Distributed enhanced mining test platform and method for deep geothermal resources

Abstract

The invention discloses a distributed enhanced mining test platform and method for deep geothermal resources, and relates to the technical field of mine safety engineering and disaster prevention and control. Wherein the test platform comprises an outer shell, an inner shell, a three-way pressurizing device, a counter-force frame, a multifunctional injection well and a production well; a three-way pressurizing device is arranged between the outer shell and the inner shell, a hot rock test piece is placed in the inner shell, and a multifunctional injection well, a production well and a sensor hole are formed in a groove of the reaction frame; the test method comprises the following steps of: loading a test piece, simulating a field environment by zone heating and stress application, constructing an artificial heat reservoir by step-by-step zone fracturing, circularly collecting heat in modes of an integral area, a combined area, an independent area and the like, and changing parameters to compare and evaluate the mining efficiency. According to the method, the whole deep geothermal exploitation process can be truly reproduced, the fracturing and exploitation scheme is accurately optimized, and scientific test support is provided for safe and efficient development of an enhanced geothermal system.

Description

Technical Field

[0001] This invention relates to the field of mine safety engineering and disaster prevention technology, specifically to a distributed enhanced mining test platform and method for deep geothermal resources. Background Technology

[0002] Geothermal resources are a vast amount of thermal energy hidden within the Earth, originating from the primordial heat generated during the Earth's formation and the continuous thermal energy produced by the decay of radioactive elements. They possess core advantages such as being clean and low-carbon, having enormous reserves, being stable and continuous, and being cyclically renewable. They are one of the key renewable energy sources for replacing fossil fuels and addressing climate change in the global energy transition. For dry, hot rock reservoirs with "no natural fractures and poor permeability," Enhanced Geothermal System (EGS) technology artificially fractures the reservoir and constructs "artificial thermal reservoirs," achieving a cycle of cold water injection, heat absorption, and hot water / steam production, breaking the traditional geothermal dependence on "natural thermal reservoirs." However, in hot dry rock reservoirs above 3000 meters underground, temperatures often reach 150-300℃ and pressures exceed 30MPa. Controlling artificial fractures is extremely difficult. During fracturing, the direction, density, and permeability of fractures are hard to precisely control, resulting in poor long-term reservoir stability. When fluid circulates in artificial fractures, "thermal stress changes" and "chemical scaling and blockage" occur, leading to a gradual decline in reservoir permeability. This necessitates frequent repeated fracturing to maintain production capacity, further increasing costs and potentially triggering perceptible or even destructive earthquakes. Simultaneously, the reliance on a few main fractures limits the contact area with the rock, resulting in low thermal extraction efficiency and rapid temperature decay of the outlet water. Furthermore, predicting changes in reservoir temperature and pressure, adequacy of fluid supply, and the possibility of localized "thermal breakthroughs" due to excessively rapid cold liquid injection during long-term extraction is challenging, all impacting equipment operation and efficiency. Therefore, a novel EGS extraction method that improves thermal extraction efficiency, stability, and safety is urgently needed. Summary of the Invention

[0003] The purpose of this invention is to propose a distributed enhanced mining test platform and method for deep geothermal resources to solve the problems existing in the prior art.

[0004] The technical solution adopted by this invention is as follows: Firstly, this invention proposes a distributed enhanced exploitation test platform for deep geothermal resources, comprising:

[0005] outer shell;

[0006] The inner shell, located inside the outer shell, is used to hold the dry hot rock specimen;

[0007] The three-dimensional pressurization device is located between the outer shell and the inner shell and is used to apply three-dimensional pressure to the dry hot rock specimen. The three-dimensional pressurization device is respectively placed on the top, left side and front end of the inner shell. The three-dimensional pressurization device includes a combined hydraulic cylinder and a distributed pressure plate, and the combined hydraulic cylinder and the distributed pressure plate are connected by a piston rod.

[0008] A reaction frame is located inside the outer shell, on the lower and right sides of the inner shell; a slot is opened at the bottom of the reaction frame, which contains a multi-functional injection well and a production well, which extend into and are fixed inside the dry hot rock specimen; a slot is opened in the middle of the reaction frame, which contains a sensor hole.

[0009] As a further improvement of the present invention, the combined hydraulic cylinders are all composed of multiple individual hydraulic cylinders, and the distributed pressure plates are all composed of multiple individual pressure plates. The individual hydraulic cylinders are connected to the individual pressure plates through piston rods.

[0010] As a further improvement of the present invention, the outer shell is cylindrical, closed at one end and provided with a detachable end cap at the other end; the bottom is supported by a base; the inner shell is cuboid.

[0011] As a further improvement of the present invention, the multifunctional injection wells are provided in multiple sets, equidistantly arranged within the hot dry rock specimen, dividing the hot dry rock specimen into multiple regions; the outer wall of the multifunctional injection wells within the hot dry rock specimen has perforations for water injection and fracturing; resistance wires are distributed on the surface; and the inlets of the multifunctional injection wells outside the hot dry rock specimen are equipped with a sealing device group, which includes multiple packers.

[0012] Secondly, this invention also proposes a distributed enhanced exploitation test method for deep geothermal resources, employing the aforementioned distributed enhanced exploitation test platform for deep geothermal resources, comprising the following steps:

[0013] Step S1: For the reservoir to be exploited for geothermal extraction, test the physical and mechanical parameters such as formation stress, temperature, and strength on site. Divide the extraction areas according to the formation stress and temperature on site, formulate a preliminary extraction plan and parameters, and prefabricate dry hot rock specimens.

[0014] Step S2: Open the inner shell, install the dry hot rock specimen, and install multi-functional injection wells, production wells and sensors in different mining areas respectively;

[0015] Step S3: Turn on the heating switch of the multi-functional injection well, heat different areas of the dry hot rock specimen according to the formation temperature distribution, and keep it constant; start the three-dimensional pressurization device to apply stress to different mining areas and simulate the stress distribution law in the field.

[0016] Step S4: Open the multi-functional injection well and packer to fracturing the first area. After fracturing is completed, close the packer and open the packer to fracturing the next area. Fracturing is carried out in sequence to complete all areas.

[0017] Step S5: Open all packers and simultaneously inject cold water from the multi-functional injection well. After circulation, hot water flows out through the production well.

[0018] Step S6: Repeat step 5, open the packer, and simultaneously inject cold water from the corresponding multi-functional injection wells of the first two mining areas. After circulation, hot water flows out through the production well. Then, open the two packers simultaneously in sequence to mine geothermal energy in other areas until the end.

[0019] Step S7: Repeat step 5, open the first packer, inject cold water from the multi-functional injection well corresponding to the first mining area, circulate it and then flow out hot water through the production well; then extract geothermal energy from other areas one by one.

[0020] Step S8: Change different fracturing parameters, combinations and sequences of mining areas, etc., and conduct tests respectively. After the test, quantitatively evaluate the mining efficiency by comprehensively comparing the changes in reservoir parameters and the heat recovery situation, so as to optimize the distributed enhanced geothermal mining scheme.

[0021] Compared with the prior art, the present invention has the following technical advantages:

[0022] (1) The test platform of the present invention accurately reproduces the deep geothermal environment. Through the three-dimensional pressurization device and the zoned heating function, it restores the stress and temperature distribution law of the formation on site. It integrates multi-functional and multi-dimensional monitoring. The injection well integrates heating, fracturing and water injection functions. With the sensor hole, it realizes real-time monitoring of parameters such as temperature, water pressure and deformation. It has flexible control capability. The combined oil cylinder and distributed pressure plate can realize balanced or unbalanced pressure application. The packer supports zoned fracturing and mining control. It reduces the test cost and cycle. Compared with the field test, it has good repeatability and convenient operation, and provides a universal test carrier for geothermal mining research.

[0023] (2) The experimental method of the present invention optimizes the construction of artificial thermal reservoirs, and the step-by-step and zone-based fracturing method precisely controls the direction and density of fractures to improve the stability of thermal reservoirs; it improves the efficiency of heat extraction, and expands the contact area between fluid and rock through multiple modes of heat extraction such as overall, combined area and individual area, thereby slowing down the water temperature decay; it achieves precise optimization of mining schemes, and conducts comparative tests by changing fracturing parameters, mining combination and sequence to quantitatively evaluate efficiency and optimize schemes; it clarifies the dynamic changes of thermal reservoirs and provides scientific data for predicting changes in thermal reservoir temperature and pressure, fluid supply and "thermal breakthrough" risk. Attached Figure Description

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] Figure 1 This is a cross-sectional view of the test platform for the distributed enhanced mining method for deep geothermal resources according to the present invention;

[0026] Figure 2 This is a cross-sectional view of the test platform for the distributed enhanced mining method for deep geothermal resources according to the present invention;

[0027] In the figure, 1-outer shell; 2-inner shell; 3-base; 4-dry hot rock specimen; 5, 8, 12-combined hydraulic cylinder; 6, 9, 13-distributed pressure plate; 7, 10-reaction frame; 11-sensor hole; 14-multifunctional injection well; 15-production well; 16-packer assembly; 16-1~16-8-packers. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0029] like Figure 1 and Figure 2 As shown, a distributed enhanced mining test platform for deep geothermal resources according to the present invention includes an outer shell 1, an inner shell 2, a pressurization device, and reaction frames 7 and 10. Specifically, the outer shell 1 is closed at one end and has an openable end cap at the other end. It is supported at the bottom by a base 3, has a diameter of 2 meters, and a length of 4 meters. The inner shell 2 is placed inside the outer shell 1 and is used to place the dry hot rock specimen 4. The inner shell 2 is rectangular with a square cross-section and a side length of 1 meter. Both the outer shell 1 and the inner shell 2 are made of thin steel plates.

[0030] The three-dimensional pressurization device is located between the outer shell 1 and the inner shell 2, and is used to apply pressure to the hot dry rock specimen 4. The three-dimensional pressurization device is respectively positioned on the top, left side, and front end of the inner shell 2, providing triaxial (X, Y, and Z) stress to the hot dry rock specimen 4. Each pressurization device includes distributed pressure plates 6, 9, and 13 and combined hydraulic cylinders 5, 8, and 12. Specifically, the combined hydraulic cylinders 5, 8, and 12 are composed of multiple individual hydraulic cylinders. The individual hydraulic cylinders are driven by a hydraulic system, and each individual hydraulic cylinder is equipped with a solenoid valve, which is controlled by a PLC to control the movement of the individual hydraulic cylinder. The distributed pressure plates 6, 9, and 13 are composed of multiple individual pressure plates. The individual hydraulic cylinders are connected to the individual pressure plates via piston rods, and the hot dry rock specimen 4 contacts the individual pressure plates when force is applied. During pressurization, the PLC drives all the individual cylinders in the combined hydraulic cylinders 5, 8, and 12 to operate simultaneously, applying a uniform pressure across the entire cross-section of the hot dry rock specimen 4, or driving some of the individual cylinders on the three faces of the coal and rock specimen 4 to operate, simulating the application of non-uniform pressure to each face of the hot dry rock specimen 4, thereby more realistically simulating the stress distribution of the coal seam in the field.

[0031] The reaction frames 7 and 10 are located inside the outer shell 1, below and on the right side of the inner shell 2. A slot is formed at the bottom of the reaction frame 7, housing a multi-functional injection well 14 and a production well 15. A slot is formed in the middle of the reaction frame 10, housing a sensor hole 11. The sensor hole 11 is used to connect sensors for measuring temperature, pressure, etc.

[0032] Specifically, multiple sets of multifunctional injection wells 14 are installed inside the hot dry rock specimen 4 via their inner walls, arranged linearly to divide the specimen into several regions. The outer walls of the multifunctional injection wells 14 inside the hot dry rock specimen 4 have perforations for water injection and fracturing; resistance wires are distributed on the surface of the multifunctional injection wells 14 for heating; and the openings of the multifunctional injection wells 14 outside the hot dry rock specimen 4 are equipped with a packer assembly 16, including eight packers, such as… Figure 2 As shown.

[0033] This invention, through a three-dimensional pressurization device and the zoned heating function of the multi-functional injection well 14, can precisely apply corresponding stresses and maintain constant temperatures to different mining areas of the hot dry rock specimen 4 according to the stress and temperature distribution patterns of the formation, realistically simulating the complex environment of hot dry rock reservoirs (temperature 150-300℃, pressure exceeding 30MPa) at depths of over 3000 meters underground. The multi-functional injection well 14 integrates heating and water injection functions, featuring a compact structure and synergistic functions. It eliminates the need for multiple additional sets of equipment, efficiently completing the entire process from environmental simulation to heat extraction, thus solving the problems of single-function and cumbersome operation of traditional equipment.

[0034] This invention also proposes a distributed enhanced exploitation test method for deep geothermal resources, comprising the following steps:

[0035] Step S1: For the reservoir to be exploited for geothermal extraction, test the physical and mechanical parameters such as formation stress, temperature, and strength on site. Divide the extraction areas according to the formation stress and temperature on site, formulate a preliminary extraction plan and parameters, and prefabricate dry hot rock specimens 4.

[0036] Step S2: Open the inner shell 2, insert the dry hot rock specimen 4, and install the multi-functional injection well 14, production well 15 and sensors in different mining areas respectively;

[0037] Step S3: Turn on the heating switch of the multi-functional injection well 14, heat different areas of the dry hot rock specimen 4 according to the formation temperature distribution, and keep it constant; start the three-way pressurization device to apply stress to different mining areas and simulate the stress distribution law on site.

[0038] Step S4: Open the multi-functional injection well 14 and packer 16-1 to fracturing the first area. After fracturing is completed, close packer 16-1 and open packer 16-3 to fracturing the next area. Fracturing is carried out in sequence for all areas.

[0039] Step S5: Open all packers and simultaneously inject cold water from the multi-functional injection well 14. After circulation, hot water flows out through the production well 15.

[0040] Step S6: Repeat step 3, open packers 16-1, 16-2, 16-3, and 16-4, and simultaneously inject cold water from the multi-functional injection wells 14 corresponding to the first two mining areas. After circulation, hot water flows out through the production well 15. Then, open the four packers in the last two areas in sequence to mine geothermal energy in other areas until the end.

[0041] Step S7: Repeat step 3, open packers 16-1 and 16-2, inject cold water from the multi-functional injection well 14 corresponding to the first mining area, and after circulation, hot water flows out through the production well 15; then extract geothermal energy from other areas separately in turn.

[0042] Step S8: Change different fracturing parameters, combinations and sequences of mining areas, etc., and conduct tests respectively. After the test, quantitatively evaluate the mining efficiency by comprehensively comparing the changes in reservoir parameters and the heat recovery situation, so as to optimize the distributed enhanced geothermal mining scheme.

[0043] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes that can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention are all within the protection scope of the claims of the present invention.

Claims

1. A distributed enhanced exploitation test platform for deep geothermal resources, characterized in that, include: Outer shell (1); The inner shell (2) is placed inside the outer shell (1) and is used to place the dry hot rock specimen (4); The three-dimensional pressurization device is located between the outer shell (1) and the inner shell (2) and is used to apply three-dimensional pressure to the dry hot rock specimen (4). The three-dimensional pressurization device is respectively placed on the top, left side and front end of the inner shell (2). The three-dimensional pressurization device includes a combination cylinder (5, 8, 12) and a distributed pressure plate (6, 9, 13). The combination cylinder (5, 8, 12) and the distributed pressure plate (6, 9, 13) are connected by a piston rod. The reaction frame (7, 10) is located inside the outer shell (1), below and on the right side of the inner shell (2); a slot is opened at the bottom of the reaction frame (7), and a multi-functional injection well (14) and a production well (15) are provided inside, and the injection well (14) and the production well (15) extend into the dry hot rock specimen (4) and are fixed; a slot is opened in the middle of the reaction frame (10), and a sensor hole (11) is provided inside.

2. The deep geothermal resource distributed enhanced exploitation test platform according to claim 1, characterized in that, The combined hydraulic cylinders (5, 8, 12) are all composed of multiple individual hydraulic cylinders, and the distributed pressure plates (6, 9, 13) are all composed of multiple individual pressure plates. The individual hydraulic cylinders are connected to the individual pressure plates through piston rods.

3. The deep geothermal resource distributed enhanced exploitation test platform according to claim 1, characterized in that, The outer shell (1) is cylindrical, closed at one end and provided with a detachable end cap at the other end; the bottom is supported by a base (3); the inner shell (2) is cuboid.

4. The deep geothermal resource distributed enhanced exploitation test platform according to claim 1, characterized in that, The multifunctional injection wells (14) are provided in multiple groups and are equidistantly arranged in the dry hot rock specimen (4), dividing the dry hot rock specimen into multiple areas; the outer wall of the multifunctional injection wells (14) in the dry hot rock specimen (4) has perforations for water injection and fracturing; resistance wires are distributed on the surface, and the pipe opening of the multifunctional injection wells (14) outside the dry hot rock specimen (4) is provided with a sealing device group (16), which includes multiple packers.

5. A method for distributed enhanced exploitation of deep geothermal resources, employing the distributed enhanced exploitation platform for deep geothermal resources as described in claims 1-4, characterized in that, Includes the following steps: Step S1: For the reservoir to be exploited for geothermal extraction, test the physical and mechanical parameters such as formation stress, temperature and strength on site, divide different mining areas according to the formation stress and geothermal temperature on site, formulate preliminary mining plans and parameters, and prefabricate dry hot rock specimens (4). Step S2: Open the inner shell (2), insert the dry hot rock specimen (4), and install multi-functional injection wells (14), production wells (15) and sensors in different mining areas respectively; Step S3: Turn on the heating switch of the multi-functional injection well (14), heat different areas of the dry hot rock specimen (4) according to the formation temperature distribution, and keep it constant; start the three-way pressurization device to apply stress to different mining areas and simulate the stress distribution law on site; Step S4: Open the multi-functional injection well (14) and packer (16-1) to fracturing the first area. After fracturing is completed, close the packer (16-1) and open the packer (16-3) to fracturing the next area. Fracturing is carried out in sequence for all areas. Step S5: Open all packers and simultaneously inject cold water from the multi-functional injection well (14). After circulation, hot water flows out through the production well (15). Step S6: Repeat step 3, open packers (16-1, 16-2, 16-3, 16-4), and simultaneously inject cold water from the corresponding multi-functional injection wells (14) in the first two mining areas. After circulation, hot water flows out through the production well (15). Then, open the four packers in the last two areas in sequence to mine geothermal energy in other areas until the end. Step S7: Repeat step 3, open the packer (16-1, 16-2), inject cold water from the multi-functional injection well (14) corresponding to the first mining area, and after circulation, hot water flows out through the production well (15); then mine the geothermal energy of other areas separately in turn. Step S8: Change different fracturing parameters, combinations and sequences of mining areas, etc., and conduct tests respectively. After the test, quantitatively evaluate the mining efficiency by comprehensively comparing the changes in reservoir parameters and the heat recovery situation, so as to optimize the distributed enhanced geothermal mining scheme.

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