A method for improving hydraulic fracturing top cutting and pressure relief efficiency

Abstract

The present invention discloses a method for improving the efficiency of hydraulic fracturing and top cutting and pressure relief. First, the distribution of ground stress in the mine tunnel is explored, and then the drilling spacing is planned according to the magnitude and direction of the ground stress. The drilling holes are arranged in a serpentine shape to fully utilize the ground stress. Then, cracks are prefabricated with the help of hydraulic cutting equipment to provide a path for subsequent fracturing. Finally, water is injected and fractured to form a three-dimensional fracture network to achieve the effect of top cutting and pressure relief. Through the present invention, the drilling holes can be reasonably arranged, and the ground stress can be fully utilized to induce crack expansion, thereby reducing the required water pressure, ensuring safe mining of the coal mine, and improving the efficiency of hydraulic fracturing.

Description

Technical Field

[0001] The present invention relates to the technical field of mine safety, and in particular to a method for improving the efficiency of hydraulic fracturing and top cutting and pressure relief. Background Art

[0002] During the mining process, the emergence of ground pressure often presents significant challenges. It not only endangers production safety but can also cause partial mine shutdowns and even the collapse of the entire mine. Roof fracture impacts are a major type of ground pressure in coal mines, particularly in mining tunnels with access to open space. The combined effects of these pressures increase the frequency and intensity of ground pressure impacts. Therefore, pre-cracking the roof is used to weaken its integrity and reduce its overall strength, allowing it to collapse in a timely manner, thus avoiding the risk of impact-induced disasters caused by large areas of suspended roof.

[0003] Hydraulic fracturing is a common method for pre-cracked roof slabs, inducing cracking and propagation in coal rock through water pressure. Directed hydraulic fracturing, on the other hand, pre-creates fractures before drilling and fracturing. This significantly reduces the initiation pressure for hydraulic fracturing and provides a favorable path for crack propagation, driving the fractures to propagate along the direction of the pre-created cuts, effectively weakening or shearing the roof slab.

[0004] Since roof fractures are primarily tensile failures caused by bending deformation of the goaf roof under gravity, the fracture surface is most likely to develop along the vertical crack direction. Therefore, vertical cracks along the thickness of the roof are the main controlling cracks for roof fracture failure. In addition, failure often occurs along the direction of the principal stress (i.e., the direction of the maximum principal stress σ1 and the intermediate principal stress σ2). Under the action of ground stress, the direction of roof crack expansion in coal rock also follows this law. Therefore, rationally arranging drill holes and fully utilizing ground stress can greatly reduce water pressure, increase the density of the fracture network, and improve the efficiency of prefabricated fractures and subsequent hydraulic fracturing.

[0005] However, currently, prefabricated fractures are mainly produced by the water jet method, which uses a rotating water jet to cut annular fractures perpendicular to the borehole axis. The prefabricated guide fractures are almost perpendicular to the rock formation's own weight stress and thickness direction, and the boreholes are arranged in a straight line. The main fractures formed by fracturing cannot expand along the optimal cutting direction, which has a great impact on the effect of hydraulic fracturing.

[0006] Therefore, designing a method to improve the efficiency of hydraulic fracturing top cutting and pressure relief, rationally arranging drilling holes, and making full use of ground stress to induce crack expansion are the keys to ensuring safe coal mining and improving the efficiency of hydraulic fracturing. Summary of the Invention

[0007] In view of the above-mentioned technical deficiencies, the object of the present invention is to provide a method for improving the efficiency of hydraulic fracturing and top cutting and pressure relief.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] The present invention provides a method for improving the efficiency of hydraulic fracturing and top cutting and pressure relief, comprising the following steps:

[0010] (1) Measuring ground stress: Drill holes around the tunnel to measure its vertical and horizontal ground stresses, determine the magnitude and direction of the ground stress, and provide prerequisites for subsequent safe construction and efficient use of ground stress for hydraulic fracturing;

[0011] (2) Pre-drilling: Based on the ground stress measured in step (1), the maximum principal stress σ1 and the intermediate principal stress σ2 are determined according to the ground stress direction and magnitude, and the first borehole is drilled in the preset pre-cracking area of the roof with a borehole diameter of 0.08-0.12 meters and a depth of 30-50 meters. Subsequently, the second borehole is drilled at intervals of 0.5-1.0 meters horizontally, i.e., in the direction of the intermediate principal stress, and at intervals of 0.3-0.6 meters vertically, i.e., in the direction of the maximum principal stress. Following this interval, all boreholes are drilled in a serpentine arrangement on the roof in sequence, inducing the cracks generated by subsequent fracturing to expand along this direction;

[0012] (3) Hydraulic fracturing: Using a hydraulic fracturing machine, the boreholes are hydraulically fractured in the order of drilling in step (2) to provide prefabricated fractures for subsequent hydraulic fracturing. After completion, a group of initial fracture arrays with a diameter of 2-6 cm, a length of 1-2 m, and a spacing of 0.5-2 m between each other, and a circular cross-section are formed in each borehole;

[0013] (4) Perform hydraulic fracturing: After the slitting in step (3) is completed, the borehole is subjected to segmented water injection fracturing. The fracturing speed is controlled at 5-10 m / h and the fracturing pressure is controlled at 20-50 MPa. The hole is sealed with a packer. When the sealing pressure is reached, the mode is automatically switched to the fracturing mode, and the adjacent borehole is used as an observation hole. When water is obviously discharged from the observation hole, it indicates that the cracks between the two holes are connected, and fracturing is stopped, that is, a three-dimensional fracture network is formed in the pre-fracture area.

[0014] Preferably, in step (1), the ground resistivity method is used to measure the ground stress.

[0015] Preferably, the first borehole has a diameter of 0.1 m and a depth of 40 m.

[0016] Preferably, the second borehole is 0.8 meters away from the first borehole in the direction of the intermediate principal stress and 0.5 meters away from the first borehole in the direction of the maximum principal stress.

[0017] Preferably, in step (2), the holes drilled are arranged in a serpentine pattern to cover the entire top plate.

[0018] Preferably, in step (3), a group of initial crack arrays with a diameter of 4 cm, a length of 1.5 m, a spacing of 1 m from each other, and a circular cross-section are formed in each borehole.

[0019] Preferably, in step (4), the borehole is subjected to staged water injection fracturing, the fracturing speed is controlled at 6 m / h, and the fracturing pressure is controlled at 40 MPa.

[0020] Preferably, in step (2), the drill holes arranged in a serpentine pattern form a serpentine turning arrangement with every three adjacent drill holes.

[0021] Preferably, the hydraulic seam cutter in step (3) adopts a ZGF-100 ultra-high pressure hydraulic seam cutter.

[0022] The beneficial effects of the present invention are:

[0023] 1. The present invention adopts high-pressure jet cutting technology to pre-form cracks before fracturing, which can induce fracturing to produce directional cracks and improve fracturing efficiency.

[0024] 2. The present invention adopts a serpentine drilling array, which can fully utilize the ground stress, reduce the fracturing pressure and improve the crack generation efficiency.

[0025] 3. The present invention adopts staged fracturing technology, which facilitates fracturing progress control and can improve the safety and efficiency of top cutting and pressure relief. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 This is a flow chart of a method for improving hydraulic fracturing top cutting and pressure relief efficiency provided by the present invention;

[0028] Figure 2 Schematic diagram of drilling arrangement in an embodiment of the present invention;

[0029] Figure 3 is a cross-sectional view of a roadway after drilling in an embodiment of the present invention;

[0030] Figure 4 Schematic diagram of prefabricated cracks in an embodiment of the present invention;

[0031] Figure 5 Schematic diagram of a three-dimensional seam network in an embodiment of the present invention.

[0032] Description of reference numerals:

[0033] 1. Pre-crack area on the top plate; 2. Drilling; 3. Prefabricated cracks; 4. Three-dimensional seam network. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] Example 1:

[0036] like Figures 1 to 5 As shown, this embodiment provides a method for improving the efficiency of hydraulic fracturing and top cutting and pressure relief, which specifically includes the following steps:

[0037] Step 1: Measure the ground stress: Drill holes around the tunnel to measure the vertical and horizontal ground stresses, determine the magnitude and direction of the ground stresses, and provide prerequisites for subsequent safe construction and efficient use of ground stress for hydraulic fracturing.

[0038] Step 2, pre-drilling: Based on the measurement data of step 1, the maximum principal stress σ1 and the intermediate principal stress σ2 are determined according to the direction and magnitude of the ground stress, and the first borehole is drilled in the preset pre-cracking area 1 of the roof. The borehole diameter is about 0.1 meters and the depth is 30-50 meters. Then, relative to the first borehole, the horizontal interval is 0.5-1.0 meters in the intermediate principal stress direction and the vertical interval is 0.3-0.6 meters in the maximum principal stress direction. The second borehole is drilled. Following this interval, all boreholes 2 are drilled on the roof in a serpentine arrangement. The boreholes are arranged in a serpentine pattern to cover the entire roof. Every three adjacent boreholes form a serpentine turning arrangement, thereby inducing the cracks generated by subsequent fracturing to expand along this direction. Figure 2 、 3 As shown;

[0039] Step 3, hydraulic cutting: With the help of a hydraulic cutter, the borehole 2 is hydraulically cut according to the drilling sequence of step 2 to provide prefabricated cracks 3 for subsequent hydraulic fracturing. After completion, a group of initial crack arrays with a diameter of 2-6 cm, a length of 1-2 meters, and a spacing of 0.5-2 meters are formed in each borehole, and the cross section is arranged in a circular shape. Figure 4 As shown;

[0040] The hydraulic slotting device of this embodiment adopts the ZGF-100 ultra-high pressure hydraulic slotting device well known to those skilled in the art. Its specific use method also adopts the existing method well known to those skilled in the art and will not be described in detail here.

[0041] Step 4, hydraulic fracturing: After the slitting is completed, the borehole is subjected to staged water injection fracturing. The fracturing speed is controlled at about 5-10 meters per hour, and the fracturing pressure is controlled at 20-50 MPa. The packer is used to seal the hole. When the sealing pressure is reached, it will automatically switch to the fracturing mode and use the adjacent borehole as an observation hole. When water is obviously discharged from the observation hole, it indicates that the cracks between the two holes are connected, and fracturing is stopped. That is, a three-dimensional fracture network 4 is formed in the pre-fracture area. Figure 5 shown.

[0042] This embodiment uses the georesistivity method well known to those skilled in the art to measure geostress. Other measurement methods known to those skilled in the art are also within the scope of protection of this application.

[0043] This embodiment uses terms such as pre-cracked area 1, drilled hole 2, prefabricated cracks 3, and three-dimensional crack network 4, but does not preclude the use of other terms. These terms are used solely to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitations is contrary to the spirit of the present invention. Therefore, descriptions of other terms are also within the scope of protection of this application.

[0044] Example 2: The difference between this example and Example 1 is that the diameter of the first borehole is 0.1 meters and the depth is 40 meters.

[0045] Example 3: The difference between this example and Example 1 is that the second borehole is 0.8 meters away from the first borehole in the direction of the intermediate principal stress and 0.5 meters away from the first borehole in the direction of the maximum principal stress.

[0046] Example 4: The difference between this example and Example 1 is that in step (3), an initial crack array with a diameter of 4 cm, a length of 1.5 m, a spacing of 1 m between each other, and a circular cross-section is formed in each drill hole.

[0047] Example 5: The difference between this example and Example 1 is that: in step (4), the borehole is subjected to staged water injection fracturing, the fracturing speed is controlled at 6 m / h, and the fracturing pressure is controlled at 40 MPa.

[0048] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for improving the efficiency of hydraulic fracturing and top cutting and pressure relief, characterized in that: The following steps are involved: (1) Measuring ground stress: Drill holes around the tunnel to measure its vertical and horizontal ground stresses, determine the magnitude and direction of the ground stress, and provide prerequisites for subsequent safe construction and efficient use of ground stress for hydraulic fracturing; (2) Pre-drilling: Based on the ground stress measured in step (1), the maximum principal stress σ1 and the intermediate principal stress σ2 are determined according to the ground stress direction and magnitude, and the first borehole is drilled in the preset pre-cracking area of the roof with a borehole diameter of 0.08-0.12 meters and a depth of 30-50 meters. Subsequently, the second borehole is drilled at intervals of 0.5-1.0 meters horizontally, i.e., in the direction of the intermediate principal stress, and at intervals of 0.3-0.6 meters vertically, i.e., in the direction of the maximum principal stress. Following this interval, all boreholes are drilled in a serpentine arrangement on the roof in sequence, inducing the cracks generated by subsequent fracturing to expand along this direction; (3) Hydraulic fracturing: Using a hydraulic fracturing machine, the boreholes are hydraulically fractured in the order of drilling in step (2) to provide prefabricated fractures for subsequent hydraulic fracturing. After completion, a group of initial fracture arrays with a diameter of 2-6 cm, a length of 1-2 m, and a spacing of 0.5-2 m between each other, and a circular cross-section are formed in each borehole; (4) Perform hydraulic fracturing: After the slitting in step (3) is completed, the borehole is subjected to segmented water injection fracturing. The fracturing speed is controlled at 5-10 m / h and the fracturing pressure is controlled at 20-50 MPa. The hole is sealed with a packer. When the sealing pressure is reached, the mode is automatically switched to the fracturing mode, and the adjacent borehole is used as an observation hole. When water is obviously discharged from the observation hole, it indicates that the cracks between the two holes are connected, and fracturing is stopped, that is, a three-dimensional fracture network is formed in the pre-fracture area.

2. A method for improving hydraulic fracturing top cutting and pressure relief efficiency according to claim 1, characterized in that: Step (1) uses the ground resistivity method to measure the ground stress.

3. The method for improving the efficiency of hydraulic fracturing and top cutting and pressure relief according to claim 1, wherein: The first borehole has a diameter of 0.1 m and a depth of 40 m.

4. The method for improving the efficiency of hydraulic fracturing and top cutting and pressure relief according to claim 1, wherein: The second borehole is 0.8 meters away from the first borehole in the direction of the intermediate principal stress and 0.5 meters away from the first borehole in the direction of the maximum principal stress.

5. The method for improving the efficiency of hydraulic fracturing and top cutting and pressure relief according to claim 1, wherein: In step (2), the holes are drilled in a serpentine arrangement to cover the entire top plate.

6. The method for improving the efficiency of hydraulic fracturing and top cutting and pressure relief according to claim 1, wherein: In step (3), a group of initial crack arrays with a diameter of 4 cm, a length of 1.5 m, a spacing of 1 m between each other, and a circular cross-section are formed in each borehole.

7. The method for improving the efficiency of hydraulic fracturing and top cutting and pressure relief according to claim 1, wherein: Step (4) The borehole is subjected to staged water injection fracturing, with the fracturing speed controlled at 6 m / h and the fracturing pressure controlled at 40 MPa.

8. A method for improving hydraulic fracturing top cutting and pressure relief efficiency according to claim 1 or 5, characterized in that: In step (2), the drill holes are arranged in a serpentine pattern, and every three adjacent drill holes form a serpentine turning arrangement.

9. The method for improving the efficiency of hydraulic fracturing and top cutting and pressure relief according to claim 1, wherein: In step (3), the hydraulic seam cutter adopts the ZGF-100 ultra-high pressure hydraulic seam cutter.

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