Coal seam long borehole fracturing and protection integrated method

Abstract

This invention discloses an integrated method for fracturing and protecting long coal seams. Foamed macroporous mortar serves as both the fracturing medium and the borehole protection material. First, it is used as the fracturing medium, with pulsating foamed macroporous mortar fracturing the coal body surrounding the borehole to enhance permeability. Then, when the foamed macroporous mortar reaches its final setting time, it begins to generate supporting strength. The directional drilling rig is then activated, and the drill rod breaks up the formed foamed macroporous mortar within the borehole, ensuring that the solidified mortar does not block the borehole. Furthermore, the foamed macroporous mortar absorbs a large amount of water during solidification, ensuring its strength and performance. This forms a cluster of foamed macroporous mortar particles, ensuring the borehole protection effect and reducing the amount of water absorption and collapse of the soft coal body surrounding the borehole. This maximizes the unobstructed flow of gas extraction channels, ultimately achieving an integrated effect of fracturing and protecting long coal seams.

Description

Technical Field

[0001] This invention relates to the field of enhanced gas extraction through long boreholes in coal seams, specifically to an integrated method for fracturing and protection of long boreholes in coal seams. Background Technology

[0002] Methane gas is an associated gas in coal, existing in both free and adsorbed states within the coal seam or surrounding rock. Methane hazards seriously threaten safe production in coal mines. Currently, methane control requires the construction of numerous methane control roadways and boreholes, resulting in high costs. In recent years, relevant mines have innovated drilling construction technologies and processes, employing directional drilling rigs to construct large-diameter, long boreholes, achieving the goal of "replacing roadways with boreholes," reducing methane control projects, and lowering methane control costs.

[0003] Due to the complex geological conditions of coal seams in my country, soft and low-permeability coal seams are prevalent. Mining these seams is difficult, gas drainage is challenging, and gas hazards significantly limit mining efficiency. Therefore, coal seam modification is necessary, with the most common method being drilling boreholes for gas drainage. Currently, long boreholes are widely used due to their high drilling efficiency, concentrated gas drainage volume, high drainage efficiency, and long decay period. However, for soft and low-permeability coal seams, the effect of long borehole gas drainage is not ideal because of low permeability and the tendency for boreholes to collapse. This is because long boreholes do not fundamentally solve the gas drainage problem in soft, low-permeability coal seams.

[0004] Currently, the most common method for enhancing permeability in long coal seam boreholes is hydraulic permeability enhancement. However, in soft coal seams, this method is prone to a "water-locking effect," which reduces the effectiveness of fracturing and permeability enhancement. Protection methods for long coal seam boreholes mainly involve using casing or screen pipes to support and protect the borehole, preventing it from closing due to ground pressure and maximizing its service life. However, due to the considerable length of long boreholes, this method suffers from problems such as difficulty in properly positioning the casing; additionally, the high pressure caused by ground pressure in long boreholes can easily lead to breakage or collapse of the casing, ultimately causing borehole failure.

[0005] Given the problems with the existing technologies, one of the research directions in this industry is to provide a new method that can effectively fracturing and permeability enhancement in soft coal seams, while also providing better support for subsequent drilling, and ultimately ensuring the stability of coal seam gas extraction. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides an integrated method for long-bore fracturing and protection of coal seams, which can effectively induce fracturing and increase permeability in soft coal seams, while also providing good support for subsequent boreholes, ultimately ensuring efficient and stable coal seam gas extraction.

[0007] To achieve the above objectives, the technical solution adopted by this invention is: an integrated method for long-bore fracturing and protection of coal seams, the specific steps of which are as follows:

[0008] A. Construction of Long Coal Seam Boreholes and Installation of Grouting System: First, determine the construction location and length according to the coal seam gas extraction design requirements. Install hollow drill rods on the directional drilling rig, and install an openable directional drill bit at one end of the hollow drill rods. Use the directional drilling rig to drive the hollow drill rods and directional drill bit to start drilling the long coal seam borehole at the construction location until the long coal seam borehole reaches the design length, thus completing the construction of the long coal seam borehole. Then, control the directional drill bit to open, so that the hollow drill rod is connected to the inside of the long coal seam borehole. Connect the other end of the hollow drill rod at the directional drilling rig to the outlet of the grouting pump through a pipeline. Connect the inlet of the grouting pump to the holding container through a pipeline, thus completing the assembly of the grouting system.

[0009] B. Sealing long boreholes in coal seams: Long boreholes in coal seams are sealed using perforated conical rubber, and then fixed and reinforced.

[0010] C. Initial grouting of long boreholes in coal seams: First, prepare foamed macroporous mortar in a container. After preparation, start the grouting pump and inject the foamed macroporous mortar into the long borehole of the coal seam at a constant flow rate through the hollow drill rod. When the level of the foamed macroporous mortar in the container no longer changes, it indicates that the borehole has been filled with foamed macroporous mortar, which is in preparation for subsequent pulsed fracturing. Then, stop the grouting pump.

[0011] D. Pulsating Fracturing of Long Coal Seams: Disconnect the other end of the hollow drill rod at the directional drilling rig from the grouting pump and connect it to the outlet of the pulsating pump. Connect the inlet of the pulsating pump to a container via a pipeline. Start the pulsating pump and control the pulsating pressure to 30–35 MPa and the pulsating frequency to 150–220 Hz. This allows the foamed macroporous mortar to continue being injected into the long coal seam borehole at the set pulsating pressure and frequency. This causes the foamed macroporous mortar inside the long coal seam borehole to continuously fracture and permeate the surrounding borehole walls under pulsating pressure. During the operation of the pulsating pump, continuously observe the pressure on the pipeline between the pulsating pump and the hollow drill rod. Regarding the pressure gauge readings, when the pressure reading of the long coal seam borehole suddenly drops, it indicates that some of the foamed macroporous slurry has fractured the surrounding borehole wall and entered the fracture, causing a sudden drop in the borehole pressure. Continue to maintain the operation of the pulse pump until the pressure gauge reading rises from a drop to a stable state (i.e., the pulse fracturing can no longer generate more fractures) and remains stable for 1-2 hours. This indicates that the long coal seam borehole has completed the pulse fracturing of the coal body. Then, turn off the pulse pump and disconnect the hollow drill rod from the pulse pump. At this time, some of the foamed macroporous slurry in the long coal seam borehole is discharged from the borehole through the hollow drill rod.

[0012] E. Support and Protection for Long Coal Seam Boreholes: The remaining portion of the long coal seam borehole is filled with foamed macroporous mortar. Based on the setting time of the foamed macroporous mortar, once it reaches its final setting time, it gradually foams to generate support strength. At this point, the perforated conical rubber is removed, and the directional drilling rig is slowly started to rotate the drill rod and directional drill bit, thereby breaking up the formed foamed macroporous mortar into particles. Simultaneously, the drill rod is continuously retracted until complete, maintaining the connectivity of the long coal seam borehole. After a period of time, once the foamed macroporous mortar has completely solidified, it forms a group of foamed macroporous mortar particles, which are used for full-process support and protection of the long coal seam borehole, ultimately achieving integrated fracturing and protection of the long coal seam borehole.

[0013] Furthermore, the specific process for preparing foamed macroporous mortar is as follows: select each raw material according to the following mass ratio, mix and stir to prepare foamed macroporous mortar, the specific ratio is: water: cement: hydrogen peroxide: fly ash: fine aggregate = 1: (1~2): (0.08~0.15): (0.3~0.8): (0.5~0.1).

[0014] Furthermore, the fine aggregate is polyurethane particles with a diameter of 2-4 mm and a density of 100-200 kg / m³. 3 .

[0015] Furthermore, the perforated conical rubber has a length of 6 to 10 m, and can withstand a liquid pressure of 35 to 40 MPa after sealing long boreholes in coal seams.

[0016] Furthermore, the directional drill bit is opened via electrical control. This facilitates opening the directional drill bit after the drilling work is completed.

[0017] Compared with existing technologies, this invention first uses foamed macroporous mortar as a fracturing medium. The coal body around the long borehole is fracturing by pulsating foamed macroporous mortar. During the fracturing process, some of the foamed macroporous mortar is pressed against the borehole wall, which improves the fracturing effect on the coal body. After the coal seam fracturing is completed, the foamed macroporous mortar inside the directional borehole is released to prevent the foamed macroporous mortar from solidifying inside the directional borehole. This can prevent the blockage of the hollow drill rod and will not affect the reuse of the hollow drill rod. Once the foamed macroporous mortar inside the borehole reaches its final setting time, it completely loses its plasticity and begins to generate supporting strength. The perforated conical rubber is removed, and the directional drilling rig is slowly started. The drill rod breaks up the formed foamed macroporous mortar inside the borehole, forming foamed macroporous mortar particles. Simultaneously, the drill rod is continuously retracted until it is fully recovered. This creates gaps between the foamed macroporous mortar particles and the pores within the solidified foamed macroporous mortar itself, providing channels for gas migration and enabling efficient gas extraction. Furthermore, during the solidification process, a small portion of the water is absorbed by the surrounding coal seam, while the majority is used for the hydration and hardening of the foamed macroporous mortar, ensuring its strength and performance. The solidified foamed macroporous mortar particle group provides full support and protection throughout the long borehole in the coal seam. The gaps between the foamed macroporous mortar particles maximize the unobstructed flow of gas extraction channels. Simultaneously, the use of foamed macroporous mortar as a fracturing medium reduces the amount of water absorption and collapse of the soft coal body around the borehole, thus reducing the "water-locking effect." This invention fully utilizes the foamed macroporous mortar, using it as both a fracturing medium and a borehole protection material, achieving an integrated effect of fracturing and protection in long coal seam boreholes. It has good fracturing and permeability enhancement effects and can achieve full-process borehole protection, ensuring efficient gas extraction. In addition, the foamed macroporous mortar in this invention absorbs a large amount of water during solidification, thereby mitigating the "water-locking" problem caused by hydraulic fracturing in long coal seam boreholes. Since there is no need for casing or screen pipe support, it solves the problems of difficulty in installing screen pipes in long coal seam boreholes, easy breakage, and borehole failure caused by crushing. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the workflow of the present invention. Detailed Implementation

[0019] The present invention will be further described below.

[0020] like Figure 1 As shown, the specific steps of this invention are as follows:

[0021] A. Construction of Long Coal Seam Boreholes and Installation of Grouting System: First, determine the construction location and length according to the coal seam gas extraction design requirements. Install hollow drill rods on the directional drilling rig, and install an openable directional drill bit at one end of the hollow drill rods. The directional drilling rig drives the hollow drill rods and directional drill bit to start drilling the long coal seam borehole at the construction location until the long coal seam borehole reaches the design length, thus completing the construction of the long coal seam borehole. Then, control the directional drill bit to open through electrical control, so that the hollow drill rod is connected to the inside of the long coal seam borehole. Connect the other end of the hollow drill rod at the directional drilling rig to the outlet of the grouting pump through a pipeline, and connect the inlet of the grouting pump to the holding container through a pipeline, thus completing the assembly of the grouting system.

[0022] B. Sealing long boreholes in coal seams: Long boreholes in coal seams are sealed using perforated conical rubber, and then fixed and reinforced; the length of the perforated conical rubber is 6 to 10 m, and it can withstand a liquid pressure of 35 to 40 MPa after sealing the long boreholes in coal seams.

[0023] C. Initial grouting of long coal seam boreholes: First, prepare foamed macroporous mortar in a container. The specific process is as follows: select the raw materials according to the following mass ratio, mix and stir to prepare foamed macroporous mortar, the specific ratio is: water: cement: hydrogen peroxide: fly ash: fine aggregate = 1: (1~2): (0.08~0.15): (0.3~0.8): (0.5~0.1); the fine aggregate is polyurethane particles with a diameter of 2~4mm and a density of 100~200Kg / m³. 3 Within the above-mentioned ratio range, fine adjustments should be made based on the actual softness of the coal seam. After preparation, start the grouting pump and inject foamed macroporous mortar into the long borehole of the coal seam through the hollow drill rod at a constant flow rate. When the level of the foamed macroporous mortar in the container is no longer observed to change, stop the grouting pump.

[0024] D. Pulsating Fracturing of Long Coal Seams: Disconnect the other end of the hollow drill rod at the directional drilling rig from the grouting pump and connect it to the outlet of the pulsating pump. Connect the inlet of the pulsating pump to a container via a pipeline. Start the pulsating pump and control the pulsating pressure to 30–35 MPa and the pulsating frequency to 150–220 Hz. This allows the foamed macroporous mortar to continue being injected into the long coal seam borehole at the set pulsating pressure and frequency. This causes the foamed macroporous mortar inside the long coal seam borehole to continuously fracture and permeate the surrounding borehole walls under pulsating pressure. During the operation of the pulsating pump, continuously observe the pressure on the pipeline between the pulsating pump and the hollow drill rod. Regarding the pressure gauge readings, when the pressure reading of the long coal seam borehole suddenly drops, it indicates that some of the foamed macroporous slurry has fractured the surrounding borehole wall and entered the fracture, causing a sudden drop in the borehole pressure. Continue to maintain the operation of the pulse pump until the pressure gauge reading rises from a drop to a stable state (i.e., the pulse fracturing can no longer generate more fractures) and remains stable for 1-2 hours. This indicates that the long coal seam borehole has completed the pulse fracturing of the coal body. Then, turn off the pulse pump and disconnect the hollow drill rod from the pulse pump. At this time, some of the foamed macroporous slurry in the long coal seam borehole is discharged from the borehole through the hollow drill rod.

[0025] E. Support and Protection for Long Coal Seam Boreholes: The remaining portion of the long coal seam borehole is filled with foamed macroporous mortar. Based on the setting time of the foamed macroporous mortar, once it reaches its final setting time, it gradually begins to generate support strength. At this point, the perforated conical rubber is removed, and the directional drilling rig is slowly started to rotate the drill rod and directional drill bit, thereby breaking up the formed foamed macroporous mortar into foamed macroporous mortar particles. Simultaneously, the drill rod is continuously retracted until complete, maintaining the connectivity of the long coal seam borehole. After a period of waiting, once the foamed macroporous mortar has completely solidified, it forms a group of foamed macroporous mortar particles, which are used for full-process support and protection of the long coal seam borehole, ultimately achieving integrated fracturing and protection of the long coal seam borehole.

[0026] The aforementioned directional drilling rig, hollow drill rod, openable directional drill bit, pulse pump, grouting pump, and container are all existing equipment or components that can be purchased directly from the market.

[0027] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for integrated fracturing and protection of long boreholes in coal seams, characterized in that, The specific steps are as follows: A. Construction of Long Coal Seam Boreholes and Installation of Grouting System: First, determine the construction location and length according to the coal seam gas extraction design requirements. Install hollow drill rods on the directional drilling rig, and install an openable directional drill bit at one end of the hollow drill rods. Use the directional drilling rig to drive the hollow drill rods and directional drill bit to start drilling the long coal seam borehole at the construction location until the long coal seam borehole reaches the design length, thus completing the construction of the long coal seam borehole. Then, control the directional drill bit to open, so that the hollow drill rod is connected to the inside of the long coal seam borehole. Connect the other end of the hollow drill rod at the directional drilling rig to the outlet of the grouting pump through a pipeline. Connect the inlet of the grouting pump to the holding container through a pipeline, thus completing the assembly of the grouting system. B. Sealing long boreholes in coal seams: Long boreholes in coal seams are sealed using perforated conical rubber, and then fixed and reinforced. C. Initial grouting of long boreholes in coal seams: First, prepare foamed macroporous mortar in a container. After preparation, start the grouting pump and inject the foamed macroporous mortar into the long borehole of the coal seam at a constant flow rate through the hollow drill rod. When the level of the foamed macroporous mortar in the container no longer changes, stop the grouting pump. D. Pulsating Fracturing of Long Coal Seams: Disconnect the other end of the hollow drill rod at the directional drilling rig from the grouting pump and connect it to the outlet of the pulsating pump. Connect the inlet of the pulsating pump to a container via a pipeline. Start the pulsating pump and control the pulsating pressure to 30–35 MPa and the pulsating frequency to 150–220 Hz. This allows the foamed macroporous mortar to continue being injected into the long coal seam borehole at the set pulsating pressure and frequency. Consequently, the foamed macroporous mortar inside the long coal seam borehole continuously fractures and permeates the surrounding borehole walls under pulsating pressure. During the operation of the pulse pump, continuously observe the pressure gauge reading on the pipeline between the pulse pump and the hollow drill rod. When the pressure gauge reading of the long coal seam borehole suddenly drops, continue to maintain the operation of the pulse pump until the pressure gauge reading rises from the drop to a stable state and remains stable for 1 to 2 hours. This indicates that the long coal seam borehole has completed the pulse fracturing of the coal body. Then, turn off the pulse pump and disconnect the hollow drill rod from the pulse pump. At this time, a portion of the foamed macroporous slurry in the long coal seam borehole is discharged from the borehole through the hollow drill rod. E. Support and Protection for Long Coal Seam Boreholes: The remaining portion of the long coal seam borehole is filled with foamed macroporous mortar. Based on the setting time of the foamed macroporous mortar, once it reaches its final setting time, it gradually begins to generate support strength. At this point, the perforated conical rubber is removed, and the directional drilling rig is slowly started to rotate the drill rod and directional drill bit. This breaks up the already formed foamed macroporous mortar near the borehole axis, forming foamed macroporous mortar particles. Simultaneously, the drill rod is continuously retracted until complete, maintaining the connectivity of the long coal seam borehole. After a period of waiting, once the foamed macroporous mortar has completely solidified, it forms a group of foamed macroporous mortar particles, which are used for full-process support and protection of the long coal seam borehole, ultimately achieving integrated fracturing and protection for the long coal seam borehole.

2. The integrated method for long-bore fracturing and protection of coal seams according to claim 1, characterized in that, The specific process for preparing foamed macroporous mortar is as follows: select each raw material according to the following mass ratio, mix and stir to prepare foamed macroporous mortar, the specific ratio is: water: cement: hydrogen peroxide: fly ash: fine aggregate = 1: (1~2): (0.08~0.15): (0.3~0.8): (0.5~0.1).

3. The integrated method for long-bore fracturing and protection of coal seams according to claim 2, characterized in that, The fine aggregate is polyurethane particles with a diameter of 2-4 mm and a density of 100-200 kg / m³. 3 .

4. The integrated method for long-bore fracturing and protection of coal seams according to claim 1, characterized in that, The perforated conical rubber has a length of 6 to 10 m and can withstand a liquid pressure of 35 to 40 MPa after sealing long boreholes in coal seams.

5. The integrated method for long-bore fracturing and protection of coal seams according to claim 1, characterized in that, The directional drill bit is opened via electronic control.

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