Methods and systems for recovering oil from subterranean reservoirs

Abstract

A method and system for recovering oil from a subterranean reservoir. The method includes delivering an injection gas through an injection flow path into a plurality of regions of the reservoir via a plurality of outflow devices arranged along the injection flow path, producing oil from a plurality of regions of the subterranean reservoir via a production flow path with a plurality of inflow devices arranged along the production flow path, and restricting flow of the injection gas into the production flow path from the reservoir. The restricting of the flow in injection gas may be by choking the flow of the injection gas through at least one of the plurality of inflow devices such that the residence time of the injection gas within the subterranean reservoir is increased.

Claims

1. A method for recovering oil from a subterranean reservoir, the method comprising: delivering an injection gas through an injection flow path into a first region of the subterranean reservoir via a first outflow device arranged along the injection flow path, the first outflow device configured to provide a first pressure drop across the first outflow device; delivering an injection gas through an injection flow path in to a second region of the subterranean reservoir via a second outflow device arranged along the injection flow path, the second outflow device configured to provide a second pressure drop across the second outflow device, wherein the first pressure drop and second pressure drop are different in order to suit the subterranean reservoir; producing oil from a plurality of regions of the reservoir via a production flow path with a plurality of inflow devices arranged along the production flow path; and restricting flow of the injection gas into the production flow path from the reservoir by choking the flow of the injection gas through at least one of the plurality of inflow devices such that a residence time of the injection gas within the reservoir is increased.

2. A method according to claim 1, wherein the flow of the injection gas through at least one of the plurality of inflow devices is choked while oil is produced through at least one of the plurality of inflow devices.

3. A method according to claim 1, wherein restricting flow of the injection gas into the production flow path comprises selectively choking the flow of fluid through at least one of the plurality of inflow devices such that the flow of injection gas through the at least one of the plurality of inflow devices is choked more than the flow of oil.

4. A method according to claim 3, wherein the flow of fluid through the at least one of the plurality of inflow devices is selectively choked based on at least one of a viscosity of the fluid and a density of the fluid.

5. A method according to claim 1, wherein producing oil from a plurality of regions of the subterranean reservoir comprises an initial production phase before delivering injection gas and a subsequent production phase after delivering injection gas.

6. A method according to claim 1, wherein delivering an injection gas through an injection flow path, producing oil from a plurality of regions of the subterranean reservoir and restricting flow of the injection gas into the production flow path are undertaken simultaneously.

7. A method according to claim 1, wherein the injection flow path and the production flow path are in a single well.

8. A method according to claim 1, wherein the injection flow path is in a first well and the production flow path is in a second well.

9. A method according to claim 1, further comprising stopping all fluid flow in the injection flow path and the production flow path to control the residence time of the injection gas within the subterranean reservoir.

10. A system for recovering oil from a subterranean reservoir, the system comprising: an injection flow path for delivering injection gas into a plurality of regions of a subterranean reservoir; wherein the injection flow path comprises a plurality of outflow devices arranged along the injection flow path; wherein a first one of the plurality of outflow devices, located in a first region of the reservoir, is configured to provide a first pressure drop across the device; and a second one of the plurality of outflow devices, located in a second region of the reservoir, is configured to provide a second pressure drop, wherein the first pressure drop and second pressure drop are different in order to suit the subterranean reservoir; a production flow path for producing oil from a plurality of regions of the subterranean reservoir; wherein the production flow path comprises a plurality of inflow devices arranged along the production flow path; wherein at least one of the plurality of inflow devices is configured to choke the flow of the injection gas into the production flow path from the reservoir such that a residence time of the injection gas within the subterranean reservoir is increased.

11. A system according to claim 10, wherein the plurality of inflow devices are configured to choke the flow of the injection gas into the production flow path in a first region of the reservoir while oil is produced from a second region of the reservoir via the production flow path.

12. A system according to claim 10, wherein at least one of the plurality of inflow devices is configured to selectively choke the flow of fluid such that the flow of injection gas through the inflow device is choked more than the flow of oil.

13. A system according to claim 12, wherein the at least one of the plurality of inflow devices is configured to selectively choke the flow of fluid therethrough based on at least one of a viscosity of the fluid and a density of the fluid.

14. A system according to any of claim 10, wherein the system is configured to simultaneously deliver injection gas through the injection flow path; produce oil through the production flow path; and choke the flow of injection gas into the production flow path.

15. A system according to claim 10, wherein the injection flow path and production flow path are provided as part of a single completion apparatus for use in a single well.

16. A system according to claim 10, wherein: the system comprises a first completion apparatus for use in a first well and a second completion apparatus for use in a second well located adjacent the first well; the first completion apparatus comprises the injection flow path; and the second completion apparatus comprises the production flow path.

17. A system according to claim 10, wherein the system is configured to stop fluid flow in the injection flow path and the production flow path to control the residence time of the injection gas within the subterranean reservoir.

18. A system according to claim 10, wherein: at least one of the outflow devices is configured to prevent fluid entering the injection flow path from the reservoir; and/or at least one of the inflow devices is configured to prevent fluid entering the reservoir via the production flow path.

19. A system according to claim 10, wherein at least one of the inflow devices is also an outflow device.

20. A method for recovering oil from a subterranean reservoir, the method comprising: delivering an injection gas through an injection flow path into a plurality of regions of the subterranean reservoir via a plurality of outflow devices arranged along the injection flow path; producing oil from a first region of the reservoir using one or more first inflow devices arranged along the production flow path, the first inflow devices configured to define a first pressure drop across the first inflow device; producing oil from a second region of the reservoir using one or more second inflow devices arranged along the production flow path, configured to define a second pressure drop across the second inflow device, arranged along the production flow path, wherein the second pressure drop is different to the first pressure drop, in order to balance production across the subterranean reservoir; and restricting flow of the injection gas into the production flow path from the reservoir by choking the flow of the injection gas through at least one of the plurality of inflow devices such that a residence time of the injection gas within the reservoir is increased.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Examples of the disclosure will now be described, purely by way of example, with reference to the following figures, in which:

(2) FIG. 1 is a schematic representation of a system according to the disclosure;

(3) FIG. 2 is a schematic representation of a further system according to the disclosure;

(4) FIG. 3 is a schematic representation of a section of the system of FIG. 1;

(5) FIG. 4 is a schematic representation of the system of FIG. 3 during use;

(6) FIG. 5 is a schematic representation of the system of FIG. 3 during use;

(7) FIG. 6 is a schematic representation of the system of FIG. 3 during use;

(8) FIG. 7 is a schematic representation of a system according to the disclosure;

(9) FIG. 8 is a schematic representation of an exemplar outflow device for use with a system according to the disclosure; and

(10) FIG. 9 is a schematic representation of an exemplar inflow device for use with a system according to the disclosure;

(11) FIG. 1 schematically illustrates a system 10 for recovering oil from a subterranean reservoir according to the disclosure.

(12) The portion of the system 10 in a well 12 depicted in FIG. 1 is below ground in a subterranean reservoir. The reservoir is an unconventional oil reservoirfor example a shale reservoir. Accordingly, the permeability of the formation is very low which can lead to low oil recovery efficiency. As such, an improved enhanced oil recovery technique according to the present disclosure may be employed.

(13) The horizontal well 12 has been drilled using a directional drill. Once the drilling equipment is removed from the well 12, the bore has been lined with casing 14 which has been cemented in place. Fractures 16 are created in the reservoir proximal and radiating out from the well 12, for example by using a plug and perf technique. The fractures 16 are introduced to aid in oil production.

(14) Once the equipment for creating the fractures 16 is removed from the well 12, the system 10 for recovering oilthat is, the completionis installed in the well 12. The system 10 is according to this disclosure.

(15) The system 10 comprises a liner 18 which comprises tubing running down the centre of the well 11. The liner 18 is concentrically arranged with the casing 14. Swell packers 20 are installed at various locations along the length of the well 12 in the annulus between the liner 18 and casing 14. The swell packers 20 are set to separate the well into a plurality of regions 22a-e. Each of the regions 22 is isolated from its neighbours and has access to a corresponding region of the reservoir such that oil from the corresponding region of the reservoir can enter the annulus 24 through holes/perforations in the casing 14 and from there enter the liner 18 via inflow devices 34 (discussed below).

(16) Fluids may be transported between the liner 18 and the surface via further liners and tubing arranged in the vertical part of the well.

(17) The liner 18 comprises or provides two flow pathsan injection flow path 28 and a production flow path 30. FIG. 3 schematically illustrates the injection flow path 28 and the production flow path 30 connected to their respective flow devices. FIGS. 4 and 5 schematically show flow through the injection flow path 28 and production flow path 30, respectively.

(18) The injection flow path 28 is configured to deliver injection gas into a plurality of regions 22 of the reservoir in order to increase oil recovery efficiency. The injection flow path 28 comprises a plurality of outflow devices 32 which are located in the interface of the liner 18 and annulus 24. The outflow devices 32 are arranged axially along the injection flow path 28 and hence the liner 18.

(19) In some embodiments, the injection flow path 28 may comprise tubing (not shown) running inside the liner 18.

(20) The injection flow path 28 and outflow devices 32 are configured to deliver an injection gas into the reservoir. Injection gas is delivered from the surface, through the liner 18, out of outflow devices 32 into the annulus 24 and from the annulus 24 into the regions of the reservoir in which the outflow devices 32 are located.

(21) The outflow devices 32 of a region control the characteristics (pressure, flow rate . . . ) of the injection gas output by the injection flow path 28 in that region. In the present embodiment, the outflow devices 32 are inflow control devices (ICDs), albeit arranged to control outflow, rather than inflow. The outflow devices 32 are configured to define a rate dependent pressure drop when fluid flows through them.

(22) The outflow devices 32 in each region 22 are configured to be suited to the geological properties of the formation in that region. As such, the pressure drop and/or maximum flow rate defined by the outflow devices 32 in a first region 22a of the reservoir are different to those in a second region 22b of the reservoir, since the geological properties of the formation in the two regions 22a, 22b vary.

(23) The outflow devices 32 act as a check valve preventing fluid flow from the reservoir into the injection flow path 28 (i.e. inflowing fluid). Accordingly, no fluid can enter the injection flow path 28 from the reservoir via the outflow devices.

(24) The production flow path 30 is configured to receive oil from the reservoir and transport it to the surface. The production flow path 30 comprises a plurality of inflow devices 34 which are located in the interface of the liner 18 and the annulus 24. The inflow devices 34 are arranged axially along the production flow path 30 and hence the liner 18.

(25) In some embodiments, the production flow path 30 may comprise tubing (not shown) running inside the liner 18.

(26) The production flow path 30 and inflow devices 34 are configured to receive and deliver oil to the surface. Oil from the reservoir enters the annulus 24 (often via the fractures 16) and enters the production flow path 30 via inflow devices 34. Oil then travels up the production flow path 30 to the surface.

(27) Each of the inflow devices 34 is configured to selectively choke the flow of fluid through the device 34 such that injection gas flows through the device 34 less readily (at a slower rate) than oil. As such, each of the inflow devices 34 acts to prevent injection gas from leaving the reservoir via the production flow path and thus the average residence time and pressure of the injection gas in the reservoir is increased. This acts to increase the recovery efficiency without further well intervention.

(28) The inflow devices 34 of the embodiment of FIG. 1 are autonomous inflow control devices (AICDs). The AICDs of FIG. 1 use the viscosity of the fluid flowing through them to adapt the flow ratehigh viscosity fluids (e.g. oil) have a much higher flow rate than low viscosity fluids (e.g. injection gas).

(29) The inflow devices 34 act as check valves for outflowing fluidi.e. fluid flow into the reservoir from the production flow path 30 via inflow devices 34. Accordingly, fluid can only flow through the inflow devices 34 from the reservoir into the production flow path 30, not the other direction.

(30) FIG. 2 depicts a further example of the present disclosure. In FIG. 2, the system comprises a plurality of flow devices 33. Each of the flow devices 33 is configured to act as an outflow device and an inflow device. As such, the flow devices 33 have the properties of an outflow device as described herein when fluid is flowing through them from the injection flow path into the reservoir and the properties of an inflow device as described herein when fluid is flowing through them from the reservoir into the production flow path. Both of the injection flow path and the production flow path (not shown) are connected to each of the flow devices 33.

(31) FIG. 3 depicts a section of a completion according to the disclosure. FIG. 3 schematically illustrates an injection flow path 28 and a production flow path 30 and how the outflow devices 32 and the inflow devices 34 allow fluid to flow out from and in to their respective flow paths.

(32) The flow paths 28, 30 shown in FIG. 3 may be schematic in the case where the liner 18 acts as the conduit for both flow paths (i.e. independent tubing is not provided for each flow path 28, 30) or more literal in the case where each flow path comprises a conduit/tubing which is independent to that of the other flow path.

(33) FIGS. 4 and 5 schematically illustrate the section of the system of FIG. 3 during use.

(34) Once the well 12 has been drilled and lined with casing 14 and the fractures 16 have been induced, the completion is installed in the well 12 by locating the liner 18 within the casing 14 and engaging the packers 20 to isolate the separate regions of the well 12 and reservoir and hold the completion in place.

(35) An initial production phase may be undertaken, during which oil is produced through the production flow path 30 to the surface.

(36) After a period of time, the pressure in the reservoir and the production rate will drop, due to a reduction in the readily available oil in the reservoir. Once the pressure in the reservoir drops to a predetermined value, an enhanced oil recovery method may be employed as described herein.

(37) Injection gas may be delivered into the reservoir via the injection flow path 30, as shown in FIG. 4. The injection gas (represented by the arrows in FIG. 4) may be hydrocarbon gas, carbon dioxide, nitrogen, steam or any other gas suitable for enhanced oil recovery methods. The injection gas is delivered from the surface and travels through tubing of the injection flow path 28 (which may be the liner 18 itself). The injection gas enters the annulus 24 via outflow devices 32. Once in the annulus, the injection gas diffuses into the reservoir, largely via the fractures 16.

(38) The outflow devices 32 define the pressure at which the injection gas enters the annulus 24 (and thus the region of the reservoir). The pressure of the injection gas may vary across different regions 22 of the well 12 in order to be optimised for the geological properties of the formation in that region 22.

(39) An enhanced oil recovery method according to the disclosure may then employ a soak period, during which time the well is effectively shut whereby there is no fluid flow in the liner 18 (for example by preventing fluid flow in the injection flow path and production flow path). This allows the injection gas to diffuse within the reservoir. The production of oil using the current method is largely based on the expansion of the oil and injection gas within the low-permeability formation. As such, allowing the injection gas a period of time in which to diffuse within the reservoir increases diffusion distances and will often increase oil production once production begins.

(40) The required length of soak period will be dependent on the geological properties of the reservoir and the diffusion properties of the injection gas, among other things. Typical soak periods may last days or weeks.

(41) Once the soak period has been completed, oil can be produced, as illustrated in FIG. 5.

(42) Oil present in the formation (represented by the arrows in FIG. 5) will have expanded within the reservoir and, when the pressure within the production flow path 30 has been reduced to allow fluid flow therethrough, will enter the production flow path 30 via the fractures 16, the annulus 24 and inflow devices 34. The oil will then travel through the production flow path 32 and to the surface to be processed.

(43) Turning now to FIG. 6, a first region 22a of the reservoir is producing oil, which enters the production flow path 30 via the inflow devices 34 as described above. However, a second region of the reservoir 22b is not producing oil. Instead, the injection gas trapped in the reservoir is trying to enter the production flow path 30 through the inflow devices 34.

(44) The inflow devices 34 are configured to selectively choke the flow rate of fluid through the inflow device based on the viscosity of the fluid. As the injection gas has a much lower viscosity than oil, the flow of injection gas through the inflow devices 34 in the second region 22b is choked. As such, the amount of injection gas which enters the production flow path 30 is much lower than it otherwise would be and the flow rate is much lower than that of the oil. Accordingly, more injection gas is left in the reservoir than would otherwise be the case and the average residence time is increased. This increase in residence time increases the diffusion within the reservoir and thus increases the recovery efficiency of the well 12.

(45) In some examples according to the disclosure, the injection gas can be delivered into the reservoir via the injection flow path 28 at the same time as oil is produced via the production flow path 30. The operation of the two flow paths will be largely similar to that discussed above, since both flow paths can operate largely independently.

(46) In an arrangement where the injection gas is delivered into the reservoir simultaneously with the production flow path 30 producing oil and choking the flow of injection gas, the outflow devices 32 and inflow devices 34 may be arranged in groups or banks of like devices. For example, there may be a section of the well (e.g, part of or multiple regions) comprising only outflow devices 32 and a section of the well (e.g. part of or multiple regions) comprising only inflow devices 34.

(47) FIG. 7 illustrates an alternative system according to the disclosure. In FIG. 7 the injection flow path 28 and production flow path 30 are separated into different wells 12a 12b. The individual operation of the injection flow path 28 and production flow path 30 are as described above, the only difference being that the two flow paths are located in separate wells. The embodiment of FIG. 7 can be used for sequential huff and puff operation, in which injection gas is delivered to the reservoir, a soak period allows the injection gas to diffuse within the reservoir and then the production flow path 30 is opened (i.e. depressurised) such that oil can be produced therethrough.

(48) The embodiment of FIG. 7 can also be used in a simultaneous method, whereby delivering an injection gas through the injection flow path 28, producing oil from a plurality of regions of the subterranean reservoir through production flow path 30 and restricting flow of the injection gas into the production flow path 30 are undertaken simultaneously

(49) FIG. 8 illustrates an example of a suitable device for use as an outflow device 32. Fluid can flow through the device via ports 36 on the top, sides and underneath the device. The device comprises an internal cavity comprising a movable member which can act to restrict flow therethrough.

(50) The illustrated device is an ICD and the illustrated example is the Tendeka FloSure Bypass Valve (http://www.tendeka.com/technologies/inflow-control/flosure-bypass-valve/), although many other suitable examples exist and examples of the present disclosure are in no way limited to this specific device.

(51) FIG. 9 illustrates an example of a suitable device for use as an inflow device 34. Fluid can flow through the device via ports 38 on the top and underneath the device. The device comprises an internal cavity comprising a movable member 40 which can act to restrict flow therethrough.

(52) The illustrated device is an AICD and the illustrated example is the Tendeka FloSure AICD (http://www.tendeka.com/technologies/inflow-control/flosure-aicd-screens/), although many other suitable examples exist and examples of the present disclosure are in no way limited to this specific device.

(53) The present invention has been described above purely by way of example. Modifications in detail may be made to the present invention within the scope of the claims as appended hereto.