CN103776703B - Based on hydrofracturing water filling charger and the test method of rocks resin test specimen - Google Patents

Abstract

The invention discloses a hydraulic fracturing water injection loading device based on a rock-like resin test piece, which includes a water injection mechanism and a loading mechanism. The equipment includes a support, and the support is respectively equipped with a fixed water storage pipe and a power mechanism that can move back and forth on the support. The piston is connected, the inner cavity of the water storage pipe is connected with the water inlet and outlet device, and one end of the water storage pipe is connected with the water pressure transmission equipment. The pads of the water pressure transmission equipment are matched with the specimen model, and the pads and the specimen model are pressed tightly by the loading mechanism. ; The digital control system is respectively connected with the power mechanism and the pressure sensor arranged in the water storage pipe to monitor the change of water pressure. The invention also discloses a test method using the device. The invention overcomes the difficult problems of presetting hollow cracks and water injection in the specimen model.

Description

Hydraulic fracturing water injection loading device and test method based on rock-like resin specimens

technical field

The invention relates to a hydraulic fracturing water injection loading device and a test method based on a rock-like resin test piece.

Background technique

The failure process of brittle materials and the evolution law of internal crack propagation have always been the focus and difficulty of solid mechanics research including rock mechanics. Because rock mass generally contains many three-dimensional cracks and most of them are hollow, they strongly affect the deformation and strength properties of rock mass. Therefore, the expansion and evolution of three-dimensional fractures or other materials has always been one of the key contents of rock mechanics research.

At present, laboratory experiments are the main research means to study the law of three-dimensional crack propagation in rocks. The production of built-in three-dimensional cracks is mainly realized by pre-embedding polyester sheets or metal sheets in the process of making test pieces. The accurate positioning (inclination angle, spatial position, etc.) of three-dimensional hollow cracks in the test piece is the key to the success of the test. The key (and the basis for analyzing the test results). Because this technology is quite difficult, no one has done or at least very rare to study experiments with three-dimensional hollow fractures and water injection in them.

In terms of hydraulic fracturing, there is not much work on the mechanism of hydraulic fracturing using laboratory methods. In China, only a small amount of rock blocks or mortar blocks are drilled from the outside for experimental research; in the United States, some scholars use plexiglass to simulate the rock mass from the outside to its center, and then inject water pressure or air pressure to produce splitting cracks. . The disadvantage of the above test methods is that the former is difficult to prefabricate the internal cracks because the test piece is opaque, and it is also difficult to track and record the development process of the internal rupture, so it is very difficult to study the rupture mechanism. Even if some scholars use the cold and hot cycle method to make cracks, but the cracks are randomly distributed, it is difficult to do repeated experiments. Moreover, the cracks are connected to the surface of the test piece, and it is difficult to pass high water pressure inside, so there are relatively large defects. As for Alpern, J (2012) who used plexiglass as a test piece when studying shale gas ventilation technology in foreign countries, although the development of internal fracture can be seen clearly, the mechanical properties of plexiglass are far from those of rock, and its representativeness is relatively small. Difference. Moreover, it is difficult to prefabricate certain cracks in plexiglass, and it is even more difficult to make hollow cracks, so they only study the case of no cracks in the middle of the test piece, that is, the method of drilling and fracturing directly from the outside, which is easier to do. of.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art, and provide a hydraulic fracturing water injection loading device and test method based on rock-like resin specimens containing three-dimensional hollow cracks.

To achieve the above object, the present invention adopts the following technical solutions:

A hydraulic fracturing water injection loading device based on a rock-like resin specimen, including a water injection mechanism and a loading mechanism,

The water injection mechanism includes an electric pressurization execution device, a digital control system and a water pressure transmission device. The electric pressurization execution device includes a support, and the support is respectively provided with a fixedly installed water storage pipe and a power unit capable of moving back and forth on the support. Mechanism, the power mechanism is connected with the airtight piston arranged in the water storage pipe and can move axially along the water storage pipe through the power transmission mechanism. The pads of the equipment are matched with the specimen model, and the pads and the specimen model are pressed tightly by the loading mechanism; the digital control system is respectively connected with the power mechanism and the pressure sensor installed in the water storage pipe to monitor the change of the hydraulic pressure.

The water storage pipe is a closed cylinder, one end of which is provided with a threaded hole for the passage of the power transmission mechanism and matched with it, and the other end is provided with an opening communicating with the water pressure transmission equipment, and the side of one end of the closed cylinder is provided with an inlet and outlet A through hole through which the water device is communicated.

The power mechanism includes a motor, the lower part of the motor is clamped on the track, and the track is fixed on the support.

The power transmission mechanism includes a bolt rod, one end of the bolt rod is connected with the power output shaft of the power mechanism, and the other end is connected with the airtight piston through a threaded hole passing through one end of the water storage pipe.

The water inlet and outlet device includes a pipeline connected with the through hole on the water storage pipe, the pipeline is provided with a first valve, and the upper end of the pipeline is provided with a water storage tank communicated with it.

The water pressure transmission device includes a water guide pipe connected to the opening on the water storage pipe, a second valve is arranged on the water guide pipe, and the other end of the water guide pipe is connected with the pad.

The pad is provided with a water outlet that communicates with the water guide and matches the water injection conduit of the specimen model, and the water outlet is recessed into the surface of the pad to form a circular groove, and a rubber gasket is added on the edge of the groove. In order to ensure the tightness of the interface when the specimen model is injected with pressurized water.

The loading mechanism is a simple true triaxial loading device, which is located in a freezing laboratory at -30°C, which can ensure that the test is carried out under low temperature conditions to ensure the cold brittleness of the resin specimen model. The simple true triaxial loading The equipment includes a high-pressure loading system and a reaction device system. The high-pressure loading system includes a jack and a loading plate. One end of the jack is connected to the loading plate, and the other end is connected to the reaction device system. The six loading plates connected to the jack are respectively attached to the test The front, rear, left, right, upper and lower six sides of the model; the oil inlet and outlet of the jack are respectively connected with the hand pump through the oil pipe, and form the oil return pipeline; the reaction force device system includes the model reaction force device, method The blue plate and the reaction force transmission plate, the model reaction force device is composed of box-type cast steel components and angle steel components connected by high-strength connecting bolts; one side of the reaction force transmission plate is close to the inner wall of the model reaction force device, and the flange plate is connected by hexagon socket bolts It is fixed on the other opposite side of the reaction force transmission plate, and the jack of the high-pressure loading system is fixed on the flange by hexagon socket bolts.

There are three pairs of jacks, which are respectively the first pair of jacks loaded on the upper and lower surfaces of the specimen model, the second pair of jacks loaded on the left and right surfaces of the specimen model, and the third pair of jacks loaded on the upper and lower surfaces of the specimen model. The pair of jacks are connected in parallel with the corresponding hand pump through the oil pipe.

The oil inlet and outlet of the first pair of jacks communicate with the first hand pump through two parallel first oil pipes and second oil pipes, and valves A and B are respectively arranged on the first oil pipe and the second oil pipe;

The oil inlet and outlet of the second pair of jacks are connected with the second hand pump through two parallel third oil pipes and fourth oil pipes, and corresponding valves are set on the third oil pipes and the fourth oil pipes and valve And the valve The fourth oil pipe between the jack and the jack is respectively connected with an accumulator and a pressure relief pipe, the oil pipe connecting the accumulator and the fourth oil pipe is provided with a valve C, and the pressure relief pipe is provided with a pressure relief valve

The oil inlet and outlet of the third pair of jacks communicate with the third hand pump through two parallel fifth oil pipes and sixth oil pipes, and valves E and F are respectively arranged on the fifth oil pipes and sixth oil pipes.

The digital control system includes a voltage division control part and a visual human-computer interaction interface, and the two parts are connected through a line. The loading instruction is input through the visual human-computer interaction interface, and the pressure division control part processes and converts the obtained loading instruction into an electrical signal and then inputs it to the pressurization execution part, dynamically monitors the pressure change of the system and feeds it back to the visual human-computer interaction interface for real-time display and recording storage.

The partial pressure control part is composed of a pressure monitoring unit, a central control unit and a pressure output unit. The pressure monitoring unit and the pressure output unit are respectively connected to the central control unit. The pressure monitoring unit converts the pressure value into an electrical signal and feeds it back to the central control unit through a line. unit, the central control unit converts these pressure values into digital signals and then displays and stores them on the visual human-computer interaction interface; The pressure value is converted into an electrical signal and then input to the pressure output unit; the pressure output unit controls the electric pressurization device to start and stop the motor through the relay to realize the control of the pressurization execution system.

The system can automatically control the synchronous loading of the model in three pairs of directions, front and rear, left and right, and up and down, but each pair of directions can be loaded independently, effectively realizing the true three-dimensional loading of the model system, and also realizing the one-dimensional, two-dimensional and 3D loading. The size of the three-dimensional model specimen model is a cuboid, and the specimen models of different sizes can be loaded by making pads and guide frames of different sizes.

A test method for a hydraulic fracturing water injection loading device based on a rock-like resin specimen model, including:

1) Prepare rock-like resin specimen model;

2) To prepare for the loading test, first put the specimen model into a water storage tank, then inject alcohol into the water storage tank until the liquid surface submerges the water injection conduit port of the specimen model; then put the water storage tank into a vacuum Vacuumize the tank; due to the continuous drop of air pressure outside the liquid surface, the air in the water injection conduit in the specimen model and the air in the elliptical thin cavity will continue to emerge from the liquid surface, and the alcohol can enter and fill the air inside the entire specimen model. Cavity, that is, the water injection conduit and the oval thin cavity, and then put the water storage tank containing the specimen model into an ultra-low temperature refrigerator, and freeze it at -20°C for 24 hours;

3) Loading test; set the cold storage to -20°C, first turn on the water injection mechanism, and perform several pressure water injection tests to exhaust the air in the entire water injection equipment, pipelines and pads to fill them with water; then take out the test piece Place the block of the water injection equipment above the specimen model, and align the water outlet of the block with the water injection conduit of the specimen model, and then put the two into the simple true triaxial loading device, and vertically A load is applied in the vertical direction to deform the rubber ring to ensure the sealing of the water injection pipe and the water outlet of the cushion block; according to the experimental requirements, enter the command on the visual human-computer interaction interface to start water injection, and start the simple true triaxial loading equipment at the same time. The specimen model is loaded, and the failure process of the cracks in the specimen model is observed.

The water in step 3) is a mixture of pure water and alcohol with a volume ratio of 1:1 to prevent the pure water from freezing at low temperatures.

The specific steps of loading the specimen model in step 3) are:

(1) Start the first hand pump, the second hand pump and the third hand pump with a small pressure of 0.1MP first, and the first hand pump uses 0.1MP pressure to pass through valve A, valve B, the first oil pipe, The second oil pipe, the first pair of jacks, and the second hand pump pass through the valve with a pressure of 0.1MP valve The third oil pipe, the fourth oil pipe and the second pair of jacks, and the third hand pump use 0.1MP pressure to pass through the valve E, valve F, fifth oil pipe, sixth oil pipe and the third pair of jacks respectively, and fix the specimen model on the set Fix the position and press it to make it immobile;

(2) Then increase the oil pressure of the second hand pump, the valve and valve Both are open, and the oil pressure applies the set pressure σ2 to the left and right surfaces of the specimen model through the second pair of jacks, and at the same time there is the same pressure in the accumulator, and the valve is closed and valve

(3) Then increase the oil pressure of the first hand pump, open valve A and valve B, apply pressure σ1 to the top and bottom of the specimen model through the oil pressure through the first pair of jacks; close valve A and valve B,

(4) Finally, increase the oil pressure of the third hand pump, open valve E and valve F, apply horizontal pressure σ3 to the front and rear surfaces of the specimen model through the third pair of jacks, and close valve E and valve F; , the pressures σ2 and σ3 are both lateral pressures, and the directions are perpendicular to each other;

(5) If the accumulator cannot keep the lateral pressure σ2 constant, use a pressure relief valve Add a little oil slowly to keep σ2 constant;

(6) Then continue to use the first hand pump, open valve A and valve B, and then continue to increase the pressure σ1; so repeatedly adjust.

The preparation method of the rock-like resin specimen model in step 1) is as follows:

The raw materials include CY-39 resin and YS-T31 curing agent, the mass ratio of the two is 100:34 or the volume ratio is 100:41; the specific steps are:

(1) Material weighing

Weigh the test raw materials according to the design requirements: resin, curing agent;

(2) Material mixing

Pour the resin and curing agent into the mixing drum according to the mixing ratio, and stir continuously with a glass rod to make it fully mixed to form a mixture. When stirring, pay attention to the materials at the bottom of the container and the side wall, so that the materials at this part are also fully mixed, and then Put it in a vacuum box for half an hour to remove air bubbles;

(3) Casting and maintenance

The mold with pre-set three-dimensional slits consists of 5 completely transparent plexiglass plates. It is a square box with an opening on one side, and is sealed with organic insulating silicone grease to form a whole; holes are drilled at different positions on the left and right sides of the square box, and prefabricated cracks are pulled, connected and fixed with thin wires. The end is fixed in the holes on both sides of the plate to achieve the effect of accurate positioning, and the three-dimensional crack (group) specimen model with different numbers, different angles and different positions is produced. Due to the good transparency of the plexiglass mold, the curing process of the entire specimen model can be directly observed, and the change of the position of the cracked piece in the container can be observed and controlled. Define the angle between the crack surface and the horizontal plane as the inclination angle of the three-dimensional crack, and the developed mold can preset the specimen model containing three-dimensional cracks (groups) with a tilt angle of 60°, 45°, 30°, etc.; it can also be preset Three-dimensional fracture group specimen models with different numbers, such as double-fissure, three-fissure, four-fissure, etc.; three-dimensional fracture group specimen models with various combinations of longitudinal, interstaggered, and top-to-top types can also be prefabricated.

The prefabricated crack connecting the water injection pipe is as follows: two identical oval prefabricated cracks are bonded together by handmade O-shaped plasticine sealing rings, and the upper and lower two pieces are stacked together to form a hollow oval thin cavity , and pre-drill a hole in the center of the prefabricated crack on one side and lead out the water injection conduit, and then paste the oval thin cavity to the corresponding position of the cotton thread. Each joint must be strictly sealed with glue during the above process.

Place the mold with pre-set three-dimensional cracks on the worktable, guide the mixture prepared and processed in step (2) into the mold with a glass rod and cast it into the mold; after casting, put the mold into a vacuum box for degassing treatment for 20~ 25 minutes, then put it into a constant temperature blast drying oven at 18°C for 36 to 40 hours; when it has a mechanical strength greater than 50MPa, remove the mold; put the sample model after demoulding into a constant temperature blast drying oven at 70°C After curing for 48-50 hours, the production can be completed.

The prefabricated cracks use mica sheets with a thickness of 0.12mm. Compared with other materials (such as metal sheets (copper sheets, aluminum sheets, etc.), polyethylene sheets, etc.), mica sheets have low rigidity, will not restrain the deformation of the specimen model, facilitate the positioning of cracks, and are closer to the rock mass cracks. In order to ensure the accuracy of the crack size, oval steel molds of three sizes were made, which can cut the mica sheet into a precise oval shape, avoiding the dimensional error caused by manual cutting in previous experiments.

The elliptical steel mold includes an upper plate, a base and several guide columns. The lower end of the guide column is fixed on the base, and the upper plate is sleeved on the guide column that can move up and down along it; An open cavity, the upper surface of the base is provided with an oval hole communicating with the cavity.

The beneficial effects of the present invention are that the resin test piece model with good brittleness and transparency adopted by the present invention can visually observe the expansion state of the crack in the hydraulic fracturing test; The difficulty of prefabricating cracks; overcoming the technical difficulties of presetting hollow cracks and water injection in the specimen model, new tests can be carried out by injecting pressurized water from the outside, which greatly advances the previous work.

Description of drawings

Fig. 1 is the load-strain curve diagram of the specimen model whose size is 50mm*50mm*100mm;

Fig. 2 is the specimen model used for the hydraulic fracturing test;

Fig. 3 is the structural representation of water injection equipment;

Fig. 4 is a structural schematic diagram of a true three-axis loading device;

Fig. 5 is a schematic diagram of the operation flow of the true three-axis loading device;

Among them, 1. Motor, 2. Bolt rod, 3. Sealed piston, 4. Water storage pipe, 5. Pipeline, 6. First valve, 7. Water storage tank, 8. Pressure sensor, 9. Second valve, 10. Aqueduct, 11. O-ring, 12. Block, 13. Specimen model, 14. Water injection conduit, 15. The first pair of jacks, 16. The second pair of jacks, 17. The third pair of jacks, 18. The first Oil pipe, 19. second oil pipe, 20. first hand pump, 21. third oil pipe; 22. fourth oil pipe; 23. second hand pump, 24. accumulator, 25. pressure relief pipe.

detailed description

Below in conjunction with the test of accompanying drawing and single fissure water injection specimen model, the present invention is further described.

A hydraulic fracturing water injection loading device based on a rock-like resin test piece, including a water injection mechanism and a loading mechanism, the water injection mechanism includes an electric pressurization execution device, a digital control system and a hydraulic pressure transmission device, and the electric pressurization execution device includes The support is respectively provided with a fixedly installed water storage pipe 4 and a power mechanism that can move back and forth on the support. The power mechanism is arranged in the water storage pipe 4 and can move axially along the water storage pipe 4 through the power transmission mechanism The airtight piston 3 is connected, the inner cavity of the water storage pipe 4 is connected with the water inlet and outlet device, and one end of the water storage pipe 4 is connected with the water pressure transmission equipment, and the cushion block 12 of the water pressure transmission equipment is matched with the specimen model 13, and the cushion block is moved by the loading mechanism. 12 is compressed with the specimen model 13; the digital control system is respectively connected with the power mechanism and the pressure sensor 8 arranged in the water storage pipe 4 to monitor the change of hydraulic pressure.

The water storage pipe 4 is a closed cylinder, one end of which is provided with a threaded hole for the passage of the power transmission mechanism and matched with it, and the other end is provided with an opening communicating with the hydraulic transmission equipment, and the side of one end of the closed cylinder is provided with a water inlet and outlet. Through holes for device communication.

The power mechanism includes a motor 1, the lower part of the motor 1 is clamped on a track, the track is fixed on a support, and the motor 1, the track and the support are jointly arranged in a housing. The power transmission mechanism includes a bolt rod 2 , one end of the bolt rod 2 is connected with the power output shaft of the power mechanism, and the other end is connected with the airtight piston 3 through a threaded hole passing through one end of the water storage pipe 4 .

The water inlet and outlet device includes a pipeline 5 communicating with the through hole on the water storage pipe 4 , the pipeline 5 is provided with a first valve 6 , and the upper end of the pipeline 5 is provided with a water storage tank 7 communicating with it.

The water pressure transmission equipment includes a water guide pipe 10 communicating with the opening on the water storage pipe 4 , the water guide pipe 10 is provided with a second valve 9 , and the other end of the water guide pipe 10 is connected with a pad 12 .

The pad 12 is provided with a water outlet that communicates with the water guide pipe 10 and matches the water injection conduit 14 of the specimen model 13, and the water outlet is recessed into the surface of the pad to form a circular groove and an O-shaped groove is added on the edge of the groove Ring 11 (rubber washer) is used to ensure the tightness of the interface when the specimen model is injected with pressurized water.

The loading mechanism is simple true triaxial loading equipment, which is located in a freezing laboratory at -30°C, which can ensure that the test is carried out under low temperature conditions to ensure the cold brittleness of the resin specimen model. The simple true triaxial loading equipment includes High-pressure loading system and reaction device system. The high-pressure loading system includes a jack and a loading plate. One end of the jack is connected to the loading plate, and the other end is connected to the reaction device system. The six loading plates connected to the jack are respectively attached to the specimen model. The front, rear, left, right, upper and lower six sides of the jack; the oil inlet and outlet of the jack are respectively connected with the hand pump through the oil pipe, and form an oil return pipeline; the reaction force device system includes a model reaction force device, a flange And the reaction force transmission plate, the model reaction force device is composed of box-type cast steel components and angle steel components connected by high-strength connecting bolts; one side of the reaction force transmission plate is close to the inner wall of the model reaction force device, and the flange is fixed on the On the other opposite side of the reaction force transmission plate, the jack of the high-pressure loading system is fixed on the flange plate by hexagon socket bolts.

As shown in Figure 4, there are three pairs of jacks, which are the first pair of jacks 15 loaded on the upper and lower surfaces of the specimen model, the second pair of jacks 16 loaded on the left and right surfaces of the specimen model, and the first pair of jacks 16 loaded on the upper and lower surfaces of the specimen model. Three pairs of jacks 17, each pair of jacks are connected in parallel with corresponding hand pumps through oil pipes.

As shown in Figure 5, the oil inlet and outlet ports of the first pair of jacks 15 communicate with the first hand pump 20 through two parallel first oil pipes 18 and second oil pipes 19, and the first oil pipe 18 and the second pipe The oil pipe 19 is respectively provided with a valve A and a valve B correspondingly;

The oil inlet and outlet ports of the second pair of jacks 16 communicate with the second hand pump 23 through two parallel third oil pipes 21 and fourth oil pipes 22, and the third oil pipes 21 and the fourth oil pipes 22 are respectively provided with corresponding valves and valve And the valve The fourth oil pipe 22 between the jack and the jack is respectively connected with an accumulator 24 and a pressure relief pipe 25. The oil pipe connecting the accumulator 24 and the fourth oil pipe 22 is provided with a valve C, and the pressure relief pipe 25 is provided with a pressure relief pipe. valve

The oil inlet and outlet ports of the third pair of jacks communicate with the third hand pump through two parallel fifth oil pipes and sixth oil pipes, and valves E and F are respectively set on the fifth oil pipes and sixth oil pipes ( not shown in the figure).

The digital control system includes a voltage division control part and a visual human-computer interaction interface, and the two parts are connected through a line. The loading instruction is input through the visual human-computer interaction interface, and the pressure division control part processes and converts the obtained loading instruction into an electrical signal and then inputs it to the pressurization execution part, dynamically monitors the pressure change of the system and feeds it back to the visual human-computer interaction interface for real-time display and recording storage.

The partial pressure control part is composed of a pressure monitoring unit, a central control unit and a pressure output unit. The pressure monitoring unit and the pressure output unit are respectively connected to the central control unit. The pressure monitoring unit converts the pressure value into an electrical signal and feeds it back to the central control unit through a line. unit, the central control unit converts these pressure values into digital signals and then displays and stores them on the visual human-computer interaction interface; The pressure value is converted into an electrical signal and then input to the pressure output unit; the pressure output unit controls the electric pressurization device to start and stop the motor through the relay to realize the control of the pressurization execution system.

The system can automatically control the synchronous loading of the model in three pairs of directions, front and rear, left and right, and up and down, but each pair of directions can be loaded independently, effectively realizing the true three-dimensional loading of the model system, and also realizing the one-dimensional, two-dimensional and 3D loading. The size of the three-dimensional model specimen model is a cuboid, and the specimen models of different sizes can be loaded by making pads and guide frames of different sizes.

A test method for a hydraulic fracturing water injection loading device based on a rock-like resin specimen model, including:

1) Prepare rock-like resin specimen model;

2) To prepare for the loading test, first put the test piece into a water storage tank, then inject alcohol into the water storage tank until the liquid surface submerges the water injection conduit port of the test piece model; then put the water storage tank into the vacuum box vacuum treatment in the middle; due to the continuous drop of air pressure outside the liquid surface, the air in the water injection conduit and the elliptical thin cavity in the specimen model will continue to emerge from the liquid surface, and the alcohol can enter and fill the cavity inside the entire specimen model , that is, into the water injection conduit and the oval thin cavity, and then put the water storage tank containing the specimen model into an ultra-low temperature refrigerator, and freeze it at -20°C for 24 hours;

3) Loading test; set the cold storage to -20°C, first turn on the water injection mechanism, and perform several pressure water injection tests to exhaust the air in the entire water injection equipment, pipelines and pads to fill them with water; then take out the test piece Place the block of the water injection equipment above the specimen model, and align the water outlet of the block with the water injection conduit of the specimen model, and then put the two into the simple true triaxial loading device, and vertically A load is applied in the vertical direction to deform the rubber ring to ensure the sealing of the water injection pipe and the water outlet of the cushion block; according to the experimental requirements, enter the command on the visual human-computer interaction interface to start water injection, and start the simple true triaxial loading equipment at the same time. The specimen model is loaded, and the failure process of the cracks in the specimen model is observed.

The water in step 3) is a mixture of pure water and alcohol with a volume ratio of 1:1 to prevent the pure water from freezing at low temperatures.

The specific steps of loading the specimen model in step 3) are:

(1) Start the first hand pump 20, the second hand pump 25 and the third hand pump with a small pressure of 0.1 MP first, and the first hand pump 20 passes through valve A, valve B, and the The first oil pipe 18, the second oil pipe 19, the first pair of jacks 15, and the second hand pump 25 respectively pass through the valve with 0.1MP pressure valve The third oil pipe 21, the fourth oil pipe 22 and the second pair of jacks 16, the third hand pump with 0.1MP pressure respectively through the valve E, the valve F, the fifth oil pipe, the sixth oil pipe and the third pair of jacks, the specimen model Fix it at the set position and press it tightly so that it does not move;

(2) Increase the oil pressure of the second hand pump 25, the valve and valve Both are open, and the oil pressure applies the set pressure σ2 to the left and right surfaces of the specimen model through the second pair of jacks 16. At the same time, there is the same pressure in the accumulator 23, and the valve is closed. and valve

(3) Then increase the oil pressure of the first hand pump 20, open valve A and valve B, and apply pressure σ1 to the top and bottom of the specimen model through the first pair of jacks 15; close valve A and valve B;

(4) Finally, increase the oil pressure of the third hand pump, open valve E and valve F, apply horizontal pressure σ3 to the front and rear surfaces of the specimen model through the third pair of jacks, and close valve E and valve F; , the pressures σ2 and σ3 are both lateral pressures, and the directions are perpendicular to each other; at this time, the lateral pressure σ2 will not change significantly under the adjustment of the accumulator 23;

(5) If the accumulator 23 cannot keep the lateral pressure σ2 unchanged, use the pressure relief valve Add a little oil slowly to keep σ2 constant;

(6) Then continue to activate the first hand pump 20, open valve A and valve B, and then continue to increase the pressure σ1; so repeatedly adjust.

The preparation method of the rock-like resin specimen model in step 1) is as follows:

The raw materials include CY-39 resin and YS-T31 curing agent, the mass ratio of the two is 100:34 or the volume ratio is 100:41; the specific steps are:

(1) Material weighing

Measure 500ml of CY-39 resin material and 200ml of YS-T31 curing agent.

(2) Material mixing

Pour the resin and curing agent into the mixing drum according to the mixing ratio, and stir continuously with a glass rod to make it fully mixed to form a mixture. When stirring, pay attention to the materials at the bottom of the container and the side wall, so that the materials at this part are also fully mixed, and then Put it in a vacuum box for half an hour to remove air bubbles;

(3) Casting molding and maintenance

Make two plexiglass plates of 50mm*50mm and three pieces of 50mm*100mm, and seal them with organic insulating silicone grease to form a whole, that is, a cuboid with open sides. On the two opposite boards with a size of 50mm*100mm, use a small drill to drill two small holes, and calculate and determine the position of the small holes before drilling. Then use a soft cotton thread to pass through each small hole in turn, and tighten and fix the cotton thread; two identical oval-shaped prefabricated slits are glued together by hand-made O-shaped plasticine sealing rings, The upper and lower pieces are stacked together to form a hollow oval thin cavity, and a hole is drilled in the center of the prefabricated crack on one side to lead out the water injection conduit, and then the oval thin cavity is pasted to the corresponding position of the cotton thread. Each joint must be strictly sealed with glue during the above process.

Place the mold with pre-set three-dimensional cracks on the workbench, apply a release agent on the inner surface of the mold, guide the mixture prepared and processed in step (2) into the mold with a glass rod, and cast it into the mold; after casting, put the mold into a vacuum Do air-removing treatment in the box for 20-25 minutes, and then put it in a 18°C constant temperature blast drying oven for curing for 36-40 hours; when the mechanical strength is greater than 50MPa, remove the mold; put the sample model after demoulding into the constant temperature The production can be completed after 48-50 hours of curing in a constant temperature blast drying oven at 70°C.

The prefabricated cracks use mica sheets with a thickness of 0.12mm. Compared with other materials (such as metal sheets (copper sheets, aluminum sheets, etc.), polyethylene sheets, etc.), mica sheets have low rigidity, will not restrain the deformation of the specimen model, facilitate the positioning of cracks, and are closer to the rock mass cracks. In order to ensure the accuracy of the crack size, oval steel molds of three sizes were made, which can cut the mica sheet into a precise oval shape, avoiding the dimensional error caused by manual cutting in previous experiments.

The elliptical steel mold includes an upper plate, a base and several guide columns. The lower end of the guide column is fixed on the base, and the upper plate is sleeved on the guide column that can move up and down along it; An open cavity, the upper surface of the base is provided with an oval hole communicating with the cavity.

(3) Preparation for loading test

The specimen model must first be put into a water storage tank with a capacity of 1L, and then alcohol (low freezing point, no water) should be injected into the water storage tank until the liquid level submerges the water injection conduit port of the specimen model; The cans are placed in a vacuum box for vacuuming. Due to the continuous drop of air pressure outside the liquid surface, the air in the water injection conduit and the elliptical thin cavity will continue to emerge from the liquid surface, and the alcohol can enter and fill the cavity inside the entire specimen model, that is, the water injection conduit and the elliptical thin cavity. Then put the water storage tank containing the specimen model into an ultra-low temperature refrigerator, and freeze it at -20°C for 24 hours (do not use water, just to prevent freezing during this process).

(4) Loading test

Set the freezer to -20°C. Open the water injection mechanism first, and perform several pressure injection tests to exhaust the air in the entire water injection equipment, pipelines and pads to make them full of water. Then take out the specimen model, place the special cushion block of the water injection equipment on the specimen model, and align the water outlet of the cushion block with the water injection conduit port of the specimen model, and then put the two into the triaxial loading equipment, And apply a certain load in the vertical direction to deform the rubber ring to ensure the sealing of the water injection pipe and the water outlet of the cushion block; according to the experimental requirements, enter the command on the visual human-computer interaction interface to start water injection, and start the three-axis loading at the same time equipment, load the specimen model according to the aforementioned test steps and methods, and observe the failure process of the cracks in the specimen model. (Note: The "water" referred to here is a mixture of water and alcohol in a certain ratio to prevent freezing at low temperatures.)

The rock-like material thus formulated has good brittleness and high transparency at lower temperatures, and exhibits brittle fracture characteristics when pressurized. The tension-compression strength ratio can reach 1/6.6 at -15°C, which is higher than the brittleness of the predecessors at -50°C. The corresponding mechanical parameters at -15°C are as follows:

This kind of rock resin material is extremely transparent, and it is possible to clearly observe the internal rupture process of the test piece model after pressurization and the initiation, expansion and evolution process of cracks. Therefore, it is suitable for the study of the law of rock fracture expansion. It solves the problem that it is difficult to prefabricate hollow cracks in the specimen model in the hydraulic fracturing test; new tests can be carried out by injecting pressurized water from the outside, which greatly advances the previous work. In particular, the tension-compression strength ratio (brittleness index) of the new material is more than double that of the corresponding index of the materials used by predecessors at home and abroad. It should be considered closer to the brittleness of real rocks.

Although the specific implementation of the present invention has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art do not need to pay creative work Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (9)

1. A test method based on a hydraulic fracturing water injection loading device for a rock-like resin test piece, the hydraulic fracturing water injection loading device based on a rock-like resin test piece includes a water injection mechanism and a loading mechanism, and the water injection mechanism Including electric pressurized executive equipment, digital control system and water pressure transmission equipment, electric pressurized executive equipment includes a support, and the support is respectively equipped with a fixedly installed water storage pipe and a power mechanism that can move back and forth on the support, and the power mechanism The power transmission mechanism is connected with the airtight piston arranged in the water storage pipe and can move axially along the water storage pipe, the inner cavity of the water storage pipe is connected with the water inlet and outlet device, one end of the water storage pipe is connected with the water pressure transmission equipment, and the cushion block of the water pressure transmission equipment Cooperate with the test piece model, and press the block and the test piece model through the loading mechanism; the digital control system is respectively connected with the power mechanism and the pressure sensor installed in the water storage pipe to monitor the change of the water pressure pressure. Its characteristics include: 1) Prepare a rock-like resin specimen model; 2) To prepare for the loading test, first put the test piece model into a water storage tank, then inject alcohol into the water storage tank until the liquid level submerges the water injection conduit port of the test piece model; then put the water storage tank into a vacuum Vacuumize the tank; due to the continuous drop of air pressure outside the liquid surface, the air in the water injection conduit in the specimen model and the air in the elliptical thin cavity will continue to emerge from the liquid surface, and the alcohol can enter and fill the air inside the entire specimen model. Cavity, that is, the water injection conduit and the oval thin cavity, and then put the water storage tank containing the specimen model into an ultra-low temperature refrigerator, and freeze it at -20°C for 24 hours; 3) Loading test; set the cold storage to -20°C, first turn on the water injection mechanism, and perform several pressure water injection tests to exhaust the air in the entire water injection equipment, pipelines and pads, and make them full of water; then take out the test piece Place the block of the water injection equipment above the specimen model, and align the water outlet of the block with the water injection conduit of the specimen model, and then put the two into the simple true triaxial loading device, and vertically A load is applied in the vertical direction to deform the rubber gasket to ensure the sealing of the water injection conduit and the water outlet of the cushion block; according to the experimental requirements, enter the command on the visual human-computer interaction interface to start water injection, and start the simple true triaxial loading equipment at the same time. The specimen model is loaded, and the destruction process of the cracks in the specimen model is observed; the water is a mixture of pure water and alcohol, and the volume ratio is 1:1, so as to prevent the pure water from freezing at low temperature. 2. the test method of the hydraulic fracturing water injection loading device based on the rock-like resin test piece as claimed in claim 1, it is characterized in that, the water storage pipe is an airtight cylinder, and one end has a power transmission mechanism to pass through and The other end of the matched threaded hole is provided with an opening communicating with the water pressure transmission equipment, and the side of one end of the airtight cylinder is provided with a through hole communicating with the water inlet and outlet device. 3. the test method of the hydraulic fracturing water injection loading device based on the rock-like resin test piece as claimed in claim 2, it is characterized in that, the power mechanism comprises a motor, and the lower part of the motor is clamped on the track, and the track is fixed on the support seat; The power transmission mechanism includes a bolt rod, one end of the bolt rod is connected with the power output shaft of the power mechanism, and the other end is connected with the airtight piston through the threaded hole passing through one end of the water storage pipe; The water inlet and outlet device includes a pipeline connected with the through hole on the water storage pipe, the pipeline is provided with a first valve, and the upper end of the pipeline is provided with a water storage tank communicated with it. 4. the test method of the hydraulic fracturing water injection loading device based on the rock-like resin test piece as claimed in claim 2, it is characterized in that, the hydraulic pressure conduction equipment comprises a water conduit communicated with the opening on the water storage pipe, and the conduit The water pipe is provided with a second valve, and the other end of the water pipe is connected with the pad. 5. the test method of the hydraulic fracturing water injection loading device based on the rock-like resin test piece as claimed in claim 4, it is characterized in that, the described pad is provided with the water injection that communicates with the aqueduct and is connected with the test piece model The pipe matches the water outlet, and the water outlet is recessed into the surface of the pad to form a circular groove and a rubber gasket is added on the edge of the groove. 6. the test method of the hydraulic fracturing water injection loading device based on the rock-like resin test piece as claimed in claim 1, is characterized in that, the loading mechanism comprises a high-pressure loading system and a counterforce device system, and the high-pressure loading system comprises a jack One end of the jack is connected to the loading plate, and the other end is connected to the reaction device system. The six loading plates connected to the jack are respectively attached to the front, rear, left, right, upper and lower six of the specimen model. On the side; the oil inlet and outlet of the jack are respectively connected with the hand pump through oil pipes, and form an oil return pipeline; the reaction force device system includes a model reaction force device, a flange plate and a reaction force transmission plate, and the model reaction force device is made of a box-type casting Steel members and angle steel members are connected by high-strength connecting bolts; one side of the reaction force transmission plate is close to the inner wall of the model reaction force device, and the flange plate is fixed on the other opposite side of the reaction force transmission plate by hexagon socket bolts. The high-pressure loading system The jack is fixed on the flange by hexagon socket bolts. 7. the test method of the hydraulic fracturing water injection loading device based on the rock-like resin test piece as claimed in claim 6, is characterized in that, there are three pairs of said jacks, which are respectively the first ones loaded on the upper and lower surfaces of the test piece model. For the jacks, the second pair of jacks loaded on the left and right surfaces of the specimen model and the third pair of jacks loaded on the upper and lower surfaces of the specimen model, each pair of jacks is connected in parallel with the corresponding hand pump through the oil pipe; The oil inlet and outlet of the first pair of jacks communicate with the first hand pump through two parallel first oil pipes and second oil pipes, and valves A and B are respectively arranged on the first oil pipe and the second oil pipe; The oil inlet and outlet of the second pair of jacks are connected with the second hand pump through two parallel third oil pipes and fourth oil pipes, and corresponding valves are set on the third oil pipes and the fourth oil pipes and valve And the valve The fourth oil pipe between the jack and the jack is respectively connected with an accumulator and a pressure relief pipe, the oil pipe connecting the accumulator and the fourth oil pipe is provided with a valve C, and the pressure relief pipe is provided with a pressure relief valve The oil inlet and outlet of the third pair of jacks communicate with the third hand pump through two parallel fifth oil pipes and sixth oil pipes, and valves E and F are respectively arranged on the fifth oil pipes and sixth oil pipes. 8. The test method of the hydraulic fracturing water injection loading device based on the rock-like resin test piece as claimed in claim 1, wherein the digital control system includes a partial pressure control part and a visual man-machine interface, two partly connected by wire; The partial pressure control part is composed of a pressure monitoring unit, a central control unit and a pressure output unit. The pressure monitoring unit and the pressure output unit are respectively connected to the central control unit. The pressure monitoring unit converts the pressure value into an electrical signal and feeds it back to the central control unit through a line. unit, the central control unit converts these pressure values into digital signals and displays and stores them on the part of the visual human-computer interaction interface; the central control unit will issue various instructions loaded by the system, and the central control unit will input them on the visual human-computer interaction interface The pressure value is converted into an electrical signal and then input to the pressure output unit; the pressure output unit controls the electric pressurization device to start and stop the motor through the relay to realize the control of the pressurization execution system. 9. method as claimed in claim 1, is characterized in that, described 3) in concrete steps to specimen model loading are: (1) Start the first hand pump, the second hand pump and the third hand pump with a small pressure of 0.1MP first, and the first hand pump uses 0.1MP pressure to pass through valve A, valve B, the first oil pipe, The second oil pipe, the first pair of jacks, and the second hand pump pass through the valve with a pressure of 0.1MP valve The third oil pipe, the fourth oil pipe and the second pair of jacks, and the third hand pump use 0.1MP pressure to pass through the valve E, valve F, fifth oil pipe, sixth oil pipe and the third pair of jacks respectively, and fix the specimen model on the set Fix the position and press it to make it immobile; (2) Then increase the oil pressure of the second hand pump, the valve and valve Both are open, and the oil pressure applies the set pressure σ2 to the left and right surfaces of the specimen model through the second pair of jacks, and at the same time there is the same pressure in the accumulator, and the valve is closed and valve (3) Then increase the oil pressure of the first hand pump, valve A and valve B are both opened, and the oil pressure applies pressure σ1 to the top and bottom of the specimen model through the first pair of jacks; close valve A and valve B; (4) Finally increase the oil pressure of the third hand pump, valve E and valve F are both opened, the oil pressure applies horizontal pressure σ3 to the front and rear surfaces of the specimen model through the third pair of jacks, and valve E and valve F are closed; , the pressures σ2 and σ3 are both lateral pressures, and the directions are perpendicular to each other; (5) If the accumulator cannot keep the lateral pressure σ2 unchanged, use the pressure relief valve Add a little oil slowly to keep σ2 constant; (6) Then continue to use the first hand pump, open valve A and valve B, and then continue to increase the pressure σ1; so repeatedly adjust.