WO2010016767A2

WO2010016767A2 - Subsurface reservoir drainage system

Info

Publication number: WO2010016767A2
Application number: PCT/NO2009/000268
Authority: WO
Inventors: Henning Hansen
Original assignee: Ziebel As
Priority date: 2008-08-08
Filing date: 2009-07-20
Publication date: 2010-02-11
Also published as: WO2010016767A3

Abstract

A subsurface reservoir drainage system includes a primary well drilled through subsurface rock formations including a subsurface reservoir. At least one import/export well is drilled through the subsurface rock formations and intersects the primary well. A pump is disposed in the at least one import/export well for pumping fluid into or out of the at least one primary well.

Description

SUBSURFACE RESERVOIR DRAINAGE SYSTEM

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. Provisional Application No. 61/087196, filed August 8, 2008.

FIELD The invention relates generally to production of fluids, e.g., hydrocarbons, from a subsurface reservoir. More specifically, the invention relates to structures for wellbores for producing fluids from and/or injecting fluids into subsurface reservoirs .

BACKGROUND

Fluids are typically produced from a subsurface reservoir through one or more production wells that extend from the Earth's surface, marine platform or sea floor and into the reservoir. A tubing and/or casing may be provided in the production well for transporting the reservoir fluids to the surface. The reservoir fluids may be lifted through the tubing and/or casing by natural pressure in the reservoir, with the assistance of a pump, or by artificial lift. As the reservoir becomes depleted other recovery techniques may be needed to produce the fluids from the reservoir. For example, an injection well may be drilled into the reservoir at a location spaced apart from the production well and used to inject fluid into the reservoir, where the injected fluid would promote flow of fluids from the reservoir into the production well. U.S.

Patent No. 7,073,577 describes a permeable zone connecting a vertical production well to a vertical injection well, where both wells are drilled into a subsurface reservoir. The permeable zone includes a patterned web of channels radiating from the outlet end of the vertical injection well and connecting to the inlet end of the production well. A heated fluid flows from the outlet of the injection well into the permeable zone to mobilize fluids in the reservoir so that the reservoir fluids flow into the inlet of the production well. The shape of the permeable zone may be such that it induces gravity- drainage of the reservoir fluids into the inlet of the production well.

There continues to be a need for improved well configurations to produce fluid from and/or inject fluid into subsurface reservoirs.

SUMMARY

In one aspect, the invention relates to a subsurface reservoir drainage system. The system comprises a primary well drilled through subsurface rock formations comprising a subsurface reservoir. The system further comprises at least one import/export well drilled through the subsurface rock formations and intersecting the primary well. The system further comprises a pump disposed in the at least one import/export well for pumping fluid into or out of the at least one primary well.

Other aspects and advantages of the invention will be apparent from the detailed description, the appended claims , and the accompanying drawings .

BRIEF DESCRIPTION OF DRAWINGS FIGS. IA and IB are schematics of a subsurface reservoir drainage system with import/export wells intersecting a primary well and pumps disposed in the import/export wells for pumping fluid into or out of the primary well.

FIG. 1C is a schematic of a subsurface reservoir drainage system with import/export wells intersecting a primary well at different depths. FIG. ID is a schematic of a subsurface reservoir drainage system with laterally-opposed import/export wells intersecting a primary well and pumps disposed in the laterally-opposed import/export wells linked by a connecting rod.

FIG. 2A is a plan view of a subsurface reservoir drainage system showing connections between import/export wells and a primary well.

FIG. 2B is another plan view of a subsurface reservoir drainage system showing connections between import/export wells and a primary well.

FIG. 2C is a plan view of a subsurface reservoir drainage system showing connections between import/export wells and primary wells in different zones of a subsurface reservoir.

FIG. 3 shows electrical cables installed inside the casing strings of the import/export wells of a subsurface reservoir drainage system.

FIG. 4 shows electrical submersible pumps disposed in the import/export wells of a subsurface reservoir drainage system and powered by electrical cables installed inside the casing strings of the import/export wells.

FIG. 5A is a cross-sectional view of a piston pump with a flapper valve.

FIG. 5B is a cross-sectional view of a piston pump with a rotating auger construction.

FIG. 6 illustrates gas well dewatering with a subsurface reservoir drainage system. FIG. 7 illustrates use of import/export wells to transport separated fluids .

DETAILED DESCRIPTION

The invention will now be described in detail with reference to a few specific examples and the accompanying drawings. In describing the specific examples, certain details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without some or all of such specific details. In other instances, well-known features and/or process steps have not been described in detail so as not to unnecessarily obscure the invention. In addition, like or identical reference numerals may be used to identify common or similar elements within the several drawings.

FIG. IA schematically shows an example subsurface reservoir drainage system 10 including a primary well 12 drilled through rock formations 13, 14, 16 from the Earth's surface 15. The number and layering of rock formations are used only for illustration purposes. It will also be appreciated by those skilled in the art that the surface 15 may also be the bottom of a body of water or a bottom supported or floating marine production platform or drilling platform, and the invention is not limited on scope to wells having upper terminations on land. In one aspect, the rock formation 16 is a subsurface reservoir bearing fluids such as oil and gas. In one aspect, the primary well 12 is a production well and is drilled through the subsurface reservoir 16 for production (or recovery) of fluids from the subsurface reservoir 16. The primary well 12 may be vertical, as shown in FIG. IA, or may be deviated or horizontal, as known in the art. A "production well" as that term is used herein is a well traversing a subsurface reservoir and including selected equipment and/or structures for production of fluids from the subsurface reservoir. For example, the primary well 12 may include a pipe or casing string 18, which may provide structural integrity to the well during production, hydraulically isolate the rock formations from each other and provide a conduit for produced fluids. If the casing string 18 extends all the way to the subsurface reservoir 16, as shown in FIG. IA, the portion of the casing string 18 disposed adjacent to the subsurface reservoir 16 is typically perforated to allow fluid from the subsurface reservoir 16 to flow into the primary well 12. Alternatively, if the casing string 18 does not extend all the way to the subsurface reservoir 16, permeable devices, such as sand screens or gravel pack, may be installed in the open section of the primary well 12 to provide structural integrity to the primary well 12 while allowing flow of fluid from the subsurface reservoir 16 into the primary well 12. The portion of the primary well 12 above the subsurface reservoir 16 may be isolated from the area below by a suitable sealing element such as a packer 20. A tubing 22 may be inserted into the casing string 18 in the primary well 12 to increase the velocity of fluids from the subsurface reservoir 16 up the primary well 12. A production tree 24 including flow control valves may be installed at the surface of the primary well 12 to direct fluids from the tubing 22 into a fluid processing device (not shown) or distribution network (not shown) and to allow access into the interior of the primary well 12 when needed.

The subsurface reservoir drainage system 10 further includes one or more import/export wells 26 drilled through the rock formations 13, 14, 16 and connected to or intersecting the primary well 12. For illustration purposes, two import/export wells 26 are shown in FIG. IA. In one aspect, the import/export wells 26 are used to pump fluids into the primary well 12, thereby driving fluid up the primary well 12, (e.g., in the tubing 22 or casing string 18), to the surface 15. The import/export wells 26 may pump fluid into the primary well 12 one at a time or at the same time. In another aspect, the import/export wells 26 are used to pump fluids away from the primary well 12. In another aspect, the import/export wells 26 are used to inject chemicals or fluids into the primary well 12 in order to improve the flow of certain reservoir fluids, e.g., "heavy" oil, up the primary well 12. The import/export wells 26 may also be used to introduce into the primary well 12 chemicals or treatment fluids that can be used to, for example, reduce scale, reduce corrosion, and reduce fluid flow friction, among other types of wellbore treatment chemicals.

The surface entry point 17 of each import/export well 26 is separated from the surface entry point 19 of the primary well 12. The surface entry points 17 of the import/export wells 26 may be submerged below the surface 15, as shown in FIG. IA, so that the import/export wells 26 are not visible from the surface 15. This may make it possible to locate the import/export wells 26 in areas occupied by communities that do not want visible wellheads and flow lines. Alternatively, the surface entry point 17 of each import/export well 26 may be visible from the surface 15, as shown in FIG. IB. In one aspect, each import/export well 26 intersects the primary well 12 at a selected depth below the surface 15 and substantially within the subsurface reservoir 16. Multiple import/export wells 26 may intersect the primary well 12 at the same depth relative to the surface 15, e.g., as shown in FIGS. IA and IB, or at different depths relative to the surface 15, e.g., as shown in FIG. 1C.

In one aspect, each import/export well 26 can be a deviated well (meaning it is inclined from vertical so as to separate the surface location 17 from the location at depth) or a horizontal well. In one aspect, each import/export well 26 has an inflow section 28 located substantially within the subsurface reservoir 16 and through which fluids can flow from the subsurface reservoir 16 into the import/export well 26. Casing 25 may be installed in the import/export well 26. If the casing 25 extends into inflow section 28 of the import/export well 26, the portion of the casing 25 in the inflow section 28 can be perforated to allow flow of fluids from the subsurface reservoir 16 into the inflow section 28 of the import/export well 26. A tubing (not shown) , similar in structure to the tubing 22 in the primary well 12 may also be disposed inside the import/export well 26, either to carry fluids to or away from the import/export well 26, or to deploy equipment in the import/export well 26. Barriers 27 may be disposed in the import/export wells 26 to prevent the fluids received in the inflow sections 28 of the import/export wells 26 from flowing to the surface of the import/export wells 26.

The subsurface reservoir drainage system 10 further includes at least one pump 30 disposed in a pumping section 29 in each import/export well 26. The pumping section 29 is typically disposed between the inflow section 28 and the intersection of the import/export well 26 with the primary well 12. In one aspect, the pump 30 receives fluids from the inflow section 28, which is in communication with the subsurface reservoir 16, and discharges the fluids into the primary well 12. Various types of downhole pumps may be used as the pumps 30. Examples include, but are not limited to, magnetically- powered pumps, progressive cavity pumps, and electrical submersible pumps.

In one aspect, the pump 30 used in an import/export well 26 is a magnetically-powered pump, e.g., one known as the MagLev pump and described in Norwegian Patent 323081 and International Patent Application Publication No. WO 2006/126886. MagLev is a trademark of Ziebel AS, Tanager, Norway, also the assignee of the present invention In general, the MagLev pump includes a pumping unit disposed within a pipe string, where at least a portion of the pipe string includes a plurality of electromagnets. The electromagnets generate the magnetic field that drives the pumping unit along the pipe string and within the portion of the pipe string containing the electromagnets. A magnet may also be provided in the pumping unit that will interact with the electromagnets to provide the necessary magnetic field to drive the pumping unit. The benefit of such a magnetically-powered pump is that it is not necessary to connect an electrical cable or other physical driving devices to the pumping unit. In one aspect, a magnetically-powered positive displacement pump such as a piston pump is used as the pump 30. Magnetic powering of the positive dispacement pump may be performed as described above. The positive displacement pump may be, for example, an inline axial piston pump including check valves to direct flow in and out of the cylinders enclosing the pistons. FIG. 5A shows an example of a piston pump 30 having a through-bore 31 with a flapper type check valve 37 installed therein. When the positive displacement pump is pumping, the flapper valve 37 is open. When the piston pump is not pumping, the flapper valve 37 is closed. FIG. 5B shows another example of a positive displacement pump 30 having a rotating auger (or Archimedes) construction.

In the example of FIGS. IA and IB, two laterally-opposed import/export wells 26 including positive displacement pumps 30 of the piston and check valve design are shown. In FIG. IA, the pump 30 on the left is in the fully discharged position, i.e., wherein all fluid previously drawn into the pumping section 29 has been discharged into the primary well 12. In FIG. IB, the pump 30 on the left is in a position where fluids may be drawn into the pumping section 29. The pumps 30 reciprocate within the pumping section 29 while drawing fluid into the respective pumping sections 29 and discharging fluid from the respective pumping sections 29.

If the pumps 30 are magnetically-powered pumps, each import/export well 36 may be outfitted with a casing string having a plurality of electromagnets provided in a section thereof for driving the respective pump 30. Electrical power may be provided to the electromagnets through any suitable power arrangement. For example, in FIG. 3, an electrical cable 38 that connects to a coupler 40 in the import/export well 26 is used to provide electrical power to the electromagnets (not shown individually) in a section 55 of the casing string 36. The coupler 40 may be provided as an integrated part of the casing string 36 in a downhole section of the casing string 36 near the pumping section 29. An alternative to including electromagnets in the casing string 36 is to insert a tubing string into the import/export well 26, where the tubing string would have one or more sections with the electromagnets to drive the pump in the import/export well. FIG. ID shows pumps 30a, 30b disposed in laterally-opposed import/export wells 26a, 26b and coupled together by a connecting rod 32, with the piston-type pump 30a in the import/export well 26a connected to a cable 34 running to the surface. Water can be pumped, e.g., using a surface pump 33, from the surface into one of the import/export wells 26a, 26b, e.g., import/export well 26a, to push the piston 30a toward the production well 12, thereby causing fluids in the pumping section 29a of the import/export well 26a to be pushed into the production well 12. When the pump 30a reaches the end of its travel length, the pump 30a can be pulled up again to the starting location in the import/export well 26a, for example, by a surface winch 35 connected to the cable 34. The pump 30a in the opposing import/export well 26b will be moved correspondingly by means of the connecting rod 32. While the piston 30a in the import/export well 26a is pushing fluid into the production well 12, the piston 30b in the opposing import/export well 26 would be allowing fluid to flow from the respective inflow section 28b into the pumping section 29b, where the fluid in the pumping section 29b would then be pushed into the production well 12 in the next pumping cycle. The foregoing operation may be repeated to achieve steady pumping.

Although several examples have been described above with respect to use of piston pumps in the import/export wells, it should be clear that the subsurface drainage reservoir system is not limited to use of piston pumps in the import/export wells. For example, FIG. 4 shows electrical submersible pumps 30 disposed in import/export wells 26. The electrical submersible pumps 30 are powered by cables 42 from the surface. Other suitable means of powering the electrical submersible pumps 30 may also be used. Powering of the pumps in the respective import/export wells 26 can generate some local heating that can make the reservoir fluids in the import/export wells 26 less viscous and allow the pumps 30 to reciprocate more freely within the pumping section 29 of the respective import/export wells 26. If the fluids in the import/export wells 26 are too viscous to allow the pumps 30 to function properly, chemicals can be injected from the surface to reduce the viscosity of the fluids. A heating system may also be lowered down into the primary well 12 to provide heat in the intersection between the import/export wells 26.

FIGS. 2A and 2B are plan views of various example import/export well geometries, with the primary well identified at 12 and the import/export wells identified at 26. The import/export well geometry may be selected to most advantageously drain the particular subsurface reservoir traversed by the primary well 12. FIG. 2C shows an example of how the import/export wells 26 can also be connected to other and later-stage drilled import/export wells 26a from other sections of the reservoir. The import/export wells 26a may also be connected to another primary well 12a. By such configuration, a much larger commingled pattern of underground wells can be connected, including wells from other separate zones or separated reservoirs .

FIG. 6 illustrates use of the subsurface reservoir drainage system 10 for the purpose of gas well dewatering. In this case, the import/export wells 26 are connected to the bottom of the primary well 12 and to a water zone 41 located below the subsurface reservoir 12. Water entering the primary well 12 naturally drains to the bottom of the primary well 12 by gravity. As will be appreciated by those skilled in the art, the hydrostatic pressure of such water can reduce the available pressure differential between the reservoir and the well, so as to reduce the rate of gas production. Dewatering is a process by which the hydrostatic pressure of the water is reduced by removing or displacing the water or modifying its specific gravity. In FIG. 6, the pumps 30 in the import/export wells 26 pump the water from the bottom of the primary well 12 into the water zone 41. The pumps 30 in the import/export wells 26 can be located in a horizontal section or vertical section of the import/export wells 26. The system in FIG. 6 can reduce the need for surface water separation treatment systems and water export flow lines, and by reducing hydrostatic pressure of the water, may result in increased gas production.

FIG. 7 shows several import/export wells 26 intersecting a primary well 42, where the import/export wells 26 are used to transport separated fluids away from the primary well 42. The primary well 42 and import/export wells 26 are drilled through rock formations as explained above. The primary well 42 may or may not be a production well. In the present example, a pump 30 is disposed in each of the import/export wells 26. Pumps 44, 46 are also disposed in the primary well 42. A separator 48 is disposed at the intersection of the import/export wells 26 with the primary well 42. Pump 44 in the primary well 42 is used to deliver produced fluids from the reservoir to the separator 48, which separates the fluids by fluid type, e.g., water from gas. Barriers 49, e.g., packers, may be used to isolate the separated fluids generated by the separator 48 from the production fluids delivered to the separator 48 by the pump 44. Each import/export well 26 receives one of the separated fluids and transports the separated fluid away from the primary well 42. In one example, one of the import/export wells 26 may transport water away from the primary well 42, where the water is used for pressure support to an oil reservoir. Another one of the import/export wells 26 may transport gas away from the primary well 42, where the gas is also used for pressure support to an oil reservoir. Alternatively, the gas may be transported through a dedicated export well to a surface production facility, a gas reservoir, or other similar structure.

A subsurface reservoir drainage system according to the various aspects of the invention may provide one or more of the following benefits. The system may allow fewer surface facilities and flow lines to be used in draining a larger portion of a reservoir. The surface facilities can be made less visible, e.g., by submerging them below the surface, substantially reducing long-term environmental visual footprint. Substantial reduction in surface flow lines improves safety, both for facilities and the public. Pumps in the import/export wells can be replaced without halting production. The import/export wells provide increased reservoir contact, which increases the total reservoir drainage. The production well can be made simple. The production well would not need installation of an artificial lift system, which would reduce the need for stick-up and visual pollution in environmental- sensitive areas. The system allows testing of various artificial lift methods without exposing the production well to risk of failures. The field production can be more stable, with less impact on production due to single or few pump failures. The system can enable more efficient drainage of "sweet spots" without adding new long-term surface facilities. The system can be used for more efficient gas well dewatering. While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims .

Claims

CLAIMS What is claimed is:

1. A subsurface reservoir drainage system, comprising: a primary well drilled through subsurface rock formations comprising a subsurface reservoir; at least one import/export well drilled through the subsurface rock formations and intersecting the primary well; and a pump disposed in the at least one import/export well for pumping fluid into or out of the at least one primary well.

2. The subsurface reservoir drainage system of claim 1, wherein the primary well is a production well extending substantially from the top of the subsurface rock formations to the subsurface reservoir.

3. The subsurface reservoir drainage system of claim 2, wherein the at least one import/export well extends from proximate the top of the subsurface rock formations, at a location separated from the location of the top of the primary well, to the subsurface reservoir .

4. The subsurface reservoir drainage system of claim 1, wherein the pump is configured to withdraw fluid from the subsurface reservoir into the at least one import/export well and discharge the withdrawn fluid into the primary well.

5. The subsurface reservoir drainage system of claim 1, wherein the pump comprises a magnetically-operated piston pump.

6. The subsurface reservoir drainage system of claim 1, wherein the end of the at least one import/export well proximate the top of the subsurface rock formations is disposed below the Earth's surface.

7. The subsurface reservoir drainage system of claim 1, wherein the at least one import/export well comprises a conduit for conducting a well treatment chemical .

8. The subsurface reservoir drainage system of claim 1, wherein the at least one import/export well intersects the primary well within the subsurface reservoir.

9. The subsurface reservoir drainage system of claim 1, further comprising at least one additional import/export well drilled through the subsurface rock formations and intersecting the primary well.

10. The subsurface reservoir drainage system of claim 9, wherein the at least one import/export well and the at least one additional import/export well intersect the primary well at substantially the same depth relative to the top of the subsurface rock formations .

11. The subsurface reservoir drainage system of claim 10, wherein each of the at least one import/export well and the at least one additional import/export well comprises a piston pump, and wherein the piston pump of the at least one import/export well is coupled to the piston pump of the at least one additional import/export well by a connecting rod.

12. The subsurface reservoir drainage system of claim 11, further comprising a cable extending from a surface position of the at least one import/export well and coupled to the piston pump in the at least one import/export well, wherein the piston pumps are displaced within their respective import/export wells by withdrawing the cable from the at least one import/export well.

13. The subsurface reservoir drainage system of claim 12, further comprising means for pumping fluid into the at least one import/export well above the piston pump disposed in the at least one import/export well, whereby the piston of the piston pump is displaced along the at least one import/export well by fluid pressure.

14. The subsurface reservoir drainage system of claim 1, wherein the pump comprises an electrical submersible pump.

15. The subsurface reservoir drainage system of claim 1, wherein the pump is configured to withdraw fluid from the primary well and discharge the withdrawn fluid into the at least one import/export well.

16. The subsurface reservoir drainage system of claim 15, further comprising a separator disposed in the primary well to separate fluids in the primary well by fluid type.

17. The system of claim 16, which comprises a plurality of import/export wells including the at least one import/export well and a pump disposed in each of the import/export wells for pumping each of the separate fluids into a respective one of the import/export wells.