BOOSTING WELL PERFORMANCE IN GEOTHERMAL SYSTEMS

Abstract

Methods and systems are provided for extracting thermal energy from a conventional geothermal reservoir. One aspect involves drilling or accessing a production well that intersects the conventional geothermal reservoir, and detonating at least one linear shaped charge to enlarge or open a naturally-occurring fracture of the conventional geothermal reservoir at the intersection of the naturally-occurring fracture and the production well, which reduces pressures loss of fluid flow into the production well from the naturally-occurring fracture. The reduction in pressure loss can increase fluid flow into the production well to increase the amount of captured heat. The detonation of the linear shaped charge(s) can increase aperture size of at least one naturally-occurring fracture at a wellbore surface.

Claims

1. A method for extracting thermal energy from a conventional geothermal reservoir that includes at least one naturally-occurring fracture, comprising: drilling or accessing a production well that intersects the conventional geothermal reservoir; and detonating at least one linear shaped charge to enlarge or open a naturally-occurring fracture of the conventional geothermal reservoir at the intersection of the naturally-occurring fracture and the production well, which reduces pressures loss of fluid flow into the production well from the naturally-occurring fracture.

2. The method according to claim 1, wherein: the reduction in pressure loss increases fluid flow into the production well to increase the amount of captured heat.

3. The method according to claim 1, wherein: the detonation of the at least one linear shaped charge increases aperture size of the naturally-occurring fracture at a wellbore surface.

4. The method according to claim 1, further comprising: positioning and orienting the at least one linear shaped charge such that penetration pattern of the at least one linear shaped charge that results from detonation intersects the naturally-occurring fracture.

5. The method according to claim 1, wherein: the at least one linear shaped charge is supported by a downhole tool.

6. The method according to claim 5, further comprising: determining position of the naturally-occurring fracture from well log data; and aligning position of the downhole tool to the position of the naturally-occurring fracture as determined from the well log data such that penetration pattern of the at least one linear shaped charge that results from detonation intersects the naturally-occurring fracture.

7. The method according to claim 6, wherein: the position of the downhole tool and the position of the naturally-occurring fracture are defined in a reference coordinate system.

8. The method according to claim 7, wherein: the reference coordinate system includes well depth and azimuth angle.

9. The method according to claim 5, wherein: the downhole tool has a central axis, and the at least one linear shaped charge is supported by the downhole tool in an orientation generally parallel to the central axis of the downhole tool.

10. The method according to claim 1, wherein: the naturally-occurring fracture carries a flow of pressurized hot water or brine into the production well; and the production well is configured to carry a flow of the pressurized hot water or brine through the production well for delivery to the surface.

11. The method according to claim 1, further comprising: detonating at least one additional linear shaped charge to enlarge or open at least one additional naturally-occurring fracture of the conventional geothermal reservoir at the intersection of the at least one additional naturally-occurring fracture and the production well, which reduces pressures loss of fluid flow into the production well from the at least one additional naturally-occurring fracture.

12. A method for extracting thermal energy from a geothermal reservoir, comprising: drilling a production well that intersects the geothermal reservoir in two stages that includes an upper stage and a lower stage, wherein a larger diameter wellbore is drilled from the surface or near the surface to an intermediate depth in the upper stage, and a smaller diameter wellbore is drilled below the intermediate depth to intersect the geothermal reservoir such that the smaller diameter wellbore of the lower stage extends below the larger diameter wellbore of the upper stage to the geothermal reservoir.

13. The method according to claim 12, wherein: the production well carries a flow of heated fluid through the production well for delivery to the surface.

14. The method according to claim 12, wherein: the geothermal reservoir comprises a conventional geothermal reservoir that includes at least one naturally-occurring fracture that carries a flow of pressurized hot water or brine into the lower stage of the production well.

15. The method according to claim 12, wherein: the geothermal reservoir comprises a non-conventional geothermal reservoir that provides a source of pressurized hot fluid that flows into the lower stage of the production well.

16. The method for extracting thermal energy from a geothermal reservoir, comprising: drilling a secondary production well to intersect a primary production well at a point above the geothermal reservoir.

17. The method according to claim 16, wherein: both the primary and secondary production wells are configured to carry a flow of heated fluid therethrough for delivery to the surface.

18. The method according to claim 17, wherein: the heated fluid flows from the geothermal reservoir up the primary production well to the point of intersection, and then flows up both the primary and secondary production wells from the point of intersection of the primary and secondary production wells.

19. The method according to claim 16, wherein: the geothermal reservoir comprises a conventional geothermal reservoir that includes at least one naturally-occurring fracture that carries a flow of pressurized hot water or brine into the primary production well below the point of intersection of the primary and secondary production wells.

20. The method according to claim 16, wherein: the geothermal reservoir comprises a non-conventional geothermal reservoir that provides a source of pressurized hot fluid that flows into the primary production well below the point of intersection of the primary and secondary production wells.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The subject disclosure is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of the subject disclosure, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

[0025] FIG. 1 is a schematic diagram of a geothermal system having a production well that intersects and connects to a naturally-occurring fracture extending through a conventional geothermal reservoir;

[0026] FIG. 2 depicts plots of pressure loss (loss of pressure head) along a flow path from a 3 mm fracture that extends through a conventional geothermal reservoir and up a production well to the surface of a geothermal system. The plots of pressure loss are labeled for varying surface pressure applied at the surface wellhead in the range from 100 to 550 psi;

[0027] FIG. 3 depicts a flowchart of an example workflow that uses one or more linear shaped charges to enlarge the aperture of one or more naturally-occurring fractures that extend through a conventional geothermal reservoir and intersect a production well of a geothermal system;

[0028] FIG. 4 depicts a reference coordinate system that employs wellbore depth and azimuth angle;

[0029] FIG. 5 depicts a linear shaped charge;

[0030] FIG. 6 depicts a downhole tool (e.g., labeled capsule gun) that supports one or more linear shaped charges for deployment in a well for controlled denotation of the linear shaped charge(s) in the well;

[0031] FIG. 7 depicts plots of available power extracted from a conventional geothermal reservoir with varying fracture aperture size in the range of 1 mm, 3 mm and 5 mm;

[0032] FIG. 8 depicts plots of available power extracted from a conventional geothermal reservoir with varying fracture aperture size in the range of 1 mm, 3 mm and 5 mm and varying wellbore diameter of 8.5 inches, 12.25 inches, and 18.5 inches;

[0033] FIG. 9 depicts an example production well that intersects a conventional geothermal reservoir where the production well is drilled in two stages, referred to herein as an upper stage and a lower stage. In the upper stage, a larger diameter wellbore is drilled from the surface (or near the surface) to an intermediate depth. In the lower stage, a smaller diameter wellbore is drilled below the intermediate depth such that the smaller diameter wellbore of the lower stage extends below the larger diameter wellbore of the upper stage to the conventional geothermal reservoir;

[0034] FIG. 10 depicts plots of available power extracted from a conventional geothermal reservoir with a production well having a single diameter of 8.5 inches as well as production wells having two-stage diameters of 12.5 inches and 8.5 inches with varying depths for the transition between stages ranging from 2000, 4000, 6000, and 8000 feet;

[0035] FIG. 11 depicts an embodiment for a geothermal system where a secondary production well is drilled to intersect an existing production well above a conventional geothermal reservoir; and

[0036] FIG. 12 depicts plots of available power extracted from a conventional geothermal reservoir with a single production well having a diameter of 8.5 inches as well as a system with a primary production well having a diameter of 8.5 inches that extends to the conventional geothermal reservoir together with a secondary production well having a diameter of 8.5 inches that intersects the primary production well above the conventional geothermal reservoir at varying depths ranging from 2000, 4000, 6000, and 8000 feet.

DETAILED DESCRIPTION

[0037] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the subject disclosure only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the subject disclosure. In this regard, no attempt is made to show structural details in more detail than is necessary for the fundamental understanding of the subject disclosure, the description taken with the drawings making apparent to those skilled in the art how the several forms of the subject disclosure may be embodied in practice. Furthermore, like reference numbers and designations in the various drawings indicate like elements.

[0038] Embodiments of the present disclosure are directed to boosting or improving the performance of geothermal systems that include a conventional geothermal reservoir, which is a volume of subsurface rock that contains a natural source of pressurized hot water or brine. One or more production wells are drilled from the surface into and through the conventional geothermal reservoir and intersect one or more naturally-occurring factures in the subsurface rock of the conventional geothermal reservoir. These naturally-occurring factures provide a flow path of the pressurized hot water or brine into the production well(s) where it flows through the production well(s) to the surface. The thermal energy (heat) from the hot fluid that flows to the surface can be extracted and used by an energy conversion plant for power generation, large scale heating or cooling, industrial/agricultural processes, or other geothermal applications.

[0039] Flow loss can occur where the naturally-occurring facture intersects and fluidly couples to the production well of the system. Specifically, the aperture of a naturally-occurring fracture at the intersection of the production well can act as a flow restrictor that limits fluid flow through the fracture and into the production well. This can limit the amount of heat captured by the system and delivered to the surface and thus decrease the productivity of the system. These pressure losses are illustrated in FIG. 2, which includes plots of pressure loss (loss of pressure head) along a flow path from a 3 mm naturally-occurring fracture and up a production well to the surface of a geothermal system. The pressure loss along the flow path is from the far field though the 3 mm fracture that enters the production well (at x=0) and flows to the surface (at x=8000). The plots of pressure loss are labeled for varying surface pressure applied at the surface wellhead in the range from 100 to 550 psi. The plots of FIG. 2 are derived from simulations, which assume that the naturally-occurring fracture is defined by a flat and parallel disc that surrounds the production well with radial inflow. In this case, the aperture of the naturally-occurring fracture forms an annular void of a well-defined height (in this case 3 mm) that encircles the production well with the circumference of the annular void corresponding to the wellbore diameter. The flow through the naturally-occurring fracture is assumed to be laminar flow that transitions to turbulent flow with the transition at the point where the laminar and turbulent friction factors are equal. The far field is assumed to be at a constant pressure source. The actual pressure drop for the laminar flow is minimal. The pressure drop for the turbulent flow is higher as evidenced by the plot. The bigger pressure drop is at the entrance (intersection) of the naturally-occurring fracture into the production well.

[0040] According to one or more embodiments of the present disclosure, one or more downhole tools can be configured to position and detonate one or more linear shaped charges in a production well of a geothermal system to enlarge or open a naturally-occurring facture at the intersection of the naturally-occurring fracture and the production well to reduce pressure loss and increase the flow rate of pressurized hot water or brine carried by the naturally-occurring fracture into the production well. This can increase the amount of heat captured by the system and delivered to the surface and thus increase the productivity of the system. This can be performed on multiple naturally-occurring fractures that connect to the production well. This can also be applied to multiple production wells that intersect a conventional geothermal reservoir.

[0041] FIG. 3 is a flowchart of an example workflow that uses one or more linear shaped charges to enlarge the aperture or connection of one or more naturally-occurring fractures that extend through a conventional geothermal reservoir and intersect a production well of a geothermal system.

[0042] In block 301, a production well (also commonly referred to as a production wellbore) is drilled such that the production well intersects one or more naturally-occurring fractures of a conventional geothermal reservoir. The one or more naturally-occurring fractures extend through the conventional geothermal reservoir and connect to the production well. The one or more naturally-occurring fractures provide for fluid flow of the hot water or brine sourced from the conventional geothermal reservoir into the production well as shown in FIG. 1. Conventional or unconventional drilling methods can be used. In embodiments, the production well can optionally be completed, for example with a perforated casing or perforated liner as an open wellbore at least in the interval(s) that intersect the one or more naturally-occurring fractures of the conventional geothermal reservoir.

[0043] In block 303, well log data can be analyzed to determine the position or depth of one or more naturally-occurring fractures intersected by the production well of block 301. For example, borehole pressure measurements, caliper measurements, resistivity measurements, acoustic or ultrasonic borehole imaging measurements, and/or other downhole measurements can be analyzed to determine wellbore depth for one or more naturally-occurring fractures. These measurements can be performed while-drilling or by a wireline tool after drilling. For example, borehole pressure measurements can be analyzed for pressure loss while drilling. When the drilling crosses a naturally-occurring fracture, the borehole pressure will decrease. The depth of such pressure loss can be detected and used as the wellbore depth of the naturally-occurring fracture. FIG. 4 illustrates a reference coordinate system that employs wellbore depth, which corresponds to the depth looking down the production wellbore. The reference coordinate system also employs an azimuth angle, which is measured relative to magnetic north.

[0044] In block 305, a downhole tool (e.g., capsule gun) can be located in the production well of block 301 with one or more linear shape charges at a position (e.g., wellbore depth) corresponding to one or more naturally-occurring fractures characterized in block 303. The linear shaped charge is a continuous core of explosive material enclosed in an elongate narrow seamless metal sheath housing. The charge can be shaped in the form of an inverted V having a larger length (labeled L) relative to a smaller width (labeled W) as shown in FIG. 5, which allows the continuous metal sheath liner and encased explosive to produce a uniform linear cutting action upon detonation The linear shape charge(s) can be positioned and oriented at a wellbore depth and azimuth angle such that the penetration pattern of the linear shaped charge(s) that results from detonation intersects the naturally-occurring fracture(s) at the wellbore wall (rock face) and enlarges the size of the aperture(s) of the naturally-occurring fracture(s) at the wellbore wall and reduces pressure loss of the fluid flow through the naturally-occurring fracture(s) at the wellbore wall (rock face).

[0045] In block 307, the downhole tool can be operated to denotate the linear shape charge(s). The penetration pattern of the linear shaped charge(s) that results from such detonation intersects one or more naturally-occurring fractures at the wellbore wall and enlarges or opens the naturally-occurring fracture(s) at the intersection of the naturally-occurring fracture(s) and the production well, which reduces pressure loss of the fluid flow through the naturally-occurring fracture(s) at the wellbore wall (rock face). This can increase the fluid flow through the naturally-occurring fracture(s) that connects the production well of the system, which can increase the amount of heat captured by the system and delivered to the surface and thus increase the productivity of the system.

[0046] In embodiments, the aperture of a naturally-occurring fracture at the wellbore wall can have a larger width or circumference dimension relative to a smaller height dimension, such as in the shape of a flattened disc. In this configuration, the linear shaped charge can be configured such that the major length dimension (L) of the linear shaped charge(s) is larger than the minor height dimension of the naturally-occurring fracture with the minor width dimension (W) of the linear shaped charge(s) less than the major width or circumferential dimension of the naturally-occurring fracture. The linear shaped charge(s) can be positioned and oriented such that the major length dimension (L) of the linear shaped charge(s) extends in a direction generally orthogonal or across the minor height dimension of the naturally-occurring fracture with the minor width dimension (W) of the linear shaped charge(s) extending parallel or across a part of the major width or circumference dimension of the naturally-occurring fracture. In this configuration, the constraints on aligning the position and orientation of the linear shaped charge(s) with the aperture of the naturally-occurring fracture can be relaxed. This can reduce complexity and possibly errors in such alignment while permitting the detonation of the linear shaped charge(s) to provide a penetration pattern that intersects the naturally-occurring fracture and enlarges the size of the aperture of the naturally-occurring fracture at the wellbore wall and reduces pressure loss of the fluid flow through the naturally-occurring fracture at the wellbore wall (rock face).

[0047] In optional block 309, the operations of blocks 305 to 307 can be repeated with the same or additional downhole tools to locate and detonate additional linear shape charge(s) to reduce pressure loss of the fluid flow through other naturally-occurring fracture(s) that intersect the production well.

[0048] In optional block 311, debris resulting from the operation of 307 can be cleaned out and removed from the production well, for example, using coiled tubing. This can also increase the flow rate of pressurized hot water or brine into the production well.

[0049] FIG. 6 illustrates a downhole tool (e.g., labeled capsule gun) 600 that can be used as part of the workflow of FIG. 3. Specifically, the capsule gun includes a tool body 601 that can be conveyed in the production well by coiled tubing, wireline cable or other conveyance means. The tool body 601 supports a detonation control module 603 and one or more linear shaped charges (one shown as 605). The detonation control module 603 is operably coupled to the linear shaped charge(s) 605 and can be remotely controlled from the surface to activate the denotation of the linear shaped charge(s) 605. The position and orientation (e.g., wellbore depth and azimuth angle) of the capsule gun 600 can be set such that the linear shape charge(s) are positioned and oriented in the production well at a desired depth and azimuth angle in the well such that the penetration pattern of the linear shaped charge(s) that results from detonation intersects the naturally-occurring fracture(s) at the wellbore wall (rock face) as described herein. In some applications, the production well can be substantially vertical, and the naturally-occurring fracture(s) close to horizontal. In this case, the linear shape charge(s) 605 can be aligned parallel to the central axis of the tool body such that the slot-like penetration pattern of the linear shaped charge(s) that results from detonation intersects the naturally-occurring fracture(s) at the wellbore wall (rock face) and extends perpendicular to the naturally-occurring fracture(s).

[0050] FIG. 7 includes plots of available power from a conventional geothermal reservoir with varying fracture aperture size in the range of 1 mm, 3 mm and 5 mm. Note that an increase in fracture aperture size from 1 mm to 3 mm results in an increase in performance. Similarly, an increase in fracture aperture size from 3 mm to 5 mm results in a further increase in performance, which is even more that the increase that results from the 1 mm to 3 mm increase in facture aperture size. The plots of FIG. 7 are derived from simulations, which assumes an 8.5 inch wellbore, and the same pressure/temperature at the far field. The fracture is modelled as a disc. The pressure loss in the actual fracture is small compared to that at the wellbore entry, as in FIG. 2. The well is flowed at different rates measuring pressure at the bottom of the well to characterize the losses in the fracture and the wellbore entry.

[0051] FIG. 8 includes plots of available power extracted from a conventional geothermal reservoir with varying fracture aperture size in the range of 1 mm, 3 mm and 5 mm and varying wellbore diameters of 8.5 inches, 12.25 inches, and 18.5 inches. The plots of FIG. 8 are derived from simulations similar to those described above for FIG. 7. Note that generally an increase in fracture aperture size from 1 mm to 3 mm results in an increase in performance, and an increase in fracture aperture size from 3 mm to 5 mm results in a further increase in performance.

[0052] In another aspect, the performance of a geothermal system can also be improved by drilling the production well that intersects a conventional geothermal reservoir in two stages, referred to herein as an upper stage and a lower stage. In the upper stage, a larger diameter wellbore (e.g., 12.5 inches in diameter) is drilled from the surface (or near the surface) to an intermediate depth. In the lower stage, a smaller diameter wellbore (e.g., 8.5 inches in diameter) is drilled below the intermediate depth such that the smaller diameter wellbore of the lower stage extends below the larger diameter wellbore of the upper stage to the conventional geothermal reservoir as shown in FIG. 9. The intermediate depth can be selected to balance the benefits versus risks and costs. The lower stage wellbore can be completed with a perforated casing or perforated liner as an open wellbore at least in the interval(s) that intersects the one or more naturally-occurring fractures of the conventional geothermal reservoir. The naturally-occurring fracture(s) carries a flow of pressurized hot water or brine into the lower stage of the production well. This architecture can also be used to access a non-conventional geothermal reservoir that provides a source of pressurized hot fluid that flows into the lower stage of the production well.

[0053] FIG. 10 includes plots of available power extracted from a conventional geothermal reservoir with a production well having a single diameter of 8.5 inches as well as production well having two-stage diameters of 12.5 inches and 8.5 inches with varying depths for the transition between stages ranging from 2000, 4000, 6000, and 8000 feet. The plots of FIG. 10 are derived from simulations similar to those described above for FIG. 7. In this case, the production well has a larger diameter closer to the surface, so the fluid flows into the larger pipe. Note that the production well of two-stage diameters results in an increase in performance related to the single diameter wellbore. Furthermore, moving the transition between stages downward from 2000 feet to 4000 feet to 6000 feet to 8000 feet can provide incremental increases in performance.

[0054] In yet another aspect, for the case where an existing production well has been drilled, a secondary production well can be drilled to intersect the existing production well above a conventional geothermal reservoir as shown in FIG. 11. In this case, the existing production well is labeled as a primary well and the fluid flows from the conventional geothermal reservoir up the primary well to the point of intersection, and then flows up both the primary and secondary wells from that point as indicated by arrows in FIG. 11. The primary well can be completed with a perforated casing or perforated liner as an open wellbore at least in the interval(s) that intersect the one or more naturally-occurring fractures of the conventional geothermal reservoir. The naturally-occurring fracture(s) carries a flow of pressurized hot water or brine into the production well below the point of intersection of the primary and secondary production wells. This architecture can also be used to access a non-conventional geothermal reservoir that provides a source of pressurized hot fluid that flows into the primary production well below the point of intersection of the primary and secondary production wells.

[0055] FIG. 12 includes plots of available power extracted from a conventional geothermal reservoir with a single production well having a diameter of 8.5 inches as well as a system with a primary production well having a diameter of 8.5 inches that extends to the conventional geothermal reservoir together with a secondary production well having a diameter of 8.5 inches that intersects the primary production well above the conventional geothermal reservoir at varying depths ranging from 2000, 4000, 6000, and 8000 feet. The plots of FIG. 10 are derived from simulations similar to those described above for FIG. 7. In this case, the secondary production well intersects with the primary production well to allow a larger flow area to the surface. Note that the system with the primary and secondary production wells results in an increase in performance related to the single production well. Furthermore, moving the depth of intersection of the secondary production well and the primary production well downward from 2000 feet to 4000 feet to 6000 feet to 8000 feet can provide incremental increases in performance.

[0056] In still other embodiments, a two-stage production well or combination primary production well and secondary production well can be used in conjunction with methods for enlarging the aperture size of naturally-occurring fractures as described herein.

[0057] There have been described and illustrated herein several embodiments of geothermal systems and related methods used to capture and extract thermal energy (heat) from a geothermal reservoir. While particular configurations have been disclosed in reference to the geothermal systems and related methods, it will be appreciated that other configurations could be used as well. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope as claimed.

[0058] Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures. It is the express intention of the applicant not to invoke 35 U.S.C. 112, paragraph 6 for any limitations of any of the claims herein, except for those in which the claim expressly uses the words means for together with an associated function.