An underground in-situ oxidation heat extraction system and method for organic-rich rock formations

Abstract

The present invention provides an underground in-situ oxidation heat extraction system and method for organic-rich rock formations. The system includes two oxidant docking wells, the lower ends of which are located in the organic-rich rock formation. The lower ends of the two oxidant docking wells are connected by an oxidant connecting well. The two oxidant docking wells and the oxidant connecting well form an oxidant convection well. The well walls of the oxidant connecting wells are provided with oxidant leakage holes, and the oxidant leakage holes extend toward the organic-rich rock formation. Several heat exchange convection wells are constructed around the oxidant convection wells. Using the above-mentioned system for mining can improve the thermal energy utilization efficiency of the underground thermal field, reduce the difficulty of mining, and effectively avoid the problems of ground subsidence and soil erosion during the mining process.

Description

Technical Field

[0001] The present invention belongs to the technical field of geothermal energy resource development, and in particular relates to an underground in-situ oxidation heat extraction system and method for organic-rich rock formations. Background Art

[0002] The large-scale development and utilization of coal and oil shale resources has led to a series of ecological and environmental problems, including ground subsidence, soil erosion, vegetation destruction, and air and soil pollution. Furthermore, direct mining of coal and oil shale at great depths is extremely difficult. Consequently, conventional mining techniques struggle to balance economic and ecological benefits. Therefore, an underground in-situ oxidation heat extraction system and method are needed to address these issues. Summary of the Invention

[0003] The purpose of the present invention is to provide an underground in-situ oxidation heat extraction system and method for organic-rich rock formations to solve the problems mentioned in the background art.

[0004] To achieve the above-mentioned objectives, in the first aspect, the present invention provides an underground in-situ oxidation heat extraction system for organic-rich rock formations, comprising two oxidant docking wells, the lower ends of the oxidant docking wells being located in the organic-rich rock formation, the lower ends of the two oxidant docking wells being connected through an oxidant connecting well, the two oxidant docking wells and the oxidant connecting well forming an oxidant convection well, the well wall of the oxidant connecting well being provided with oxidant leakage holes, and the oxidant leakage holes extending toward the organic-rich rock formation, and a number of heat exchange convection wells being constructed around the oxidant convection well.

[0005] In a second aspect, the present invention further provides a method for underground in-situ oxidation heat extraction in organic-rich rock formations, the method comprising the following steps:

[0006] Step 1: Drill two oxidant docking wells in the upper rock formation, drill the lower ends of the oxidant docking wells to the organic-rich rock formation, connect the lower ends of the two oxidant docking wells through an oxidant connecting well, and cement the oxidant docking wells and the oxidant connecting wells to form an oxidant convection well;

[0007] Step 2: After the cementing of the oxidant docking well and the oxidant connection well is completed, holes are drilled in the wall of the oxidant connection well by perforating to serve as oxidant leakage holes;

[0008] Step 3: construct several heat exchange convection wells around the oxidant convection well according to the thickness of the organic-rich rock layer;

[0009] Step 4: Injecting oxidant into the organic-rich rock formation through one end of the oxidant docking well. The oxidant injection pressure is higher than the formation fluid pressure. Simultaneously with the injection of the oxidant, circulating cold water is injected into the injection end of the heat exchange convection well. The circulating water exchanges heat with the oxidized heat-generating organic-rich rock formation in the heat exchange convection well and is ultimately output from the hot water output port of the heat exchange convection well to a heat utilization terminal.

[0010] Step 5: Collect and monitor the carbon dioxide in the gas components at the outlet end of the oxidant convection well to determine the extent of the underground in-situ oxidation reaction. Based on the extent of the underground in-situ oxidation reaction, terminate the oxidant injection and continue circulating water for heat extraction until the recoverable heat has no economic value and then shut down the in-situ oxidation heat extraction project in the area.

[0011] Furthermore, the method also includes: step six, using the shut-down organic-rich rock formation as a carbon dioxide adsorbent, injecting carbon dioxide into the organic-rich rock formation through an oxidant convection well to achieve underground storage of carbon dioxide.

[0012] Furthermore, in step 3, when the thickness of the organic-rich rock layer is greater than 4 m, four heat exchange convection wells are constructed, and the four heat exchange convection wells are evenly distributed in the upper, lower, left, and right directions around the oxidant convection well;

[0013] When the thickness of the organic-rich rock layer does not exceed 4m, take the oxidant convection well as the reference and construct three groups of heat exchange convection wells directly above the top and at 45 degrees above the top on both sides.

[0014] Furthermore, step three also includes: after the construction of the heat exchange convection well is completed, injecting air with a pressure higher than the formation fluid pressure into the organic-rich rock formation through the oxidant docking well to drive away the organic-rich rock formation water in the oxidation zone.

[0015] Furthermore, the organic-rich rock layer is a coal seam, and when the temperature of the coal seam is lower than 70°C, the oxidant is oxygen, and the concentration of the oxygen injected in step 4 is not lower than 45%, and the temperature is not lower than 100°C.

[0016] Furthermore, the organic-rich rock layer is an oil shale layer, the oxidant is oxygen, and when the temperature of the oil shale layer is lower than 70°C, the concentration of the oxygen injected in step 4 is 45%-55%, and the oxygen temperature is not lower than 300°C.

[0017] Furthermore, the distance between the perforation and the upper rock layer and the lower rock layer is not less than 1 m.

[0018] Furthermore, in step 4, the concentration of injected oxygen gradually decreases as the temperature of the organic-rich rock formation increases.

[0019] Furthermore, the distance between the heat exchange convection well and the oxidant convection well is 2m.

[0020] The advantages of the present invention are: the present invention provides such an underground in-situ oxidation heat extraction system and method for organic-rich rock formations, which utilizes the oxidation heat generation principle of the organic-rich rock formations themselves to create an underground thermal field. When extracting heat, it is only necessary to drill wells on the surface, which will not damage the vegetation on the ground and cause soil erosion. Moreover, the solid matter after the reaction of the organic-rich rock formations is located underground, so ground subsidence can be effectively avoided. Moreover, the method reasonably selects geothermal energy development technical solutions for strata of different depths and distribution conditions, improves the thermal energy utilization efficiency of the artificial thermal field, reduces the difficulty of mining, and at the same time, uses the organic-rich resources that are not fully oxidized in the underground as carbon dioxide adsorbents, converting them into underground carbon sinks, thereby reducing carbon emissions.

[0021] The present invention is described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the present invention.

[0023] Figure 2 This is a schematic diagram of the locations of the oxidant convection well and the heat exchange convection well when the thickness of the organic-rich rock layer does not exceed 4m.

[0024] Explanation of the accompanying symbols: 1. Oxidant convection well; 101. Oxidant docking well; 102. Oxidant connection well; 2. Oxidant leakage hole; 3. Heat exchange convection well; 4. Organic-rich rock formation; 5. Upper rock formation; 6. Lower rock formation. DETAILED DESCRIPTION

[0025] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose, the specific implementation methods, structural features and effects of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0026] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0027] In the description of the present invention, it should be understood that the terms "center", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "aligned", "overlap", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0028] The terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more of such features; and in the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0029] Example 1

[0030] like Figure 1 As shown, this embodiment provides an underground in-situ oxidation heat extraction system for organic-rich rock formations, including two oxidant docking wells 101, the lower ends of the oxidant docking wells 101 are located in the organic-rich rock formation 4, the lower ends of the two oxidant docking wells 101 are connected through an oxidant connecting well 102, the two oxidant docking wells 101 and the oxidant connecting well 102 form an oxidant convection well 1, the well wall of the oxidant connecting well 101 is provided with an oxidant leakage hole 2, and the oxidant leakage hole 2 extends toward the organic-rich rock formation, and a plurality of heat exchange convection wells 3 are constructed around the oxidant convection well 1.

[0031] Example 2

[0032] This embodiment provides a method for underground in-situ oxidation heat extraction in organic-rich rock formations, the method comprising the following steps:

[0033] Step 1: Drill two oxidant docking wells 101 in the upper rock formation 5. The lower ends of the oxidant docking wells 101 are drilled to the organic-rich rock formation 4. The lower ends of the two oxidant docking wells 101 are connected through an oxidant connecting well 102. The oxidant docking wells 101 and the oxidant connecting well 102 are cemented to form an oxidant convection well 1.

[0034] Step 2: After the cementing of the oxidant docking well 101 and the oxidant connection well 102 is completed, a hole is drilled in the wall of the oxidant connection well 102 by perforation to serve as the oxidant leakage hole 2;

[0035] Specifically, when the thickness of the organic-rich rock layer 4 is greater than 4 m, the perforation is required to be uniformly controlled in all directions of the organic-rich rock layer 4, and the penetration distance is based on the thickness of the organic-rich rock layer 4. It is not advisable to penetrate the organic-rich rock layer 4. For example, when the thickness of the organic-rich rock is 8 m, the drilling depth of the oxidant convection well 1 in step 1 should be 4 m below the top of the organic-rich rock, and then the vertical perforation distance should be controlled within 3 m, and the coal seam must not be penetrated.

[0036] When the thickness of the organic-rich rock layer 4 does not exceed 4m, the perforation is required to be directional perforation, with the perforation direction being upward from the oxidant convection well 1, and the distance should not penetrate the coal seam roof. For example, when the thickness of the organic-rich rock layer 4 is 3.5m, the perforation distance should be 2.5m.

[0037] Step 3: construct a number of heat exchange convection wells 3 around the oxidant convection well 1 according to the thickness of the organic-rich rock layer 4;

[0038] Specifically, when the thickness of the organic-rich rock layer 4 is greater than 4 m, four heat exchange convection wells 3 are constructed, and the four heat exchange convection wells 3 are evenly distributed in the upper, lower, left, and right directions around the oxidant convection well 1;

[0039] When the thickness of organic-rich rock layer 4 does not exceed 4m, Figure 2 As shown, taking the oxidant convection well 1 as a reference, three groups of heat exchange convection wells 3 are constructed directly above the top and at 45 degrees above the top on both sides. Specifically, the depth of the oxidant convection well 1 is 1 meter above the lower rock layer 6. Each heat exchange convection well 3 is less than 1 meter below the lower part of the upper rock layer 5 and has the same distance from the oxidant convection well 1.

[0040] After the heat exchange convection well 3 is constructed, air at a pressure higher than the formation fluid pressure is injected into the organic-rich rock formation 4 through the upper end of one of the oxidant docking wells 101. The formation fluid pressure is measured. The high-pressure air displaces water from the organic-rich rock formation 4 within the oxidation zone. Other mobile products, such as CO2, CO, and hydrocarbon gases, generated during the oxidation process are discharged from the upper end of the other oxidant docking well 101 and can be collected and sorted during discharge. After discharging the water from the organic-rich rock formation 4, or if the water content of the organic-rich rock formation 4 is very low, proceed directly to step 4.

[0041] Step 4: Inject oxidant into the organic-rich rock formation 4 through the oxidant docking well 101. The oxidant injection pressure is higher than the formation fluid pressure. Simultaneously with the oxidant injection, circulating cold water is injected into the injection end of the heat exchange convection well 3. The circulating water exchanges heat with the oxidized heat-generating organic-rich rock formation 4 in the heat exchange convection well 3, and is ultimately output from the hot water output port of the heat exchange convection well 3 to the heat use terminal.

[0042] Step 5: Collect and monitor the carbon dioxide in the gas components at the outlet end of the oxidant convection well 1 to determine the degree of the underground in-situ oxidation reaction. Based on the degree of the underground in-situ oxidation reaction, terminate the oxidant injection and continue to circulate water for heat extraction until the recoverable heat has no economic value and then shut down the in-situ oxidation heat extraction project in the area.

[0043] The primary product of oxidation of organic-rich rock stratum 4 is carbon dioxide. The carbon and oxygen isotopic characteristics of carbon dioxide change regularly as the coal oxidation process progresses. Therefore, based on this pattern, the extent of the underground in-situ oxidation reaction can be determined by sampling and monitoring the carbon dioxide in the gas composition at the outlet of oxidant convection well 1. For example, if the maximum oxidation limit of a coal seam in a certain area is 45%, the carbon isotope value of the carbon dioxide in the oxidation product at this time is -20.5‰. When the carbon isotope value of carbon dioxide reaches -20.5‰, oxidant injection is terminated, and circulating water heat extraction continues until the recoverable heat is no longer economically valuable, at which point the in-situ oxidation heat extraction project in that area is shut down.

[0044] Step 6: After the shutdown, the organic-rich rock layer 4 is used as a carbon dioxide adsorbent, and carbon dioxide is injected into the organic-rich rock layer 4 through the oxidant convection well 1 to achieve underground storage of carbon dioxide.

[0045] Specifically, when the organic-rich rock layer 4 is a coal seam, the oxidant is oxygen, and when the temperature of the coal seam is lower than 70°C, the concentration of oxygen injected in step 4 is not lower than 45% and the temperature is not lower than 100°C, thereby promoting underground oxidation and heating of the coal seam.

[0046] Specifically, when the organic-rich rock layer 4 is an oil shale layer, the oxidant is oxygen, and the temperature of the oil shale layer is below 70°C. The oxygen concentration injected in step 4 is 45%-55%, more specifically, 50%, and the oxygen temperature is not less than 300°C, thereby ensuring that the oil shale layer generates heat due to underground oxidation. As the organic matter oxidizes and releases heat, the gas injection temperature is gradually lowered to room temperature, and the oxygen concentration is adjusted according to the degree of reaction. Parameters such as gas injection pressure and flow rate are based on the formation fluid pressure and the oxidation reaction activity of the oil shale layer.

[0047] Furthermore, the distance between the perforation and the upper rock layer 5 and the lower rock layer 6 is not less than 1 m.

[0048] Furthermore, in step 4, the injected oxygen concentration gradually decreases as the temperature of the organic-rich rock formation 4 increases, thereby controlling the oxidation reaction rate of the organic-rich rock formation 4. Specifically, after the coal seam temperature rises to 180°C, the injected oxygen concentration is reduced to 5%-15%. Simultaneously, as the coal seam temperature rises, the injected oxygen temperature drops to room temperature. By adjusting the oxygen concentration, the reaction intensity of the organic-rich rock formation 4 can be controlled, thereby adjusting the temperature of the organic-rich rock formation 4 and thereby regulating the terminal temperature of the heat user.

[0049] Furthermore, in order to avoid ground collapse caused by excessive oxidation of the organic-rich rock layer 4, it is necessary to control the degree of underground in-situ oxidation by adjusting the oxygen concentration so as not to exceed the maximum tolerance limit of the oxidation reaction in the area.

[0050] Furthermore, the distance between the heat exchange convection well 3 and the oxidant convection well 1 is 2 m, which can ensure the thermal energy utilization efficiency of the underground thermal field.

[0051] In summary, the present invention utilizes the oxidation heat generation principle of the organic-rich rock strata themselves to create an underground thermal field. When extracting heat, it is only necessary to drill wells on the surface, which will not damage the vegetation on the ground and cause soil erosion. In addition, the solid matter after the reaction of the organic-rich rock strata is located underground, so it can effectively avoid ground subsidence. Moreover, this method reasonably selects geothermal energy development technical solutions for strata of different depths and distribution conditions, improves the thermal energy utilization efficiency of the artificial thermal field, reduces the difficulty of mining, and at the same time, uses the organic-rich resources that are not fully oxidized in the underground as carbon dioxide adsorbents, converting them into underground carbon sinks, thereby reducing carbon emissions.

[0052] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for underground in-situ oxidation heat extraction from organic-rich rock formations, characterized by: An underground in-situ oxidation heat extraction system for an organic-rich rock formation comprises two oxidant docking wells (101), wherein the lower ends of the oxidant docking wells (101) are located in an organic-rich rock formation (4), the lower ends of the two oxidant docking wells (101) are connected via an oxidant connecting well (102), and the two oxidant docking wells (101) and the oxidant connecting well (102) form an oxidant convection well (1), the well wall of the oxidant connecting well (101) is provided with an oxidant leakage hole (2), and the oxidant leakage hole (2) extends toward the organic-rich rock formation (4), and a plurality of heat exchange convection wells (3) are constructed around the oxidant convection well (1); The method for obtaining heat from underground in-situ oxidation of organic-rich rock strata comprises the following steps: Step 1: Drill two oxidant docking wells (101) in the upper rock formation (5), drill the lower ends of the oxidant docking wells (101) to the organic-rich rock formation (4), connect the lower ends of the two oxidant docking wells (101) through the oxidant connecting well (102), and cement the oxidant docking wells (101) and the oxidant connecting well (102) to form an oxidant convection well (1); Step 2: After the cementing of the oxidant docking well (101) and the oxidant connection well (102) is completed, a hole is drilled in the wall of the oxidant connection well (102) by perforation to serve as an oxidant leakage hole (2); Step 3: construct a plurality of heat exchange convection wells (3) around the oxidant convection well (1) according to the thickness of the organic-rich rock layer (4); Step 4: Inject an oxidant into the organic-rich rock formation (4) through one end of the oxidant convection well (1). The oxidant injection pressure is higher than the formation fluid pressure. While injecting the oxidant, circulating cold water is injected into the injection end of the heat exchange convection well (3). The circulating water exchanges heat with the oxidized heat-generating organic-rich rock formation (4) in the heat exchange convection well (3), and is finally output from the hot water output port of the heat exchange convection well (3) to the heat use terminal. Step 5: Collect and monitor the carbon dioxide in the gas components at the outlet of the oxidant convection well (1) to determine the extent of the underground in-situ oxidation reaction. Based on the extent of the underground in-situ oxidation reaction, terminate the oxidant injection and continue circulating water for heat extraction until the recoverable heat has no economic value, and shut down the in-situ oxidation heat extraction project in the area. The organic-rich rock layer (4) is a coal seam, the oxidant is oxygen, and when the temperature of the coal seam is lower than 70° C., the concentration of the oxygen injected in step 4 is not lower than 45%, and the temperature is not lower than 100° C.; The organic-rich rock layer (4) is an oil shale layer, the oxidant is oxygen, and when the temperature of the oil shale layer is lower than 70°C, the concentration of oxygen injected in step 4 is 45%-55%, and the temperature is not lower than 300°C.

2. The method for obtaining heat from underground in-situ oxidation of organic-rich rock formations according to claim 1, characterized in that: The method further comprises: step six, using the shut-down organic-rich rock layer (4) as a carbon dioxide adsorbent, injecting carbon dioxide into the organic-rich rock layer (4) through the oxidant convection well (1), thereby achieving underground storage of carbon dioxide.

3. The method for underground in-situ oxidation heat extraction from organic-rich rock formations according to claim 1, characterized in that: In step 3, when the thickness of the organic-rich rock layer (4) is greater than 4 m, four heat exchange convection wells (3) are constructed, and the four heat exchange convection wells (3) are evenly distributed in the upper, lower, left, and right directions around the oxidant convection well (1); When the thickness of the organic-rich rock layer (4) does not exceed 4m, taking the oxidant convection well (1) as a reference, three groups of heat exchange convection wells (3) are constructed directly above the top and at 45 degrees above the top on both sides.

4. The method for underground in-situ oxidation heat extraction from organic-rich rock formations according to claim 1 or 3, characterized in that: Step three also includes: after the construction of the heat exchange convection well (3) is completed, air with a pressure higher than the formation fluid pressure is injected into the organic-rich rock layer (4) through the oxidant docking well to drive away water from the organic-rich rock layer (4) in the oxidation zone.

5. The method for obtaining heat from underground in-situ oxidation of organic-rich rock formations according to claim 1, characterized in that: The distance between the perforation and the upper rock layer (5) and the lower rock layer (6) is not less than 1 m.

6. The method for obtaining heat from underground in-situ oxidation of organic-rich rock formations according to claim 1, characterized in that: In step 4, the concentration of injected oxygen gradually decreases as the temperature of the organic-rich rock formation increases.

7. The method for obtaining heat from underground in-situ oxidation of organic-rich rock formations according to claim 1, wherein: The distance between the heat exchange convection well (3) and the oxidant convection well (1) is 2m.

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