CN110306964B - Hydraulic fracturing coal seam crack visualization and permeability increasing effect evaluation method - Google Patents
Hydraulic fracturing coal seam crack visualization and permeability increasing effect evaluation method Download PDFInfo
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Abstract
A hydraulic fracturing coal seam crack visualization and permeability improvement effect evaluation method is used for coal seam hydraulic fracturing detection in a laboratory. The method comprises an early preparation stage, a ground stress loading stage, a gas extraction before fracturing, a hydraulic fracturing coal body stage, a gas extraction after fracturing and fracturing effect evaluation. The method has the advantages of simple steps and good detection effect, effectively simulates the enhanced gas extraction process under different combination modes, synchronously monitors and acquires the pressure, the temperature, the surface crack form and the extracted gas flow of the coal seam gas, and provides an effective means for researching the gas extraction efficiency and optimizing the extraction measures under different enhanced extraction conditions.
Description
Technical Field
The invention relates to an evaluation method, in particular to a hydraulic fracturing coal seam crack visualization and permeability increasing effect evaluation method which is suitable for coal seam hydraulic fracturing detection in a laboratory
Background
The coal bed gas storage condition of China generally has the characteristics of three low and one high (low saturation, low permeability, low reservoir pressure and high metamorphism degree), and the permeability of most mining areas coal beds in China is 10-4～10-3mD is 3-4 orders of magnitude lower than that of the United states and the like, coal seam gas extraction under the conditions is a worldwide problem, and meanwhile, various enhanced gas extraction measures are also proposed and implemented successively, such as a hydraulic fracturing technology, a deep hole blasting permeability-increasing technology, a high-pressure abrasive jet flow slotting permeability-increasing technology, a high-pressure electric pulse coal breaking permeability-increasing technology, a gas injection displacement production-increasing technology and the like.
According to the hydraulic fracturing technology, high-pressure water is injected into a drill hole, a coal bed is fractured under the dual actions of the ground stress and the high-pressure water, a plurality of macroscopic cracks and branch cracks are formed around the drill hole, the macroscopic cracks extend to the deep part of the coal bed, a channel is provided for desorption and seepage of coal bed gas, and the extraction range of the drill hole is improved. Therefore, the development and the expansion process of the coal seam cracks in the hydraulic fracturing process are key factors influencing the fracturing effect. Therefore, the method for visualizing the hydraulic fracturing coal seam cracks and evaluating the permeability increasing effect has the main advantages that: (1) the large-scale coal seam hydraulic fracturing process under the condition of a true triaxial mining stress field can be simulated, and the large-scale coal seam hydraulic fracturing process is closer to the real complex geological condition of a site; (2) the surface cracks of the coal bed in the hydraulic fracturing process can be monitored in real time in the whole process; (3) and evaluating the hydraulic fracturing effect based on gas extraction operation on the coal seam before and after fracturing.
Disclosure of Invention
Aiming at the defects of the technical comparison, the hydraulic fracturing coal seam crack visualization and permeability increasing effect evaluation method is simple in structure and good in using effect, and can simulate the coal and gas delay outburst process under the multi-field coupling conditions of different true triaxial stresses, gas pressures and coal seam temperatures.
In order to achieve the technical purpose, the method for visualizing the hydraulic fracturing coal seam cracks and evaluating the anti-reflection effect comprises the following steps of: the method comprises the following steps of preparing in an early stage, loading the ground stress, extracting gas before fracturing, fracturing coal body by using water power, extracting gas after fracturing and evaluating the fracturing effect; the method comprises the following specific steps:
1a) sampling a coal outburst layer from a coal mine area to be tested, carrying out on-site investigation, measuring relevant parameters of the coal outburst layer by using the coal block samples collected on site, and determining test parameters such as ground stress, water injection rate, fracturing position and the like in a test scheme;
1b) using a crushing sieve to sample and sieve the collected coal blocks into coal particles with the particle size of 0-1mm, adding water into the coal particles, and stirring to prepare a coal sample with the water content of 6% for later use;
1c) the method comprises the following steps of loading a coal sample with 6% of water content into a visual box body, wherein the bottom of the visual box body is provided with a spongy multifunctional metal plate, the multifunctional metal plate is provided with an inflation inlet, the top of the visual box body, the left side wall and the front side wall of the visual box body are provided with a plurality of transparent loading plates, the transparent loading plates at the top of the visual box body are respectively provided with X1-X6 in six serial numbers, the transparent loading plates on the front side wall of the visual box body are respectively provided with Y1-Y6 in six serial numbers, the transparent loading plate on the left side wall of the visual box body is Z1, each transparent loading plate is provided with a loading piston; the back of the visual box body is provided with a plurality of sensor mounting holes which are uniformly installed, and a row of multifunctional drill holes are arranged at the same time, wherein the tail part of each multifunctional drill hole is provided with an external connector on the visual box body, a sealing gasket is arranged between the external connector and the box body wall of the visual box body, each multifunctional drill hole comprises a hole sealing section and a fracturing section, the total length of each multifunctional drill hole is 0.5m, the length of each hole sealing section is 0.15m, the length of each fracturing section is 0.35m, air holes are distributed in the circumferential direction and the radial direction of the pipe wall of each fracturing section, the serial number of each multifunctional drill hole is A1-A6, a sensor mounting hole formed in the back of the visual box body is utilized by the visual box body to embed an air pressure sensor into a coal sample with the water content of 6% in the visual box body, and finally a loading;
1c) the cover plate of the visual box body and the box body are fastened in a sealing mode through a sealing ring and a screw, a high-pressure gas bottle, a vacuum pump and a flowmeter I are sequentially connected, the output end of the flowmeter I is connected with a gas charging port of a multifunctional metal plate through a pipeline, an external connector is arranged in a multifunctional drilling hole with the sequence number of A6 at the rear part of the visual box body and connected with a flowmeter II, an external connector is arranged in a multifunctional drilling hole with the sequence number of A3 at the rear part of the visual box body and connected with a gas inlet of a flowmeter III, a gas outlet pipeline of the flowmeter III is connected with a fracturing pump, and the sealing;
1d) a high-speed camera is arranged on the outer side of the visual box body and used for monitoring the change in the visual box body;
2a) carrying out triaxial stress loading operation on the coal sample in the visual box body, wherein the stress of 6 transparent loading plates with serial numbers of X1-X6 at the upper part of the coal sample in the visual box body is 6MPa, and the stress of 6 transparent loading plates with serial numbers of Y1-Y6 at the front side is 8 MPa; the stress of 1 transparent loading plate with the left serial number of Z1 is 10 MPa;
2b) starting a vacuum pump to vacuumize the coal sample until the air pressure in the coal body is less than 100Pa, and closing the vacuum pump, wherein the time is about 12 hours;
2c) opening a high-pressure gas cylinder to perform gas filling operation on the coal sample, dividing the operation into four stages to ensure that the adsorption equilibrium pressure of the coal sample is 1.0MPa, inflating for 12 hours and the inflation pressure to 0.3MPa in the first stage, and then closing the gas cylinder to stabilize for 6 hours; in the second stage, the gas is filled for 12 hours, the gas filling pressure is 0.6MPa, and then the gas cylinder is closed and stabilized for 6 hours; in the third stage, the gas is filled for 12 hours, the gas filling pressure is 0.9MPa, then the gas cylinder is closed, and the stability is 6 hours; in the fourth stage, gas is filled for 6 hours, the gas is filled and stabilized to 1.0MPa, then the gas cylinder is closed, the total time of the gas cylinder is 60 hours, and the gas filling amount is recorded through a flow meter I in the gas filling process;
3a) the gas extraction process before hydraulic fracturing is carried out according to the test scheme, the A6 drill hole is opened, gas extraction is started, and the gas extraction amount is recorded through the flowmeter II;
3b) finishing extraction after 24h, unloading stress and emptying gas;
4a) repeating steps 2a-2 c;
4b) controlling a fracturing pump to inject water into a coal sample arranged in a visual box body through a multifunctional drilling hole with the serial number of A3, wherein the water injection rate is 10 mL/s;
4c) observing the change of the coal sample in the water injection process of the fracturing pump by a high-speed camera arranged on the side of the visual box body, and closing the fracturing pump to stop water injection when the coal rock surface is observed to generate cracks;
4d) finishing the fracturing, closing the high-speed camera, and unloading the stress;
5a) carrying out a gas extraction process after hydraulic fracturing according to a test scheme, opening a multifunctional drill hole with the serial number of A6 to extract gas, and recording the gas extraction amount through a flowmeter II;
5b) finishing extraction after 24h, unloading stress and emptying gas;
5c) changing the positions of hydraulic fracturing drill holes and the conditions of water injection rate, repeating the steps 1c-2c and 4a-5b, and carrying out hydraulic fracturing and post-fracturing gas extraction tests under other conditions.
6a) Analyzing the growth and expansion rules of cracks on the surface of the coal body in the hydraulic fracturing process under different conditions according to the coal body pictures shot by the high-speed camera, performing sketch treatment on the final shape of the crack by using PS (polystyrene), and analyzing the relationship between different fracturing parameters such as the fracturing drilling position and water injection rate and the quantity, area and fracture initiation pressure of the fracturing crack;
6b) respectively calculating the gas extraction rate before fracturing according to the gas filling amount and the extraction amount, wherein the gas extraction rate before fracturing comprises the gas extraction amount accounting for the filling amount and different fracturing parameters: the method comprises the steps of fracturing the position of a drill hole and the gas extraction rate after water injection rate fracturing; analyzing the relationship among the number, the area and the fracture initiation pressure of the fracturing cracks and the gas extraction rate;
6c) and quantitatively evaluating the yield increasing effect of the hydraulic fracturing based on the gas extraction rate before and after fracturing, and optimizing hydraulic fracturing parameters.
Has the advantages that:
the method can simulate the fluid fracturing coal bed, fluid displacement gas, gas extraction process and the enhanced gas extraction process in different combination modes under different true triaxial stress, gas pressure and coal bed temperature multi-field coupling conditions indoors, can synchronously monitor and acquire the coal bed gas pressure, temperature, surface crack morphology and extracted gas flow, and provides an effective means for researching the gas extraction efficiency and optimizing the extraction measures under different enhanced extraction conditions.
Description of the drawings:
fig. 1 is a schematic structural view of a transparent box body used in the hydraulic fracturing coal seam crack visualization and permeability increasing effect evaluation method.
FIG. 2 is a top view of a transparent box body used in the hydraulic fracturing coal seam crack visualization and permeability increasing effect evaluation method.
FIG. 3 is a rear view of a transparent box used in the hydraulic fracturing coal seam crack visualization and permeability increasing effect evaluation method of the invention.
Fig. 4 is a structural schematic diagram of a loading system used in the hydraulic fracturing coal seam crack visualization and permeability increasing effect evaluation method of the invention.
Fig. 5(a) is a schematic view of the installation of the air pressure sensor of the present invention.
Fig. 5(b) is a schematic view of the temperature sensor installation of the present invention.
Fig. 5(c) is a schematic view of the multifunctional drilling structure of the present invention.
Fig. 6 is a schematic diagram of a camera shooting position used in the hydraulic fracturing coal seam crack visualization and permeability increasing effect evaluation method.
Fig. 7 is a schematic diagram of a hydraulic fracturing combination mode used by the hydraulic fracturing coal seam crack visualization and permeability increasing effect evaluation method.
In the figure: 1-visual box body, 2-box body cover plate, 3-box body cavity body, 4-sealing ring, 5-sealing bolt, 6-multifunctional metal plate, 7-thermal resistance wire, 8-inflation inlet, 9-wiring inlet, 10-sensor mounting hole, 11-multifunctional drilling mounting hole, 12-transparent loading plate, 13-loading piston, 14-high-speed camera, 15-sealing gasket a, 16-air pressure sensor, 17-PU pneumatic connector, 18-PU pipe, 19-sealing gasket b, 20-data line, 21-conversion connector, 22-temperature sensor, 23-stress sensor, 24-external connector, 25-multifunctional drilling hole, 26-fracturing section, 27-sealing section and 28-ventilation small hole, 29-high pressure gas cylinder, 30-vacuum pump, 31-flowmeter I, 32-flowmeter II, 33-flowmeter III, 34-fracturing pump.
DETAILED DESCRIPTION OF EMBODIMENT (S) OF INVENTION
Embodiments of the present application are further described below with reference to the accompanying drawings:
according to the method for visualizing the hydraulic fracturing coal seam cracks and evaluating the anti-reflection effect by using the device, the early preparation stage, the ground stress loading stage, the gas extraction before fracturing, the hydraulic fracturing coal body stage, the gas extraction after fracturing and the fracturing effect evaluation are carried out;
as shown in fig. 1, 2 and 3, a visual box 1 with a cuboid structure is used, the visual box 1 comprises a box cavity 3 and a box cover plate 2 arranged at the top, a sealing ring 4 is arranged between the box cavity 3 and the box cover plate 2 and is fixed by a sealing bolt 5, a plurality of mounting holes 10 for mounting various sensors and mounting holes 11 for multifunctional drilling are uniformly arranged on the rear side wall of the box cavity 3, the mounted sensors comprise air pressure sensors 16, the temperature sensor 22 and the stress sensor 23 are arranged, the multifunctional drilling hole 25 is arranged in the multifunctional drilling hole 11, the multifunctional metal plate 6 which is as large as the bottom of the visual box body 1 is arranged at the bottom in the box body cavity 3, the multifunctional metal plate 6 is made of foam metal with good air permeability, the bottom of the multifunctional metal plate 6 is provided with an air charging port 8 communicated with the outer side of the box body cavity, and the air charging port 8 is connected with an air source system through a pipeline;
the loading system comprises a plurality of transparent loading plates 12 arranged in a box cover plate at the top of the visual box body 1, the left side wall and the front side wall of the box body cavity 3, each transparent loading plate 12 is provided with a loading piston 13, and the loading pistons 13 penetrate through the wall of the box body and are communicated with a pressurizing oil cylinder;
the gas source system comprises a high-pressure gas bottle, the gas pressure is not lower than 6MPa, the high-pressure gas bottle is connected with an inflation inlet 8 on a multifunctional metal plate 6 in the visual box body 1 through a vacuum pump by utilizing a gas pipe, and a flowmeter is arranged on the gas pipe;
the temperature control system comprises a thermal resistance wire 7 arranged on the surface of the multifunctional metal plate 6, and the thermal resistance wire 7 is in line connection with the temperature adjusting device through a wiring port 9 arranged on the multifunctional metal plate 6 and is used for heating the coal sample arranged in the visual box body 1;
the air pressure sensor 16 is inserted into the sensor mounting hole 10 from the outer side of the visual box body 1 through a sealing gasket a15, the tail end of the air pressure sensor 16 is connected with a control system through a data line 20 and data acquisition, the inner side of the sensor mounting hole 10 is provided with a PU pipe 18 extending and arranged inside a coal sample, the position of the opening end of the PU pipe 18 is adjusted to test the gas pressure at different positions, and a PU pneumatic connector 17 is arranged between the PU pipe 18 and the wall of the visual box body 1.
As shown in fig. 5(a) and 5(b), the temperature sensor 22 and the stress sensor 23 have the same mounting structure, the data line 20 connected to the tail of the temperature sensor 22 and the stress sensor 23 is fixed in the sensor mounting hole 10 of the visual box 1 through the adapter 21 and the gasket a15, and the data line 20 at the head of the temperature sensor 22 and the stress sensor 23 is buried at a position in the coal sample where temperature or stress needs to be detected.
As shown in fig. 5(c), a multifunctional borehole 25 is arranged in the multifunctional borehole mounting hole 11, an external joint 24 is arranged at the tail of the multifunctional borehole 25 on the visual box 1, a sealing gasket a15 is arranged between the external joint 24 and the box wall of the visual box 1, a sealing gasket b19 is arranged between the inner side of the box wall of the visual box 1 and the multifunctional borehole 25, a part of the multifunctional borehole 25 extending into the coal sample comprises a borehole sealing section 27 and a fracturing section 26, the total length of the multifunctional borehole 25 is 0.5m, the length of the borehole sealing section 27 is 0.15m, the length of the fracturing section 26 is 0.35m, a plurality of small ventilation holes 28 are distributed in the circumferential direction and the radial direction of the wall of the fracturing section 26, the small ventilation holes 28 have a diameter of 2mm, and the interval of 5mm, and have functions of fracturing.
The method comprises the following specific steps:
1a) sampling a coal outburst layer from a coal mine area to be tested, carrying out on-site investigation, measuring relevant parameters of the coal outburst layer by using the coal block samples collected on site, and determining test parameters such as ground stress, water injection rate, fracturing position and the like in a test scheme;
1b) using a crushing sieve to sample and sieve the collected coal blocks into coal particles with the particle size of 0-1mm, adding water into the coal particles, and stirring to prepare a coal sample with the water content of 6% for later use;
1c) as shown in fig. 4, a coal sample with a water content of 6% is loaded into a visual box body 1, the bottom of the visual box body 1 is provided with a spongy multifunctional metal plate 6, the multifunctional metal plate 6 is provided with an inflation inlet 8, the top of the visual box body 1 and the left side wall and the front side wall of the visual box body are provided with a plurality of transparent loading plates 12, the transparent loading plates 12 at the top of the visual box body 1 are respectively provided with X1-X6 in six serial numbers, the transparent loading plates 12 at the front side wall of the visual box body 1 are respectively provided with Y1-Y6 in six serial numbers, the transparent loading plates 12 at the left side wall of the visual box body 1 are Z1, each transparent loading plate 12 is provided with a loading piston 13, and the loading pistons; the back of the visual box body is provided with a plurality of sensor mounting holes 10 which are uniformly installed, and a row of multifunctional drill holes 25 are arranged at the same time, wherein the tail of each multifunctional drill hole 25 is provided with an external connector 24 on the visual box body 1, a sealing gasket a15 is arranged between each external connector 24 and the box body wall of the visual box body 1, the serial number of each multifunctional drill hole is A1-A6, the sensor mounting holes 10 formed in the back of the visual box body 1 are utilized by the visual box body to embed air pressure sensors 16 into coal samples with the water content of 6% in the visual box body 1 respectively, and finally, a loading piston 13 is used for driving a transparent loading plate 12 to enable the coal samples with the water content of 6% to be molded for 1 hour under the condition;
1c) as shown in fig. 7, a cover plate of the visualization box body 1 and the box body are tightly sealed and fastened by using a sealing ring and screws, a high-pressure gas cylinder 29, a vacuum pump 30 and a flowmeter i 31 are sequentially connected, the output end of the flowmeter i 31 is connected with an inflation inlet 8 of a multifunctional metal plate 6 through a pipeline, an external connector 24 is arranged in a multifunctional drilling hole 25 with the serial number of A6 at the rear part of the visualization box body 1 and connected with a flowmeter ii 32, an external connector 24 is arranged in the multifunctional drilling hole 25 with the serial number of A3 at the rear part of the visualization box body 1 and connected with an air inlet of a flowmeter iii 33, an air outlet pipeline of the flowmeter iii 33 is connected with a fracturing pump 34, and the;
1d) as shown in fig. 6, a high-speed camera 14 is installed outside the visualization box body 1 for monitoring the change of the visualization box body 1;
2a) carrying out triaxial stress loading operation on the coal sample in the visualization box body 1, wherein the stress of 6 transparent loading plates 12 with serial numbers of X1-X6 at the upper part of the coal sample in the visualization box body 1 is 6MPa, and the stress of 6 transparent loading plates 12 with serial numbers of Y1-Y6 at the front side is 8 MPa; the stress of 1 transparent loading plate 12 with the left serial number of Z1 is 10 MPa;
2b) starting a vacuum pump 30 to vacuumize the coal sample until the air pressure in the coal body is less than 100Pa, and closing the vacuum pump 30 for about 12 hours;
2c) opening a high-pressure gas cylinder 29 to perform gas filling operation on the coal sample, dividing the operation into four stages to ensure that the adsorption equilibrium pressure of the coal sample is 1.0MPa, inflating for 12h and the inflation pressure to 0.3MPa in the first stage, and then closing the gas cylinder 29 to stabilize for 6 h; in the second stage, the gas is filled for 12 hours, the gas filling pressure is 0.6MPa, and then the high-pressure gas cylinder 29 is closed and stabilized for 6 hours; in the third stage, the gas is filled for 12 hours, the gas filling pressure is 0.9MPa, and then the high-pressure gas cylinder 29 is closed and stabilized for 6 hours; the fourth stage is inflated for 6 hours and is stabilized to 1.0MPa, then the high-pressure gas cylinder 29 is closed, the time is 60 hours in total, and the gas filling amount is recorded through a flow meter I31 in the inflating process;
3a) the method comprises the steps of (1) carrying out a gas extraction process before hydraulic fracturing according to a test scheme, opening a multifunctional drill hole with the serial number of A6, starting gas extraction, and recording the gas extraction amount through a flowmeter II 32;
3b) finishing extraction after 24h, unloading stress and emptying gas;
4a) repeating steps 2a-2 c;
4b) controlling the fracturing pump 34 to inject water into the coal sample arranged in the visual box body 1 through the multifunctional drilling hole 25 with the serial number of A3, wherein the water injection rate is 10 mL/s;
4c) observing the change of the coal sample in the water injection process of the fracturing pump 34 by a high-speed camera 14 arranged on the side of the visual box body 1, and closing the fracturing pump 34 to stop water injection when the coal rock surface is observed to generate cracks;
4d) the fracturing is finished, the high-speed camera 14 is closed, and the stress is unloaded;
5a) the process of gas extraction after hydraulic fracturing is carried out according to the test scheme, the multifunctional drill hole 25 with the serial number of A6 is opened to extract gas, and the gas extraction amount is recorded through a flowmeter II 32;
5b) finishing extraction after 24h, unloading stress and emptying gas;
5c) changing the positions of hydraulic fracturing drill holes and the conditions of water injection rate, repeating the steps 1c-2c and 4a-5b, and carrying out hydraulic fracturing and post-fracturing gas extraction tests under other conditions.
6a) Analyzing the growth and expansion rules of cracks on the surface of the coal body in the hydraulic fracturing process under different conditions according to the coal body photos shot by the high-speed camera 14, performing sketch treatment on the final shape of the crack by using PS (polystyrene), and analyzing the relationship between different fracturing parameters such as the fracturing drilling position, the water injection rate and the like and the quantity, the area and the fracture initiation pressure of the fracture crack;
6b) respectively calculating the gas extraction rate before fracturing according to the gas filling amount and the extraction amount, wherein the gas extraction rate before fracturing comprises the gas extraction amount accounting for the filling amount and different fracturing parameters: the method comprises the steps of fracturing the position of a drill hole and the gas extraction rate after water injection rate fracturing; analyzing the relationship among the number, the area and the fracture initiation pressure of the fracturing cracks and the gas extraction rate;
6c) and quantitatively evaluating the yield increasing effect of the hydraulic fracturing based on the gas extraction rate before and after fracturing, and optimizing hydraulic fracturing parameters.
Several experimental protocols exemplified in this example are given below:
the boreholes in the fracture locations in the upper table are hydraulic fracture boreholes.
Claims (1)
1. A hydraulic fracturing coal seam crack visualization and permeability increasing effect evaluation method is characterized by comprising the following steps: the method comprises the following steps of preparing in an early stage, loading the ground stress, extracting gas before fracturing, fracturing coal body by using water power, extracting gas after fracturing and evaluating the fracturing effect; the method comprises the following specific steps:
1a) sampling a coal outburst layer from a coal mine area to be tested, carrying out on-site investigation, measuring relevant parameters of the coal outburst layer by using the coal block samples collected on site, and determining the crustal stress, the water injection rate and the fracturing position in the test scheme;
1b) using a crushing sieve to sample and sieve the collected coal blocks into coal particles with the particle size of 0-1mm, adding water into the coal particles, and stirring to prepare a coal sample with the water content of 6% for later use;
1c) the coal sample with the water content of 6 percent is filled into a visual box body, the visual box body comprises a box body cavity and a box body cover plate arranged at the top, a sealing ring is arranged between the box body cavity and the box body cover plate and is fixed by a sealing bolt, the bottom of the visual box body is provided with a spongy multifunctional metal plate, the multifunctional metal plate is provided with an inflation inlet, a plurality of transparent loading plates are arranged on the top of the visual box body and the left side wall and the front side wall of the visual box body, the six transparent loading plates on the top of the visual box body are respectively X1-X6 in serial number, the six transparent loading plates on the front side wall of the visual box body are respectively Y1-Y6 in serial number, the transparent loading plate on the left side wall of the visual box body is a transparent loading plate with the serial number Z1, each transparent loading plate is provided with a loading piston, and the loading piston penetrates through the box body wall of the visual box body and is communicated with a pressurizing oil cylinder; the back of the visual box body is uniformly provided with a plurality of sensor mounting holes, and a row of multifunctional drill holes are arranged at the same time, wherein the tail part of each multifunctional drill hole is provided with an external connector on the visual box body, a sealing gasket is arranged between the external connector and the box body wall of the visual box body, each multifunctional drill hole comprises a hole sealing section and a fracturing section, the total length of each multifunctional drill hole is 0.5m, the length of each hole sealing section is 0.15m, the length of each fracturing section is 0.35m, air holes are distributed in the circumferential direction and the radial direction of the pipe wall of each fracturing section, the serial number of each multifunctional drill hole is A1-A6, a sensor mounting hole formed in the back of the visual box body is utilized on the visual box body to respectively embed an air pressure sensor into a coal sample with the water content of 6% in the visual box body, and finally a loading piston is;
1d) the box cover plate and the box cavity of the visual box body are tightly sealed and fastened by utilizing a sealing ring and a sealing bolt, a high-pressure gas cylinder, a vacuum pump and a flowmeter I are sequentially connected, the output end of the flowmeter I is connected with a gas charging port of a multifunctional metal plate through a pipeline, an external connector arranged at a multifunctional drilling hole with the serial number of A6 on the back surface of the visual box body is connected with a flowmeter II, an external connector arranged at a multifunctional drilling hole with the serial number of A3 on the back surface of the visual box body is connected with a gas inlet hole of a flowmeter III, a gas outlet pipeline of the flowmeter III is connected with a fracturing pump, and the sealing effect of the connection of the visual;
1e) a high-speed camera is arranged on the outer side of the visual box body and used for monitoring the change in the visual box body;
2a) carrying out triaxial stress loading operation on the coal sample in the visual box body, wherein the stress of 6 transparent loading plates with serial numbers of X1-X6 at the upper part of the coal sample in the visual box body is 6MPa, and the stress of 6 transparent loading plates with serial numbers of Y1-Y6 at the front side is 8 MPa; the stress of 1 transparent loading plate with the left serial number of Z1 is 10 MPa;
2b) starting a vacuum pump to vacuumize the coal sample until the air pressure in the coal body is less than 100Pa, and closing the vacuum pump, wherein the time is about 12 hours;
2c) opening a high-pressure gas cylinder to perform gas filling operation on the coal sample, dividing the operation into four stages to ensure that the adsorption equilibrium pressure of the coal sample is 1.0MPa, inflating for 12 hours and the inflation pressure to 0.3MPa in the first stage, and then closing the gas cylinder to stabilize for 6 hours; in the second stage, the gas is filled for 12 hours, the gas filling pressure is 0.6MPa, and then the gas cylinder is closed and stabilized for 6 hours; in the third stage, the gas is filled for 12 hours, the gas filling pressure is 0.9MPa, then the gas cylinder is closed, and the stability is 6 hours; the fourth stage is used for inflating for 6 hours, inflating and stabilizing to 1.0MPa, then the gas cylinder is closed, the total time consumption is 60 hours, and the gas filling amount is recorded through the flowmeter I in the inflating process;
3a) the method comprises the steps of (1) carrying out a gas extraction process before hydraulic fracturing according to a test scheme, opening a multifunctional drill hole with the serial number of A6, starting gas extraction, and recording the gas extraction amount through a flowmeter II;
3b) finishing extraction after 24h, unloading stress and emptying gas;
4a) repeating steps 2a) -2 c);
4b) controlling a fracturing pump to inject water into a coal sample arranged in a visual box body through a multifunctional drilling hole with the serial number of A3, wherein the water injection rate is 10 mL/s;
4c) observing the change of the coal sample in the water injection process of the fracturing pump through a high-speed camera arranged on the outer side of the visual box body, and closing the fracturing pump to stop water injection when the coal rock surface is observed to generate cracks;
4d) finishing the fracturing, closing the high-speed camera, and unloading the stress;
5a) carrying out a gas extraction process after hydraulic fracturing according to a test scheme, opening a multifunctional drill hole with the serial number of A6 to extract gas, and recording the gas extraction amount through a flowmeter II;
5b) finishing extraction after 24h, unloading stress and emptying gas;
5c) changing the positions of hydraulic fracturing drill holes and water injection rate conditions, repeating the steps 1c) -2c) and 4a) -5b), and carrying out hydraulic fracturing and post-fracturing gas extraction tests under other conditions;
6a) analyzing the growth and expansion rules of cracks on the surface of the coal body in the hydraulic fracturing process under different conditions according to the coal body pictures shot by the high-speed camera, performing sketch treatment on the final shape of the crack by using PS (polystyrene), and analyzing the relationship between different fracturing parameters such as the fracturing drilling position and the water injection rate and the quantity, area and fracture initiation pressure of the fracturing crack;
6b) respectively calculating the gas extraction rate before fracturing and the gas extraction rate after fracturing according to the gas filling amount and the gas extraction amount, wherein the gas extraction amount accounts for the filling amount; analyzing the relationship among the number, the area and the fracture initiation pressure of the fracturing cracks and the gas extraction rate;
6c) and quantitatively evaluating the yield increasing effect of the hydraulic fracturing based on the gas extraction rate before and after fracturing, and optimizing hydraulic fracturing parameters.
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| CN112253251A (en) * | 2020-11-04 | 2021-01-22 | 贵州紫森源集团投资有限公司 | Be used for colliery gas to take out and adopt effect evaluation system |
| CN113073977B (en) * | 2021-03-29 | 2021-12-24 | 中国矿业大学 | Integrated hydraulic fracturing device and method for underground coal rock stratum |
| CN113513313A (en) * | 2021-04-28 | 2021-10-19 | 中煤科工集团重庆研究院有限公司 | Experimental device and method for simulating coal seam hydraulic fracturing |
| CN113567257A (en) * | 2021-07-14 | 2021-10-29 | 太原理工大学 | High-voltage electric pulse rock breaking and fracturing device and method under true triaxial surrounding pressure |
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