GB2091816A - A well pumping system - Google Patents

Abstract

The pumping of water from a gas well is effected by a pump driven by a gas motor having first and second pistons 15, 16 located in first and second chambers respectively. The pistons are fixed together and a piston rod 17 extends from the motor and is connected to a well pumping apparatus which in operation extends downwardly into the well. Gas applied to the first piston 15 counter-balances the weight of the pistons and well apparatus, while the second piston 16 is responsive to pressure variations of gas on each side to effect a reciprocating motion of the piston rod. A control unit 7 is connected to each chamber portion of the second chamber on opposite sides of the second piston and also to a pressure medium store 8 and an outlet of the gas well. The control unit is operable to feed gas from the well alternately to one or the opposed chamber portions while simultaneously directing gas exhausted from the respective opposite chamber portion to the store. <IMAGE>

Description

SPECIFICATION A well pumping system The present invention relates to a well pumping system, and more particularly to a pumping system for a gas producing well.

It is known from the production of natural gas from gas wells that not only gas but also water enters the well casing and often, particularly when the pressure of gas in a gas strata becomes lower as gas is removed, the level of water within the casing rises to a height sufficient to provide a pressure head of water which impedes the flow of gas from the well and in some cases actually prevents the further flow of gas from the well. It is generally considered in this art that when such a state is reached the known methods of removing the water, such as by pumping, the introduction of effervescent tablets, or the introduction of compressed air, are uneconomic in view of the recurring water deposits and also that such methods inevitably result in a great loss of the natural gas to the atmosphere.For these reasons and also the low gas pressures within the well which indicate that a well is exhausted it is generally considered that further extraction of gas is too costly in relation to the gas output. Consequently, such wells are closed down.

It is an object of the present invention to overcome these disadvantages and to render wells previously considered to be exhausted operable economically relative to the amount of gas subsequently produced by a well.

According to one aspect of the present invention there is provided a pump for a well pumping system, including first and second pistons located in first and second chambers, respectively, which pistons are fixed one relative to the other, a piston rod connected with at least one piston and extending outwardly of the pump for connection to well apparatus to be operated by the pump, the first piston constituting a counter-balancing piston for counter-balancing the weight of the pistons and well apparatus connectable to the piston rod and the second piston constituting an operating piston having a reciprocating motion in response to pressure variations on each side of the piston, and control means connected with input/output means of the second chamber for controlling the flow of pressure medium to and from each side of the second piston.

In one particular embodiment of a pump the first and second chambers are axially spaced together along a common axis. The first and second pistons are interconnected by the piston rod which extends along the common axis.

Operative means are provided which are responsive to the position of the second piston for effecting operation of the control means to determine the direction of flow of the pressure medium through the control means. Preferably, operative means is a rod which lies external of the first and second chambers and its opposite ends projecting to respective ones of the opposed ends of the first and second chambers. Three pistons and their respective chambers may be axially spaced together with the pistons connected to a common piston rod.

According to another aspect of the invention there is provided a pumping system for a well, including a pump having first and second pistons located in the first and second chambers, respectively, which pistons are fixed one relative to the other, a piston rod connected to at least one piston extending from the pump and connected to a well apparatus in operation extending downwardly into a well, the first piston serving as a counter-balancing piston for counter-balancing the weight of the pistons and well apparatus connected to the piston rod, and the second piston being responsive to pressurevaria- tions on each side thereof to effect reciprocating motion of the piston rod, and control means con nectedto each chamber portion of the second chamber on opposed sides of the second piston and to both a pressure medium store and an outlet of the well, so as to feed pressure medium alternatively to one or the opposed chambers portions and simultaneously direct pressure medium exhausted from the respective opposite chamber portion to the store.

In a preferred embodiment of a pumping system according to the invention the first and second chambers are axially spaced together on a common axis with the piston rod extending along the common axis. The piston rod has a coupling means for interconnecting the same with the well apparatus which may comprise a rod string connected to a ball-check pump at the bottom of the well Preferably, a reservoir is connected with the first piston chamber and to an outlet of the well. More particularly, the reservoir is connected to a first chamber portion of the first chamber is effect a lifting motion on the first piston. The chamber portion on the opposite side of the first piston to the first chamber portion of the first chamber is vented to the atmosphere.

A control valve is located in the connection between the reservoir and the outlet of the well, while the reservoir may be provided with a pressure relief valve for protecting the reservoir against internal pressure changes due to temperature.

Preferably, a control valve is connected in the connection between the control means and the outlet of the well. Such control valves may be manually operable.

Preferably, three piston chambers are axially spaced together with their respective pistons connected to a common piston rod.

An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which, Figure 1 is a diagrammatic part-sectional side elevational view of a pumping system according to the present invention, and Figure 2 is a diagrammatic part-sectional side elevational view of well casing attached to the pumping system of Figure 1.

Referring now particularly to Figure 1 a pump generally designated 1 is connected with a well casing 2 by means of easing flanges 3 and spaced supports 4.

On the left-hand side of Figure 1 the pump 1 is shown to be connected with a gas outlet 5 of the well casing 2 via a gas reservoir 6. On the right-hand side in the Figure a further gas outlet 5 from the well casing 2 is shown to be connected to the pump 1 through a directional control unit 7 which is also connected to a gas collection and storage system represented by the block 8.

The pump 1 is of an elongate cylindrical construction having a central dividing wall 10 and end plates 11 and 12. The central plate 10 divides the cylinder into two separate equally dimensioned chambers 13 and 14 in each ofwhich is located a piston 15, 16, respectively. The pistons are interconnected by a common piston rod 17 which further extends through the bottom end plate 12 for connection to a rod string 18 which extends downwardly within the well casing 2. The interconnection between the rods 17 and 18 is made by a coupling 19 of any conventionally known type and for this reason will not be further described.

The pistons 15 and 16 divide the chambers 13 and 14 into separate portions 13a, 13b and 14a, 14o, respectively. The chamber portion 1 3a above the piston 15 is vented to the atmosphere via pipe 20 whilst the chamber portion 13b is connected by pipe 21 to the gas reservoir 6. Gas in the reservoir 6 is supplied from the gas in the well via the well casing outlet 5, pipe 22 and a manually operable valve 23 connected in the pipe 22. The size of the reservoir and the gas pressure within the reservoir 6 are such as to allow the easy flow of gas to and from the chamber portion 13b in dependence upon the reciprocating motion of the piston 15. To avoid undue changes in pressure caused by external temperature changes, a relief valve 24 is provided on the reservoir 6.

Interference between the gas in chamber portions 13b and 14a is prevented by a seal 10a in the dividing plate 10 between the plate and the piston rod 17. A similar seal 12a is located in end plate 12 between the plate and piston rod 17 to prevent gas in chamber portion 14b escaping to the atmosphere.

The effect of the gas pressure within the reservoir 6 is simply to counter-balance the weight of the pistons 15, 16 and the rods 17 and 18 together with any apparatus within the well connected to the rod string 18. In the present instance such apparatus would constitute a conventional ball-check pump 25 which is shown in Figure 2. The gas within the chamber portion 1 3b therefore has a counterbalancing effect upon the piston 15 which can be adjusted by adjustment of the valve 23. In the counter-balanced state any movement of the pistons 15 and 16 can be effected by small changes in gas pressure applied alternately within the chamber portion 14a and 14b as will be described below.

Chamber portion 14a is coupled via pipe 26, the control unit 7 and pipe 27 to the second gas outlet 5 of the well casing, or alternately, via pipes 26, control unit 7 and pipe 28 to the gas storage system 8.

Chamber portion 14b is also coupled with the second gas outlet 5 of the well casing 2 via pipe 29, the control unit 7 and the pipe 27. Again the chamber portion 14b can also be interconnected via the control unit 7 and pipe 28 to the gas storage system 8. A manually operable valve 30 is provided in pipe 27 for reasons to be hereinafter described.

The control unit 7 is a conventional unit comprising a series of selectively operable valves and conduits and accordingly will not be described in further detail other than to say that in the presently described embodiment the control unit has two actuating elements 35,36 which are engageable by lugs 37,38 extending transversely from a control rod 39 having extensions 40,41 which project through seals (not shown) into the chamber portions 13a, 14b, respectively. The rod 39 is movable with an up and down movement, in the drawing, in dependence upon whether piston 15 engages the projection 40 or piston 16 engages the projection 41. In the first instance the lug 37 will engage the actuating member 35, whilst in the second instance the lug 38 engages the actuating member 36, to alter the gas flow within the control unit 7.

The storage system 8 of Figure 1 comprises a series of gas pipes and gas storage tanks which serve to collect gas from a number of wells located in the immediate vicinity of the presently described well in a conventional manner.

Referring now particularly to Figure 2 where elements referred to with reference to Figure 1 have been allocated the same reference numerals, the well casing 2 is shown in more detail. In the drawing, the well casing 2 extends downwardly into the earth's crust or outer strata 49 and into a gas strata 50 which contains gas and water. The well casing 2 is provided with apertures 51 through which the gas and water pass. Bubbles 52 of gas flow upwardly through the water into a gaseous region within the casing 2 above the water level 53. The gas within this region flows from the well casing through the gas outlets 5. In Figure 2 the gas in the gaseous region is indicated by continued reference to bubbles 52.

The ball-check pump 25 serves to pump the water in the bottom of the well casing upwardly through an annular pipe string 54 and out through an outlet 55 to any suitable drainage means (not shown).

The rod string 18 which is connected to the piston rod 17 via coupling 19 extends downwardly to the ball-check pump through the annular pipe string 54.

The operation of the above embodiment will now be described. When the pump 1 has been connected to the well casing 2 and the rod string 18 coupled to the piston rod 17 so as to operate the ball-check pump 25 at the well bottom, valve 23 is opened to permit the gas in the well casing 2 to flow into the reservoir 6 and then to the chamber portion 13b The gas pressure in the reservoir 6 and chamber portion 13b serves to balance the weight of the pistons 15, 16, rod string 17, 18 and the ball-check pump 25, effectively putting the rod string into a weightless state. Once this balancing effect is achieved valve 30 is opened and gas from the well casing 2 flows alternately into chamber portions 14a, 14b to operate the ball-check pump 25 by re-direction of the gas flow through the control unit 7. Simultaneously, gas in thatchamber portion 14a, 146 which is being exhausted during the stroke of the piston 16 is directed through the control unit 7 to flow into the gas storage system 8.

Assuming the position shown in Figure 1, piston 16 is moving in a downwardly direction and gas from the well casing 2 flows through valve 30, pipe 27, control unit 7 and pipe 26 into the chamber portion 1 4a to effect this movement of the piston 16.

Simultaneously, gas within the chamber portion 14b flows out via pipe 29, control unit 7 and pipe 28 into the gas storage system 8. When the piston 16 reaches the bottom of its stroke it engages the protruding end 41 of the control rod 39. This moves the control rod 39 in a downwardly direction in Figure 1 so that the lug 37 engages the actuating member 35 thereby operating the control unit 7 to redirect gas flow therethrough. Accordingly, well gas flowing through the pipe 27 is redirected through the control unit 7, into pipe 29 and the chamber portion 14b Simultaneously, the gas in chamber portion 14a is forced out, by the upward movement of the piston 16, through the pipe 26, the control unit 7 and pipe 28 into the gas storage system 8. Therefore, a substantially constant flow of gas is fed to the gas storage system.

When the piston 16 reaches its uppermost position the piston 15 engages the protruding end 40 of the control rod 39 and moves the control rod in an upwardly direction. Accordingly, the lug 38 engages the actuating member 36 and the gas flow within the control unit 7 is redirected so that the piston 16 moves in a downwardly direction as previously described.

The movement of the pistons 15,16 and hence the rod string 18 operates the ball-check pump 25 at the bottom of the well, with the minimum of effort in view of the counter-balancing effect on piston 15, and causes water to be pumped upwardly within the annular rod string 54 and out of the outlet 55 to a suitable drainage system (not shown).

It is common knowledge in the art of producing natural gas from gas wells that water enters the well casing 2 as well as the required gas. The water builds up within the well casing 2 and forms a pressure head which is sufficient to reduce the flow of gas from the well and, in some cases, to bring such gas flow to a stop. Although pumps may be used to operate the rod string 18 such pumps are large since they must be capable of operating the rod string 18 and ball-check pump 25 and draw their energy from an independent source. Such pumps are inefficient and expensive to run, rendering it uneconomic to operate the well to provide further gas production.

Advantageously, the pump system of the present invention operates by the use of the gas within the well and because of the counter-balancing effect of the gas within the chamber portion 13b only small changes of gas pressure in the chamber portions 14a and 14b will serve to operate the piston 16.

When the pump system is connected to a gas well in which the water level or pressure head within the well is such as to reduce gas flow almost to zero, the pumping system may be interconnected with the gas storage system 8 which will provide gas at sufficient pressure to initially cause operation of the pumping system in the manner described above until the water level 53 within the well casing 2 is sufficiently reduced to allow gas flow from the well in question, whereupon the valves 23 and 30 can be adjusted so that gas which then flows from the well to which the pump system is connected takes over the operation of the pump. In this manner wells which have been closed as unproductive or uneconomic can be reopened and operated to produce gas in an efficient and economic manner.

As the water level is lowered within the well casing 2 and the gas begins to flow readily, adjustments of the valves 23 and 30 will maintain pumping speeds suitable to the particular installation and also maintain the water within the well casing at a level that will result in maximum gas production.

It is to be noted that the pumping system is a completely closed system and no gas is pumped to the atmosphere or lost.

The pump system of the present invention can be operated in a push pull arrangement with another such pump or, alternatively, a cross arrangement of three or more pumps coupled together in a vertical or horizontal fashion to provide more pumping power in the case of extremely deep gas wells. There is no limitation on the number of pumps which can be used.

To illustrate the size and capabilities of the pump system just described the practical details of one particular pump system will now be given. In such a pump system the pump cylinder has a diameter of 2.85 cm (1.125 inches) and the piston stroke is 91.44 cm (3 ft.). The gas reservoir 6 has a diameter of 30.48 cm (12 inches).

In order to operate the pump the minimum required operating pressure differential, that is the pressure differential between the well head pressure and the normal gas collection and storage system, is 0.211 kg/cm2 (3PSI) for each 304.8 m (1000 ft.) of well depth. This value corresponds to 60 per cent of the efficiency of the pumping system, such efficiency being reduced by friction, viscosity, accelaration forces and rod string drag.

The required operating gas volume (by weight) is 0.133 m3 (4.67 ft3) of gas head pressure per pump cycle at 6 cycles per minute. This is equal to 0.793 m3 (23 ft.3) per minute at well head pressure.

With such a pump having these dimensions it can be calculated that a maximum of 5064.7 litres per day of water may be pumped from a well. Furthermore, a well of 1,219.2 m (4000 ft.) in depth can be pumped with a pressure differential of 4 kg/cm2 (9.0 Ib.) between the well pressure and the gas storage system. In practice, slightly higher pressure differentials may be required as a result of extraction speed requirements.

The foregoing example demonstrates the advantages related to the use of this pumping system which is designed to produce pumping at an absolute minimum energy loss combined with the economic recouperation of operating gas.

Claims (22)

1. A pump for a well pumping system, including first and second pistons located in first and second chambers, respectively, which pistons are fixed one relative to the other, a piston rod connected with at least one piston and extending outwardly of the pump for connection to well apparatus to be operated by the pump, the first piston constituting a counter-balancing piston for counter-balancing the weight of the pistons and well apparatus connectable to the piston rod and the second piston constituting an operating piston having a reciprocating motion in response to pressure variations on each side of the piston, and control means connected with inputioutput means of the second chamber for controlling the flow of pressure medium to and from each side of the second piston.

2. A pump as claimed in claim 1, wherein the first and second chambers are axially spaced together along a common axis.

3. A pump as claimed in claim 2, wherein the first and second pistons are interconnected by the piston rod which extends along the common axis.

4. A pump as claimed in any one of the preceding claims, including operative means responsive to the position of the second piston for effecting operation of the control means to determine the direction of flow of the pressure medium through the control means.

5. A pump as claimed in claim 4, wherein the operative means is a rod.

6. A pump as claimed in claim 5, wherein the rod lies external of the first and second chambers and its opposite ends project into respective ones of the opposed ends of the first and second chambers.

7. A pump as claimed in any one of the preceding claims, wherein three pistons and their respective chambers are axially spaced together with the pistons connected to a common piston rod.

8. A pump substantially as hereinbefore described with reference to, and as illustrated in, Figure 1 of the accompanying drawings.

9. A pumping system for a well, including a pump having first and second pistons located in first and second chambers, respectively, which pistons are fixed one relative to the other, a piston rod connected to at least one piston extending from the pump and connected to a well apparatus in operation extending downwardly into a well, the first piston serving as a counter-balancing piston for counter-balancing the weight of the pistons and well apparatus connected to the piston rod, and the second piston being responsive to pressure variations on each side thereof to effect reciprocating motion of the piston rod, and control means connected to each chamber portion of the second chamber on opposed sides of the second piston and to a pressure medium store and an outlet of the well, so as to feed pressure medium alternatively to one or the opposed chamber portions and simultaneously direct pressure medium exhausted from the respective opposite chamber portion to the store.

10. A system as claimed in claim 9, wherein the first and second chambers are axially spaced together on a common axis with the piston rod extending along the common axis.

11. A system as claimed in claim 10, including coupling means for interconnecting the piston rod with the well apparatus.

12. A system as claimed in claim 11, wherein the well apparatus comprises a rod string connected to a ball-check pump at the bottom of the well.

13. A system as claimed in any one of claims 9 to 12, including a reservoir connected with the first piston chamber.

14. A system as claimed in claim 13, wherein the reservoir is further connected to an outlet of the well.

15. A system as claimed in claim 13 or 14, wherein the reservoir is connected to a first chamber portion of the first chamber to effect a lifting motion on the first piston.

16. A system as claimed in claim 15, wherein the chamber portion on the opposite side of the first piston to the first chamber portion of the first chamber is vented to the atmosphere.

17. A system as claimed in any one of claims 13 to 16, including a control valve located in the connection between the reservoir and the outlet of the well.

18. A system as claimed in any one of claims 13 to 17, wherein the reservoir is provided with a pressure relief valve.

19. A system as claimed in any one of claims 9to 18, including a control valve connected in the connection between the control means and outlet of the well.

20. A system as claimed in claim 17 or 19, wherein the control valves are manually operable valves.

21. A system as claimed in any one of claims 9 to 20, wherein three piston chambers are axially spaced together with their respective pistons connected to a common piston rod.

22. A pumping system substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawings.