Microbial flora combined plugging method for gas leakage of coal seam gas extraction hole

Abstract

The purpose of this invention is to provide a combined microbial community sealing method for leaking gas extraction holes in coal seams, belonging to the field of coal seam borehole sealing technology. By introducing the biomineralization capabilities of aerobic and facultative anaerobic microorganisms, and combining them with cement mortar and bag sealing processes, a "four-plug, two-injection, one-sealing" sealing system is formed. Under different operating conditions, this system induces the generation of carbonate minerals to actively and passively repair potential gas leakage channels in the sealing cement, borehole walls, and surrounding coal seams. Addressing the low efficiency of existing gas extraction technologies, this invention provides a green prevention and control solution from a microbial perspective. The microbial remediation method disclosed in this invention is simple to operate, uses a wide range of microbial communities with strong environmental adaptability, ensures long-term effectiveness of crack repair, and extends the service life of gas extraction holes, making it suitable for widespread application.

Description

Technical Field

[0001] This invention belongs to the field of coal seam borehole sealing technology, specifically relating to a method for combined sealing of leaking gas extraction holes in coal seams using microbial communities. Background Technology

[0002] Mine gas is one of the most significant safety hazards in coal mining. Currently, my country mainly uses underground gas drainage for prevention and control, with borehole gas drainage accounting for over 90% of the total drainage volume. As a highly efficient and clean energy source, the effectiveness and concentration of coal seam gas drainage determine whether it can be reused.

[0003] The sealing performance of boreholes is a major factor affecting the efficiency of coal seam gas drainage. Currently, the conventional cement mortar sealing process focuses on primary sealing. While it provides effective sealing in the initial stages of drainage, with continuous drainage and face advancement, the stress on the coal seam constantly changes, leading to the formation of new fractures and the reconnection of old fractures. Simultaneously, the sealing cement itself can crack and become conductive under stress changes, affecting the borehole's sealing performance and ultimately causing a decrease in gas drainage concentration and efficiency. These newly formed and developed fractures are difficult to treat externally again, resulting in the overall drainage efficiency of most gas drainage boreholes being far below the theoretical value within their service life.

[0004] Secondary sealing is currently the most common technique for improving the performance of gas drainage boreholes. However, this method is not long-lasting, and the drainage effect will still decrease over time, hindering underground mining operations. To achieve stable drainage concentrations in the borehole over the long term and improve drainage efficiency and borehole lifespan, it is necessary to adopt technological measures that can still improve borehole performance and prevent gas leakage after sealing. Microbially induced carbonate precipitation (MICP), as a biomineralization technology, can induce the formation of carbonate minerals, thereby blocking pore spaces, cementing fracture matrix, and repairing primary and secondary fractures in the coal seam. To address the issue of air leakage in borehole walls, patents CN111155960A and CN115559686A disclose a "method for sealing coal seam gas drainage boreholes based on MICP technology" and a "long-term sealing device and method for coal seam boreholes under the synergistic effect of microorganisms." However, the mineralizing bacteria used in these methods are all aerobic urease-producing bacteria, which cannot guarantee the durability of the seal under low-oxygen or even anaerobic conditions during gas drainage. Furthermore, these methods cannot simultaneously seal the two major potential leakage channels—the interior of the drainage borehole and the adjacent coal seam—leaking potential risks remain. Summary of the Invention

[0005] The purpose of this invention is to provide a combined microbial community sealing method for leaks in coal seam gas drainage holes. This method combines MICP technology with cement mortar and bag sealing processes, utilizing the biochemical reaction between microorganisms and calcium sources to form carbonate minerals that cement the pore structure between the coal seam and the sealing cement. By using aerobic mineralizing bacteria, facultative anaerobic mineralizing bacteria, cement mortar, and bags in combination, a "four-plug, two-inject, one-seale" sealing system is formed. This system prevents leaks before they occur and repairs them afterward, thereby improving coal mine gas drainage efficiency, ensuring coal mining safety, and extending the service life of gas drainage holes.

[0006] The present invention adopts the following technical solution: A method for combined microbial community sealing of leaking coal seam gas extraction holes includes the following steps: Step 1: Drill a gas extraction borehole into the pre-mined coal seam, and install an expansion bag as a sealing device at distances of 8-12m, 16-20m, 22-26m and 30-34m from the borehole opening. This creates a sealed space within the borehole consisting of "Aerobic Bacteria-Cement Mortar Sealing Zone 1", "Aerobic Bacteria-Cement Mortar Sealing Zone 2", and a "Facultative Bacteria Mineralization Treatment Zone". Step 2: In the middle of the facultative bacteria mineralization treatment area, high-pressure water jets are used to vertically cut the adjacent upper and lower coal seams, forming a cutting groove with a length of 0.5-1m, which serves as a channel for the diffusion of bacterial liquid. The gas extraction pipe is passed through the aerobic bacteria-cement mortar sealing zone one, the facultative bacteria mineralization treatment zone and the aerobic bacteria-cement mortar sealing zone two in sequence, and extends into the bottom of the gas extraction borehole. The grouting sleeve is passed through the aerobic bacteria-cement mortar sealing zone one and the facultative bacteria mineralization treatment zone in sequence, and extends into the aerobic bacteria-cement mortar sealing zone two, while ensuring the airtightness of each treatment zone. Step 4: The aerobic bacteria-cement mixed mortar is injected into the aerobic bacteria-cement mortar sealing zone 1 and aerobic bacteria-cement mortar sealing zone 2 through the combined grouting sleeve. During operation, the calcium carbonate induced by the aerobic bacteria can seal the cracks in the cement and the cracks at the cement-coal interface. Step 5: Extract the remaining mixed mortar from the combined grouting casing, and then inject the facultative bacteria treatment solution into the facultative bacteria mineralization treatment area through the combined grouting casing. The solution will spread through the diffusion of the bacteria solution and the cutting. During operation, the calcium carbonate induced by the facultative bacteria can seal the borehole wall and coal seam fractures. Step 6: During the gas extraction process, when the gas extraction concentration is too low to be reused, facultative bacteria treatment solution is injected into the facultative bacteria mineralization treatment area through a combined grouting casing to ensure the remediation efficiency of the facultative bacteria mineralization treatment area.

[0007] Furthermore, the four expansion bags mentioned in the first step divide the gas extraction hole into three areas, with the "facultative bacteria mineralization treatment area" located between the "aerobic bacteria-cement mortar sealing area one" and the "aerobic bacteria-cement mortar sealing area two".

[0008] Furthermore, the combined grouting sleeve described in the third step is composed of a rotatable inner pipe and an outer pipe. The outer pipe is equipped with vertical guide ports in the aerobic bacteria-cement mortar sealing zone one, the aerobic bacteria-cement mortar sealing zone two, and the facultative bacteria mineralization treatment zone. The inner pipe is equipped with grout outlets and bacteria outlets at corresponding positions, arranged vertically. Rotating the inner pipe, when the grout outlet of the inner pipe aligns with the guide port of the outer pipe, opens the grouting channel, allowing mixed mortar to be injected into the aerobic bacteria-cement mortar sealing zone one and the aerobic bacteria-cement mortar sealing zone two; when the bacteria outlet of the inner pipe aligns with the guide port of the outer pipe, opens the bacteria injection channel, allowing facultative bacteria treatment solution to be injected into the facultative bacteria mineralization treatment zone.

[0009] Furthermore, the gas extraction pipe diameter mentioned in step three is 1-2 cm. The inner diameter of the outer pipe and the outer diameter of the inner pipe of the combined grouting casing are both 0.8-0.9 cm, and there is good sealing between the inner and outer pipes. The diameters of the vertical guide port of the outer pipe, the slurry outlet and the bacteria outlet of the inner pipe are all 0.2-0.4 cm, the length of the combined grouting casing is 24-32 m, and the length of the vertical guide port of the outer pipe is 0.4-0.6 cm.

[0010] Furthermore, the aerobic bacteria mentioned in the fourth step can be urease-producing bacteria with aerobic mineralization function, such as Bacillus pasteurellii, Bacillus megaterium, and Bacillus spheroides; or carbonic anhydrase-producing bacteria, such as Bacillus mucilaginosus and Bacillus pumilus.

[0011] Furthermore, the aerobic bacteria-cement mixed mortar mentioned in the fourth step is made by mixing aerobic bacteria repair capsules with cement mortar, and the amount of aerobic bacteria repair capsules is 4%-8% of the cement mass.

[0012] Furthermore, the facultative bacteria mentioned in the fifth step are selected from denitrifying bacteria with denitrification-induced mineralization function, which can be enriched from original coal seams, goaf areas, activated sludge, etc., with original coal seam bacteria being preferred.

[0013] Furthermore, the facultative bacteria treatment solution described in step five is composed of a mixture of facultative mineralizing bacteria solution and a basic mineralizing solution, with the facultative mineralizing bacteria solution accounting for 10% of the volume of the facultative bacteria treatment solution. The injection volume of the facultative bacteria treatment solution is 2-4 mg / L. 3 .

[0014] Furthermore, as described in step six, when the gas extraction concentration is below 50%, facultative bacteria treatment solution is injected into the facultative bacteria mineralization treatment area through a combined grouting casing to ensure the remediation efficiency of the treatment solution. The injection volume is 1-2 m³. 3 / time. Facultative bacteria treatment solution can directly repair borehole wall cracks and enhance the strength of the extraction hole; it can also play a sealing role in coal seam pore fracture channels at a greater distance through bacterial diffusion cuts, preventing gas from seeping into the extraction hole.

[0015] Furthermore, the aerobic bacteria repair capsule is made of low-alkali cement, and the admixture consists of aerobic mineralizing bacteria spores, nutrients, and calcium sources.

[0016] Furthermore, when oxygen seeps into the capsule or the capsule ruptures due to stress changes, the aerobic bacterial repair capsule can release spores that transform into aerobic mineralizing bacteria, actively repairing cracks within the cement and at the cement-coal interface. After repair, the spores can revert to dormancy and be reactivated upon the next oxygen leak.

[0017] Furthermore, the "aerobic bacteria-cement mortar sealing zone" can significantly reduce the oxygen content in the pore, promote the initial reproduction of facultative bacteria and the expression of mineralization function. The injection of facultative bacteria treatment solution can also bring mineralized substrates and nutrients to the aerobic bacteria-cement sealing section, further improving the durability of the sealing effect of the "aerobic bacteria-cement mortar sealing zone". The two complement each other and promote each other.

[0018] Furthermore, the basic mineralization solution comprises: 19.83 g / L CaCl2, 2.49 g / L NaNO3, and 2.15 g / L NaNO3.

[0019] The beneficial effects of this invention are as follows: This invention provides a method for the synergistic repair of gas leakage in coal seam gas extraction wells by microorganisms. By introducing the biomineralization capabilities of aerobic and facultative anaerobic bacteria, carbonate minerals are induced to form under different operating conditions, thereby sealing potential gas leakage channels in the sealing cement, borehole walls, and surrounding coal seams.

[0020] 1. This invention can repair the two main gas leakage pathways (cement cracks in boreholes and coal seam cracks) during gas extraction, and completely seal the gas leakage channels.

[0021] 2. This invention combines aerobic and anaerobic microbial mineralization technologies to actively and passively repair gas leakage channels. The two technologies complement and promote each other, ensuring the long-term effectiveness of the repair and extending the service life of gas extraction wells.

[0022] 3. The process of this invention is simple to operate, the bacterial groups used are widely available and have strong environmental adaptability, and it has good economic benefits. Attached Figure Description

[0023] Figure 1This is a schematic diagram of the microbial synergistic sealing method for leaking coal seam gas extraction holes according to the present invention; wherein, 1: pre-mined coal seam; 2: bacterial liquid diffusion slit; 3: facultative bacteria mineralization treatment zone; 4: aerobic bacteria-cement mortar sealing zone one; 5: gas extraction pipe; 6: combined grouting casing; 7: expansion bag; 8: aerobic bacteria-cement mortar sealing zone two.

[0024] Figure 2 The diagram shows the combined grouting casing. Figure (a) shows the casing state when the mixed mortar is injected, and Figure (b) shows the casing state when the facultative bacteria treatment solution is injected. Wherein, 9: bacteria outlet; 10: flow guide; 11: outer pipe; 12: inner pipe; 13: grout outlet.

[0025] Figure 3 X-ray diffraction pattern of carbonate minerals formed by biomineralization.

[0026] Figure 4 This is a scanning electron microscope (SEM) diagram illustrating the cementation and blockage of pores by biomineralized calcium carbonate; the arrow points to the calcium carbonate generated by biomineralization. Detailed Implementation

[0027] An embodiment of the present invention will be further described with reference to the accompanying drawings: Step 1: Drill a gas drainage borehole into a coal seam to be mined. Install expansion bags at distances of 8m, 16m, 22m, and 30m from the borehole opening as sealing devices, creating a sealed space within the borehole consisting of "Aerobic Bacteria-Cement Mortar Sealing Zone 1," "Aerobic Bacteria-Cement Mortar Sealing Zone 2," and a "Facultative Bacteria Mineralization Treatment Zone." The four expansion bags divide the borehole into three areas. The "Facultative Bacteria Mineralization Treatment Zone" is located between "Aerobic Bacteria-Cement Mortar Sealing Zone 1" and "Aerobic Bacteria-Cement Mortar Sealing Zone 2," as shown below. Figure 1 .

[0028] Step 2: In the middle of the facultative bacterial mineralization treatment area, high-pressure water jets are used to vertically cut the adjacent upper and lower coal seams, forming a cutting groove with a length of 0.5m on each side, which serves as a channel for bacterial liquid diffusion.

[0029] Step 3: The gas extraction pipe is sequentially passed through the aerobic bacteria-cement mortar sealing zone 1, the facultative bacteria mineralization treatment zone, and the aerobic bacteria-cement mortar sealing zone 2, extending into the bottom of the gas extraction borehole. The combined grouting sleeve is sequentially passed through the aerobic bacteria-cement mortar sealing zone 1 and the facultative bacteria mineralization treatment zone, extending into the aerobic bacteria-cement mortar sealing zone 2, ensuring the airtightness of each treatment zone. The combined grouting sleeve consists of a rotatable inner pipe and an outer pipe. The outer pipe has vertical guide ports in the aerobic bacteria-cement mortar sealing zone 1, the aerobic bacteria-cement mortar sealing zone 2, and one facultative bacteria mineralization treatment zone. The inner pipe has grout outlets and bacteria outlets at corresponding positions, arranged vertically. Rotate the inner pipe. When the grout outlet of the inner pipe aligns with the guide port of the outer pipe, open the grouting channel to inject mixed mortar into the aerobic bacteria-cement mortar sealing zone. When the bacteria outlet of the inner pipe aligns with the guide port of the outer pipe, open the bacteria injection channel to inject facultative bacteria treatment solution into the facultative bacteria mineralization treatment zone. The gas extraction pipe has a diameter of 1 cm. The inner diameter of both the outer and inner pipes of the combined grouting casing is 0.8 cm, and there is good sealing between the inner and outer pipes. The diameters of the vertical guide port of the outer pipe, the grout outlet of the inner pipe, and the bacteria outlet are all 0.2 cm. The combined grouting casing is 24 m long, and the length of the vertical guide port of the outer pipe is 0.4 cm.

[0030] Step 4: The aerobic bacteria-cement mortar mixture is injected into the aerobic bacteria-cement mortar sealing zone 1 and aerobic bacteria-cement mortar sealing zone 2 through the combined grouting sleeve. During operation, the calcium carbonate induced by the aerobic bacteria can seal the internal cracks in the cement and the cracks at the cement-coal interface. The aerobic bacteria selected are Bacillus subtilis, which has aerobic mineralization function. Nutrients and calcium sources (12.0 g / L glucose, 3.0 g / L YEAST, 1.5 g / L K2HPO4, and 3.0 g / L CaCl2) are continuously sprayed onto the surface of the powdered Bacillus subtilis spores using a sugar coating method, forming 1.5-2.5 mm spheres. These spheres are then encapsulated with low-alkali cement to create aerobic bacterial repair capsules of 3.5-4.0 mm in size. The sealing cement grout is made with ordinary Portland cement as the base material, mixed at a water-cement ratio of 1:1.

[0031] Step 5: Extract the remaining mixed mortar from the combined grouting casing. Then, inject the facultative bacteria treatment solution into the facultative bacteria mineralization treatment zone through the combined grouting casing and transport it to the bacterial solution diffusion area. During operation, the calcium carbonate induced by the facultative bacteria can seal the borehole wall and coal seam fractures. The facultative bacteria treatment solution is a mixture of facultative mineralizing bacteria solution and basic mineralizing solution, with the facultative mineralizing bacteria solution accounting for 10% of the total volume of the facultative bacteria treatment solution. The injection volume of the facultative bacteria treatment solution is 2m³. 3The facultative bacteria are selected from a mixed denitrifying bacterial community with denitrification-inducing mineralization function, enriched from the original coal seam. The basic mineralization solution includes: 19.83 g / L CaCl2, 2.49 g / L Na2O4·6H2O, and 2.15 g / L NaNO3.

[0032] After the aerobic bacteria-cement mortar has cured, when oxygen seeps in or the capsules rupture due to stress changes, Bacillus subtilis can be activated, thereby actively repairing cracks within the cement and at the cement-coal interface. After repair, it can revert to dormant spores and be reactivated upon the next oxygen leak. The facultative bacteria treatment solution can directly repair borehole wall cracks and enhance borehole strength; it can also diffuse through the bacterial solution to cut fissures in more distant coal seam pores, acting as a sealant to prevent gas from seeping into the extraction borehole.

[0033] The "aerobic bacteria-cement mortar sealing zone" can significantly reduce the oxygen content in the pore, promote the initial reproduction of facultative bacteria and the expression of mineralization function. The injection of facultative bacteria treatment solution can also bring mineralized substrates and nutrients to the aerobic bacteria-cement sealing section, further improving the durability of the sealing effect of the "aerobic bacteria-cement mortar sealing zone". The two complement each other and promote each other.

[0034] The mineralization products formed by microbial mineralization are calcite, which has stable physical and chemical properties. Figure 3 It can cement and seal pores and fractures in various matrices, including coal seams and cement. Figure 4 This reduces gas leakage channels, thereby improving the sealing of gas extraction holes.

[0035] Step 6: During the gas extraction process, when the gas extraction concentration is below 50%, facultative bacteria treatment solution is injected into the facultative bacteria mineralization treatment area through a combined grouting casing to ensure the remediation efficiency of the treatment solution. The injection volume is 1m³. 3 / Second-rate.

Claims

1. A microbial flora combined plugging method for gas leakage of a coal seam gas extraction hole, characterized in that: Includes the following steps: Step 1: Drill a gas extraction borehole into the pre-mined coal seam, and install an expansion bag as a sealing device at distances of 8-12m, 16-20m, 22-26m and 30-34m from the borehole opening. This creates a sealed space within the borehole consisting of "Aerobic Bacteria-Cement Mortar Sealing Zone 1", "Aerobic Bacteria-Cement Mortar Sealing Zone 2", and a "Facultative Bacteria Mineralization Treatment Zone". Step 2: In the middle of the facultative bacteria mineralization treatment area, high-pressure water jets are used to vertically cut the adjacent upper and lower coal seams, forming a cutting groove with a length of 0.5-1m, which serves as a channel for the diffusion of bacterial liquid. Step 3: Pass the gas extraction pipe through the aerobic bacteria-cement mortar sealing zone 1, the facultative bacteria mineralization treatment zone, and the aerobic bacteria-cement mortar sealing zone 2 in sequence, and extend it into the bottom of the gas extraction borehole. Then, pass the grouting sleeve through the aerobic bacteria-cement mortar sealing zone 1 and the facultative bacteria mineralization treatment zone in sequence, and extend it into the aerobic bacteria-cement mortar sealing zone 2, ensuring the airtightness of each treatment zone. Step 4: The aerobic bacteria-cement mixed mortar is injected into the aerobic bacteria-cement mortar sealing zone 1 and aerobic bacteria-cement mortar sealing zone 2 through the combined grouting sleeve. During operation, the calcium carbonate induced by the aerobic bacteria can seal the cracks in the cement and the cracks at the cement-coal interface. Step 5: Extract the remaining mixed mortar from the combined grouting casing, and then inject the facultative bacteria treatment solution into the facultative bacteria mineralization treatment area through the combined grouting casing. The solution will spread through the diffusion of the bacteria solution and the cutting. During operation, the calcium carbonate induced by the facultative bacteria can seal the borehole wall and coal seam fractures. Step 6: During the gas extraction process, when the gas extraction concentration is too low to be reused, facultative bacteria treatment solution is injected into the facultative bacteria mineralization treatment area through a combined grouting casing to ensure the remediation efficiency of the facultative bacteria mineralization treatment area. The four expansion bags mentioned in the first step divide the gas extraction hole into three areas, with the "facultative bacteria mineralization treatment area" located between the "aerobic bacteria-cement mortar sealing area one" and the "aerobic bacteria-cement mortar sealing area two". The combined grouting sleeve described in the third step consists of a rotatable inner pipe and an outer pipe. The outer pipe is equipped with vertical guide ports in the aerobic bacteria-cement mortar sealing zone one, the aerobic bacteria-cement mortar sealing zone two, and the facultative bacteria mineralization treatment zone. The inner pipe is equipped with grout outlets and bacteria outlets at corresponding positions, arranged vertically. When the inner pipe is rotated, the grout outlet of the inner pipe is aligned with the guide port of the outer pipe, opening the grouting channel and injecting mixed mortar into the aerobic bacteria-cement mortar sealing zone one and the aerobic bacteria-cement mortar sealing zone two. When the bacteria outlet of the inner pipe is aligned with the guide port of the outer pipe, the bacteria injection channel is opened, injecting facultative bacteria treatment solution into the facultative bacteria mineralization treatment zone.

2. The microbial flora combined plugging method for gas leakage of a coal seam gas extraction hole according to claim 1, characterized in that: The gas extraction pipe in the third step has a diameter of 1-2 cm. The inner diameter of the outer pipe and the outer diameter of the inner pipe of the combined grouting casing are both 0.8-0.9 cm. There is good sealing between the inner and outer pipes. The diameter of the vertical guide port of the outer pipe, the slurry outlet and the bacteria outlet of the inner pipe are all 0.2-0.4 cm. The length of the combined grouting casing is 24-32 m, and the length of the vertical guide port of the outer pipe is 0.4-0.6 cm.

3. The microbial flora combined plugging method for gas leakage of a coal seam gas extraction hole according to claim 1, characterized in that: The aerobic bacteria mentioned in the fourth step are selected from urease-producing bacteria with aerobic mineralization function, including any one of Bacillus pasteurellii, Bacillus megaterium, and Bacillus spheroidis; or carbonic anhydrase-producing bacteria, including any one of Bacillus mucilaginosus and Bacillus pumilus.

4. The microbial flora combined plugging method for gas leakage of a coal seam gas extraction hole according to claim 1, characterized in that: The aerobic bacteria-cement mixed mortar mentioned in step four is made by mixing aerobic bacteria repair capsules with cement mortar, and the amount of aerobic bacteria repair capsules is 4%-8% of the cement mass.

5. The method for combined microbial community sealing of leaking coal seam gas extraction holes according to claim 1, characterized in that: The facultative bacteria mentioned in the fifth step are denitrifying bacteria with denitrification-induced mineralization function, which are enriched from the original coal seam, goaf, and activated sludge.

6. The microbial flora combined plugging method for gas leakage of a coal seam gas extraction hole according to claim 1, characterized in that: The facultative bacteria treatment solution described in step five is composed of a mixture of facultative mineralizing bacteria solution and a basic mineralizing solution. The facultative mineralizing bacteria solution accounts for 10% of the volume of the facultative bacteria treatment solution, and the injection volume of the facultative bacteria treatment solution is 2-4 m³. 3 ; The basic mineralization solution comprises: 19.83 g / L CaCl2, 2.49 g / L NaNO3, and 2.15 g / L NaNO3.

7. The microbial flora combined plugging method for gas leakage of a coal seam gas extraction hole according to claim 1, characterized in that: In the sixth step, when the gas extraction concentration is less than 50%, the facultative bacteria treatment liquid is supplemented and injected into the facultative bacteria mineralization treatment area through the combined grouting casing to ensure the repair efficiency of the treatment liquid, and the injection amount is 1-2 m 3 / second.

8. The microbial flora combined plugging method for gas leakage of a coal seam gas extraction hole according to claim 4, characterized in that: The aerobic bacteria repair capsule is made of low-alkali cement, and the admixture consists of aerobic mineralizing bacteria spores, nutrients, and calcium sources.

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