid apparatus. The apparatus includes a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit, a first piston housed in the first barrel section for axial movement therein and a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit. The first and second pistons define a variable volume chamber between the first and second pistons. The apparatus also includes a biasing element coupled to at least one of the first and second pistons, an inlet check valve operable to permit fluid to flow from the fluid source into the variable volume chamber, and an outlet check valve operable to permit fluid to flow from the variable volume chamber into the discharge conduit. The apparatus also includes a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit, the bypass passageway being in fluid communication with the variable volume chamber, and wherein the inlet check valve is disposed at the inlet end of the bypass passageway and operable to permit fluid to flow through the bypass passageway into the variable volume chamber, and the outlet check valve is positioned at the outlet end of the bypass passageway and operable to permit fluid to be discharged from the variable volume chamber through the bypass passageway. The apparatus also includes provisions for connecting the first and second pistons to cause movement of the first piston in response to movement of the second piston caused by the actuating pressure.
The respective movements of the first and second pistons are operable to increase the volume of the variable volume chamber thereby drawing fluid into the variable volume chamber through the inlet check valve while causing energy to be stored in the biasing element. The stored energy in the biasing element is subsequently operable to cause respective return movement of the first and second pistons when the actuating pressure is decreased. The respective return movements of the first and second pistons are operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the variable volume chamber through the outlet check valve.
In accordance with another aspect of the invention there is provided a fluid apparatus. The apparatus includes a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit. The apparatus also includes a first piston housed in the first barrel section for axial movement therein, a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit, the first and second pistons defining a variable volume chamber between the first and second pistons. The apparatus also includes a biasing element coupled to at least one of the first and second pistons, an inlet check valve operable to permit fluid to flow from the fluid source into the variable volume chamber, and an outlet check valve operable to permit fluid to flow from the variable volume chamber into the discharge conduit. The apparatus also includes a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit. The bypass passageway is in fluid communication with the variable volume chamber, wherein the inlet check valve is disposed at the inlet end of the bypass passageway and is operable to permit fluid to flow through the bypass passageway into the variable volume chamber, and the outlet check valve is positioned at the outlet end of the bypass passageway and is operable to permit fluid to be discharged from the variable volume chamber through the bypass passageway. The apparatus also includes a connector between the first and second pistons. The connector is operably configured to cause movement of the first piston in response to movement of the second piston caused by the actuating pressure. The respective movements of the first and second pistons are operable to increase the volume of the variable volume chamber thereby drawing fluid into the variable volume chamber through the inlet check valve while causing energy to be stored in the biasing element.
The stored energy in the biasing element is subsequently operable to cause respective return movement of the first and second pistons when the actuating pressure is decreased. The respective return movements of the first and second pistons are operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the variable volume chamber through the outlet check valve.
In accordance with another aspect of the invention there is provided a method for producing accumulated liquids from a gas well. The method involves positioning a fluid apparatus in a wellbore and forming an annulus therebetween. The fluid apparatus includes a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit. The apparatus also includes a first piston housed in the first barrel section for axial movement therein and a second piston housed in the second barrel section for axial movement therein. The first and second pistons define a variable volume chamber between the first and second pistons. The apparatus also includes a biasing element coupled to at least one of the first and second pistons, an inlet check valve operable to permit fluid to flow from the fluid source to the variable volume chamber and an outlet check valve operable to permit fluid to flow from the variable volume chamber to the discharge conduit. The apparatus also includes a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit. The bypass passageway is in fluid communication with the variable volume chamber, wherein the inlet check valve is disposed at the inlet end of the bypass passageway and is operable to permit fluid to flow through the bypass passageway into the variable volume chamber and the outlet check valve is disposed at the outlet end of the bypass passageway and is operable to permit fluid to be discharged from the variable volume chamber through the bypass passageway. The apparatus also includes a connector between the first and second pistons. The connector is operably configured to cause movement of the first piston in response to movement of the second piston. The method also involves producing gas to surface through the annulus to cause liquid to accumulate in the wellbore adjacent the distal end of the conduit and cyclically applying an actuating pressure at the discharge conduit to cause the first and second pistons to move to increase the volume of the variable volume chamber thereby drawing accumulated liquid into the variable volume chamber through the inlet check valve while causing energy to be stored in the biasing element. The method also involves releasing the actuating pressure to permit the stored energy in the biasing element to cause respective return movement of the first and second pistons. The respective return movements of the first and second pistons are operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the variable volume chamber through the outlet check valve to the discharge conduit.
In accordance with another aspect of the invention there is provided a fluid apparatus. The apparatus includes a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit, a first piston housed in the first barrel section for axial movement therein and a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit. The first and second pistons define a variable volume chamber between the first and second pistons. The apparatus also includes a biasing element coupled to at least one of the first and second pistons and a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit. The bypass passageway is in fluid communication with the variable volume chamber through at least one port. The bypass passageway further includes first one-way valve provisions for permitting one-way fluid flow into the bypass passageway, the first one-way valve provisions being operable to facilitate fluid flow from the inlet end, through the at least one port, into the variable volume chamber. The bypass passageway also includes second one-way valve provisions for permitting one-way fluid flow out of the bypass passageway. The second one-way valve provisions are operable to facilitate fluid flow from the variable volume chamber, through the at least one port, and out the outlet end into the discharge conduit. The apparatus also includes a connector between the first and second pistons. The connector is operably configured to cause movement of the first piston in a first axial direction in response to movement of the second piston in the first axial direction caused by the actuating pressure. The respective movements of the first and second pistons in the first axial direction is operable to increase the volume of the variable volume chamber thereby drawing fluid into the variable volume chamber through the first one-way valve provisions while causing energy to be stored in the biasing element. The stored energy in the biasing element is subsequently operable to cause respective movement of the first and second pistons in a second axial direction, opposite to the first axial direction. When the actuating pressure is decreased, the respective movement of the first and second pistons in the second axial direction is operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the variable volume chamber, through the second one-way valve provisions, and into the discharge conduit.

In accordance with another aspect of the invention there is provided a fluid apparatus. The apparatus includes a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit. The first barrel section has a diameter greater than the second barrel section. The first and second barrel sections are fluidly connected therebetween. The apparatus includes a first piston housed in the first barrel section for axial movement therein, a second piston housed in the second barrel section for axial movement therein and provisions connecting between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position. The first and second pistons are spaced apart for forming a chamber of variable volume therebetween. The apparatus includes biasing provisions for biasing the first and second pistons to the discharge position, wherein the biasing provisions are positioned within the second barrel. The apparatus also includes an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit. When an actuating pressure sufficient to overcome the biasing provisions is applied to the second piston through the discharge conduit, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve into the variable volume chamber. When the actuating pressure is released, the biasing provisions returns the first and second pistons to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the outlet valve to the discharge conduit.
In accordance with another aspect of the invention there is provided a fluid apparatus. The apparatus includes a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit. The apparatus also includes a first piston housed in the first barrel section for axial movement therein and a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit. The first and second pistons define a variable volume chamber between the first and second pistons. The apparatus also includes a biasing element coupled to the second piston and at least partially located in the second barrel section, an inlet check valve operable to permit fluid to flow from the fluid source into the variable volume chamber, and an outlet check valve operable to permit fluid to flow from the variable volume chamber into the discharge conduit. The apparatus also includes provisions for connecting the first and second pistons to cause movement of the first piston in response to movement of the second piston caused by the actuating pressure. The respective movements of the first and second pistons are operable to increase the volume of the variable volume chamber thereby drawing fluid into the variable volume chamber through the inlet check valve while causing energy to be stored in the biasing element. The stored energy in the biasing element is subsequently operable to cause respective return movement of the first and second pistons when the actuating pressure is decreased. The respective return movements of the first and second pistons are operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the variable volume chamber through the outlet check = =
valve.
In accordance with another aspect of the invention there is provided a fluid apparatus. The apparatus includes a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit. The first barrel section has a diameter greater than the second barrel section. The first and second barrel sections are fluidly connected therebetween. The apparatus also includes a first piston housed in the first barrel section for axial movement therein, a second piston housed in the second barrel section for axial movement therein, and a connector between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position. The first and second pistons are spaced apart for forming a chamber of variable volume therebetween. The first and second pistons are biased to the discharge position by biasing provisions. The apparatus also includes an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit. When an actuating pressure is applied to the second piston through the discharge conduit sufficient to overcome a biasing force applied by the biasing provisions to the first and second pistons, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve into the variable volume chamber. When the actuating pressure is released, the first and second pistons are biased to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the outlet valve to the discharge conduit. The biasing provisions include a liquid spring comprising a sealed spring chamber, a compressible fluid stored in the sealed spring chamber, and a displacing element operatively connected to the first and second pistons for reducing the volume of the sealed spring chamber when the connected first and second pistons are moved to the inlet position and for biasing the first and second pistons to the discharge position.
In accordance with another aspect of the invention there is provided a fluid apparatus. The apparatus includes a pump barrel forming at least a portion of a sealed spring chamber for containing a compressible fluid and having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit. The apparatus also includes a first piston housed in the first barrel section for axial movement therein and a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit. The first and second pistons define a variable volume chamber between the first and second pistons. The apparatus also includes a liquid spring biasing element including the sealed spring chamber and a displacing element received in the sealed spring chamber for reducing the volume of the sealed spring chamber. The displacing element is coupled to at least one of the first and second pistons. The sealed spring chamber includes a portion of the first barrel section of the pump barrel. The apparatus also includes an inlet check valve operable to permit fluid to flow from the fluid source into the variable volume chamber, an outlet check valve operable to permit fluid to flow from the variable volume chamber into the discharge conduit, and a connector between the first and second pistons. The connector is operably configured to cause movement of the first piston in response to movement of the second piston caused by the actuating pressure. The respective movements of the first and second pistons are operable to increase the volume of the variable volume chamber thereby drawing fluid into the chamber through the inlet check valve while causing energy to be stored in the liquid spring biasing element. The stored energy in the liquid spring biasing element is subsequently operable to cause respective return movement of the first and second pistons when the actuating pressure is decreased. The respective return movements of the first and second pistons are operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the chamber through the outlet check valve.
In accordance with another aspect of the invention there is provided a method for producing accumulated liquids from a gas well. The method involves positioning a fluid apparatus in a wellbore and forming an annulus therebetween. The fluid apparatus includes a pump barrel forming at least a portion of a sealed spring chamber for containing a compressible fluid and having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit, a first piston housed in the first barrel section for axial movement therein and a second piston housed in the second barrel section for axial movement therein. The first and second pistons define a variable volume chamber between the first and second pistons. The apparatus also includes a liquid spring biasing element comprising the sealed spring chamber and a displacing element received in the sealed spring chamber for reducing the volume of the sealed spring chamber. The displacing element is operably coupled to at least one of the first and second pistons. The sealed spring chamber includes a portion of the first barrel section of the pump barrel. The apparatus also includes an inlet check valve operable to permit fluid to flow from the fluid source to the variable volume chamber, an outlet check valve operable to permit fluid to flow from the variable volume chamber to the discharge conduit and a connector between the first and second pistons, the connector being operably configured to cause movement of the first piston in response to movement of the second piston. The method also involves producing gas to surface through the annulus, while liquid is accumulating in the wellbore adjacent a distal end of the conduit. The method also involves cyclically applying an actuating pressure at the discharge conduit to cause the first and second pistons to move to increase the volume of the variable volume chamber thereby drawing accumulated liquid into the chamber through the inlet check valve while causing energy to be stored in the liquid spring biasing element.
The method also involves releasing the actuating pressure to permit the stored energy in the liquid spring biasing element to cause respective return movement of the first and second pistons. The respective return movements of the first and second pistons are operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the chamber through the outlet check valve to the discharge conduit.
In accordance with another aspect of the invention there is provided a fluid apparatus. The apparatus includes a pump barrel forming at least a portion of a sealed spring chamber configured to contain a compressible fluid and having a first barrel section proximate the sealed spring chamber and in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit. The apparatus also includes a first piston housed in the first barrel section for axial movement therein, a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit. The first and second pistons define a variable volume chamber between the first and second pistons. The apparatus also includes a liquid spring biasing element comprising the sealed spring chamber and a displacing element received in the sealed spring chamber for reducing the volume of the sealed spring chamber.
The displacing element is coupled to at least one of the first and second pistons.
The apparatus includes an inlet check valve operable to permit fluid to flow from the fluid source into the variable volume chamber, an outlet check valve operable to permit fluid to flow from the variable volume chamber into the discharge conduit and a connector between the first and second pistons. The connector is operably configured to cause movement of the first piston in response to movement of the second piston caused by the actuating pressure. The respective movements of the first and second pistons are operable to increase the volume of the variable volume chamber thereby drawing fluid into the chamber through the inlet check valve while causing energy to be stored in the liquid spring biasing element. The stored energy in the liquid spring biasing element is subsequently operable to cause respective return movement of the first and second pistons when the actuating pressure is decreased. The respective return movements of the first and second pistons are operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the chamber through the outlet check valve.
In accordance with another aspect of the invention there is provided a fluid apparatus. The apparatus includes a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit, a first piston housed in the first barrel section for axial movement therein and a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit. The first and second pistons define a variable volume chamber between the first and second pistons. The apparatus also includes a biasing element coupled to at least one of the first and second pistons. The biasing element includes a liquid spring including a sealed chamber operable to hold a compressible fluid and a displacing element operable to be received in the sealed chamber to reduce the volume thereof. The displacing element includes a spring rod received in the sealed chamber and adapted to avoid buckling when an unsupported free end of the spring rod is maximally extended into the sealed chamber during operation. The apparatus also includes an inlet check valve operable to permit fluid to flow from the fluid source into the variable volume chamber, an outlet check valve operable to permit fluid to flow from the variable volume chamber into the discharge conduit and a connector between the first and second pistons. The connector is operably configured to cause movement of the first piston in response to movement of the second piston caused by the actuating pressure. The respective movements of the first and second pistons are operable to increase the volume of the variable volume chamber thereby drawing fluid into the chamber through the inlet check valve while causing energy to be stored in the biasing element. The stored energy in the biasing element is subsequently operable to cause return movement of the first and second pistons when the actuating pressure is decreased. The return movements of the first and second pistons are operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the chamber through the outlet check valve.
In accordance with another aspect of the invention there is provided a fluid apparatus including a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit. The first barrel section has a diameter greater than the second barrel section and the first and second barrel sections are fluidly connected therebetween. The apparatus also includes a first piston housed in the first barrel section for axial movement therein, a second piston housed in the second barrel section for axial movement therein and provisions connecting between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position, the first and second pistons being spaced apart for forming a chamber of variable volume therebetween. The apparatus also includes biasing provisions for biasing the first and second pistons to the discharge position, wherein the biasing provisions comprises a liquid spring, an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber, and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit. When an actuating pressure sufficient to overcome the biasing provisions is applied to the second piston through the discharge conduit, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve into the variable volume chamber. When the actuating pressure is released, the biasing provisions returns the first and second pistons to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the outlet valve to the discharge conduit.
In accordance with another aspect of the invention there is provided a method for producing accumulated liquids from a gas well. The method involves positioning a fluid apparatus in the wellbore and forming an annulus therebetween. The apparatus includes a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit. The first barrel section has a diameter greater than the second barrel section, the first and second barrel sections being fluidly connected therebetween. The apparatus includes a first piston housed in the first barrel section for axial movement therein, a second piston housed in the second barrel section for axial movement therein and a connector between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position. The first and second pistons are spaced apart for forming a chamber of variable volume therebetween and the first and second pistons are biased to the discharge position. The apparatus also includes an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit. When an actuating pressure, sufficient to overcome a biasing force, is applied to the second piston through the discharge conduit, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve into the variable volume chamber. When the actuating pressure is released, the first and second pistons are biased to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the outlet valve to the discharge conduit. The method also involves producing gas to surface through the annulus, liquid accumulating in the wellbore adjacent the distal end of the conduit. The method also involves applying an actuating pressure at the discharge conduit such that when the force of the actuating pressure is greater than the force exerted by the biasing provisions and a force of pressure at the fluid source. The discharge valve operates to the closed position, and the first and second pistons move to the inlet position and the inlet valve operates to the open position for charging the accumulated fluids from the wellbore into the variable volume chamber. The method also involves releasing the actuating pressure so that the first and second pistons are biased to return to the discharge position with the inlet valve moving to the closed position, the discharge valve moving to the open position and pumping the differential volume from the variable volume chamber through the discharge valve to the discharge conduit. The method also involves activating the fluid apparatus at predetermined intervals in response to data representing historical liquid accumulation for a particular reservoir type.
Generally, in exemplary embodiments, a fluid apparatus for moving fluid from a fluid source to a discharge incrementally pumps a differential volume of fluid due to a chamber having a variable volume formed between two connected pistons which are moveable axially within a pump barrel of stepped diameter.
In some embodiments, a fluid apparatus comprises: a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit, the first barrel section having a diameter greater than the second barrel section, the first and second barrel sections being fluidly connected therebetween; a first piston housed in the first barrel section for axial movement therein; a second piston housed in the second barrel section for axial movement therein; means connecting between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position, the first and second pistons being spaced apart for forming a chamber of variable volume therebetween; biasing means for biasing the first and second pistons to the discharge position; an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber; and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit, wherein when an actuating pressure sufficient to overcome the biasing means is applied to the second piston through the discharge conduit, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve into the variable volume chamber; and when the actuating pressure is released, the biasing means returns the first and second pistons to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the outlet valve to the discharge conduit.
In some embodiments, the biasing means can be housed within the variable volume chamber or in the pump barrel below the first piston and is connected between the pump barrel and one of either the first or second piston.

The inlet and discharge valves are positioned at an inlet end and a discharge end, respectively, of the pump pistons or alternately at an inlet and discharge end of a bypass passageway fluidly connected to the variable volume chamber.
Embodiments of the invention are used to move fluid from a source location to a discharge location and may be particularly advantageous for remote actuation in wellbores for deliquifying wellbores having an accumulation of liquid therein which reduces or potentially stops wellbore production.
Therefore in some embodiments, a method for producing accumulated liquids from a gas well comprises: positioning a fluid apparatus in the wellbore and forming an annulus therebetween, the apparatus having a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit, the first barrel section having a diameter greater than the second barrel section, the first and second barrel sections being fluidly connected therebetween; a first piston housed in the first barrel section for axial movement 1 therein; a second piston housed in the second barrel section for axial movement 2 therein; means connecting between the first and second pistons for concurrent 3 axial movement within the pump barrel between an inlet position and a discharge 4 position, the first and second pistons being spaced apart for forming a chamber of variable volume therebetween; biasing means for biasing the first and second 6 pistons to the discharge position; an inlet check valve to permit fluid to move 7 from the fluid source to the variable volume chamber; and an outlet check valve 8 to permit fluid to move from the variable volume chamber to the discharge 9 conduit, wherein when an actuating pressure sufficient to overcome the biasing means is applied to the second piston through the discharge conduit, the outlet 11 valve closes and the first and second pistons move to the inlet position and 12 increase the variable volume chamber by a differential volume, opening the inlet 13 valve and permitting the flow of the differential volume of fluid from the fluid 14 source through the inlet valve into the variable volume chamber; and when the actuating pressure is released, the biasing means returns the first and second 16 pistons to the discharge position for displacing the differential volume of fluid 17 from the variable volume chamber, closing the inlet valve and opening the outlet 18 valve for discharging the differential volume of fluid through the outlet valve to 19 the discharge conduit; producing gas to surface through the annulus, liquid accumulating in the wellbore adjacent the distal end of the conduit;
cyclically 21 applying an actuating pressure at the discharge conduit such that when the force 22 of the actuating pressure is greater than the force exerted by the biasing means 23 and a force of pressure at the fluid source, the discharge valve operates to the 24 closed position, the first and second pistons move to the inlet position and the inlet valve operates to the open position for charging the accumulated fluids from 1 the wellbore into the variable volume chamber; and releasing the actuating 2 pressure so that the first and second pistons are urged to return to the discharge 3 position, the inlet valve moving to the closed position, the discharge valve 4 moving to the open position and pumping the differential volume from the variable volume chamber through the discharge valve to the discharge conduit.

8 Figures 1A-1C
are partial longitudinal sectional views of a pump 9 according to an embodiment of the invention, first and second pistons positioned in a pump barrel connected to a single conduit and biasing means for storing 11 energy to return the pistons located below the first piston, more particularly, 12 Fig. 1A
illustrates an idle position wherein an outlet valve and an 13 inlet valve are in a closed position;
14 Fig. 1B
illustrates the first position wherein the first and second pistons are moved causing the inlet valve to open and a variable volume 16 chamber between the first and second pistons to be charged with fluid;
17 and 18 Fig. 1C
illustrates a second position wherein the first and second 19 pistons are moved causing the outlet valve to be be opened, the fluid being displaced from the variable volume chamber, pumping a differential 21 volume created by the variable volume chamber into the conduit above 22 the pump barrel;
23 Figure 1D is a cross sectional view along section A-A, according to 24 Fig. 1A;

1 Figures 2A-2C
are partial longitudinal sectional views of a pump 2 according to one embodiment of the invention, the biasing means being 3 positioned between the first and second piston in the variable volume chamber, 4 more particularly, Fig. 2A illustrates an idle position wherein an outlet valve and an 6 inlet valve are in a closed position;
7 Fig. 2B
illustrates the first position wherein the first and second 8 pistons are moved causing the inlet valve to open and a variable volume 9 chamber between the first and second pistons to be charged with fluid;
and 11 Fig. 20 illustrates a second position wherein the first and second 12 pistons are moved causing the outlet valve to be be opened, the fluid 13 being displaced from the variable volume chamber, pumping a differential 14 volume created by the variable volume chamber into the conduit above the pump barrel;
16 Figure 2D is a cross sectional view along section B-B, according to 17 Fig. 2A;
18 Figures 3A-3C
are partial longitudinal sectional views of a pump 19 according to one embodiment of the invention, the biasing means being positioned in the variable volume chamber, the inlet valve and outlet valve being 21 housed in a third chamber fluidly connected to the variable volume chamber, 22 more particularly, 23 Fig. 3A
illustrates an idle position wherein an outlet valve and an 24 inlet valve are in a closed position;

1 Fig. 3B
illustrates the first position wherein the first and second 2 pistons are moved causing the inlet valve to open and a variable volume 3 chamber between the first and second pistons to be charged with fluid;
4 and Fig. 3C illustrates a second position wherein the first and second 6 pistons are moved causing the outlet valve to be opened, the fluid being 7 displaced from the variable volume chamber, pumping a differential 8 volume created by the variable volume chamber into the conduit above 9 the pump barrel;
Figure 3D is a cross sectional view along section C-C, according to 11 Fig. 3A;
12 Figure 4A is a partial longitudinal sectional view of a pump 13 according to Fig. 1A, the biasing means being a Belleville spring;
14 Figure 4B is a partial longitudinal sectional view of a pump according to Fig. 1A, the biasing means being a coil spring;
16 Figure 5 is a partial longitudinal sectional view of a pump according 17 to Figs. 2A-2C positioned in a wellbore, the pump having a single conduit 18 extending to surface for producing accumulated liquids from the wellbore, gas 19 being produced to surface in an annulus between the conduit and the wellbore;
Figures 6A-6C are partial longitudinal sectional views of a pump 21 according to one embodiment of the invention, the biasing means being a 22 compressible liquid spring, more particularly 23 Fig. 6A
illustrates an idle position wherein an outlet valve and an 24 inlet valve are in a closed position;

1 Fig. 6B
illustrates the first position wherein the first and second 2 pistons are moved causing the inlet valve to open and a variable volume 3 chamber between the first and second pistons to be charged with fluid, a 4 rod extending downwardly from the first piston and into a sealed spring chamber moving into the liquid spring for compressing liquid therein; and 6 Fig. 6C
illustrates a second position wherein the first and second 7 pistons are moved causing the outlet valve to be opened, the fluid being 8 displaced from the variable volume chamber, pumping a differential 9 volume created by the variable volume chamber into the conduit above the pump barrel, the rod extending downwardly from the first piston being 11 moved out of the sealed spring chamber to release compression of the 12 liquid in the liquid spring;
13 Figure 6D is a cross sectional view along section D-D, according to 14 Fig. 6A;
Figure 7 is a graphical representation of the percentage compressibility of silicone versus pressure in an embodiment of the invention;
17 and 18 Figure 8 is a graphical representation of buckling forces versus 19 unsupported length of a displacing element or rod in an embodiment of the invention.

2 Embodiments of the invention are disclosed herein in the context of 3 a fluid device, or pump, particularly useful in the production of fluids through a 4 single discharge conduit extending from surface to a subterranean zone of interest. Description in this context is in no way intended to limit the scope of the 6 invention to fluid devices for use in a subterranean wellbore, the device being 7 equally applicable for remotely actuating and pumping fluids from any fluid 8 source to a discharge in a variety of contexts, including from a sump, lake or 9 pipeline.
Having reference to Figs. 1A-1D, 2A-2D, 3A-3D, 4A, 4B, 5 and 6A-11 6D and in a wellbore context, a subterranean zone of interest or fluid source F
12 (Fig. 5) is located remote from the surface where the fluid, such as a liquid, is to 13 be produced.
A discharge conduit 1 having a liquid discharge end 2 at surface 3 14 extends downhole to an inlet end 4 in fluid communication with the fluid source F. A fluid apparatus or pump 10, according to an embodiment of the invention, is 16 fluidly connected at the inlet end 4 for pumping liquid from the fluid source F to 17 surface 3 as a result of an actuating pressure P being applied to the discharge 18 conduit 1, typically at surface 3.
19 Having reference to Figs. 1A-1D and 2A-2D, the pump 10 comprises a pump barrel 11 having a first barrel section 12 and a second barrel 21 section 13 the first and second sections 12,13 being fluidly connected 22 therebetween.
The first barrel section 12 is in fluid communication with the fluid 23 source F and the second barrel section 13 is in fluid communication with the 24 discharge conduit 1. A diameter of the first barrel section 12 is greater than the diameter of the second barrel section 13. A pump piston comprises a first piston 1 14 housed within the first barrel section 12 for axial movement therein, and a 2 second piston 15 housed within the second barrel section 13 for axial movement 3 therein. The first and second pistons 14,15 are connected therebetween and 4 spaced apart by a connector such as a rod 16, forming a variable volume chamber 17 therebetween which changes volume as the pistons 14,15 are 6 actuated to concurrently move axially within the barrel sections 12,13.
As the 7 pistons 14,15 move towards the first barrel section 12, the variable volume 8 chamber 17 increases in volume and as the pistons 14,15 move towards the 9 second barrel section 13, the variable volume chamber 17 decreases in volume.
More particularly, a differential volume is created when the 11 connected pistons 14,15 are actuated to move toward the first larger diameter 12 barrel section 12 which permits a larger volume of fluid to enter the variable 13 volume chamber 17 than the chamber 17 will contain when the connected 14 pistons 14,15 are subsequently actuated to move toward the second smaller diameter barrel section 13. Reciprocating movement or stroking of the pump 16 pistons 14,15 in the pump barrel 11 creates the differential volume which is 17 forcibly discharged from the variable volume chamber 17 to the discharge 18 conduit 1 on each pump stroke.
19 More specifically, an inlet one way or check valve 18 is positioned at an inlet end 20 of the pump barrel 11 to permit the flow of fluid from the fluid 21 source F into the variable volume chamber 17. A discharge one way or check 22 valve 19 is positioned at a discharge end 21 of the pump barrel 11 to permit the 23 flow of fluid from the variable volume chamber 17 to the discharge conduit 1.
24 Having reference again to Figs. 1A-1D and 2A-2D and in one embodiment, the inlet check valve 18 is located in the first piston 14, and the 1 discharge check valve 19 is located in the second piston 15. In one embodiment, 2 the inlet check valve 18 and the discharge check valve 19 are ball valves.
3 In use, to actuate the pump 10, pressure is cyclically exerted at a 4 discharge end 22 of the discharge conduit 1. The connected first and second pistons 14,15 are actuated to move from an idle position (Figs. 1A, 2A, 3A and 6 6A) to a first inlet position (Figs. 1B, 2B, 3B and 6B) wherein the first and second 7 pistons 14,15 are moved toward the inlet end 20 of the pump barrel 11, typically 8 a downhole movement in the context of a wellbore pump. To complete the 9 pumping cycle, the first and second pistons 14,15 move to a second discharge position (Figs. 1C, 2C, 3C and 6C), returning to the discharge end 21 of the 11 pump barrel 11.
12 In the idle and discharge positions, fluid pressure at the inlet check 13 valve 18 causes the inlet check valve 18 to close. As the first and second 14 pistons 14,15 are moved to the first inlet position, the volume in the variable volume chamber 17 becomes larger. The inlet check valve 18 is caused to open 16 and fluid L from the fluid source F adjacent the inlet end 20 of the pump barrel 11 17 is caused to be sucked into the variable volume chamber 17 through the inlet 18 check valve 18.
19 Optionally, the inlet and discharge valves 18, 19 can form the pistons 14,15 which sealably engage the barrel 11 or the inlet and discharge 21 valves 18,19 can be supported in a piston housing. As shown, each piston 18, 22 19 comprises a cylindrical housing 23 having ports 24 formed therein for 23 conducting fluids from the inlet and discharge check valves 18, 19 through the 24 pistons 14,15.

1 Biasing means 25 acting between the pump pistons 14,15 and 2 pump barrel 11 to store energy as the first and second pistons 14,15 are moved 3 downhole to the inlet position. Preferably, the biasing means 25 is a spring, 4 pressurized bellows, elastomeric element or the like. As shown, examples of the spring 25 include a spring washer, such as a Belleville spring (Figs 1A-4A.), or, 6 as schematically represented in Fig. 4B, a coil spring or as shown in Figs 6A-6D
7 a compressible liquid spring.
8 Thus, when the force of the actuating pressure P applied to the 9 discharge conduit 1 and acting at the second piston 15 exceeds the combined force of the pressure at a fluid source F and the spring 25 biasing, the pistons 11 14,15 are caused to move to the inlet position, typically downhole in the context 12 of a wellbore. Release of the actuating pressure P permits the spring 25 to 13 release stored energy and causes the pistons 14,15 to move to the discharge 14 position, typically uphole in the context of a wellbore.
As the pistons 14,15 are caused to move to the discharge position, 16 the volume of the variable volume chamber 17 becomes smaller resulting in a 17 differential volume, being the difference in volume of the variable volume 18 chamber between the inlet and discharge positions. The inlet check valve 18 is 19 caused to close and as the volume of the variable volume chamber 17 becomes smaller, the discharge check valve 19 is opened and the differential volume is 21 discharged into the discharge conduit 1. Cyclically repeating the application and 22 the release of pressure P at the discharge end 22 of the discharge conduit 1, 23 results in fluids being pumped from the fluid source F, through the pump 10 and 24 into the discharge conduit 1 for eventual transport to a discharge 2, such as at surface 3.

1 In an embodiment of the invention a hydraulic circuit (not shown) 2 may be used to apply actuating pressure P at the discharge end 22. Alternately, 3 actuating pressure P may be applied using a positive displacement pump, such 4 as a plunger pump (not shown).
In one embodiment of the invention shown in Figs. 1A-1C, the 6 biasing means 25 is housed in the pump barrel 11 between the first piston 14 7 and a stop 26 formed adjacent the inlet end 20 of the pump barrel 11. An inlet 8 port 27 is formed in the stop 26 to permit fluid L from the fluid source F to enter 9 the pump 10.
As the pistons 14,15 are moved to the inlet position, the biasing means 25 is compressed by the pistons 14,15 against the stop 26, thereby 11 storing energy in the biasing means 25. When the actuating pressure P is 12 released at the discharge end 22 of the discharge conduit 1, the biasing means 13 25 acts between the stop 26 and the pistons 14, 15 to move the pistons 14,15 to 14 the discharge position. Preferably, the biasing means is a spring 25.
In one embodiment as shown in Figs. 2A-2C, the biasing means 25 16 is positioned in the variable volume chamber 17 between the second piston 15 17 and a stop 28 formed adjacent a lower end 29 of the second barrel section 13.
18 One or more ports 30 are formed in the stop 28 to permit passage of the rod 16 19 and for the flow of fluids L therethrough between the first and second pump sections 12,13. Further, the rod 16 is hollow to aid in moving fluids from the inlet 21 valve 18 to the discharge valve 19.
22 In one embodiment shown in Figs. 3A-3D, the pump barrel 11 23 further comprises a bypass passageway 40 for forming a second chamber 41 24 which is fluidly connected to the variable volume chamber 17. The inlet valve 18 is positioned at an inlet end 42 of the second chamber 41 in fluid communication with the fluid source F. The discharge valve 19 is positioned at a discharge end 2 43 of the second chamber 41 in fluid communication with the discharge conduit 1.
3 A port 44 is formed between the variable volume chamber 17 and the second 4 chamber 41 and between the first and second pistons 14,15. As actuating pressure P is applied at the discharge end 22 of the discharge conduit 1 and the 6 discharge valve is in the closed position, the pistons 14, 15 are caused to move 7 to the inlet position and the inlet valve 18 is opened for admitting fluid L to the 8 second chamber 41 and through port 44 to the variable volume chamber 17.
As 9 the actuating pressure P is released at the discharge end 22 of the discharge conduit 1, the inlet valve 18 is caused to close, the pistons 14,15 are biased to 11 the discharge position by the biasing means 25 and the discharge valve 19 12 opens for discharging the differential volume of fluid from the second chamber 13 41 into the discharge conduit 1. Ports 24 are not required in the pistons 14,15 in 14 this embodiment as fluid flow is directed through port 44.
The biasing means 25, like the previous embodiments, may be 16 housed in the same manner in the variable volume chamber 17 or in the pump 17 barrel 11 below the first piston 14.
18 As shown in Figs. 6A-6D and in an embodiment of the invention 19 wherein the biasing means 25 is a compressible liquid spring, the liquid spring comprises a sealed, pressurized spring chamber 50 which is operatively 21 connected to the first and second pistons 14,15 for compressing and releasing a 22 compressible fluid FC stored therein. One such suitable fluid FC is silicone 23 however any compressible fluid may be used which is suitable to meet the 24 desired design specifications.

1 In one embodiment shown in Figs. 6A-6D, the sealed pressurized 2 spring chamber 50 is formed within or in an extended portion of the pump barrel 3 11 and spaced below the first piston 14. An upper wall 51 of the spring chamber 4 50 comprises a port 52 through which a displacing element 53, such as a spring rod, protrudes, operatively connected to and extending downwardly from the first 6 piston 14.
The port 52 further comprises a chamber seal 54 which seals about 7 the spring rod 53 which reciprocates therethrough. The inlet 27 for fluid 8 communication with the fluid source F is formed in the first barrel section 12 9 between the first piston 14 and the upper wall 51 of the spring chamber 50.
Similarly, in embodiments of the invention, the spring 25 shown in 11 Figs. 2A-3D
could be substituted with a compressible fluid FC, the second barrel 12 portion 13 being sealed at the stop 28 for forming the pressure chamber 50, the 13 compressible fluid FC being compressed upon movement of the first and second 14 pistons 14, 15 to the inlet position.
As the first and second pistons 14,15 are caused to move to the 16 inlet position, as previously described by cyclical application of pressure at 17 surface, the spring rod 53 is moved into the fluid FC in the spring chamber 50 18 and acts to displace and compress the fluid FC sealed within the chamber 50, 19 storing energy therein. As pressure is released at surface, the first and second pistons 14,15 are biased to the discharge position as a result of release of the 21 energy stored in the fluid FC and acting upon the spring rod 53.
22 Actuation of the pump 10 is accomplished remotely through the 23 application and release of pressure at the discharge 21 and therefore a prime 24 mover is not required to be situated at or near the pump in the wellbore. Further, where a plurality of wells are situated in close proximity, the plurality of wells 1 could be connected hydraulically to a single source of cyclic pressure for 2 operating the plurality of wells.
3 Where the fluid source F is positioned substantially vertical and up 4 to about a 60 degree inclination relative to the discharge 21, ball and seat valves are suitable for use as the inlet and discharge check valves 18,19. However, 6 where the fluid source F is positioned substantially horizontal to the discharge 7 21, such as in a horizontal pipeline, spring loaded check valves may be more 8 suitable for use as the inlet and discharge valves 18,19.
9 One particular use as shown in Fig. 5, wherein embodiments of the invention are particularly well suited, is the deliquification of gas wells. A
distal 11 end of a single conduit, such as a tubing string 114, is fit with a pump 12 according to an embodiment of the invention. The pump 110 is lowered into a 13 wellbore 111 of a gas well and forms an annulus 112 between the conduit 14 and the wellbore 111. The discharge end 122 of the conduit 114 is positioned at surface 3. The pump 110 is positioned adjacent a zone of interest 115 where 16 liquid L co-produced from the gas-producing formation accumulate and, which if 17 left in the wellbore 111, would eventually hinder or stop gas production. Gas G is 18 typically produced through the annulus 112 from the zone of interest 115 to 19 surface 3. The inlet end 4 of conduit 114 is typically positioned below perforations in the zone of interest. The inlet end 4 of conduit 114 typically 21 extends below the inlet end 20 of the pump 110 sufficient to urge the liquid L to 22 enter the pump 110 while the gas G is directed to the annulus 112.
23 Actuation pressure P is cyclically applied and released at the 24 discharge end 122 of the conduit 114 such as through a hydraulic circuit or a positive displacement pump. The actuation pressure P acts at piston 15 of the 1 pump 110. The pump 110 is actuated, as discussed herein, to produce 2 accumulated liquids L to surface 3 through the conduit 114 thereby reducing any 3 hydrostatic head caused by the accumulation of the liquids L in the wellbore 111 4 and permitting production of the gas G through the annulus 112.
Actuation of the pump 110 can be continuous or intermittent. If 6 operated continuously, the pump 110 removes even small accumulations of 7 liquid L. Alternatively, the pump 110 can be operated intermittently on a fixed 8 (similar to continuous) or a dynamically controlled periodic basis.
Typically, a 9 controller would activate the pump 110 either at regular predetermined intervals based on historical liquid accumulation for a particular reservoir type, or 11 dynamically in response to a remote sensor which is able to sense a 12 predetermined volume of fluid accumulation. In either case, actuation of the 13 pump 110 would typically require very low power, such as can be provided by, 14 for example, a natural gas powered engine in remote locations not accessible to a utility grid or using an electric motor where electricity is available.
Further, an 16 accumulator on a hydraulic circuit or a flywheel on a plunger pump drive may be 17 used to conserve energy.

19 Examples Mechanical Biasing Means 21 A variety of configurations of embodiments of the pump 110 22 disclosed herein have been modeled for use in wellbore casings of different 23 diameter. Various configurations using Belleville springs are shown in Table A.
24 Embodiments of the invention using Belleveille springs as the biasing means may be more suitable for shallower pump applications to avoid 1 excessive spring height required to achieve a desired stroke for deeper well 2 pumps within the confines of the narrow pump diameter required for wellbore 3 applications.

Table A
Units 1 2 3 4 5 Outlet barrel bore API inches 1.5 2.25 1.5 2.25 1.5 Inlet barrel bore API inches 2.25 2.75 2.75 3.25 3.25 Outlet barrel bore, metric mm 38.1 57.15 38.1 57.15 38.1 Inlet barrel bore, metric mm 57.15 69.85 69.85 82.55 82.55 Outlet barrel x-section area mm2 1140 2564 1140 2564 1140 Inlet barrel x-section area mm' 2564 3830 3830 5349 5349 Ratio of inlet to outlet areas 2.250 1.494 3.361 2.086 4.694 Depth of pump m 500 500 500 500 500 Static head on pump w. water column Bar 50 50 50 50 50 Static force on outlet piston N 5695 12814 5695 12814 Pressure applied at surface Bar 80 90 130 150 100 (target -3x static at pump) Additional force on outlet piston N 9112 23066 14808 38443 Total force on outlet piston N 14808 35880 20503 51258 17086 Ratio static to pressurized P at pump 2.60 2.80 3.60 4.00 3.00 Belleville spring # D5025425 , D633135 D63313 D80364 D80363 Height mm 3.9 4.9 4.8 6.2 5.7 Thickness mm 2.5 3.5 3 4 3 Cone height (H-t) mm 1.4 1.4 1.8 2.2 2.7 # disks per stack 2 3 2 3 2 Height of one disk stack mm 6.4 11.9 7.8 14.2 8.7 75% force, one stack N 9063 15025 12356 21400 11919 75% force, stacked disks N 18126 45075 25072 64200 23838 (max deflection) 75% deflection, one disk stack mm 1.05 1.05 1.35 1.65 2.025 Static (initial) deflection mm 0.330 0.299 0.307 0.329 0.484 One disk stack Ratio, initial to 75% deflection 0.314 0.284 0.227 0.200 0.239 Total deflection with applied pressure mm 0.858 0.836 1.104 1.317 1.451 Ratio, operating to 75% deflection 0.82 0.80 0.82 0.80 0.72 (target 80%) .
Effective stroke one disk stack mm 0.528 0.537 0.797 0.988 0.968 Target stroke length mm 500 500 750 500 750 Volume of fluid pumped per stroke mmi , 712196 633063 2017889 Volume of fluid pumped per stroke bbls/d 0.712 0.633 2.018 1.393 3.157 Cycles per minute 6.0 6.0 6.0 6.0 6.0 Volume of fluid pumped per day mi/d 6.2 5.5 17.4 12.0 27.3 Volume of fluid pumped per day bbls/d 38.8 34.5 109.8 75.8 171.9 # disk pairs to achieve target stroke 947 931 941 506 775 length .
Total # disks 1894 2793 1882 1518 1550 Total disk height mm 6062 11074 7337 7186 6743 1 As discussed above, the volume of the variable volume chamber 2 17 is greater when the pistons 14,15 are in the inlet position than when the 3 pistons 14, 15 are in the discharge position. Various arrangements can result in 4 this characteristic including the embodiments of Figs. 1A-3D wherein the first piston 14 and first barrel section 12 have a larger diameter than the second 6 piston 15 and second barrel section 13. A connecting rod 16 fixes the spacing of 7 the first and second pistons 14,15. An advantage includes maximizing the barrel 8 diameter for inserting into a wellbore or other annular constraint at the fluid 9 source F.
Another example of an arrangement causing a differential swept 11 volume includes replacing the fixed connecting rod 16 with an axial movement 12 multiplier between the first and second pistons 14,15 such that the axial 13 movement of the first piston 14 is augmented relative to the second piston 15. A
14 simple mechanical lever with an offset fulcrum would suffice.
Further, the inlet and discharge valves 18,19 can be integrated with 16 the pistons 14,15, as shown in Figs. 1A- 2C or as shown in Figs. 3A-3C, one or 17 both can be located in a second chamber 41 positioned along a sidewall of the 18 pump barrel 11 and fluidly connected thereto through a port 44 between the first 19 and second pistons 14,15 to the variable volume chamber 17 therebetween.

1 Compressible Liquid Biasing Means 2 As shown in Figs. 6A-6D and in an embodiment of the invention, a 3 liquid spring can be used as the biasing means 25.
4 A compressible fluid FC, such as silicone or any other suitable compressible fluid, may be used. In an embodiment of the invention, silicone 6 was selected as it is a low viscosity fluid and is chemically inert, non-flammable 7 and is thermally stable. An interpolation of available data was performed to 8 determine compressibility of silicone under operating pressure of from about 70 9 barg (1015 psi) to about 415 barg (6020 psi), assuming approximately linear compressibility properties. The data is shown in Fig. 7.
11 Assuming an operating temperature of about 40 C and the data 12 shown in Fig. 7, the expected compressibility of silicone was determined to be 13 about 0.0106% per bar of pressure to achieve a desired stroke of about 50 cm.
14 Based upon wellbore conditions, such as in a demanding 1000m total vertical depth (TVD) well, generated pressures and expected displacements 16 were calculated for both the static (input) and pressurized (discharge) positions 17 as shown in Table B.

1 Table B
Static condition (inlet position) cc of fluid /
Rod compresses 5.717352 cm of movement Compressibility 0.010645 % / bar Static pressure in coil 98.1 bar Load on liquid spring 11174 N
Pressure in spring chamber 19.54429 N/mmA2 (Mpa) Pressure in spring chamber 195.4429 bar Volume of spring chamber 13.5 litres Volume of spring chamber 13500 cc Compressed liquid dV) 280.8661 cc Rod movement 49.1252 cm Pressurized position (discharge position) Additional pressure 100 bar Additional load 11391 N
Added pressure in chamber 19.92282 N/mmA2 (Mpa) Added pressure in chamber 199.2282 bar Total pressure in chamber 394.6711 bar Volume of spring chamber 13.5 litres Volume of spring chamber 13500 cc Compressed liquid (dV) 567.172 cc Additional Movement 50.07666 cm Totals Coiled tubing pressure 100 bar at surface CT pressure at depth 198.1 bar at depth Total force on rod 22565 N
Total pressure in spring 394.6711 bar Total Movement 99.20186 cm Length of liquid spring cylinder 5.262734 m 3 As determined from Table B, a spring rod 53 length of 4 approximately 1m is required to achieve a 50cm stroke. To minimize buckling force, the diameter of spring rod 53 used to compress the fluid F in the 6 pressurized sealed spring chamber 50 was selected to have an OD of 27mm (1-7 1/16") for a spring chamber 50 having a volume of 13.51. Further, it was 8 determined that the spring rod 53 would therefore have a maximum unsupported 1 length of 1.2m at 70% allowable force as demonstrated on Fig. 8 which was 2 created using the following calculations:
3 Johnson's Equation for Short Column Buckling (Local Buckling):
4 F lb = Sy*As*(1-(L/R/G)^2/(2*(S Rc)A2)) and 6 Euler's Equation for Long Column Buckling (Major Axis Buckling):
7 Feb = (3.14)^2*E*1/(L)A2 8 Where: As = steel cross sectional area 9 Sy = yield stress of steel I = moment of inertia 11 RG = radius of gyration 12 SR = slenderness ratio for a given length 13 SRc = critical slenderness ratio 14 L = unsupported length 16 At maximum compression, approximately 1m of the spring rod 53 17 is freely extending into the fluid FC in the spring chamber 50, the freely 18 extending portion of the spring rod 53 being supported thereabouts by the fluid 19 FC which exerts an equal pressure around the spring rod 53 decreasing any tendency for buckling.
21 In one embodiment, a fill port was formed in a bottom wall of the 22 spring chamber 50 to permit filling with compressible fluid FC after assembly of 23 the pump. Further, a bleed screw was included to permit removal of all air 24 present in the chamber 50.
In one embodiment, a standard API pump barrel 11 having an OD
26 of 69.9 mm (2.75") and an ID of 57.15 mm (2.25") was used for the spring 27 chamber 50 cylinder. The cylinder was made of AISI C1040 Carbon Steel and 28 behaved essentially as a pressure vessel containing a pressurized fluid.
Fatigue 1 calculations using thick-walled cylinder assumptions and Von Mises stress 2 analysis were performed to determine the factor of safety the cylinder provided 3 under maximum loading at 1000m TVD. The resulting fatigue factor of safety for 4 a fluctuating pressure from 200 barg (2900psi) to 400 barg (5800psi) was 1.86.
The chamber seal 54, utilized to seal about the spring rod 53 6 extending through the port 52 in the spring chamber 50, was required to provide 7 a reliable seal at approximately 400 barg (5800 psi) psi. Using silicone as the 8 compressible fluid F of choice in this embodiment, the chemical properties of the 9 chamber seal 54 were constrained only in that the material for the seal 54 could not be a like material, in this case silicone. In an embodiment of the invention, a 11 nitrile t-seal having nylon backups and a wiper to protect the seal 54 from 12 produced fluids within the wellbore was selected.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A fluid apparatus comprising:
a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit, the first barrel section having a diameter greater than the second barrel section, the first and second barrel sections being fluidly connected therebetween;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein;
means connecting between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position, the first and second pistons being spaced apart for forming a chamber of variable volume therebetween;
biasing means for biasing the first and second pistons to the discharge position;
an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber; and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit, a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit, the bypass passageway forming a second chamber fluidly connected to the variable volume chamber, wherein the inlet check valve is positioned at the inlet end of the bypass passageway and the outlet check valve is positioned at the outlet end of the bypass passageway;
wherein when an actuating pressure sufficient to overcome the biasing means is applied to the second piston through the discharge conduit, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve into the variable volume chamber; and when the actuating pressure is released, the biasing means returns the first and second pistons to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the outlet valve to the discharge conduit.

2. The fluid apparatus of claim 1 wherein the second chamber is fluidly connected to the variable volume chamber through a port.

3. The fluid apparatus of claim 1 or 2 wherein the biasing means is positioned within the first barrel.

4. The fluid apparatus of claim 1 or 2 wherein the biasing means is positioned within the second barrel.

5. A method for producing accumulated liquids from a gas well comprising:
positioning a fluid apparatus in the wellbore and forming an annulus therebetween, the apparatus having:

a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit, the first barrel section having a diameter greater than the second barrel section, the first and second barrel sections being fluidly connected therebetween;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein;
a connector between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position, the first and second pistons being spaced apart for forming a chamber of variable volume therebetween, the first and second pistons being biased to the discharge position;
an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber; and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit, and a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit, the bypass passageway forming a second chamber fluidly connected to the variable volume chamber, wherein the inlet check valve is positioned proximate the inlet end of the bypass passageway and the outlet check valve is positioned proximate the outlet end of the bypass passageway;

wherein when an actuating pressure, sufficient to overcome a biasing force, is applied to the second piston through the discharge conduit, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve and the bypass passageway into the variable volume chamber;
and when the actuating pressure is released, the first and second pistons are biased to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the bypass passageway to the discharge conduit;
producing gas to surface through the annulus, liquid accumulating in the wellbore adjacent the distal end of the conduit;
cyclically applying an actuating pressure at the discharge conduit such that when the force of the actuating pressure is greater than the force exerted by the biasing means and a force of pressure at the fluid source, the discharge valve operates to the closed position, the first and second pistons move to the inlet position and the inlet valve operates to the open position for charging the accumulated fluids from the wellbore into the variable volume chamber; and releasing the actuating pressure so that the first and second pistons are biased to return to the discharge position, the inlet valve moving to the closed position, the discharge valve moving to the open position and pumping the differential volume from the variable volume chamber through the discharge valve to the discharge conduit.

6. The method of claim 5 further comprising continuously alternating applying and releasing the actuating pressure.

7. The method of claim 5 further comprising intermittently alternating applying and releasing the actuating pressure.

8. The method of any one of claims 5 to 7 further comprising:
sensing an accumulation of liquid; and cyclically applying and releasing the pressure to pump the differential volume into the discharge conduit.

9. The method of any one of claims 5 to 8 wherein the actuating pressure is applied to the discharge conduit by a hydraulic circuit.

10. The method of any one of claims 5 to 8 wherein the actuating pressure is applied to the discharge conduit by a plunger pump.

11. A fluid apparatus comprising:
a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit, the first and second pistons defining a variable volume chamber between the first and second pistons;
a biasing element coupled to at least one of the first and second pistons;

an inlet check valve operable to permit fluid to flow from the fluid source into the variable volume chamber;
an outlet check valve operable to permit fluid to flow from the variable volume chamber into the discharge conduit;
a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit, the bypass passageway being in fluid communication with the variable volume chamber, and wherein the inlet check valve is disposed at the inlet end of the bypass passageway and operable to permit fluid to flow through the bypass passageway into the variable volume chamber and the outlet check valve is positioned at the outlet end of the bypass passageway and operable to permit fluid to be discharged from the variable volume chamber through the bypass passageway; and means for connecting the first and second pistons to cause movement of the first piston in response to movement of the second piston caused by the actuating pressure, the respective movements of the first and second pistons being operable to increase the volume of the variable volume chamber thereby drawing fluid into the variable volume chamber through the inlet check valve while causing energy to be stored in the biasing element, the stored energy in the biasing element being subsequently operable to cause respective return movement of the first and second pistons when the actuating pressure is decreased, the respective return movement of the first and second pistons being operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the variable volume chamber through the outlet check valve.

12. The fluid apparatus of claim 11 wherein the inlet check valve is not disposed in the first piston and the outlet check valve is not positioned in the second piston.

13. The fluid apparatus of claim 11 wherein the means for connecting comprises a rod.

14. The fluid apparatus of claim 11 wherein the fluid source is a zone of interest in a wellbore; and wherein the inlet position is downhole and the discharge position is uphole.

15. The fluid apparatus of claim 11 wherein the biasing element comprises a spring.

16. The fluid apparatus of claim 11 wherein the biasing element is disposed within the first barrel section.

17. The fluid apparatus of claim 11 wherein the biasing element is disposed within the second barrel section.

18. The fluid apparatus of claim 11 wherein the biasing element is connected between the pump barrel and at least one of the first and second pistons.

19. The fluid apparatus of claim 11 wherein the bypass passageway is in fluid communication with the variable volume chamber through a port.

20. A fluid apparatus comprising:
a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit, the first and second pistons defining a variable volume chamber between the first and second pistons;
a biasing element coupled to at least one of the first and second pistons;

an inlet check valve operable to permit fluid to flow from the fluid source into the variable volume chamber;
an outlet check valve operable to permit fluid to flow from the variable volume chamber into the discharge conduit;
a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit, the bypass passageway being in fluid communication with the variable volume chamber, wherein the inlet check valve is disposed at the inlet end of the bypass passageway and is operable to permit fluid to flow through the bypass passageway into the variable volume chamber and the outlet check valve is positioned at the outlet end of the bypass passageway and is operable to permit fluid to be discharged from the variable volume chamber through the bypass passageway; and a connector between the first and second pistons, the connector being operably configured to cause movement of the first piston in response to movement of the second piston caused by the actuating pressure, the respective movements of the first and second pistons being operable to increase the volume of the variable volume chamber thereby drawing fluid into the variable volume chamber through the inlet check valve while causing energy to be stored in the biasing element, the stored energy in the biasing element being subsequently operable to cause respective return movement of the first and second pistons when the actuating pressure is decreased, the respective return movement of the first and second pistons being operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the variable volume chamber through the outlet check valve.

21. The fluid apparatus of claim 20 wherein the inlet check valve is not disposed in the first piston and the outlet check valve is not disposed in the second piston.

22. The fluid apparatus of claim 20 wherein the connector comprises a rod.

23. The fluid apparatus of claim 20 wherein the fluid source is a zone of interest in a wellbore; and wherein the inlet position is downhole and the discharge position is uphole.

24. The fluid apparatus of claim 20 wherein the biasing element comprises a spring.

25. A method for producing accumulated liquids from a gas well, the method comprising:
positioning a fluid apparatus in a wellbore and forming an annulus therebetween, the fluid apparatus having:
a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein, the first and second pistons defining a variable volume chamber between the first and second pistons;
a biasing element coupled to at least one of the first and second pistons;
an inlet check valve operable to permit fluid to flow from the fluid source to the variable volume chamber;
an outlet check valve operable to permit fluid to flow from the variable volume chamber to the discharge conduit;
a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit, the bypass passageway being in fluid communication with the variable volume chamber, wherein the inlet check valve is disposed at the inlet end of the bypass passageway and is operable to permit fluid to flow through the bypass passageway into the variable volume chamber and the outlet check valve is disposed at the outlet end of the bypass passageway and is operable to permit fluid to be discharged from the variable volume chamber through the bypass passageway; and a connector between the first and second pistons, the connector being operably configured to cause movement of the first piston in response to movement of the second piston;
producing gas to surface through the annulus to cause liquid to accumulate in the wellbore adjacent the distal end of the conduit;
cyclically applying an actuating pressure at the discharge conduit to cause the first and second pistons to move to increase the volume of the variable volume chamber thereby drawing accumulated liquid into the variable volume chamber through the inlet check valve while causing energy to be stored in the biasing element; and releasing the actuating pressure to permit the stored energy in the biasing element to cause respective return movement of the first and second pistons, the respective return movement of the first and second pistons being operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the variable volume chamber through the outlet check valve to the discharge conduit.

26. The method of claim 25 wherein applying and releasing the actuating pressure comprises continuously alternating applying and releasing the actuating pressure.

27. The method of claim 25 wherein applying and releasing the actuating pressure comprises intermittently alternating applying and releasing the actuating pressure.

28. The method of claim 25 further comprising:
sensing an accumulation of liquid in the wellbore adjacent the distal end of the conduit; and cyclically applying and releasing the pressure to pump the liquid into the discharge conduit.

29. The method of claim 25 wherein applying and releasing the actuating pressure comprises causing a hydraulic circuit to apply pressure to the discharge conduit.

30. The method of claim 25 wherein applying and releasing the actuating pressure comprises causing a plunger pump to apply pressure to the discharge conduit.

31. The apparatus of claim 10 wherein the means for connecting is operably configured to cause the first and second pistons to have corresponding motions within the pump barrel and wherein the first barrel section has a first diameter and the second barrel section has a second diameter, the first diameter being greater than the second diameter to cause the volume of the variable volume chamber to increase in response to the application the actuating pressure, and to subsequently decrease when the actuating pressure is reduced.

32. The apparatus of claim 20 wherein the connector is operably configured to cause the first and second pistons to have corresponding motions within the pump barrel and wherein the first barrel section has a first diameter and the second barrel section has a second diameter, the first diameter being greater than the second diameter to cause the volume of the variable volume chamber to increase in response to the application of the actuating pressure, and to subsequently decrease when the actuating pressure is reduced.

33. The apparatus of claim 20 wherein the connector is operably configured to cause a greater axial motion of the first piston than the axial motion of the second piston caused by the actuating pressure, the respective motions of the first and second pistons being operable to cause increasing and decreasing separation between the first and second pistons within the barrel thereby respectively increasing and decreasing the volume of the variable volume chamber.

34. The apparatus of claim 33 wherein the connector comprises an axial movement multiplier extending between the first and second pistons.

35. The apparatus of claim 20 wherein the biasing element is disposed within the first barrel section.

36. The apparatus of claim 20 wherein the biasing element is connected between the pump barrel and at least one of the first and second pistons.

37. The apparatus of claim 11 wherein the first and second pistons are operably configured for coordinated axial movement comprising:
axial movement in a first direction whereby the first piston moves away from the second barrel section while the second piston moves towards the first barrel section in response to the actuating pressure; and axial movement in a second direction, opposite to the first direction of axial movement, whereby the second piston moves toward the second barrel section while the second piston moves away from the first barrel section when the actuating pressure is decreased.

38. The apparatus of claim 20 wherein the first and second pistons are operably configured for coordinated axial movement comprising:
axial movement in a first direction whereby the first piston moves away from the second barrel section while the second piston moves towards the first barrel section in response to the actuating pressure; and axial movement in a second direction, opposite to the first direction of axial movement, whereby the second piston moves toward the second barrel section while the second piston moves away from the first barrel section when the actuating pressure is decreased.

39. A fluid apparatus comprising:
a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit, the first and second pistons defining a variable volume chamber between the first and second pistons;
a biasing element coupled to at least one of the first and second pistons;
a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit, the bypass passageway being in fluid communication with the variable volume chamber through at least one port, the bypass passageway further comprising:
(i) a first one-way valve means for permitting one-way fluid flow into the bypass passageway, the first one-way valve means being operable to facilitate fluid flow from the inlet end, through the at least one port, into the variable volume chamber;
and (ii) a second one-way valve means for permitting one-way fluid flow out of the bypass passageway, the second one-way valve means being operable to facilitate fluid flow from the variable volume chamber, through the at least one port, and out the outlet end into the discharge conduit; and a connector between the first and second pistons, the connector being operably configured to cause movement of the first piston in a first axial direction in response to movement of the second piston in the first axial direction caused by the actuating pressure, the respective movements of the first and second pistons in the first axial direction being operable to increase the volume of the variable volume chamber thereby drawing fluid into the variable volume chamber through the first one-way valve means while causing energy to be stored in the biasing element, the stored energy in the biasing element being subsequently operable to cause respective movement of the first and second pistons in a second axial direction, opposite to the first axial direction, when the actuating pressure is decreased, the respective movement of the first and second pistons in the second axial direction being operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the variable volume chamber, through the second one-way valve means, and into the discharge conduit.

40. The fluid apparatus of claim 39 wherein at least one of the first one-way valve means and the second one-way valve means comprises a ball and seat check valve.

41. The fluid apparatus of claim 39 wherein at least one of the first one-way valve means and the second one-way valve means comprises a spring-loaded . check valve.

42. The fluid apparatus of claim 39 wherein the first one-way valve means are positioned at the inlet end of the bypass passageway and the second one-way valve means are positioned at the outlet end of the bypass passageway.

43. The fluid apparatus of claim 39 wherein the connector comprises a rod.

44. A fluid apparatus comprising:
a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit, the first barrel section having a diameter greater than the second barrel section, the first and second barrel sections being fluidly connected therebetween;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein;
means connecting between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position, the first and second pistons being spaced apart for forming a chamber of variable volume therebetween;
biasing means for biasing the first and second pistons to the discharge position, wherein the biasing means is positioned within the second barrel;
an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber; and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit;
wherein when an actuating pressure sufficient to overcome the biasing means is applied to the second piston through the discharge conduit, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve into the variable volume chamber; and when the actuating pressure is released, the biasing means returns the first and second pistons to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the outlet valve to the discharge conduit.

45. The fluid apparatus of claim 44 wherein the inlet check valve is positioned in the first piston and the outlet check valve is positioned in the second piston.

46. The fluid apparatus of any one of claims 44 to 45 wherein the fluid source is a zone of interest in a wellbore and wherein the inlet position is downhole and the discharge position is uphole.

47. A fluid apparatus comprising:
a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit, the first and second pistons defining a variable volume chamber between the first and second pistons;
a biasing element coupled to the second piston and at least partially located in the second barrel section;
an inlet check valve operable to permit fluid to flow from the fluid source into the variable volume chamber; and an outlet check valve operable to permit fluid to flow from the variable volume chamber into the discharge conduit;
means for connecting the first and second pistons to cause movement of the first piston in response to movement of the second piston caused by the actuating pressure, the respective movements of the first and second pistons being operable to increase the volume of the variable volume chamber thereby drawing fluid into the variable volume chamber through the inlet check valve while causing energy to be stored in the biasing element, the stored energy in the biasing element being subsequently operable to cause respective return movement of the first and second pistons when the actuating pressure is decreased, the respective return movement of the first and second pistons being operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the variable volume chamber through the outlet check valve.

48. A fluid apparatus comprising:
a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit, the first barrel section having a diameter greater than the second barrel section, the first and second barrel sections being fluidly connected therebetween;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein;
a connector between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position, the first and second pistons being spaced apart for forming a chamber of variable volume therebetween, the first and second pistons being biased to the discharge position by a biasing means;
an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber; and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit, wherein when an actuating pressure is applied to the second piston through the discharge conduit sufficient to overcome a biasing force applied by the biasing means to the first and second pistons, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve into the variable volume chamber; and when the actuating pressure is released, the first and second pistons are biased to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the outlet valve to the discharge conduit;
wherein the biasing means comprises a liquid spring comprising a sealed spring chamber, a compressible fluid stored in the sealed spring chamber, and a displacing element operatively connected to the first and second pistons for reducing the volume of the sealed spring chamber when the connected first and second pistons are moved to the inlet position and for biasing the first and second pistons to the discharge position.

49. The fluid apparatus of claim 48 wherein the displacing element is a spring rod operatively connected to the first piston and protruding downwardly therefrom into the sealed spring chamber, the liquid spring further comprising a seal formed between the displacing element and the sealed spring chamber.

50. The fluid apparatus of any one of claims 48 to 49 wherein the inlet position is downhole and the discharge position is uphole.

51. A fluid apparatus comprising:
a pump barrel forming at least a portion of a sealed spring chamber for containing a compressible fluid and having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit, the first and second pistons defining a variable volume chamber between the first and second pistons;
a liquid spring biasing element comprising the sealed spring chamber and a displacing element received in the sealed spring chamber for reducing the volume of the sealed spring chamber, the displacing element being coupled to at least one of the first and second pistons, wherein the sealed spring chamber comprises a portion of the first barrel section of the pump barrel;
an inlet check valve operable to permit fluid to flow from the fluid source into the variable volume chamber;
an outlet check valve operable to permit fluid to flow from the variable volume chamber into the discharge conduit; and a connector between the first and second pistons, the connector being operably configured to cause movement of the first piston in response to movement of the second piston caused by the actuating pressure, the respective movements of the first and second pistons being operable to increase the volume of the variable volume chamber thereby drawing fluid into the chamber through the inlet check valve while causing energy to be stored in the liquid spring biasing element, the stored energy in the liquid spring biasing element being subsequently operable to cause respective return movement of the first and second pistons when the actuating pressure is decreased, the respective return movement of the first and second pistons being operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the chamber through the outlet check valve.

52. The fluid apparatus of claim 51 wherein the inlet check valve is disposed in the first piston and the outlet check valve is positioned in the second piston.

53. The fluid apparatus of claim 51 wherein the connector comprises a rod.

54. The fluid apparatus of claim 51 wherein the fluid source is a zone of interest in a wellbore; and wherein the inlet position is downhole and the discharge position is uphole.

55. The fluid apparatus of claim 51 further comprising:
a bypass passageway having an inlet end in fluid communication with the fluid source and an outlet end in fluid communication with the discharge conduit, the bypass passageway being in fluid communication with the variable volume chamber, and wherein the inlet check valve is disposed at the inlet end of the bypass passageway and operable to permit fluid to flow through the bypass passageway into the variable , volume chamber and the outlet check valve is positioned at the outlet end of the bypass passageway and operable to permit fluid to be discharged from the variable volume chamber through the bypass passageway.

56. The fluid apparatus of claim 55 wherein the bypass passageway is in fluid communication with the variable volume chamber through a port.

57. The fluid apparatus of claim 51 wherein the liquid spring biasing element acts on the first piston.

58. The fluid apparatus of claim 51 wherein the sealed spring chamber of the liquid spring biasing element is formed within or in an extended portion of the pump barrel.

59. The fluid apparatus of claim 58 wherein the displacing element comprises a spring rod operatively connected to the first piston and protruding downwardly therefrom into the sealed spring chamber, and further comprising:
a seal formed between the displacing element and the sealed spring chamber.

60. A method for producing accumulated liquids from a gas well, the method comprising:
positioning a fluid apparatus in a wellbore and forming an annulus therebetween, the fluid apparatus having:
a pump barrel forming at least a portion of a sealed spring chamber for containing a compressible fluid and having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein, the first and second pistons defining a variable volume chamber between the first and second pistons;
a liquid spring biasing element comprising the sealed spring chamber and a displacing element received in the sealed spring chamber for reducing the volume of the sealed spring chamber, the displacing element being operably coupled to at least one of the first and second pistons, wherein the sealed spring chamber comprises a portion of the first barrel section of the pump barrel;
an inlet check valve operable to permit fluid to flow from the fluid source to the variable volume chamber;

an outlet check valve operable to permit fluid to flow from the variable volume chamber to the discharge conduit;
a connector between the first and second pistons, the connector being operably configured to cause movement of the first piston in response to movement of the second piston;
producing gas to surface through the annulus, while liquid is accumulating in the wellbore adjacent a distal end of the conduit;
cyclically applying an actuating pressure at the discharge conduit to cause the first and second pistons to move to increase the volume of the variable volume chamber thereby drawing accumulated liquid into the chamber through the inlet check valve while causing energy to be stored in the liquid spring biasing element; and releasing the actuating pressure to permit the stored energy in the liquid spring biasing element to cause respective return movement of the first and second pistons, the respective return movement of the first and second pistons being operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the chamber through the outlet check valve to the discharge conduit.

61. The method of claim 60 wherein applying and releasing the actuating pressure comprises continuously alternating applying and releasing the actuating pressure.

62. The method of claim 60 wherein applying and releasing the actuating pressure comprises intermittently alternating applying and releasing the actuating pressure.

63. The method of claim 60 further comprising:
sensing an accumulation of liquid in the wellbore adjacent the distal end of the conduit; and cyclically applying and releasing the pressure to pump the liquid into the discharge conduit.

64. The method of claim 60 wherein applying and releasing the actuating pressure comprises causing a hydraulic circuit to apply pressure to the discharge conduit.

65. The method of claim 60 wherein applying and releasing the actuating pressure comprises causing a plunger pump to apply pressure to the discharge conduit.

66. The apparatus of claim 51 wherein the connector is operably configured to cause the first and second pistons to have corresponding motions within the barrel and wherein the first barrel section has a first diameter and the second barrel section has a second diameter, the first diameter being greater than the second diameter to cause the volume of the variable volume chamber to increase in response to the application the actuating pressure, and to subsequently decrease when the actuating pressure is reduced.

67. The apparatus of claim 51 wherein the connector is operably configured to cause a greater axial motion of the first piston than the axial motion of the second piston caused by the actuating pressure, the respective motions of the first and second pistons being operable to cause an increasing and a decreasing separation between the first and second pistons within the barrel thereby respectively increasing and decreasing the volume of the variable volume chamber.

68. The apparatus of claim 67 wherein the connector comprises an axial movement multiplier extending between the first and second pistons.

69. The apparatus of claim 59 wherein the sealed spring chamber is disposed within the barrel.

70. A fluid apparatus comprising:
a pump barrel forming at least a portion of a sealed spring chamber configured to contain a compressible fluid and having a first barrel section proximate the sealed spring chamber and in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit, the first and second pistons defining a variable volume chamber between the first and second pistons;
a liquid spring biasing element comprising the sealed spring chamber and a displacing element received in the sealed spring chamber for reducing the volume of the sealed spring chamber, the displacing element being coupled to at least one of the first and second pistons;
an inlet check valve operable to permit fluid to flow from the fluid source into the variable volume chamber;
an outlet check valve operable to permit fluid to flow from the variable volume chamber into the discharge conduit; and a connector between the first and second pistons, the connector being operably configured to cause movement of the first piston in response to movement of the second piston caused by the actuating pressure, the respective movements of the first and second pistons being operable to increase the volume of the variable volume chamber thereby drawing fluid into the chamber through the inlet check valve while causing energy to be stored in the liquid spring biasing element, the stored energy in the liquid spring biasing element being subsequently operable to cause respective return movement of the first and second pistons when the actuating pressure is decreased, the respective return movement of the first and second pistons being operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the chamber through the outlet check valve.

71. The apparatus of claim 51 wherein the displacing element comprises a compressible fluid contacting portion for contacting the compressible fluid in the chamber, the entire compressible fluid contacting portion having a substantially constant diameter.

72. The apparatus of claim 51 wherein the liquid spring biasing element has a stroke length of at least 50 cm.

73. The apparatus of claim 51 wherein the sealed spring chamber comprises a fill port accessible to permit filling of the sealed spring chamber with the compressible fluid after the apparatus is assembled.

74. The apparatus of claim 51 further comprising the compressible fluid.

75. A fluid apparatus comprising:
a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein in response to application of an actuating pressure to the discharge conduit, the first and second pistons defining a variable volume chamber between the first and second pistons;
a biasing element coupled to at least one of the first and second pistons, wherein the biasing element comprises a liquid spring comprising a sealed chamber operable to hold a compressible fluid and a displacing element operable to be received in the sealed chamber to reduce the volume thereof;
wherein the displacing element comprises a spring rod received in the sealed chamber and adapted to avoid buckling when an unsupported free end of the spring rod is maximally extended into the sealed chamber during operation;
an inlet check valve operable to permit fluid to flow from the fluid source into the variable volume chamber;

an outlet check valve operable to permit fluid to flow from the variable volume chamber into the discharge conduit; and a connector between the first and second pistons, the connector being operably configured to cause movement of the first piston in response to movement of the second piston caused by the actuating pressure, the respective movements of the first and second pistons being operable to increase the volume of the variable volume chamber thereby drawing fluid into the chamber through the inlet check valve while causing energy to be stored in the biasing element, the stored energy in the biasing element being subsequently operable to cause return movement of the first and second pistons when the actuating pressure is decreased, the return movement of the first and second pistons being operable to reduce the volume of the variable volume chamber thereby causing fluid to be discharged from the chamber through the outlet check valve.

76. The apparatus of any one of claims 75 to 76 wherein the sealed chamber comprises a port operable to allow passage therethrough of at least a portion of the displacing element.

77. The apparatus of any one of claims 75 to 76 wherein a distal end of the displacing element received in the sealed chamber is substantially of the same diameter as the port.

78. The apparatus of any one of claims 75 to 77 wherein the displacing element comprises a spring rod connected to the first piston.

79. The apparatus of any one of claims 75 to 78 wherein the displacing element received in the sealed chamber does not comprise a piston.

80. The apparatus of any one of claims 75 to 79 wherein the sealed chamber comprises cylindrical side walls and wherein each outer portion of the displacing element received in the sealed chamber during operation is equally spaced apart from a corresponding inner portion of the cylindrical side walls, as viewed in a transverse sectional view.

81. The apparatus of any one of claims 75 to 80 wherein the displacing element comprises a compressible fluid contacting portion for contacting the compressible fluid in the sealed chamber, the entire compressible fluid contacting portion having a substantially constant diameter.

82. The apparatus of any one of claims 75 to 81 wherein the port comprises a chamber seal made of a material unlike that of the compressible liquid.

83. The apparatus of claim 82 wherein the chamber seal comprises a nitrile T-seal.

84. The apparatus of claim 82 wherein the chamber seal has backups and a wiper.

85. The apparatus of any one of claims 75 to 84 wherein the sealed chamber comprises a standard API pump barrel.

86. The apparatus of any one of claims 75 to 85 wherein the compressible fluid has a compressibility of about 0.01% per bar of pressure at an operating temperature of about 40 degrees C.

87. A fluid apparatus comprising:
a pump barrel having a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit, the first barrel section having a diameter greater than the second barrel section, the first and second barrel sections being fluidly connected therebetween;
a first piston housed in the first barrel section for axial movement therein;

a second piston housed in the second barrel section for axial movement therein;
means connecting between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position, the first and second pistons being spaced apart for forming a chamber of variable volume therebetween;
biasing means for biasing the first and second pistons to the discharge position, wherein the biasing means comprises a liquid spring;
an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber; and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit, wherein when an actuating pressure sufficient to overcome the biasing means is applied to the second piston through the discharge conduit, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve into the variable volume chamber; and when the actuating pressure is released, the biasing means returns the first and second pistons to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the outlet valve to the discharge conduit.

88. A method for producing accumulated liquids from a gas well, comprising:
positioning a fluid apparatus in the wellbore and forming an annulus therebetween, the apparatus comprising a pump barrel having:
a first barrel section in fluid communication with a fluid source and a second barrel section in fluid communication with a discharge conduit, the first barrel section having a diameter greater than the second barrel section, the first and second barrel sections being fluidly connected therebetween;
a first piston housed in the first barrel section for axial movement therein;
a second piston housed in the second barrel section for axial movement therein;
a connector between the first and second pistons for concurrent axial movement within the pump barrel between an inlet position and a discharge position, the first and second pistons being spaced apart for forming a chamber of variable volume therebetween, the first and second pistons being biased to the discharge position;
an inlet check valve to permit fluid to move from the fluid source to the variable volume chamber; and an outlet check valve to permit fluid to move from the variable volume chamber to the discharge conduit, wherein when an actuating pressure, sufficient to overcome a biasing force, is applied to the second piston through the discharge conduit, the outlet valve closes and the first and second pistons move to the inlet position and increase the variable volume chamber by a differential volume, opening the inlet valve and permitting the flow of the differential volume of fluid from the fluid source through the inlet valve into the variable volume chamber; and when the actuating pressure is released, the first and second pistons are biased to the discharge position for displacing the differential volume of fluid from the variable volume chamber, closing the inlet valve and opening the outlet valve for discharging the differential volume of fluid through the outlet valve to the discharge conduit;
producing gas to surface through the annulus, liquid accumulating in the wellbore adjacent the distal end of the conduit;
applying an actuating pressure at the discharge conduit such that when the force of the actuating pressure is greater than the force exerted by the biasing means and a force of pressure at the fluid source, the discharge valve operates to the closed position, the first and second pistons move to the inlet position and the inlet valve operates to the open position for charging the accumulated fluids from the wellbore into the variable volume chamber;
releasing the actuating pressure so that the first and second pistons are biased to return to the discharge position, the inlet valve moving to the closed position, the discharge valve moving to the open position and pumping the differential volume from the variable volume chamber through the discharge valve to the discharge conduit; and activating the fluid apparatus at predetermined intervals in response to data representing historical liquid accumulation for a particular reservoir type.