CN112065350B - Hydraulic fracturing fracture propagation mechanism and fracturing after-effect test system and method - Google Patents

Abstract

Hydraulic fracturing fracture propagation mechanism and fracturing after-effect test system and method, bottom plate including pumping pressure system and level setting, be equipped with four stands of arranging in four summit positions of a square perpendicularly on the bottom plate, stand upper end level is equipped with the roof, be equipped with the installation frame on the bottom plate between four stands, the installation frame bottom is equipped with the gyro wheel, be equipped with the board-like test piece subassembly of level setting in the installation frame, installation frame front side and left side are equipped with first horizontal pressure device and second horizontal pressure device respectively, be equipped with vertical pressure device and high-speed camera device on the roof, board-like test piece subassembly middle part upside is equipped with the inlet, the inlet passes through high-pressure pipe and pumping pressure headtotail. The invention adopts the plate-shaped test piece with small thickness and large expansion surface, can visually observe the fracture propagation mechanism and the post-fracturing effect in real time, and establishes the fracture network fractal characteristics, the long-acting flow guide mechanism, the fracture propagation mechanism, the volume openness and the additional ground stress relationship.

Description

Hydraulic fracturing fracture propagation mechanism and fracturing after-effect test system and method

technical field

The invention belongs to the technical field of unconventional oil and gas (such as shale gas, tight sandstone gas and coalbed methane) development, and particularly relates to a hydraulic fracturing fracture propagation mechanism and fracturing after-effect test system and method.

Background technique

Hydraulic fracturing is the main technology for the development of unconventional natural gas (such as shale gas, tight sandstone gas and coalbed methane). By injecting pressure fluid into the underground reservoir, the reservoir expands, cracks and increases the permeability, so as to make the natural gas inside the reservoir. Desorption, diffusion and seepage converge and flow to the surface through the wellbore steel pipe.

、韧性系数

和滤失系数

：The fracture propagation mechanism is the basic physical mechanism of hydraulic fracturing. It is a comprehensive reflection of the interaction of various factors such as the physical and mechanical properties of the reservoir rock, in-situ stress, fluid flow and viscosity, and injection time. It determines the fracture length, opening degree, and fluid pressure distribution. its time evolution. The fracture propagation mechanism involves the influence of many factors, but can be determined by three dimensionless parameters: the in-situ stress coefficient

, toughness coefficient

and filter loss coefficient

:

（1）

(1)

、流量

、流体注入时间t,以及平面应变粘性

、滤失性

、储层弹性

和断裂韧性

。这些平面应变参数通过以下换算得到,identified from a number of factors. These factors include ground stress

,flow

, the fluid injection time t , and the plane strain viscosity

, filtration

, reservoir elasticity

and fracture toughness

. These plane strain parameters are obtained by the following conversions,

（2）

(2)

是断裂韧性，

是流体粘度，

是滤失系数,

是实际的注入体积流量，h是岩层厚度。where E and v are Young's modulus and Poisson's ratio, respectively,

is the fracture toughness,

is the fluid viscosity,

is the filter loss coefficient,

is the actual injected volume flow, and h is the formation thickness.

）表示的参数平面中，划分为四种极限情形(

)和一般情形，其中不同的断裂传播机制代表不同的缝内流动条件和裂缝演化规律。These fracture propagation mechanisms are in (

) in the parameter plane represented by four limit cases (

) and the general case, where different fracture propagation mechanisms represent different intrafracture flow conditions and fracture evolution laws.

The mechanism, the viscous-storage mechanism, represents flow conditions where rock strength is relatively weak, fluid viscosity is relatively high, and fluid loss is minimal. Under this condition, the energy consumption of hydraulic fracturing is mainly used to overcome the viscous resistance of the fluid, and at the same time, due to the small fluid loss, the fracture opening can be stabilized in a short period of time. Therefore, as long as the filtration conditions of no permeability or very low permeability in the vertical direction of crack propagation are met, such as hydraulic fracturing crack expansion in soft and brittle rock, preexisting cracks in rock, artificial grouting or magma flow in rock cracks, belong to this mechanism.

The mechanism, the viscous-fluid loss mechanism, represents the fracture propagation conditions where the rock strength is weak, the fluid viscosity is relatively high, but the fluid loss is large. Due to the high fluid loss, fracture opening takes a long time to stabilize.

The mechanism, the ductility-storage mechanism, represents fracture propagation conditions where rock is highly ductile, fluid viscosity is relatively low, and fluid loss is minimal. Under this condition, the energy consumption of hydraulic fracturing is mainly used to overcome the rock fracture resistance, and at the same time, due to the small filtration loss, the fracture opening can be stabilized in a relatively short period of time. Fracture propagation in tight intact granites or low-viscosity fluids in well-integrated reservoirs belongs to this mechanism.

The mechanism, namely the toughness-fluid loss mechanism, represents the fracture propagation condition that the rock has high toughness, relatively low fluid viscosity, and large fluid loss, resulting in the fracture opening taking a long time to stabilize.

Fracturing after-effect refers to the fracture network shape and long-term conductivity mechanism generated by hydraulic fracturing, which plays a decisive role in the later gas production efficiency and stable production period. Fracture network description should use fractal concept, including fracture network fractal type, fractal dimension and fractal expansion level. Persistence after fracturing refers to the long-term conduction mechanism of natural gas due to the opening of residual pore-fractures after the fracturing fluid flows back. It is equivalent to the reservoir's response to the "temper" of the hydromechanical action mechanism. Only by finding out the "temper" of the reservoir can it be possible to scientifically and rationally evaluate the reservoir's permeability enhancement effect and long-term conductivity mechanism. This patent does not consider the role of proppant for the time being, but reveals its long-term conductivity mechanism from the elasto-plastic-viscous evolution properties of the volume opening of the reservoir fracture network.

The current problems in hydraulic fracturing tests in the industry are: first, the experimental design lacks advanced theoretical guidance, mainly for simple strength verification, and there is no concept of fracture propagation mechanism and fracturing after-effect; second, fracture propagation cannot be displayed in real time; third, The thickness of the specimen is not conducive to the description of the effect.

In view of this situation, the present invention aims to develop a thin, visual, real-time, and intuitively displayed test system, to conduct experimental observations on the fracture propagation mechanism and fracturing effect of the interaction between hydrodynamics and underground reservoirs, and to establish a unified evaluation of the anti-permeability effect. The method provides an experimental basis for theoretical research and engineering design.

SUMMARY OF THE INVENTION

In order to solve the deficiencies in the prior art, the present invention provides a hydraulic fracturing fracture propagation mechanism and a fracturing after-effect test system and method. The plate-shaped specimen with small thickness and large plane can be used to better demonstrate hydraulic pressure. The crack propagation mechanism of the crack is convenient for real-time observation and statistical observation of the crack network.

In order to solve the above-mentioned technical problems, the present invention adopts the following technical solutions: a hydraulic fracturing fracture propagation mechanism and a fracturing after-effect test system, including a pump pressure system and a horizontally arranged bottom plate, and four vertical vertices are arranged on the bottom plate at four vertices of a square. The vertical columns are arranged in positions. The upper end of the vertical column is provided with a top plate horizontally, and the bottom plate is provided with a mounting frame between the four vertical columns. The bottom of the mounting frame is provided with rollers. The left side is provided with a first horizontal pressurizing device and a second horizontal pressurizing device, the top plate is provided with a vertical pressurizing device and a high-speed camera device, and a liquid inlet is provided on the upper side of the middle of the plate specimen assembly, and the liquid inlet passes through the high pressure The tubing is connected to the pumping system.

The installation frame has a back-shaped structure, the first horizontal pressure device, the second horizontal pressure device and the vertical pressure device are all hydraulic jacks, and the first horizontal pressure device and the second horizontal pressure device are all arranged inside the installation frame, The front side of the installation frame is provided with a first U-shaped buckle for fixing the first horizontal pressure device, and the two ends of the first U-shaped buckle are respectively connected with the upper and lower sides of the bottom of the first horizontal pressure device. The left side of the frame is provided with a second U-shaped clip for fixing the second horizontal pressing device, and two ends of the second U-shaped clip are respectively connected with the bottom upper side and the lower side of the second horizontal pressing device.

The plate specimen assembly includes a flat specimen, a supporting backing plate, a transparent plexiglass, an upper transparent silicone pad, a lower silicone pad and a fracturing tube. The top view of the flat specimen is a square, and the center of the flat specimen is provided with an upper and lower transparent The fracturing hole, the supporting pad, the lower silicone pad, the flat specimen, the upper transparent silicone pad and the transparent plexiglass are laid sequentially from bottom to top on the upper surface of the bottom plate. There is a lower accommodating hole for accommodating the plugging head, the thickness of the support pad is less than or equal to the height of the roller, and the fracturing tube passes through the lower silicone pad, fracturing hole, upper transparent silicone pad and transparent plexiglass sequentially from top to top The fracturing pipe is provided with a number of liquid permeable holes on the outer circumference of the fracturing pipe. The upper part of the fracturing pipe is threadedly connected with a compression nut. The center of the transparent plexiglass is provided with an upper accommodating hole. The fracturing pipe is sleeved with a The upper copper pad located between the lower end face of the compression nut and the upper surface of the upper transparent silicone pad and the lower copper pad located between the upper end face of the plugging head and the upper surface of the lower silicone pad, the lower end of the compression nut passes through the upper copper pad, the upper transparent silicone pad and the flat plate The test piece is crimped, and the liquid inlet is the upper port of the fracturing tube.

The front side of the flat specimen is press-fitted with the right end of the first horizontal pressing device, the rear side of the flat specimen is press-fitted with the rear side of the inner wall of the mounting frame, and the left side of the flat specimen is press-fitted with the right end of the second horizontal pressing device. , the right side of the flat specimen is crimped with the right side of the inner wall of the mounting frame.

The central part of the top plate is provided with an installation hole, a high-speed camera device is arranged in the installation hole and takes pictures of the surface of the transparent plexiglass, several vertical pressure devices are arranged, and the several vertical pressure devices are evenly arranged along the circumferential direction of the installation hole, The lower end of the vertical pressing device is crimped with the surface of the transparent plexiglass.

The right side of the bottom plate is provided with a slope for passing the rollers, and the left and rear sides of the upper surface of the bottom plate are respectively provided with a left positioning baffle and a rear positioning baffle. When the plate and the rear positioning baffle are in contact, the mounting holes correspond up and down with the perforations.

The test method of hydraulic fracturing fracture propagation mechanism and fracturing after-effect test system includes the following steps:

(1) Assemble the plate specimen assembly, connect the pumping system to the upper port of the fracturing pipe through the high-pressure pipe, and pump a small amount of fracturing fluid to check the tightness of the fracturing hole;

(2) Push the mounting frame to the bottom plate, place the support pad under the central square hole of the mounting frame, and make the left and rear sides of the mounting frame contact the left positioning baffle and the rear positioning baffle respectively;

(3) Install the plate specimen assembly into the installation frame, and lay transparent plexiglass on the upper surface of the upper transparent silicone pad;

(4) Control the first horizontal pressing device and the second horizontal pressing device to slowly apply confining pressure to the side of the flat specimen, and then control the vertical pressing device to slowly apply confining pressure downward to the transparent plexiglass;

(5) After the confining pressure of the three-dimensional space is applied, a high-speed camera device is installed at the upper mounting hole on the top plate, the high-speed camera device is turned on, and the pump pressure system is turned on. The liquid-permeable hole on the pipe is injected into the flat specimen, and the high-speed camera device monitors the surface of the flat specimen through the transparent plexiglass and the upper transparent silicone pad, and records the whole process of hydraulic fracturing;

(6) After the experiment, turn off the pumping system and high-speed camera device, then slowly withdraw the vertical pressure device, and then slowly withdraw the first horizontal pressure device and the second horizontal pressure device to prevent the flat specimen from being damaged twice, resulting in failure to Restore the original fracturing damage of the specimen;

(7) Finally, take out the plate specimen from the mounting frame, pull the mounting frame out of the base plate and clean the surface of the base plate and its surroundings.

The specific process of assembling the plate specimen assembly in step (1) is as follows: drilling a hole in the center of the fabricated flat specimen as a fracturing hole, and assembling the lower silicone pad, the flat specimen, the upper transparent silicone pad and the transparent plexiglass to form the fracturing hole. Set up in sequence from bottom to top, apply glue on the upper surface of the lower silicone pad to adhere to the flat specimen to prevent the lower silicone pad from sagging, and then pass the fracturing tube with the lower copper pad through the lower silicone pad from top to top. , The fracturing hole of the flat specimen, the transparent silicone pad, the copper pad and the transparent plexiglass, and screw the compression nut.

A fluorescent tracer is added to the fracturing fluid, and the fluorescent tracer is pressed into the flat plate specimen with the fracturing fluid. The flat plate specimen adopts a small thickness and a large flat plate-shaped specimen to ensure that the surface cracks are consistent with the internal cracks of the specimen; Fluorescent tracers show crack propagation traces in cracks;

The high-speed camera device records the crack propagation process of the flat specimen. First, the fracture propagation mechanism is identified, that is, the fracture propagation mechanism is identified according to the physical and mechanical properties of the flat specimen, confining pressure conditions, injected liquid flow, and viscosity; The hydraulic fracturing test was carried out under fault propagation to observe the fracture volume opening, fractal characteristics and long-term conductivity mechanism; after the test, the fractal characteristics of the fracture network and the fracture propagation mechanism, volume opening and additional in-situ stress were established by processing the recorded data. relationship; establish the relationship between the fracture long-term conductivity mechanism and the fracture propagation mechanism, the volume opening degree and the additional in-situ stress; establish the volume opening degree-in-situ stress response constitutive relationship.

The high-speed camera device observes the fracture propagation mechanism and fracturing after-effect. Including volume opening, fracture network morphology and long-term conduction mechanism.

Using the above technical solution, the support pad is used to support the vertical pressure of the flat specimen to avoid the roller being damaged by the pressure, and the sealing of the upper port of the fracturing hole adopts a crimping structure in which the upper copper pad is pressed against the transparent silicone pad. The sealing of the lower port of the hole adopts the crimping structure in which the lower copper pad presses the lower silicone pad, and the vertical pressure of the sealing is realized by the compression nut.

The three-dimensional confining pressure consists of two-way horizontal confining pressure and vertical confining pressure (ie hydraulic jack). Universal rollers are set at the bottom of the installation frame to facilitate the transfer of the hydraulic jack. At the same time, in order to ensure the coordination between the horizontal hydraulic jack and the flat specimen, use The U-shaped buckle connects the horizontal hydraulic jack and the installation frame, which is firmly fixed and easy to disassemble. The vertical pressure device is composed of four uprights, a horizontally arranged top plate and several hydraulic jacks. The vertically arranged hydraulic jacks are distributed along the boundary of the plate specimen, and the vertical pressure at the center of the plate specimen is provided by the tightening nut.

The test piece adopts a small thickness and a large flat plate-shaped test piece to ensure that the surface cracks are consistent with the internal cracks of the test piece during the fracturing process; fluorescent tracers are added to the fracturing fluid to show the crack propagation trace; the high-speed camera device adopts a high-definition camera, and the high-definition camera Photographs to record the crack propagation process. The pumping system includes a liquid storage tank and a constant-flow pump. The constant-flow pump can record fluid pressure and flow over time.

In the present invention, it is necessary to ensure the flatness of the surface of the flat plate specimen and the periphery of the fracturing hole, so as to ensure the sealing effect. When the triaxial three-dimensional confining pressure is applied, it should be applied slowly at the same time to avoid the damage of the flat specimen before hydraulic fracturing. Similarly, after the experiment is over, it should be withdrawn slowly at the same time to avoid secondary damage to the specimen.

To sum up, the present invention is scientific in principle, novel in design, compact in structure, and easy to operate. By adopting plate-shaped specimens with small thickness and large developed surface, the crack propagation mechanism and the after-effect of fracturing can be observed in real time and intuitively, and the cracks can be established. Network fractal characteristics, long-term diversion mechanism and fracture propagation mechanism, volumetric opening and the relationship between additional in-situ stress.

Description of drawings

Fig. 1 is the overall structure schematic diagram of the present invention;

Figure 2 is a cross-sectional view of the plate specimen assembly along the vertical direction;

Fig. 3 is the top view of the mounting frame in Fig. 1;

Fig. 4 is the top view of the first U-shaped buckle in Fig. 3;

FIG. 5 is a plan view of FIG. 1 .

Detailed ways

As shown in Figures 1 to 5, the hydraulic fracturing fracture propagation mechanism and fracturing after-effect test system of the present invention includes a pumping system 1 and a horizontally arranged bottom plate 2, and the bottom plate 2 is vertically provided with four in a square four There are vertical columns 3 arranged at the apex positions. The upper end of the vertical columns 3 is horizontally provided with a top plate 4 . The bottom plate 2 is provided with a mounting frame 5 between the four vertical columns 3 . The bottom of the mounting frame 5 is provided with rollers 6 . The plate type specimen assembly, the front side and left side of the installation frame 5 are respectively provided with a first horizontal pressing device 7 and a second horizontal pressing device 8, the top plate 4 is provided with a vertical pressing device 9 and a high-speed camera device 10, the plate type A liquid inlet is provided on the upper side of the middle part of the test piece assembly, and the liquid inlet is connected to the pumping system 1 through a high-pressure pipe 11 .

The installation frame 5 has a back-shaped structure, the first horizontal pressing device 7, the second horizontal pressing device 8 and the vertical pressing device 9 are hydraulic jacks, and the first horizontal pressing device 7 and the second horizontal pressing device 8 are all hydraulic jacks. It is arranged inside the installation frame 5. The front side of the installation frame 5 is provided with a first U-shaped buckle 12 for fixing the first horizontal pressing device 7. The two ends of the first U-shaped buckle 12 are respectively connected to the first horizontal pressing device. The upper side and the lower side of the bottom of the device 7 are connected, the left side of the mounting frame 5 is provided with a second U-shaped buckle 13 for fixing the second horizontal pressing device 8, and the two ends of the second U-shaped buckle 13 are respectively connected to the second U-shaped buckle 13. The upper and lower sides of the bottom of the two horizontal pressing devices 8 are connected. The lower end portions of the first U-shaped buckle 12 and the second U-shaped buckle 13 are provided with a support plate 28 for supporting the hydraulic jack.

The plate specimen assembly includes a flat specimen 14, a supporting backing plate 15, a transparent plexiglass 16, an upper transparent silicone pad 17, a lower silicone pad 18 and a fracturing tube 19. The flat specimen 14 has a square top view, and the flat specimen 14 The upper and lower transparent fracturing holes are opened at the center of the bottom plate, and the supporting pad 15, the lower silicone pad 18, the flat plate test piece 14, the upper transparent silicone pad 17 and the transparent plexiglass 16 are laid on the upper surface of the bottom plate 2 sequentially from bottom to top. The fracturing tube 19 is provided with a plugging head 20 at the lower end, and a lower accommodating hole 21 for accommodating the plugging head 20 is opened in the center of the support pad 15. The thickness of the support pad 15 is less than or equal to the height of the roller 6, and the fracturing tube 19 is It passes through the lower silica gel pad 18, the fracturing hole, the upper transparent silica gel pad 17 and the transparent plexiglass 16 in sequence from top to top. A compression nut 22 is threadedly connected to the upper part of 19, an upper accommodating hole 23 is opened at the center of the transparent plexiglass 16, and a fracturing tube 19 is sleeved with an upper surface located between the lower end face of the compression nut 22 and the upper surface of the upper transparent silicone pad 17. The copper pad 24 and the lower copper pad 25 located on the upper end face of the plugging head 20 and the upper surface of the lower silicone pad 18, the lower end of the compression nut 22 is crimped with the flat plate test piece 14 through the upper copper pad 24 and the upper transparent silicone pad 17. The liquid inlet is the upper port of the fracturing pipe 19 .

The front side of the flat specimen 14 is press-fitted with the right end of the first horizontal pressing device 7, the rear side of the flat specimen 14 is crimped with the rear side of the inner wall of the mounting frame 5, and the left side of the flat specimen 14 is pressurized with the second horizontal The right end of the device 8 is press-fitted, and the right side of the flat plate test piece 14 is press-fitted with the right side of the inner wall of the mounting frame 5 .

The central part of the top plate 4 is provided with a mounting hole 26, the high-speed camera device 10 is arranged in the mounting hole 26 and shoots the surface of the transparent plexiglass 16, several vertical pressing devices 9 are provided, and several vertical pressing devices 9 are installed along the The holes 26 are evenly arranged in the circumferential direction, and the lower end of the vertical pressing device 9 is pressed against the surface of the transparent organic glass 16 .

The right side of the bottom plate 2 is provided with a slope 27 for passing the rollers 6, and the left and rear sides of the upper surface of the bottom plate 2 are respectively provided with a left positioning baffle 28 and a rear positioning baffle. When the sides are in contact with the left positioning baffle 28 and the rear positioning baffle respectively, the mounting holes 26 correspond up and down with the perforations.

The test method of hydraulic fracturing fracture propagation mechanism and fracturing after-effect test system includes the following steps:

(1) Assemble the plate specimen assembly, connect the pumping system 1 to the upper port of the fracturing pipe 19 through the high-pressure pipe 11, and pump a small amount of fracturing fluid to check the tightness of the fracturing hole;

(2) Push the mounting frame 5 onto the base plate 2, place the support pad 15 under the central square hole of the mounting frame 5, and make the left and rear sides of the mounting frame 5 align with the left positioning baffle 28 and the rear respectively. baffle contact;

(3) Install the plate specimen assembly into the installation frame 5, and lay the transparent plexiglass 16 on the upper surface of the upper transparent silicone pad 17;

(4) Control the first horizontal pressing device 7 and the second horizontal pressing device 8 to slowly apply confining pressure to the side of the flat test piece 14 , and then control the vertical pressing device 9 to slowly apply confining pressure downward to the transparent plexiglass 16 ;

(5) After the confining pressure in the three-dimensional space is applied, the high-speed camera device 10 is installed at the upper mounting hole 26 on the top plate 4, the high-speed camera device 10 is turned on, the pump pressure system 1 is turned on, and the fracturing fluid is injected from the high-pressure pipe 11 into the fracturing system. The pipe 19 is injected into the flat specimen 14 through the liquid-permeable hole on the fracturing pipe 19. The high-speed camera 10 monitors the surface of the flat specimen 14 through the transparent plexiglass 16 and the upper transparent silicone pad 17, and records the hydraulic force. The whole process of fracturing;

(6) After the experiment, turn off the pumping system 1 and the high-speed camera device 10, then slowly withdraw the vertical pressing device 9, and then slowly withdraw the first horizontal pressing device 7 and the second horizontal pressing device 8 to prevent the flat specimen 14 Secondary damage, resulting in failure to restore the original fracturing damage of the specimen;

(7) Finally, take out the flat plate specimen 14 from the installation frame 5, pull the installation frame 5 out of the base plate 2 and clean the surface of the base plate 2 and its surroundings.

The specific process of assembling the plate specimen assembly in step (1) is as follows: drilling a hole in the center of the fabricated flat specimen 14 as a fracturing hole, and placing the lower silicone pad 18, the flat specimen 14, the upper transparent silicone pad 17 and the The transparent plexiglass 16 is arranged in sequence from bottom to top, and glue is applied on the upper surface of the lower silicone pad 18 to adhere to the flat specimen 14 to prevent the lower silicone pad 18 from sagging, and then the fracturing tube 19 covered with the lower copper pad 25 is fracturing The tube 19 passes through the lower silicone pad 18 , the fracturing hole of the flat specimen 14 , the upper transparent silicone pad 17 , the upper copper pad 24 and the transparent plexiglass 16 sequentially from top to top, and the compression nut 22 is screwed on.

A fluorescent tracer is added to the fracturing fluid, and the fluorescent tracer is pressed into the plate specimen 14 along with the fracturing fluid. The plate specimen 14 adopts a small thickness and a large plane plate specimen to ensure surface cracks and internal cracks in the specimen. Consistent; the fluorescent tracer shows crack propagation traces in the fracture;

The high-speed camera device 10 records the crack propagation process of the flat specimen 14. First, the fracture propagation mechanism is identified, that is, the fracture propagation mechanism is identified according to the physical and mechanical properties of the flat specimen 14, confining pressure conditions, flow rate of injected liquid, and viscosity; then, Hydraulic fracturing tests were carried out under different fracture propagation conditions to observe the fracture volume opening, fractal characteristics and long-term conductivity mechanism. Additional in-situ stress relationship; establish the relationship between the fracture long-term conductivity mechanism and the fracture propagation mechanism, volume opening degree and additional in-situ stress; establish the volume opening-in-situ stress response constitutive relationship.

The high-speed camera device 10 observes the fracture propagation mechanism and the after-effect of fracturing, wherein the fracture propagation mechanism includes a viscous-no fluid loss mechanism, a viscous-fluid loss mechanism, a toughness-no fluid loss mechanism, and a toughness-fluid loss mechanism. The effects include volume opening, fracture network morphology, and long-term conduction mechanism.

This embodiment does not limit the shape, material, structure, etc. of the present invention in any form, and any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention belong to the protection of the technical solution of the present invention scope.

Claims (5)

1. Hydraulic fracturing fracture propagation mechanism and fracturing after-effect test system, it is characterized in that: comprise pumping system and horizontally arranged base plate, the base plate is vertically provided with four uprights arranged at four vertex positions of a square, the upper end of the uprights A top plate is arranged horizontally, an installation frame is arranged between the four uprights on the bottom plate, a roller is arranged at the bottom of the installation frame, a horizontally arranged plate-type specimen assembly is arranged in the installation frame, and the front side and the left side of the installation frame are respectively provided with a first The horizontal pressurizing device and the second horizontal pressurizing device, the top plate is provided with a vertical pressurizing device and a high-speed camera device, a liquid inlet is provided on the upper side of the middle of the plate-type specimen assembly, and the liquid inlet is connected with the pumping system through a high-pressure pipe; The installation frame has a back-shaped structure, the first horizontal pressure device, the second horizontal pressure device and the vertical pressure device are all hydraulic jacks, and the first horizontal pressure device and the second horizontal pressure device are all arranged inside the installation frame, The front side of the installation frame is provided with a first U-shaped buckle for fixing the first horizontal pressure device, and the two ends of the first U-shaped buckle are respectively connected with the upper and lower sides of the bottom of the first horizontal pressure device. The left side of the frame is provided with a second U-shaped buckle for fixing the second horizontal pressure device, and the two ends of the second U-shaped buckle are respectively connected with the bottom upper side and the lower side of the second horizontal pressure device; The plate specimen assembly includes a flat specimen, a supporting backing plate, a transparent plexiglass, an upper transparent silicone pad, a lower silicone pad and a fracturing tube. The top view of the flat specimen is a square, and the center of the flat specimen is provided with an upper and lower transparent The fracturing hole, the supporting pad, the lower silicone pad, the flat specimen, the upper transparent silicone pad and the transparent plexiglass are laid sequentially from bottom to top on the upper surface of the bottom plate. There is a lower accommodating hole for accommodating the plugging head, the thickness of the support pad is less than or equal to the height of the roller, and the fracturing tube passes through the lower silicone pad, fracturing hole, upper transparent silicone pad and transparent plexiglass sequentially from top to top The fracturing pipe is provided with a number of liquid permeable holes on the outer circumference of the fracturing pipe. The upper part of the fracturing pipe is threadedly connected with a compression nut. The center of the transparent plexiglass is provided with an upper accommodating hole. The fracturing pipe is sleeved with a The upper copper pad located between the lower end face of the compression nut and the upper surface of the upper transparent silicone pad and the lower copper pad located between the upper end face of the plugging head and the upper surface of the lower silicone pad, the lower end of the compression nut passes through the upper copper pad, the upper transparent silicone pad and the flat plate The test piece is crimped, and the liquid inlet is the upper port of the fracturing pipe; The front side of the flat specimen is press-fitted with the right end of the first horizontal pressing device, the rear side of the flat specimen is press-fitted with the rear side of the inner wall of the mounting frame, and the left side of the flat specimen is press-fitted with the right end of the second horizontal pressing device. , the right side of the flat specimen is crimped with the right side of the inner wall of the mounting frame; The central part of the top plate is provided with an installation hole, a high-speed camera device is arranged in the installation hole and takes pictures of the surface of the transparent plexiglass, several vertical pressure devices are arranged, and the several vertical pressure devices are evenly arranged along the circumferential direction of the installation hole, The lower end of the vertical pressing device is crimped with the surface of the transparent plexiglass; The right side of the bottom plate is provided with a slope for passing the rollers, and the left and rear sides of the upper surface of the bottom plate are respectively provided with a left positioning baffle and a rear positioning baffle. When the plate and the rear positioning baffle are in contact, the mounting holes correspond up and down with the perforations. 2. The test method of hydraulic fracturing fracture propagation mechanism and fracturing after-effect test system according to claim 1, characterized in that: comprising the following steps: (1) Assemble the plate specimen assembly, connect the pumping system to the upper port of the fracturing pipe through the high-pressure pipe, and pump a small amount of fracturing fluid to check the tightness of the fracturing hole; (2) Push the mounting frame to the bottom plate, place the support pad under the central square hole of the mounting frame, and make the left and rear sides of the mounting frame contact the left positioning baffle and the rear positioning baffle respectively; (3) Install the plate specimen assembly into the installation frame, and lay transparent plexiglass on the upper surface of the upper transparent silicone pad; (4) Control the first horizontal pressing device and the second horizontal pressing device to slowly apply confining pressure to the side of the flat specimen, and then control the vertical pressing device to slowly apply confining pressure downward to the transparent plexiglass; (5) After the confining pressure of the three-dimensional space is applied, a high-speed camera device is installed at the upper mounting hole on the top plate, the high-speed camera device is turned on, and the pump pressure system is turned on. The liquid-permeable hole on the pipe is injected into the flat specimen, and the high-speed camera device monitors the surface of the flat specimen through the transparent plexiglass and the upper transparent silicone pad, and records the whole process of hydraulic fracturing; (6) After the experiment, turn off the pumping system and high-speed camera device, then slowly withdraw the vertical pressure device, and then slowly withdraw the first horizontal pressure device and the second horizontal pressure device to prevent the flat specimen from being damaged twice, resulting in failure to Restore the original fracturing damage of the specimen; (7) Finally, take out the plate specimen from the mounting frame, pull the mounting frame out of the base plate and clean the surface of the base plate and its surroundings. 3. The test method of hydraulic fracturing fracture propagation mechanism and fracturing after-effect test system according to claim 2, characterized in that: the specific process of assembling the plate specimen assembly in step (1) is: The center of the specimen is drilled as a fracturing hole, the lower silicone pad, the flat specimen, the upper transparent silicone pad and the transparent plexiglass are arranged in sequence from bottom to top, and glue is applied on the upper surface of the lower silicone pad to adhere to the flat specimen to prevent Prevent the lower silicone pad from sagging, and then pass the fracturing tube covered with the lower copper pad through the lower silicone pad, the fracturing hole of the flat specimen, the upper transparent silicone pad, the upper copper pad and the transparent plexiglass from top to top. Tighten the nut. 4. The test method of hydraulic fracturing fracture propagation mechanism and fracturing after-effect test system according to claim 2, characterized in that: a fluorescent tracer is added in the fracturing fluid, and the fluorescent tracer follows the fracturing fluid. It is pressed into the flat test piece, and the flat test piece adopts a small thickness and a large flat plate-shaped test piece to ensure that the surface cracks are consistent with the internal cracks of the test piece; the fluorescent tracer shows the crack expansion trace in the crack; The high-speed camera device records the crack propagation process of the flat specimen. First, the fracture propagation mechanism is identified, that is, the fracture propagation mechanism is identified according to the physical and mechanical properties of the flat specimen, confining pressure conditions, injected liquid flow, and viscosity; The hydraulic fracturing test was carried out under fault propagation to observe the fracture volume opening, fractal characteristics and long-term conductivity mechanism; after the test, the fractal characteristics of the fracture network and the fracture propagation mechanism, volume opening and additional in-situ stress were established by processing the recorded data. relationship; establish the relationship between the fracture long-term conductivity mechanism and the fracture propagation mechanism, the volume opening degree and the additional in-situ stress; establish the volume opening degree-in-situ stress response constitutive relationship. 5. The test method of hydraulic fracturing fracture propagation mechanism and fracturing after-effect test system according to claim 2, characterized in that: the high-speed camera device observes the fracture propagation mechanism and the fracturing after-effect, wherein the fracture propagation mechanism comprises: Viscous-no fluid loss mechanism, viscous-fluid loss mechanism, toughness-no fluid loss mechanism and toughness-fluid loss mechanism, the after effects of fracturing include volume opening, fracture network morphology and long-term conductivity mechanism.

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