System and method for energy and resource extraction with reduced emissions

Abstract

A heat extraction system (400) for extracting heat from a reservoir, the system comprising: a coaxial tool (420) configured to be placed underground, the coaxial tool (420) having an outer tube (520) and an inner tube (510) located within the outer tube (520), each of the outer tube (520) and the inner tube (510) being connected to a seat (530) such that a fluid flows through an annular space (512) defined by the inner tube and the outer tube to the seat, and flow through a hole (514) of the inner tube (510); and a generator (430) fluidly connected to the chemical treatment unit (410) to receive the fluid (422) and further fluidly connected to the inner tube (510) of the coaxial tool (420) through a first port and to the outer tube (520) of the coaxial tool (420) through a second port. A difference in temperature of the fluid (422) at the generator (430) and at the coaxial tool (420) drives the generator (430) to generate energy.

Description

Technical Field

[0001] Embodiments of the subject matter disclosed herein generally relate to a system and method for extracting energy and / or valuable resources from coal or similar reservoirs, and more particularly, to a process and associated systems for developing underground coal reservoirs without mining the coal and bringing it to the surface for combustion in a power facility, which process and associated systems reduce pollution. Background Art

[0002] Hydrogen and geothermal energy are two key components of the transition to green energy. Besides being an essential resource for the chemical industry, hydrogen, when burned solely for power, produces fresh water as a byproduct. The use of geothermal energy (generated naturally by the Earth or artificially, for example by burning coal in its underground location) ranges from power generation to a variety of localized direct uses, such as district heating, industrial processes, heating for agriculture and aquaculture, and leisure and bathing.

[0003] Since the 1960s, global energy consumption has been increasing linearly (approximately 2,200 terawatt-hours per year), and coal remains one of the three major energy resources alongside oil and natural gas. Figure 1A and Figure 1B Excerpted from Ritchie, H., Roser, M., and Rosado, P. (2022). "Energy," published online at OurWorldInData.org and retrieved from ourworldindata.org / energy. Coal consumption continues to grow, and its contribution to global consumption remains stable. In many parts of the world, coal remains the primary fuel source for energy and chemical production. If the world is to rapidly and massively reduce CO2 emissions, decarbonizing coal mining appears to be one of the challenges that must be addressed.

[0004] Underground coal gasification (UCG) has been studied since the early 20th century and has developed several successful long-term production cases. UCG is considered a promising option for advanced clean coal mining. UCG is an in-situ gasification process of naturally occurring coal. The gasification process involves the controlled combustion of coal-bearing formations and coal seams to produce a gas mixture (called syngas) including methane and hydrogen, but also carbon dioxide and carbon monoxide. It should be noted that the coal-bearing formation is not extracted from the ground, but rather burned in its underground location in a controlled manner.

[0005] There are different development methods for in situ gasification of coal resources. These methods all involve introducing steam and air or oxygen into the coal seam via injection wells, igniting the coal, and transporting the generated gas to the surface via production wells. Regarding mining design, there are various methods involving injection wells and production wells connected by a series of processes, including connected vertical wells (LVW), controlled retreat injection points (CRIP), single well integrated flow pipes (SWIFT) and steeply dipping seams (SDS). The applicability of these UCG methods depends on parameters such as the natural permeability of the coal seam, the geochemical characteristics of the coal, the thickness of the coal seam, the depth and the inclination.

[0006] The ratio of various gas components in syngas mainly depends on the quality and grade of coal, the depth of coal seam and the gasification agent (oxygen or air). Figure 2A and Figure 2B The syngas composition of different projects reported in the literature is shown. The black line refers to the calorific value of the gas, MJ / m 3 The graph shows the product gas volume percentage (dry state, STP) on the right axis, and the product gas volume percentage on the left axis, corresponding to the bar graph. The main components of syngas are H2, CO, CH4, CO2, as well as N2, H2S, and COS. In principle, all of these components can be used or reinjected underground, thus avoiding the emission of greenhouse gases into the atmosphere while providing useful elements for energy conversion. Some of these components provide fuel for power plants and raw materials for the chemical industry.

[0007] For example, H2, which is mainly used to produce chemical products, is now a promising energy source. UCG has conducted several experiments to increase hydrogen production [1-4]. Depending on the nature of the coal, depth, operating parameters, hydrogeological environment and combustion process, hydrogen may be the main syngas product of UCG, while CO2 and CO gases may be relatively minor components, such as Figure 2A and Figure 2B Previous UCG industrial-scale trials have shown that the hydrogen content of syngas is above 70%, and in laboratory tests it has reached 84%. Methane (CH4) is another component of syngas that can be used to produce chemical ingredients.

[0008] Research on UCGs over the past two decades has focused on the re-injection and storage of CO2 directly in the cavities formed by UCGs[5]. Numerical simulations conducted by [5] and long-term storage of CO2 to a depth of approximately 1 km in commercial-scale post-UCG multi-cavities have demonstrated that CO2 injection and storage in UCG cavities is a viable concept. Other projects have considered coupled CCS, but not within the cavities themselves.

[0009] Another component of syngas, CO, can be used to produce other commodities such as methanol or fertilizer.

[0010] Because these components of syngas can be efficiently used to provide fuel or raw materials for the chemical industry, the UCG process is attractive for decarbonization of the coal industry.

[0011] Another important factor to consider when implementing decarbonization with the UCG process is the high temperatures associated with the process. Surface coal gasification temperatures typically exceed 1000°C. Underground combustion temperatures are typically lower due to groundwater inflow, but can still exceed 600°C. Research on underground heat generated in coal seams and surrounding formations has primarily focused on thermodynamic processes and the effects on syngas quality and thermodynamics, rather than on harnessing the heat as an energy source. However, few studies have predicted the persistence of high temperatures in coal seams and surrounding formations for extended periods of time, such as Figure 3 The temperature diagram shown is an example and is taken from [6].

[0012] The heat generated by coal combustion represents a huge amount of energy, and the temperature in the cavity is about 600 ° C. For example, for a calorific value of 32MJ / kg, a coal seam thickness of 4m, and an area of ​​1km 2 The medium volatile smoke coal is estimated to have 5.4 million tons of coal with a potential total thermal energy of 174.1 joules (assuming a continuous coal seam density of 1350 kg / m 3 After applying a 50% reduction to unburned coal (which is difficult to access and reserved for topside support), and considering that even the efficiency of heat-to-electricity capture is only 2‰, this equates to about 48GWh or 28,235 barrels of oil equivalent. This is enough energy to meet significant industrial needs.

[0013] Considering that this example reflects only a very small portion of the available coal seam that could be used for clean, green underground coal gasification, it is clear that a large amount of energy could be utilized with minimal emissions. Several technical solutions have been proposed to capture a portion of the heat generated by the combustion process. In this regard, [7] proposed the circulation of water in the cooling pipes of the production well, which has a dual end use: cooling the production well to mitigate damage caused by extreme conditions, and capturing waste heat. The authors in [8] proposed the use of two-in-one heat exchangers or complex heat-gas cogeneration equipment [9-10] to extract heat from the production well. The authors in

[11] proposed circulating fluid between the injection well and the production well to capture heat directly through a heat exchanger inserted in the production well. The authors in

[12] proposed such a special device that includes a coolant transport pipe inserted in the production well to capture heat and cool the well. The authors in

[13] proposed such a system based on a heat transfer pipe inserted in a vertical borehole and connected to a thermoelectric power generation system to generate electricity using heat. The authors in

[14] rely on an integrated system inserted in a horizontal well to ignite the coal, extract heat and store carbon dioxide.

[0014] Others have proposed using shafts and tunnels for UCG. For example, the authors in

[15] proposed excavating a pipe channel in the overburden before the UCG involves the shaft. The authors in

[16] proposed using a solenoid in a spirally wound pipe wall. Both methods are applicable to shaft mining. Other coal mining methods, such as deep coal in situ fluidized mining methods, or surface coal combustion using reactions, are related to heat extraction. In addition, as discussed in

[17] , some previous research has focused on extracting heat from the synthesis gas produced by UCG using ground heat exchanger systems. Similarly, the authors in

[18] studied and developed methods for utilizing waste heat from coking plants.

[0015] Devices for extracting heat from shallow coal-burning zones (natural or artificial, usually shallow) have been disclosed in [19, 20] and are based on horizontal steel pipes located in the coalfield fire zone, which introduce heat carriers to extract thermal energy, or on large vertical shell-and-tube drilled heat exchangers (up to 30 m in diameter) consisting of a high thermal conductivity cylindrical shell.

[0016] When installed in a production well, the heat that can be collected is limited, and the remaining heat in the UCG cavity is largely unused. In addition, the device inserted directly into the coal will be subject to extreme conditions that may endanger its life. Other technologies based on extracting heat from the overburden by using horizontal wells

[21] may violate the limits of the coal and bring pollution risks (gas leakage).

[0017] Therefore, existing methods are either prone to damage to the equipment used due to the direct heat experienced by the various components designed to extract heat, or are harmful to the environment due to the risk of contamination. Therefore, there is a need for complementary and adaptable solutions (applicable to even deeper coal seams) designed to collect greater amounts of heat and limit the risk of damage to heat extraction devices. Furthermore, these new methods and systems need to achieve minimal disturbance of the overburden and monitor the environment to mitigate potential environmental impacts due to uncontrolled gas leaks and ground movement. Summary of the Invention

[0018] According to an embodiment, there is a heat extraction system for extracting heat from a reservoir, and the system includes a coaxial tool configured to be placed underground, the coaxial tool having an outer tube and an inner tube positioned within the outer tube, each of the outer tube and the inner tube being connected to a shoe so that fluid flows through an annular space defined by the inner and outer tubes, reaches the shoe, and flows through a bore of the inner tube. The system also includes a generator fluidly connected to a chemical processing unit to receive the fluid, and is also fluidly connected to the inner tube of the coaxial tool through a first port and to the outer tube of the coaxial tool through a second port. A temperature difference between the fluid at the generator and the coaxial tool drives the generator to generate energy.

[0019] According to a preferred embodiment of the present invention, the heat extraction system preferably further comprises:

[0020] a chemical processing unit configured to receive syngas from a burning coal seam located underground and to extract CO2 and H2 from the syngas; and

[0021] - a compressor fluidically connected between the chemical treatment unit and the generator to produce supercritical CO2 used as the fluid.

[0022] According to another embodiment of the invention, only the seat is configured to be placed in the coal seam.

[0023] According to another preferred embodiment of the present invention, the heat extraction system preferably further comprises an additional compressor, wherein the additional compressor is configured to pump air or oxygen into the coal seam for promoting combustion of the coal.

[0024] According to another embodiment of the present invention, the seat is made of a material capable of withstanding temperatures greater than 500° C., the outer tube is attached to the seat, the inner tube is concentrically located within the outer tube and forms the annular space with the outer tube, and the coaxial tool further comprises:

[0025] a flexible connection configured to connect the outer tube to the seat so that the outer tube is allowed to extend and contract without leaking the fluid in the annular space,

[0026] wherein the inner tube and the outer tube are configured to form an uninterrupted annular path for the fluid between the top of the annular space and the top of the hole, while also allowing the fluid to directly contact the seat. According to this embodiment, the coaxial tool further comprises:

[0027] - a filter element located between the inner tube and the seat; and

[0028] - an additional flexible connection between the inner tube and the filter element, wherein the annular path extends from the annular space to the bore through a plurality of apertures formed in the filter element.

[0029] According to another embodiment, there is a method for extracting heat from a reservoir, and the method includes placing one or more coaxial tools underground, the coaxial tools having an outer tube and an inner tube located within the outer tube, each of the outer tube and the inner tube being connected to a seat so that a fluid flows through the annular space of the inner tube and the outer tube, reaches the seat, and also flows through the bore of the inner tube, wherein only the seat is in contact with a coal seam located underground, fluidly connecting a generator to a chemical processing unit to receive the fluid, and also fluidly connecting a first port of the generator to the inner tube of the coaxial tool and a second port of the generator to the outer tube of the coaxial tool, and generating energy using the generator solely based on the temperature difference between the fluid at the generator and the coaxial tool.

[0030] According to a preferred embodiment of the present invention, the method may further include:

[0031] - fluidly connecting the production well to a chemical processing unit configured to receive syngas produced by burning the coal seam located underground and configured to extract CO2 from the syngas;

[0032] - separating the CO2 from the synthesis gas in the chemical processing unit; and

[0033] - compressing the CO2 to produce supercritical CO2 for use as the fluid

[0034] - circulating the supercritical CO2 through the annular space and the bore of the coaxial tool to reach the seat and extract heat from the burning coal seam; and

[0035] - Circulating heated supercritical CO2 through the generator to produce electrical energy.

[0036] - Extracting H2 from the synthesis gas using the chemical processing unit.

[0037] - injecting the supercritical CO2 into the cavity formed by replacing the burned coal seam; and

[0038] - A well sealed to the chamber for storing the CO2 underground.

[0039] According to another preferred embodiment of the present invention, the method may further include:

[0040] Air or oxygen is injected into the coal seam to sustain the combustion.

[0041] According to yet another embodiment, there is a heat extraction system for extracting heat from a reservoir, the system comprising: a coaxial tool configured to be placed underground, the coaxial tool having an outer tube and an inner tube positioned within the outer tube, the coaxial tool configured such that a fluid flows through an annular space between the inner and outer tubes, reaches a closed end of the outer tube, and also flows through a bore of the inner tube; and a generator fluidly connected to a chemical processing unit to receive the fluid, and also fluidly connected to the inner tube of the coaxial tool through a first port and to the outer tube of the coaxial tool through a second port. A temperature difference between the fluid at the generator and the fluid at the coaxial tool drives the generator to generate energy.

[0042] According to this further embodiment of the present invention, the heat extraction system may further comprise:

[0043] a chemical processing unit configured to receive syngas from a burning coal seam located underground and to extract CO2 and H2 from the syngas; and

[0044] - a compressor fluidly connected between the chemical processing unit and the generator,

[0045] To produce supercritical CO2 used as the fluid.

[0046] - an additional compressor configured to pump air or oxygen into the coal seam for promoting combustion of the coal.

[0047] In this further embodiment of the heat extraction system, the inner and outer tubes can be configured to be positioned obliquely relative to the vertical below the bottom of the coal seam. Furthermore, the inner and outer tubes can be configured to form an uninterrupted annular path for the fluid between the top of the annular space and the top of the bore, while also allowing the fluid to directly contact the closed end of the outer tube.

[0048] According to yet another embodiment, there is a method for extracting heat from a reservoir, and the method includes placing one or more coaxial tools underground, the coaxial tools having an outer tube and an inner tube located within the outer tube, and configured so that a fluid flows through the annular space between the inner tube and the outer tube, reaches the closed end of the outer tube, and also flows through the bore of the inner tube, fluidly connecting the generator to a chemical processing unit to receive the fluid, and also fluidly connecting a first port of the generator to the inner tube of the coaxial tool and a second port of the generator to the outer tube of the coaxial tool, and generating energy using the generator based solely on the temperature difference between the fluid at the generator and the coaxial tool. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to provide a more complete understanding of the present invention, the following description is now provided with reference to the accompanying drawings, in which:

[0050] Figure 1A and Figure 1B It shows the energy consumption in the world and the proportion of energy in the total energy consumed;

[0051] Figure 2A and Figure 2B The syngas compositions of different coals under UCG conditions using air or oxygen injection are shown;

[0052] Figure 3 The temperature model of the coal seam and other formations in the reservoir at different simulation times is shown;

[0053] Figure 4 A system for extracting heat and resources from a burning coal seam is schematically illustrated;

[0054] Figure 5 is a schematic diagram of a heat extraction tool having a seat for thermally protecting an inner tube and an outer tube;

[0055] Figure 6A is a schematic diagram of a seat of a heat extraction tool with a filter element, and Figure 6B is a schematic diagram of the seat without the filter element;

[0056] Figure 7 is a schematic diagram of another heat extraction tool having a seat for thermally protecting an inner tube and an outer tube;

[0057] Figure 8 is a schematic diagram of yet another heat extraction tool having a seat for thermally protecting an inner tube and an outer tube;

[0058] Figure 9 is a schematic diagram of yet another heat extraction tool having a seat for thermally protecting an inner tube and an outer tube;

[0059] 10A to 10C Various shapes of seats are shown;

[0060] Figure 11A Shows drilling for heat extraction tools, Figure 11B shows an arrangement where the heat extraction tool is advanced into the well so that only the seat enters the burning coal seam, and Figure 11C shows the closure of the well after the heat has been extracted and the heat extraction tool has been removed;

[0061] Figure 12 is by using a Figure 5A flow chart of a method of extracting heat from a subterranean reservoir using a tool of the seat shown;

[0062] Figure 13 A system for extracting heat from a burning coal seam underground using a tool without a seat is shown;

[0063] Figure 14 Another system for extracting heat from a burning coal seam underground using a tool without a seat is shown;

[0064] Figure 15 is a flow chart of a method for determining a configuration for extracting heat from a subsurface reservoir;

[0065] Figure 16 is by using a Figures 5 to 9 A flow chart of a method of extracting heat from a burning underground coal reservoir by a tool of the seat shown in any of the Figures; and

[0066] Figure 17 is a flow chart of a method of extracting heat from an inclined underground reservoir of burning coal using a tool located below the reservoir. DETAILED DESCRIPTION

[0067] The following embodiments are described with reference to the accompanying drawings. The same reference numerals in the different figures represent the same or similar elements. The detailed description below does not limit the invention. On the contrary, the scope of the invention is defined by the appended claims. For simplicity, the following embodiments are discussed with respect to a heat collection system comprising a coaxial tool provided with an end shoe for entering a high temperature reservoir to collect energy. The system can also be configured to extract and / or produce one or more raw materials for a chemical plant. However, the embodiments to be discussed next are not limited to coaxial tools with end shoes, but can be applied to other tools for extracting heat, such as tools without end shoes.

[0068] Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the disclosed subject matter. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0069] According to one embodiment, a novel system for extracting heat and raw materials from an underground coal oxidation process is described, and the system is configured to reduce the amount of pollution associated with traditional coal mining. The system is configured to capture heat generated in the UCG process using one or more coaxial tools, each having a seat end, and also to capture syngas generated by the UCG process, and to separate various raw materials from the syngas for industrial use, and includes the reinjection, recycling, and underground storage of greenhouse gases (GHGs) in the syngas that cannot be used for industrial purposes.

[0070] In one application, the system uses a complementary and adaptable solution to generate electricity by extracting heat from the ground using coaxial tools (e.g., a coaxial well in a cavity, a coaxial deviated well in the underlying rock formation, or a steel base of a serpentine well in the underlying rock formation). In one embodiment, the end products of the system are electricity from the underground heat and hydrogen from the syngas. Depending on commercial needs, other raw materials for the chemical industry, such as methanol, can also be extracted. The other syngas components will be reinjected into the ground. No greenhouse gases are emitted to the atmosphere.

[0071] The system can be implemented in different configurations. Techno-economic models based on thermal-hydraulic simulations allow the definition of the optimal system design for a given geological setting. These designs can be "adjusted" to the technologies used for UCG: with or without vertical shafts, controlled withdrawal injection points, connected vertical wells, integrated flow pipes in a single well, and methods relevant for high-angle coal seams.

[0072] The system may include multiple coaxial tools deployed in a well drilled into a reservoir. In one application, some or all of the coaxial tools are pushed into the ground without drilling a well. Different patterns can be used for multiple wells / tools to extract heat, i.e., the number and geographical distribution of tools across the reservoir can be calculated based on the parameters of the reservoir. Each coaxial tool in the well uses a closed loop working fluid flow (wherein there is no contact between (1) the rock mass and its components and coal and (2) the working fluid circulating in the well). Heat is extracted from the medium by conduction through the wellbore liner / outer pipe or a stainless steel seat along the bottom of the tool. Convection may occur in high permeability areas (cavities, permeable formations and fractures); this increases the transfer rate of extractable heat and allows the system to have better performance.

[0073] A range of working fluids can be used in the closed loop of the coaxial tool. However, in one application, supercritical CO2 (S-CO2) is used as the working fluid due to several advantages. CO2 is one of the components of syngas and appears to be a low-cost, local solution. The supercriticality of CO2 can be achieved above its critical temperature (31°C) and critical pressure (7.4 MPa). In addition, S-CO2 is chemically stable and non-flammable. S-CO2 is a promising candidate for use in the topping cycle of high-temperature equipment to improve thermal efficiency. In fact, high-temperature S-CO2 (>500°C) shows excellent system performance (>50% thermal efficiency), especially when used in the Brayton cycle, but can also be used in the Rankin cycle, combined gas turbine (CCGT) and supercritical CO2 direct and indirect cycles.

[0074] Various scenarios for extracting heat and / or raw materials from underground coal deposits will now be discussed with reference to the accompanying figures. Figure 4 A scenario is shown in which system 400 includes a chemical processing unit 410, one or more coaxial tools 420, and a generator 430. Chemical processing unit 410 is optional, as system 400 can extract heat without it. Generator 430 is fluidly connected to both chemical processing unit 410 and coaxial tool 420 via piping system 440. The generator may include a turbine driven by the S-CO2 stream and an alternator configured to convert the mechanical rotation of the turbine into electrical energy. Other devices may be used to utilize the thermal and / or kinetic energy of the S-CO2 stream, such as a heat exchanger in place of or in addition to generator 430. In one application, generator 430 is fluidly connected to the inner tube of coaxial tool 420 via a first port and to the annular space formed by the inner and outer tubes of coaxial tool 420 via a second port. Chemical processing unit 410 may include any known elements of a chemical plant for separating syngas into its primary components. The components of coaxial tool 420 will be discussed later.

[0075] Figure 4A coal seam or formation 401 of thickness H is shown, buried a distance h below the ground 402. The figure shows an overburden cap 403 and an underburden 404 above and below the coal seam 401, respectively. The figure also shows that a portion of the coal seam 401 has been burned, leaving a cavity 405. The cavity contains some ash 406 and syngas 407. An oxidant injection well 450 is drilled into the coal seam 401 on one side for supplying air or oxygen 452 to burn the coal. A compressor 453 can be used to pump the air or oxygen 452 into the well 450. On the other side away from the oxidant injection well 450, a product extraction well 454 is also drilled into the coal seam 401 for extracting the syngas 407. The product extraction well 454 is fluidly connected to a chemical processing unit 410.

[0076] Chemical processing unit 410 separates syngas 407 into its various components, such as CO2, H2, CO, CH4, etc. As described above, CO2 can be used as fluid 422 flowing into coaxial tool 420. Fluid 422 can be CO2, which is first converted to supercritical CO2 with the aid of, for example, compressor 412, and then injected into pipeline 440. A one-way valve 442 can be present in pipeline 440 to ensure that the supercritical CO2 flows along the desired path, i.e., from generator 430 to the inner tube of coaxial tool 420, and back to the generator through the annular space formed by the inner and outer tubes of tool 420. This flow direction can be reversed, with the supercritical CO2 first entering the annular space, continuing into the coal seam, and then upward through the bore of the inner tube. In this way, the supercritical CO2 flow continues to power the generator as long as heat is extracted from coal seam 401. After the compressor 412 starts the S-CO2 flow, the flow is self-sustaining even if the compressor is shut down (valve 412A is closed) because the temperature difference T2-T1 maintains the flow, where T1 is the temperature of the S-CO2 flow at the generator 430 and T2 is the temperature of the S-CO2 flow at the bottom of the coaxial tool 420. It is noted that the temperature difference T2-T1 can be about 500°C or more.

[0077] The CO produced in the chemical processing unit 410 can be treated with oxygen from the oxygen source 414 to increase the amount of available CO2 so that enough CO2 can be pumped through the pipeline 440 to fill the one or more coaxial tools 420. At the end of the process, that is, when the coal seam 401 has been completely burned, the spent CO2 can be injected back into the cavity 405 so that no CO2 is released into the atmosphere. It is important to note that Figure 4It is shown that as the coal combustion progresses, there are various temperature zones in the chamber 405, such as a drying and pyrolysis zone A, where the temperature is about 200°C to 550°C; a reduction zone B, where the temperature is about 550°C-900°C; and an oxidation zone C, where the temperature is above 900°C.

[0078] In one application, the coaxial tool 420 is installed before the coal is burned and remains in place during the burning process. Figure 4 As shown, the tool's base is inserted into the coal seam to be burned. Depending on the mechanical strength of the coal, depth, and technical challenges, a pre-drilled hole can be drilled, or if the coal is sufficiently soft, the base can be pushed into the coal. Coring the coal seam prior to gasification provides a better understanding of the coal's characteristics, including composition, porosity, thermal properties, and other relevant parameters. This deeper understanding of coal characteristics provides valuable insights into its behavior during the gasification process.

[0079] In one application, the wellbore is completely encased and isolated from the overburden rock mass. Cementation is not required, and depending on the specific operational characteristics of the site, the system can be removed after treatment if placed in an appropriate outer casing (in this case, as described below, the outer casing seat must be above the coal seam). The seat is in direct contact with the coal to be burned. This makes the system more resilient to potential damage caused by ultra-high temperatures and the corrosive processes that occur during combustion. The seat is designed to withstand thermomechanical strains caused by thermal stresses, ground movement during the connection process, and roof spalling. The seat is made of an alloy that must withstand high temperatures (up to 1000°C), corrosive environments, thermal stresses, burst strength, and sufficient thermal conductivity at the relevant temperatures. At very high temperatures, thermal stability is a primary consideration, as this may limit specific alloy types from the perspective of softening or, more commonly, embrittlement, and may result in changes in thermal properties (particularly thermal conductivity). It is important to note that since the seat is not a supporting element but merely a heat transfer tool, it is allowed to accommodate large deformations. Therefore, creep rupture strength at high temperatures is the basis for alloy selection.

[0080] Now refer to Figure 5Discussion of the coaxial tool 420. The coaxial tool 420 (also referred to herein as a "well tool" or "tool" or "heat extraction tool") includes an inner tube 510, an outer tube 520 concentric with the inner tube 510, and an end seat 530. The outer tube 520 is connected to the end seat 530 by a first flexible connector 540, and the inner tube 510 is connected to the end seat 530 by a second flexible connector 541. The flexible connector 540 / 541 is any connector between two different elements that allows one or both elements to expand due to thermal reasons while maintaining the integrity of the fluid flow through the connector, i.e., without leaking the fluid. An example of such a flexible connector is described in International Patent Application

[22] , which is incorporated herein by reference. The flexible connector 540 / 541 allows two connected elements (e.g., 510 and 530 or 520 and 530) to achieve a fluid connection that can expand when the temperature rises without causing the fluid to collide or leak to the outside.

[0081] It should be noted that, in order to achieve connection with the outer tube 520, in one embodiment, as Figure 6A and Figure 6B As shown, the seat 530 has a thread 610 on the outer surface 532 near the top surface 536. In order to achieve the connection with the inner tube 510, Figure 6A In the embodiment of the present invention, the seat 530 further comprises a filter element 550, which is made integrally with the main body 531 of the seat. The filter element 550 is formed as a sleeve having an inner hole, and the side wall of the sleeve has a plurality of holes 552. Figure 6B In the embodiment of FIG. 5 , to achieve connection with the inner tube, the seat portion 530 has a shoulder portion 534 protruding from its top surface 536. In addition to the threads 610 formed on the side surface 532 of the body 531, threads 610 are also formed on the side surface 534A of the shoulder portion 534. Those skilled in the art will understand that this embodiment is only one of many possible embodiments of the flexible connector 540.

[0082] return Figure 5, when a filter element 550 is present, the inner tube 510 can be connected to the filter element 550 by a further flexible connector 541. As described below, there are embodiments in which the filter element 550 is omitted. The filter element 550 can be a tube having the same inner and / or outer diameter as the inner tube 510 and a plurality of orifices 552 for allowing a fluid 554 to exit the annular space 512 formed by the outer surface of the inner tube 510 and the inner surface of the outer tube 520 and enter the bore 514 of the inner tube 510. In this way, the fluid 554 can be pumped from the ground into the annular space 512, allowed to directly contact the seat 530, and then returned to the ground through the bore 514 while carrying with it the heat transferred from the seat. Thus, a loop or path 556 is formed from the top of the annular space 512 to the seat 530 and then to the top of the bore 514. In some cases, the direction of flow along the loop can be the same as Figure 5 The reverse is shown. It is important to note that the top 558 of the tool 420 corresponds to the portion of the tool that is configured to attach to a casing element before being lowered into the well or pushed into the ground. This means that the top 558 of the tool 420 can have threads 559 for attaching to the casing element. Thus, the inner tube 510 and the outer tube 520 are configured to form an uninterrupted annular path 556 for the fluid 554 between the top of the annular space 512 and the top of the bore 514, while also allowing the fluid 554 to directly contact the seat 530.

[0083] exist Figure 5 In the illustrated embodiment, the seat is solid, meaning that, aside from the filter element 550 having the orifice 552, the seat body 531 has no orifices or channels. The body and filter can be made from a single piece of material. The seat is made from a metal or alloy capable of withstanding high temperatures (e.g., between 500°C and 1200°C) and / or high pressures (e.g., up to 20 MPa). In one application, the seat is made from tungsten or titanium. In another application, where the price of the seat is as low as possible, high-quality alloys can be used. For example, stainless steel is initially considered, as it offers a good balance between price and resistance to extreme environments, particularly alloys commonly used in thermal reactors and combustion chambers, which have high tensile strength at high temperatures. Alloys including chromium, aluminum, and titanium offer good resistance to extreme conditions (high-temperature deformation and corrosion mechanisms). It should be noted that the cost increases with increasing alloy grade.

[0084] In another embodiment, Figure 7 As shown, the filter element 550 may be omitted (i.e., using Figure 6B530 shown), and the orifice 552 can be formed directly in the lower part of the inner tube 510. In this case, the flexible connection 541 between the inner tube and the filter element does not exist because the inner tube is directly connected to the seat 530, but has the flexible connection 541 shown in the figure.

[0085] In yet another embodiment, Figure 8 As shown, the inner tube 510 is fixedly attached to the outer tube 520 via one or more lugs 810. In this case, the lower end 510A of the inner tube 510 is located above the seat 530, so that a free path 556 exists for the fluid 554 from the annular space 512 to the bore 514. In other words, in this embodiment, the filter element 550 and the orifice 552 associated with the end seat 530 are not present. The lugs 810 can also be used in the previous embodiment to fix the inner tube relative to the outer tube. However, in the previous embodiment, it is also possible for the inner tube to be independent of the outer tube, that is, the inner tube and the outer tube do not contact each other through any components other than the filter element and / or the seat.

[0086] In yet another embodiment, Figure 9 As shown, the inner tube 510 is directly connected to the seat 530, for example, by a flexible connection 541, and there is no orifice 552 in the inner tube. For this embodiment, a Figure 6B The configuration of the seat 530 shown. Therefore, for this embodiment, there is no direct fluid flow from the annular space 512 to the bore 514. In this case, there are a plurality of channels 910 formed through the body of the seat 530, the plurality of channels 910 fluidly connecting the annular space 512 to the bore 514 so that the fluid flow 556 still flows from the annular space to the bore, but through the body of the seat. In this case, when the fluid effectively enters the seat, it is expected that the fluid will remove more heat from the body of the seat. Although all of the above embodiments show flexible connections 540 / 541 between the inner tube, outer tube and end seat, those skilled in the art will understand that non-flexible connections can also be used, even if there are fluid leaks. It is to be noted that for all of the above embodiments, the seat simply comprises a solid body with no other components (i.e. no orifices, channels, valves, etc.). Only Figure 9 The embodiment presents an additional structure, namely channel 910.

[0087] Regarding the shape of the seat 530, the previous embodiment shows that the seat is shaped like a bullet, for example, the maximum outer diameter of the seat matches the outer diameter of the outer tube, and as shown in FIG. Figure 5 The body is shown with an apex 538. The length of the body (i.e., from shoulder 534 to apex 538) can be selected based on the width of the reservoir to be explored. Figure 5In the illustrated embodiment, the length of the filter element 550 is selected based on the diameter of the well in which the tool 420 is placed.

[0088] In one application, such as Figure 10A As shown, the body 531 of the seat 530 has a spiral portion 533 extending along the length of the seat. The spiral portion can be added or formed into the body 531 to facilitate advancement of the seat into the ground when a well has not been pre-drilled for lowering the tool 420. It should be noted that if the ground is soft, the tool 420 can be lowered into a pre-drilled well or pushed into the ground. Figure 10B Another embodiment is shown in which the seat 530 is in the shape of a smooth cone. Figure 10C Yet another embodiment is shown in which the seat 530 is cylindrical in shape 1010 and has a pointed end 1012, such as a cone. Those skilled in the art will appreciate that other shapes may also be used.

[0089] When it is desired to use tool 420 (eg Figures 11A to 11C ), before lowering (pushing) the tool into the ground, in step 1200 (see Figure 12 Various data (e.g., seismic surveys, or information obtained during drilling, etc.) are collected in the flowchart of the process. Figures 11A to 12 The use of a single tool 420 is discussed, but the same procedure can also be used Figure 4 Based on the collected information, the upper boundary of the coal seam 401 is determined. In step 1202, the well 1102 is drilled to the top of the coal seam, as shown in FIG. Figure 11A As shown, then, in step 1204, the tool 420 is lowered (or pushed if no well has been pre-drilled) into the well 1102 until the seat 530 directly contacts the coal seam. Figure 11BAs shown, only the seat is in direct contact with the coal seam, while the inner and outer pipes are not in contact with the coal seam. This makes the system 1100 more resilient to potential damage caused by corrosion processes occurring in ultra-high temperature and high temperature fluids. The seat 530 is designed to resist thermo-mechanical strains generated during heat extraction due to thermal stresses and ground movements. As mentioned above, the seat can be made of an alloy that is resistant to high temperatures (up to 1000°C), corrosive environments, thermal stresses, burst strength and has sufficient thermal conductivity at the relevant temperatures. At very high temperatures, thermal stability is the first factor to be considered, as this may limit the specific type of alloy from the perspective of softening or embrittlement, and changes in thermal properties (such as thermal conductivity) with temperature changes. It is important to note that since the seat is not a supporting element of the tool 420, but only a heat transfer element, the seat is allowed to accommodate large deformations. In other words, the tool 420 is supported inside the well 1102 by a corresponding casing 1110, which can include multiple casing elements connected to each other, as shown in FIG. Figure 11B As shown. The casing element can have a length of about 12m. Tool 420 can have a similar or smaller length. As is known in the art, multiple casing elements can be connected to each other by threads. Tool 420 can be connected to the lower end of the last casing element by threads.

[0090] The high thermal conductivity of the alloy at high temperatures allows heat to be transferred from the metal seat 530 to the coaxial tubes 510 / 520. Thermal hydraulic numerical simulations were performed to optimize the design of the tool and the corresponding wells (seat length and diameter, well diameter, number and location of coaxial well systems with seats).

[0091] Figure 11A Surface casing 1104 and sacrificial casing 1106 are shown installed in a well 1102 drilled by a drill string 1108. Note that both casings are installed above the coal seam. The drill string 1108 may have a drill bit 1109 for drilling the well 1102. A rotary table 1112 mounted at the surface of the well drives the drill bit. When the well is ready, the drill bit 1109 and drill string 1108 are removed and the tool 420 is lowered into the well, as shown in FIG. Figure 11B To align the tool 420 with the longitudinal axis of the well 1102, a centering device 1114 may be mounted on the tool 420, as shown in the figure. Figure 11BAs shown, to prevent fluids from the coal seam from entering the casing 1106, a packer 1116 may be installed, for example, just above the seat 530. For safety reasons, to prevent a violent release of fluids from the well 1102 or the casing 1110 to the surface, a blowout preventer 1118 may be installed at the wellhead. The blowout preventer 1118 is essentially a powerful valve that is configured to close (seal) the well if the pressure in the well becomes greater than a given pressure. In one application, the annular space between the sacrificial casing 1106 and the coaxial tool 420 is filled with a suitable viscous gel that ensures thermal insulation of the heat extraction tool while limiting thermal stresses on the sacrificial casing and its cement.

[0092] After the heat of the coal seam has been extracted in step 1206 (which may take months or even years), the CO2 can be stored in the chamber 405 and then used as described in the following example, just before the casing 1110 and associated tools 420 are removed from the well in step 1208. Figure 11C As shown, well 1102 is sealed with a cement plug 1120 in step 1210. This minimizes the likelihood that any fluid in the well will escape to the surface after the well is abandoned. Abandonment occurs when, after a certain period of time (depending on the ultra-high heat source), the heat at the seat is no longer sufficient to be economically extracted, and the coaxial tool with the seat can be removed if such a design has been selected. Abandonment design will take into account the predicted effective duration of the heat source, which can be a coal or peat fire, underground coal gasification, or a thin rock vein or bedrock.

[0093] The intelligent and safe implementation of this technology can be matched with monitoring methods, for example, with a specific focus on the temperature, pressure, and mechanical behavior of the tool and the host rock mass. Depending on the nature of the coal seam or UCG, additional specific monitoring may be required. For example, a distributed acoustic sensing (DAS) system 1103 bonded behind a sacrificial casing 1106 would allow monitoring of the temperature and pressure at the interface between the rock mass and the tool, while a DAS fiber inserted into the coaxial tool 420 and fixed to the inner or outer tube would provide temperature and pressure variations with depth in the coaxial loop. In one application, such as Figure 11A As schematically shown in FIG, a network of seismic sensors 1130 at the surface (or buried in a noisy environment) provides an additional system to detect and locate the potential creation of faults and fractures due to induced thermal stresses or shearing. This network can also be used to determine the location of the coal seam and ensure that only the seat 530 enters the coal seam, and not the inner and outer pipes.

[0094] By using the novel combination of technologies disclosed herein, large amounts of hydrogen and heat generated by the underground oxidation of coal can be collected from syngas 407 without releasing harmful emissions into the atmosphere. This opens the door to a greener use of the world's abundant coal resources. The technologies discussed herein can be configured to optimize the capture of heat generated during underground coal oxidation and then present in rocks or fluids, for example, by determining how many wells 1102 are needed for a given coal seam 401, as well as the distribution of wells on the coal seam 401, and the implicit tools 420. The captured heat can provide all the electricity needed to meet the needs of on-site operations, including drilling, pumping, measuring, monitoring and verification, and the processing of hydrogen. This means that these technologies can be applied on a stand-alone basis and do not require additional use of hydrogen to meet the energy needs of the site. Excess electricity can be used locally for industrial activities or supplied to the power grid.

[0095] The delivery of hydrogen can be optimized based on local market conditions, for example, by transporting it via pipeline, compressing and cooling it for output as a liquid, or converting it into ammonia for output as fuel or fertilizer. One or more benefits of one or more embodiments discussed herein for industries currently burning coal is that these existing facilities do not need to be shut down, as rapid technological advances indicate that coal-fired power plants can be converted to burn hydrogen, while cement manufacturing and steel production can utilize hydrogen and green energy.

[0096] Although Figure 4 and Figures 11A to 11C The embodiment shows the process of extracting heat directly from the coal seam 401, but in Figure 13 In another embodiment shown, heat can be extracted from the underlying rock formation of the coal seam. More specifically, Figure 13 A well 1302 is shown drilled beneath a coal seam 401, where the well makes a non-zero angle α with the horizontal plane XY when the coal seam is inclined. However, this method can also be used when the coal seam is not inclined. In this case, heat is extracted from the layer of material below the hot, burning coal seam, and therefore, tool 420 is modified (shown as tool 1320) to not have seat 530. In addition, tool 1320 has a closed distal end 520A of the outer tube 520, so that fluid from inside the outer tube or the inner tube does not communicate with well 1302. Only inner tube 510 and outer tube 520 are present in well 1302, and fluid 422 circulates from the bore of the inner tube to the annular space between the two tubes, and vice versa. The fluid reaches the bottom of well 1302 and absorbs heat from the tubes as it flows through them. The coal seam 401 is combusted with the aid of an oxidant 452 injected at an oxidant injection well 450 , and syngas 407 is extracted at a product extraction well 454 and processed in a chemical processing unit 410 .

[0097] In one application, a well 1302 is drilled prior to gasification. The upper portion of the well 1302 can be isolated from the overburden rock using insulating grout 1304. The bottom of the well 1302 (below the future cavity 405) can be cemented using heat enhanced grout 1306. As described above, the working fluid 422, which can be supercritical CO2 from the syngas 407, is injected through the inner tube 510 and pumped out through the annular space formed between the inner tube 510 and the outer tube 520. The trajectory of the lower portion of the well (where heat will be collected) depends on the UCG method. When gasification involves a method based on vertical wells 450 and 454, such as Figure 13 Schematically, heat extraction is performed using a deviated coaxial tool 1320. Note that while this figure shows a single deviated well and a single tool 1320, multiple deviated wells and multiple tools 1320 may also be used. The trajectory of the tool 1320 is parallel to the inclination of the coal seam 401 and is located below the future cavity 405 created by the UCG process.

[0098] If the CRIP method is used to achieve gasification, another design can be used to collect heat from the well 1402. In this case, if Figure 14 As shown, system 1400 is based on a serpentine trajectory drilled in the underburden 404 in a plane 1410 parallel to the bottom wall 1412 of the coal seam 401 . Figure 14 A coal seam 401 is shown inclined at a non-zero angle α relative to the horizontal XY plane, and a cavity 405 is formed within the coal seam due to the combustion of the coal. As shown, the oxidant injection well 450 and the product extraction well 454 are offset from the vertical. In one application, all of the wells 450, 454 and 1402 are formed in a plane 1410 that extends generally parallel to a plane 1414 of a bottom wall 1412 that defines the cavity 405. It is noted that both planes 1410 and 1414 are angularly offset from the XY horizontal plane by an angle α. However, in another embodiment, it is possible that plane 1410 is offset by an angle α and plane 1414 is offset by an angle α' that is different from angle α. In one application, the horizontal portions of the wells 450, 454 and 1402 do not lie in the same plane, but rather lie in two or more different planes.

[0099] Wells 450 and 454 in Figure 14 1402 is shown as following a curved trajectory, i.e., starting from the vertical direction and then slowly turning to the horizontal direction, but both follow a straight line along the vertical portion and along the horizontal portion. However, well 1402 is different because well 1402 forms a serpentine shape in plane 1410, i.e., well 1402 does not follow a straight line. After leaving the vertical direction, the shape of well 1402 can also follow the shape of the letter "S" or other curved contours, for example, a coil shape with any number of loops. In one application, Figure 14The embodiment shown is used with a controlled retraction injection point method, which means that the injection point of the fluid 452 is moved along the direction 1420 in the figure, which extends the combustion zone of the coal seam. For this configuration, the well 1402 is configured to accommodate the tool 1320, which includes the above-mentioned Figure 5 The inner tube 510 and outer tube 520 discussed above are shown in FIG. 1 , but without the seat 530. In other words, the construction of the tool 1320 in this embodiment may be similar to that of the tool 1320 in FIG. Figure 13 However, in one embodiment, tool 420 may be used instead of tool 1320.

[0100] Clean and safe implementation of these techniques requires appropriate risk assessment and risk mitigation. In particular, the following risks must be closely monitored: groundwater contamination, gas leakage, and ground movement. With respect to groundwater contamination, depending on the geological and hydrogeological circumstances, contaminating elements included in the combustion ash 406 may be leached by groundwater following cavity flooding due to groundwater ingress. In one application, risk mitigation is based on maintaining the cavity pressure below the static pressure of the surrounding fluid to help retain the contaminated fluid within the cavity. With respect to gas leakage, during and after coal oxidation, if the cavity is not confined by impermeable overburden, or if a discontinuity provides a permeable connection from the cavity to the overburden and / or ground, there is a risk of gas release into the overburden and atmosphere. Therefore, these factors should be monitored. With respect to ground movement, depending on the geological circumstances, including the depth and thickness of the target coal seam, subsidence may be encountered. To mitigate this risk, a system of pillars and cavities may be used.

[0101] In addition to properly designing operations to prevent these risks, these locations also need to be monitored to prevent risks. In one application, the above description of Figure 11A The DAS systems discussed are, for example, cemented behind the casing of the various wells (production and injection wells, but also including coaxial tools with seats and coaxial serpentines). These systems allow monitoring of temperature (to monitor and control heat extraction), pressure (to maintain the decompression of the cavity relative to the surrounding aquifer), and seismic activity (which can indicate the creation or shearing of faults and fractures, which could be pathways for gas leakage).

[0102] In addition, a network of seismic sensors can be used on the ground (see Figure 11AThe network 1130) (buried in a noisy environment) can be used as an additional system to detect and locate the creation or shearing of faults and fractures. Other possible risk prevention methods include time-lapse gravity and electromagnetic (EM) surveys to "visualize" the location and size of underground cavities. Depending on the geological situation, methods using active sources such as CSEM (controlled source electromagnetic) can provide good reproducibility, allowing the evolution of cavities over time to be measured, and / or the use of interferometric synthetic aperture radar (INSAR) and other geodetic sensors to monitor ground movement.

[0103] Now we discuss the methods for optimizing the design of heat extraction and monitoring systems. The optimization of heat extraction design is based on hydrothermal numerical simulations, including site-specific data, and using a general design that is adjusted to suit the environment, thereby fast-tracking the workflow. The monitoring design is included in Figure 15 The method includes step 1500 of receiving site-specific data, such as one or more of a geological model, petrochemical properties, thermal properties, and the like. In step 1502, additional data may be stored in a property database, such as coal-related properties, combustion rate, oxygen content, and the like. Missing parameters in the various models are populated using data from the property database. In step 1504, one or more general models (e.g., monitoring system, test design) are input into the system by the operator of the coal seam. In step 1506, adjustments to the site-specific conditions may be performed based on the actual conditions of the site (e.g., geometry, geology, UCG design (if predefined), rock physics, and thermal properties (if available)). In step 1508, various hydrothermal simulations are performed on the site based on the input data. In step 1510, an estimate of the energy generated is calculated, for example, based on the number of wells in tool 420, the material used in tool 420, the depth of the tool, and the like. In step 1512, the results of these simulations are compared to the other designs received in step 1504, and adjustments are made to the site-specific conditions in step 1514. Finally, in step 1516, the monitoring system and extraction design are optimized, and a final design is generated.

[0104] Because of the very high temperatures involved, the above simulations can be run using a fully coupled hydrothermal software multiphase (liquid and gas) flow model. The fluid can flow in the rock matrix, faults / fractures (if any), and cavities. The predefined generic model received in step 1504 can involve generic geology (horizontal and inclined coal seams) at an appropriate depth (e.g., 1 km) and generic rock physical and thermal properties based on the range of data available in the relevant database.

[0105] The techniques discussed above can be implemented as various methods in the art. For simplicity, only two such methods are discussed herein, but those skilled in the art will appreciate that variations of these methods are also possible. Figure 4 This configuration can be used to generate electrical energy at the generator 430 based solely on the temperature difference between the fluid 422 at the seat 530 (temperature T2) and the fluid 422 at the generator 430 (temperature T1, which is less than T2).

[0106] More specifically, if Figure 16 Schematically illustrated, a method for extracting heat from a reservoir 401 includes a step 1600 of placing one or more coaxial tools 420 underground, the coaxial tools 420 having an outer tube 520 and an inner tube 510 positioned within the outer tube 520. Each of the outer tube 520 and the inner tube 510 is connected to a seat 530 such that fluid flows through an annular space 512 between the inner and outer tubes, reaches the seat 530, and then flows through the bore 514 of the inner tube 510, wherein only the seat 530 is in contact with the coal seam 401 located underground. Note that the flow can be reversed, i.e., the fluid first flows through the bore 514, contacts the seat 530, and then flows upward through the annular space 512.

[0107] In optional step 1602, production well 454 is fluidly connected to chemical processing unit 410, which is configured to receive syngas 407 produced by burning a coal seam located underground, and is also configured to extract CO2 from syngas 407. It should be noted that the chemical processing unit can be a refinery, a chemical plant, etc. In step 1604, generator 430 is fluidly connected to chemical processing unit 410 to receive fluid 422. The generator is also fluidly connected to inner tube 510 of coaxial tool 420 via a first port and to outer tube 520 of coaxial tool 420 via a second port 430B. In step 1606, the generator generates electrical energy based solely on the temperature difference between the fluid 422 at generator 430 and coaxial tool 420.

[0108] The method may further include the steps of separating CO2 from the syngas in the chemical processing unit, and compressing the CO2 to prepare supercritical CO2 for use as a fluid. The method may further include the steps of circulating the supercritical CO2 through the annular space and the bore of the coaxial tool to reach the seat and extract heat from the burning coal seam, and circulating the heated supercritical CO2 through a generator to produce electrical energy. Optionally, the method may include the steps of injecting air or oxygen into the coal seam to maintain combustion, and / or extracting H2 from the syngas using a chemical processing unit. When the method is deemed no longer economically viable, the method may include the steps of injecting supercritical CO2 into a cavity formed in place of the burned coal seam, and sealing a well connected to the cavity to store the CO2 underground.

[0109] Figure 13 and Figure 14 The construction shown can now be Figure 17 The method for extracting heat from a reservoir includes a step 1700 of placing one or more coaxial tools 1320 underground, the coaxial tools 1320 having an outer tube 520 and an inner tube 510 positioned within the outer tube 520 and configured such that a fluid 422 flows through the inner tube and the annular space 512 between the outer tube, reaches the closed end 520A of the outer tube 520, and then flows through the bore 514 of the inner tube 510. The fluid flow can be reversed, i.e., first flowing through the bore 514 and then through the annular space 512.

[0110] In step 1702, production well 454 is fluidly connected to chemical processing unit 410, which is configured to receive syngas 407 generated by burning a coal seam located underground and to extract CO2 from syngas 407. Note that this step is optional. In step 1704, generator 430 is fluidly connected to chemical processing unit 410 to receive fluid 422, and is also fluidly connected to inner tube 510 of coaxial tool 1320 via a first port of the generator, and is fluidly connected to outer tube 520 of coaxial tool 1320 via a second port of the generator. In step 1706, energy is generated using the generator based solely on the temperature difference between fluid 422 at the generator and at the coaxial tool.

[0111] The method may further comprise the steps of deploying the coaxial tool in a plane below the bottom of the coal seam and the plane being at a non-zero angle to the horizontal and / or deploying the coaxial tool to follow a serpentine line in the plane.

[0112] The term "about" as used in this application refers to a variation of up to 20% of the parameter characterized by the term. It should be understood that although the terms first, second, etc. can be used to describe various elements here, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, without departing from the scope of this disclosure, a first object or step can be referred to as a second object or step, and similarly, a second object or step can be referred to as a first object or step. The first object or step and the second object or step are both objects or steps, but they cannot be considered to be the same object or step.

[0113] The terms used in the description herein are intended to describe specific embodiments and are not intended to be limiting. As used in this specification and the appended claims, the singular forms "a" and "the" are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "and / or" used herein refer to and include any possible combination of one or more of the relevant listed items. It will also be understood that the terms "include" and / or "comprising" when used in this specification specify the presence of stated features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof. In addition, as used herein, the term "if" may be interpreted to mean "when..." or "under..." or "in response to determining..." or "in response to detecting," depending on the context.

[0114] The disclosed embodiments provide various methods for placing one or more coaxial tools with or without seats in a reservoir to extract heat when the reservoir exhibits one or more extreme parameters (such as high temperature). It should be understood that this description is not intended to limit the present invention. On the contrary, these embodiments are intended to cover replacements, modifications and equivalents within the spirit and scope of the present invention as defined by the appended claims. In addition, in the detailed description of the embodiments, many specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, it will be understood by those skilled in the art that the various embodiments may be practiced without these specific details.

[0115] Although features and elements of the embodiments are described in particular combinations in the embodiments, each feature or element can be used alone without the other features and elements of the embodiments, or in various combinations with or without the other features and elements disclosed herein.

[0116] This written description uses examples of the disclosed subject matter to enable any person skilled in the art to practice the subject matter, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims.

[0117] References

[0118] All publications listed herein are incorporated by reference into this patent application in their entirety.

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Claims

1. A heat extraction system (400) for extracting heat from a reservoir, the system comprising: a coaxial tool (420) configured to be placed underground, the coaxial tool (420) having an outer tube (520) and an inner tube (510) located within the outer tube (520), each of the outer tube (520) and the inner tube (510) being connected to a seat (530) so that a fluid flows through an annular space (512) defined by the inner tube and the outer tube, reaches the seat (530), and flows through a hole (514) of the inner tube; and a generator (430) fluidly connected to the chemical processing unit (410) to receive the fluid (422) and also fluidly connected to the inner tube (510) of the coaxial tool (420) through a first port and fluidly connected to the outer tube (520) of the coaxial tool (420) through a second port, The temperature difference between the fluid (422) at the generator (430) and the coaxial tool (420) drives the generator (430) to generate energy.

2. The heat extraction system according to claim 1, further comprising: a chemical processing unit (410) configured to receive syngas (407) from a burning coal seam located underground and to extract CO2 and H2 from the syngas (407); as well as A compressor is fluidly connected between the chemical processing unit and the generator to produce supercritical CO2 for use as the fluid.

3. The heat extraction system according to claim 1, wherein: Only the seat is configured to be placed in the coal seam.

4. The heat extraction system of claim 1 , further comprising: An additional compressor (453) is configured to pump air or oxygen into the coal seam for promoting combustion of the coal.

5. The heat extraction system according to claim 1, wherein: The seat (530) is made of a material capable of withstanding a temperature greater than 500° C., the outer tube (520) is attached to the seat (530), the inner tube (510) is concentrically located within the outer tube (520) and forms the annular space (512) with the outer tube (520), and the coaxial tool further comprises: a flexible connector (540) configured to connect the outer tube (520) to the seat (530) such that the outer tube (520) is allowed to extend and contract without leaking the fluid (422) within the annular space (512), Wherein, the inner tube (510) and the outer tube (520) are configured to form an uninterrupted annular path (556) for the fluid (422) between the top of the annular space (512) and the top of the hole (514), while also allowing the fluid (420) to directly contact the seat (530).

6. The heat extraction system according to claim 5, wherein: The coaxial tool also includes: a filter element (150) located between the inner tube and the seat; and an additional flexible connection between the inner tube and the filter element, wherein the annular path extends from the annular space to the bore through a plurality of apertures formed in the filter element.

7. A method for extracting heat from a reservoir, the method comprising: placing one or more coaxial tools (420) underground (1600), the coaxial tool (420) having an outer tube (520) and an inner tube (510) located inside the outer tube (520), each of the outer tube (520) and the inner tube (510) being connected to a seat (530) so that a fluid flows through an annular space (512) between the inner tube and the outer tube, reaches the seat (530), and also flows through a hole (514) of the inner tube (510), wherein only the seat (530) is in contact with a coal seam (401) located underground, Fluidly connecting (1604) a generator (430) to a chemical processing unit (410) to receive a fluid (422), and also fluidly connecting a first port of the generator (430) to the inner tube (510) of the coaxial tool (420) and fluidly connecting a second port of the generator (430) to the outer tube (520) of the coaxial tool (420); and Energy (1606) is generated using the generator (430) based solely on the temperature difference of the fluid (422) at the generator (430) and at the coaxial tool (420).

8. The method according to claim 7, further comprising: fluidly connecting (1602) the production well (454) to a chemical processing unit (410) configured to receive syngas (407) produced by burning the coal seam located underground, and configured to extract CO2 from the syngas (407); separating the CO2 from the syngas in the chemical processing unit; and The CO 2 is compressed to produce supercritical CO 2 for use as the fluid.

9. The method according to claim 8, further comprising: circulating the supercritical CO2 through the annular space and the bore of the coaxial tool to reach the seat and extract heat from the burning coal seam; and The heated supercritical CO2 is circulated through the generator to produce electrical energy.

10. The method according to claim 7, further comprising: Air or oxygen is injected into the coal seam to sustain the combustion.

11. The method according to claim 8, further comprising: H2 is extracted from the syngas using the chemical processing unit.

12. The method according to claim 8, further comprising: injecting the supercritical CO2 into the cavity formed by replacing the burned coal seam; as well as A well is sealed to the chamber for storing the CO2 underground.

13. A heat extraction system (1300, 1400) for extracting heat from a reservoir, the system comprising: a coaxial tool (1320) configured to be placed underground, the coaxial tool (1320) having an outer tube (520) and an inner tube (510) located within the outer tube (520), and configured such that a fluid (422) flows through an annular space (512) between the inner tube and the outer tube, reaches a closed end (520A) of the outer tube (520), and also flows through a hole (514) of the inner tube (510); and a generator (430) fluidly connected to the chemical processing unit (410) to receive the fluid (422) and also fluidly connected to the inner tube (510) of the coaxial tool (420) through a first port and fluidly connected to the outer tube (520) of the coaxial tool (420) through a second port, The temperature difference between the fluid (422) at the generator (430) and the coaxial tool (420) drives the generator (430) to generate energy.

14. The heat extraction system of claim 13, further comprising: a chemical processing unit (410) configured to receive syngas (407) from a burning coal seam located underground and to extract CO2 and H2 from the syngas (407); as well as A compressor is fluidly connected between the chemical processing unit and the generator to produce supercritical CO2 for use as the fluid.

15. The heat extraction system of claim 13, wherein: The inner tube and the outer tube are configured to be placed obliquely relative to the vertical direction below the bottom of the coal seam.

16. The heat extraction system of claim 13, further comprising: An additional compressor (453) is configured to pump air or oxygen into the coal seam for promoting combustion of the coal.

17. The heat extraction system of claim 13, wherein: The inner tube (510) and the outer tube (520) are configured to form an uninterrupted annular path (556) for the fluid (422) between the top of the annular space (512) and the top of the hole (514), while also allowing the fluid (422) to directly contact the closed end (520A) of the outer tube.

18. A method for extracting heat from a reservoir, the method comprising: placing one or more coaxial tools (1320) underground (1700), the coaxial tool (1320) having an outer tube (520) and an inner tube (510) located within the outer tube (520), and configured such that a fluid (422) flows through an annular space (512) between the inner tube and the outer tube, reaches a closed end (520A) of the outer tube (520), and also flows through a bore (514) of the inner tube (510); fluidly connecting (1704) a generator (430) to a chemical processing unit (410) to receive the fluid (422), and also fluidly connecting a first port of the generator (430) to the inner tube (510) of the coaxial tool (1320) and fluidly connecting a second port of the generator (430) to the outer tube (520) of the coaxial tool (1320); and Energy (1706) is generated using the generator (430) based solely on the temperature difference of the fluid (422) at the generator (430) and at the coaxial tool (1320).

19. The method according to claim 18, further comprising: The coaxial tool is deployed in a plane below the bottom of the coal seam and the plane is at a non-zero angle with the horizontal.

20. The method according to claim 19, further comprising: The coaxial tool is deployed to follow a serpentine line in the plane.

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