A negative carbon coal mining method for storing carbon dioxide in the goaf floor

Abstract

The present invention relates to the field of coal filling mining, specifically a negative carbon coal mining method for storing carbon dioxide in the floor of the goaf, comprising: first selecting a rock layer under the floor of the goaf as a carbon dioxide storage layer, then constructing a directional drilling hole to hydraulically fracture it to form horizontal and vertical cracks, then injecting a composite slurry to seal the cracks, and finally injecting carbon dioxide for storage. At this time, the solidified composite slurry will further fill the cracks under the action of high-pressure carbon dioxide; after the carbon dioxide is injected, the floor rock layer above the carbon dioxide storage layer produces an upward arch to lift the floor rock layer to support the goaf, thereby controlling the sinking of the overlying rock layer and controlling surface subsidence. The present invention can not only store carbon dioxide to reduce greenhouse gas emissions and achieve negative carbon mining, but also control rock stratum movement and surface subsidence to a certain extent, bring environmental benefits to coal mining, and help achieve low-carbon and green mining goals.

Description

Technical Field

[0001] The present invention relates to the field of coal filling mining, and in particular to a negative carbon coal mining method in which carbon dioxide is sealed in the floor of a goaf. Background Art

[0002] Safe, efficient, green, and low-carbon mining is an enduring theme. Near-zero rock burst, near-zero ecological damage, and low-carbon, zero-carbon, and even negative-carbon mining will become new requirements for ensuring energy security and green, low-carbon development. Backfill mining is the inevitable path to achieving this. However, existing backfill mining principles and technical equipment systems struggle to overcome the technical bottlenecks of high-yield, high-efficiency, and low-carbon mining. Innovation in backfill materials and methods is imperative.

[0003] Common goaf filling materials include solid filling, paste filling, and high-water-density filling. These methods typically fill the goaf to prevent further collapse, support overburden, and reduce surface subsidence. However, while these traditional filling materials can effectively ensure goaf stability, most of them themselves cannot effectively address carbon emissions. This is especially true given the increasing severity of climate change, where emissions of greenhouse gases such as carbon dioxide have become a major challenge for global environmental governance.

[0004] Carbon dioxide storage technology is an important means of reducing carbon emissions and addressing climate change. Its basic principle is to capture carbon dioxide from industrial emission sources (such as coal-fired power plants and steel mills) or the atmosphere and store it in geological formations for a long time, preventing it from entering the atmosphere. This reduces greenhouse gas emissions and mitigates global warming. Currently, carbon dioxide storage technology is mainly applied in deep underground rock formations or mines, but most of these technologies fail to effectively utilize the spatial resources of mined-out areas. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the present invention proposes a negative carbon mining method for storing carbon dioxide in the floor of a goaf, comprising the following steps:

[0006] S1: Determine the extent of the floor failure zone below the coal seam, and select a rock layer of a certain thickness below the floor failure zone as an isolation and protection layer. The isolation and protection layer arches upward under high-pressure carbon dioxide pressure, but does not generate cracks that connect to the upper floor failure zone, or the generated cracks do not connect to the cracks in the floor failure zone;

[0007] S2: Select a single rock layer below the isolation protection layer as the CO2 storage layer;

[0008] S3: constructing directional drilling holes in the tunnels on one side or both sides of the working face, wherein the horizontal section of the directional drilling holes is constructed in the carbon dioxide storage layer, the directional drilling holes are constructed in the direction of the opposite tunnel in the width direction of the working face, and the directional drilling holes are constructed in the direction of the eye cutting in the direction of the working face advancement;

[0009] S4: Horizontal fracturing of the CO2 storage layer by directional drilling at the mining location of the advanced working face to form fractures;

[0010] S5: The advanced working face injects a composite slurry of polymer and inorganic gelling material into the fracture through directional drilling;

[0011] S6: After the working face has mined through a horizontal section of a directional drill hole and before reaching the orifice of the directional drill hole, inject carbon dioxide into the carbon dioxide storage layer through the directional drill hole;

[0012] S7: The working face continues to be mined, and the directional drill holes are fractured, composite slurry is injected, and carbon dioxide is injected according to the cycle of steps S4-S6.

[0013] Preferably, in step S2, the carbon dioxide storage layer has the characteristics of high porosity and great thickness.

[0014] Preferably, in step S3, the directional drilling is parallel to the width direction of the working surface.

[0015] Preferably, in step S4, the horizontal fractures of the hydraulic fractures are located in the lower middle region of the carbon dioxide storage layer.

[0016] Preferably, in step S5, the polymer is silicone rubber or butyl rubber modified material, and the inorganic gelling material is cement or gypsum.

[0017] Preferably, the directional drilling for fracturing in step S4 and the directional drilling for polymer injection in step S5 should be separated by a sufficient distance to prevent mutual interference.

[0018] Preferably, the directional drilling holes for polymer injection in step S5 and the directional drilling holes for carbon dioxide injection in step S6 should be spaced sufficiently apart to prevent mutual interference.

[0019] Beneficial effects of the present invention: The present invention first selects a rock layer under the bottom plate of the goaf as a carbon dioxide storage layer, then constructs directional drilling to perform hydraulic fracturing on it to form horizontal and vertical cracks, then injects composite slurry to seal the cracks, and finally injects carbon dioxide for storage. At this time, the solidified composite slurry will further fill the cracks under the action of high-pressure carbon dioxide; after the injection of carbon dioxide, the bottom plate rock layer above the carbon dioxide storage layer produces an upward arch to lift the bottom plate rock layer to support the goaf, thereby controlling the sinking of the overlying rock layer and controlling surface subsidence. The present invention can not only seal carbon dioxide to reduce greenhouse gas emissions and achieve negative carbon mining, but also control rock movement and surface subsidence to a certain extent, bring environmental benefits to coal mining, and help achieve low-carbon and green mining goals. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the plan layout of directional drilling in the present invention;

[0021] Figure 2 It is a schematic cross-sectional diagram of the target rock formation for directional drilling and fracturing in the present invention;

[0022] Figure 3 This is a cross-sectional schematic diagram of directional drilling for carbon dioxide storage in the present invention;

[0023] In the figure: CO2 storage layer-1, isolation protection layer-2; bottom plate uniform fracture zone-3, bottom plate crushing and expansion zone-4, fracturing crack-5; collapse zone-6, fracture zone-7, directional drilling-8, grouting slurry-9, tunnel-10. DETAILED DESCRIPTION

[0024] The following is a more detailed description of the technical solution of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Figure 1-3 As shown, the present invention proposes a negative carbon coal mining method for storing carbon dioxide in the floor of the goaf, and the specific steps include:

[0025] S1: Based on the lithology and thickness of the floor rock formation, the range of the floor damage zone below the coal seam is determined. The floor damage zone includes a floor crushing and expansion zone 4 and a floor uniform fracture zone 3. The floor rock formation in the floor crushing and expansion zone 4 is broken in an irregular network, and the broken blocks are relatively small. Since there are gaps between the broken blocks, there are certain expansion characteristics. The floor rock formation in the floor uniform fracture zone 3 is broken in regular vertical and horizontal cracks, forming regular relatively large broken blocks. The floor damage zone can form a water and gas conduction channel. A rock formation of a certain thickness (usually including multiple rock formations) is selected below the floor damage zone as an isolation and protection layer 2. The isolation and protection layer 2 arches upward under high-pressure carbon dioxide pressure, but does not generate cracks that connect to the upper floor damage zone, or the generated cracks are not connected to the cracks in the floor damage zone.

[0026] S2: Selecting a single rock layer below the isolation protection layer 2 as the carbon dioxide storage layer 1. The carbon dioxide storage layer 1 preferably has a high porosity and a large thickness to accommodate a large amount of carbon dioxide;

[0027] S3: Constructing directional drill holes 8 in the tunnels 10 on one or both sides of the working face. The horizontal sections of the directional drill holes 8 are constructed in the CO2 storage layer 1. The directional drill holes 8 are constructed in the working face width direction toward the opposite tunnels 10. The directional drill holes are preferably parallel to the working face width direction. The directional drill holes 8 are constructed in the working face advancement direction (i.e., the working face length direction) toward the cut-eye direction.

[0028] S4: At a first distance from the mining position of the advanced working face, the carbon dioxide storage layer 1 is horizontally fractured through a directional drill hole 8 to form fractures 5. The fractures 5 include horizontal fractures and longitudinal fractures communicating with the horizontal fractures. However, the fractures 5 do not extend beyond the carbon dioxide storage layer 1. Preferably, the horizontal fractures are located in the middle and lower region of the carbon dioxide storage layer 1, i.e., the horizontal section of the directional drill hole 8 is located in the middle and lower region of the carbon dioxide storage layer 1. The fracture methods include carbon dioxide blasting, hydraulic fracturing, and the like.

[0029] S5: For the directional drill hole 8 that has completed the fracturing step, a composite slurry of polymer (silicone rubber or butyl rubber modified material) and inorganic gelling material (such as cement or gypsum) is injected into the fracturing fissure through the directional drill hole 8 at a second distance ahead of the working face. The composite slurry has good fluidity and plugging properties and can effectively fill the fracturing fissure 5, thereby forming a closed space capable of sealing carbon dioxide around the horizontal section of the directional drill hole 8; the first distance is greater than the second distance, and the directional drill hole for fracturing in step S4 and the directional drill hole for polymer injection in step S5 should be separated by a sufficient distance to prevent mutual interference between the two.

[0030] S6: When the working face has been mined through a certain horizontal section of a directional drill hole 8 and before reaching the opening of the directional drill hole 8 (e.g. Figure 1The solid line position in the middle working surface), the composite slurry near the directional drilling hole 8 has solidified; carbon dioxide is injected into the carbon dioxide storage layer 1 through the directional drilling hole 8, and the carbon dioxide storage layer 1 expands after the injection of carbon dioxide to form a carbon dioxide storage space. The deformation of the upper and lower rock layers in the expanded carbon dioxide storage space itself will produce cracks, but because they have been pre-fractured by fracturing means to form cracks and sealed by composite slurry, new cracks will not be generated after the subsequent injection of carbon dioxide, or new cracks can also be blocked by the already injected composite slurry (the gaps of old cracks become larger), thereby avoiding carbon dioxide leakage and improving its sealing performance. After the injection of carbon dioxide, the floor rock layer above the carbon dioxide storage layer 1 produces an arched and lifted isolation protective layer 2, a floor uniform fracture zone 3 and a floor damage zone 4; the floor uniform fracture zone 3 and the floor crushing and expansion zone 4 will increase the damage range under the action of the expanded carbon dioxide storage space, and the looseness of the irregular rock blocks in the floor crushing and expansion zone 4, that is, the degree of crushing and expansion, will also increase, further enriching the goaf space, and together with the volume expansion of the carbon dioxide storage space, offset part of the space formed by coal seam mining, thereby reducing the equivalent mining height of the coal seam, lowering the height of the collapse zone 6 and the fracture zone 7, and controlling the sinking of the overlying rock layer, thereby reducing surface subsidence;

[0031] The directional drilling for polymer injection in step S5 and the directional drilling for carbon dioxide injection in step S6 should be separated by a sufficient distance to prevent the two from interfering with each other;

[0032] S7: The working face continues to be mined, and the directional drill holes are fractured, composite slurry is injected, and carbon dioxide is injected according to the cycle of steps S4-S6.

[0033] The present invention is not limited to the above-mentioned optimal implementation mode. Anyone can derive other various forms of methods under the inspiration of the present invention. However, any technical solution that is the same or similar to that of the present application falls within the scope of protection of the present invention.

Claims

1. A negative carbon mining method for storing carbon dioxide in the floor of a goaf, characterized by: The following steps are involved: S1: Determine the extent of the floor failure zone below the coal seam, and select a rock layer of a certain thickness below the floor failure zone as an isolation and protection layer. The isolation and protection layer arches upward under high-pressure carbon dioxide pressure, but does not generate cracks that connect to the upper floor failure zone, or the generated cracks do not connect to the cracks in the floor failure zone; S2: Select a single rock layer below the isolation protection layer as the CO2 storage layer; S3: constructing directional drilling holes in the tunnels on one side or both sides of the working face, wherein the horizontal section of the directional drilling holes is constructed in the carbon dioxide storage layer, the directional drilling holes are constructed in the direction of the opposite tunnel in the width direction of the working face, and the directional drilling holes are constructed in the direction of the eye cutting in the direction of the working face advancement; S4: Horizontal fracturing of the CO2 storage layer by directional drilling at the mining location of the advanced working face to form fractures; S5: The advanced working face injects a composite slurry of polymer and inorganic gelling material into the fracture through directional drilling; S6: After the working face has mined through a horizontal section of a directional drill hole and before reaching the orifice of the directional drill hole, CO2 is injected into the CO2 storage layer through the directional drill hole; S7: The working face continues to be mined, and the directional drill holes are fractured, composite slurry is injected, and carbon dioxide is injected according to the cycle of steps S4-S6.

2. The negative carbon mining method for storing carbon dioxide in the goaf floor according to claim 1 is characterized in that: In step S2, the carbon dioxide storage layer has high porosity and great thickness.

3. The negative carbon mining method for storing carbon dioxide in the goaf floor according to claim 1 is characterized in that: In step S3, the directional drilling is parallel to the width direction of the working surface.

4. The negative carbon mining method for storing carbon dioxide in the goaf floor according to claim 1 is characterized in that: In step S4, the horizontal fractures of the hydraulic fractures are located in the lower middle region of the carbon dioxide storage layer.

5. The negative carbon mining method for storing carbon dioxide in the goaf floor according to claim 1 is characterized in that: In step S5, the polymer is silicone rubber or butyl rubber modified material, and the inorganic gelling material is cement or gypsum.

6. The negative carbon mining method for storing carbon dioxide in the goaf floor according to claim 1 is characterized in that: The directional drilling for fracturing in step S4 and the directional drilling for polymer injection in step S5 should be separated by a sufficient distance to prevent mutual interference.

7. The negative carbon mining method for storing carbon dioxide in the goaf floor according to claim 1 or 6, characterized in that: The directional drilling holes for polymer injection in step S5 and the directional drilling holes for carbon dioxide injection in step S6 should be separated by a sufficient distance to prevent mutual interference.

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