Coal seam fracturing range monitoring method based on borehole peeping and nanometer detection

Abstract

The invention discloses a coal seam fracturing range monitoring method based on borehole peeping and nanometer detection, which utilizes the advantages of small size and far signal transmission of nanometer detectors, after fractures are generated by sectional type hydraulic fracturing, the nanometer detectors with different densities are moved into the fractures along with high-pressure water, and the fractures are detected by the nanometer detectors. Each nano detector automatically flows into cracks in different directions according to the density condition between the nano detector and the high-pressure water; then, a drill hole peeping instrument and a signal receiver are placed in the fractured drill hole, the drill hole peeping instrument is used for obtaining the crack initiation position of each crack in the wall of the drill hole in each packing interval, and the signal receiver is used for receiving signals sent by each nanometer detector in each crack; according to the method, the depth position and azimuth data of the cracks where the nano detectors are located are obtained, in-situ monitoring of the cracks is achieved, the actual space distribution characteristics of the cracks around the current directional long drill hole are obtained after comprehensive analysis, and then data support is provided for actual optimization of a directional long drill hole fracturing scheme.

Description

Technical Field

[0001] The invention relates to a coal seam fracturing range monitoring method by borehole peeping and nanometer detection, belonging to the technical field of coal seam hydraulic fracturing monitoring. Background Art

[0002] Hydraulic fracturing is a technology used to increase the production of oil and natural gas. It is also applied to the fracturing and permeability enhancement engineering of deep low-permeability coal seams. This technology injects high-pressure liquid into the coal seam to force the rock to break, generate a large number of new cracks, promote the desorption of adsorbed gas, and thus improve the extraction efficiency of coal seam gas. Under the action of the water wedge with large pore pressure, the weaker coal body on the borehole wall is first tensilely damaged, forming new cracks. Driven by continuous high-pressure water, the fracturing cracks continue to expand and extend, and penetrate with the original pore fracture structure of the coal body, thus forming a complex multi-scale pore fracture structure. The extension of fractures is mainly affected by factors such as ground stress and reservoir occurrence conditions. Hydraulic fractures usually start in the weakened area and then extend along the direction of the maximum principal stress; at the same time, the reservoir structure strength and the original bedding structure will have a great influence on the fracture extension path, but the true direction and distribution of the fractures in the coal seam are still unclear.

[0003] At present, crack monitoring during hydraulic fracturing of coal seams is an important link to ensure the safety, efficiency and environmental impact of the fracturing process. The existing monitoring technologies mainly include shallow well array imaging technology and microseismic monitoring technology in the well. The former determines the induced seismic signals recorded in the previous exploration as the noise background of the underground structure, and uses a broadband three-component microseismic station to detect the fracturing process, which can provide information such as crack length and orientation; the latter uses downhole multi-component microseismic geophones to record microseismic events during the crack generation process, which can provide information such as crack height, length, and width. These two methods have the problems of low data interpretation accuracy and poor adaptability. The fracture data provided are global, and there is no way to focus on the information display of the actual spatial distribution of fractures around the fracturing borehole, making it difficult to provide data support for the actual optimization of directional long borehole fracturing schemes.

[0004] Therefore, there is an urgent need for a new method that can accurately obtain the actual spatial distribution information of cracks around the fracturing borehole, realize in-situ monitoring of the cracks, and then provide data support for the actual optimization of directional long-hole fracturing schemes, which is the research direction required by the present invention. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for monitoring the fracturing range of coal seams by borehole peeping and nano-detection, which can accurately obtain the actual spatial distribution information of cracks around the fracturing borehole, realize in-situ monitoring of the cracks, and further provide data support for the actual optimization of directional long borehole fracturing schemes.

[0006] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a method for monitoring the fracture range of coal seams by drilling peek and nano-detection, the specific steps of which are:

[0007] Step 1: Use a directional drill bit to construct a directional long borehole from the side wall of the tunnel to the target coal seam to the designed length. The opening angle, deflection angle and length of the directional long borehole are determined according to the design plan based on the actual occurrence of the coal seam.

[0008] Step 2: After the construction is completed, the first high-pressure packer is placed in the directional long borehole for sealing, so that the first isolation interval is formed between the bottom of the directional long borehole and the first high-pressure packer, and one end of the fracturing pipe is extended into the directional long borehole until it reaches the first isolation interval.

[0009] Step three, the other end of the fracturing pipe is connected to the hydraulic fracturing device through a high-pressure hose. The hydraulic fracturing device injects high-pressure water into the first isolation interval along the fracturing pipe, and continues to inject water into the first isolation interval until the injection pressure value reaches the set P value. The injection of high-pressure water is stopped and the high pressure is maintained for a period of time. When the pressure value drops significantly, it indicates that the coal seam around the first isolation interval is fractured and cracks are generated, allowing high-pressure water to enter the cracks, completing the hydraulic fracturing process of the first isolation interval.

[0010] Step 4: Extend one end of the guide tube into the first isolation interval, and transport multiple nanodetectors A, nanodetector B and nanodetector C into the first isolation interval, wherein the density of nanodetector A is less than the density of high-pressure water, the density of nanodetector B is equal to the density of high-pressure water, and the density of nanodetector C is greater than the density of high-pressure water. After the transportation is completed, the first isolation interval is refilled with high-pressure water through the hydraulic fracturing device and the pressure value reaches P value, and the pressure value is maintained for a period of time; at this time, affected by the injection water pressure and the different densities of each nanodetector, the nanodetector A flows into the cracks above the directional long borehole, the nanodetector B flows into the cracks on both sides of the directional long borehole, and the nanodetector C flows into the cracks below the directional long borehole.

[0011] Step 5. After the maintenance time is reached, stop injecting high-pressure water and discharge the high-pressure water in the first isolation interval out of the directional long borehole. At this time, nanodetectors A, nanodetectors B and nanodetectors C in the cracks each detect the drop in surrounding pressure and automatically open their legs to fix each nanodetector in its own crack to prevent it from being discharged from the directional long borehole along with the high-pressure water.

[0012] Step six, place a second high-pressure packer into the directional long borehole for sealing, so that a second isolation interval is formed between the second high-pressure packer and the first high-pressure packer, and one end of the fracturing pipe is in the second isolation interval; after completion, repeat steps three to five to realize the hydraulic fracturing and nano-detector placement process of the second isolation interval; repeat this process to realize the hydraulic fracturing and nano-detector placement process of the coal seam around the directional long borehole in stages.

[0013] Step seven, after the coal fracturing process of all isolation sections is completed, the borehole peep instrument and the signal receiver are sent to the first isolation interval, the second isolation interval, ..., the Nth isolation interval in turn, wherein the borehole peep instrument is used to obtain the starting position of each crack on the borehole wall of each isolation interval, and the signal receiver is used to receive the signal emitted by each nanodetector in the crack around each isolation interval, and then obtain the depth position and azimuth data of the crack where each nanodetector is located.

[0014] Step 8: Comprehensively analyze the starting positions of each crack on the borehole wall of each isolation interval and the depth position and azimuth data of each surrounding crack obtained in step 7 to obtain the actual spatial distribution characteristics of each crack around the current directional long borehole.

[0015] Furthermore, the diameter of the directional long drill hole is 110 mm, and the opening angle is 20° to 60°.

[0016] Furthermore, during the directional long hole drilling process, the drilling speed is controlled to be 2-3 m / min, and the water injection and drainage volumes are controlled to reduce the possibility of hole collapse caused by stress concentration in the longer hole.

[0017] Furthermore, the length of each isolation interval is 20 to 30 m, the maximum expansion stress of the high-pressure resistant packer is 60 MPa, and the compressive strength is 90 MPa.

[0018] Furthermore, all nanodetectors are provided with a hydrophobic layer formed of a highly hydrophobic material on their surfaces, which is used to separate from water and reduce the impact of water flow when high-pressure water is discharged.

[0019] Furthermore, the nanodetector A, nanodetector B and nanodetector C have the same structure and are all spheres with a diameter of 20 nm. They are all existing devices, and the only difference is that the density of the material used for the external sphere of each nanodetector is different; and the frequency of electromagnetic waves released by each nanodetector is 30 MHz to 30 GHz.

[0020] Furthermore, the borehole peep instrument has a detection accuracy of 1px and a sampling rate of 0.5m-3m / min, and is used to obtain the circumferential distribution of the hydraulic fractures on the borehole wall in each isolation interval.

[0021] Furthermore, the signal receiving range of the signal receiver in each isolation interval is a spherical range with a diameter of 2m centered on the signal receiver, and the signal receiving frequency is 30MHz-30GHz.

[0022] Furthermore, after the signal receiver in step seven receives the signals emitted by each nanodetector, it uses the Fourier transform method to perform peak separation on the signals received in different directions, and defines the distribution distances of the nanodetectors in the cracks in different directions according to the signal attenuation law, thereby obtaining the depth position and azimuth data of the cracks where each nanodetector is located.

[0023] Furthermore, after obtaining the actual spatial distribution characteristics of each crack around the current directional long borehole in step eight, a cluster analysis algorithm is used to perform a three-dimensional reconstruction analysis on the overall hydraulic fracture distribution of the directional long borehole.

[0024] Compared with the prior art, the present invention starts from the perspective of in-situ monitoring of hydraulic fracturing cracks, takes into account the non-uniform characteristics of crack expansion, and utilizes the advantages of small size and long signal transmission of nanodetectors. After staged hydraulic fracturing to generate cracks, the nanodetectors are placed in high-pressure water. At this time, nanodetectors of different densities are transported to each crack with the high-pressure water. On the one hand, each nanodetector automatically flows to the cracks in different directions according to the density between itself and the high-pressure water (that is, the nanodetectors with a density greater than that of high-pressure water sink to the bottom of the water body and subsequently flow into the cracks below the borehole; the nanodetectors with a density less than that of high-pressure water are at the top of the water body due to buoyancy and subsequently flow into the cracks above the borehole; the nanodetectors with a density equal to that of high-pressure water are inside the water body and subsequently flow into the cracks on both sides of the borehole), reflecting the real path distribution of the fracturing cracks in different directions around; on the other hand, after the borehole is drained and depressurized, the nanodetector can automatically open the fixed bracket to support and fix it in the crack to prevent it from flowing out with the drainage. Then, the borehole peep instrument and signal receiver are placed in the borehole after fracturing. The borehole peep instrument is used to obtain the starting position of each crack on the borehole wall of each isolation interval, and the signal receiver is used to receive the signals emitted by each nanodetector in the cracks around each isolation interval, and then obtain the depth position and azimuth data of the cracks where each nanodetector is located, so as to realize in-situ monitoring of the cracks. After comprehensive analysis, the actual spatial distribution characteristics of each crack around the current directional long borehole are obtained, thereby providing data support for the actual optimization of the directional long borehole fracturing plan. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the overall process of the present invention. DETAILED DESCRIPTION

[0026] The present invention will be further described below.

[0027] like Figure 1 As shown, the specific steps of the present invention are:

[0028] Step 1: Use a directional drill bit to construct a directional long borehole from the side wall of the tunnel to the target coal seam to the designed length. The opening angle, deflection angle and length of the directional long borehole are determined according to the design plan of the actual occurrence of the coal seam; the aperture of the directional long borehole is 110 mm, and the opening angle is 20°~60°; during the drilling of the directional long borehole, the drilling speed is controlled to 2~3m / min, and the water injection and drainage volume are controlled to reduce the possibility of hole collapse caused by stress concentration in the longer borehole.

[0029] Step 2: After the construction is completed, the first high-pressure packer is placed in each directional long borehole for sealing, so that a first isolation interval is formed between the bottom of the directional long borehole and the first high-pressure packer, and one end of the fracturing pipe is extended into the directional long borehole until it enters the first isolation interval;

[0030] Step 3: The other end of the fracturing pipe is connected to the hydraulic fracturing device through a high-pressure hose. The hydraulic fracturing device injects high-pressure water into the first isolation interval along the fracturing pipe, and continues to inject water into the first isolation interval until the injection pressure value reaches the set P value. The injection of high-pressure water is stopped and the high pressure is maintained for a period of time. When the pressure value drops significantly, it indicates that the coal seam around the first isolation interval is fractured and cracks are generated, so that high-pressure water enters the cracks, and the hydraulic fracturing process of the first isolation interval is completed;

[0031] Step 4, extend one end of the guide tube into the first isolation interval, and transport multiple nanodetectors A, nanodetectors B and nanodetectors C into the first isolation interval, wherein the density of nanodetector A is less than the density of high-pressure water, the density of nanodetector B is equal to the density of high-pressure water, and the density of nanodetector C is greater than the density of high-pressure water. After the transportation is completed, the first isolation interval is refilled with high-pressure water through the hydraulic fracturing device and the pressure value reaches P value, and the pressure value is maintained for a period of time; at this time, affected by the injection water pressure and the different densities of each nanodetector, the nanodetector A flows into the cracks above the directional long borehole, the nanodetector B flows into the cracks on both sides of the directional long borehole, and the nanodetector C flows into the cracks below the directional long borehole; the surface of all nanodetectors is provided with a hydrophobic layer formed by a strong hydrophobic material, which is used to separate from water when the high-pressure water is unloaded and discharged to reduce the impact of water flow. The nanodetector A, nanodetector B and nanodetector C have the same structure and are all spheres with a diameter of 20 nm. They are all existing devices, and the only difference is that the density of the material used for the external sphere of each nanodetector is different; and the frequency of the electromagnetic wave released by each nanodetector is 30 MHz to 30 GHz.

[0032] Step 5: After the maintenance time is reached, the injection of high-pressure water is stopped, and the high-pressure water in the first isolation interval is discharged out of the directional long borehole. At this time, the nano-detectors A, B and C in the cracks detect the decrease in the surrounding pressure and automatically open the legs to fix each nano-detector in its own crack to prevent it from being discharged out of the directional long borehole along with the high-pressure water.

[0033] Step six, place a second high-pressure packer into the directional long borehole for sealing, so that a second isolation interval is formed between the second high-pressure packer and the first high-pressure packer, and one end of the fracturing pipe is in the second isolation interval; after completion, repeat steps three to five to realize the hydraulic fracturing and nano-probe placement process of the second isolation interval; repeat this process to realize the hydraulic fracturing and nano-probe placement process of the coal seam around the directional long borehole in sections; the length of each isolation interval is 20 to 30 m, the maximum expansion stress of the high-pressure packer is 60 MPa, and the compressive strength is 90 MPa.

[0034] Step 7. After the coal fracturing process of all isolation sections is completed, the borehole peep instrument and the signal receiver are sent to the first isolation interval, the second isolation interval, ..., and the Nth isolation interval in turn, wherein the borehole peep instrument is used to obtain the starting position of each crack on the borehole wall of each isolation interval, and the signal receiver is used to receive the signal emitted by each nanodetector in the crack around each isolation interval, and the Fourier transform method is used to perform peak separation on the signals received in different directions, and the distribution distance of the nanodetectors in the cracks in different directions is defined according to the signal attenuation law, so as to obtain the depth position and azimuth data of the cracks where each nanodetector is located. The detection accuracy of the borehole peep instrument is 1px, and the sampling rate is 0.5m~3m / min, which is used to obtain the circumferential distribution of the fracturing cracks in each isolation interval on the borehole wall; the signal receiving range of the signal receiver in each isolation interval is a spherical range with a diameter of 2m centered on the signal receiver, and the signal receiving frequency is 30MHz-30GHz.

[0035] Step 8: Comprehensively analyze the starting positions of each crack on the borehole wall of each isolation interval and the depth position and azimuth data of each surrounding crack obtained in step 7 to obtain the actual spatial distribution characteristics of each crack around the current directional long borehole.

[0036] As an improvement of the present invention, after obtaining the actual spatial distribution characteristics of each crack around the current directional long borehole in step eight, a cluster analysis algorithm is used to perform a three-dimensional reconstruction analysis on the overall fracturing crack distribution of the directional long borehole.

[0037] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for monitoring the fracture range of coal seams by drilling peek and nano-detection, characterized in that: The specific steps are: Step 1: Use a directional drill bit to construct a directional long borehole from the side wall of the tunnel to the target coal seam to the designed length. The opening angle, deflection angle and length of the directional long borehole are determined according to the design plan of the actual occurrence of the coal seam; Step 2: After the construction is completed, the first high-pressure packer is placed in each directional long borehole for sealing, so that a first isolation interval is formed between the bottom of the directional long borehole and the first high-pressure packer, and one end of the fracturing pipe is extended into the directional long borehole until it enters the first isolation interval; Step 3: The other end of the fracturing pipe is connected to the hydraulic fracturing device through a high-pressure hose. The hydraulic fracturing device injects high-pressure water into the first isolation interval along the fracturing pipe, and continues to inject water into the first isolation interval until the injection pressure value reaches the set P value. The injection of high-pressure water is stopped and the high pressure is maintained for a period of time. When the pressure value drops significantly, it indicates that the coal seam around the first isolation interval is fractured and cracks are generated, so that high-pressure water enters the cracks, and the hydraulic fracturing process of the first isolation interval is completed; Step 4, extending one end of the guide tube into the first isolation interval, and transporting a plurality of nanodetectors A, nanodetectors B and nanodetectors C into the first isolation interval, wherein the density of nanodetector A is less than the density of high-pressure water, the density of nanodetector B is equal to the density of high-pressure water, and the density of nanodetector C is greater than the density of high-pressure water. After the transportation is completed, the first isolation interval is refilled with high-pressure water through the hydraulic fracturing device and the pressure value reaches P value, and the pressure value is maintained for a period of time; at this time, affected by the injection water pressure and the different densities of the nanodetectors, the nanodetector A flows into the cracks above the directional long borehole, the nanodetector B flows into the cracks on both sides of the directional long borehole, and the nanodetector C flows into the cracks below the directional long borehole; Step 5: After the maintenance time is reached, the injection of high-pressure water is stopped, and the high-pressure water in the first isolation interval is discharged out of the directional long borehole. At this time, the nano-detectors A, B and C in the cracks detect the decrease in the surrounding pressure and automatically open the legs to fix each nano-detector in its own crack to prevent it from being discharged out of the directional long borehole along with the high-pressure water. Step 6: Place a second high-pressure packer into the directional long borehole for sealing, so that a second isolation interval is formed between the second high-pressure packer and the first high-pressure packer, and one end of the fracturing pipe is in the second isolation interval; after completion, repeat steps 3 to 5 to achieve the hydraulic fracturing and nano-detector placement process of the second isolation interval; repeat this process to achieve the hydraulic fracturing and nano-detector placement process of the coal seam around the directional long borehole in stages; Step 7: After the coal body fracturing process of all isolation sections is completed, the borehole peep instrument and the signal receiver are sent to the first isolation interval, the second isolation interval, ..., the Nth isolation interval in sequence, wherein the borehole peep instrument is used to obtain the cracking position of each crack on the borehole wall of each isolation interval, and the signal receiver is used to receive the signal emitted by each nano detector in the crack around each isolation interval, and then obtain the depth position and azimuth data of the crack where each nano detector is located; Step 8: Comprehensively analyze the starting positions of each crack on the borehole wall of each isolation interval and the depth position and azimuth data of each surrounding crack obtained in step 7 to obtain the actual spatial distribution characteristics of each crack around the current directional long borehole.

2. The method for monitoring the fracture range of coal seams by drilling peek and nano-detection according to claim 1 is characterized in that: The diameter of the directional long drill hole is 110 mm, and the opening angle is 20° to 60°.

3. The method for monitoring the fracture range of coal seams by drilling peek and nano-detection according to claim 1 is characterized in that: During the directional long hole drilling process, the drilling speed is controlled to be 2-3 m / min, and the water injection and drainage volumes are controlled to reduce the possibility of hole collapse caused by stress concentration in the long hole.

4. The method for monitoring the fracture range of coal seams by drilling peek and nano-detection according to claim 1 is characterized in that: The length of each isolation interval is 20 to 30 m, the maximum expansion stress of the high-pressure resistant isolation packer is 60 MPa, and the compressive strength is 90 MPa.

5. The method for monitoring the fracture range of coal seams by drilling peek and nano-detection according to claim 1 is characterized in that: The surface of all nanodetectors is provided with a hydrophobic layer formed by a highly hydrophobic material, which is used to separate from water when high-pressure water is discharged to reduce the impact of water flow.

6. The method for monitoring the fracture range of coal seams by drilling peek and nano-detection according to claim 1 is characterized in that: The nanodetector A, nanodetector B and nanodetector C have the same structure and are all spheres with a diameter of 20 nm. The only difference is that the density of the material used for the outer sphere of each nanodetector is different; and the frequency of the electromagnetic wave released by each nanodetector is 30 MHz to 30 GHz.

7. The method for monitoring the fracture range of coal seams by drilling peek and nano-detection according to claim 1 is characterized in that: The borehole peep instrument has a detection accuracy of 1px and a sampling rate of 0.5m-3m / min, and is used to obtain the circumferential distribution of the fracturing cracks on the borehole wall in each isolation interval.

8. The method for monitoring the fracture range of coal seams by drilling peek and nanometer detection according to claim 1 is characterized in that: The signal receiving range of the signal receiver in each isolation interval is a spherical range with a diameter of 2m centered on the signal receiver, and the signal receiving frequency is 30MHz-30GHz.

9. The method for monitoring the fracture range of coal seams by drilling peek and nanometer detection according to claim 1 is characterized in that: After the signal receiver receives the signals emitted by each nanodetector in step seven, it uses the Fourier transform method to perform peak separation on the signals received in different directions, and defines the distribution distances of the nanodetectors in the cracks in different directions according to the signal attenuation law, thereby obtaining the depth position and azimuth data of the cracks where each nanodetector is located.

10. The method for monitoring the fracture range of coal seams by drilling peek and nanometer detection according to claim 1, characterized in that: After obtaining the actual spatial distribution characteristics of each crack around the current directional long borehole in step eight, a cluster analysis algorithm is used to perform a three-dimensional reconstruction analysis on the overall fracturing crack distribution of the directional long borehole.

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