Negative carbon coal mining method for sealing and storing carbon dioxide on goaf bottom plate

Abstract

The invention relates to the field of coal mine filling mining, in particular to a negative carbon coal mining method for storing carbon dioxide in a goaf bottom plate, which comprises the following steps: firstly, selecting a rock stratum below the goaf bottom plate as a carbon dioxide storage layer, and then constructing directional drilling to perform hydraulic fracturing on the carbon dioxide storage layer to form a horizontal fracture and a longitudinal fracture; then, composite slurry is injected to block the cracks, finally, carbon dioxide is injected for sealing, and at the moment, the solidified composite slurry can further fill the cracks under the action of high-pressure carbon dioxide; after carbon dioxide is injected, the bottom plate rock stratum above the carbon dioxide sealing layer arches upwards to lift the bottom plate rock stratum to support the goaf, and then the overlying rock stratum is controlled to sink, and surface subsidence is controlled. According to the invention, carbon dioxide can be stored, greenhouse gas emission can be reduced, negative carbon mining can be realized, rock stratum movement and surface subsidence can be controlled to a certain extent, environmental protection benefits are brought to coal mining, and low-carbon and green mining targets can be assisted to be realized.

Description

Technical Field

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

[0002] Safe, efficient, green and low-carbon mining in mines is an eternal theme. Near-zero rock burst, near-zero ecological damage, and low-carbon, zero-carbon, and negative-carbon green mining will become new requirements for ensuring energy security supply and green and low-carbon development. Backfill mining is the inevitable way to achieve this requirement. However, the existing backfill mining principle and technical equipment system are difficult to break through the technical bottleneck of high-yield, high-efficiency, and low-carbon mining. It is imperative to change the backfill materials and backfill modes.

[0003] Common goaf filling materials mainly include solid filling, paste filling and high-water material filling. These filling methods usually prevent further collapse of the goaf, support the overlying rock layer and reduce surface subsidence by filling the goaf space. However, although these traditional filling materials can effectively ensure the stability of the goaf, most of them cannot effectively solve the carbon emission problem. Especially in the context of increasingly serious climate change, the emission of greenhouse gases such as carbon dioxide has become a major challenge for global environmental governance.

[0004] Carbon dioxide storage technology is an important technical means to reduce carbon emissions and respond to climate change. Its basic principle is to capture carbon dioxide from industrial emission sources (such as coal-fired power plants, steel mills, etc.) or the atmosphere, and seal it in geological layers for a long time to prevent carbon dioxide from entering the atmosphere, thereby reducing greenhouse gas emissions and alleviating climate warming. At present, carbon dioxide storage technology is mainly used in deep underground rock formations or mines, but most of these technologies fail to effectively utilize the space resources of goaf 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 scope of the floor damage zone below the coal seam, select a rock layer of a certain thickness below the floor damage zone as an isolation protection layer, the isolation protection layer arches up under the 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;

[0007] S2: Select a single rock layer below the isolation protection layer as the carbon dioxide 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 advancing direction of the working face;

[0009] S4: The advanced working face mining position is located to form fracturing fractures by horizontally fracturing the CO2 storage layer through directional drilling;

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

[0011] S6: After the working face has been mined and pushed through a horizontal section of a directional borehole and before reaching the orifice of the directional borehole, carbon dioxide is injected into the carbon dioxide storage layer through the directional borehole;

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

[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 in height.

[0016] Preferably, in step S5, the polymer is a 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 from each other to prevent mutual interference.

[0019] Beneficial effects of the present invention: The present invention first selects a rock layer under the floor of the goaf as a carbon dioxide storage layer, then constructs directional drilling to hydraulically fracture it, forming horizontal and longitudinal 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 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 the 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, bringing environmental benefits to coal mining, and helping to 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 diagram of the cross section of the target rock formation for directional drilling and fracturing in the present invention;

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

[0023] In the figure: carbon dioxide 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 technical solution of the present invention will be described in more detail below 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 a goaf, and the specific steps include:

[0025] S1: Based on the lithology and thickness of the bottom plate rock formation, the scope of the bottom plate damage zone below the coal seam is determined. The bottom plate damage zone includes a bottom plate crushing and expansion zone 4 and a bottom plate uniform fracture zone 3. The bottom plate rock formation in the bottom plate 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 bottom plate rock formation in the bottom plate uniform fracture zone 3 is broken in regular vertical and horizontal cracks, forming regular relatively large broken blocks, and the bottom plate damage zone can form a water and gas conduction channel; a certain thickness of rock formation (usually including multiple rock formations) is selected below the bottom plate damage zone as an isolation protective layer 2, and the isolation protective layer 2 is arched under the high-pressure carbon dioxide pressure, but does not generate cracks that conduct the upper bottom plate damage zone, or the generated cracks are not connected to the cracks in the bottom plate damage zone;

[0026] S2: selecting a single rock layer below the isolation protection layer 2 as the carbon dioxide storage layer 1, wherein the carbon dioxide storage layer 1 preferably has a rock layer with high porosity and great thickness so as to accommodate a large amount of carbon dioxide;

[0027] S3: constructing a directional drill hole 8 in the tunnel 10 on one side or both sides of the working face, wherein the horizontal section of the directional drill hole 8 is constructed in the carbon dioxide storage layer 1, and the directional drill hole 8 is constructed in the direction of the opposite tunnel 10 in the width direction of the working face, and the directional drill hole is preferably parallel to the width direction of the working face, and the directional drill hole 8 is constructed in the direction of the eye cutting in the advancing direction of the working face (i.e., the length direction of the working face);

[0028] S4: at the first distance of the advance working face recovery position, the carbon dioxide storage layer 1 is horizontally fractured by a directional drilling hole 8 to form a fracture 5, wherein the fracture 5 includes a horizontal fracture and a longitudinal fracture connected to the horizontal fracture, but the fracture 5 does not exceed the carbon dioxide storage layer 1, and preferably the horizontal fracture is located in the middle and lower region of the carbon dioxide storage layer 1 in height, that is, the horizontal section of the directional drilling hole 8 is located in the middle and lower part of the carbon dioxide storage layer 1 in height; the fracture means include carbon dioxide blasting, hydraulic fracturing and other means;

[0029] S5: For the directional borehole 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 cracks through the directional borehole 8 at a second distance ahead of the working face. The composite slurry has good fluidity and plugging properties and can effectively plug the fracturing cracks 5, thereby forming a closed space capable of sealing carbon dioxide around the horizontal section of the directional borehole 8; the first distance is greater than the second distance, and the directional borehole for fracturing in step S4 and the directional borehole for polymer injection in step S5 should be separated by a sufficient distance to prevent the two from interfering with each other;

[0030] S6: When the working face has been mined through a certain horizontal section of a directional borehole 8 and before reaching the opening of the directional borehole 8 (e.g. Figure 1The 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. After the carbon dioxide is injected, the carbon dioxide storage layer 1 expands to form a carbon dioxide storage space. The deformation of the upper and lower rock strata walls of the expanded carbon dioxide storage space will itself produce cracks, but because the cracks have been pre-fractured by fracturing means and sealed by the composite slurry, no new cracks will be generated after the subsequent injection of carbon dioxide, or the new cracks can also be blocked by the already injected composite slurry (the gaps of the old cracks become larger), thereby avoiding carbon dioxide leakage and improving its sealing performance. After the injection of carbon dioxide, the bottom rock layer above the carbon dioxide storage layer 1 produces an arched and lifted isolation protection layer 2, a bottom uniform fracture zone 3 and a bottom damage zone 4; the bottom uniform fracture zone 3 and the bottom 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 bottom 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 the space formed by part of the coal seam mining, thereby reducing the equivalent mining height of the coal seam, reducing 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 hole for injecting polymer in step S5 and the directional drilling hole for injecting carbon dioxide 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 borehole is fractured, composite slurry is injected, and carbon dioxide is injected according to steps S4-S6 in a cycle.

[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. Any technical solution that is the same or similar to that of the present application falls within the protection scope of the present invention.

Claims

1. A negative carbon mining method for storing carbon dioxide in the floor of a goaf, characterized in that: The following steps are involved: S1: Determine the scope of the floor damage zone below the coal seam, select a rock layer of a certain thickness below the floor damage zone as an isolation protection layer, the isolation protection layer arches up under the 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; S2: Select a single rock layer below the isolation protection layer as the carbon dioxide 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 advancing direction of the working face; S4: The advanced working face mining position is located to form fracturing fractures by horizontally fracturing the CO2 storage layer through directional drilling; S5: The advanced working face injects a composite slurry of polymer and inorganic gelling material into the fracturing cracks through directional drilling; S6: After the working face has been mined and pushed through a horizontal section of a directional borehole and before reaching the orifice of the directional borehole, carbon dioxide is injected into the carbon dioxide storage layer through the directional borehole; S7: The working face continues to be mined, and the directional borehole is fractured, composite slurry is injected, and carbon dioxide is injected according to steps S4-S6 in a cycle.

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 in terms of height.

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 floor of a goaf 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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