A method of hydraulic fracturing coal body weakening

Abstract

This invention discloses a method for weakening coal seams through hydraulic fracturing. A directional drilling rig is used to drill a hole perpendicular to the working face in the haulage or auxiliary haulage roadway. A packer and fracturing rod are then placed into the hole. After the packer and fracturing rod are lowered to the bottom of the hole, the fracturing rod is connected to a pulse pump. Once the pipeline is connected, the pulse pump is started. The pump is stopped after the designed fracturing time is reached, and the fracturing rod is then withdrawn 2-5 meters outwards for another fracturing operation. This process continues until fracturing reaches near the borehole opening, completing the fracturing of one borehole. This fracturing cycle is repeated. During the fracturing process, monitoring equipment is used to monitor the fracturing flow rate and fracturing pressure in real time. This short-distance, high-frequency fracturing method allows for more than 60 fracturing operations per borehole. Therefore, the accompanying packer is a high-pressure resistant and fatigue-resistant packer that can be reused multiple times.

Description

Technical Field

[0001] This invention belongs to the field of hydraulic fracturing technology in coal mines, and specifically discloses a method for weakening coal bodies through hydraulic fracturing. Background Technology

[0002] Of the currently proven coal reserves, hard coal seams account for as much as 43%, and the difficulty in cutting these hard seams has always been a prominent problem restricting the development of fully mechanized mining. Due to the hardness, density, high toughness, and underdeveloped joints and fractures of the coal seams, the grinding action of the mining machine is significant, making coal cutting extremely difficult. Furthermore, the hardness and density of the coal seams, coupled with underdeveloped joints and fractures, result in high energy consumption and slow mining speed of the mining machine during the extraction process, leading to frequent accidents. Moreover, the mining machine's cutting teeth suffer from severe wear, generating large amounts of coal dust and increasing the frequency of tooth maintenance and replacement, significantly impacting normal production. The persistently high coal dust content not only harms the physical and mental health of underground workers but also poses a safety hazard of coal dust explosions. On the other hand, it results in a high content of fine coal and a low rate of lump coal, affecting sales prices and hindering efficient, safe, and environmentally friendly mining, thus preventing further increases in mine output and profits.

[0003] Therefore, for mining hard coal seams, it is often necessary to weaken the coal seam through artificial intervention. Commonly used weakening methods include explosive blasting, water injection softening, and mechanical vibration. After weakening, a large number of weakened structural surfaces are generated inside the coal body to reduce the strength of the coal seam and improve the recovery rate.

[0004] In existing technologies, the application of blasting techniques in fully mechanized mining faces poses significant safety hazards. Firstly, coal, as a fossil fuel, is inherently combustible. Secondly, the presence of methane gas within the coal seam and coal dust at the working face can easily trigger explosions. Furthermore, the explosion process is difficult to control, leading to equipment damage and a sharp increase in the possibility of personnel casualties. Therefore, the use of blasting techniques underground places extremely high pressure on safety production management.

[0005] The Honghui No. 1 Mine in China once experimented with shallow-hole loosening blasting of the coal face. However, this method significantly disrupted normal mining operations, and the blasted coal fragments easily damaged the support columns and hydraulic lines. Furthermore, the length of fully mechanized mining faces in China is generally between 200-250m, meaning that blasting-induced fracturing cannot completely cover the entire face, limiting its effectiveness in addressing engineering scale issues. Considering these factors, blasting-induced fracturing technology has not been widely adopted in fully mechanized mining of hard coal seams.

[0006] Low-pressure coal seam water injection weakening technology is mostly used in coal mining to reduce the dust content of the working face. Coal seam water injection is also used in the research of coal mine rockburst prevention. The coal seam water injection process is actually a water-gas displacement process. Its water injection radius is limited and it can no longer form cracks in the coal body, so its impact on the integrity of the coal body is limited.

[0007] In addition, conventional shallow-hole hydraulic fracturing technology in coal mines is limited by factors such as fracturing process, equipment, and borehole length. On the one hand, it cannot effectively destroy the coal body, and on the other hand, it cannot cover the entire working face, thus failing to meet engineering applications. Summary of the Invention

[0008] In order to fully destroy the integrity of the coal face, this invention discloses a hydraulic fracturing method for weakening the coal body. This method adopts a construction scheme of "long distance-short interval-large flow rate-strong pulse", which can achieve coverage of a large working face and effectively destroy the coal body.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for weakening coal seams through hydraulic fracturing, comprising the following steps:

[0010] Step 1: Collect geological data of the target area and understand the basic production geological conditions of the working face;

[0011] Step 2: Conduct basic geomechanical parameter tests in the target area, including borehole inspection and in-situ coal strength testing, to understand the structure and physical and mechanical parameters of hard coal seams;

[0012] Step 3: Based on the data collected in Step 1 and Step 2, formulate a preliminary coal body weakening plan. The weakening plan can be dynamically revised and adjusted according to the on-site implementation and effects.

[0013] Step 4: Based on the weakening scheme in Step 3, select a suitable drilling rig and a high-flow pulse high-pressure pump;

[0014] Step 5: Using a directional drilling rig, drill a hole perpendicular to the working face in the haulage or auxiliary haulage roadway. Then, place a packer and fracturing rod into the hole. After the packer and fracturing rod are at the bottom of the hole, connect the fracturing rod to the pulse pump. After the pipeline is connected, start the pulse pump. When the fracturing reaches the designed fracturing time, stop the pump. Then, withdraw the fracturing rod 2-5m outward (compared to conventional fracturing, shorten the fracturing interval between adjacent fracturing sections and increase the number of fracturing operations per hole), and then perform a new fracturing operation until fracturing reaches near the borehole opening, completing the fracturing work of one borehole. Repeat the above fracturing operation. During the fracturing process, use monitoring equipment to monitor the fracturing flow rate and fracturing pressure in real time.

[0015] Step 6: After a single borehole is completed, the fracturing borehole is inspected to compare the distribution of cracks inside the borehole before and after fracturing, and then the fracturing operation of the next borehole is carried out.

[0016] Step 7: After all boreholes have been fracturing, withdraw the construction equipment and clean up the construction site. When the working face is mined back to the fracturing zone, calculate the coal cutting efficiency, energy consumption, and cutting tooth consumption of the coal mining machine, as well as the lump coal rate and dust concentration, and comprehensively evaluate the fracturing effect.

[0017] In step 5, staggered drilling is used, with the spacing between adjacent layers in the vertical plane being 0.5m to 2m, the spacing between fracturing holes in the same layer being 10m to 20m, and the spacing between adjacent staggered fracturing holes being 5m to 10m.

[0018] This method allows for drilling lengths of up to 600m or more, covering the entire working face width.

[0019] Furthermore, because a short-distance, high-frequency fracturing method is adopted, with more than 60 fracturing cycles per hole, the matching packer is a high-pressure resistant and fatigue-resistant packer. This packer can be reused multiple times, thereby achieving short-interval, high-frequency fracturing, and the construction efficiency will not be seriously affected by frequent packer damage.

[0020] The pulse pump is a high-flow pulse high-pressure pump, which helps to form fractures; the high-pressure water injection pump used in this method is a double-plunger high-flow pulse water injection pump with a fracturing flow rate of not less than 27.5 m3 / h, a maximum pressure of not less than 45 MPa, and a pulse frequency of not less than 1060 times / min.

[0021] The beneficial effects of this invention are as follows: This invention employs a "long-distance, short-interval, high-flow, strong-pulse" hard coal body weakening technology, which is safe, reliable, and simple to construct. It can efficiently destroy hard coal bodies and can be carried out before the working face is mined. The weakened hard coal body, due to its fully disrupted integrity, is beneficial for the coal mining machine to cut, thus increasing the cutting speed, reducing the consumption of cutting teeth, and increasing the lump coal rate. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the terrain structure for the construction of this invention;

[0023] Figure 2 This is a top view of the construction area of ​​the present invention.

[0024] Figure 3 yes Figure 2 Schematic diagram of the cross-section structure along direction A;

[0025] Figure 4 yes Figure 2 Schematic diagram of the B-section structure;

[0026] Figure 5 This is a diagram showing the construction parameters in this embodiment; Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings.

[0028] Example 1: A method for weakening coal seams through hydraulic fracturing, comprising the following steps:

[0029] Step 1: Collect geological data of the target area and understand the basic production geological conditions of the working face. In this embodiment, the construction operation is carried out at the ridge.

[0030] Step 2: Conduct basic geomechanical parameter tests in the target area, including borehole inspection and in-situ coal strength testing, to understand the structure and physical and mechanical parameters of hard coal seams;

[0031] Step 3: Based on the data collected in Step 1 and Step 2, formulate a preliminary coal body weakening plan. The weakening plan can be dynamically revised and adjusted according to the on-site implementation and effects.

[0032] Step 4: Based on the weakening scheme in Step 3, select a suitable drilling rig and a high-flow pulse high-pressure pump; the pulse pump is a high-flow pulse high-pressure pump, which helps in the formation of fractures; the high-pressure water injection pump used in this method is a dual-plunger high-flow pulse water injection pump, with a fracturing flow rate of not less than 27.5 m3 / h, a maximum pressure of not less than 45 MPa, and a pulse frequency of not less than 1060 times / min;

[0033] Step 5: Using a directional drilling rig, drill holes perpendicular to the working face in the haulage or auxiliary haulage roadway. Place a packer and fracturing rod into the hole. Once the packer and fracturing rod are at the bottom of the hole, connect the fracturing rod to the pulse pump. After the pipeline is connected, start the pulse pump. When the designed fracturing time is reached, stop the pump and then retract the fracturing rod 2m to 5m outwards. Perform a new fracturing operation until fracturing reaches near the borehole opening, completing the fracturing work for one borehole. Repeat the above fracturing operation. During the fracturing process, use monitoring equipment to monitor the fracturing flow rate and fracturing pressure in real time. In Step 5, staggered drilling is used. The spacing between adjacent layers of holes in the vertical plane is 0.5m to 2m, the spacing between fracturing holes in the same layer is 10m to 20m, and the spacing between adjacent staggered fracturing holes is 5m to 10m.

[0034] Step 6: After a single borehole is completed, the fracturing borehole is inspected to compare the distribution of cracks inside the borehole before and after fracturing, and then the fracturing operation of the next borehole is carried out.

[0035] Step 7: After all boreholes have been fracturing, withdraw the construction equipment and clean up the construction site. When the working face is mined back to the fracturing zone, calculate the coal cutting efficiency, energy consumption, and cutting tooth consumption of the coal mining machine, as well as the lump coal rate and dust concentration, and comprehensively evaluate the fracturing effect.

[0036] This method allows for drilling lengths of up to 600m or more, covering the entire working face width.

[0037] Furthermore, because a short-distance, high-frequency fracturing method is adopted, with more than 60 fracturing cycles per hole, the matching packer is a high-pressure resistant and fatigue-resistant packer. This packer can be reused multiple times, thereby achieving short-interval, high-frequency fracturing, and the construction efficiency will not be seriously affected by frequent packer damage.

[0038] The beneficial effects of this invention are as follows: This invention employs a "long-distance, short-interval, high-flow, strong-pulse" hard coal body weakening technology, which is safe, reliable, and simple to construct. It can efficiently destroy hard coal bodies and can be carried out before the working face is mined. The weakened hard coal body, due to its fully disrupted integrity, is beneficial for the coal mining machine to cut, thus increasing the cutting speed, reducing the consumption of cutting teeth, and increasing the lump coal rate.

Claims

1. A method for weakening coal seams through hydraulic fracturing, characterized in that: It includes the following steps: Step 1: Collect geological data of the target area and understand the basic production geological conditions of the working face; Step 2: Conduct basic geomechanical parameter tests in the target area, including borehole inspection and in-situ coal strength testing, to understand the structure and physical and mechanical parameters of hard coal seams; Step 3: Based on the data collected in Step 1 and Step 2, formulate a preliminary coal body weakening plan. The weakening plan can be dynamically revised and adjusted according to the on-site implementation and effects. Step 4: Based on the weakening scheme in Step 3, select a suitable drilling rig and a high-flow pulse high-pressure pump; Step 5: Using a directional drilling rig, drill a hole perpendicular to the working face in the haulage or auxiliary haulage roadway. Then, place a packer and fracturing rod into the hole. After the packer and fracturing rod are placed at the bottom of the hole, connect the fracturing rod to the pulse pump. After the pipeline is connected, start the pulse pump. When the fracturing reaches the designed fracturing time, stop the pump and then retract the fracturing rod 2-5m outwards. Then, perform a new fracturing operation until the fracturing reaches near the borehole opening, completing the fracturing work for one borehole. Repeat the above fracturing operation. During the fracturing process, use monitoring equipment to monitor the fracturing flow rate and fracturing pressure in real time. Step 6: After a single borehole is completed, the fracturing borehole is inspected to compare the distribution of cracks inside the borehole before and after fracturing, and then the fracturing operation of the next borehole is carried out. Step 7: After all boreholes have been fracturing, withdraw the construction equipment and clean up the construction site.

2. The method for weakening coal seams by hydraulic fracturing as described in claim 1, characterized in that: In step 5, staggered drilling is used, with the spacing between adjacent layers in the vertical plane being 0.5m to 2m, the spacing between fracturing holes in the same layer being 10m to 20m, and the spacing between adjacent staggered fracturing holes being 5m to 10m.

3. The method for weakening coal seams by hydraulic fracturing as described in claim 1, characterized in that: This method allows for drilling lengths greater than 600m, covering the entire working face width.

4. The method for weakening coal seams by hydraulic fracturing as described in claim 1, characterized in that: This invention employs a short-distance, high-frequency fracturing method, with more than 60 fracturing cycles per hole. Therefore, the matching packer is a high-pressure resistant and fatigue-resistant packer.

5. The method for weakening coal seams by hydraulic fracturing as described in claim 1, characterized in that: The pulse pump is a high-flow pulse high-pressure pump; the high-pressure water injection pump is a dual-plunger high-flow pulse water injection pump with a fracturing flow rate greater than 27.5 m3 / h, a maximum pressure greater than 45 MPa, and a pulse frequency greater than 1060 times / min.

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