Hard rock long hole directional hydraulic fracturing pressure relief method

Abstract

This invention relates to the field of mine safety and rock strata control technology, specifically to a safe decompression method for long-bore directional hydraulic fracturing in hard rock strata. First, based on the geological conditions, geostress, and mechanical parameters of the target hard rock strata, the design parameters for the long directional borehole are determined. Then, directional drilling combined with a drilling-while-guided system is used to ensure precise borehole positioning within the target rock strata. A segmented isolation device is lowered to form a high-pressure sealed chamber. According to the design parameters, a retreating fracturing process is used to fracture segment by segment, initiating fractures and extending them to the far field. Finally, the fracturing effect is verified through real-time monitoring to complete safe decompression. This invention is a spark-free, low-vibration static operation with no toxic gas generation, ensuring high safety. It can transform the overall impact collapse of rock strata into a layered, small-step, stable collapse, resulting in excellent fracturing control. The use of multi-segment fracturing within a single borehole reduces drilling site and equipment relocation, lowers treatment costs, and is suitable for decompression treatment of hard rock strata in underground coal mines, ensuring safe mine production.

Description

Technical Field

[0001] This invention relates to the field of mine safety and rock strata control technology, specifically to a safe depressurization method for long-hole directional hydraulic fracturing in hard rock strata. Background Technology

[0002] As the depth and scope of coal mining continue to increase, underground geological conditions are becoming increasingly complex, and the impact of faults, hard rock strata, and other geological structures on coal mine safety is becoming more and more prominent. During the advancement of coal mining faces, areas with hard rock faults are frequently encountered. These rock strata have a high strength coefficient, high integrity, and strong clamping effect, resulting in high stress concentration in the roof, large collapse steps, and severe mine pressure manifestations. This seriously restricts the normal and orderly advancement of the working face and easily induces dynamic disasters such as roof collapse and rock bursts, posing a significant threat to the safe and efficient production of the mine.

[0003] Currently, the common method for treating hard rock strata and faults underground is loosening blasting. While this method is simple to operate, it has many insurmountable drawbacks: blasting operations generate strong vibrations and impact loads, easily damaging roadway support structures and critical machinery used for coal mining, tunneling, and transportation; the blasting process produces toxic and harmful gases such as carbon monoxide and nitrogen oxides, polluting the underground working environment and seriously threatening the health of workers; blasting involves open flames, posing a high risk of sparks, particularly in high-gas and high-pressure mines; furthermore, the direction and extent of crack expansion after blasting are uncontrollable, and the degree of rock fragmentation is difficult to precisely control, making it impossible to achieve a planned and stable roof collapse, resulting in unstable treatment effects. In addition, loosening blasting generates significant noise and dust pollution, contradicting the safety and environmental protection concepts of green and intelligent mine construction, and failing to meet the long-term development needs of modern mines.

[0004] Conventional hydraulic fracturing and other alternative technologies suffer from problems such as insufficient borehole depth, poor sealing effect, limited fracture extension distance, and random propagation paths. They cannot achieve large-scale, long-distance, and directional controllable rock strata weakening and pressure relief, and thus cannot fundamentally solve the technical challenge of hard rock strata and faults restricting working face advancement. Therefore, developing a safe, efficient, green, and controllable hard rock strata pressure relief technology has become an urgent need to ensure the safe and efficient mining of deep coal resources. Summary of the Invention

[0005] The purpose of this invention is to provide a safe pressure relief method for long-hole directional hydraulic fracturing of hard rock strata, which can achieve precise weakening and smooth collapse of hard rock strata, thereby improving the safety and economy of mine production.

[0006] To achieve the above objectives, the technical solution of this application is: a safe depressurization method for long-hole directional hydraulic fracturing in hard rock formations, comprising: Step 1: Based on the geological conditions, stress distribution, and mechanical parameters of the target hard rock layer, obtain the design parameters for directional long boreholes, including the layer position, angle, fracturing pressure, spacing, and number of fracturing stages; Step 2: Based on the aforementioned strata and angle, construct a long borehole using directional drilling equipment. The drill bit attitude is monitored and dynamically adjusted in real time through the drilling guidance system to ensure that the borehole trajectory smoothly traverses and is stably positioned inside the target hard rock strata. Step 3: Insert segmented packers into the long borehole that has been drilled. According to the spacing, pressurize and seal the pre-set single-segment fracturing zone so that the packers fit tightly against the borehole wall, thereby forming a high-pressure resistant, sealed fracturing chamber inside the borehole. Step 4: Inject fracturing medium into the sealed fracturing chamber through a high-pressure pumping system. Based on the fracturing pressure and the number of fracturing stages, perform hydraulic fracturing stage by stage using a retreating process to initiate fracturing and extend it to the far field. Step 5: Collect data during the fracturing process through real-time monitoring stations, analyze the fracture development, verify the rationality of the directional long borehole design parameters and the effect of segmented hydraulic fracturing, and achieve safe pressure relief for long-hole directional hydraulic fracturing in hard rock formations.

[0007] In another implementation of the present invention, the layers include deep-hole fracturing layers and shallow-hole fracturing layers; The deep-hole fracturing layer is determined using the key layer theory, by obtaining the first... Loads generated when one layer affects the first layer To determine: in, For elastic modulus, For layer thickness; For density; subscript , ..., Representing the first to the second level respectively Layered rock layers; The shallow-hole fracturing layer, through the shallow-hole cut-off height To determine: in, The coefficient of expansion is denoted as 'splitting coefficient'. To extract high.

[0008] In another implementation of the present invention, the angle is the deep hole cutting angle: in, The angle of friction of the rock block. For the working surface orientation, The thickness is the direct top thickness.

[0009] In another implementation of the present invention, the fracturing pressure is the fracturing initiation pressure, obtained according to the maximum tensile stress criterion: in, For the maximum principal stress, For the minimum principal stress, It represents the tensile strength of the rock.

[0010] In another implementation of the present invention, the spacing is obtained based on the relationship between the water injection volume in the fracturing borehole, the fracturing initiation pressure, and the radius of fracture propagation in the surrounding rock: in, The radius of the hydraulic fracturing fracture. ; For crack initiation pressure, ; This refers to the water injection volume. ; For water filling time, ; For the crack extension height, ; For the elastic modulus of rock, ; This is the crack superposition coefficient; For spacing.

[0011] In another implementation of the present invention, the method for obtaining the number of fracturing stages is as follows: , in, This represents the total number of cracks. As a damage variable, This represents the fracturing volume. The depth of the crack. This represents the coefficient of interaction between joints. Where is the crack radius. The dip angle of the joint surface. The friction angle of the joint surface; It is a constant. The value is Poisson's ratio of the rock mass.

[0012] In another implementation of the present invention, in step two, when constructing a long borehole, a large-diameter drill bit is used to open the hole and a steel borehole pipe is inserted. After full-length grouting and sealing, the high-pressure fracturing sealing requirements are met. After the long borehole construction is completed, a hole cleaning operation is carried out to remove sediment from the bottom of the hole to ensure unobstructed flow inside the hole.

[0013] In another implementation of the present invention, in step three, the segmented sealing device includes a bidirectional expansion packer and a push rod that cooperates with it, used to achieve long-distance positioning and high-pressure sealing within the hole.

[0014] In another implementation of the present invention, in step four, the retreating process is a continuous multi-segment fracturing of a single hole, with each segment being set, fracturing, extending, depressurizing, and shifting to form a continuous fracturing network.

[0015] In another implementation of the present invention, in step five, the real-time monitoring station uses a microseismic monitoring system or an in-hole pressure sensor to analyze the fracture development and the effect of segmented hydraulic fracturing by analyzing the collected images or data.

[0016] By adopting the above technical solution, the present invention can achieve the following technical effects: 1. This invention adopts a sparkless and low-vibration static hydraulic fracturing process. The entire process is free of open flames and explosive impacts, and will not produce toxic and harmful gases such as carbon monoxide. It has no destructive impact on the roadway support structure or underground machinery and equipment, and the working environment is friendly. It fundamentally avoids the safety hazards of loosening blasting methods, greatly improves the safety of underground operations, and is fully in line with the construction concept of green mines and safe mines.

[0017] 2. This invention precisely targets hard rock strata with directional long boreholes and forms a controllable network of fractures through segmented hydraulic fracturing, fundamentally changing the complete physical structure of the rock mass. It transforms the traditional mode of "large-area overall strong impact collapse" of hard roof into "layered small-step stable collapse", effectively reducing stress concentration, suppressing dynamic disasters such as rockburst and roof collapse, and ensuring the safe and efficient advancement of the working face.

[0018] 3. This invention adopts a backward segmented continuous fracturing process to achieve continuous operation of "one hole, multiple segments", which greatly reduces the number of underground drilling sites and the time cost of frequent equipment relocation; under the premise of achieving the same rock weakening effect, it significantly reduces the treatment cost and material consumption per ton of ore, improves construction efficiency, and combines technological advancement with economic rationality, which is suitable for the needs of large-scale, long-distance hard rock treatment in modern mines. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the force relationship of the rock block in an embodiment of the present invention; Figure 2 This is a schematic diagram of the directional long borehole in this invention. Figure 3 This is a cross-sectional view of the directional long borehole arrangement in this invention; Figure 4 This is a schematic diagram of the hydraulic fracturing formation in the directional long borehole of this invention; Figure 5 This is a schematic diagram of segmented hydraulic fracturing of long-hole directional rock formations in this invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0023] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the accompanying drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values.

[0024] This embodiment provides a safe pressure relief method for long-hole directional hydraulic fracturing in hard rock formations, including the following steps: Step 1: Based on the geological conditions, stress distribution, and mechanical parameters of the target hard rock layer, obtain the design parameters for directional long boreholes, including the layer position, angle, fracturing pressure, spacing, and number of fracturing stages; Specifically, the working face has a strike length of 5225.3m and a dip width of 340m. Top and bottom conditions: Upper roof (direct roof): Gray siltstone, silty texture, mainly composed of quartz, containing small amounts of mica and black minerals, as well as abundant plant root fossils. Thickness: 14.15–18.61m. Direct bottom: Light gray fine sandstone, fine-grained sandy texture, mainly composed of quartz and feldspar, containing plant debris fossils. Thickness: 4.04–8.95m. Upper bottom: Grayish-black to dark gray mudstone, with a smooth surface, semi-hard, wavy bedding, thickness: 16.71–25.9m.

[0025] The strata include deep-hole fracturing strata and shallow-hole fracturing strata; the deep-hole fracturing strata are determined by using the key layer theory to identify the key and sub-key layers in the rock strata.

[0026] The load generated when the nth layer affects the first layer can be The fracture distance of the rock strata can be obtained from... calculate; in, For the first The load generated when the first layer affects the second layer ; The magnitude of the load on the rock strata. ; For density, ; For layer thickness, ; For elastic modulus, , The thickness is the direct top thickness.

[0027] Based on the geological data of the mining area and the physical parameters of the rock strata obtained from mechanical tests, substitute them into the above formula. The following two points should be noted: First, the hydraulic fracturing height of the deep borehole should reach the subcritical stratum; second, if there are support anchors around the borehole location, the deep borehole location should be reasonably adjusted to avoid affecting them. In this embodiment, the deep borehole location is taken as 37.7m.

[0028] The shallow-hole fracturing layer was determined by: shallow-hole top cutting height. as follows: in, The coefficient of expansion is taken as 1.23. For the purpose of setting the extraction height, 5m is taken. Based on the actual situation, the water pressure pre-fracturing height of the shallow hole is 23m.

[0029] like Figure 1 The force relationship at the interlocking point of the rock blocks is shown; the angle mentioned is the shear angle, which satisfies the following equation: Among them, friction angle °; Working face inclination Direct top thickness Based on a comprehensive consideration of the actual measurement conditions, the cutting angle for deep holes was set at 30°, and the cutting angle for shallow holes was set at 45°.

[0030] The fracturing pressure is the fracturing initiation pressure: in, For tensile strength, take 7.8 MPa. =8.5MPa =4.6MPa Substituting into the equation, we get... =17.03MPa, taking all factors into consideration Take 17 MPa.

[0031] The spacing is the borehole row spacing: in, The radius of the hydraulic fracturing fracture. ; For crack initiation pressure, ; This refers to the water injection volume. ; For water filling time, ; For the crack extension height, ; For the elastic modulus of rock, .Will =17MPa =6 , =30 , =5 , =15.6 Substituting, we can obtain The crack propagation radius of the root borehole is 8.75. Introduction The crack superposition factor is set to 0.8. The borehole spacing can then be obtained. Take 14m.

[0032] The fracturing stage number and lake area method are as follows: In the above formula, The total number of cracks, damage variable The fracturing volume was determined to be 0.3. Crack depth The coefficient of interaction between joints is 0.5m. The crack radius is 1.4. The dip angle of the joint surface is 7m. The friction angle of the joint surface is 20°. 34°, number of holes It is 21.

[0033] The results showed that there were 10 fracturing stages for deep holes and 8 fracturing stages for shallow holes.

[0034] Step 2: Based on the aforementioned strata and angle, construct a long borehole using directional drilling equipment. The drill bit attitude is monitored and dynamically adjusted in real time through the drilling guidance system to ensure that the borehole trajectory smoothly traverses and is stably positioned inside the target hard rock strata. Specifically, the drilling process involves: initial drilling using a large-diameter drill bit, followed by the insertion of a steel wellhead pipe and full-length grouting for sealing. It is crucial to ensure that the sealed section can withstand the expected maximum fracturing pressure to prevent grout leakage or wellhead blowout during fracturing. Directional drilling utilizes the bend in the screw drill string to change the drilling direction. By adjusting the "tool face angle" of the drill rod, the drill bit can be steered vertically, horizontally, and laterally within the target rock formation. Finally, borehole cleaning is performed after reaching the predetermined depth to remove sediment from the bottom of the borehole.

[0035] Taking a working face in a mining area as an example, a long-hole fracturing drill site was set up in the No. 7 connecting roadway, and two directional long boreholes were drilled into the immediate roof, with the main borehole direction along the dip of the working face. Borehole No. 1 was used to fracture the second critical layer (siltstone) with a thickness of 8.3m, and its planar location was 40m from the working face in the main return airway, and 23m from the roadway roof in the vertical direction. Borehole No. 2 was also used to fracture the same second critical layer (siltstone) with a thickness of 8.3m, and its planar location was 20m from the working face, and also 23m from the roadway roof in the vertical direction. The borehole layout plan is shown below. Figure 2 As shown, the cross-sectional view is as follows Figure 3 As shown.

[0036] Step 3: Insert segmented packers into the long borehole that has been drilled. According to the spacing, pressurize and seal the pre-set single-segment fracturing zone so that the packers fit tightly against the borehole wall, thereby forming a high-pressure resistant, sealed fracturing chamber inside the borehole. Step 4: Inject fracturing medium into the sealed fracturing chamber through a high-pressure pumping system. Based on the fracturing pressure and the number of fracturing stages, perform hydraulic fracturing stage by stage using a retreating process to initiate fracturing and extend it to the far field. Specifically, the hydraulic fracturing method using a retreating process for staged fracturing is as follows: 1) Start the high-pressure pump to inject water into the tubing at a low flow rate; 2) When the pressure inside the pipe reaches the packer's operating pressure, the rubber packer sleeve expands and presses tightly against the borehole wall, achieving a set seal; 3) Gradually increase the pump set discharge rate to increase the pressure inside the borehole until the target rock layer produces initial cracks; 4) Maintain a high discharge rate and stable water injection to allow the cracks to continue extending into the deeper rock layers under water pressure, forming a crack network.

[0037] After completing this section of fracturing, stop water injection and release the residual pressure inside the tubing through the orifice relief valve, allowing the packer to contract and reset. Then, pull the drill pipe back to the next preset fracturing position and repeat the above steps until the entire borehole section is fracturing. A schematic diagram of borehole fracturing is shown below. Figure 4-5 As shown.

[0038] Step 5: Collect data during the fracturing process through real-time monitoring stations, analyze the fracture development, verify the rationality of the directional long borehole design parameters and the effect of segmented hydraulic fracturing, and achieve safe pressure relief for long-hole directional hydraulic fracturing in hard rock formations.

[0039] Specifically, the sensors integrated into the fracturing pump station collect and analyze pressure and flow data in real time to ensure the packer functions effectively and completes fracturing, guaranteeing construction safety, or optimizing hydraulic fracturing parameters to ensure construction efficiency. After fracturing, mine pressure monitoring and hydraulic fracturing effect verification are conducted to complete the weakening effect.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A safe pressure relief method for directional hydraulic fracturing of long-hole rock formations in hard rock formations, characterized in that, include: Step 1: Based on the geological conditions, stress distribution, and mechanical parameters of the target hard rock layer, obtain the design parameters for directional long boreholes, including the layer position, angle, fracturing pressure, spacing, and number of fracturing stages; Step 2: Based on the aforementioned strata and angle, construct a long borehole using directional drilling equipment. The drill bit attitude is monitored and dynamically adjusted in real time through the drilling guidance system to ensure that the borehole trajectory smoothly traverses and is stably positioned inside the target hard rock strata. Step 3: Insert segmented packers into the long borehole that has been drilled. According to the spacing, pressurize and seal the pre-set single-segment fracturing zone so that the packers fit tightly against the borehole wall, thereby forming a high-pressure resistant, sealed fracturing chamber inside the borehole. Step 4: Inject fracturing medium into the sealed fracturing chamber through a high-pressure pumping system. Based on the fracturing pressure and the number of fracturing stages, perform hydraulic fracturing stage by stage using a retreating process to initiate fracturing and extend it to the far field. Step 5: Collect data during the fracturing process through real-time monitoring stations, analyze the fracture development, verify the rationality of the directional long borehole design parameters and the effect of segmented hydraulic fracturing, and achieve safe pressure relief for long-hole directional hydraulic fracturing in hard rock formations.

2. The safe pressure relief method for long-hole directional hydraulic fracturing in hard rock formations according to claim 1, characterized in that, The layers include deep-hole fracturing layers and shallow-hole fracturing layers; The deep-hole fracturing layer is determined using the key layer theory, by obtaining the first... Loads generated when one layer affects the first layer To determine: in, For elastic modulus, For layer thickness; For density; subscript , ..., Representing the first to the second level respectively Layered rock layers; The shallow-hole fracturing layer, through the shallow-hole cut-off height To determine: in, The coefficient of expansion is denoted as 'splitting coefficient'. To extract high.

3. The safe pressure relief method for long-hole directional hydraulic fracturing in hard rock formations according to claim 1, characterized in that, The angle mentioned is the deep hole cutting angle: in, The angle of friction of the rock block. For the working surface orientation, The thickness is the direct top thickness.

4. The safe pressure relief method for long-hole directional hydraulic fracturing in hard rock formations according to claim 1, characterized in that, The fracturing pressure is the initiation pressure, obtained according to the maximum tensile stress criterion: in, For the maximum principal stress, For the minimum principal stress, It represents the tensile strength of the rock.

5. The safe pressure relief method for long-hole directional hydraulic fracturing in hard rock formations according to claim 4, characterized in that, The spacing is determined based on the relationship between the water injection volume in the fracturing hole, the fracturing pressure, and the radius of fracture propagation in the surrounding rock. in, The radius of the hydraulic fracturing fracture. ; For crack initiation pressure, ; This refers to the water injection volume. ; For water filling time, ; For the crack extension height, ; For the elastic modulus of rock, ; This is the crack superposition coefficient; For spacing.

6. The safe pressure relief method for long-hole directional hydraulic fracturing in hard rock formations according to claim 1, characterized in that, The method for obtaining the number of fracturing stages is as follows: ， in, This represents the total number of cracks. As a damage variable, This represents the fracturing volume. The depth of the crack. This represents the coefficient of interaction between joints. Where is the crack radius. The dip angle of the joint surface. The friction angle of the joint surface; It is a constant. The value is Poisson's ratio of the rock mass.

7. The safe pressure relief method for long-hole directional hydraulic fracturing in hard rock formations according to claim 1, characterized in that, In step two, when drilling long holes, a large-diameter drill bit is used to open the hole and a steel orifice pipe is inserted. After full-length grouting and sealing, the hole meets the high-pressure fracturing sealing requirements. After the long hole is completed, a hole cleaning operation is carried out to remove sediment from the bottom of the hole to ensure unobstructed flow inside the hole.

8. The safe pressure relief method for long-hole directional hydraulic fracturing in hard rock formations according to claim 1, characterized in that, In step three, the segmented sealing device includes a bidirectional expansion packer and a push rod that works in conjunction with it, used to achieve long-distance positioning and high-pressure sealing within the hole.

9. The safe pressure relief method for long-hole directional hydraulic fracturing in hard rock formations according to claim 1, characterized in that, In step four, the retreating process is a continuous fracturing process with multiple segments in one hole, where each segment is set, fracturing is initiated, extended, depressurized, and displaced to form a continuous fracturing network.

10. The safe pressure relief method for long-hole directional hydraulic fracturing in hard rock formations according to claim 1, characterized in that, In step five, the real-time monitoring station uses a microseismic monitoring system or an in-hole pressure sensor to analyze the fracture development and the effect of segmented hydraulic fracturing by analyzing the collected images or data.

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