Modular subsurface lift engine

Abstract

A modular subsurface lift engine lifts hydrocarbons directly or indirectly from a cased wellbore. The modular subsurface lift engine has a surface drive system with a fluid pump that pumps a lift fluid into an isolated annulus of the cased well bore surrounding subsurface lift engine. A lift capacity of the subsurface lift engine is increased by increasing the number of lift engine modules.

Claims

1. A modular subsurface lift engine, comprising: an upper valve housing with an upper valve seat and an upper valve for controlling a flow of produced fluid hydrocarbons through the subsurface lift engine during a down-stroke thereof; an upper crossover sleeve connected to a bottom end of the upper valve housing; an upper transition sleeve connected to a bottom end of the upper crossover sleeve; an upper crossover tube connected to an upper travel limiter that reciprocates within the upper transition sleeve, the upper crossover tube extending through a central passage in a bottom of the upper transition sleeve; at least one subsurface lift engine module connected to a bottom end of the upper transition sleeve, respectively comprising a modular cylinder sleeve, a modular cylinder piston that reciprocates within the modular cylinder sleeve, and a modular cylinder tube connected to a lower side of the modular cylinder piston and extending through a passage in a modular cylinder sleeve bottom wall of the modular cylinder sleeve; and a lower crossover sleeve adapted to connect to a production packer that isolates an annulus of the cased well bore surrounding the modular subsurface lift engine from the annulus of the cased well bore below the production packer.

2. The modular subsurface lift engine as claimed in claim 1 wherein the lower crossover sleeve further comprises a lower valve housing with a lower valve seat and a lower valve for controlling a flow of produced fluids through the subsurface lift engine during an up-stroke thereof.

3. The modular subsurface lift engine as claimed in claim 1 further comprising a sucker rod string connected to a bottom end a of a lower crossover tube of the modular subsurface lift engine, the sucker rod string extending through the production packer and connecting to a downhole fluid pump.

4. The modular subsurface lift engine as claimed in claim 1 wherein the upper valve housing is adapted to connect to a production tubing supported by a wellhead of the cased well bore.

5. The modular subsurface lift engine as claimed in claim 1 wherein each modular cylinder sleeve comprises modular cylinder sleeve ports through a sidewall thereof, the modular cylinder sleeve ports being adjacent the modular cylinder sleeve bottom wall and modular cylinder tube ports adjacent a bottom end of the respective modular cylinder tubes.

6. The modular subsurface lift engine as claimed in claim 1 wherein the upper valve and the lower valve respectively comprise a ball valve and an upper valve limiter in the upper valve housing and a ball valve and lower valve limiter in the lower valve housing.

7. The modular subsurface lift engine as claimed in claim 5 further comprising a piston upper travel limiter on an upper side of the respective modular cylinder pistons to limit an upward travel of the respective modular cylinder pistons in the respective modular cylinder sleeves and a piston lower travel limiter on a lower side of the respective modular cylinder pistons to limit a downward travel of the respective modular cylinder pistons in the respective modular cylinder sleeves.

8. The modular subsurface lift engine as claimed in claim 4 wherein the upper crossover sleeve is elongated and houses a downstroke spring that constantly urges the modular subsurface lift engine to a bottom-of-stroke condition.

9. The modular subsurface lift engine as claimed in claim 5 further comprising a modular surface lift engine drive system that comprises: a fluid pump adapted to continuously pump a lift fluid from a lift fluid reservoir at a predetermined rate; and at least two control valves for controlling a flow of the lift fluid so that the lift fluid is supplied from the lift fluid reservoir to the isolated annulus during an upstroke of the modular subsurface lift engine and diverted to the lift fluid reservoir while lift fluid is drained from the isolated annulus to the lift fluid reservoir during a downstroke of the modular subsurface lift engine.

10. The modular subsurface lift engine as claimed in claim 9 wherein the modular subsurface lift engine drive system comprises: a lift fluid supply line connected between the lift fluid reservoir and an input of the fluid pump to supply the lift fluid to the fluid pump; a lift fluid pressure line connected to an output of the fluid pump and in fluid communication with the isolated annulus above the production packer; a first control valve in the lift fluid pressure line adapted to control a flow of lift fluid through the lift fluid pressure line by selectively diverting the lift fluid to a lift fluid bypass line interconnecting the first control valve and the lift fluid reservoir; a lift fluid dump line providing fluid communication between the isolated annulus and the lift fluid reservoir; a second control valve in the lift fluid dump line adapted to control lift fluid flow through the lift fluid dump line; a control circuit for controlling the first and second control valves; and at least one lift fluid pressure sensor connected to the control circuit, the lift fluid pressure sensor sensing a pressure of the lift fluid in the isolated annulus.

11. The modular subsurface lift engine as claimed in claim 10 wherein the first control valve and the second control valve are respectively controlled by solenoids connected to the control circuit.

12. A modular subsurface lift engine, comprising: an upper valve housing adapted to connect to a production tubing supported by a wellhead of a cased well bore, the upper valve housing having an upper valve seat and an upper valve for controlling a flow of produced fluid through the subsurface lift engine during a down-stroke thereof; an upper crossover sleeve connected to a bottom end of the upper valve housing; an upper transition sleeve connected to a bottom end of the upper crossover sleeve, the upper transition sleeve having an upper crossover tube that is connected to a bottom of a transition travel limiter, the crossover sleeve extending through a central passage in a bottom of the upper transition sleeve; at least one subsurface lift engine module connected to a bottom end of the upper transition sleeve and comprising a modular cylinder sleeve, a modular cylinder piston that reciprocates within the modular cylinder sleeve, and a modular cylinder tube connected to a lower side of the modular cylinder piston and extending through a passage in a modular cylinder sleeve bottom wall of the modular cylinder sleeve; and a lower crossover sleeve having a lower valve housing with a lower valve seat and a lower valve for controlling a flow of produced fluids through the subsurface lift engine during an up-stroke thereof, the lower crossover sleeve being adapted to connect to a production packer that isolates an annulus of the cased well bore surrounding the modular subsurface lift engine from the annulus of the cased well bore below the production packer.

13. The modular subsurface lift engine as claimed in claim 12 wherein each modular cylinder sleeve comprises modular cylinder sleeve ports through a sidewall thereof, the modular cylinder sleeve ports being adjacent the modular cylinder sleeve bottom wall and providing fluid communication between the isolated annulus and a lift chamber within the modular cylinder sleeve.

14. The modular subsurface lift engine as claimed in claim 13 further comprising modular cylinder tube ports adjacent a bottom end of the respective modular cylinder tubes to provide fluid communication between a respective modular cylinder lift chamber of the respective modular cylinder sleeves and an interior of the respective modular cylinder tubes.

15. The modular subsurface lift engine as claimed in claim 12 wherein the upper valve and the lower valve respectively comprise one of a ball valve and a flapper valve.

16. The modular subsurface lift engine as claimed in claim 12 wherein each subsurface lift engine module further comprises a piston upper travel limiter on an upper side of the modular cylinder piston to limit an upward travel of the modular cylinder piston in the modular cylinder sleeve, the piston upper travel limiter being adapted to connect to a modular cylinder tube of another subsurface lift engine module connected to a top end thereof, and a piston lower travel limiter on a lower side of the respective modular cylinder pistons to limit a downward travel of the respective modular cylinder pistons in the respective modular cylinder sleeves, and the respective modular cylinder tubes are respectively connected to the respective lower piston travel limiters.

17. The modular subsurface lift engine as claimed in claim 12 wherein the upper crossover sleeve is elongated and houses a downstroke spring that constantly urges the modular subsurface lift engine to a bottom-of-stroke condition.

18. The modular subsurface lift engine as claimed in claim 12 further comprising a modular surface lift engine drive system that comprises: a fluid pump adapted to continuously pump a lift fluid from a lift fluid reservoir at a predetermined rate; and at least two control valves for controlling a flow of the lift fluid so that lift fluid is supplied from the lift fluid reservoir to the isolated annulus during an upstroke of the modular subsurface lift engine and diverted to the lift fluid reservoir while lift fluid is drained from the isolated annulus to the lift fluid reservoir as the modular subsurface lift engine downstrokes.

19. The modular subsurface lift engine as claimed in claim 18 wherein the modular subsurface lift engine drive system comprises: a lift fluid supply line connected between of the lift fluid reservoir and an input of the fluid pump; a lift fluid pressure line connected to an output of the fluid pump and in fluid communication with the isolated annulus above the production packer; a first control valve in the lift fluid pressure line adapted to control a flow of lift fluid through the lift fluid pressure line by selectively diverting the lift fluid to a lift fluid bypass line interconnecting the first control valve and the lift fluid reservoir during a downstroke of the modular lift engine; a lift fluid dump line providing fluid communication between the annulus and the lift fluid reservoir; a second control valve in the lift fluid dump line adapted to control lift fluid flow through the lift fluid dump line, to permit lift fluid to flow through the lift fluid dump line only during the downstroke of the modular lift engine; a control circuit for controlling the first and second control valves; and at least one lift fluid pressure sensor connected to the control circuit, the lift fluid pressure sensor sensing a pressure of the lift fluid in the isolated annulus.

20. A modular subsurface lift engine, comprising: at least one subsurface lift engine module adapted to be connected end-to-end to other subsurface lift engine modules, each subsurface lift engine module comprising: a modular cylinder sleeve having an open top end, a cylinder sleeve bottom wall with a central passage therein, and at least two cylinder sleeve ports adjacent the cylinder sleeve bottom wall to provide fluid communication through the modular cylinder sleeve with a modular cylinder lift chamber; a modular cylinder piston with a modular piston seal that provides a high-pressure fluid seal between an inner wall of the modular cylinder sleeve and the modular cylinder piston, the modular cylinder piston having an upper travel limiter and a lower travel limiter to limit travel of the modular cylinder piston in the modular cylinder sleeve; a modular cylinder tube connected to the bottom travel limiter of the modular cylinder piston and extending through a high pressure fluid seal in the central passage in the modular cylinder bottom wall, the modular cylinder tube having at least two modular cylinder tube ports that provide fluid communication through a sidewall of the modular cylinder tube with a modular cylinder pump chamber above the modular cylinder piston in an adjacent lower modular cylinder sleeve; an upper valve housing adapted to connect a production tubing supported by a wellhead of a cased well bore, the upper valve housing having an upper valve seat and an upper valve for controlling a flow of produced fluids through the subsurface lift engine during a down-stroke thereof; an upper crossover sleeve connected to a bottom end of the upper valve housing; an upper transition sleeve connected to a bottom end of the upper crossover sleeve, the upper transition sleeve having a bottom end connected to the at least one lift engine module, and further having an upper crossover tube that is connected to a bottom end of an upper transition travel limiter that reciprocates within the upper transition sleeve, the upper crossover tube extending through a central passage in a bottom of the upper transition sleeve; and a lower crossover sleeve having a lower valve housing with a lower valve seat and a lower valve for controlling a flow of produced fluid hydrocarbons through the subsurface lift engine during an up-stroke thereof, the lower crossover sleeve being adapted to connect to a production packer that isolates the subsurface lift engine from an annulus of the cased well bore below it, the production packer supporting a production tubing that extends downwardly to hydrocarbon fluids in the cased well bore.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, in which:

(2) FIG. 1a is a cross-sectional view of an embodiment of a modular subsurface lift engine in accordance with the invention configured to directly produce fluids from a cased well bore, shown in an installed condition in the cased wellbore equipped with a production wellhead;

(3) FIG. 1b is the cross-sectional view of the embodiment of the modular subsurface lift engine shown in FIG. 1a, enlarged to more clearly illustrate the elements of the subsurface lift engine;

(4) FIG. 2 is a schematic view of one embodiment of surface equipment used to drive the modular subsurface lift engine shown in FIGS. 1a and 1b and 5;

(5) FIG. 3a is a cross-sectional view of the modular subsurface lift engine shown in FIGS. 1a and 1b in an up-stroke condition;

(6) FIG. 3b is a cross-sectional view of the modular subsurface lift engine shown in FIGS. 1a and 1b in a top-of-stroke condition;

(7) FIG. 4a is a cross-sectional view of the modular subsurface lift engine shown in FIGS. 1a and 1b in a down-stroke condition;

(8) FIG. 4b is a cross-sectional view of the modular subsurface lift engine shown in FIGS. 1a and 1b in a bottom-of-stroke condition;

(9) FIG. 5 is a cross-sectional view of one embodiment of a modular subsurface lift engine configured to indirectly produce hydrocarbons from a cased well bore.

(10) FIG. 6 is a cross-sectional view of another embodiment of the modular subsurface lift engine in accordance with the invention configured to directly produce fluids from a cased well bore, shown in an installed condition in the cased wellbore equipped with a production wellhead; and

(11) FIG. 7 is a cross-sectional view of the embodiment of the modular subsurface lift engine installed in a horizontal wellbore.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(12) The invention provides a modular subsurface lift engine adapted to directly or indirectly produce fluids from a cased wellbore. Subsurface lift engine modules are respectively connected end-to-end to provide a lift capacity required to lift the fluids from the cased wellbore. The number of lift engine modules required for a particular installation depends on any one or more of several factors. In the case of directly lifting the fluid from the wellbore, those factors may include: a viscosity of the fluids; a vertical lift requirement; a diameter of the wellbore production casing; a diameter of the wellbore production tubing; and, a desired rate of production. In the case of indirectly lifting the fluids from the cased wellbore, the subsurface lift engine may be connected to a downhole reciprocal pump, such as a tubing pump or an insert pump, using a subsurface sucker rod string and the factors determining the number of lift engine modules may include: a viscosity of the fluids; a vertical lift requirement; a diameter of the wellbore production casing; a diameter of the wellbore production tubing; a desired rate of production; a weight of the sucker rod string; and, power requirements of the driven pump.

(13) In the embodiment of the modular lift engine used to directly lift liquid hydrocarbons from a wellbore, an upper valve housing connects the interconnected lift engine modules to a production tubing joint suspended from a production wellhead. An upper valve is housed in the upper valve housing. The upper valve may be any one of a ball valve, a check valve or a flapper valve. The upper valve prevents the backflow of lifted fluids during a downstroke of the lift engine. The upper valve housing is mounted to a top of an upper crossover sleeve. In one embodiment the upper crossover sleeve is elongated and a downstroke spring is inserted between a top end of the upper crossover sleeve and an upper transition travel limiter. The downstroke spring constantly urges the modular subsurface lift engine to a bottom-of-stroke condition to provide a positive downstroke when the modular subsurface lift engine is installed in a highly deviated wellbore, a horizontal wellbore, is used to produce very viscous fluid, or is used to provide a very long vertical lift. An upper transition sleeve connected to a bottom of the upper crossover sleeve supports the interconnected lift engine modules.

(14) A lower crossover sleeve connects the interconnected lift engine modules to a production packer that isolates the modular subsurface lift engine from the cased wellbore below the production packer. A production tubing string is connected to a lower end of the production packer. The production tubing string extends down through the cased wellbore to the fluids to be produced from the cased well bore.

(15) Each lift engine module includes a modular cylinder sleeve having an open top end and a modular cylinder sleeve bottom wall that connects the modular cylinder sleeve to a lift engine module below it. Each modular cylinder sleeve bottom wall has a central opening that accommodates a modular cylinder tube. A lower end of each modular cylinder sleeve includes at least two modular cylinder sleeve ports that provide fluid communication between an annulus of the cased well bore and a lift chamber of the modular cylinder sleeve. Each modular cylinder sleeve houses a modular cylinder piston having a piston seal that provides a high pressure fluid seal between the modular cylinder piston and an inner wall of the modular cylinder sleeve. Each modular cylinder piston has a top travel limiter that limits piston travel during an up-stroke of the subsurface lift engine. Each modular cylinder piston also has a bottom travel limiter that limits the piston travel during a down-stroke of the cylinder piston. The bottom travel limiter prevents the cylinder piston from occluding the modular cylinder sleeve ports at the bottom of a down-stroke of the subsurface lift engine. A modular cylinder tube is threadedly connected to a lower end of each piston lower travel limiter and a top end of a piston upper travel limiter of an adjacent lower module. The modular cylinder tubes provide an uninterrupted fluid path through the interconnected cylinder modules. Each modular cylinder tube has at least two modular cylinder tube ports that provide fluid communication with a modular cylinder pump chamber above the modular cylinder piston of each subsurface lift engine module. The piston upper travel limiters prevent the modular cylinder tube ports from reaching a high-pressure fluid seal in the bottom wall of an adjacent lift engine module above it.

(16) The lower crossover sleeve includes a lower valve housing with a lower valve seat and a lower valve that controls fluid flow through the subsurface lift engine modules during an up-stroke of the subsurface lift engine. The lower valve may be any one of a ball valve, a check valve or a flapper valve.

(17) The subsurface lift engine is driven by surface equipment assembled using components well known in the art. In one embodiment a high-pressure fluid pump pumps a lift fluid from a lift fluid reservoir. The lift fluid may be any stable, non-corrosive fluid such as, for example, corrosion inhibited water or a light oil such as diesel fuel, kerosene, hydraulic fluid, or the like. Lift fluid is supplied to the high-pressure pump through a lift fluid supply line. Lift fluid exits the high-pressure fluid pump via a pump pressure line to a pump pressure valve, for example a solenoid-controlled valve, that selectively routes the lift fluid thorough the lift fluid pressure line to the annulus of the hydrocarbon well isolated by the production packer, or to a lift fluid pressure bypass line connected to the lift fluid reservoir. The annulus of the hydrocarbon well is also connected to a lift fluid dump line, which is in turn connected to the lift fluid reservoir. A dump fluid valve controls flow through the lift fluid dump line.

(18) In operation, the high-pressure pump continuously pumps the lift fluid at a predetermined pump rate. During an upstroke of the subsurface lift engine, the solenoid-controlled valve in the lift fluid pressure line is open and the lift fluid dump valve in the lift fluid dump line is closed. The lift fluid therefore flows into the isolated annulus of the hydrocarbon well and through the modular cylinder sleeve ports into the respective modular cylinder lift chambers, urging the respective modular cylinder pistons upwardly. The upward movement of the modular cylinder pistons forces produced fluid out of the modular cylinder produced fluid chambers through the modular cylinder tube ports, up through the respective modular cylinder tubes to the production tubing in the wellhead, and out through a hydrocarbon production pipe to a hydrocarbon production reservoir, which may be a tank, a pipeline, or the like. When the modular cylinder piston upper travel limiters contact the modular cylinder bottom wall of an adjacent lift engine module, a pressure spike occurs in the lift fluid. The pressure spike is sensed by a pressure sensor that trips the lift fluid dump valve to open the lift fluid dump line and simultaneously trips the pump pressure line control valve to shift to reroute the lift fluid through the lift fluid bypass line to the lift fluid reservoir. These valve movements drain lift fluid pressure from the subsurface lift engine and the annulus of the wellbore, and the subsurface lift engine down-strokes under its own weight and, in one embodiment, the pressure of the downstroke spring. The down-stroke closes the upper valve and opens the lower valve as the modular cylinder pistons downward movements create suction in the respective modular cylinder produced fluid chambers, which sucks produced fluid up into the respective modular cylinder produced fluid chambers. When the pressure sensor senses an absence of fluid pressure in the dump fluid line, the lift fluid dump valve is closed and the lift fluid bypass valve is shifted to reroute the lift fluid from the lift fluid bypass line to the lift fluid pressure line and another up-stroke commences. During the up-stroke, the subsurface lift engine lower valve is closed and the subsurface lift engine upper valve opens as the produced fluids flow from the modular cylinder produced fluid chambers to the hydrocarbon reservoir, as described above.

(19) TABLE-US-00001 Part No. Part Desc1ription 10 Modular subsurface lift engine 10a Subsurface lift engine (indirect production configuration) 10b Subsurface lift engine (downstroke spring assist) 12 Wellhead 14 Production casing 16 Production tubing pup joint 18 Upper crossover sleeve 18b Elongated upper crossover sleeve 20 Upper transition sleeve 21 Upper transition travel limiter 22 Upper valve housing 23 Upper crossover tube 24 Upper valve seat 26 Upper transition sleeve cap 28 Upper valve fluid seal 30 Upper ball valve 31 Upper valve limiter 32a-32d Subsurface lift engine modules 34a-34d Modular cylinder sleeves 35a-35d Modular cylinder sleeve bottom walls 36a-36h Modular cylinder sleeve ports 37a-37d Modular cylinder sleeve bottom wall passage 38a-38d Modular cylinder pistons 39a-39d Modular cylinder sleeve inner walls 40a-40d Modular cylinder piston seals 42a-42d Piston upper travel limiters 44a-44d Piston lower travel limiters 45a-45d Modular cylinder lift chambers 46b-46d Modular cylinder tubes 48c-48h Modular cylinder tube ports 49b-49d Modular cylinder produced fluid chambers 50a-50d Modular cylinder tube upper seals 52a-52d Modular cylinder tube lower seals 54 Lower crossover sleeve 55 Lower crossover tube 55a Lower crossover tube (indirect production configuration) 56 Lower valve housing 58 Lower valve seat 60 Lower valve seal cap 62 Lower valve fluid seal 64 Lower ball valve 65 Lower valve limiter 66 Production packer 68 Production packer slips 70 Production tubing string 72 Sucker rod string 74 Downhole pump 75a, 75a Lower crossover tube ports 76 Lower crossover tube thread 100 Surface equipment 102 Fluid pump 104 Lift fluid reservoir 106 Lift fluid supply line .sup.108a-b Lift fluid pressure line 110 Pump pressure line control valve 112 Lift fluid bypass line .sup.114a-b Lift fluid dump line 116 Lift fluid dump valve 117 Lift fluid pressure sensor 118 Solenoid control circuit 120 Hydrocarbon production pipe 122 Hydrocarbon reservoir 124 Lift fluid 126 Produced fluid 128 Isolated well bore annulus 130 Downstroke spring

(20) FIG. 1a is a cross-sectional view of one embodiment of a modular subsurface lift engine 10 in accordance with the invention, configured to directly produce hydrocarbons from a cased well bore 14. The modular subsurface lift engine 10 is shown in an installed condition in the production casing 14 of a cased well bore, which is equipped with a production wellhead 12. Surface components of the cased well bore, such as the conductor, etc. are not shown. A top end of the modular subsurface lift engine 10 is connected to the wellhead 12 by a production tubing pup joint 16 in a manner well known in the art. A bottom end of the modular subsurface lift engine 10 is connected to a production packer 66, which is well known in the art. The production packer 66 provides a high-pressure fluid seal to isolate an annulus of the production casing 14 around the modular subsurface lift engine 10 from an annulus of the production casing 14 below the production packer 14, the purpose of which will be explained in detail below with reference to FIGS. 1b and 2. The production packer 66 is supported in the production casing 14 by production packer slips 68, in a manner also well understood in the art. A production tubing string 70, which extends down to a production zone of the cased well bore, is connected to a downhole end of the production packer 66.

(21) FIG. 1b is the cross-sectional view of the embodiment of the modular subsurface lift engine 10 shown in FIG. 1a, enlarged to more clearly illustrate the elements of the modular subsurface lift engine 10. The modular subsurface lift engine 10 includes an upper valve housing 22 connected to the production tubing pup joint 16. An upper valve seat 24 is connected to a bottom end of the upper valve housing 22. An upper valve housing cap 26 is connected to a top end of the upper valve housing 22. The upper valve housing cap 26 supports an upper valve fluid seal 28, which provides a high-pressure fluid seal between the production tubing pup joint 16 and the upper valve housing 22. The upper valve seat 24 supports an upper valve, which in this embodiment is an upper ball valve 30, although the upper valve may be a flapper valve or a check valve, both of which are well known in the art. Upward travel of the upper ball valve 30 is restrained by an upper valve limiter 31, which is only required when the upper valve is the upper ball valve 30. A bottom end of the upper valve housing 22 is connected to an upper crossover sleeve 18. An upper transition sleeve 20 is connected to a bottom end of the upper crossover sleeve 18. The upper transition sleeve 20 receives an upper transition travel limiter 21 connected to an upper crossover tube 23.

(22) Connected to a bottom end of the upper transition sleeve 20 is a first subsurface lift engine module 32a. Each subsurface lift engine module 32a-32d includes a modular cylinder sleeve 34a-34d, which has a modular cylinder sleeve bottom wall 35a-35d. Just above the modular cylinder sleeve bottom wall are a plurality of modular cylinder sleeve ports 36a-36h, only two of which are shown in each modular cylinder sleeve 34a-34d. The function of the modular cylinder sleeve ports 36a-36h be explained below with reference to FIGS. 2-4b. Each modular cylinder sleeve bottom wall 35a-35d also includes a modular cylinder sleeve bottom wall passage 37a-37d that accommodates a modular cylinder tube 46b-46d, as will be explained below in more detail. A modular cylinder piston 38a-38d reciprocates within each modular cylinder sleeve 34a-34d. A modular cylinder piston seal 40a-40d provides a high-pressure fluid seal between respective modular cylinder sleeve inner walls 39a-39d of the respective modular cylinder sleeves 34a-34d and the respective modular cylinder pistons 38a-38d. Each modular cylinder piston 38a-38d includes piston upper travel limiters 42a-42d which limits upward travel of the respective modular cylinder pistons 38a-38d in the respective modular cylinder sleeves 34a-34d to prevent an occlusion of modular cylinder tube ports 48c-48h in the respective modular cylinder tubes 46b-46d. Each modular piston 38a-38d also includes piston lower travel limiters 44a-44d. The piston lower travel limiters 44a-44d limit downward travel of the respective modular cylinder pistons 38a-38d in the respective modular cylinder sleeves 32a-32d to prevent an occlusion by the respective modular cylinder pistons 38a-38d of modular cylinder sleeve ports 36a-36h in the respective modular cylinder sleeves 34a-34d. Each modular cylinder piston 38a-38d divides an interior of the respective modular cylinder sleeves 34a-34d into a modular cylinder lift chamber 45a-45d and a modular cylinder produced fluid chamber 49a-49d, the respective functions of which will be explained below in detail.

(23) A respective modular cylinder tube 46b-46d interconnects a respective piston lower travel limiter 44a-44d to a respective piston upper travel limiter 42a-42d. A respective modular cylinder tube upper seal 50a-50e provides a high-pressure fluid seal around a top end of the respective modular cylinder tubes 46a-46d where they pass through the respective modular cylinder sleeve bottom walls 35a-35d. A respective modular cylinder tube lower seal 52a-52d provides a high-pressure fluid seal around a bottom end of the respective modular cylinder tubes 46a-46d where they connect to the respective modular cylinder pistons 38a-38d.

(24) A lower crossover sleeve 54 is connected to a lowest subsurface lift engine module, 32d in this example. A bottom end of the lower crossover sleeve 54 is connected to the production packer 66. The lower crossover sleeve 54 houses a lower valve housing 56, which reciprocates within the lower crossover sleeve 54. The lower valve housing 56 has a lower valve seat 58 and a lower valve seat seal cap 60. The lower valve seat cap 60 is connected to a lower crossover tube 55 having a top end connected to the piston lower travel limiter 44d. The lower valve seat 58 supports a lower valve fluid seal 62 that provides a high-pressure fluid seal between the lower valve housing 56 and the lower crossover sleeve 54. A lower valve, in this example lower ball valve 64 is received in the lower valve seat 58. A lower valve limiter 65 limits an upward travel of the lower ball valve 64 during a downstroke of the modular lift engine 10.

(25) FIG. 2 is a schematic view of one embodiment of surface equipment 100 used to power the modular subsurface lift engine 10 shown in FIGS. 1a and 1b. In this embodiment, the surface equipment 100 includes a high-pressure fluid pump 102, the specifications of which are readily computed by one skilled in the art of hydraulics. Lift fluid 124 is stored in a lift fluid reservoir 104, the capacity of which is dependent on a diameter of an annulus of the production casing 14 and a number of subsurface lift engine modules 32 in the modular subsurface lift engine 10, as will be readily understood by those skilled in the art. A lift fluid supply line 106 supplies lift fluid 124 from the lift fluid reservoir 104 to the fluid pump 102. The lift fluid selected depends on an operating environment in which the modular lift engine is used. A light hydrocarbon, such as kerosene or diesel fuel, is acceptable in most environments, though corrosion and, if necessary, frost-inhibited, water may also be used. A lift fluid pressure line 108a connects an output of the fluid pump 102 to a pump pressure line control valve 110 that in one embodiment is operated by a solenoid that switches fluid flow through the lift fluid pressure line 108a to one of a lift fluid pressure line 108b and a lift fluid bypass line 112. As explained above, during an upstroke of the modular subsurface lift engine 10, the lift fluid flows into the annulus of the cased well bore 14. In one embodiment, at the top of stroke, a pressure spike in the lift fluid is detected by a lift fluid pressure sensor 117 connected to a solenoid control circuit 118, which switches the pump pressure line control valve 110 to bypass mode so the lift fluid 124 is diverted through a lift fluid bypass line 112. The lift fluid 124 is thus returned to the lift fluid reservoir 104. In one embodiment a solenoid control circuit 118 interconnects the pump pressure line control valve 110 and a lift fluid dump valve 116, which in one embodiment is also controlled by a solenoid. When the pump pressure line control valve 110 switches to the bypass mode, a signal sent through the solenoid control circuit 116 to the lift fluid dump valve 116 opens the lift fluid dump valve 116 and allows lift fluid 124 to flow from the annulus of the production casing 14 of the cased well bore to the lift fluid reservoir 104 through lift fluid dump lines 114a, 114b. As lift fluid 124 is dumped from the modular subsurface lift engine 10 it begins a downstroke under its own weight. At the bottom of the downstroke, fluid flow through the lift fluid dump lines 114a, 114b stops and pressure in the lift fluid dump lines 114a, 114b drops. The pressure drop is sensed by the lift fluid pressure sensor 117 which sends a signal through the solenoid control circuit 118 that causes the lift fluid dump valve 116 to close and the pump pressure line control valve 110 to switch lift fluid flow from the lift fluid bypass line 112 to the lift fluid pressure line 108b. This starts the modular subsurface lift engine on another upstroke, lifting hydrocarbon through a hydrocarbon production pipe 120 to a hydrocarbon reservoir 122, which may be a tank, a pipeline, or the like.

(26) FIG. 3a is a cross-sectional view of an embodiment of the modular subsurface lift engine 10 shown in FIGS. 1a and 1b in an up-stroke condition. As explained above, during an upstroke the lift fluid 124 is being pumped into the isolated annulus 128 of the production casing 14 and is forced through the modular cylinder sleeve ports 36a-36f into the respective cylinder lift chambers 45a-45d, which urges the respective modular cylinder pistons 38a-38d upwardly. The upward movement of the modular cylinder pistons 45a-45d urges produced fluid 126 out of the respective modular cylinder produced fluid chambers 49a-49d and into the modular cylinder tubes 46b-46d. Initiation of the up-stroke closes the lower ball valve 64 and opens the upper ball valve 30, pumping fluid through the wellhead 12 and into the hydrocarbon production pipe 120. When the modular subsurface lift engine reaches top of stroke, the piston upper travel limiters 42a-42d contact a respective modular cylinder sleeve bottom wall 35a-35d, which halts further movement of the modular cylinder pistons 45a-45d, causing a pressure spike in the lift fluid 124, as described above with reference to FIG. 2.

(27) FIG. 3b is a cross-sectional view of the modular subsurface lift engine 10 shown in FIGS. 1a and 1b in a top-of-stroke condition. In this condition, the upper ball valve 30 and the lower ball valve 60 both rest on their respective valve seats.

(28) FIG. 4a is a cross-sectional view of the modular subsurface lift engine 10 shown in FIGS. 1a and 1b in a down-stroke condition. When, as described above with reference to FIG. 2, the pump pressure line control valve 110 diverts lift fluid from the lift fluid pressure line 108a to the lift fluid bypass line 112, lift fluid 124 stops flowing into the isolated annulus 128 of the production casing 14 and the weight of the moveable parts of the modular subsurface lift engine 10 returns those parts to a bottom-of-stroke condition. This creates fluid pressure in the respective modular cylinder lift chambers 45a-45d, forcing lift fluid 124 out of those modular cylinder lift chambers 45a-45d, into the isolated annulus 128 and up through the lift fluid dump lines 114a and 114b to the lift fluid reservoir 104 (see FIG. 2). It also creates suction in the respective modular cylinder produced fluid chambers 49b-49d, which draws produced fluid 126 up into those chambers from the production tubing string 70. The lower ball valve 64 remains open until the respective modular cylinder produced fluid chambers 49b-49d are full and the modular subsurface lift engine is at bottom stroke, where the respective piston lower travel limiters 44a-44d contact the respective modular cylinder sleeve bottom walls 35a, 35d.

(29) FIG. 4b is a cross-sectional view of the modular subsurface lift engine 10 shown in FIGS. 1a and 1b in a bottom-of-stroke condition. In this condition, the upper ball valve 30 and the lower ball valve 60 both rest on their respective valve seats.

(30) FIG. 5 is a cross-sectional view of one embodiment of a modular subsurface lift engine 10a configured to indirectly produce hydrocarbons from a cased well bore. In this configuration, the modular subsurface lift engine 10a is as described above with reference to FIG. 1b, except that the lower valve housing 56 (see FIG. 1b), and all components within it, is removed from the lower crossover sleeve 54, and the lower crossover tube 55a is provided with lower crossover tube ports 75a, 75b and internal tread 76 for the connection of a top end of a sucker rod string 72. The sucker rod string 72 extends down through the production packer and the production tubing string 70 and is operatively connected a downhole pump 74 for lifting the produced fluid 126 from the cased well bore. The downhole pump 74 may be a sucker rod pump, which connect to a bottom end of a production tubing string 70, or an insert pump secured within a bottom end of the production tubing string 70. The downhole pump is selected to have a stroke length equal to a travel of the subsurface lift engine 10a from bottom-of-stroke to top-of-stroke.

(31) In use, the modular subsurface lift engine 10a operates as described above with reference to FIG. 2. As understood by those skilled in the art, the number of subsurface lift engine modules 32 selected for the subsurface lift engine 10a is dependent on an output of the fluid pump 102, a weight of the sucker rod string 72, and power requirements of the downhole pump 74.

(32) FIG. 6 is a cross-sectional view of another embodiment of the modular subsurface lift engine 10b in accordance with the invention configured to directly produce fluids from a cased well bore, shown in an installed condition in the cased wellbore equipped with a production wellhead 12. The subsurface lift engine 10b is identical to the subsurface lift engine described above with reference to FIGS. 1A and 18, except that the upper crossover sleeve 18 is replaced with an elongated upper crossover sleeve 18b, which accommodates a downstroke spring 130 that provides downstroke assist to the modular subsurface lift engine 10b. The downstroke spring 130 constantly urges the modular subsurface lift engine 10b to the bottom-of-stroke condition. The compression force of the downstroke spring 130 is selected to provide a predetermined downstroke return force in the modular subsurface lift engine that is dependent on factors such as a viscosity of the produced fluid 126, a height of lift required to produce fluid 126, etc. The modular subsurface lift engine 10b is also ideally suited for installation in a highly deviated or a horizontal well bore, as will be explained below with reference to FIG. 7.

(33) FIG. 7 is a cross-sectional view of the embodiment of the modular subsurface lift engine 10b installed in a horizontal wellbore with a production casing 14. Since the downstroke force for the modular subsurface lift engine 10b is provided by the downstroke spring 130, the modular subsurface lift engine can be installed within a horizontal wellbore, which ensures maximum production of produced fluid 124. When installed in a highly deviated or horizontal well bore, the upper and lower ball valves are also replaced with spring-biased flapper valves 132 to ensure valve operation in any orientation.

(34) The explicit embodiments of the invention described above have been presented by way of example only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.