CN110700823B - Loading body for true triaxial crack propagation simulation and permeability synchronous experiment and permeability test characterization method - Google Patents

Abstract

The scheme relates to a loading body for a true triaxial crack propagation simulation and permeability synchronous experiment and a permeability test characterization method, wherein the loading body comprises: the loading frame is internally provided with a test piece which is integrally cubic; a feeding device for feeding the test piece is arranged on one side of the front end face of the loading frame body; the test piece loading device comprises a plurality of groups of pistons which respectively load a test piece from the X direction, the Y direction and the Z direction of a loading frame body, wherein the plurality of groups of pistons respectively form sealing, fixing and pressurizing between each direction and the loading frame body; a drill hole is arranged on the front surface of the test piece facing to the front end face, and a shaft is arranged in the drill hole; the rest five surfaces of the test piece except the front surface are attached with backing plates, and the backing plates are provided with ventilation structures; the backing plate is provided with a gas collecting pipeline. The method solves the problem that the conventional test method can not complete the permeability test of the large compact test piece before and after the crack propagation experiment, and provides an effective means for quantitatively evaluating the crack propagation experiment effect under different stress environments.

Description

A true triaxial fracture propagation simulation and permeability synchronous experiment loading body and permeability Transmittance Test Characterization Method

technical field

The invention relates to the technical field of rock mass mechanics and engineering, in particular to a loading body and a permeability test and characterization method for true triaxial crack propagation simulation and permeability synchronous experiment.

Background technique

The exploration, development and utilization of unconventional oil and gas resources has become a key area of oil and gas energy development, and hydraulic fracturing technology is one of the key technologies for economical and efficient development of such resources. The effect of hydraulic fracturing technology is directly related to the development and utilization value of such resources, and it is very important to accurately evaluate the effect of hydraulic fracturing technology to transform reservoirs. Fracture propagation experiments and permeability testing of reservoirs to simulate underground environment are the main means to evaluate the effect of stimulation. At present, due to the limitations of equipment conditions and methods for crack propagation simulation experiments at home and abroad, under the original experimental stress conditions, it is impossible to accurately conduct crack propagation experiments or permeability tests at the same time; Limited stress magnitude and inaccurate permeability testing and characterization methods.

Patent CN109975140A discloses an experimental device and method integrating supercritical carbon dioxide pulse cracking and permeability testing, including various data acquisition modules, power modules and an in-situ environment simulation system. It can realize supercritical carbon dioxide pulse fracturing experiment and permeability test before and after fracturing. However, the size of the simulated specimen is small, and the stress environment is a pseudo-triaxial stress environment. Patent CN1041328880B discloses an experimental method for testing the permeability of reservoir cores before and after hydraulic fracturing under triaxial conditions, including mobile trolleys and pressure chambers, etc., which can measure the permeability of reservoirs before and after hydraulic fracturing under triaxial stress conditions in situ. There is no need to decompress the specimen, but the required specimen is small, which cannot meet the requirements of the crack propagation experiment, and there is no specific characterization method for permeability. Patent CN108663298A discloses an experimental device and method integrating true triaxial fracture propagation simulation and permeability testing, which includes true triaxial loading system, fracturing system, acoustic emission detection system and permeability testing system, which can realize rock pressure Integrated test of crack and permeability test. However, the true triaxial loading frame is unknown, and the permeability characterization before fracturing is incomplete.

Therefore, in order to realize the fracture propagation and permeability testing experiments under in-situ in-situ stress environment, it is necessary to develop a true triaxial fracture propagation and permeability simultaneous experimental loading and permeability testing characterization method.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a loading body and permeability test characterization method for true triaxial fracture propagation simulation and permeability synchronous experiment, so as to realize the integrated test of rock fracturing and permeability, which can effectively characterize the fracturing experiment before and after The permeability of the scale is used to evaluate the effect of fracturing.

The technical scheme of the present invention is:

The invention provides a loading body for true triaxial fracture propagation simulation and permeability synchronous experiment, including:

a loading frame, in which a test piece that is a cube as a whole is placed;

A feeding device is provided on one side of the front end surface of the loading frame, and the test piece is fed into the interior of the loading frame through the feeding device;

Multiple groups of pistons are used to load the specimen from the X, Y and Z directions of the loading frame, respectively, and the multiple groups of pistons form sealing, fixing and pressurized;

The front surface of the test piece is provided with a borehole, and a wellbore for introducing permeability test gas or fracturing fluid into the test piece is installed in the borehole;

A backing plate is attached to the remaining five surfaces of the test piece except the front surface, and a backing plate is arranged on the backing plate for flowing the test piece to the outer surface of the test piece when the test piece is subjected to the permeability test. A ventilation structure for collecting the permeability test gas; a gas collecting line for collecting the permeability test gas collected by the ventilation structure is installed on the backing plate.

Preferably, the backing plate includes:

A plurality of inner backing plates are respectively attached to the remaining five surfaces of the test piece except the front surface, and each of the inner backing plates is provided with a plurality of air passages for transmission of the permeability test gas on the outer end face of the test piece;

Each of the inner pads is attached with an outer pad, and the outer pad is provided with a conducting wire groove and an air collecting hole that communicate with each other;

One end of the gas collecting line is connected to the external manifold, and the other end extends into the gas collecting hole from the wire groove, and the permeability test gas transmitted by the plurality of air passages is collected in the gas collecting hole, and then passes through the gas collecting hole. The gas collecting line flows out to the external manifold;

The ventilation structure includes the ventilation channel and the air collecting hole.

Preferably, the plurality of air passages provided on the inner backing plate include:

a plurality of first ventilation grooves arranged along a first direction and a plurality of second ventilation grooves arranged along a second direction, the first direction and the second direction being perpendicular;

A ventilation hole is provided at the intersection of the first ventilation groove and the second ventilation groove;

Neither the first ventilation groove nor the second ventilation groove is communicated with the side end surface of the inner backing plate;

The air collecting holes provided on the outer backing plate include:

A first air collecting hole is opened on the end surface of the outer backing plate facing the inner backing plate, and a second air collecting hole is opened on the end surface of the outer backing plate away from the inner backing plate; the first air collecting hole the air hole communicates with the second air collecting hole;

The inner diameter of the first air-collecting hole is smaller than the inner diameter of the second air-collecting hole, and the second air-collecting hole is provided with an inner thread screwed with the air-collecting pipeline;

The wire grooves provided on the outer backing plate include:

A first guide groove is provided on the end surface of the outer backing plate away from the inner backing plate, and a second guide groove is provided on the side end surface of the outer backing plate, one end of the first guiding groove is connected to the The second guide groove is connected with the second air collecting hole at the other end.

Preferably, a plurality of parallel-arranged test-piece feeding slots are provided on the outer backing plate provided on one side of the lower surface of the test piece.

Preferably, the wellbore comprises: a first wellbore section and a second wellbore section that are connected;

A plurality of uniformly arranged annular grooves are provided on the outer circumferences of the first wellbore section and the second wellbore section;

The outer diameter of the first wellbore section is greater than the outer diameter of the second wellbore section;

The outer diameter of the second wellbore section is smaller than the hole diameter of the borehole in the test piece, and the difference between the outer diameter of the second wellbore section and the hole diameter of the borehole in the test piece is Between 1mm and 3mm.

Preferably, the test piece is square;

The annular gap between the wellbore and the borehole of the test piece is sealed with annular resin;

The twelve sides of the test piece are sealed by a rubber mold with an integral structure, the inner backing plate forms a support for the rubber mold, and the outer backing plate is pressed on the inner backing plate and the rubber mold. superior.

Preferably, the loading body further comprises:

a frame support frame installed on the lower side of the loading frame;

a slide rail installed on one side of the front end face of the loading frame;

The backing plate attached to the lower surface of the test piece is placed on the feeding device, and the feeding device is installed on the sliding rail to send the test piece into the interior of the loading frame ;

After the specimen is fed into the loading frame, the feeding device and the loading frame are screwed and fixed, and the feeding device is connected to the first side end face of the loading frame. form a seal.

The present invention also provides a permeability test characterization method of the above-mentioned loading body, comprising:

1) Specimen preparation: according to the experimental requirements, make the test specimens that are required for the experiment as a whole in a cubic shape;

2) Triaxial stress loading: According to the triaxial stress conditions required by the experiment, the pistons in the three directions of X, Y and Z are controlled by hydraulic drive to achieve the required triaxial stress;

3) Permeability test before the crack propagation experiment: The overall permeability test of the test piece is carried out by using the pulse permeability test method, and the overall permeability of the test piece is characterized as:

After the overall permeability test is completed, a single-sided permeability test is performed on the test piece; wherein, any one of the upper surface, the lower surface, the left surface and the right surface on the test piece adjacent to the front surface has a The permeability is characterized as:

The permeability of the rear surface opposite the front surface on the test piece is characterized by:

Among them, in the above three groups of formulas: K is the permeability, β is the gas compressibility coefficient, α is the fitting value, μ is the gas viscosity, r _e is the circumscribed circle radius of the specimen, r _w is the outer diameter of the wellbore, and h ₂ is the perforation length or open hole length, t is the test time, P _u,0 is the initial pressure in the upstream chamber, P _d,0 is the initial pressure in the downstream chamber, P _u is the end pressure of the experiment in the upstream chamber, P _d is the downstream chamber Indoor experiment end pressure;

4) Fracture propagation experiment: According to the pre-planned pumping procedure, pump fracturing fluid into the specimen through the wellbore, and stop pumping fracturing fluid until the specimen is completely fractured;

5) Permeability test after the crack propagation experiment: The overall permeability test of the cracked specimen is carried out by using the conventional permeability test method, and the overall permeability of the specimen is characterized as:

After the overall permeability test is completed, a single-sided permeability test is performed on the cracked specimen; wherein any one of the upper surface, the lower surface, the left surface and the right surface adjacent to the front surface of the specimen is The permeability of the surface is characterized as:

The permeability of the rear surface opposite the front surface on the test piece is characterized by:

Among them, in the above three groups of formulas: K is the permeability, ΔP is the pressure difference between the center of the specimen and the end face of the measured permeability, ρ is the gas density, ε is the pore characteristic parameter of the specimen, μ is the gas viscosity, and Q is the fluid flow rate , H is the width of the cube specimen, _h1 is the length of the wellbore section, _h2 is the length of the perforation or the length of the open hole section, _{r e} is the radius of the circumscribed circle of the specimen, and rw is the outer diameter of the wellbore.

6) Observation of the results of the crack propagation experiment: unload the triaxial stress, take out the specimen from the experimental loading body, and describe the crack development of the specimen for the crack propagation experiment according to the predetermined requirements;

7) The end of the experiment: the above experiment content is completed, and the experimental equipment is adjusted to the pre-experiment state according to the predetermined procedure.

The present invention has beneficial effects as follows:

It can realize the permeability test and quantitative characterization before and after the fracturing fracture expansion experiment under in-situ in-situ stress conditions, which solves the difficulty of permeability testing of large-sized specimens under in-situ in-situ stress conditions, and the collection of test gas is complicated and cannot be well tested. The problem of permeability before and after fracture propagation. At the same time, it solves the problem that the conventional test method cannot complete the permeability test of large dense specimens before the crack propagation test. The achievement of the invention provides a powerful means for quantitatively evaluating the experimental effect of crack propagation under different conditions.

Description of drawings

Fig. 1 is the schematic diagram of the loading body of the present invention;

Fig. 2 is the schematic diagram of the piston of the present invention;

Fig. 3 is the schematic diagram of the piston of the present invention;

Fig. 4 is the A-A sectional schematic diagram of Fig. 3;

Fig. 5 is the cross-sectional schematic diagram of B-B of Fig. 3;

Fig. 6 is the structural representation of the outer backing plate of the lower side;

FIG. 7 is a schematic diagram of the cooperation of the feeding device, the lower backing plate on the lower side and the test piece;

8 is a schematic structural diagram of the outer pads on the left side, the right side, the rear side and the upper side;

Figure 9 is a schematic structural diagram of the inner backing plate;

Figure 10 is a schematic structural diagram of a wellbore;

Figure 11 is a schematic diagram of the structure of the test piece;

Figure 12 is a schematic structural diagram of a loading body of the present invention;

13 is a schematic structural diagram of a loading body of the present invention;

Description of reference numerals: 1—Z direction piston, 101—bolt hole, 102—piston push rod, 103—piston cavity, 104—piston inner cavity, 2—loading frame, 3—X direction piston, 4—Y direction Piston, 5—frame support frame, 6—slide rail, 7—feeding device, 8—first guide groove, 9—second wire groove, 10—test piece feeding groove, 11—first air collecting hole, 12 - the second air collecting hole, 13 - the outer backing plate; 14 - the test piece, 15 - the front body, 16 - the bolt, 17 - the first ventilation groove, 18 - the second ventilation groove, 19 - the ventilation hole, 20 - the first wellbore Section, 21-second wellbore section, 22-gas inlet channel, 23-open hole section or perforation section, 24-wellbore section; 25, inner backing plate.

Detailed ways

Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present invention are shown in the drawings, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that the present invention will be more thoroughly understood, and will fully convey the scope of the present invention to those skilled in the art.

Referring to FIGS. 1 to 13 , the present invention provides a loading body for true triaxial fracture propagation simulation and permeability synchronous experiment, including: a loading frame body 2 , in which a cube-shaped test piece is placed in the loading frame body 2 14; A feeding device 7 is provided on one side of the front end face of the loading frame 2, and the test piece 14 is fed into the interior of the loading frame 2 through the feeding device 7; Multiple groups of pistons for loading the test piece 14 in the X, Y and Z directions of the loading frame 2, and the multiple groups of pistons form sealing, fixing and pressurization with the loading frame 2 from all directions; The front surface of the test piece 14 facing the front end face is provided with a borehole, and a wellbore for introducing permeability test gas or fracturing fluid into the test piece 14 is installed in the borehole; A backing plate is attached to the remaining five surfaces of the test piece 14 except the front surface, and the backing plate is provided with a backing plate for flowing the test piece 14 to the outside of the test piece 14 when the test piece 14 is subjected to the permeability test. A ventilation structure for collecting the permeability test gas on the surface; a gas collecting line for collecting the permeability test gas collected by the ventilation structure is installed on the backing plate.

As shown in FIG. 1 , the multiple groups of pistons include: X-direction pistons 3 arranged along the X-direction of the loading frame 2, Y-direction pistons 4 arranged along the Y-direction of the loading frame 2, and Y-direction pistons 4 arranged along the Z-direction of the loading frame 2 Set the Z direction piston 1. The working pressure of each group of pistons can reach 60MPa, and the axial stress in the three directions of X, Y and Z can reach 40MPa. The three groups of pistons jointly realize the loading of different sizes of stress on the specimen 14 in the three-axis direction. The three groups of pistons use hydraulic pressure. drive. The piston rods of each group of pistons are connected to the end face of the outer backing plate 13 on the side away from the inner backing plate 25 , and the rigid loading of the test piece 14 is realized by the outer backing plate 13 .

Specimen 14 is loaded with different stresses through a true triaxial loading system, which specifically includes a pressure chamber, an X-axis hydraulic cylinder, a Y-axis hydraulic cylinder, a Z-axis hydraulic cylinder, and an X-axis connected to the X-axis hydraulic cylinder. Hydraulic control assembly, Y-axis hydraulic control assembly connected with Y-axis hydraulic cylinder and Z-axis hydraulic control assembly connected with Z-axis hydraulic cylinder, X-axis hydraulic control assembly, Y-axis hydraulic control assembly and Z-axis hydraulic control assembly are specifically hydraulic Pump. The output end of the X axis hydraulic cylinder is connected to the piston rod of the X direction piston 3, the output end of the Y axis hydraulic cylinder is connected to the piston rod of the Y direction piston 4, and the Z axis hydraulic cylinder output end is connected to the piston rod of the Z direction piston 1.

By adjusting the hydraulic control components in the three directions of X, Y, and Z, the true triaxial confining pressure on the test piece 14 is realized. The hydraulic value in the cavity 104 is adjusted to realize the adjustment of the magnitude of the axial pressure in this direction. The X-direction piston 3, the Y-direction piston 4 and the Z-direction piston 1 are connected and sealed with the loading frame 22 through threads, and bolt holes 101 are evenly arranged on the loading piston. The screw connection between the body 2. The piston cavity 104 is filled with hydraulic oil, and the hydraulic oil in the piston cavity 104 is compressed by the hydraulic control assembly (hydraulic pump) to drive the piston push rod 102 to move forward and backward to provide the required stress for loading and unloading of the specimen 14. The piston cavity The body 103 and the piston push rod 102 adopt a cylindrical structure.

As shown in FIG. 7, for the feeding device 7, a plurality of bolts 16 are arranged on the feeding device 7 for sealing and fixing. A front end body 15 is arranged on the feeding device 7 toward the front end of the loading frame body 2 .

Referring to FIGS. 6 to 9 , the backing plate includes: a plurality of inner backing plates 25 , which are cube-shaped plates, respectively attached to the remaining five surfaces of the test piece 14 except the front surface, Each of the inner backing plates 25 is provided with a plurality of air passages (specifically, the air passages are shown in Fig. The ventilation groove and the ventilation hole 19 in 9); each of the inner backing plates 25 is attached with an outer backing plate 13, and the outer backing plate 13 is provided with connected wire grooves and air-collecting holes; One end of the gas collection line is connected to the external manifold, and the other end extends into the gas collection hole from the wire groove, and the permeability test gas transmitted by the plurality of air passages is collected in the gas collection hole, and then passes through the gas collection hole. The air collecting line flows out to the external manifold; the ventilation structure includes the air passage and the air collecting hole.

Specifically, as shown in FIG. 9 , the plurality of ventilation channels provided on the inner backing plate 25 include: a plurality of first ventilation grooves 17 arranged along the first direction and a plurality of second ventilation grooves arranged along the second direction 18, the first direction and the second direction are perpendicular; the intersection of the first ventilation groove 17 and the second ventilation groove 18 is provided with a ventilation hole 19; the first ventilation groove 17 and the The two ventilation grooves 18 are not connected to the side end surface of the inner backing plate 25 , and it can be seen from FIG. , so that the permeability test gas from each position of the end face of the test piece 14 can be collected to the first gas collecting hole 11 . When the permeability test is performed, the permeability test gas is input from the wellbore, and the permeability test gas passing through each end face of the test piece 14 converges through the first ventilation groove 17 , the second ventilation groove 18 and the ventilation hole 19 on the inner backing plate 25 at the first air collecting hole 11 . The inner backing plate 25 is a thin backing plate of steel alloy material, the first ventilation groove 17, the second ventilation groove 18 and the ventilation hole 19 are symmetrically distributed on two opposite end faces of the inner backing plate 25, and the thickness of the inner backing plate 25 is 1-3mm , which can withstand axial pressure above 60MPa and shear stress of a certain size.

Referring to FIGS. 6 to 8 , the outer backing plate 13 is a cubic plate, which includes two types, one is the outer backing plate 13 shown in FIGS. 6 and 7 , and the outer backing plate 13 of this shape is mainly arranged in the test The lower side of the test piece 14; one is the outer backing plate 13 shown in FIG. 8, and the outer backing plate 13 of this shape is mainly arranged on the upper, left, right and rear sides of the test piece 14; the difference is that, The outer backing plate 13 shown in FIG. 6 has a specimen feeding slot 10 added to the outer padding plate 13 in FIG. 8 . on the backing plate 13. The specimen feeding slot 10 is used for inserting an external tool to assist in placing the whole formed by the specimen 14 and the inner backing plate 25 on the outer backing plate 13 . Specifically, as shown in FIGS. 6 to 8 , the air-collecting holes provided on the outer backing plate 13 include: a first air-collecting hole 11 opened on the end surface of the outer backing plate 13 facing the inner backing plate 25 ; The outer backing plate 13 is away from the second air collecting hole 12 opened on the end surface of the inner backing plate 25; the first air collecting hole 11 is communicated with the second air collecting hole 12; the inner diameter of the first air collecting hole 11 is smaller than The inner diameter of the second air-collecting hole 12, the second air-collecting hole 12 is provided with an inner thread screwed with the air-collecting pipeline; the wire groove set on the outer backing plate 13 includes: A first guide groove 8 is provided on the end surface of the plate 13 away from the inner backing plate 25, and a second guide groove is provided on the side end surface of the outer backing plate 13. One end of the first guide groove is connected to the The other end of the second guide groove communicates with the second air collecting hole 12 . The permeability test gas is input into the wellbore through the upstream pressure chamber (the pressure in this chamber is measured to obtain P _{μ, 0} and P _μ ), and part of the permeability test gas passing through the wall of the test piece 14 passes through the inner backing plate 25 The first ventilation groove 17, the second ventilation groove 18 or the ventilation hole 19 on the upper part converge to the first air collecting hole 11, and in the pressure chamber connected to the external manifold through the air collecting pipeline, the pressure chamber is the rear The downstream chamber in the formula, P _d,0 and P _d hereinafter are obtained by measuring the pressure in the pressure chamber.

Referring to FIG. 10 , the wellbore is cylindrical in shape, and a gas inlet channel 22 is arranged in the wellbore, and the permeability test gas and fracturing fluid are injected into the test piece 14 through the gas inlet channel 22 , and the wellbore includes: a first wellbore section connected 20 and the second wellbore section 21; the outer circumferences of the first wellbore section 20 and the second wellbore section 21 are provided with a plurality of uniformly arranged annular grooves; the outer diameter of the first wellbore section 20 is greater than the outer diameter of the second wellbore section 21; the outer diameter of the second wellbore section 21 is smaller than the hole diameter of the borehole in the test piece 14, and the outer diameter of the second wellbore section 21 and the test piece The difference between the hole diameters of the drilled holes in 14 is between 1mm and 3mm. The outer diameter of the first wellbore section 20 approximates the bore diameter of the borehole in the specimen 14. The wellbore can be embedded in advance when the test piece 14 is poured, or can be drilled to install the wellbore after the test piece 14 is poured.

As shown in FIG. 7 , the test piece 14 is square; the annular gap between the wellbore and the borehole of the test piece 14 is sealed with annular resin; the twelve sides of the test piece 14 are of an integral structure The inner pad 25 forms a support for the rubber mould, and the outer pad 13 is pressed on the inner pad 25 and the rubber mould.

As shown in FIG. 1 , the loading body further includes: a frame body support frame 5 installed on the lower side of the loading frame body 2 , and the frame body support frame 5 is a trapezoidal structure, which mainly supports the loading frame body 2 It supports the loading frame 2 to be higher than the ground, which is convenient for the loading of the specimen 14; the slide rail 6 is installed on the side of the front end surface of the loading frame 2; the pad attached to the lower surface of the specimen 14 is placed On the feeding device 7, the feeding device 7 is installed on the sliding rail 6 to feed the test piece 14 into the inside of the loading frame 2, and the feeding device 7 adopts a thickening The steel body is made of steel, and is fixed and sealed with the loading frame 2 by a plurality of bolts; after the test piece 14 is sent into the loading frame 2, the feeding device 7 and the loading frame 2 It is screwed and fixed, and the feeding device 7 forms a seal with the first side end face of the loading frame body 2 .

The above-mentioned loading body in this embodiment can realize the overall permeability test of the test piece 14 and the upper, lower, left, right and permeability testing of the last five surfaces. Specifically, the permeability of the specimen 14 was low before the crack propagation, and the principle of the pulse attenuation method was used to conduct the permeability test; The principle of the method is tested. Wherein, the principle of the conventional permeability testing method refers to performing the permeability testing according to the method in the patent application with publication number "CN108663298A".

Specifically, the above-mentioned loading body of the present application mainly includes the following steps during the test:

1) Specimen preparation: According to the experimental requirements, the overall cubic specimen 14 required for the experiment is made, specifically: selecting natural or artificial rocks, processing the rock into a specimen 14 of 30×30×30 cm, and then placing the specimen 14 on the specimen 14. Drill a hole with a diameter of 2cm and a depth of 20cm at the center of one end face of the machine, embed the wellbore in the center hole, prefabricate a plurality of evenly arranged annular grooves on the wellbore, and match the annular resin to the gap between the wellbore and the drilled hole. Seal, and then encapsulate the test piece 14 with a rubber mold as a whole structure, and use adhesive glue to stick the rubber mold and the twelve sides and eight corners of the test piece 14 together; the edge width of the rubber mold is 25mm, and the thickness is 25mm. 1-3mm, the eight corners adopt a conical structure, which plays the role of fully wrapping the 14 eight corners of the specimen;

2) Triaxial stress loading: According to the triaxial stress conditions required by the experiment, the pistons in the three directions of X, Y and Z are controlled by hydraulic drive to achieve the required triaxial stress, specifically: the pressure in the true triaxial loading system An outer backing plate 13 is arranged in each of the three directions of X, Y and Z in the room, and then the packaged test piece 14 is sent into the loading frame 2 through the feeding device 7, and the nozzle of the wellbore is kept outside. Axial pressure of 0-0.5MPa is applied to each of the three directions of X, Y, and Z of the specimen 14 to fix the specimen 14 and maintain the sealability of the rubber mold to the edges and corners of the specimen 14; then load the specimen 14 as required The three-axis stress, the area of the end face of the specimen 14 and the area of the core pressure plate are converted to the hydraulic chamber oil pressure, and the hydraulic control component is adjusted to increase the hydraulic chamber oil pressure in the three directions of X, Y, and Z to the converted value, so that the three directions of the specimen 14 are achieve the required axial stress;

3) Permeability test before the fracture propagation experiment: connect the gas input unit of the permeability test system to the wellbore through the pipeline, and the gas output unit of the permeability test system to the first gas collection hole on the outer backing plate 13 through the pipeline 11 is connected, and the end face where the nozzle of the fracturing pipe is located cannot be provided with an air outlet valve, so the permeability test can also be performed on the remaining five surfaces of the specimen 14 (5 surfaces in total after up, down, left, and right). Start the permeability test system. If you need to measure the permeability of one side of the specimen 14, first close the outlet valves of the other four end faces, open the permeability test surface of one end face, and use the pulse decay method to input gas through the gas input unit, record The pressure and flow rate of the gas inlet and outlet during the test process can be calculated by the formula to obtain the single-sided permeability of the test piece 14 before fracturing; if the overall permeability of the test piece 14 needs to be determined, the pulse permeability test method shall be used to conduct For the overall permeability test, open the gas outlet valves on the five end faces, and then record the pressure and flow rate of the gas inlet and outlet during the test process, and calculate the overall permeability of specimen 14 before fracturing by formula;

4) Carry out the fracture propagation experiment: According to the pre-planned pump injection procedure, pump the fracturing fluid into the test piece 14 through the wellbore, and stop pumping the fracturing fluid until the test piece 14 is completely fractured, specifically: for the test piece 14 Perform fracturing, disconnect the communication pipeline of the permeability test system, and then connect the injection pump of the fracturing system to the wellbore through the fracturing pipeline. The sound emission detection system is debugged, and after the debugging is completed, the fracturing fluid is pumped, and the fracturing specimen 14;

5) Permeability test after the crack propagation experiment: use the conventional permeability test method to test the overall permeability of the fractured specimen 14, specifically: disconnect the communication pipeline between the fracturing system and the fracturing pipe, repeat Step 3), at this time, the input gas is input through the principle of the conventional permeability test method, and then the single-sided permeability and the overall permeability of the test piece 14 after fracturing are obtained by calculating the relevant formula;

Wherein, before the crack propagation experiment is performed, that is, in step 3, the overall permeability of the test piece 14 is characterized as:

The permeability of any one of the upper surface, lower surface, left surface and right surface adjacent to the front surface on the test piece 14 is characterized by:

The permeability of the rear surface opposite to the front surface on the test piece 14 is characterized by:

Among them, in the above three sets of formulas: K is the permeability, is the gas compressibility coefficient, is the fitting value, μ is the gas viscosity, r _e is the circumscribed circle radius of the test piece 14, and r _w is the outer diameter of the wellbore h ₁ is the length of the wellbore section 24, h ₂ is the length of the perforation section or the open-hole section 23, t is the permeability test time, P _μ,0 is the initial pressure in the upstream chamber, and P _d,0 is the pressure in the downstream chamber The initial pressure, P _μ is the end pressure of the experiment in the upstream chamber, and P _d is the end pressure of the experiment in the downstream chamber.

In addition, after the crack propagation experiment is performed, that is, in step 5, the overall permeability of the test piece 14 is characterized as:

The permeability of any one of the upper surface, lower surface, left surface and right surface adjacent to the front surface on the test piece 14 is characterized by:

The permeability of the rear surface opposite to the front surface on the test piece 14 is characterized by:

Among them, in the above three groups of formulas: K is the permeability, ΔP is the pressure difference between the center of the specimen and the end face of the measured permeability, ρ is the gas density, ε is the pore characteristic parameter of the specimen, μ is the gas viscosity, and Q is the fluid flow rate , H is the width of the cube specimen, _h1 is the length of the wellbore section, _h2 is the length of the perforation or the length of the open hole section, _{r e} is the radius of the circumscribed circle of the specimen (14), and rw is the outer diameter of the wellbore.

6) Observation of the results of the crack propagation experiment: unload the triaxial stress, take out the test piece 14 after fracturing, take pictures to record the crack propagation situation of the test piece 14, then cut the test piece 14, and take pictures to record the internal crack propagation situation of the test piece 14, The test is over.

7) The end of the experiment: the above experiment content is completed, and the experimental equipment is adjusted to the pre-experiment state according to the predetermined procedure.

The loading body of the present invention can realize the permeability test and quantitative characterization before and after the fracturing crack expansion experiment under the condition of in-situ in-situ stress, and solves the difficulty in the permeability test of large-size specimens under the condition of in-situ in-situ stress and the complicated collection of test gas. , the permeability problem before and after crack propagation cannot be well tested. At the same time, it solves the problem that the conventional test method cannot complete the permeability test of large dense specimens before the crack propagation test. The achievement of the invention provides a powerful means for quantitatively evaluating the experimental effect of crack propagation under different conditions.

The above-described embodiments describe only one or more embodiments of some of the present invention, but those skilled in the art will appreciate that the present invention may be embodied in many other forms without departing from the spirit and scope thereof. Accordingly, the examples and embodiments shown are to be regarded as illustrative and not restrictive, and various modifications are possible within the present invention without departing from the spirit and scope of the invention as defined by the appended claims. with replacement.

Claims (6)

1. a loading body for true triaxial crack propagation simulation and permeability synchronous experiment, is characterized in that, comprises: a loading frame body (2), a test piece (14) that is in the form of a cube as a whole is placed in the loading frame body (2); A feeding device (7) is provided on one side of the front end face of the loading frame (2), and the test piece (14) is fed into the loading frame (2) through the feeding device (7). internal; Multiple groups of pistons for loading the specimen (14) from the X direction, the Y direction and the Z direction of the loading frame body (2) respectively, and the multiple groups of pistons are connected to the loading frame body (14) from all directions respectively. 2) Seal, fix and pressurize between; A borehole is provided on the front surface of the test piece (14), and a wellbore for introducing permeability test gas or fracturing fluid into the test piece (14) is installed in the borehole; A backing plate is attached to the remaining five surfaces of the test piece (14) except the front surface, and a backing plate is provided on the backing plate for allowing the test piece (14) to flow to the test piece (14) during the permeability test. A ventilation structure for collecting the permeability test gas on the outer surface of the test piece (14); a gas collecting pipeline for collecting the permeability test gas collected by the ventilation structure is installed on the backing plate; the backing plate includes : A plurality of inner backing plates (25) are respectively attached to the remaining five surfaces of the test piece (14) except the front surface, and each of the inner backing plates (25) is provided with a a plurality of air passages for transmitting the permeability test gas flowing from the inside of the test piece (14) to the outer end face of the test piece (14); An outer backing plate (13) is attached to each of the inner backing plates (25), and the outer backing plate (13) is provided with communicating wire grooves and air collecting holes; One end of the gas collecting line is connected to the external manifold, and the other end extends into the gas collecting hole from the wire groove, and the permeability test gas transmitted by the plurality of air passages is collected in the gas collecting hole, and then passes through the gas collecting hole. The gas collecting line flows out to the external manifold; The ventilation structure includes the ventilation channel and the air collecting hole; the multiple ventilation channels provided on the inner backing plate (25) include: a plurality of first ventilation grooves (17) arranged along a first direction and a plurality of second ventilation grooves (18) arranged along a second direction, the first direction and the second direction being perpendicular; A ventilation hole (19) is provided at the intersection of the first ventilation groove (17) and the second ventilation groove (18); Neither the first ventilation groove (17) nor the second ventilation groove (18) is communicated with the side end surface of the inner backing plate (25); The air collecting holes provided on the outer backing plate (13) include: A first air collecting hole (11) is opened on the end surface of the outer backing plate (13) facing the inner backing plate (25), and the outer backing plate (13) is away from the inner backing plate (25) The second air collecting hole (12) opened on the end face of the air inlet; the first air collecting hole (11) is communicated with the second air collecting hole (12); The inner diameter of the first air-collecting hole (11) is smaller than the inner diameter of the second air-collecting hole (12), and the second air-collecting hole (12) is provided with an inner thread screwed with the air-collecting pipeline; The wire grooves provided on the outer backing plate (13) include: A first guide groove (9) provided on the end surface of the outer backing plate (13) away from the inner backing plate (25), and a second guide groove (9) provided on the side end surface of the outer backing plate (13) A groove (8), one end of the first guide groove (9) communicates with the second guide groove (8), and the other end communicates with the second air collecting hole (12). 2 . The loading body according to claim 1 , wherein a plurality of parallel-arranged specimen feeding slots are provided on the outer backing plate ( 13 ) provided on one side of the lower surface of the specimen ( 14 ). 3 . (10). 3. The loading body according to claim 1, wherein the wellbore comprises: a first wellbore section (20) and a second wellbore section (21) that are connected; A plurality of uniformly arranged annular grooves are provided on the outer circumferences of the first wellbore section (20) and the second wellbore section (21); The outer diameter of the first wellbore section (20) is greater than the outer diameter of the second wellbore section (21); The outer diameter of the second wellbore section is smaller than the hole diameter of the borehole in the test piece (14), and the outer diameter of the second wellbore section (21) and the borehole in the test piece (14) The difference between the hole diameters is between 1mm and 3mm. 4. The loading body according to claim 1, characterized in that, The test piece (14) is square; The annular gap between the wellbore and the borehole of the test piece (14) is sealed with annular resin; The twelve sides of the test piece (14) are sealed by a rubber mold with an integral structure, the inner backing plate (25) forms a support for the rubber mold, and the outer backing plate (13) is pressed against the outer backing plate (13). on the inner backing plate (25) and the rubber mold. 5. The loading body according to claim 1, wherein the loading body further comprises: a frame support frame (5) installed on the lower side of the loading frame (2); a slide rail (6) installed on one side of the front end face of the loading frame (2); The backing plate attached to the lower surface of the test piece (14) is placed on the feeding device (7), and the feeding device (7) is installed on the sliding rail (6) to move the The test piece (14) is sent into the inside of the loading frame (2); After the test piece (14) is fed into the loading frame (2), the feeding device (7) and the loading frame (2) are screwed and fixed, and the feeding The device (7) forms a seal with the first side end face of the loading frame (2). 6. A permeability test characterization method of a loading body as claimed in any one of claims 1 to 5, characterized in that, comprising: 1) Preparation of the test piece: according to the experimental requirements, make the test piece (14) that is in the form of a cube as a whole required for the experiment; 2) Triaxial stress loading: According to the triaxial stress conditions required by the experiment, the pistons in the three directions of X, Y and Z are controlled by hydraulic drive to achieve the required triaxial stress; 3) The permeability test before the crack propagation experiment: the overall permeability test of the test piece (14) is carried out by using the pulse permeability test method, and the overall permeability of the test piece (14) is characterized as:

After the overall permeability test is completed, a single-sided permeability test is performed on the test piece (14); wherein, the upper surface, the lower surface, the left surface and the right surface of the test piece (14) adjacent to the front surface are The permeability of any one of the surfaces is characterized by:

The permeability of the rear surface opposite to the front surface on the test piece (14) is characterized by:

Among them, in the above three groups of formulas: K is the permeability, β is the gas compressibility coefficient, α is the fitting value, μ is the gas viscosity, r _e is the radius of the circumscribed circle of the specimen (14), r _w the outer diameter of the wellbore, h ₂ is the perforation length or the length of the open hole section, t is the test time, P _u,0 is the initial pressure in the upstream chamber, P _d,0 is the initial pressure in the downstream chamber, P _u is the end pressure of the experiment in the upstream chamber, P _d end pressure of the experiment in the downstream chamber; 4) Carry out the fracture propagation experiment: according to the pre-planned pump injection procedure, pump the fracturing fluid into the test piece (14) through the wellbore, and stop pumping the fracturing fluid until the test piece (14) is completely fractured; 5) Permeability test after the crack propagation experiment: The overall permeability test of the cracked test piece (14) is carried out by using a conventional permeability test method, and the overall permeability of the test piece (14) is characterized as:

After the overall permeability test is completed, the single-sided permeability test is performed on the cracked test piece (14); wherein, the upper surface, the lower surface, the left surface and the adjacent front surface of the test piece (14) The permeability of any one of the right surfaces is characterized by:

The permeability of the rear surface opposite to the front surface on the test piece (14) is characterized by:

Among them, in the above three groups of formulas: K is the permeability, ΔP is the pressure difference from the center of the specimen to the end face of the measured permeability, ρ is the gas density, ε is the pore characteristic parameter of the specimen, μ is the gas viscosity, and Q is the fluid flow rate , H is the width of the cube specimen, _h1 is the length of the wellbore section, h2 is the length of the perforation or open _- hole section, _{r e} is the radius of the circumscribed circle of the specimen (14), and rw is the outer diameter of the wellbore; 6) Observation of the results of the crack propagation experiment: unload the triaxial stress, take out the test piece (14) from the experimental loading body, and describe the crack development of the test piece (14) for the crack propagation test according to predetermined requirements; 7) The end of the experiment: the above experiment content is completed, and the experimental equipment is adjusted to the pre-experiment state according to the predetermined procedure.

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