WO2025079002A1

WO2025079002A1 - Dual mode fracture tool and methods therefor

Info

Publication number: WO2025079002A1
Application number: PCT/IB2024/059927
Authority: WO
Inventors: Marek KOZIKOWSKI; Axel-Pierre BOIS
Original assignee: XGS Energy Inc
Current assignee: XGS Energy Inc
Priority date: 2023-10-13
Filing date: 2024-10-10
Publication date: 2025-04-17
Anticipated expiration: 2026-04-13
Also published as: WO2025079002A4

Abstract

A fissure with controlled geometry is formed in hot dry rock by iterative application of increasing mechanical and hydraulic stresses in which the mechanical stress is applied by a contact device with typically opposing contact elements to incrementally open a mouth portion of the fissure while the hydraulic stress is used to then expand the fissure. However, it is also contemplated that the contact device may also be used for expansion and/or propagation of existing fissures that are naturally occurring or initiated by hydraulic fracturing. Fissures created with the devices and methods presented herein will avoid thermal bottlenecks in thermally conductive materials placed within such fissures. Moreover, the wide mouth portion of such fissures will help ensure continuous heat transfer from the thermally conductive materials placed within such fissures to a thermally conductive materials placed within a wellbore from which the fissures originate.

Description

DUAL MODE FRACTURE TOOL AND METHODS THEREFOR

[0001] This application claims priority to our copending US provisional patent application with the serial number 63/590,379, filed 10/13/2023, which is incorporated by reference herein.

Field

[0002] The field of the disclosure is devices and methods for generating fractures in dry rock with controlled geometry, particularly as it relates to generation of fractures for thermal reach enhancement structures in geothermal wells for geoheat recovery.

Background

[0003] The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.

[0004] Generation of fractures in oil and gas-bearing formations is well known in the field of hydrocarbon production and can be performed in a variety of manners. While such fracturing is relatively common, fracture generation in wells intended for heat harvesting, and particularly in heat harvesting for power generation is not routinely employed. For example, rock can be fractured between an injection well and a production well in enhanced geothermal systems to increase heat harvest relative to conventional geothermal systems as described in US 7320221 and US 2017/0211849. Alternatively, fractures can be formed in a hot rock formation and filled with a thermally conductive material to so help transfer thermal energy from the rock to a heat harvesting structure (typically a closed-loop system) in a geothermal well as is described in WO 2023/069703 and WO 2023/150466. However, despite such improvements in heat recovery, the geometry of the fractures and, subsequently, the efficiency of heat transfer and harvest remain difficult to control.

[0005] Thus, even though various systems and methods of generating fractures in a geological formation are known in the art, all or almost all of them suffer from several drawbacks. Therefore, there remains a need for compositions and methods for improved devices that are able to generate fractures in dry rock with controlled geometry. Summary

[0006] The disclosure is directed to various systems, devices, and methods of generating a fissure in a geothermal well in a rock formation in which the fissure has a controlled, typically wedge-shaped geometry. The inventors have now discovered that the geometries and methods presented herein are especially advantageous in the context of thermal energy transfer from a (typically hot dry rock) formation to a heat harvesting element located in the geothermal well, typically via a thermally conductive sheath surrounding the heat harvesting element and where a thermally conductive material present in the fissure and the sheath.

[0007] In one aspect of the disclosure, the inventors contemplate a method of forming a fissure with controlled geometry in wellbore located within a rock formation that includes a step of placing a contact device in the wellbore at a target location, wherein the contact device has at least two movable contact elements, and a further step of using the contact elements at the target location to apply a stress force in the rock formation to thereby create an initial fissure. While maintaining the first stress force, the initial fissure is then expanded using hydraulic fracturing to thereby create an expanded fissure, wherein the expanded fissure has a mouth portion at a wall of the wellbore. Contemplated methods will further repeatedly perform steps (a) and (b) in sequence, wherein (a) uses the contact elements to apply a further stress force at the target location in the rock formation to thereby increase the width of the mouth portion; and (b) further applies hydraulic pressure at the target location to further expand the fissure. In such methods, these repeated steps advantageously generate a wedge-shaped fissure in which the mouth portion at the wall of the wellbore is wider than a proximal portion of the fissure, and in which the proximal portion of the fissure is wider than a distal portion of the fissure.

[0008] In another aspect of the disclosure, the inventors also contemplate a method of directionally fracturing rock in a wellbore that involves placing at a first downhole position a contact device in the wellbore at a target location, wherein the contact device has at least two movable contact elements, moving the contact elements in the wellbore at the first downhole position at the target location in a direction against a wall of the wellbore to apply a stress in the rock formation, thereby creating an initial fissure, and while maintaining the stress, expanding the initial fissure using the contact elements, thereby creating an expanded fissure, repeatedly performing steps (a) and (b) in sequence: (a) using the contact elements to apply a further stress force at the target location in the rock formation to thereby increase the width of the mouth portion and (b) using the contact elements at the target location to further expand the fissure.

[0009] It is also contemplated that the above method may further comprise a step of placing the contact device at a second downhole position that is different from the first downhole position, wherein the contact device is placed such that the contact elements have a radial offset in the wellbore relative to the contact elements at the first downhole position, and further comprising applying stress in the rock formation at the second downhole position, thereby creating a second initial fissure, and while maintaining the stress, expanding the second initial fissure using the contact elements, thereby creating a second expanded fissure. In some embodiments, the steps (a) and (b) may additionally be performed at the second downhole position.

[0010] Most typically, the radial offset is at least 30 degrees and the difference in distance between the first and second downhole positions is between 10 m and 100 m.

[0011] In some embodiments, the movable contact elements of the contact device are configured to conform to the wall of the wellbore and will typically be located on opposite sides of the contact device. Preferably, but not necessarily, the contact device will be configured such that the movable contact elements move using hydraulic force. It is further generally preferred that the rock formation is a dry hot rock formation (e.g., intrusive igneous, granitic, basaltic, sedimentary, or metamorphous rock), for example, with a target location at a depth of between 150 m and 20,000 m and/or has a temperature of between about 120 °C to 600 °C.

[0012] In further embodiment, the stress is applied at a force of between about 10 and 100 MPa. (e.g., 10-50 MPa), and the further stress is between about 1.1-fold and 1.5-fold of the stress, (e.g., 1.1-1.3-fold). In most instances, steps (a) and (b) are repeatedly performed in sequence between 2-6 times, but more frequent iterations are not excluded.

[0013] Using contemplated devices and methods, the mouth portion at the wall of the wellbore has a width of between 1 mm and 100 mm, the proximal portion of the fissure has a width of between 3 mm and 25 mm, and/or the distal portion of the fissure has a width of between 0.5 mm and 2 mm. Most typically, the fissure has a length of between 1 m and 200 m as measured from the mouth portion to the distal end, and/or the fissure has a vertical orientation and a height of between 1 m and 40 m. [0014] Consequently, the inventors also contemplate a wellbore with a fissure within a rock formation wherein the fissure has a controlled geometry, and wherein the fissure is formed in a manner as described above. Most typically, the controlled geometry is such that a mouth portion of the fissure at a wall of the wellbore is wider than a proximal portion of the fissure, and that the proximal portion of the fissure is wider than a distal portion of the fissure.

[0015] It is still further contemplated that the fissure is filled with a first thermally conductive material, preferably having a k-value of at least 5 W/mK. Additionally, it is contemplated that the first thermally conductive material is thermally coupled to a second thermally conductive material surrounding a heat harvesting element, and that the thermal conductivity constants of the first and second thermally conductive materials differ by no more than 10% as measured by their respective k-values. Alternatively, the first and second thermally conductive materials can be the same.

[0016] Viewed from a different perspective, the inventors also contemplate a method of facilitating thermal energy transfer in a geothermal well having a wellbore with a thermal reach enhancement structure at a target location within a rock formation. Such methods will generally include a step of forming the thermal reach enhancement structure to include a fissure in which a mouth portion of the fissure at a wall of the wellbore is wider than a proximal portion of the fissure, and in which the proximal portion of the fissure is wider than a distal portion of the fissure, and a further step of filling the fissure with a first thermally conductive material. In still a further step, a heat harvesting element located in the wellbore is thermally coupled with the first thermally conductive material using a second thermally conductive material. Most preferably, the thermal conductivity constants of the first and second thermally conductive material differ by no more than 10% as measured by their respective k-values or are the same.

[0017] In some embodiments, the fissure in the thermal reach enhancement structure is formed using the method as described above. In other embodiments, the fissure in the thermal reach enhancement structure is naturally occurring, formed using hydraulic fracking, formed using a contact device, or formed using mechanical fracking. Therefore, in at least some embodiments the thermal reach enhancement structure is configured as a longitudinal/lateral (bilateral or biwing) vertical structure. In other embodiments, the thermal reach enhancement structure may be configured as a radial/transverse structure. As will be readily appreciated, the fissure in the thermal reach enhancement structure is widened and/or propagated using a directionally controlled contact device to create a predictable structure. For example, the mouth portion at the wall of the wellbore has a width of between 1 mm and 100 mm, the proximal portion of the fissure has a width of between 3 mm and 25 mm, the distal portion of the fissure has a width of between 0.5 mm and 2 mm, and/or the fissure has a length of between 1 and 200 m as measured from the mouth portion to the distal end.

[0018] In further embodiments, the first thermally conductive material has a thermal conductivity of between 50 W/mK and 400 W/mK, and/or the first and/or second thermally conductive materials are materials other than cementitious materials. It is still further contemplated that the heat harvesting element comprises a closed loop circuit in which heat is transferred from the second thermally conductive material to a casing of the heat harvesting element. Preferably, the second thermally conductive material is then configured as a sheath surrounding the casing of the heat harvesting element.

[0019] Additionally, it is contemplated that the step of filling the fissure with the first thermally conductive material includes a step of compressing the first thermally conductive material using geostatic pressure and/or using mechanical compression (e.g., during placement of the heat harvesting element into the wellbore) to so ensure a continuous heat transfer path.

[0020] Viewed from another perspective, the inventors also contemplate a wellbore with a fissure within a rock formation wherein the fissure has a controlled geometry, formed by hydraulic fracking or by using a contact device, wherein the controlled geometry is such that a mouth portion of the fissure at a wall of the wellbore is wider than a proximal portion of the fissure, and that the proximal portion of the fissure is wider than a distal portion of the fissure.

[0021] It is still further contemplated that the fissure is filled with a first thermally conductive material, preferably having a k-value of at least 5 W/mK. For example, the first thermally conductive material may comprise a material selected from the group consisting of zinc, graphite, graphene, tungsten, aluminum, silicon carbide, aluminum nitride, silicon nitride, boron nitride, gold, copper, silver, diamond, aluminum alloys, aluminum oxides, rhodium, cobalt, copper alloys, nickel, iron, platinum, palladium, tin, steel, zirconium, titanium, carbon fiber, carbon black, Hastelloy, carbon-based inorganic, metal, metal oxides, metal nitrides, alloys, or hybrids. Additionally, it is contemplated that the first thermally conductive material is thermally coupled to a second thermally conductive material surrounding a heat harvesting element, and that the thermal conductivity constants of the first and second thermally conductive materials differ by no more than 10% as measured by their respective k-values. Alternatively, the first and second thermally conductive materials can be the same. The second thermally conductive material may also comprise a material selected from the group consisting of zinc, graphite, graphene, tungsten, aluminum, silicon carbide, aluminum nitride, silicon nitride, boron nitride, gold, copper, silver, diamond, aluminum alloys, aluminum oxides, rhodium, cobalt, copper alloys, nickel, iron, platinum, palladium, tin, steel, zirconium, titanium, carbon fiber, carbon black, Hastelloy, carbon-based inorganic, metal, metal oxides, metal nitrides, alloys, or hybrids.

[0022] In some embodiments, the contact device is involved in fissure formation, fissure widening, and/or fissure propagation. Most typically, the contact device is directionally controllable to allow rotation and application in a direction of choice. As previously mentioned, the mouth portion at the wall of the wellbore is contemplated to have a width of between 1 mm and 100 mm, the proximal portion of the fissure is contemplated to have a width of between 3 mm and 25 mm, the distal portion of the fissure is contemplated to have a width of between 0.5 mm and 2 mm, and/or the fissure is contemplated to have a length of between 1 and 200 m as measured from the mouth portion to the distal end.

[0023] As will be readily appreciated, the wellbore may be a greenfield new well, a brownfield geothermal well, or a brownfield oil and gas well.

[0024] Viewed from yet another perspective, the inventors additionally contemplate a system configured to initiate a fissure within a wellbore in a rock formation in a desired direction that includes a contact device that has at least two movable elements, wherein the contact elements are configured to allow application of mechanical stress in the rock formation at a target location to thereby create an initial fissure in the well bore in a direction that is substantially perpendicular to a direction in which the contact elements move, and a controller that is configured to maintain a pressure of a hydraulic fluid within the initial fissure while the contact device is expanding and/or propagating the fissure.

[0025] As previously mentioned, it is generally contemplated that the wellbore is a greenfield new well, a brownfield geothermal well, or a brownfield oil and gas well.

[0026] In some embodiments, the initial fissure is a dual fissure that extends longitudinally from the wellbore in opposite directions. In other embodiments, the fissure within the rock formation does not follow a naturally occurring feature in the rock formation. Most typically, a mouth portion at a wall of the wellbore is contemplated to have a width of between 1 mm and 100 mm, a proximal portion of the fissure a width of between 3 mm and 25 mm, a distal portion of the fissure a width of between 0.5 mm and 2 mm, and wherein the fissure is contemplated to have a length of between 1 m and 200 m as measured from the mouth portion to the distal end. Generally, the fissure has a controlled geometry such that a mouth portion of the fissure at a wall of the wellbore is wider than a proximal portion of the fissure, and wherein the proximal portion of the fissure is wider than a distal portion of the fissure.

[0027] Preferably, the contact device is configured to allow successive movement in the same direction to thereby promote fissure widening, and/or fissure propagation. Moreover, the contact device is directionally controllable to allow rotation relative to a direction of the initial fissure and application of further mechanical stress in a different direction.

[0028] It is also contemplated that the controller is further configured to control movement of the contact elements and maintains pressure within the fissure hydraulically or mechanically.

[0029] Viewed from yet another perspective, the inventors contemplate a method of expanding an existing fissure in a wellbore that includes, placing at a first downhole position a contact device in the wellbore at a target location proximal to the existing fissure, wherein the contact device has at least two movable contact elements, and moving the contact elements in the wellbore at the first downhole position at the target location in a direction against a wall of the wellbore to expand the existing fissure using the contact elements, thereby creating an expanded fissure.

[0030] It is generally contemplated that the existing fissure is naturally occurring, initiated using hydraulic fracturing, initiated using mechanical fracturing, or initiated using the contact device. In some embodiments, the contact elements are used to apply a further stress force at the target location in the rock formation to thereby increase the width of the mouth portion. This further applied stress force is most typically repeatedly performed between 2-6 times.

[0031] As will be readily appreciated, the above-contemplated features involving rock formation, target location depth, target location temperature, expanded fissure widths, expanded fissure orientation and height, as well as a first and/or second thermally conductive material are all also considered in the present perspective. [0032] Various objects, features, aspects, and advantages of the disclosure will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawings.

Brief Description of The Drawing

[0033] FIGS.1A-1F are schematic and exemplary illustrations depicting selected steps in the deployment and operation of a contact device.

Detailed Description

[0034] Generation of fractures in various geological formations is commonly used for oil and gas production, and there are a large number of options are known in the art to generate fractures with complex geometry and/or wide reach within a formation. Among other options, explosive fracking and hydraulic fracturing are most frequently used. However, and as noted above, such methods generally fail to allow for control of the fracture geometry. Similarly, fractures can be generated in a formation using a mechanical tool as described in US 2776014 that applies pressure to a rock formation via flexible boots to fracture the rock at the point of applied stress. While such systems and methods allow for control over the location of a fracture within a wellbore, direction or geometry of the fracture is once more not controlled.

[0035] In further examples, such as disclosed in US 2015/0322760, fractures are generated using mechanical and hydraulic forces where a mechanical tool is deployed to a desired location and where the tool is expanded to thereby induce stress in the formation. A hydraulic fracturing step is then applied to fracture the rock and to propagate the fracture. The tool is then collapsed, and the pressure of the hydraulic fluid is reduced for removal of the tool. Similarly, US 9664024 and US 8875790 disclose the use of a packer jack to produce a locally fractured rock, followed by deflation of the packer jack, and hydraulic fracturing of the locally fractured rock, with this process being repeated at different depths. While such systems and methods allow for control of the location and to some extent direction of the fracture, control over the geometry of the fracture is typically not achieved. Moreover, such systems and methods were only contemplated for use in oil, gas, or water bearing formations.

[0036] Viewed from a different perspective, it should therefore be appreciated that all or almost all of the fissures generated using conventional methods will result in fissures with a geometry that is predominantly determined by the particular rock composition, existing faults, cracks, and/or stress zones. As a result, so produced fissures will in most cases be formed as narrow channels with an equally narrow mouth portion. Such conventional fissure geometry is especially disadvantageous where the fissure is to be filled with a thermally conductive material for heat transfer. For example, conventional fissures tend to be prone to inadvertent fracture closure, leading to a loss in thermal transfer. Moreover, the inventors have discovered that conventional fissures with a relatively narrow mouth portion will typically result in poor thermal coupling to thermally conductive material disposed in the wellbore and thereby result in loss of recoverable thermal energy.

[0037] To overcome these difficulties and improve thermal energy transport, the inventors have now developed various systems and methods of fissure generation in a geological formation, and particularly in a hot dry rock formation, in which the geometry of the fissure can be controlled to produce a wedge-shaped fissure. Such geometry is especially advantageous in the context of thermal energy transfer from a (typically hot dry rock) formation to a heat harvesting element located in the geothermal well where thermal energy is transferred through thermally conductive materials placed in the fissure and wellbore. Indeed, using such wedge- shaped geometry in conjunction with a thermally conductive material disposed in the fissure (to so form a thermal reach enhancement structure) will advantageously reduce or even entirely avoid thermal bottlenecks to thermal energy flow from the formation to the heat harvesting structure and help ensure continuous thermal coupling between thermally conductive material disposed in the fissure and thermally conductive material disposed in the wellbore as is shown in more detail below.

[0038] In most embodiments, it should further be appreciated that the rock formation at the target location is a dry hot rock formation such as an intrusive igneous or metamorphous rock formation. However, the target location may also be in hot wet rock, a “greenfield”, a “brownfield”, the ocean floor, and/or oil/gas wells. The rock formation may be permeable or impermeable and additional rock types may include granitic, basaltic, or sedimentary rock. In terms of using oil/gas wells, geothermal energy may be harnessed through the retrofitting of inactive or unproductive wells and co-production on active wells. In terms of drilling on the ocean floor, it is contemplated that a complete geothermal system could be placed at or near seafloor spreading rifts. Drilling on the ocean floor may also be anywhere else that geothermal energy can be extracted, such as major tectonic plate boundaries or rift zones. [0039] Regardless of where the drilling of the wellbore occurs, it is preferable that the target location (or target production zone) has a target temperature of at least 100 °C, at least 200 °C, at least 300 °C, at least 350 °C, at least 400 °C, at least 450 °C, or at least 500 °C, or at least 600 °C and/or the target location may be below ground at a depth of at least 100 m, at least 200 m, at least 300 m, at least 500 m, at least 600 m, at least 700 m, at least 800 m, at least 900 m, at least 1,000 m, at least 1,250 m, at least 1,500 m, at least 1,750 m, at least 2,000 m, at least 2,500 m, at least 3,000 m, at least 4,000 m, at least 5,000 m, at least 10,000 m, or at least 20,000 m. Therefore, suitable target temperature will be between 150 °C and 350 °C, or between 200 °C and 400 °C, or between 250 °C and 450 °C, or between 300 °C and 600 °C. Likewise, contemplated depths of between 100 m and 300 m, or between 200 m and 800 m, or between 500 m and 1,500 m, or between 1,000 m and 3,000 m, or between 2,000 m and 6,000 m.

[0040] In one exemplary embodiment of the present disclosure, a contact device is configured to allow deployment of the device to a target location within a wellbore at which the fissure is to be generated. Preferred contact devices have at least two movable contact elements that are movably coupled to opposite sides of the contact device such that the contact elements will move from a retracted position (typically used during deployment) into an extended contact position in which the contact elements have increased radial distance from a hypothetical central axis of the contact device. The contact device may be part of a system that is configured to initiate a fissure within a wellbore in a rock formation in a desired direction. Most typically, the contact device is directionally controllable to allow rotation relative to a direction of the initial fissure and application of further mechanical stress in a difference direction. For example, the contact elements may be configured to allow application of mechanical stress in the rock formation at a target location to thereby create an initial fissure in the wellbore in a direction that is substantially perpendicular to a direction in which the contact elements move. In most embodiments, the movable contact elements of the contact device are configured to conform at least in part to the wall of the wellbore (e.g., will have a curved contact surface). In some embodiments, a controller may be used that is configured to maintain a pressure of a hydraulic fluid within the initial fissure while the contact device is expanding and/or propagating the fissure. Preferably, the controller maintains pressure within the hydraulically or mechanically, but is nonetheless configured to control movement of the contact elements.

[0041] As will be readily appreciated, in contexts where the contact device initiates a fissure, the initial fissure may be a dual fissure that extends longitudinally from the wellbore in opposite directions. The contact device may also be configured to allow successive movement in the same direction to thereby promote fissure widening and/or fissure propagation.

[0042] It is still further contemplated that the contact elements in the contact device will be movable by mechanic or hydraulic actuation such that upon contact of the contact elements with the wall of the wellbore, continued actuation will result in an increasing stress in the rock surrounding the well bore. Therefore, where two contact elements are oppositely forced by mechanic or hydraulic actuation against the wall of a wellbore, increasing force will ultimately lead to a fracture in the rock formation that is approximately between and perpendicular to the direction of the movement of the contact elements. As will be readily appreciated, the fracture may be initiated/created in such method by continued increase of mechanic or hydraulic actuation of the contact elements to exert stress beyond the fracture stress of the rock, or by a combination of mechanic or hydraulic actuation of the contact elements to a point below the fracture stress of the rock followed additional pressure provided to the target area using conventional hydraulic fracturing. Regardless of the manner of initial fracture generation, it is then contemplated to use hydraulic fracturing to thereby expand the initial fissure to an expanded fissure. As a result, use of the contact device in combination with hydraulic fracturing will produce an expanded fissure in the rock.

[0043] However, in some embodiments, rather than being created with the contact device, a fracture may instead be naturally occurring or created by any other engineered fracking approaches. Nonetheless, the contact device may be used to also (or only) widen or propagate the fracture. As will be readily appreciated, the contact device also can provide directional control. For example, the contact device can be rotated to create/widen/propagate natural or engineered fractures in the direction of choice to thereby allow for more predictable fracturing in rock formations. Indeed, the contact device may be place at a first downhole position in a wellbore at a target location, where the contact device has at least two movable contact elements. As previously mentioned, the contact elements are adjusted in the wellbore at the first downhole position in a direction against a wall of the wellbore to apply a stress in the rock formation to thereby create an initial fissure. While maintaining the stress, the initial fissure is expanded using the contact elements. In most embodiments where the contact device is used for expansion, steps (a) and (b) are repeatedly performed in sequence: (a) using the contact elements to apply a further stress force at the target location in the rock formation to thereby increase the width of the mouth portion, and (b) using the contact elements at the target location to further expand the fissure. Steps (a) and (b) may be repeated between 2-6, including at least once, at least twice, at least three times, at least four times, at least five times, and at least six times.

[0044] It is generally preferred that the contact device may also be placed at a second downhole position that is different from the first downhole position. In various embodiments, the contact device may also be placed at a third, fourth, or fifth downhole position. Where desired, the contact device may be placed at more than five downhole positions. Nonetheless, the contact device may be placed such that the contact elements have a radial offset in the wellbore relative to the contact elements at the first downhole position, and further comprising applying stress in the rock formation at the second, third, fourth, or fifth downhole positions to thereby create a second, third, fourth, or fifth initial fissure. While maintaining the stress, the contact elements may also expand the subsequent initial fissure thereby creating a second, third, fourth, or fifth expanded fissure. Most typically, aforementioned steps (a) and (b) will be repeated at the second, third, fourth, or fifth downhole position.

[0045] Preferably, with more than one downhole position, the radial offset is at least 30 degrees, at least 45 degrees, or at least 90 degrees. Whereas the difference in distance between the first and second, or second and third, or third and fourth downhole positions is between 10 m and 100 m. The differences in distance may be the same between each downhole position, or they may be different. For example, the difference in distance between the first and second downhole position may be 50 m, while the difference in distance between the third and fourth downhole position may be 80 m. On the other hand, the difference in distance between the first and second downhole position and the difference in distance between the third and fourth downhole position may bother be 40 m.

[0046] As will be readily appreciated, the contact device may be placed in a vertical position within the wellbore, or it may be placed in a lateral or horizontal position within a fissure or wellbore depending on the construction of the wellbore and/or corresponding fissures. For example, in one embodiment, the contact device may be placed vertically within a wellbore to initiate a fissure, then subsequently placed horizontally within a fissure to further expand and/or propagate the fissure.

[0047] In further steps of contemplated methods, the pressure of the hydraulic fracturing fluid will be maintained at the target location to thereby maintain the expanded fissure in the rock, while the contact elements are further actuated into a position and to a degree at which the contact elements exert additional stress to the rock formation. As will be readily appreciated, the so applied stress will open the fissure mouth portion and/or assist in opening of the fissure mouth portion once further hydraulic fracturing is performed at the same location. The further hydraulic fracturing will once more expand the fissure. In this context, it should be appreciated that these further steps (applying additional stress using the contact elements and subsequent hydraulic fracturing) can be repeatedly performed to thereby generate a fissure in which the mouth portion at the wall of the wellbore is significantly wider than a proximal portion of the fissure, and in which the proximal portion of the fissure is wider than a distal portion of the fissure.

[0048] However, in alternative contemplated methods, the contact device may also be used to expand existing fissures in a wellbore. In certain embodiments, the contact device may be placed at a first downhole position at a target location proximal to the existing fissure, wherein the contact device has at least two movable contact elements. Subsequently, the contact elements are moved in the wellbore at the first depth at the target location in a direction against a wall of the wellbore to expand the existing fissure using the contact elements, thereby creating an expanded fissure. In this context, the existing fissure is most typically naturally occurring, initiated using hydraulic fracturing, initiated using mechanical fracturing, or initiated using the contact device. Indeed, the contact elements are generally used to apply a further stress force at the target location in the rock formation to thereby increase the width of the mouth portion. Application of this further stress force is contemplated to be repeatedly performed between 2- 6 times. However, it may also be performed less than 2 or more than 6 times.

[0049] Selected steps of such method are exemplarily depicted in FIG.1A-1F in which the top portion depicts a side view of an exemplary contact device, and in which the bottom portion depicts a horizontal cross section of the above depicted contact device in a wellbore. More specifically, in FIG.1A shows the contact device in a retracted position in which the contact elements are substantially flush with the remainder of the device. The device can be placed into the wellbore at a target location having a desired depth and the contact elements are then actuated to move into contact with the wall of the wellbore as is exemplarily shown in FIG.1B. Continued actuation of the contact elements will progressively produce stress in the rock formation as schematically indicated by the arrows in FIG.1C. As noted above, the actuation of the contact elements may be to a point below, at, or above fracture stress of the rock at the target location. Therefore, it should be appreciated that the actuation of the contact elements can results in a stressed location, micro-fissures, or an initial fissure (all of which are referred to herein as an “initial fissure”).

[0050] While maintaining the stress in the rock, hydraulic fracturing is then performed at the target location, for example, using a hydraulic fluid that can be delivered through the contact device. Once the hydraulic fluid pressure exceeds the fracture pressure of the rock, the initial fissure is expanded to so form an expanded fissure as schematically shown in FIG. ID. At this time, it should be appreciated that the stress in the rock exerted by the contact elements will be significantly reduced, or even entirely abolished due to the opening of the newly created fissure at the wall of the wellbore.

[0051] Upon formation of the expanded fissure, the contact elements can then be further advanced (typically, but not necessarily in the same direction as the previous advance) to engage with the walls of the wellbore and to apply further stress to the rock as is schematically shown in FIG. IE. Using this stress and additional hydraulic fluid pressure in the fracturing fluid will then further open the fissure as schematically shown in FIG. IF. As will be appreciated, the sequential steps of FIGS.1E-F can be repeated multiple times (e.g., between 1-3 times, or 2-6 times, or 4-8 times, or 5-10 times, and even more) to so increase the width of the fissure at the mouth portion and to also deepen the fissure, thereby creating a wedge-shaped fissure in which the mouth portion at the wall of the wellbore is wider than a proximal portion of the fissure, and in which the proximal portion of the fissure is wider than a distal portion of the fissure. Viewed from a different perspective, incremental repetitive application of stress force and subsequent hydraulic fracturing will produce a geometry of the fissure that would otherwise not be achieved in a conventional single-step fracking operation.

[0052] Consequently, and contrary to conventional fracking, the methods presented herein make use of repeated steps of stress induction and hydraulic fracturing in which the stress and hydraulic fracture pressure are incrementally increased to so form a wedge-shaped fissure in the rock. Advantageously, such fissure is then filled with a first thermally conductive material to produce a continuous pathway for thermal energy transfer from the rock into the first thermally conductive material, and from the first thermally conductive material at the mouth portion of the fissure to a second thermally conductive material. Such filling may be performed at the last pressure level by replacing the fracking fluid with a slurry comprising a thermally conductive material. Upon reducing the pressure, the geostatic pressure in the formation will then advantageously express the carrier fluid in the slurry, resulting in a compacted thermally conductive material in the fissure.

[0053] In this context, it should be appreciated that the specific geometry of the fissure will reduce or even entirely avoid a ‘backing up’ of heat flux otherwise encountered by a fissure having substantially uniform thickness as is common with fissures that have been produced in conventional manner. Viewed from a different perspective, thermally conductive materials in conventional fissures having substantially uniform thickness will not have the capacity to receive and transmit thermal energy received form the formation and so create a heat flux bottleneck. In contrast, the heat transfer capacity of thermally conductive materials in fissures having a wedge-shaped geometry increases from a distal portion to a proximal portion, and again from the proximal portion to the mouth of the fissure, thereby avoiding heat flux impedance and backing up of heat into the rock formation.

[0054] In addition, the relatively large width at the mouth of the fissure provides further significant advantages: First, a mouth portion with relatively large width will reduce or even entirely avoid potential issues associated with a draining proppant and inadvertent fissure closure. Second, a mouth portion with relatively large width generates a relatively large (and typically continuous) thermal heat transfer interface from the first thermally conductive materials in the fissure to a second thermally conductive materials in the wellbore (which typically surrounds the heat harvesting element located in the wellbore). Viewed from a different perspective, a mouth portion with relatively large width will allow for an improved thermal energy flux from the first thermally conductive materials in the fissure to the second thermally conductive material and ultimately the working fluid in the heat harvesting element. Consequently, it should be appreciated that the fissure geometries and methods for generating such fissures greatly reduce bottlenecks in heat transfer otherwise encountered with conventionally generated fissures that have substantially the same width along the length of the fissure.

[0055] With respect to the dimensions of fissures, it is generally contemplated that the mouth portion of the fissure has a width of between 1 mm and 100 mm, that the proximal portion of the fissure has a width of between 3 mm and 25 mm, and that the distal portion of the fissure has a width of between 0.5 mm and 2 mm. In most typical embodiments, the fissure has a length of between 1 m and 200 m as measured from the mouth portion to the distal end, and that the fissure has a vertical orientation with a height of between 1 m and 40 m. [0056] As used herein, the term “mouth portion” of a fissure refers to the portion of the fissure that terminates at the wellbore. Viewed from a different perspective, the mouth portion will typically include the opening and the first 1-20 cm, or 1-10 cm, or 1-5 cm of the fissure as measured from the opening in direction to the distal end of the fissure. The term “proximal portion” of a fissure refers to a portion of the fissure located between the mouth portion and a distal end of the fissure. Therefore, the proximal portion of the fissure will be around a middle third section as measured along the length of the fissure. As also used herein, the term “distal portion” of the fissure refers to the end portion of the fissure, and most typically the terminal third or terminal quarter of the fissure.

[0057] However, in further embodiments, the mouth portion of the fissure can have a width of between 2 mm and 4 mm, or between 4 mm and 6 mm, or between 6 mm and 8 mm, or between 2 mm and 10 mm, or between 6 mm and 10 mm, or between 8 mm and 10 mm, or between 10 mm and 14 mm, or between 12 mm and 18 mm, or between 16 mm and 22 mm, or between 12 mm and 24 mm, or between 15 mm and 25 mm, or between 20 mm and 30 mm, or between 25 mm and 35 mm, or between 30 mm and 40 mm, or between 35 mm and 45 mm, or between 40 mm and 50 mm, or between 40 mm and 75 mm, or between 60 mm and 90 mm, or between 75 mm and 150 mm, and even wider. Similarly, the proximal portion of the fissure can have a width of between 1 mm and 2 mm, or between 2 mm and 3 mm, or between 3 mm and 5 mm, or between 1 mm and 6 mm, or between 6 mm and 8 mm, or between 7 mm and 9 mm, or between 10 mm and 12 mm, or between 12 mm and 14 mm, or between 12 mm and 16 mm, or between 13 mm and 17 mm, or between 15 mm and 20 mm, or between 20 mm and 30 mm, or between 25 mm and 35 mm, or between 30 mm and 40 mm, or between 35 mm and 60 mm, or between 50 mm and 75 mm, and even wider. Likewise, the distal portion of the fissure can have a width of between 0 mm and 0.2 mm, or between 0.2 mm and 0.5 mm, or between 0.3 mm and 0.6 mm, or between 0.6 mm and 0.8 mm, or between 0.5 mm and 1 mm, or between 0.7 mm and 1.2 mm, or between 1.2 mm and 1.5 mm, or between 1.2 mm and 1.6 mm, or between 1.5 mm and 1.7 mm, or between 1.5 mm and 1.9 mm, or between 1.5 mm and 2.0 mm, or between 2.0 mm and 2.5 mm, and even wider. Regardless of the specific dimensions in the various portions of the fissure, it is generally contemplated that the width of the mouth portion will be larger than the width at a proximal portion, and that the width at the proximal portion is larger than the width at a distal portion. Viewed from a different perspective, contemplated fissures will have an increasing capacity to transfer thermal energy along the length of the fissure (as seen from the distal portion to the mouth portion). Thus, in most embodiment the fissure will have a generally wedge-shaped geometry.

[0058] As already discussed above, it is generally contemplated that the fissure will be filled with a first thermally conductive material, which may be installed into the fissure in form of a (typically compactable) slurry, cementitious or otherwise flowable composition that may harden or otherwise cure over time. Most preferably, the first thermally conductive material will have (upon curing, compaction, or otherwise settling) a thermal conductivity that is greater than 1 W/mK, or greater than 5 W/mK, or greater than 10 W/mK, or greater than 25 W/mK, or greater than 50 W/mK, or greater than 75 W/mK, or greater than 100 W/mK, or greater than 150 W/mK, or greater than 250 W/mK, but less than 600 W/mK, or less than 400 W/mK, or less than 300 W/mK, or less than 200 W/mK. For example, the first thermally conductive material can have a thermal conductivity of 10-50 W/mK, or of about 30-90 W/mK, or of about 50-150 W/mK, or of about 100-300 W/mK, or of about 300-600 W/mK, and in some cases even higher. For example, the first thermally conductive material can include various carbon allotropes, metal particles or metal fibers (e.g., graphite powder, exfoliated graphite, flaked graphite, pyrolytic graphite, desulfurized petroleum coke, graphene, fly ash, copper powder, boron nitride, aluminum nitride, and silicon carbide), which may or may not be surface modified to increase hydrophilicity and homogenous distribution in an aqueous or cementitious phase. Additionally contemplated thermally conductive materials include zinc, graphene, tungsten, aluminum, silicon nitride, gold, copper, silver, diamond, aluminum alloys, aluminum oxides, rhodium, cobalt, copper allows, nickel, iron, platinum, palladium, tin, steel, zirconium, titanium, carbon fiber, carbon black, and Hastelloy.

[0059] With respect to the second thermally conductive material it is contemplated that the second thermally conductive material will be disposed in the wellbore and typically surrounds the heat harvesting element (most typically a closed loop system in a casing) to assist in thermal energy transfer into the working fluid. Moreover, it is contemplated that the second thermally conductive material will be thermally coupled to the first thermally conductive material by direct contact with the first thermally conductive material at the mouth portion to thereby form a continuous heat transfer interface. Most preferably, thermal transfer at the interface is ensured by compaction or other manner of compression of the second thermally conductive material against the first thermally conductive material. Moreover, it is generally preferred that the thermal conductivity of the first thermally conductive material is similar or identical to that of the second thermally conductive material. For example, it is contemplated that the thermal conductivity of the first thermally conductive material will deviate by no more than 25%, or no more than 20%, or no more than 15%, or no more than 10%, or no more than 8%, or no more than 5% from the thermal conductivity of the second thermally conductive material. Therefore, it is also contemplated that the first and second thermally conductive materials may be the same.

[0060] In some embodiments, the thermally conductive materials may be combined with void space or an “inactive” material (e.g., sand). Where an “inactive” material is one that exceeds an aggregate thermal conductivity of at least 5 W/mK once placed, to thereby create a thermal energy transfer pathway or conduit between the rock formation and casing.

[0061] Moreover, the thermally conductive material may be comprised of various shapes. For example, suitable shapes include a platelet, a flake, a sphere, an irregular shape, a cube, a rod, a disc, a prism, a needle, a tube, a fiber, an angular shape, a subangular shape, a rounded shape, a subrounded shape, a dumbbell shape, and a star shape.

[0062] Contemplated contact devices will typically have two contact elements that will be movable in opposite direction to so create stress in a formation at a controllable position (which is typically located between the contact elements). However, in further embodiments, more than two contact elements can also be used to thereby produce more than two areas of stress in the formation. As will be readily appreciated, the contact elements will generally be longitudinally oriented (e.g., parallel to the direction of the wellbore) to so generate a stress pattern that will result in fissures that extend along the longitudinal axis of the wellbore. Therefore, preferred contact elements will typically have a length of at least 20 cm, or at least 50 cm, or at least 100 cm, or at least 150 cm, or at least 200 cm, such as for example, between 20 and 40 cm, or between 25-75 cm, or between 50 and 100 cm, or between 150 and 200 cm, and even longer. As will be further readily appreciated, multiple sequentially arranged contact elements may result in a contact device that can create longitudinal fissures over significant lengths, such as at between 1 m and 5 m, or between 3 m and 10m, or between 5 m and 25 m, and even more.

[0063] As will be readily appreciated, the manner of actuation of the contact elements may vary considerably so long as the contact elements can exert a stress on the rock formation that is at about or above fracture stress in the rock. Therefore, mechanical and hydraulic actuation are particularly preferred. Among other pressures, it is contemplated that the contact elements can produce a stress of at least 5 MPa, or at least 10 MPa, or at least 20 MPa, or at least 30 MPa, or at least 40 MPa, or at least 50 MPa, such as for example, between 5-25 MPa, or between 15-40 MPa, or between 30-60 MPa, and even higher. So applied stress forces will be incremental and the additional stress forces may be incrementally increased (between successive rounds of operation as shown in FIGS.1E-F) by about 1.1-fold, or about 1.2-fold, or about 1.3-fold, or about 1.4-fold, or about 1.5-fold, or about 1.6-fold, or about 1.8-fold of the prior stress force, or even higher.

[0064] In still further embodiments, the contact elements will be configured to at least partially conform to the wall of the wellbore to so maximize application of the stress over an extended area on wall of the wellbore. Therefore, curved plate shaped contact elements are especially contemplated. However, other configurations such as pistons and bars are also deemed suitable for use herein. As will be readily appreciated, contemplated contact devices can further comprise various data logging tools, including one or more stress sensors, pressure sensors, temperature sensors, sonic imaging sensors, flow sensors, etc.

[0065] Additionally, it is contemplated that the contact device will be configured to allow delivery of a hydraulic fracturing fluid to the target location at which the contact device is deployed while the contact elements are in an extended position. As will be appreciated, the contact elements during such operation will maintain the mouth portion in an open state and prevent inadvertent closure while hydraulic fracturing will expand the fissure. Upon termination of the hydraulic fracturing, the contact elements will be advanced further against the wall of the wellbore to apply further stress in preparation for a subsequent hydraulic fracturing step. Therefore, exemplary contemplated contact devices suitable for use herein include those described in US 9664024, US 8875790, US 2015/0322760, and US 2776014, each incorporated by reference in their entirety herein.

Aspects

[0066] The present disclosure will be better understood upon reading the following numbered aspects, which should not be confused with the claims. In some instances, each of the aspects described below can be combined with other aspects, including combined with other aspects described elsewhere in the disclosure or other aspects from the examples below, without departing from the spirit of the disclosure. [0067] 1. A method of forming a fissure with controlled geometry in wellbore located within a rock formation, comprising: placing a contact device in the wellbore at a target location, wherein the contact device has at least two movable contact elements; using the contact elements at the target location to apply a stress force in the rock formation, thereby creating an initial fissure, and while maintaining the first stress force, expanding the initial fissure using hydraulic fracturing, thereby creating an expanded fissure, wherein the expanded fissure has a mouth portion at a wall of the wellbore; repeatedly performing steps (a) and (b) in sequence, wherein (a) is using the contact elements to apply a further stress force at the target location in the rock formation to thereby increase the width of the mouth portion; and (b) is further applying hydraulic pressure at the target location to further expand the fissure; to thereby generate a fissure in which the mouth portion at the wall of the wellbore is wider than a proximal portion of the fissure, and in which the proximal portion of the fissure is wider than a distal portion of the fissure.

[0068] 2. The method of aspect 1, wherein the at least two movable contact elements of the contact device are configured to conform to the wall of the wellbore.

[0069] 3. The method of any one of the preceding aspects, wherein the at least two movable contact elements of the contact device are on opposite sides of the contact device.

[0070] 4. The method of any one of the preceding aspects, wherein at least two movable contact elements are moved using hydraulic force.

[0071] 5. The method of any one of the preceding aspects, wherein the rock formation is a dry hot rock formation.

[0072] 6. The method of aspect 5, wherein the rock formation is an intrusive igneous or metamorphous rock formation.

[0073] 7. The method of any one of the preceding aspects, wherein the target location is at a depth of between 150 m and 20,000 m.

[0074] 8. The method of any one of the preceding aspects, wherein the rock formation at the target location has a temperature of between about 120 °C to 600 °C.

[0075] 9. The method of any one of the preceding aspects, wherein the stress is applied at a force of between about 10 and 100 MPa. (e.g., 10-50 MPa) [0076] 10. The method of any one of the preceding aspects, wherein the further stress is between about 1.1-fold and 1.5-fold of the stress, (e.g., 1.1-1.3-fold)

[0077] 11. The method of any one of the preceding aspects, wherein steps (a) and (b) are repeatedly performed in sequence between 2-6 times.

[0078] 12. The method of any one of the preceding aspects, wherein the mouth portion at the wall of the wellbore has a width of between 1 mm and 100 mm.

[0079] 13. The method of any one of the preceding aspects, wherein the proximal portion of the fissure has a width of between 3 mm and 25 mm.

[0080] 14. The method of any one of the preceding aspects, wherein the distal portion of the fissure has a width of between 0.5 mm and 2 mm.

[0081] 15. The method of any one of the preceding aspects, wherein the fissure has a length of between 1 m and 200 m as measured from the mouth portion to the distal end.

[0082] 16. The method of any one of the preceding aspects, wherein the fissure has a vertical orientation and a height of between 1 m and 40 m.

[0083] 17. A wellbore with a fissure within a rock formation wherein the fissure has a controlled geometry, formed by the method of any one of the preceding aspects, wherein the controlled geometry is such that a mouth portion of the fissure at a wall of the wellbore is wider than a proximal portion of the fissure, and wherein the proximal portion of the fissure is wider than a distal portion of the fissure.

[0084] 18. The wellbore of aspect 17, wherein the fissure is filled with a first thermally conductive material.

[0085] 19. The wellbore of any one of aspects 17-18, wherein the first thermally conductive material has a k-value of at least 5 W/mK.

[0086] 20. The wellbore of any one of aspects 17-19, wherein the first thermally conductive material is thermally coupled to a second thermally conductive material surrounding a heat harvesting element, and wherein thermal conductivity constants of the first and second thermally conductive materials differ by no more than 10% as measured by their respective k- values or wherein the first and second thermally conductive materials are the same. [0087] 21. A method of facilitating thermal energy transfer in a geothermal well having a wellbore with a thermal reach enhancement structure at a target location within a rock formation, comprising: forming the thermal reach enhancement structure to include a fissure in which a mouth portion of the fissure at a wall of the wellbore is wider than a proximal portion of the fissure, and in which the proximal portion of the fissure is wider than a distal portion of the fissure; filling the fissure with a first thermally conductive material; thermally coupling a heat harvesting element located in the wellbore with the first thermally conductive material in the fissure using a second thermally conductive material; and wherein thermal conductivity constants of the first and second thermally conductive material differ by no more than 10% as measured by their respective k-values.

[0088] 22. The method of aspect 21, wherein the fissure in the thermal reach enhancement structure is formed using a method according to any one of the preceding aspects.

[0089] 23. The method of any one of aspects 21-22, wherein the fissure in the thermal reach enhancement structure is naturally occurring, formed using hydraulic fracking, formed using a contact device, or formed using mechanical fracking.

[0090] 24. The method of any one of aspects 21-23, wherein the fissure in the thermal reach enhancement structure is widened and/or propagated using a directionally controlled contact device.

[0091] 25. The method of any one of aspects 21-24, wherein the fissure in the thermal reach enhancement structure has a longitudinal orientation.

[0092] 26. The method of any one of aspects 21-25, wherein the thermal reach enhancement structure is configured as a bilateral or bi-wing vertical structure.

[0093] 27. The method of any one of aspects 21-26, wherein the mouth portion at the wall of the wellbore has a width of between 1 mm and 100 mm, the proximal portion of the fissure has a width of between 3 mm and 25 mm, the distal portion of the fissure has a width of between 0.5 mm and 2 mm, and/or wherein the fissure has a length of between 1 and 200 m as measured from the mouth portion to the distal end.

[0094] 28. The method of any one of aspects 21-27, wherein the first thermally conductive material has a thermal conductivity of between 5 W/mK and 400 W/mK. [0095] 29. The method of any one of aspects 21-28, wherein the first and/or second thermally conductive materials are materials other than cementitious materials.

[0096] 30. The method of any one of aspects 21-29, wherein the heat harvesting element comprises a closed loop circuit in which heat is transferred from the second thermally conductive material to a casing of the heat harvesting element.

[0097] 31. The method of aspect 30, wherein the second thermally conductive material is configured as a sheath surrounding the casing of the heat harvesting element.

[0098] 32. The method of any one of aspects 21-31, wherein the step of filling the fissure with the first thermally conductive material includes a step of compressing the first thermally conductive material using geostatic pressure and/or using mechanical compression.

[0099] 33. The method of aspect 32, wherein the mechanical compression is generated during placement of the heat harvesting element into the wellbore.

[00100] 34. A system configured to initiate a fissure within a wellbore in a rock formation in a desired direction, comprising: a contact device that has at least two movable elements; wherein the contact elements are configured to allow application of mechanical stress in the rock formation at a target location to thereby create an initial fissure in the well bore in a direction that is substantially perpendicular to a direction in which the contact elements move; and a controller that is configured to maintain a pressure of a hydraulic fluid within the initial fissure while the contact device is expanding and/or propagating the fissure.

[00101] 35. The system of aspect 34, wherein the initial fissure is a dual fissure that extends longitudinally from the wellbore in opposite directions.

[00102] 36. The system of aspect 34, wherein the contact device is configured to allow successive movement in the same direction to thereby promote fissure widening, and/or fissure propagation.

[00103] 37. The system of aspect 34, wherein the contact device is directionally controllable to allow rotation relative to a direction of the initial fissure and application of further mechanical stress in a different direction. [00104] 38. The system of aspect 34, wherein the wellbore is a greenfield new well, a brownfield geothermal well, or a brownfield oil and gas well.

[00105] 39. The system of aspect 34, wherein a mouth portion at a wall of the wellbore has a width of between 1 mm and 100 mm, a proximal portion of the fissure has a width of between 3 mm and 25 mm, a distal portion of the fissure has a width of between 0.5 mm and 2 mm, and/or wherein the fissure has a length of between 1 m and 200 m as measured from the mouth portion to the distal end.

[00106] 40. The system of aspect 34, wherein the fissure has a controlled geometry such that a mouth portion of the fissure at a wall of the wellbore is wider than a proximal portion of the fissure, and wherein the proximal portion of the fissure is wider than a distal portion of the fissure.

[00107] 41. The system of aspect 34, wherein the controller is further configured to control movement of the contact elements.

[00108] 42. The system of aspect 34, wherein the controller maintains pressure within the fissure hydraulically or mechanically.

[00109] 43. The system of aspect 34, wherein the fissure within the rock formation does not follow a_naturally occurring feature in the rock formation.

[00110] 44. A method of directionally fracturing rock in a wellbore, comprising: placing at a first downhole position a contact device in the wellbore at a target location, wherein the contact device has at least two movable contact elements; moving the contact elements in the wellbore at the first downhole position at the target location in a direction against a wall of the wellbore to apply a stress in the rock formation, thereby creating an initial fissure, and while maintaining the stress, expanding the initial fissure using the contact elements, thereby creating an expanded fissure; repeatedly performing steps (a) and (b) in sequence (a) using the contact elements to apply a further stress force at the target location in the rock formation to thereby increase the width of the mouth portion; and (b) using the contact elements at the target location to further expand the fissure.

[00111] 45. The method of aspect 44, further comprising a step of placing the contact device at a second downhole position that is different from the first downhole position, wherein the contact device is placed such that the contact elements have a radial offset in the wellbore relative to the contact elements at the first depth, and further comprising applying stress in the rock formation at the second downhole position, thereby creating a second initial fissure, and while maintaining the stress, expanding the second initial fissure using the contact elements, thereby creating a second expanded fissure.

[00112] 46. The method of aspect 45, further comprising the steps (a) and (b) at the second downhole position.

[00113] 47. The method of aspect 45, wherein the radial offset is at least 30 degrees.

[00114] 48. The method of aspect 45, wherein the difference in distance between the first and second downhole positions is between 10 m and 100 m.

[00115] 49. The method of aspect 45, wherein the expanded fissure has a mouth portion at the wall of the wellbore that is wider than a proximal portion of the expanded fissure, and in which the proximal portion of the expanded fissure is wider than a distal portion of the expanded fissure.

[00116] 50. The method of aspect 44, wherein the rock formation is a dry hot rock formation.

[00117] 51. The method of aspect 50, wherein the hot rock formation is an intrusive igneous, granitic, basaltic, sedimentary, or metamorphous rock formation.

[00118] 52. The method of aspect 44, wherein the target location is at a depth of between

150 m and 20,000 m.

[00119] 53. The method of aspect 44, wherein the rock formation at the target location has a temperature of between about 120 °C to 600 °C.

[00120] 54. The method of aspect 44, wherein the stress is applied at a force of between about 10 and 100 MPa.

[00121] 55. The method of aspect 44, wherein the further stress is between about 1.1-fold and 1.5-fold of the stress. [00122] 56. The method of aspect 44, wherein steps (a) and (b) are repeatedly performed in sequence between 2-6 times.

[00123] 57. The method of aspect 49, wherein the mouth portion at the wall of the wellbore has a width of between 1 mm and 100 mm.

[00124] 58. The method of aspect 49, wherein the proximal portion of the expanded fissure has a width of between 3 mm and 25 mm.

[00125] 59. The method of aspect 49, wherein the distal portion of the expanded fissure has a width of between 0.5 mm and 2 mm.

[00126] 60. The method of aspect 49, wherein the expanded fissure has a length of between

1 m and 200 m as measured from the mouth portion to the distal end.

[00127] 61. The method of aspect 49, wherein the expanded fissure has a vertical orientation and a height of between 1 m and 40 m.

[00128] 62. The method of aspect 44, further comprising a step of filling the expanded fissure with a first thermally conductive material.

[00129] 63. The method of aspect 62, wherein the first thermally conductive material has a k-value of at least 5 W/mK.

[00130] 64. The method of aspect 62, wherein the first thermally conductive material is thermally coupled to a second thermally conductive material surrounding a heat harvesting element, and wherein thermal conductivity constants of the first and second thermally conductive materials differ by no more than 10% as measured by their respective k-values or wherein the first and second thermally conductive materials are the same.

[00131] 65. The method of aspect 62, wherein the first thermally conductive material comprises a material selected from the group consisting of zinc, graphite, graphene, tungsten, aluminum, silicon carbide, aluminum nitride, silicon nitride, boron nitride, gold, copper, silver, diamond, aluminum alloys, aluminum oxides, rhodium, cobalt, copper alloys, nickel, iron, platinum, palladium, tin, steel, zirconium, titanium, carbon fiber, carbon black, Hastelloy, carbon-based inorganic, metal, metal oxides, metal nitrides, alloys, or hybrids. [00132] 66. The method of aspect 44, further comprising a step of filling the expanded fissure with a second thermally conductive material.

[00133] 67. The method of aspect 66, wherein the first thermally conductive material has a k-value of at least 5 W/mK.

[00134] 68. The method of aspect 66, wherein the second thermally conductive material comprises a material selected from the group consisting of zinc, graphite, graphene, tungsten, aluminum, silicon carbide, aluminum nitride, silicon nitride, boron nitride, gold, copper, silver, diamond, aluminum alloys, aluminum oxides, rhodium, cobalt, copper alloys, nickel, iron, platinum, palladium, tin, steel, zirconium, titanium, carbon fiber, carbon black, Hastelloy, carbon-based inorganic, metal, metal oxides, metal nitrides, alloys, or hybrids.

[00135] 69. A method of expanding an existing fissure in a wellbore, comprising: placing at a first downhole position a contact device in the wellbore at a target location proximal to the existing fissure, wherein the contact device has at least two movable contact elements; and moving the contact elements in the wellbore at the first downhole position at the target location in a direction against a wall of the wellbore to expand the existing fissure using the contact elements, thereby creating an expanded fissure.

[00136] 70. The method of aspect 69, wherein the existing fissure is naturally occurring, initiated using hydraulic fracturing, initiated using mechanical fracturing, or initiated using the contact device.

[00137] 71. The method of aspect 69, wherein the contact elements are used to apply a further stress force at the target location in the rock formation to thereby increase the width of the mouth portion.

[00138] 72. The method of aspect 71, wherein applying a further stress force at the target location is repeatedly performed between 2-6 times.

[00139] 73. The method of aspect 69, wherein the rock formation is a dry hot rock formation.

[00140] 74. The method of aspect 69, wherein the hot rock formation is an intrusive igneous, granitic, basaltic, sedimentary, or metamorphous rock formation. [00141] 75. The method of aspect 69, wherein the target location is at a depth of between

150 m and 20,000 m.

[00142] 76. The method of aspect 69, wherein the rock formation at the target location has a temperature of between about 120 °C to 600 °C.

[00143] 77. The method of aspect 69, wherein a proximal portion of the expanded fissure has a width of between 3 mm and 25 mm.

[00144] 78. The method of aspect 69, wherein a distal portion of the expanded fissure has a width of between 0.5 mm and 2 mm.

[00145] 79. The method of aspect 69, wherein the expanded fissure has a length of between

1 m and 200 m as measured from the mouth portion to the distal end.

[00146] 80. The method of aspect 69, wherein the expanded fissure has a vertical orientation and a height of between 1 m and 40 m.

[00147] 81. The method of aspect 69, further comprising a step of at least partially filling the expanded fissure with a first thermally conductive material.

[00148] 82. The method of aspect 81, wherein the first thermally conductive material has a k-value of at least 5 W/mK.

[00149] 83. The method of aspect 81, wherein the first thermally conductive material is thermally coupled to a second thermally conductive material surrounding a heat harvesting element, and wherein thermal conductivity constants of the first and second thermally conductive materials differ by no more than 10% as measured by their respective k-values or wherein the first and second thermally conductive materials are the same.

[00150] 84. The method of aspect 81, wherein the first thermally conductive material comprises a material selected from the group consisting of zinc, graphite, graphene, tungsten, aluminum, silicon carbide, aluminum nitride, silicon nitride, boron nitride, gold, copper, silver, diamond, aluminum alloys, aluminum oxides, rhodium, cobalt, copper alloys, nickel, iron, platinum, palladium, tin, steel, zirconium, titanium, carbon fiber, carbon black, Hastelloy, carbon-based inorganic, metal, metal oxides, metal nitrides, alloys, or hybrids. [00151] 85. The method of aspect 69, further comprising a step of filling the expanded fissure with a second thermally conductive material.

[00152] 86. The method of aspect 85, wherein the first thermally conductive material has a k-value of at least 5 W/mK.

[00153] 87. The method of aspect 85, wherein the second thermally conductive material comprises a material selected from the group consisting of zinc, graphite, graphene, tungsten, aluminum, silicon carbide, aluminum nitride, silicon nitride, boron nitride, gold, copper, silver, diamond, aluminum alloys, aluminum oxides, rhodium, cobalt, copper alloys, nickel, iron, platinum, palladium, tin, steel, zirconium, titanium, carbon fiber, carbon black, Hastelloy, carbon-based inorganic, metal, metal oxides, metal nitrides, alloys, or hybrids.

[00154] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” As used herein, the terms "about" and "approximately", when referring to a specified, measurable value (such as a parameter, an amount, a temporal duration, and the like), is meant to encompass the specified value and variations of and from the specified value, such as variations of +/-10% or less, alternatively +/-5% or less, alternatively +/-1% or less, alternatively +/-0.1% or less of and from the specified value, insofar as such variations are appropriate to perform in the disclosed embodiments. Thus, the value to which the modifier "about" or "approximately" refers is itself also specifically disclosed. The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.

[00155] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided with respect to certain aspects herein is intended merely to better illuminate the disclosure and does not pose a limitation on the scope of the claims. No language in the specification should be construed as indicating any non-claimed element is essential.

[00156] All publications, patents, and patent applications mentioned or cited herein are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications, patents, or patent applications are cited. All such publications, patents, and patent applications are herein incorporated by references as if each individual publication, patent, or patent application were specifically and individually indicated to be incorporated by reference. Such incorporation by reference is expressly limited to the methods and/or materials described in the cited publications, patents, and patent applications and does not extend to any lexicographical definitions from the cited publications, patents, and patent applications. Any lexicographical definition in the publications, patents, and patent applications cited, including any lexicographical definition in any patent or patent application in the priority claim, that is not also expressly repeated in the instant specification should not be treated as such and should not be read as defining any terms appearing in the accompanying claims. The publications, patents, and patent applications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present disclosure is not entitled to antedate such publication by virtue of prior disclosure. Further, the dates of publication provided herein can be different from the actual publication dates, which can require independent confirmation.

[00157] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. As also used herein, and unless the context dictates otherwise, the term "coupled to" is intended to include both direct coupling (in which two elements that are coupled to each other contact each other), and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms "coupled to" and "coupled with" are used synonymously.

[00158] It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the disclosure. The disclosure, therefore, is not to be restricted except in the scope of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps can be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification or claims refer to at least one of something selected from the group consisting of A, B, C . . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.

Claims

CLAIMS What is claimed is:

1. A method of forming a fissure with controlled geometry in a wellbore located within a rock formation, comprising: placing a contact device in the wellbore at a target location, wherein the contact device has at least two movable contact elements; using the contact elements at the target location to apply a stress in the rock formation, thereby creating an initial fissure, and while maintaining the stress, expanding the initial fissure using hydraulic fracturing, thereby creating an expanded fissure, wherein the expanded fissure has a mouth portion at a wall of the wellbore; repeatedly performing steps (a) and (b) in sequence

(a) using the contact elements to apply a further stress force at the target location in the rock formation to thereby increase the width of the mouth portion; and

(b) further applying hydraulic pressure at the target location to further expand the fissure; to thereby generate a fissure in which the mouth portion at the wall of the wellbore is wider than a proximal portion of the fissure, and in which the proximal portion of the fissure is wider than a distal portion of the fissure.

2. The method of claim 1, wherein the at least two movable contact elements of the contact device are configured to conform to the wall of the wellbore.

3. The method of claim 1, wherein the at least two movable contact elements of the contact device are on opposite sides of the contact device.

4. The method of claim 1, wherein the at least two movable contact elements are moved using hydraulic force.

5. The method of claim 1, wherein the rock formation is a dry hot rock formation.

6. The method of claim 5, wherein the hot rock formation is an intrusive igneous, granitic, basaltic, sedimentary, or metamorphous rock formation.

7. The method of claim 1, wherein the target location is at a depth of between 150 m and 20,000 m.

8. The method of claim 1, wherein the rock formation at the target location has a temperature of between about 120 °C to 600 °C.

9. The method of claim 1, wherein the stress is applied at a force of between about 10 and 100 MPa.

10. The method of claim 1, wherein the further stress is between about 1.1-fold and 1.5-fold of the stress.

11. The method of claim 1, wherein steps (a) and (b) are repeatedly performed in sequence between 2-6 times.

12. The method of claim 1, wherein the mouth portion at the wall of the wellbore has a width of between 1 mm and 100 mm.

13. The method of claim 1, wherein the proximal portion of the fissure has a width of between 3 mm and 25 mm.

14. The method of claim 1, wherein the distal portion of the fissure has a width of between 0.5 mm and 2 mm.

15. The method of claim 1, wherein the fissure has a length of between 1 m and 200 m as measured from the mouth portion to the distal end.

16. The method of claim 1, wherein the fissure has a vertical orientation and a height of between 1 m and 40 m.

17. A wellbore with a fissure within a rock formation wherein the fissure has a controlled geometry, formed by the method of claim 1, wherein the controlled geometry is such that a mouth portion of the fissure at a wall of the wellbore is wider than a proximal portion of the fissure, and wherein the proximal portion of the fissure is wider than a distal portion of the fissure.

18. The wellbore of claim 17, wherein the fissure is filled with a first thermally conductive material.

19. The wellbore of claim 18, wherein the first thermally conductive material has a k-value of at least 5 W/mK.

20. The wellbore of claim 18, wherein the first thermally conductive material is thermally coupled to a second thermally conductive material surrounding a heat harvesting element, and wherein thermal conductivity constants of the first and second thermally conductive materials differ by no more than 10% as measured by their respective k-values or wherein the first and second thermally conductive materials are the same.

21. A method of facilitating thermal energy transfer in a geothermal well having a wellbore with a thermal reach enhancement structure at a target location within a rock formation, comprising: forming the thermal reach enhancement structure to include a fissure in which a mouth portion of the fissure at a wall of the wellbore is wider than a proximal portion of the fissure, and in which the proximal portion of the fissure is wider than a distal portion of the fissure; filling the fissure with a first thermally conductive material; thermally coupling a heat harvesting element located in the wellbore with the first thermally conductive material in the fissure using a second thermally conductive material; and wherein thermal conductivity constants of the first and second thermally conductive material differ by no more than 10% as measured by their respective k-values.

22. The method of claim 21, wherein the fissure in the thermal reach enhancement structure is formed using a method according to claim 1.

23. The method of claim 21, wherein the fissure in the thermal reach enhancement structure is naturally occurring, formed using hydraulic fracking, formed using a contact device, or formed using mechanical fracking.

24. The method of claim 21, wherein the fissure in the thermal reach enhancement structure is widened and/or propagated using a directionally controlled contact device.

25. The method of claim 21, wherein the fissure in the thermal reach enhancement structure has a longitudinal orientation.

26. The method of claim 21, wherein the thermal reach enhancement structure is configured as a bilateral or bi-wing vertical structure.

27. The method of claim 21, wherein the mouth portion at the wall of the wellbore has a width of between 1 mm and 100 mm, the proximal portion of the fissure has a width of between 3 mm and 25 mm, the distal portion of the fissure has a width of between 0.5 mm and 2 mm, and/or wherein the fissure has a length of between 1 m and 200 m as measured from the mouth portion to the distal end.

28. The method of claim 21, wherein the first thermally conductive material has a thermal conductivity of between 5 W/mK and 400 W/mK.

29. The method of claim 21, wherein the first and/or second thermally conductive materials are materials other than cementitious materials.

30. The method of claim 21, wherein the heat harvesting element comprises a closed loop circuit in which heat is transferred from the second thermally conductive material to a casing of the heat harvesting element.

31. The method of claim 30, wherein the second thermally conductive material is configured as a sheath surrounding the casing of the heat harvesting element.

32. The method of claim 21, wherein the step of filling the fissure with the first thermally conductive material includes a step of compressing the first thermally conductive material using geostatic pressure and/or using mechanical compression.

33. The method of claim 32, wherein the mechanical compression is generated during placement of the heat harvesting element into the wellbore.

34. A system configured to initiate a fissure within a wellbore in a rock formation in a desired direction, comprising: a contact device that has at least two movable elements; wherein the contact elements are configured to allow application of mechanical stress in the rock formation at a target location to thereby create an initial fissure in the well bore in a direction that is substantially perpendicular to a direction in which the contact elements move; and a controller that is configured to maintain a pressure of a hydraulic fluid within the initial fissure while the contact device is expanding and/or propagating the fissure.

35. The system of claim 34, wherein the initial fissure is a dual fissure that extends longitudinally from the wellbore in opposite directions.

36. The system of claim 34, wherein the contact device is configured to allow successive movement in the same direction to thereby promote fissure widening, and/or fissure propagation.

37. The system of claim 34, wherein the contact device is directionally controllable to allow rotation relative to a direction of the initial fissure and application of further mechanical stress in a different direction.

38. The system of claim 34, wherein the wellbore is a greenfield new well, a brownfield geothermal well, or a brownfield oil and gas well.

39. The system of claim 34, wherein a mouth portion at a wall of the wellbore has a width of between 1 mm and 100 mm, a proximal portion of the fissure has a width of between 3 mm and 25 mm, a distal portion of the fissure has a width of between 0.5 mm and 2 mm, and/or wherein the fissure has a length of between 1 m and 200 m as measured from the mouth portion to the distal end.

40. The system of claim 34, wherein the fissure has a controlled geometry such that a mouth portion of the fissure at a wall of the wellbore is wider than a proximal portion of the fissure, and wherein the proximal portion of the fissure is wider than a distal portion of the fissure.

41. The system of claim 34, wherein the controller is further configured to control movement of the contact elements.

42. The system of claim 34, wherein the controller maintains pressure within the fissure hydraulically or mechanically.

43. The system of claim 34, wherein the fissure within the rock formation does not follow a naturally occurring feature in the rock formation.

44. A method of directionally fracturing rock in a wellbore, comprising: placing at a first downhole position a contact device in the wellbore at a target location, wherein the contact device has at least two movable contact elements; moving the contact elements in the wellbore at the first downhole position at the target location in a direction against a wall of the wellbore to apply a stress in the rock formation, thereby creating an initial fissure, and while maintaining the stress, expanding the initial fissure using the contact elements, thereby creating an expanded fissure; repeatedly performing steps (a) and (b) in sequence

(b) using the contact elements at the target location to further expand the fissure.

45. The method of claim 44, further comprising a step of placing the contact device at a second downhole position that is different from the first downhole position, wherein the contact device is placed such that the contact elements have a radial offset in the wellbore relative to the contact elements at the first downhole position, and further comprising applying stress in the rock formation at the second position, thereby creating a second initial fissure, and while maintaining the stress, expanding the second initial fissure using the contact elements, thereby creating a second expanded fissure.

46. The method of claim 45, further comprising the steps (a) and (b) at the second downhole position.

47. The method of claim 45, wherein the radial offset is at least 30 degrees.

48. The method of claim 45, wherein the difference in distance between the first and second downhole positions is between 10 m and 100 m.

49. The method of claim 45, wherein the expanded fissure has a mouth portion at the wall of the wellbore that is wider than a proximal portion of the expanded fissure, and in which the proximal portion of the expanded fissure is wider than a distal portion of the expanded fissure.

50. The method of claim 44, wherein the rock formation is a dry hot rock formation.

51. The method of claim 50, wherein the hot rock formation is an intrusive igneous, granitic, basaltic, sedimentary, or metamorphous rock formation.

52. The method of claim 44, wherein the target location is at a depth of between 150 m and 20,000 m.

53. The method of claim 44, wherein the rock formation at the target location has a temperature of between about 120 °C to 600 °C.

54. The method of claim 44, wherein the stress is applied at a force of between about 10 and 100 MPa.

55. The method of claim 44, wherein the further stress is between about 1.1-fold and 1.5-fold of the stress.

56. The method of claim 44, wherein steps (a) and (b) are repeatedly performed in sequence between 2-6 times.

57. The method of claim 49, wherein the mouth portion at the wall of the wellbore has a width of between 1 mm and 100 mm.

58. The method of claim 49, wherein the proximal portion of the expanded fissure has a width of between 3 mm and 25 mm.

59. The method of claim 49, wherein the distal portion of the expanded fissure has a width of between 0.5 mm and 2 mm.

60. The method of claim 49, wherein the expanded fissure has a length of between 1 m and 200 m as measured from the mouth portion to the distal end.

61. The method of claim 49, wherein the expanded fissure has a vertical orientation and a height of between 1 m and 40 m.

62. The method of claim 44, further comprising a step of filling the expanded fissure with a first thermally conductive material.

63. The method of claim 62, wherein the first thermally conductive material has a k-value of at least 5 W/mK.

64. The method of claim 62, wherein the first thermally conductive material is thermally coupled to a second thermally conductive material surrounding a heat harvesting element, and wherein thermal conductivity constants of the first and second thermally conductive materials differ by no more than 10% as measured by their respective k-values or wherein the first and second thermally conductive materials are the same.

65. The method of claim 62, wherein the first thermally conductive material comprises a material selected from the group consisting of zinc, graphite, graphene, tungsten, aluminum, silicon carbide, aluminum nitride, silicon nitride, boron nitride, gold, copper, silver, diamond, aluminum alloys, aluminum oxides, rhodium, cobalt, copper alloys, nickel, iron, platinum, palladium, tin, steel, zirconium, titanium, carbon fiber, carbon black, Hastelloy, carbon-based inorganic, metal, metal oxides, metal nitrides, alloys, or hybrids.

66. The method of claim 44, further comprising a step of filling the expanded fissure with a second thermally conductive material.

67. The method of claim 66, wherein the first thermally conductive material has a k-value of at least 5 W/mK.

68. The method of claim 66, wherein the second thermally conductive material comprises a material selected from the group consisting of zinc, graphite, graphene, tungsten, aluminum, silicon carbide, aluminum nitride, silicon nitride, boron nitride, gold, copper, silver, diamond, aluminum alloys, aluminum oxides, rhodium, cobalt, copper alloys, nickel, iron, platinum, palladium, tin, steel, zirconium, titanium, carbon fiber, carbon black, Hastelloy, carbon-based inorganic, metal, metal oxides, metal nitrides, alloys, or hybrids.

69. A method of expanding an existing fissure in a wellbore, comprising: placing at a first downhole position a contact device in the wellbore at a target location proximal to the existing fissure, wherein the contact device has at least two movable contact elements; and moving the contact elements in the wellbore at the first downhole position at the target location in a direction against a wall of the wellbore to expand the existing fissure using the contact elements, thereby creating an expanded fissure.

70. The method of claim 69, wherein the existing fissure is naturally occurring, initiated using hydraulic fracturing, initiated using mechanical fracturing, or initiated using the contact device.

71. The method of claim 69, wherein the contact elements are used to apply a further stress force at the target location in the rock formation to thereby increase the width of the mouth portion.

72. The method of claim 71, wherein applying a further stress force at the target location is repeatedly performed between 2-6 times.

73. The method of claim 69, wherein the rock formation is a dry hot rock formation.

74. The method of claim 69, wherein the hot rock formation is an intrusive igneous, granitic, basaltic, sedimentary, or metamorphous rock formation.

75. The method of claim 69, wherein the target location is at a depth of between 150 m and 20,000 m.

76. The method of claim 69, wherein the rock formation at the target location has a temperature of between about 120 °C to 600 °C.

77. The method of claim 69, wherein a proximal portion of the expanded fissure has a width of between 3 mm and 25 mm.

78. The method of claim 69, wherein a distal portion of the expanded fissure has a width of between 0.5 mm and 2 mm.

79. The method of claim 69, wherein the expanded fissure has a length of between 1 m and 200 m as measured from the mouth portion to the distal end.

80. The method of claim 69, wherein the expanded fissure has a vertical orientation and a height of between 1 m and 40 m.

81. The method of claim 69, further comprising a step of at least partially filling the expanded fissure with a first thermally conductive material.

82. The method of claim 81, wherein the first thermally conductive material has a k-value of at least 5 W/mK.

83. The method of claim 81, wherein the first thermally conductive material is thermally coupled to a second thermally conductive material surrounding a heat harvesting element, and wherein thermal conductivity constants of the first and second thermally conductive materials differ by no more than 10% as measured by their respective k-values or wherein the first and second thermally conductive materials are the same.

84. The method of claim 81, wherein the first thermally conductive material comprises a material selected from the group consisting of zinc, graphite, graphene, tungsten, aluminum, silicon carbide, aluminum nitride, silicon nitride, boron nitride, gold, copper, silver, diamond, aluminum alloys, aluminum oxides, rhodium, cobalt, copper alloys, nickel, iron, platinum, palladium, tin, steel, zirconium, titanium, carbon fiber, carbon black, Hastelloy, carbon-based inorganic, metal, metal oxides, metal nitrides, alloys, or hybrids.

85. The method of claim 69, further comprising a step of filling the expanded fissure with a second thermally conductive material.

86. The method of claim 85, wherein the first thermally conductive material has a k-value of at least 5 W/mK.

87. The method of claim 85, wherein the second thermally conductive material comprises a material selected from the group consisting of zinc, graphite, graphene, tungsten, aluminum, silicon carbide, aluminum nitride, silicon nitride, boron nitride, gold, copper, silver, diamond, aluminum alloys, aluminum oxides, rhodium, cobalt, copper alloys, nickel, iron, platinum, palladium, tin, steel, zirconium, titanium, carbon fiber, carbon black, Hastelloy, carbon-based inorganic, metal, metal oxides, metal nitrides, alloys, or hybrids.