Method for treating gas in long-distance liquid nitrogen high-pressure fracturing of intermediate argillaceous rock layer
Patent Information
- Application Number
- CN202610988534.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-07-03
- Publication Date
- 2026-09-04
AI Technical Summary
[0003]但是，受地质构造和深部地热影响，深部煤（层）多表现出松软化，尤其是含泥质较多的岩层，表现出强度较小，节理不发育，受应力作用，裂隙发育较差，透气性较差，导致保护层和被保护层之间层位含有泥岩或者泥质岩时，开采保护层治理被保护层的瓦斯效果较为不理想，
利用液氮的低温特性，改变松软泥质岩层结构特性，增加了松软泥质岩层的强脆性，促进松软泥质岩层结构发育，提高了松软泥质岩层易破坏性。
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Figure CN122687992A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of argillaceous rock strata treatment technology, and specifically provides a method for controlling gas in argillaceous rock strata through long-distance liquid nitrogen high-pressure fracturing. Background Technology
[0002] Currently, coal mining depths and conditions are becoming increasingly complex, making coal seam gas control a primary challenge in deep mining. Based on past experience and in accordance with safety regulations and guidelines, the most effective method for coal seam gas control is the protective layer mining method. This involves mining adjacent, non-outburst-hazardous coal seams outside the outburst-prone seams, creating a goaf through the extraction of a protective layer. Under stress, delamination fractures occur between the protective layer and the protected layer, causing a large amount of gas to be released from the protected layer along these fractures into the goaf, thus achieving the coal seam gas control process in the protected layer.
[0003] However, due to geological structure and deep geothermal influence, deep coal seams often exhibit softening, especially those with high argillaceous content. These seams tend to have lower strength, less developed joints, poor fracture development under stress, and poor permeability. Consequently, when mudstone or argillaceous rock is present between the protective and protected layers, the effectiveness of mining the protective layer in controlling gas in the protected layer is less than ideal. Therefore, it is necessary to develop a method and supporting device for long-distance and efficient induction of fracture development in the clay protective layer, thereby changing the characteristics of the clay protective layer, increasing the degree of fracture development, enhancing the permeability of the clay protective layer, ensuring the efficiency of the clay protective layer in controlling coal seam gas in the protected layer, reducing production costs, and increasing economic benefits. Summary of the Invention
[0004] To solve the above-mentioned technical problems, the technical solution adopted by this invention is: a method for controlling gas in intermediate argillaceous rock strata by long-distance liquid nitrogen high-pressure fracturing, the specific steps of which include: Step S1, directional drilling; Multiple boreholes were drilled in parallel at the soft mudstone layer between the protective layer and the protected layer. The borehole should cover the area of the soft mudstone layer within the protected zone; Step S2: Inject liquid nitrogen; Based on the preset drilling depth, multiple nitrogen injection points are designed along the borehole; Step S3, permeability enhancement fracturing; Start the pressure control machine, adjust the output pressure, and continuously apply liquid nitrogen to the hard and brittle mudstone layer along the dedicated delivery pipeline; Step S4, unscrew the drill; The drill bit retraction operation was paused when it reached the second nitrogen injection point. Repeat steps S2 and S3 to perform nitrogen injection and fracturing operations; Repeat steps S2, S3, and S4 until nitrogen fracturing work is completed at all nitrogen injection points and the drill bit is completely withdrawn from the borehole.
[0005] Furthermore, in step S1, let the borehole diameter be r and the borehole spacing be d, then 3r≤d≤4r.
[0006] Furthermore, in step S2, multiple nitrogen injection points are distributed at equal intervals.
[0007] Furthermore, in step S4, the drill bit is controlled to retract along the borehole, with a stroke of k.
[0008] The beneficial effects of using this invention are: By utilizing the low-temperature properties of liquid nitrogen, the structural characteristics of soft argillaceous rock layers are altered, increasing their brittleness, promoting their structural development, and enhancing their susceptibility to damage.
[0009] By utilizing an independent pressure control structure, an independent and stable pressure-controlled fracturing system is established, avoiding the previous pressure and power loss, ensuring the fracturing power utilization rate during the fracturing process, and improving fracturing efficiency.
[0010] Under the dual effects of liquid nitrogen and ultra-high pressure load, the frozen argillaceous rock structure is rapidly destroyed, resulting in cracks and a large number of gas-permeable channels, which improves the gas control effect of the mining protection layer of the intermediate argillaceous rock layer. Attached Figure Description
[0011] Figure 1 This is a flowchart of the present invention; Figure 2 This is a schematic diagram of the axial section of the fracturing process of the present invention; The reference numerals in the attached drawings include: 1. Directional drilling rig; 2. Modified drilling structure; 3. Thermostatic pipe; 4. Pressure control machine; 5. Liquid nitrogen storage container; 6. Fracturing valve port. Detailed Implementation
[0012] The present invention will now be described in detail with reference to the accompanying drawings.
[0013] Reference Figure 1 and Figure 2 The method for controlling gas in intermediate argillaceous rock layers by long-distance high-pressure fracturing with liquid nitrogen employs a directional drilling rig 1, a modified drilling structure 2, a thermostatic pipe 3, a pressure control machine 4, and a liquid nitrogen storage container 5. The modified drilling structure 2 has a fracturing valve port 6 at the end of the drill rod. The liquid nitrogen storage container 5 is connected to the fracturing valve port 6 through the thermostatic pipe 3. The pressure control machine 4 is deployed at the liquid nitrogen storage container 5 and connected to the pressurization equipment. Specifically, directional drilling rig 1 adopts an existing transmission-type directional drilling rig, with representative models including: The modified drilling structure 2 adopts a drill rod with built-in dual channels and a directional drill bit; Thermostatic tube 3 is a liquid transport pipeline that meets liquid nitrogen transport standards and has a heat preservation effect; The controlled pressure unit 4 is a standard piece of equipment in existing fracturing projects; Liquid nitrogen storage container 5 is a cryogenic storage tank that meets the transportation standards for underground rail transport vehicles; The specific steps include: Step S1, directional drilling; Multiple boreholes were drilled in parallel at the soft mudstone layer between the protective layer and the protected layer. The borehole should cover the area of the soft mudstone layer within the protected zone; Preferably, if the borehole diameter is r (mm) and the borehole spacing is d (mm), then 3r≤d≤4r; Step S2: Inject liquid nitrogen; Based on the preset drilling depth, multiple nitrogen injection points are designed along the borehole; The end of the borehole is designated as the first nitrogen injection point for that borehole, and subsequent nitrogen injection points are numbered as needed. The drilling operation has reached the target location, at which point the drill bit is located at nitrogen injection point number one. Start the nitrogen injection operation, start the pressurization equipment, push the liquid nitrogen in the liquid nitrogen storage container 5 into the thermostatic tube 3, deliver it to the fracturing valve port 6, and inject it into the borehole; During this step, liquid nitrogen comes into contact with the soft mudstone layer. Due to the extremely low temperature of the liquid nitrogen, the water contained in the soft mudstone layer freezes rapidly, forming a layered crystal structure. Its properties change from the original viscous state to a multi-layered hard and brittle state, while its strength increases slightly. Step S3, permeability enhancement fracturing; Start the pressure control machine, adjust the output pressure, and continuously apply liquid nitrogen to the hard and brittle mudstone layer along the dedicated delivery pipeline; Frozen mudstone layers crack under pressure, creating fissures and joints. These fissures act as gas channels, increasing the permeability of the mudstone layer. Furthermore, gas continues to flow through these gas channels, ensuring that they remain open even after the mudstone layer thaws. This significantly increases the overall permeability of the soft mudstone layer between the protective layer and the protected layer; The range of the permeable soft mudstone layer is calculated according to the method shown in Appendix E of the "Detailed Rules for the Prevention and Control of Coal and Gas Outbursts", which is the protected range of the protected coal seam after the protective coal seam is mined. Step S4, unscrew the drill; Control the drill bit to retract along the borehole, with a stroke of k (meters); After retraction, the drill bit reaches the next nitrogen injection point; Specifically, the distance of k is set based on parameters such as the effective radius of influence of fracturing, in-situ stress, coal and rock properties, and the performance of construction equipment, with the aim of ensuring the maximum effective fracturing range. Repeat steps S2 and S3 to perform nitrogen injection and fracturing operations; Repeat steps S2, S3, and S4 until nitrogen fracturing work is completed at all nitrogen injection points and the drill bit is completely withdrawn from the borehole.
[0014] Example 1
[0015] Taking a mining area in Inner Mongolia as a sample, its main geological structure includes coal seams, argillaceous rock layers, and hard rock layers. Among them, the argillaceous rock layers are distributed between coal seams or between coal seams and hard rock layers. The argillaceous rock layer above the protected coal seam was selected as the target for construction. Select a drilling rig with a power of 15,000, featuring a double-layer, multi-channel drill rod, a multi-functional drill bit, and a high-pressure nitrogen injection system.
[0016] Based on the results of the field survey, the designed length of the directional drilling is 500 meters, the diameter of the directional drilling is 120 mm, the spacing between the drilling holes is 360 mm to 480 mm, and the directional drilling is carried out to a depth of 500 meters. The drilling process was withdrawn and the fracturing-cooling process was carried out in stages. The length of the fracturing-cooling section was 5 meters and the spacing between the fracturing-cooling sections was 5 meters.
[0017] The specific construction process is as follows: To develop the drilling site, drilling was carried out in the soft mudstone layer between the protective layer and the protected layer, parallel to the protected layer. Drilling was stopped after reaching the designed length of 500 meters. The multi-functional drill bit is fixed at the No. 1 nitrogen injection point at the deepest part of the borehole. The thermostatic pipe, pressure controller and liquid nitrogen storage container are connected through the pipeline. After checking that the sealing of the entire nitrogen injection pipeline is leak-free, the pressurization equipment and pressure controller are started. Liquid nitrogen is injected into the mudstone layer at the No. 1 nitrogen injection point through the high-pressure nitrogen injection system and the double-layer multi-channel drill rod from the fracturing valve port. After the liquid nitrogen has fully soaked and frozen the mudstone layer, the output pressure of the control press is increased to perform high-pressure fracturing on the frozen section. Once the pressure is observed to be steadily decreasing and the mudstone layer is fully cracked to produce fissures, the nitrogen injection and pressurization are stopped. Maneuver the drill bit back 5 meters along the borehole to the second nitrogen injection point, and repeat the above nitrogen injection freezing and high-pressure fracturing operations. In this manner, after each fracturing section is completed, the operator retreats 5 meters to begin the next fracturing section (i.e., unless special circumstances occur, the retreat distance follows the set distance, and the retreat distance remains fixed each time), until all fracturing sections of the entire 500-meter-long borehole are completed. The drill string was withdrawn from the borehole to complete the long-distance liquid nitrogen high-pressure fracturing and permeability enhancement operation.
[0018] According to the pre-designed drilling layout plan, repeat the drilling and penetration enhancement process to complete all drilling operations covering the protected area; In this process, until the borehole is exited and the second long-distance liquid nitrogen high-pressure fracturing process begins, the fracturing-cooling section of each borehole should be staggered with the fracturing-cooling section of the adjacent borehole.
[0019] The mining operation of the protective layer can then be started. The gas extracted from the protected layer can be smoothly discharged to the goaf of the protective layer through the fissure channel of the fractured mudstone layer, thus achieving gas control of the protected layer.
[0020] The above content is only a preferred embodiment of the present invention. For those skilled in the art, many changes can be made in the specific implementation and application scope based on the concept of the present invention. As long as these changes do not depart from the concept of the present invention, they all fall within the protection scope of the present invention.
Claims
1. A method for controlling gas in intermediate argillaceous rock strata by long-distance high-pressure fracturing with liquid nitrogen, characterized in that: The specific steps include: Step S1, directional drilling; Multiple boreholes were drilled in parallel at the soft mudstone layer between the protective layer and the protected layer. The borehole should cover the area of the soft mudstone layer within the protected zone; Step S2: Inject liquid nitrogen; Based on the preset drilling depth, multiple nitrogen injection points are designed along the borehole; Step S3, permeability enhancement fracturing; Start the pressure control machine, adjust the output pressure, and continuously apply liquid nitrogen to the hard and brittle mudstone layer along the dedicated delivery pipeline; Step S4, unscrew the drill; The drill bit retraction operation was paused when it reached the second nitrogen injection point. Repeat steps S2 and S3 to perform nitrogen injection and fracturing operations; Repeat steps S2, S3, and S4 until nitrogen fracturing work is completed at all nitrogen injection points and the drill bit is completely withdrawn from the borehole.
2. The method for controlling gas in intermediate argillaceous rock strata by long-distance liquid nitrogen high-pressure fracturing as described in claim 1, characterized in that: In step S1, let the diameter of the borehole be r and the spacing between boreholes be d, then 3r≤d≤4r.
3. The method for controlling gas in intermediate argillaceous rock strata by long-distance liquid nitrogen high-pressure fracturing as described in claim 1, characterized in that: In step S2, multiple nitrogen injection points are distributed at equal intervals.
4. The method for controlling gas in intermediate argillaceous rock strata by long-distance liquid nitrogen high-pressure fracturing as described in claim 1, characterized in that: In step S4, the drill bit is controlled to retract along the borehole, with a stroke of k.