CA2609090A1 - Method and apparatus for removing production limiting liquid volumes from natural gas wells - Google Patents

Abstract

The apparatus includes a fluid intake check valve that connects to and allows a communicable passage between two lengths of tubing hung through the wellhead and landed at depth so that the valve is immersed below the casing perforations slightly below the desired liquid level maintenance point. On the surface, the two lengths of tubing each terminate in a launcher/receiver component. An orificed sweep-pig is propelled into one tube and sweeps the contained liquid through and out of the connected tubing developing a capillary bubble phased gas lift effect. The sweep-pig follows behind this effect, expels the trapped liquids and is captured at the second launcher/receiver. The method comprises of a timer controlled arrangement of valves that will then reverse the sweep pig to travel in the opposite direction in a repeatable alternating action configured to remove undesired liquid volumes.

Description

TITLE

Method and apparatus for removing production limiting liquid volumes from natural gas wells.

TECHNICAL FIELD

The invention relates to improving the production flow volumes of hydrocarbons from a well bore casing or annulus by controlling and preventing the accumulation of liquids down hole and thereby preventing "liquid loading" problems commonly associated with wells in mature fields or in shallow or unconventional plays.
The invention presents a method and apparatus here in.

BACKGROUND OF THE INVENTION

This invention relates to a method and apparatus used to remove accumulated liquids from hydrocarbon production wells for the purpose of improving production flows and extending reservoir longevity. These liquids flow from the tapped geological formation through perforations in the well casing. As hydrocarbons are recovered from the well and reservoir pressures decline, liquid is no longer lifted out of the well and instead forms into droplets that fall out of the production stream and deposit below the perforations into the well cellar. These liquids accumulate and fill the well bore to the point where they cover and rise above the perforations hindering and eventually stalling the flow of hydrocarbons from the well. The industry term for this condition is "liquid loading."
By removing the undesirable liquids from producible wells and maintaining the level of liquid below casing perforations, the hydrostatic pressure exerted by the liquids accumulating against the producing formation will be eliminated. The fluid will be removed independently of production pressure and well flow velocities. It is therefore fair to assume extended reservoir life due to viable low-pressure hydrocarbon production.
Older, mature gas fields and the increasing exploration for and exploitation of shallow gas resources such as coalbed methane and tight-sands formations have exasperated this problem in that reservoir pressures are such that conventional de-watering techniques are proving ineffective or too costly to implement. High production costs render a marginal production well as economically unfeasible and many are shut in and abandoned simply due to liquid loading.

PRIOR ART DISCUSSION

Conventional methods of liquid removal from low-pressure hydrocarbon producing wells include beam, positive displacement and progressive cavity pumping devices that are landed down hole and driven hydraulically, mechanically or by electric motors. These methods were developed for conventional, deep, high production, high water rate wells and function adequately in those applications. They are, however susceptible to gas lock or cavitation, a condition that occurs when pump intake liquids are exhausted; this is a common situation in marginal and shallow well production where low produced liquid volumes are commonplace. Other means incorporate shutting the well in and allowing down hole pressures to recover and build to a point where a plunger lift, a siphon string or a jet pump can be used effectively. Eventually this process becomes undesirable due to long shut in times and produced liquid slugs that are difficult to handle through standard surface equipment, or impossible due to insufficient shut-in pressure recovery.
Other methods devised to facilitate the removal of liquids from wells that are under-producing due to liquid loading include dipping the liquid out of the casing using a "bailing" procedure or wiping the liquids out using a "swabbing" procedure.
These methods remove accumulated liquids only and require the well be removed from production while complex equipment is employed to service the well. The costs incurred relative to these procedures can negatively impact well production revenue to the point where the well becomes economically unviable and may be abandoned.
Several methods for removing liquids from well bores require sufficient downhole pressure to function as intended. One example is described in U.S. patent number 659,873, Hodge, 1957, where a single tubing string is landed at a suitable depth and a valve located at the top of the string is opened to create a differential pressure between the annulus and tubing bore. An improved method is represented in U.S. patent number 4.275,790, Abercrombie 1981 where a standpipe is connected to the closed lower end of the tubing and locked in a packer. Liquids are expelled from the tubing after production is shut in to create sufficient downhole pressures to create the differential pressures and flow velocity needed to blow out the liquids.
Another common industry practice involves isolating the well and injecting a high-pressure volume of gas or air down the annulus and forcing liquids out the tubing into a receiving tank. During this activity some liquid is pushed back through the perforations into the producing formation, this effect is especially undesirable in shallow well applications such as coalbed methane. A method and apparatus, U.S. patent number 6,629,566, Liknes, 2003, addresses this concern by employing a one-way pressure check that seals the casing from the production perforations during the high-pressure application. This method requires a high-pressure volume of air or gas be available, a compressor is cited. Another method described in U.S. patent number 4.509,599, Chenoweth and McStravick, 1985, also requires a compressor be utilized to provide to the requirement of flow and pressure. The cost, installation and maintenance of such equipment limits application to wells with significant production revenue.
Most marginal and shallow unconventional wells do not produce enough revenue to bear-out these costs.
In an effort to avoid these costs alternative methods utilizing shut-in controllers and single tubing strings were devised. U.S. patent number 4,226,284, Evans, 1980, describes such a method. Further improvements describe the use of a tubing plunger control method to assist liquid lift, U.S. patent number 6,241,014. Periods of well shut-in are required and liquid slugging to surface results.
Downhole pumps provide an alternative but are susceptible to gas-lock or cavitation issues when liquid to gas dilution levels are high. In U.S. patent number 6,536,522, Brickhead and Britton describe an apparatus with automated monitoring characteristics intended to mitigate this condition. Downhole pumps also require considerable capital investment, costly operating infrastructure and periodic maintenance.
The specific small-volume removal and well bore liquid level maintenance requirements of marginal producing wells using low cost and low energy consuming means is the object. One method of note is U.S. patent number 4,222,440, Parker, 1980, described as a method of small volume pumping suited for oil recovery from marginal wells. Creating, trapping and then releasing a volume of compressed gas or air within a downhole device and exhausting that volume through a capillary tube lifts liquids to surface from the well bore.
Another known technique utilizes a dual tubing string. One apparatus and method, US patent 5,211,242, Coleman & Byron-Sandel, 1993, uses a downhole fluid collection chamber connected to two strings in such an aspect as to allow a volume of pressurized gas or air to be injected into the surface opening of one of the tubes and blow the collected volume from the chamber and out the second string.
The need to reduce the venting of large quantities of hydrocarbon gases to atmosphere during blow-down or purging activities associated with liquid lift and the need for low cost apparatus suitable for marginal producing wells requires a different approach. Low volume lift method U.S. patent number 5,006,046, Buckman, Steen and Buckman describe a method and apparatus consisting of a double tubing string configured as a U-tube communicating with downhole liquids via a specifically sized orifice. One end of the tubing is opened to annulus pressure; the other is opened to atmospheric pressure within a receiving tank. This method requires sufficient well pressures to achieve the differential pressure flow velocity needed to blow the liquids from the tubing string into the tank. A quantity of hydrocarbon gases will be released to atmosphere during each blow out cycle of this apparatus. Though spent gas volumes are lower than some more traditional methods - they are still significant.
The foregoing techniques are useful in particular applications but there is still a need to provide an improved method and apparatus for removing production limiting liquid where marginal, mature, or shallow unconventional gas wells do not produce sufficient revenue to offset the capital cost, installation difficulties or operational requirements required. Improvements to make an apparatus suitable for these applications would include- 1) Low capital cost outlay. 2) Low operational costs dictate low pressurized gas or air volumes be required relative to the amount of liquid volume removed from the well. 3) Simple immersed installation into well casing or annulus through conventional well head adapters using known coiled tubing service equipment. 4) A simple and effective contrivance to facilitate optimized use of the method and apparatus and make suitable for use in a variety of sized volume applications.

5) Liquid lift apparatus works independently of well production so shut-in periods are not required.
SUMMARY OF THE INVENTION

In accordance with a form of this invention, a means and a method for removing liquid from a well bore is provided. Simplistic installation and operation are intended to enhance the hydrocarbon production of wells encumbered by low revenue generation and low volume liquid loading which cannot be alleviated economically or practically using existing liquid lift techniques. Removing the liquid to a maintained level below the casing perforations will allow the unimpeded flow of natural gas from the gas-bearing formation into the well bore for production. Relieving the hydrostatic pressure allows continuous low-pressure flows and extends reservoir life expectancy and profitability.
This apparatus comprises: two conventional tubing strings, smooth bore and sized to applicable inner diameter and length installed through a well head and connected to a pick-up assembly which is landed below casing perforations and maximum desired liquid levels in the well casing or annulus. The pick-up assembly is manufactured from materials suitable for use in downhole hydrocarbon production environments, a passage of the same inner dimension as the employed tubing is fashioned in a U-shape terminating at the upper face with provision to accept conventional tubing fittings. A
second passage communicates an opening at the lower face of the pick-up assembly to the aforementioned U-shaped passage, allowing liquid flow through the pick-up assembly and into the tubing strings. A one-way valve will be provided to prevent the back-flow of liquids when the hydrostatic pressure within the pick-up assembly and tubing equalizes with downhole pressure or when liquids are swept from the apparatus as described forthwith. The liquid entry passage has a stop-plug temporarily installed to simplify installation. Prior to commissioning the plug will be blown out and dropped into the well cellar. The two tubing strings are effectively connected to one another through the pick-up assembly creating a continuous U-tube with consistent inner bore and a one-way liquid intake point.
The upper ends of both tubing strings are each connected to a manual full-port valve which is connected to a launcher/receiver component individually equipped with a normally open valved exhaust port and a second port, with a normally open two-way valve providing either an exhaust passage or a launch charge to be admitted into the launcher/receiver. The launcher/receiver has an internal cavity of the same bore as the employed tubing; a sweep-pig is inserted into one or the launcher/receiver assemblies.
The sweep-pig is manufactured of materials suitable for application and of dimensions calculated to provide negotiation through the tubing and pick-up passage. In accordance with this method the sweep-pig allows a specific volume of propellant to pass through or around it to create a forward capillary bubble effect as it travels the length of the U-tube and sweeps the contained volume of liquid out and through the second launcher/receiver where it is exhausted to disposal, the sweep-pig will come to rest in the second launcher/receiver, the pick-up check valve will open, liquid will again be admitted into the U-tube and the cycle is reversed sending the sweep-pig in the opposite direction.
The launcher/receiver directional control valves can be operated manually or automatically. In accordance with one form of this invention the valves are solenoid actuated, controlled with a dedicated timer relay module or well-site S.C.A.D.A. system that is energized by a photo-electric power supply.

DESCRIPTION OF THE PREFERRED EMBODMENTS
Referring to the drawings, FIG. 1 is a general sectional view of the preferred embodiment of the liquid pick-up assembly.
FIG. lA is a general sectional view of the preferred embodiment of the liquid pick-up assembly as viewed from the top of the assembly.

FIG. 2 is a general sectional view of the preferred embodiment of the sweep-pig positioned within a tube or passage inner bore.
FIG. 2A is a representative drawing of the preferred embodiment of a tool used to extract or install the sweep-pig into the launcher/receiver.
FIG. 3 is a general schematic sectional view of the preferred embodiment of the invention employed in the liquid level maintenance of a producing well.
FIGs. 4, 5, 6 are general schematic sectional views of the preferred embodiment of the invention in a functional stage of operation.

DETAILED DESCRIPTION THE OF PREFERRED EMBODMENTS

FIG. 3 illustrates the elements of the invention associated in use maintaining the produced liquid level in the production casing or annulus of a flowing natural gas well bore and the interconnected surface component. Hydrocarbon gas and associated liquids are produced from the underground formation 1 though the well casing 3 perforations 2.
The produced gas flows through the casing 3 and out the well head 27, liquid 22 drops out of the gas stream and deposits in the well cellar. The liquid pick-up 4 connected to two strings of coiled tubing 5 & 6 installed though the well head 27 and landed down hole at a depth predetermined as optimal to maintain liquid leve122 below perforations 2.
The tubing strings 5 & 6 are deployed into the well head 27 through a double vertical access 7, which comprises of a coil tubing hanger and pack-off element 8. On the surface the tubing 5 & 6 is terminated and connected to a full-port isolation valve 9 which is fitted to the launcher/receiver assembly 10 & 11. As illustrated in FIG. 3 the sweep-pig 21 is inserted in launcher/receiver 10 ready for deployment.
Directional deployment of the sweep-pig is actualized by enabling a supplied volume of pressurized gas 18 into the launcher/receiver assembly 10 when the actuated valve 13(S 1) and 12(S2) are activated in conjunction with the launcher/receiver assembly 11 valves 13(S3) and 12(S4) remaining in a normally open state thereby communicating with dump line 14 and industry conventional liquid handing equipment 15 (not depicted).
The supply of sweep gas 18 has a pressure control and pressure relief component 17, and is equipped with a normally open pressure sensing switch 16 set to a calculable rising set point. The state of pressure switch 16 will input a disable to the controller timer apparatus 19 that in turn activates and deactivates valves 12 & 13.
FIG. 1 is a detailed depiction of the liquid pick-up assembly aforementioned as item 4 in FIG. 3. The pick-up assembly is manufactured in a sectional fashion to facilitate simplistic machining procedures. The upper section 32 is manufactured and assembled to manufactured section 34 by the use of thru-bolts 33. A bored passage 31 essentially completes the apparatus to a U-tube configuration by providing a means 30 to fit industry standard tubing fittings to the pick-up assembly section 32. Furthermore passage 35 communicates the U-tube passage 31 with the down hole liquid media. A means of preventing reverse flow is provided by a check valve depicted in this rendering by a ball 37 and seat 39. Allowance to facilitate flow of liquid when ball 37 is off seat 39 in the open position is managed with a channeled passage 36. To simplify installation an blow-off plug 38 is fitted into the liquid intake port of the pick-up assembly to prevent communication with down hole environments rendering the apparatus as `dead' during install procedures.

FIG. 2 is a representative sectional drawing of the sweep pig 21 depicted within the bore of a section of tubing 5. To provide an orificed allowance of propellant gas in compliance with the desired capillary effect liquid lift, the internal orificed passage 28 represents one method of such. A means of extracting the sweep-pig 21 from the launcher/receiver is accomplished by providing a threaded interface 29 into which tool as depicted in FIG 2A is employed.
FIG. 4 illustrates the deployment of the sweep-pig 21 down hole through tubing and the two-phase displacement lift of liquids 23 through the pick-up assembly and up tube 5.
FIG. 5 illustrates a forward time lapse as the sweep-pig 21 passes from tubing through the pick-up assembly at toward the surface in tubing 5. Liquid 23 is further lifted by the capillary bubble-phase lift effect toward the surface in tubing 5.
FIG. 6 illustrates a further forward time lapse as the sweep-pig 21 is propelled within tubing 5 out of the well. Liquid 23 is exhaust through the launcher/receiver 11 through valves 12(S4) and 13(S3) out the dump line 14 to facility handling equipment 15 (not depicted).

OPERATIONAL EXAMPLE

Referring to FIG. 5 as the preferred embodiment, consider that a well has been selected for liquid management. There is no requirement that the well be cleaned out of swabbed before apparatus installation by conventional coiled tubing servicing equipment.
The tubing strings 5 & 6 are installed through coiled tubing hangers and pack-off elements 8 affixed to the double vertical access 7. The pick-up assembly 4 is connected to the tubing 5 & 6, the double vertical access 7 is secured to the well head 27 and the pick-up assembly 4 is then landed down hole so as to be immersed in liquid 22 contained within the well cellar. Landing point is determined specific the well; to be below perforations but not bottomed in hole. Depth of immersion is calculable based on total liquid lift, depth of liquid leve122 and desired volume of liquids required to maintain level below production perforations 2. FIG. 5 depicts a single production zone well with the apparatus suspended in the casing 3. An alternate example would be a dual zone completion where an existing tubing string is completed to a lower zone and packed-off.
The apparatus would then be landed within the well annulus.
On the surface, a full-port manual valve 9 is fitted to the end of each of the tubing strings 5& 6 and a launcher/receiver 10 & 11 fastened thereto. The launcher/receiver assembly 10 & 11 is tied in to dump line 14 and the propellant source 18 utilizing a two-way normally open valve 12(S2 & S4) and a three-way normally open valve 13(S
1& S3) respectively. As applicable, isolation, blow-down, directional check, pressure regulating and pressure relief valves are incorporated. It is expected that components and installation are tested and documented to working pressures as required by applicable local regulations.
The installation of the apparatus complete, commissioning is initiated by establishing a low-pressure switch 16 set point. By actuating valves 13(S 1) and 12(S2) propellant 18 is admitted and free flows through the U-tube to dump line 14 and disposal 15, this will be the low limit shut off input to the timer controller 19.
Closing valve 9 at launcher/receiver 11 and providing a higher pressure into the U-tube string sufficient to blow-off the blow-off plug 38. The inlet port will now communicate with down hole liquid and pressures admitting a level of liquid into the U-tube string.
Liquid will fill the U-tube to a level equal or slightly higher than that in the casing 3. At this point the sweep-pig 21 is installed into the launcher/receiver 10 and the apparatus is enabled. As determined by liquid accumulation and disposal rates and records, the timer controller 19 is calibrated to permit the number of desired sweeping cycles per day and the sweep-pig 21 is inserted into launcher/receiver 10. Propellant pressure 18 is opened to the apparatus at a flow and pressure suited to application, pressure switch 16 is now satisfied and in a closed state. The timer / controller 19 activates valves 13(S 1) opening to propellant source 18 and 12(S2) closing and isolating the launcher/receiver 10 from dump line 14.
Valves 13(S3) and 12(S4) are not activated; they remain in a normally open state communicating launcher/receiver 11 with dump line 14 and disposal 15.
The sweep-pig is propelled from the launcher/receiver 10 into the U-tube within tubing string 6. This propellant pressure will assist gravity in seating the pick-up assembly 4 check valve in the closed position. As the sweep-pig 21 is propelled down hole, forward contained gas is trapped and forced into the contained liquids 23. The trapped volume of gas is supplemented by a higher pressure supply of propellant gas 18 via the sized orifice contained within the sweep-pig design; these gases produces a capillary bubble effect which produces a phase change in the liquid 23 lowering the surface tension of the liquids and providing a phased lift to remove the liquid 23 up toward the surface in tube 6. The sweep-pig 21 travels down hole in tube 6, through the U-tube passage in the pick-up assembly and back to surface in tube 5; as the sweep-pig 21 is propelled it in turn drives and chases the liquid 23 into the launcher/receiver 11 and subsequently into the dump line 14 to disposal 15. The sweep-pig stops (lands) in launcher/receiver 11, liquid 23 flow is completed to dump line 14 and disposal 15 and propellant now free-flows unimpeded through the U-tube apparatus creating a drop in propellant flow pressure and an opening of pressure switch 16 interrupting the energizing circuit from the timer controller 19 to valves 13(S1) and 12(S2).
Therefore, control valves 13(S1 & S3) are non-actuated and in normally open state; open to dump line 14, control valves 12(S2 & S4) are non-actuated and in normally open state; open to dump line 14, once again liquid 22 is admitted into the U-tube apparatus. As determined by configured parameters and providing pressure switch 16 is satisfied, the timer controller will now actuate valves 13(S3) and 12(S4) and launch sweep-pig 21 from launcher/receiver 11 in a reverse direction of that aforementioned.
This alternating action is intended to be repeatable and time configurable.
It should be understood that the foregoing relates to only preferred embodiments of the invention and is intended to cover any or all changes or modifications which do not

Claims (19)

1. A method for removing liquid from a well bore or annulus, intended to optimize the production of hydrocarbons by maintaining down hole liquid level and eliminating hydrostatic pressure caused by the same on producing formations utilizing a pick-up assembly communicating directly with down hole liquids and connected in a U-tube configuration with two strings of coil tubing subsequently terminated on the surface with a means to propel a sweep-pig through the U-tube in an alternating and repeatable action therein lifting liquids from the well bore to disposal.

2. A method as set forth in claim 1 wherein number of timed cycles of sweep-pig deployment is configurable and made operable by a dedicated or a multi-tasked control system.

3. A method as set forth in claim 2 whereby functionality may be controlled by manual means.

4. A method as set forth in claim 1 wherein described propellant may be provided from any gaseous source of sufficient pressure and flow volume to make apparatus operable.

5. A method of liquid lift as set forth in clam 1 whereby a capillary bubble effect is created by a bypass orifice incorporated in the design and manufacture of the sweep-pig.

6. A method as set forth in claim 1 whereby a sweep-pig launcher/receiver is configured to receive, contain, launch and reverse act a sweep-pig by means of sequenced ported valve operation.

7. A method as set forth in claim 1 whereby liquid disposal include atmospheric holding tanks or communication via check valve to low pressure flow lines or liquid separation equipment or pumping devices.

8. An apparatus for removing liquid from a well bore intended to optimize the production of hydrocarbons by maintaining down hole liquid level and eliminating hydrostatic pressure caused by the same on producing formations comprising; a liquid pick-up assembly connected to two coiled tubing strings suspended within a well bore casing or annulus and immersed below casing perforations and below the desired maintenance level of downhole liquids, said tubing will thereby be considered a U-tube configuration as tubing strings communicate with one another by means of a connecting passage incorporated in the design and manufacture of said pick-up assembly; surface termination of tubing strings to connectors and launcher/receiver assemblies ported via control and controllable valves to dump line disposal and propellant source supply manifolds.

9. An apparatus as set forth in claim 8 wherein said tubing, tubing connectors and tubing unions are deemed to have a consistent and smooth bore throughout any transition including said pick-up assembly and said launcher/receiver assemblies.

10. An apparatus as set forth in claim 9 whereas tubing product, related fasteners and connectors, and dimensional sizing may be of any common or specific material manufacture.

11. An apparatus as set forth in claim 8 wherein said pick-up assembly manufacture includes an inlet passage check valve and an installation blow-off plug.

12. An apparatus as set forth in claim 11 whereas said pick-up assembly may be of any common or specific material manufacture providing compatibility with working environment and compliance with applicable ordinance and regulation.

13. An apparatus as set forth in claim 8 whereby liquid disposal may tie-in to conventional or existing oilfield equipment and propellant source may be deemed to be found in addition to or with existing pressurized storage or existing or additional pressurized flow lines.

14. An apparatus as set forth in claim 8 wherein said launcher/receiver assemblies are manufactured of any common or specific material manufacture providing compatibility with working environment and compliance with applicable ordinance and regulation.

15. An apparatus as set forth in claim 8 wherein sweep-pig manufacture is of any common or specific material manufacture providing compatibility with working environment and application.

16. An apparatus as set forth in claim 15 where as sweep-pig design and manufacture in accordance to means to produce capillary bubble effect phased gas-lift is considered as variable and unique to this invention.

17. An apparatus as set forth in claim 8 wherein control valve function and arrangement are established as a means to facilitate a repeatable alternating directional launch of the sweep-pig as well as introduction of propellant gas and exhaust of liquids and spent propellant.

18. An apparatus as set forth in claim 8 whereby sweep cycle duration, direction and initiation is controllable by automatic or manual means.

19. An apparatus as set forth in claim 8 wherein installation may involve additional components common to industry such as, isolation, blow-down, directional check, pressure regulating and pressure relief valves in order to protect apparatus integrity and comply with local regulations, directives and ordinances.