CONSTRUCTION OF ENHANCED GEOTHERMAL SYSTEMS USING U-SHAPED WELL TECHNOLOGY

Abstract

An enhanced geothermal system includes a first well and a second well drilled through a subterranean formation. The first well includes a lateral section extending through a heat zone in the subterranean formation. The second well is a U-shaped well having a first lateral section extending through the heat zone on a first side of the lateral section of the first well, and a second lateral section extending through the heat zone on a second side of the lateral section of the first well.

Claims

1. An enhanced geothermal system, comprising: a first well drilled through a subterranean formation and including a lateral section extending through a heat zone in the subterranean formation; and a second well drilled through the subterranean formation proximate the first well, the second well being a U-shaped well having: a first lateral section extending through the heat zone on a first side of the lateral section of the first well, and a second lateral section extending through the heat zone on a second side of the lateral section of the first well.

2. The system of claim 1, wherein the first lateral section and the second lateral section of the second well intersect a fracture cloud formed through stimulation of the first well.

3. The system of claim 1, further comprising: injection equipment coupled to the second well at a surface location; and production equipment coupled to the first well at a surface location.

4. The system of claim 1, further comprising: a third well drilled through the subterranean formation and including a lateral section extending through the heat zone; a fourth well drilled through the subterranean formation proximate the third well, the fourth well being a U-shaped well having: a first lateral section extending through the heat zone on a first side of the lateral section of the third well, and a second lateral section extending through the heat zone on a second side of the lateral section of the third well; and a fifth well drilled through the subterranean formation and including a lateral section extending through the heat zone, wherein the second lateral section of the second well is on a first side of the lateral section of the fifth well, and the first lateral section of the fourth well is on a second side of the lateral section of the fifth well.

5. The system of claim 1, wherein the first and second lateral sections of the second well are located in a plane of the subterranean formation aligned with the lateral section of the first well.

6. The system of claim 1, wherein the first and second lateral sections of the second well are located in a plane above the lateral section of the first well.

7. The system of claim 1, wherein the first lateral section of the second well is located above the lateral section of the first well, and wherein the second lateral section of the second well is located below the lateral section of the first well.

8. The system of claim 1, further comprising a third well drilled through the subterranean formation proximate the first well, the third well being a U-shaped well having: a first lateral section extending through the heat zone on a third side of the lateral section of the first well, and a second lateral section extending through the heat zone on a fourth side of the lateral section of the first well.

9. A method, comprising: drilling a first well through a subterranean formation such that the first well includes a lateral section extending through a heat zone in the subterranean formation; and drilling a second well through the subterranean formation proximate the first well such that the second well is U-shaped having: a first lateral section extending through the heat zone on a first side of the lateral section of the first well, and a second lateral section extending through the heat zone on a second side of the lateral section of the first well.

10. The method of claim 9, further comprising: stimulating the first well to generate a fracture cloud surrounding the first well; and drilling the second well such that the first and second lateral sections of the second well intersect the fracture cloud.

11. A method, comprising: providing a power fluid to a U-shaped well extending through a subterranean formation, the U-shaped well having two lateral sections extending through a heat zone of the subterranean formation; injecting the power fluid into the heat zone through perforations in the two lateral sections of the U-shaped well; and producing heated power fluid from the heat zone through a second well extending through the subterranean formation proximate the U-shaped well.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0020] The drawings illustrate only example embodiments and are therefore not to be considered limiting in scope, as the example embodiments may admit to other equally effective embodiments. The elements and features shown in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the example embodiments. Additionally, certain dimensions or positions may be exaggerated to help visually convey such principles. In the drawings, reference numerals designate like or corresponding, but not necessarily identical, elements.

[0021] FIG. 1 is a schematic perspective view of an example enhanced geothermal system (EGS).

[0022] FIGS. 2A and 2B are schematic perspective and plan views of an example geothermal system having a U-shaped well, in accordance with one or more aspects of the present disclosure.

[0023] FIGS. 3A and 3B are schematic perspective and plan views of an example geothermal system having two U-shaped wells, in accordance with one or more aspects of the present disclosure.

[0024] FIG. 4 is a plan view of an example geothermal system having a plurality of U-shaped wells, in accordance with one or more aspects of the present disclosure.

[0025] FIGS. 5A and 5B are schematic perspective and plan views of an example geothermal system having a U-shaped well positioned shallower than a horizontal well, in accordance with one or more aspects of the present disclosure.

[0026] FIG. 6 is a schematic perspective view of an example geothermal system having a U-shaped well positioned above and below a horizontal well, in accordance with one or more aspects of the present disclosure.

[0027] FIG. 7 is a schematic perspective view of an example geothermal system having two U-shaped wells positioned on opposite sides of a horizontal well, in accordance with one or more aspects of the present disclosure.

[0028] FIG. 8 is a schematic perspective view of an example geothermal system having a pattern of U-shaped wells positioned above and below multiple horizontal wells, in accordance with one or more aspects of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

[0029] The present disclosure is directed to the use of U-shaped wells in geothermal applications utilizing injector and producer wells to provide or augment in situ water or other power fluid. The fluid may be used for power generation, industrial use, or district heating.

[0030] The present invention is directed to the use of U-shaped wells in different geometric orientations to provide an optimized wellbore length, while reducing the number of total wells drilled in a geothermal development. If applied in lieu of a typical three-well EGS, the total wellbore penetrations can be reduced by one. If applied in lieu of a typical seven-well EGS, the total wellbore penetrations can be reduced by two. The total number of wells that are drilled from the surface to the heat zone (and associated surface connections) can be reduced even further for larger EGSs.

[0031] In the following discussion, the term lateral section will be used to represent any section of well that is inclined or angled with respect to a vertical section of a wellbore. The lateral section may be in a horizontal plane or any other plane that is angled with respect to the vertical section. The lateral sections are generally located within a heat zone of the subterranean formation. Although the wells are illustrated as having the vertical section be in a substantially vertical direction through a lithological section of the subterranean formation above the heat zone, this vertical section of the well may be inclined relative to the vertical direction without departing from the scope of the present disclosure. The vertical sections generally extend from a surface through a lithological section of the subterranean formation located above the heat zone. The lateral section(s) of the wells disclosed herein are located after a kick-off from the vertical section of the well. The term U-shaped can refer to any well having at least two lateral sections that are connected by a turn or curve of the well. Although the lateral sections of the U-shaped wells are generally shown as being parallel to one another (with a 180 degree turn connecting them), the directions of the two lateral sections can be offset from one another in one or more planes without departing from the scope of the present disclosure. For example, the turn connecting the lateral sections can be greater than or less than 180 degrees without departing from the scope of the present disclosure. In addition to U-shaped wells, S-shaped wells having three or more lateral sections may also be used without departing from the scope of the present disclosure. The disclosed U-shaped wells may be drilled through the subterranean formation using any available directional drilling techniques.

[0032] As illustrated in FIGS. 2A and 2B, in certain exemplary embodiments, an EGS having two wells (a U-shaped well and a partner well) may be used in lieu of a typical triplet (3-well) system. As illustrated, the EGS includes a U-shaped well that effectively surrounds the partner well. The U-shaped well may be drilled at the same vertical depth as the partner well. The construction of such a system may begin with drilling a single lateral (e.g., horizontal or inclined) well and performing stimulation treatments at predetermined positions in the wellbore. These predetermined positions may include positions within the heat zone of the subterranean formation. Monitoring of microseismic responses to the stimulation would allow mapping of a fracture cloud created. The U-shaped well can then be designed and drilled to intercept the induced fracture cloud. Finally, additional stimulation treatments may be performed in either wellbore to assure and enhance communication between the wells.

[0033] As shown in FIGS. 2A and 2B, the EGS includes a first well drilled through a subterranean formation, the first well including a lateral section extending through a heat zone in the subterranean formation. The EGS also includes a second well drilled through the subterranean formation proximate the first well. The second well is a U-shaped well having: a first lateral section extending through the heat zone on a first side of the lateral section of the first well, and a second lateral section extending through the heat zone on a second side of the lateral section of the first well. The two lateral sections of the U-shaped well may be connected by a rounded section (turn) of the well. As shown most clearly in FIG. 2B, the first lateral section and the second lateral section of the second well may intersect one or more fracture clouds formed through stimulation of the first well. As indicated by arrows shown in the illustrated embodiment, the second (U-shaped) well may be in the role of injector with the first well in the role of producer. As such, injection equipment (not shown) may be coupled to the second (U-shaped) well at a surface location, and production equipment (not shown) may be coupled to the first well at a surface location. However, depending on the needs of the system the roles of these two wells may be reversed in other embodiments, with the first well being the injector and the second (U-shaped) well being the producer. As shown in FIG. 2A, the first and second lateral sections of the second (U-shaped) well may be located in a plane of the subterranean formation aligned with the lateral section of the first well.

[0034] Using the U-shaped well as shown in FIGS. 2A and 2B reduces the total system construction cost by saving the expense of drilling one of three lateral wells from the surface to the heat source (heat zone). Additional savings may be provided due to the reduction of the number of wellheads and surface connections needed. Surface and aesthetical footprint may also be reduced.

[0035] Potential additional savings may be realized with the embodiment illustrated in FIGS. 3A and 3B, which illustrates an EGS accessing the same amount of hot rock as the seven-well system shown in FIG. 1. As shown in FIGS. 3A and 3B, a reduced number of wells (five wells vs. seven wells) access the same heat resource. Specifically, this is achieved with two fewer surface to heat zone penetrations and surface well connections.

[0036] As shown in FIGS. 3A and 3B, the EGS includes a first well drilled through a subterranean formation, the first well including a lateral section extending through a heat zone in the subterranean formation. The EGS also includes a second well drilled through the subterranean formation proximate the first well. The second well is a U-shaped well having: a first lateral section extending through the heat zone on a first side of the lateral section of the first well, and a second lateral section extending through the heat zone on a second side of the lateral section of the first well. The illustrated EGS also includes a third well drilled through the subterranean formation with a lateral section extending through the heat zone. The illustrated EGS also includes a fourth well drilled through the subterranean formation proximate the third well. The fourth well is a U-shaped well having a first lateral section extending through the heat zone on a first side of the lateral section of the third well, and a second lateral section extending through the heat zone on a second side of the lateral section of the third well. The illustrated EGS also includes a fifth well drilled through the subterranean formation with a lateral section extending through the heat zone. The second lateral section of the second well is on a first side of the lateral section of the fifth well, and the first lateral section of the fourth well is on a second side of the lateral section of the fifth well.

[0037] As shown most clearly in FIG. 3B, the first lateral section and the second lateral section of the second well may intersect one or more fracture clouds formed through stimulation of the first well. Similarly, the first lateral section and the second lateral section of the fourth well may intersect one or more fracture clouds formed through stimulation of the third well. Although not explicitly shown, the second lateral section of the second well and the first lateral section of the fourth well may intersect one or more fracture clouds formed through stimulation of the fifth well.

[0038] As indicated by arrows shown in the illustrated embodiment, the second and fourth (both U-shaped) wells may be in the role of injectors with the first, third, and fifth wells in the role of producers. As such, injection equipment (not shown) may be coupled to the second and fourth (U-shaped) wells at a surface location, and production equipment (not shown) may be coupled to the first, third, and fifth wells at a surface location. However, depending on the needs of the system the roles of these wells may be reversed or otherwise changed in other embodiments. As shown in FIG. 3A, the lateral sections of each of the five wells may be aligned with each other in a plane of the subterranean formation.

[0039] The U-shaped system value increases in applications where the power need is great and the heat source is located deep underground, such as in the eastern United States, for example. FIG. 4 illustrates a plan view of an EGS equivalent to a 46 well conventionally installed system. The same volume of source rock may be accessed using only 34 wellbores when U-shaped wells are drilled. Such an application may reduce the need to drill the section above the heat zone and connect 12 out of 46 wells (26% reduction).

[0040] As indicated in the illustrated embodiment of FIG. 4, the U-shaped wells may each be in the role of injectors with the partner wells (each with a single lateral section) in the role of producers. As such, injection equipment (not shown) may be coupled to the U-shaped wells at a surface location, and production equipment may be coupled to the partner wells at a surface location. However, depending on the needs of the system the roles of these wells may be reversed or otherwise changed in other embodiments.

[0041] The systems shown in FIGS. 2A-4 illustrate an application in a fracture geometry composed of long fractures that possess a relatively short height. This is analogous to many stimulation operations in sedimentary rocks. The nature and orientation of the in-situ stress field in igneous or metamorphic rock may diverge significantly from that seen in sedimentary rocks. Because of this unknown, the fracture geometry in the source rock may not be conducive to a U-shaped application with wells in the same horizontal plane or at the same vertical depth as the partner well.

[0042] In such instances, the position or orientation of the U-shaped well(s) may be varied. FIGS. 5A and 5B illustrate an exemplary embodiment of another system where the fracture cloud formed by stimulating the producer well favors a vertically upward and outward direction. The U-shaped injector well may be positioned shallower than the producer well as required to best intercept the fracture cloud. That is, the first and second lateral sections of the U-shaped well are located in a plane above the lateral section of the first well. Other embodiments may include the U-shaped well positioned deeper than its counterpart well (i.e., in a plane below the lateral section of the first well).

[0043] As indicated by arrows shown in the illustrated embodiment, the second (U-shaped) well may be in the role of injector with the first well in the role of producer. As such, injection equipment (not shown) may be coupled to the second (U-shaped) well at a surface location, and production equipment (not shown) may be coupled to the first well at a surface location. However, depending on the needs of the system the roles of these two wells may be reversed in other embodiments, with the first well being the injector and the second (U-shaped) well being the producer.

[0044] In other embodiments, in situ stress may cause the fracture cloud to orient vertically and develop a tall but narrow geometry. In another exemplary embodiment shown in FIG. 6, a system of the present invention may entail drilling the U-shaped well in the same vertical plane as the partner well, with outgoing and incoming portions above and below. For example, the first lateral section of the second (U-shaped) well may be located above the lateral section of the first well, and the second lateral section of the second (U-shaped) well may be located below the lateral section of the first well. The illustrated application in FIG. 6 demonstrates the outgoing leg of the U-shaped well above the partner lateral with the incoming leg of the U-shaped well below the partner lateral. In alternate embodiments, the system may position the outgoing leg below the partner well with the incoming above, if dictated by system requirements. While these embodiments depict a vertical fracture orientation, however the fracture orientation may be somewhere between vertical and horizontal, in which case the U-shaped well may be oriented at the inclination of the fracture long axis.

[0045] As indicated by arrows shown in the illustrated embodiment, the second (U-shaped) well may be in the role of injector with the first well in the role of producer. As such, injection equipment (not shown) may be coupled to the second (U-shaped) well at a surface location, and production equipment (not shown) may be coupled to the first well at a surface location. However, depending on the needs of the system the roles of these two wells may be reversed in other embodiments, with the first well being the injector and the second (U-shaped) well being the producer.

[0046] In other embodiments, the in-situ stress in the heat source may be such that the fractures are similar in width and height or approaching circular. In yet another exemplary embodiment shown in FIG. 7, a system of the present invention may include two U-shaped wells per partner lateral. As shown in FIG. 7, the EGS includes a first well drilled through a subterranean formation, the first well including a lateral section extending through a heat zone in the subterranean formation. The EGS also includes a second well drilled through the subterranean formation proximate the first well. The second well is a U-shaped well having: a first lateral section extending through the heat zone on a first side of the lateral section of the first well, and a second lateral section extending through the heat zone on a second side of the lateral section of the first well. The illustrated EGS also includes a third well drilled through the subterranean formation proximate the first well. The third well is a U-shaped well having a first lateral section extending through the heat zone on a third side of the lateral section of the first well, and a second lateral section extending through the heat zone on a fourth side of the lateral section of the first well.

[0047] As indicated by arrows shown in the illustrated embodiment, the second and third (U-shaped) wells may be in the role of injectors with the first well in the role of producer. As such, injection equipment (not shown) may be coupled to the second and third (U-shaped) wells at a surface location, and production equipment (not shown) may be coupled to the first well at a surface location. However, depending on the needs of the system the roles of these wells may be reversed or otherwise changed in other embodiments.

[0048] Any of the systems described above with respect to FIGS. 5A-7 may be constructed in a repetitious application for larger scale applications. For example, FIG. 8 illustrates an EGS having a repetitious application of the well arrangement of FIG. 7, with a pattern of U-shaped injector wells positioned above and below each horizontal producer well. The system may provide access to double the volume of the heat source as the system in FIG. 3 through the position of and addition of two wells per five-well set.

[0049] As indicated by arrows shown in the illustrated embodiment, the U-shaped wells may each be in the role of injectors with the partner wells (each with a single lateral section) in the role of producers. As such, injection equipment (not shown) may be coupled to the U-shaped wells at a surface location, and production equipment may be coupled to the partner wells at a surface location. However, depending on the needs of the system the roles of these wells may be reversed or otherwise changed in other embodiments.

[0050] In accordance with certain aspects of the present disclosure, a method for constructing an enhanced geothermal system (EGS) includes drilling a first well through a subterranean formation such that the first well includes a lateral section extending through a heat zone in the subterranean formation. The method may include stimulating the first well to generate a fracture cloud surrounding the first well. The method includes drilling a second well through the subterranean formation proximate the first well such that the second well is U-shaped having: a first lateral section extending through the heat zone on a first side of the lateral section of the first well, and a second lateral section extending through the heat zone on a second side of the lateral section of the first well. The second well may be drilled such that the first and second lateral sections of the second well intersect the fracture cloud.

[0051] In accordance with certain aspects of the present disclosure, a method for operating an enhanced geothermal system (EGS) includes providing a power fluid to a U-shaped well extending through a subterranean formation. The U-shaped well has two lateral sections extending through a heat zone of the subterranean formation. The method includes injecting the power fluid into the heat zone through perforations in the two lateral sections of the U-shaped well. The method includes producing heated power fluid from the heat zone through a second well extending through the subterranean formation proximate the U-shaped well.

[0052] It will be understood that various modifications may be made to the embodiments disclosed herein. Therefore, the above description should not be construed as limiting, but merely as exemplifications of example embodiments. For example, the functions described above and implemented as the best mode for operating the present invention are for illustration purposes only. Other arrangements and methods may be implemented by those skilled in the art without departing from the scope and spirit of this invention. Moreover, those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.