Enhanced geothermal heat collection

Abstract

A system and method for improved geothermal heat collection enhancement is presented, where a well includes a closed-loop geothermal heat collection system that is thermally coupled to a hot, dry rock formation via a thermal arrival enhancement structure that extends from the well into the formation and is filled with a thermally conductive filler. Preferred configuration and / or operating parameters are determined by a model that calculates heat flow in a three-dimensional system taking into account time variations and the effects of the inherent thermal conductivity of the rock that is enhanced by the thermal arrival.

Description

[Technical Field]

[0001] This application claims priority to the inventor's co-pending U.S. Provisional Patent Application No. 63 / 270,191, filed October 21, 2021, which is incorporated herein by reference.

[0002] The technical field is a system and method for collecting geothermal heat (geoheat) from a hot, dry geological formation using a closed loop geothermal system (CLGS) thermally coupled to a thermal reach enhancement (TRE) within the formation, and a modeling system and method for optimizing the operating parameters and configuration of the TRE and CLGS. [Background technology]

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

[0004] All publications and patent applications herein are incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. In the event that a definition or use of a term in an incorporated reference contradicts or is contrary to the definition of that term provided herein, the definition of that term provided herein shall apply and the definition of that term in the reference shall not apply.

[0005] Electricity generation from renewable energy sources, such as solar, wind, and wave energy, has become increasingly feasible and economical over the past decade and is found in many countries. While attractive for its operational simplicity, the power so generated is necessarily intermittent and requires significant energy (typically electrical) storage capacity. Conventional geothermal power plants that utilize heated water / steam from formations advantageously avoid the problems associated with intermittent power production, but they suffer from a series of disadvantages inherent in the concept. Most importantly, water is becoming an increasingly scarce resource, and pumping water from geothermal wells back into the formation often raises concerns about contamination and / or seismic activity. In addition, many conventional geothermal power plants incur high field exploration, operation, and maintenance costs.

[0006] Some of these problems can be addressed using open-loop traditional enhanced geothermal systems (EGS), in which a working fluid flows through hydraulic fractures in a high-temperature formation, as exemplarily described in U.S. Patent No. 11,125,471. While such open-loop systems can, at least conceptually, capture significant amounts of energy, they require direct fluid interaction with the formation, which often makes well design and material selection difficult. Furthermore, not all of the working fluid from the injector well reaches the producer well, leading to losses of working fluid and captured energy and therefore the need for additional working fluid injection, with its attendant environmental impacts and water usage.

[0007] Alternatively, heat can be collected from hot rock using closed-loop systems, as described, for example, in U.S. Patent Application Publication No. 2020 / 0011151. Many closed-loop systems advantageously eliminate problems associated with geothermal power generation using heated water / steam extracted from the formation, eliminating internal pipe and turbine corrosion issues that often occur with traditional water / steam-based geothermal heat recovery. Additionally, closed-loop systems eliminate odors associated with hot water collection and avoid seismic activity concerns due to water removal and injection, resulting in virtually no environmental emissions or introduction of contaminants into the formation.

[0008] Unfortunately, many, if not all, hot rock energy collection systems suffer from rapid temperature decay due to the low inherent thermal conductivity of the geological formation. From a different perspective, currently known hot rock energy collection systems suffer from a mismatch between the availability of thermal energy in the formation surrounding the wellbore and the thermal conductivity of the formation at the wellbore, which can be further exacerbated by a mismatch in the mass flow of the working fluid (typically water) through the closed-loop system. Summary of the Invention [Problem to be solved by the invention]

[0009] Thus, while various systems and methods for energy collection from heated geological formations are known in the art, all or most of them suffer from certain drawbacks. Thus, there remains a need for systems and methods that allow for the creation of thermally efficient geothermal collection systems. [Means for solving the problem]

[0010] The present subject matter is directed to various improved systems and methods of thermal energy collection from hot, dry geological formations, including thermal arrival extension structures in hot rock that contain high thermal conductivity materials to enhance the inherent thermal conductivity of the surroundings of the closed-loop geothermal collection system. In further preferred aspects, the closed-loop geothermal collection system and thermal arrival extension are configured using algorithms and / or simulation tools that provide optimized deployment and operating parameters for the closed-loop geothermal system and the thermal arrival enhancement structures.

[0011] In one aspect of the present subject matter, the inventors contemplate a method of installing a closed-loop geothermal collection system that includes acquiring data from a deployment location. The acquired data is then used in a model to determine one or more configuration and / or operating parameters of the closed-loop geothermal collection system, the model further using determined or calculated thermal conductivities of the formations at the deployment location. The closed-loop geothermal collection system is then constructed and assembled based on the configuration and / or operating parameters determined by the model.

[0012] In some embodiments, data from the deployed location is obtained from rock samples taken at the deployed location and / or sensors at the deployed location. Among various options, suitable data from the deployed location includes temperature data, location data, range data, thermal conductivity data, rock composition data, and / or principal stress data. In further embodiments, the determined thermal conductivity of the formation may be an intrinsic thermal conductivity determined from the taken rock samples, and the calculated thermal conductivity of the formation may be a modified intrinsic thermal conductivity based on the intrinsic thermal conductivity and a thermal access enhancement structure in the formation. In such cases, it is generally preferred that the thermal access enhancement structure include a thermally conductive material having a thermal conductivity higher than the thermal conductivity of the formation in the absence of the thermal access enhancement structure.

[0013] For example, contemplated thermal arrival enhancement structures may have a longitudinal or radial shape. It is further contemplated that the thermal arrival enhancement structures may be thermally bonded to a thermally conductive cement located between the thermal arrival enhancement structure and the casing of the closed-loop geothermal system. Most typically, but not necessarily, the thermally conductive filler may have a k-value of at least 50 W / m°K.

[0014] In further contemplated embodiments, the model calculates heat flux using finite volume (3D) numerical calculations. Preferably, but not necessarily, the model calculates heat flux at the wall of the casing of the closed-loop geothermal collection system as a function of time, and / or the model further calculates heat flux from the formation into the mass flow of the working fluid within the closed-loop geothermal collection system. It is further contemplated that the model uses multiple calculations during a time interval in which the working fluid circulates within the closed-loop geothermal system, with thermophysical properties being recalculated during each calculation. Among various options, it is contemplated that the configuration and / or operating parameters include the mass flow rate of the working fluid, the length of the heat transfer conduit at the deployed location, the effective width of the thermal arrival enhancement structure, and / or the effective length of the thermal arrival enhancement structure.

[0015] Thus, based on an exemplary model calculation, a closed-loop geothermal heat collection system may include a well extending from an upper side to a deployment location and including a closed-loop circuit for a working fluid. Most typically, the closed-loop circuit includes a casing thermally coupled to a wall of the well via a thermally conductive cement, and the wall of the well further includes a thermally enhanced structure thermally coupled to the thermally conductive cement and filled with a thermally conductive filler. In such a system, the deployment location has a formation temperature of at least 250°C, the working fluid has a return temperature of at least 150°C, and the thermally enhanced structure has a complex, multi-fractured shape along its length and a width between 10 and 50 mm.

[0016] For example, the thermally conductive cement and / or filler may have k-values ​​of at least 5 W / m°K and 50 W / m°K, respectively, and / or the working fluid is water. Preferably, the casing, which is thermally bonded to the well wall via the thermally conductive cement, has a length of at least 3 km. In further examples of such systems, the length of the thermally enhanced structure is at least 15 m, measured from the well, and / or the working fluid has an inlet temperature greater than 100°C and a flow rate of 15-25 kg / sec.

[0017] Various objects, features, aspects and advantages of the present subject matter will become apparent from the following detailed description of preferred embodiments, taken in conjunction with the accompanying drawings, in which like numerals represent like elements. [Brief explanation of the drawings]

[0018] [Figure 1] 10 is an exemplary graph illustrating power loss over time for various heat recovery systems. [Figure 2] 1A-1C are schematic diagrams of various views of exemplary lateral thermal arrival reinforcement structures; [Figure 3] Schematic diagram of an exemplary perspective view of a radial thermal arrival enhancement structure. [Figure 4] 1 is a schematic diagram of an exemplary closed-loop geothermal heat collection system with enhanced heat delivery structures in accordance with the present inventive subject matter; [Figure 5] 5 is a schematic diagram of an exemplary detailed view of the closed-loop geothermal heat collection system with enhanced heat arrival of FIG. 4 . [Figure 6] FIG. 1 illustrates an exemplary thermal energy equation for a specific flow in a closed-loop geothermal system. DETAILED DESCRIPTION OF THE INVENTION

[0019] The inventors have discovered that the performance and efficiency of a closed-loop geothermal system can be optimized by matching various parameters of the formation at the deployment location with various configuration and / or operating parameters of the closed-loop geothermal system to optimize heat flow from the formation to the working fluid. Indeed, upon careful analysis, the inventors have discovered that a model can be constructed that allows for the simulation of various parameters to provide optimized design options for various factors that substantially affect effective heat transfer, such as the shape and / or placement of the thermal arrival enhancement structures, the materials used in such structures, the properties of the thermally conductive cement that bonds the thermal arrival enhancement structures to the casing of the closed-loop geothermal collection system, the length of the collector casing, and the mass flow of the working fluid within the closed-loop geothermal collection system.

[0020] In this context, it should be recognized that previous attempts by various parties to scale closed-loop geothermal systems to economically feasible sizes have largely failed for several reasons. Among other causes, systems that collect naturally high-temperature water or steam (e.g., conventional geothermal and EGS) typically do not scale due to the essentially fixed rate of hot water or steam production at a given location. On the other hand, systems that rely on the inherent thermal conductivity of rock formations have also failed to scale because they required excessively long exposures to the resource to collect a reasonable amount of thermal energy. Similarly, all or nearly all systems operating at formation temperatures below 200°C also fail to scale, as do closed-loop systems that do not span the desired temperature range long enough.

[0021] In an attempt to solve such problems, the inventors have discovered that heat transfer within the formation can be significantly improved beyond the inherent thermal conductivity of the formation when a thermal arrival enhancement structure is placed within the formation, the structure reaching far beyond the wellbore and providing enhanced thermal conductivity by filling such structure with a thermally conductive material having a significantly higher conductivity than the formation, thereby significantly increasing the thermal energy transfer surface of the modified wellbore and thus substantially increasing the collection of geothermal heat.

[0022] To that end, the inventors have contemplated at least two different types of thermal arrival enhancement structures that can be produced using conventional equipment and methods known from oil and gas operations. For example, depending on the particular rock formation and the fracture generation method in the rock surrounding the wellbore, the thermal arrival enhancement structures can be configured as longitudinal structures ("double-wing transverse fins") or radial structures ("radial fins"). Figure 1 shows, in a schematic and exemplary manner, the significant difference in heat collection (shown as power production) over time. Here, the top curve shows a closed-loop geothermal system with a thermal arrival enhancement structure, while the middle curve shows the heat collection of a conventional hydrothermal power plant, with reduced power output due to a reduced water / steam production rate. An example of power production over time for a conventional closed-loop geothermal system is shown by the bottom curve, demonstrating the loss of efficiency due to ineffective heat transfer.

[0023] 2 schematically illustrates exemplary lateral thermal arrival reinforcement structures extending from the wellbore, typically in opposite directions. As will be readily appreciated, inherent conditions in the formation, such as stress planes and existing boundaries in the formation, may at least partially determine the path and direction of the fractures. However, as exemplarily and schematically illustrated in FIG. 3, the thermal arrival reinforcement structures may extend from the wellbore in a disk-like orientation, and it is again noted that such fracture structures can be produced using methods known in the art.

[0024] Figure 4 depicts an exemplary closed-loop geothermal system (not to scale) in which an upper-level power generation facility is thermally coupled (typically via a heat exchanger) to a closed-loop circuit of heated working fluid circulating within the closed-loop geothermal system. Figure 5 shows a detailed view of the downhole at the end of the closed-loop circuit in its deployed position in dry hot rock 501. A casing 502 circumferentially surrounds a (typically insulated) return pipe 503, and heat from the rock formation 501 heats the working fluid traveling downward in the annular space between the casing and the return pipe. In this exemplary illustration, the casing is embedded in thermally conductive cement 504, which is in thermal communication with transverse cracks 505 filled with a thermally conductive filler.

[0025] It should be noted that the thermally conductive cement and filler have a higher thermal conductivity than the hot rock in the formation. It should also be noted that the longitudinal thermal delivery reinforcement structure is not a simple channel but more similar to a dendritic structure, which further increases the heat exchange surface area with the surrounding rock. For example, as described in detail below, it is generally preferred that the thermally conductive cement and filler have a thermal conductivity significantly higher than that of the surrounding formation, e.g., at least 1.5 times higher, at least 2.5 times higher, or at least 5 times higher. Thus, the thermally conductive cement may have a thermal conductivity of at least 2 W / m°K, more typically at least 3 W / m°K, or at least 5 W / m°K, while the thermally conductive filler may have a thermal conductivity of at least 25 W / m°K, more typically at least 35 W / m°K, or at least 50 W / m°K.

[0026] It will be appreciated, therefore, that using such a system, the difficulties associated with inefficient heat collection can be overcome in at least two ways. First, the thermally conductive cement and thermally conductive filler ensure intimate thermal contact between the formation and the casing of the closed-loop geothermal collection system. Furthermore, due to the increased high-heat surface area (and material connecting that surface area to the casing) provided by the enhanced heat arrival structure, a substantially larger heat transfer area is available for heat collection.

[0027] To verify that such a system and method would indeed provide significant advantages over conventional closed-loop geothermal heat collection systems, the inventors decided to model the heat transfer from the dry, hot formation to the working fluid circulating in the closed loop. Because heat transfer in a closed-loop geothermal heat collection system with a thermal arrival enhancement structure involves several complex variables, the inventors used a holistic approach with a two-part holistic model. Here, the holistic model consists of two parts: (1) a thermal arrival enhancement formation model that considers the intrinsic thermal conductivity of the rock and / or a modified intrinsic thermal conductivity that accounts for the thermal conductivity of the rock with the thermal arrival enhancement structure, and (2) a wellbore flow model that is coupled to the thermal arrival enhancement formation model.

[0028] It should therefore be appreciated that such a model not only allows for the determination and / or adjustment of variables such as the thermal k-values ​​of the materials used, the shape and / or size of the thermal arrival enhancement structures, the formation temperature at the deployment location, but also allows for the determination and / or adjustment of variables within the closed-loop system containing the working fluid, such as the depth of deployment, the working fluid temperature, the working fluid mass flow, etc. Viewed from a different perspective, this overall model allows for the proper sizing of the configuration of the closed-loop geothermal system and / or the setting of appropriate operating parameters for a multitude of geological formations and their associated geological features.

[0029] As a result, simulations can be performed that can take into account various formation parameters, in particular the rock temperature at the deployment location, the heat flux (specific thermal conductivity) within the formation at the deployment location, and the improvement of the heat flux within the formation by using a heat arrival enhancement structure at the interface between the formation and the casing of the closed-loop geothermal system (modified specific thermal conductivity), as well as various configuration and / or operating parameters of the closed-loop geothermal system, in particular the depth and / or length of the closed-loop geothermal system at the deployment location, the dimensions of the casing and return pipes, and / or the mass flow through the closed-loop geothermal system.

[0030] In one preferred example, the thermal arrival strengthening formation model was based on a two-dimensional transient equation using the longitudinal thermal arrival strengthening structure exemplarily shown in FIG. 2 and utilized a finite volume numerical approach. In that context, it should be noted that the use of a finite volume numerical approach enabled three-dimensional modeling, which traditional modeling systems did not account for. Furthermore, the thermal arrival strengthening formation model also calculated the heat flux at the casing wall as a function of time. And the wellbore flow model was based on the calculations for the enthalpy equation and heat flux multiplier from the above analysis coupled to the wellbore flow model.

[0031] More specifically, a block-structured, coordinate-invariant finite-volume scheme was used: the governing equations were integrated over the control volume, and Gauss's divergence theorem was applied to the RHS to express conservation as interfacial fluxes. Furthermore, a "resistors in parallel" (weighted harmonic mean) scheme was used to determine the interfacial conductivities as (known) nodal conductivities, and boundary conditions were applied to faces without neighboring elements. A sparse linear system was then constructed for the nodal temperatures, and this linear system was solved to obtain the temperatures using the stabilized preconditioned dual conjugate gradient algorithm (Van der Vorst, 1992) with an incomplete LU preconditioner.

[0032] For well coupling, the thermal energy equation in the pipe flow was used, where the transient term (energy accumulation) minus advection (streamwise energy transfer) equaled the heat transfer between the pipe and the annulus plus the heat transfer between the annulus and the formation plus adiabatic heat transfer (frictional heating), as exemplarily depicted in Figure 6. The cycle period was then divided into subperiods to allow for the recalculation of thermophysical properties, and within each time subinterval, a system of first-order PDEs (inhomogeneous wave equations) was converted into a pair of ordinary differential equations in the frequency domain by a Laplace transform of the governing equations.

[0033]

number

[0034] The formation transients were modeled in a finite domain, and the exact solution was coupled to the wellbore through Duhamel convolution in the frequency domain. Spatial derivatives were approximated by backward finite differences in the flow direction. An alternating direction marching algorithm using a set of simultaneous equations for the piping and annulus temperatures was solved at each depth, and the temperatures were converted back to physical space using a Gaver-Stehfest function sampling algorithm. Finally, the pressure profile was determined from the frictional and hydrostatic components. In such a model, the problem parameters included the resource (formation temperature), the ratio of thermal fill conductivity to formation conductivity, the effective width and length of the thermal delivery enhancement structure, the mass flow rate of the working fluid, and the thermal properties of the working fluid and the resource (formation temperature). As can be easily appreciated, such simulations and models can be run locally or remotely on a server farm, on a single computer or a computer network.

[0035] Using the model so developed, the inventors have simulated a number of closed-loop geothermal collection systems and verified that they are capable of continuous operation to recover / output thermal energy at steady state in amounts of at least 5 MWt, more typically at least 7 MWt, or at least 8 MWt, or at least 9 MWt, or at least 10 MWt, or at least 11 MWt, or at least 12 MWt. Such energy collection is particularly significant since currently known demonstration projects of closed-loop geothermal collection systems have thermal outputs well below 1 MWt.

[0036] For example, in a validated closed-loop geothermal heat collection system, a preferred system included a well extending from an upper location to a deployment location (typically at least 500 m deep) and containing a closed-loop circuit for a working fluid. The heat content of the working fluid was then recovered in a heat exchanger thermally coupled to a turbine for generating electricity. In these examples, the closed-loop circuit included a casing thermally coupled to the well wall via a thermally conductive cement, and the well wall further included a thermally enhanced structure (a) thermally coupled to the thermally conductive cement and (b) filled with a thermally conductive filler having a higher thermal conductivity than the thermally conductive cement. Both the thermally conductive cement and the thermally conductive filler had a higher thermal conductivity than the dry hot rock at the deployment location. For example, in some cases, the thermally conductive cement had a k-value of at least 5 W / m°K, and the thermally conductive filler had a k-value of at least 50 W / m°K.

[0037] Furthermore, the deployment locations in the examined cases had formation temperatures of at least 250°C, and the thermally strengthened structures had complex, multi-fractured longitudinal geometries, widths of 10-50 mm, and lengths typically measured from the wellbore of at least 10 m. In most of these cases, the working fluid (typically water) had a return temperature of at least 150°C, an inlet temperature of 110°C or less, and the working fluid was circulated at a flow rate of 15-25 kg / s. Furthermore, the casing, thermally bonded to the wellbore wall via thermally conductive cement, had a length of at least 1 km, more typically at least 2 km or at least 3 km.

[0038] With respect to formation temperature, it is generally contemplated that a suitable closed-loop geothermal collection system will be installed in a location that results in a dry formation having a temperature of at least 250°C at the deployed location, although higher formation temperatures are also contemplated, including temperatures of at least 275°C, or at least 300°C, or at least 325°C, or at least 350°C, or at least 375°C, or at least 400°C, or at least 425°C, or at least 450°C, and even higher. Furthermore, it is generally preferred that the length of conduit at the target location, with the casing thermally bonded to the wellbore wall via thermally conductive cement, have a length of at least 0.5 km, more preferably at least 1 km. However, as will be shown in more detail below, additional lengths (e.g., greater than 1 km) have been demonstrated to significantly increase thermal energy recovery in our simulations, so greater lengths are generally preferred. For example, Table 1 below shows that the length of the closed-loop geothermal collection system (in thermal contact with the deployed location) substantially increased thermal energy collection.

[0039] [Table 1]

[0040] In addition, it should be noted that the wellbore typically has a vertical orientation for at least some distance before reaching the deployment location (i.e., the location in the dry hot rock where thermal energy collection occurs), and that the orientation of the wellbore may be vertical throughout its entire length, or at least a portion of the wellbore may deviate toward the horizontal (e.g., at an angle of 30 degrees, or 60 degrees, or even 90 degrees from vertical).

[0041] Additionally, it is generally contemplated that a wellbore will include one or more thermal arrival enhancement structures, with longitudinal and radial structures being contemplated, among other structures. In a further preferred embodiment, it should be recognized that where the TRE is a longitudinal structure, such structure may be present along the entire length of the wellbore at the deployed location, or may be present in multiple sections along the entire length of the wellbore at the deployed location. On the other hand, where the TRE is a radial structure, multiple TREs along the wellbore are generally preferred. Thus, the number of TRE structures can vary considerably, and it is contemplated that a wellbore may have from 1 to 100 TRE structures (and potentially even more).

[0042] Regardless of the specific configuration, a TRE structure in a wellbore generally extends from the wellbore into the rock formation at the deployment location, and the length of the TRE structure is typically at least 1 m, or at least 2 m, or at least 5 m, or at least 5 m, or at least 15 m, or at least 20 m, or at least 25 m, and in some cases even longer (measured as the distance between the wellbore and the distal end of the TRE structure). In further contemplated embodiments, the thickness (width) of the TRE structure is significantly smaller than rock fractures commonly used in oil and gas exploration. For example, the thickness of a suitable TRE structure is between 5 and 7.5 mm, or between 7.5 and 15 mm, or between 10 and 30 mm, or between 30 and 50 mm, and in some cases somewhat thicker. Thus, exemplary TRE structures may have widths between 5 and 30 mm, or between 10 and 50 mm, or between 25 and 80 mm. Notably, the inventors have discovered that the width of the TRE structure in at least some models is a critical operating parameter for effective heat collection, and that in such cases, the width at the wellbore boundary has a significant effect (e.g., having a width between 10 and 50 mm). Furthermore, regardless of the specific configuration, it is generally preferred that the TRE structure be formed as a complex structure (e.g., a network or tree structure) rather than a single linear fracture in the rock formation, as exemplarily depicted in FIG. 5. Advantageously, such a complex structure allows for a larger heat exchange surface with the remainder of the unfractured rock at the deployment location.

[0043] As will be readily appreciated, the TRE structures contemplated herein are filled with a thermally conductive filler material having a k-value (thermal conductivity coefficient) greater than the k-value of the thermally conductive cement in the borehole surrounding the casing of the closed-loop geothermal collection system and greater than the inherent k-value of the unfractured rock in the formation at the deployment location. For example, suitable thermally conductive filler materials have k-values ​​of at least 20 W / m°K, or at least 30 W / m°K, or at least 40 W / m°K, or at least 50 W / m°K, or at least 75 W / m°K, or at least 100 W / m°K, or at least 500 W / m°K, and even higher.

[0044] In other examples, the thermally conductive cement material in the wellbore has a k-value of at least 2 W / m°K, or at least 3 W / m°K, or at least 4 W / m°K, or at least 5 W / m°K, or at least 7.5 W / m°K, or at least 10 W / m°K, or at least 15 W / m°K, or even higher. Viewed from a different perspective, the k-value of the thermally conductive filler material is at least 2 times, or at least 5 times, or at least 10 times, or at least 25 times, or at least 50 times, or at least 100 times higher than the k-value of the thermally conductive cement material. More typically, depending on the rock type, the rock in the formation at the deployment location has a characteristic k-value between about 0.6 and 0.9 W / m°K, or between about 0.9 and 1.5 W / m°K, or between about 1.5 and 2.5 W / m°K, or between about 2.5 and 3.5 W / m°K, or between about 3.5 and 4.5 W / m°K. As can be seen from the simulation results in Table 2, the effect of the k-value of the thermally conductive filler material relative to the k-value of the formation had an unexpectedly high impact on thermal energy collection.

[0045] [Table 2]

[0046] For example, contemplated thermally conductive cement compositions include a mixture of cementitious material, a retarder, and one or more high-heat-k additives. In some embodiments, improved workability results from the use of a retarder, which allows the cement composition to be placed in a well even under extreme temperature conditions (e.g., at least 300°F). Without being bound by theory, the inventors contemplate that the retarder is present in an amount effective to delay the setting of the cement mixture for at least two hours at a target location having a target temperature of at least 150°C, at least 200°F, or at least 250°C, or at least 300°C, or at least 350°C. Furthermore, the high-heat-k additive is present in an amount effective to cause the cement mixture, when set at the target location, to have a thermal conductivity of at least 2 W / m°K, or at least 3 W / m°K, or at least 4 W / m°K, or at least 5 W / m°K, or at least 7.5 W / m°K, or at least 10 W / m°K, or at least 15 W / m°K, and even higher.

[0047] Among various suitable high heat-k additives for cement compositions, particularly contemplated additives include high heat-k materials, such as graphite, sand, quartz silica, salt-free coal, various carbon allotropes, such as carbon nanotubes and graphene, boron nitride, brass, brass alloys, chromium-nickel steel, carbon steel, stainless steel, one or more transition metals (e.g., copper, cadmium, cobalt, gold, silver, iridium, iron, molybdenum, nickel, platinum, zinc, etc.), one or more transition metal alloys (e.g., copper alloys, cadmium alloys, cobalt alloys, gold alloys, silver alloys, iridium alloys, iron alloys, molybdenum alloys, nickel alloys, platinum alloys, zinc alloys, etc.), post-transition metals (e.g., lead, tin, etc.), post-transition metal alloys (e.g., lead alloys, tin alloys, etc.), alkaline earth metal alloys (e.g., beryllium alloys, magnesium alloys, etc.), aluminum, and any suitable combinations thereof. In some embodiments, the high-k material may be selected from the group consisting of graphite powder, exfoliated graphite, flake graphite, pyrolytic graphite, desulfurized petroleum coke, graphene, fly ash, copper powder, aluminum nitride, silicon carbide, and combinations thereof.

[0048] Particularly preferred additives exhibit a uniform distribution throughout the cement upon hardening; therefore, the additive may be micro- or nano-sized, in the form of platelets (e.g., in the case of carbon allotropes or carbonaceous materials), or in the form of fibers (e.g., aluminum or other metals or metal alloys). In addition, particularly if the additive is relatively hydrophobic in nature, the additive may be surface-treated to increase hydrophilicity (e.g., by oxidation or other introduction of polar groups such as keto, hydroxyl, or carboxyl groups). Furthermore, it should be appreciated that, particularly if polar groups are present in the additive, such polar groups improve contact and adhesion with the metallic casing of a closed-loop geothermal heat collection system. As will be readily appreciated, the amount of additive in the cement may vary widely, but in most typical embodiments, is between 1 and 20 wt%, or between 1 and 10 wt%, or between 1 and 5 wt%, or between 1 and 3 wt%, to achieve the desired k value of the thermally conductive cement.

[0049] Similarly, thermally conductive filler materials for thermally enhanced structures can vary widely, and it is generally preferred that the thermally conductive filler material be or include a material having a k-value significantly higher than that of the thermally conductive cement. Furthermore, it is contemplated that the thermally conductive filler material for the thermally enhanced structures may or may not include a cement component. Most typically, the thermally conductive filler material has a k-value of at least 10-20 W / m°K, as noted above. Thus, suitable thermally conductive filler materials for TRE structures are or include carbonaceous materials, in particular single-walled and / or multi-walled carbon nanotubes, graphene, graphene oxide nanosheets, graphite powder, exfoliated graphite, flaked graphite, pyrolytic graphite, desulfurized petroleum coke, fly ash, pulverized anthracite, or metal or metal oxide fibers or particles made of materials such as tin, aluminum, copper, iron, silver, gold, aluminum-copper alloys, or silver-aluminum alloys, and / or metal oxide particles such as silica, alumina, beryllia, copper oxide, zinc oxide, aluminum oxide, hematite, magnetite, and / or tin oxide. Still other suitable materials include particles made from or including barite, boron arsenite, aluminum nitride, silicon nitride, and / or silicon carbide.

[0050] In a further preferred embodiment, the thermally conductive filler material for the thermally-reached reinforcement structure has a particle size or fiber diameter suitable for deployment within the fractures created to form the thermally-reached reinforcement structure. Thus, in many cases, the appropriate size will be a particle size or fiber diameter on the order of microns to millimeters. In this context, it is specifically contemplated that the thermally-reached reinforcement structure is first created by using elevated pressure (e.g., by a hydraulic pump) to create multiple fractures in the formation at the deployment location, and then the thermally-conductive filler material is delivered to the fractures at elevated pressure. The elevated pressure can then be reduced by an amount sufficient to reduce the fracture width, allowing geomechanical compressive stresses to trap the particles and compact the filler material. Alternatively, if the thermally-conductive filler material is a cementitious composition, the composition may be delivered to the fractures and allowed to harden. As will be readily appreciated, the fracture filling may include one or more proppants, if needed or desired. Fracture creation and the filling of the fractures thus created are known in the relevant fields of oil exploration and production, and any such creation and filling methods are considered suitable for use in the present invention. In this context, it should be particularly recognized that the use of thermally conductive cement and thermally enhanced filler provides several advantages beyond efficient heat transfer from the formation to the working fluid (via the thermally enhanced structure and thermally conductive cement). Among other benefits, wells so produced, having thermally enhanced structures and thermally conductive cement encapsulating the casing, require substantially no maintenance and are not subject to well collapse.

[0051] With respect to the working fluid in the contemplated systems and methods, it should be recognized that a variety of working fluids are considered suitable, including single-component and multi-component working fluids. However, it is generally preferred that the working fluid be a single-component fluid, most preferably water. As will be recognized, mass flow in a closed-loop geothermal collection system is a function of several parameters, and it is generally preferred that mass flow be modeled in the model as described herein. Based on our model and other considerations, it is generally contemplated that mass flow can be optimized for well geometry and thermal arrival enhancement parameters, and that higher mass flow rates often result in increased energy extraction. However, such higher mass flows should be balanced with the return temperature of the working fluid. Therefore, and using our model and field testing, suitable mass flows for water as a working fluid in a closed-loop geothermal collection system are between 5 and 15 kg / s, or between 10 and 25 kg / s, or between 10 and 30 kg / s, or between 15 and 40 kg / s, or even higher in some cases.

[0052] Based on the above considerations, it should be appreciated that appropriate modeling of heat transfer from the formation to the working fluid through the thermal arrival enhancement structure and thermally conductive cement in the heat flow of a closed-loop geothermal collection system can provide useful insight into suitable structures for optimized thermal energy collection. In such cases, among other parameters, the inventors have discovered that increasing the thermal arrival by using a thermal arrival enhancement structure actually substantially increases the collected heat, and that the extracted energy increases with increasing collector length. Furthermore, the inventors have recognized that a higher thermal conductivity of the thermal arrival enhancement filler material substantially increases the collected energy, especially when the thermal arrival enhancement structure has a specific configuration (e.g., in the current state of the art, 10 2(Conductivity multipliers on the order of 1000 .mu.m have been shown to be practical.) Furthermore, using the model contemplated herein, the inventors have recognized that optimized mass flow increases the energy collected in the closed-loop geothermal collection system presented herein.

[0053] It should be noted that any reference to a computer should be construed to include any suitable combination of computing devices, including servers, interfaces, systems, databases, agents, peers, engines, modules, controllers, or other types of computing devices operating individually or collectively. It will be appreciated that a computing device comprises a processor configured to execute software instructions stored on a tangible, non-transitory computer-readable storage medium (e.g., a hard drive, solid-state drive, RAM, flash, ROM, etc.). The software instructions preferably configure the computing device to provide the roles, responsibilities, and other functions described below with respect to the disclosed apparatus. In particularly preferred embodiments, the various servers, systems, databases, or interfaces exchange data using standardized protocols or algorithms, possibly based on HTTP, HTTPS, AES, public / private key exchange, web services APIs, known financial transaction protocols, or other electronic information exchange methods. Data exchange preferably occurs over a packet-switched network, the Internet, a LAN, a WAN, a VPN, or other types of packet-switched networks.

[0054] In some embodiments, numbers expressing properties such as quantities of ingredients, concentrations, reaction conditions, and the like, used to describe and claim particular embodiments of the present invention should be understood to be modified in some instances by the word "about." Accordingly, in some embodiments, the numerical parameters set forth in the detailed description and appended claims are approximations that may vary depending upon the desired properties sought to be obtained in a particular embodiment. 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 separate value is incorporated herein as if set forth individually.

[0055] All methods described herein can be performed in any suitable order unless otherwise indicated herein or clearly contradicted by context. The use of any and all examples or exemplary language (e.g., "such as") provided herein in the context of specific embodiments is merely to better clarify the invention and does not otherwise impose limitations on the scope of the claimed invention. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

[0056] As used in the description herein and in the claims that follow, the meanings of "a," "an," and "the" include plural references 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. Also, as used herein and unless the context dictates otherwise, the word "coupled to" is intended to include both direct coupling (two elements coupled to each other are in contact with each other) and indirect coupling (at least one additional element is located between the two elements). Thus, the words "coupled to" and "coupled with" are used interchangeably.

[0057] It will be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. Accordingly, the inventive subject matter should not be limited except as by 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, "comprises" and "comprising" should be interpreted as referring to elements, components, or steps in an inclusive manner, meaning that the referenced element, component, or step may be present with, utilized in, or combined with other elements, components, or steps not expressly referenced. When this specification refers to at least one of something selected from the group consisting of A, B, C... and N, the statement should be interpreted as requiring only one of that group, and not A plus N, or B plus N, etc.

Claims

1. A method for installing an optimized closed-loop geothermal heat collection system, comprising: the closed-loop geothermal collection system comprises a wellbore and a thermal arrival enhancement structure along a length of the wellbore, the thermal arrival enhancement structure being transverse to the wellbore; The method comprises: acquiring data from the deployed location; Calculating heat fluxes within the global model using finite volume (3D) numerical calculations; using the data within the overall model, which includes (1) a thermal arrival enhancement structure model that accounts for the intrinsic thermal conductivity of the geological formation at the deployment location and the intrinsic thermal conductivity of the geological formation as modified by the thermal arrival enhancement structure, and (2) a wellbore flow model that is coupled to the thermal arrival enhancement structure model; The overall model is subjected to a simulation; the overall model determines one or more configuration and / or operating parameters of the closed-loop geothermal system; the configuration and / or operating parameters are selected from the group consisting of a mass flow rate of a working fluid, a length of a heat transfer conduit at a deployed position, an effective width of a thermal arrival enhancement, and an effective length of a thermal arrival enhancement; the global model calculates parameters for thermal reach extension based on the intrinsic thermal conductivity and the modified thermal conductivity of the geological formation at the deployment location; The method further comprises: and constructing and assembling the closed-loop geothermal system with the enhanced heat delivery structure based on the configuration and / or operating parameters determined by the model.

2. The method of claim 1 , wherein the data from the deployed location is obtained from rock samples taken at the deployed location and / or sensors located at the deployed location.

3. The method of claim 1 , wherein the data from the deployed location is selected from the group consisting of temperature data, location data, range data, thermal conductivity data, rock composition data, and principal stress data.

4. The method of claim 1 , wherein the determined thermal conductivity of the geological formation is an intrinsic thermal conductivity determined from a collected rock sample.

5. 2. The method of claim 1, wherein the calculated thermal conductivity of the geological formation is a modified intrinsic thermal conductivity based on an intrinsic thermal conductivity and the thermal access-enhancing structure in the geological formation, the thermal access-enhancing structure including a thermally conductive filler having a thermal conductivity higher than the thermal conductivity of the geological formation without the thermal access-enhancing structure.

6. The method of any one of claims 1 to 5, wherein the thermal access enhancement structure has a longitudinal shape.

7. The method of any one of claims 1 to 5, wherein the thermal access enhancement structure has a radial shape.

8. The method according to any one of claims 1 to 5, wherein the thermal access reinforcement structure has a complex network or tree-like structure and a width between 10 and 50 mm.

9. 6. The method of claim 1, wherein the thermal arrival enhancement structure is thermally bonded to a thermally conductive cement located between the geological formation containing the thermal arrival enhancement structure and a casing of the closed-loop geothermal system.

10. The method of any one of claims 1 to 5, wherein the thermally conductive filler has a k value of at least 50 W / m°K.

11. The method of any one of claims 1 to 5, wherein the model calculates the heat flux as a function of time at a wall of a casing of the closed-loop geothermal collection system.

12. The method of any one of claims 1 to 5, wherein the model further calculates heat flux from the geological formation into a mass flow of working fluid within the closed-loop geothermal collection system.

13. The method of any one of claims 1 to 5, wherein the model further calculates heat flux from the geological formation into a mass flow of working fluid within the closed-loop geothermal collection system.

14. 6. The method of claim 1, wherein the model uses multiple calculations during a time interval that a working fluid circulates in the closed-loop geothermal system, and in each of the calculations, thermophysical properties are recalculated.

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