CN111472741A - Experimental method for researching rock fracturing multi-crack propagation rule by using volume expansion material - Google Patents
Experimental method for researching rock fracturing multi-crack propagation rule by using volume expansion material Download PDFInfo
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- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
- E21B43/25—Methods for stimulating production
- E21B43/26—Methods for stimulating production by forming crevices or fractures
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
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Abstract
The invention discloses an experimental method for researching a rock fracturing multi-crack propagation rule by using a volume expansion material, which comprises the following steps: preparing a fracturing sample by adopting a rock-like material, and embedding a pressure sensor in the fracturing sample; drilling two drill holes with the same diameter and depth around the central axis of the fracturing sample; installing a plurality of acoustic emission probes along the diagonal line of the fracturing sample, and placing a thermal imager on one side of the fracturing sample; arranging pressing plates around the fracturing sample, and applying confining pressure to the fracturing sample by using a ground stress loading and control system; filling an expansion material into a drill hole of the fracturing sample, and performing a fracturing experiment; and after the fracturing experiment is finished, carrying out experiment post-treatment and data arrangement.
Description
Technical Field
The invention relates to the technical field of deep unconventional energy exploitation experiments, in particular to an experiment method for simulating the influence of a fracturing mode on the rock hydraulic fracture expansion form under a multi-cluster perforation condition by adopting a volume expansion material.
Background
The information in this background section is only for enhancement of understanding of the general background of the invention and is not necessarily to be construed as an admission or any form of suggestion that this information forms the prior art that is already known to a person of ordinary skill in the art.
Nowadays, the world faces a severe situation that conventional resources are gradually exhausted and the energy demand is gradually increased, and many countries expand to the more modern energy resource field by expanding exploration and exploitation of unconventional energy such as coal bed gas, shale gas and the like and gradually improve the consumption proportion of clean energy. The unconventional energy is mostly generated in a compact reservoir, is influenced by the buried depth and lithology, and has low reservoir permeability, so that the exploitation and utilization of the unconventional energy are hindered.
The horizontal well section multi-cluster synchronous fracturing technology is a key technology for low-permeability oil and gas production increase and enhanced geothermal system development at present. Through carrying out many clusters of perforation in same fracturing section, once only press open a plurality of cracks, and then improve reservoir permeability, increase reservoir transformation volume, reduce fracturing time and construction cost. The goal of the transformation of multiple clusters of fractures is to simultaneously form a series of dense and multiple hydraulic fracture networks extending in the direction of maximum principal stress to increase the fluid exchange efficiency. However, field operations have shown that the effect of multiple clusters of hydraulic fracturing in horizontal intervals is often not very significant. The data found show that 30% or more of the cracks do not reach the designed production effect. In the process of hydraulic fracture propagation, the initiation, extension, steering and penetration of hydraulic fractures are influenced by multiple factors such as lithology, formation conditions, ground stress level, fracturing parameters and the like. It is generally believed that during synchronous propagation of multiple fractures, the mutual interference between adjacent fractures causes some of the fractures to lose propagation stability. As a key technology for reservoir transformation, the hydraulic fracturing fracture expansion geometric form is the key for evaluating the reservoir transformation effect. However, due to excessive reservoir burial depth, it is difficult to observe the propagation and extension morphology and interaction mechanisms of multiple fractures. Limited by the state of the art, current understanding of fracturing models for multiple fractures still lacks accurate knowledge
To date, scholars at home and abroad have conducted a large number of experiments around the aspects of the size of a drilled hole, the external environment, the characteristics of reservoir rock and the like by using a non-explosive expanding agent to simulate the influence of a hydraulic fracturing technology on the expansion form of the reservoir rock fracture and the fracturing yield-increasing effect, and have achieved certain results. Studies have shown that different fracturing patterns and drilling designs will have a significant impact on fracture geometry and impact ultimate energy recovery. By adopting reasonable drilling arrangement and fracturing mode design, the influence of stress shadow effect among fractures can be effectively reduced, the expansion and communication of the fractures are facilitated, the permeability of reservoir rock is improved, and the oil gas yield is promoted to be larger. The inventor finds relevant work of simulating the rock fracturing problem of a reservoir by utilizing a swelling agent through analyzing and summarizing relevant documents of conventional hydraulic fracturing on fracturing modes and drilling hole design, and the following three problems are needed to be researched and solved further:
1. the volume expansion fracturing experiment of reservoir rock developed by using the expanding agent is used for researching the single fracture expansion rule by injecting the expanding agent into a single hole, and the research on the interaction mechanism between fractures in a multi-cluster fracture initiation expansion mode and expansion is still to be further developed.
2. In the process of a hydraulic fracturing indoor experiment, because the crack propagation speed is too high, the hydraulic fracturing experiment is mainly focused on researching the crack initiation and propagation rule of a single crack, and the research on the crack initiation and propagation form of multiple cracks and the mutual influence among the cracks is less developed. A few experimental researches on hydraulic fracturing multi-fracture are based on synchronous fracturing, and the influence of other fracturing modes such as sequential fracturing on fracture expansion morphology and interaction mechanism is difficult to simulate.
3. The existing understanding of the fracture expansion form and the mutual influence mechanism of multiple fractures in different fracturing modes is based on numerical simulation or theoretical analysis. And hydraulic fracturing experimental research surrounding multiple fractures in different fracturing modes is less developed, so that the theoretical model is difficult to verify or the numerical model is difficult to calibrate.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention aims to provide an experimental method for researching the rock fracturing multi-crack propagation rule by using a volume expansion material.
In order to achieve the above object, one or more embodiments of the present invention disclose the following technical solutions:
an experimental method for researching a rock fracturing multi-crack propagation rule by using a volume expansion material comprises the following steps:
preparing a fracturing sample by adopting a rock-like material, and embedding a pressure sensor in the fracturing sample;
drilling two drill holes with the same diameter and depth around the central axis of the fracturing sample;
installing a plurality of acoustic emission probes along the diagonal line of the fracturing sample, and placing a thermal imager on one side of the fracturing sample;
arranging pressing plates around the fracturing sample, and applying confining pressure to the fracturing sample by using a ground stress loading and control system;
filling an expansion material into a drill hole of the fracturing sample, and performing a fracturing experiment;
and after the fracturing experiment is finished, carrying out experiment post-treatment and data arrangement.
Compared with the prior art, the above one or more embodiments of the present invention achieve the following beneficial effects:
1. in the experimental method, an expanding agent injection experiment in two drill holes is used as a support, design factors such as the distance between the two drill holes and the arrangement of the drill holes are used as variable researches, and a multi-crack initiation and propagation mode and an interaction mechanism under the condition of multi-cluster-jet holes are quantitatively analyzed and researched to determine design parameters such as the optimal drill hole distance and the optimal drill hole arrangement. The experimental design can effectively fill the defects of the multi-crack form experimental research of the existing hydraulic fracturing under the condition of multi-cluster perforation, and provides experimental basis for deeply knowing the multi-cluster crack initiation and expansion mode and the interaction mechanism among the cracks in expansion.
2. The fracturing physical experiment carried out by using the expanding agent has enough time and opportunity to observe the damage phenomenon and action mechanism of a plurality of clusters of cracks because the reaction time of the expanding agent is longer than the time of hydraulic fracturing damage. The invention designs two different static fracturing modes of sequential fracturing and synchronous fracturing to research the initiation expansion mode and the interaction mechanism of the multi-cluster fracture in different fracturing modes, solves the problem that the hydraulic fracturing experiment is difficult to simulate the interaction mechanism of the multi-cluster fracture in different fracturing modes, and provides experimental support for deeply mastering the action rule of the multi-cluster fracture in different fracturing modes.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description serve to explain the invention and not to limit the invention.
FIG. 1 is a flow chart of a method of fracturing with a swelling agent in different fracturing modes in accordance with an embodiment of the present invention;
FIG. 2 is a schematic diagram of the arrangement of the drill holes in the test piece body according to an embodiment of the invention;
FIG. 3 is a schematic view of the arrangement of the drill holes in the perspective of the test piece according to an embodiment of the present invention;
FIG. 4 is a schematic view of the spatial arrangement of an acoustic emission probe according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of the ground stress loading according to the embodiment of the present invention.
In the figure, 1-fracturing test piece, 2-drilling, 3-acoustic emission probe, 4-sigma1Maximum horizontal principal stress, 5-sigma2At minimum level principal stress, 6-sigma3Is the vertical principal stress.
Detailed Description
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.
An experimental method for researching a rock fracturing multi-crack propagation rule by using a volume expansion material comprises the following steps:
preparing a fracturing sample by adopting a rock-like material, and embedding a pressure sensor in the fracturing sample;
drilling two drill holes with the same diameter and depth around the central axis of the fracturing sample;
installing a plurality of acoustic emission probes along the diagonal line of the fracturing sample, and placing a thermal imager on one side of the fracturing sample;
arranging pressing plates around the fracturing sample, and applying confining pressure to the fracturing sample by using a ground stress loading and control system;
filling an expansion material into a drill hole of the fracturing sample, and performing a fracturing experiment;
and after the fracturing experiment is finished, carrying out experiment post-treatment and data arrangement.
Due to the fact that the mechanical properties of reservoir rock are greatly different, a control experiment aiming at the influence of a certain factor is difficult to effectively develop. In order to avoid experimental errors caused by the heterogeneity of reservoir rocks, the invention adopts rock-like materials to carry out physical fracturing experiments. In addition, the fracturing experiment based on the original rock is difficult to monitor the mechanical response in the rock in the fracturing process, and the analysis and the research on the fracture propagation mechanism are limited. Therefore, the crack initiation and propagation rule of the crack can be more effectively mastered by adopting the rock-like material. According to the main mechanical parameters of reservoir rock and the proportioning requirement made by referring to rock-like materials, prefabricating rock-like test pieces with corresponding sizes; after demolding and maintaining of the rock-like test piece are completed, main mechanical parameters such as uniaxial compressive strength, tensile strength, elastic modulus, Poisson's ratio and the like of the rock-like test piece are measured, whether the mechanical parameters meet the experimental requirements or not is verified through comparison, and finally a sample close to the mechanical parameters of the reservoir rock is selected and used for a fracturing physical experiment.
And arranging measuring elements such as strain rosettes on the surface of the sample to measure the strain condition of the sample.
In some embodiments, the rock-like material is composed of the following components in parts by weight:
1 part of cement, 2-3 parts of sand, 0.4-0.6 part of water and 0.003-0.005 part of polycarboxylic acid water reducing agent.
In some embodiments, the fracture sample is a cubic structure.
In some embodiments, the pressure sensor is a miniature pressure cell. When preparing the rock-like test piece, a micro pressure box is arranged in the test piece in advance to record the expansion stress change generated by chemical reaction in the fracturing experiment process.
In some embodiments, the ratio of the diameter of the borehole to the side length of the fractured sample is 1:3 to 5 and the ratio of the depth of the borehole to the side length of the fractured sample is 0.5 to 0.8: 1.
Further, the ratio of the depth of the drilled hole to the side length of the fractured sample is 0.7: 1.
According to the description of the design parameters such as the size and the depth of the drilled hole in the related literature and the combination of the practical requirements of the physical fracturing experiment of the expanding agent, the drilling design method of the large sample and the small drilled hole can be adopted, so that the boundary effect influence of the test piece can be effectively reduced, and the reliability of the experimental result is improved. Firstly, using a symmetry principle to drill two drill holes with proper sizes and depths around the center point of a sample by using a core drill, wherein the drilling depth is preferably seventy percent of the height of the sample.
In the experiment, factors such as the distance between two drilling holes can be used as variables for research, the expanding agent is injected into the two holes, and the multi-crack initiation and propagation mode and the interaction mechanism under the multi-perforation condition are qualitatively analyzed in a planar state so as to determine the optimal drilling distance, the optimal drilling arrangement and other design conditions.
Furthermore, after drilling is finished, cleaning tools are adopted to clean sundries such as rock debris and the like remained in the drilled holes, so that the final experiment result and analysis are prevented from being adversely affected.
In some embodiments, the thermal imager is placed at 0.4-0.6m of one side of the sample, and the thermal imager and the sample form an included angle of 40-50 degrees.
Furthermore, the thermal imager is connected with the thermal image processing system. The temperature of the test sample was monitored for changes using infrared thermography.
In some embodiments, a soft rubber pad is disposed between the fracturing sample and the platen. The stress of the test piece can be ensured to be uniform.
In some embodiments, the fracturing sample is filled with a swelling material in the drilled hole, and the swelling material is filled in a sequential fracturing and synchronous fracturing.
The filling method of the two expansion materials is designed to simulate two different fracturing modes of sequential fracturing and synchronous fracturing, is used for researching the initiation and expansion modes and interaction mechanisms of multiple fractures in different fracturing modes, and analyzes the influence of the initiation and expansion modes on the fracturing effect of reservoir rock. A synchronous fracturing mode, namely, injecting a swelling agent into two pre-drilled drill holes simultaneously; and (3) a fracturing mode of sequential fracturing, namely, injecting an expanding agent into one pre-drilled drill hole, injecting an expanding agent into the other drill hole after the expanding agent in the first drill hole reacts for a period of time, wherein the injection time difference of the expanding agents in the two drill holes can be adjusted to represent the influence of interference stress fields with different degrees on the expansion rule among fractures.
The experimental research of the fracturing of the expanding agent surrounding the multiple fractures in different fracturing modes is developed, the fracture initiation and expansion rules and the mutual influence mechanism of the multiple fractures in different fracturing modes are disclosed, and experimental basis is provided for theoretical model verification and parameter calibration of a numerical model.
Further, the expansion material is calcium oxide, ferric oxide, silicon dioxide and aluminum oxide.
The expansion material is a gel compound, and after being mixed with water, the expansion material undergoes a chemical reaction, so that the microscopic volume is increased. As the reaction proceeds, the limited space in the space is gradually filled, and expansion pressure is generated toward the boundary of the space, thereby destroying the rock by the expansion pressure generated by the volume expansion.
The amount of the expanding agent and the water can be mixed according to the manufacturer's recommendation, and the expanding agent after being uniformly mixed and stirred is immediately poured into the pre-drilled holes.
Further, the ambient temperature during the experiment was controlled at 18.5-21.5 ℃.
In some embodiments, the post-experimental data processing includes at least one of:
observing the geometric size and the number of the cracks, and evaluating the number and the size of the caving rock debris;
calculating fractal dimension and fracture density;
quantifying the geometric shape of the crack by representing the fractal dimension and the crack density of the fracture surface, and quantitatively describing the induction behavior of the crack;
analyzing the influence of temperature on the volume expansion fracturing effect of reservoir rock in the reaction process of the expanding agent and water by utilizing a sample temperature change value obtained by an infrared thermal imaging technology;
analyzing the induced stress evolution law and rock mass deformation characteristics in the reservoir rock in the crack initiation and propagation process by using measuring elements distributed in the sample and on the bottom surface;
recording parameters and waveforms of acoustic emission events by using an acoustic emission probe, and positioning the crack in real time;
and adding a red tracer into the water to observe the crack on the surface of the model body and the crack propagation condition inside the model body.
In some embodiments, the method further comprises the step of correcting the theoretical model and the numerical model by using experimental data of the above experimental method.
Designing a corresponding fracturing physical experiment of the swelling agent by referring to the actual conditions of a theoretical model and a numerical model in a horizontal well section multi-cluster hydraulic fracturing experiment, comparing and verifying the obtained fracturing experiment result of the swelling agent with the simulation results of the theoretical model and the numerical model by adopting similar fracturing physical parameters, calibrating the theoretical model and the numerical model which do not accord with the experiment result, and finally determining the qualified theoretical model and the qualified numerical model. By means of correct numerical simulation and theoretical analysis models, the expansion rule and the communication condition of multiple clusters of fractures in a synchronous fracturing and sequential fracturing mode are further clarified, the microscopic mechanism of mutual influence among the fractures is disclosed, and scientific basis is provided for design and construction of hydraulic fracturing schemes in China.
Examples
As shown in fig. 1, an experimental method for researching the propagation law of multiple fractures in rock fracturing by using a volume expansion material comprises the following steps:
step 1: selection of swelling agent
According to the temperature change condition of the site fracturing operation, measuring and controlling the temperature of a laboratory to be within the temperature change range of the site fracturing operation, and selecting the type of the expanding agent adaptive to the temperature. During the whole experiment period, the experiment should be carried out in a temperature-controllable environment, and the engineering normal temperature (20 ℃) is adopted as the standard experiment temperature in the embodiment.
Step 2: sample preparation
According to the matching requirement of rock-like materials made from simulated reservoir rock, the material matching ratio is that cement and sand are 1: 2.5, water and cement are 0.5, and polycarboxylic acid water reducing agent and cement are 0.004; prefabricating a cubic rock test piece with the side length of 250mm in a prefabricated mould, and using the test piece as a static fracturing experiment; pouring a cubic rock test piece with the side length of 70mm in a prefabricated mould, carrying out variable-angle compression shearing on the cubic rock test piece to obtain an internal friction angle and cohesive force of the rock test piece, sticking a strain gauge on the test piece, and carrying out uniaxial compression on the test piece to obtain the elastic modulus, Poisson ratio and uniaxial compressive strength of the material; and pouring a cylindrical test piece with the diameter of 50mm and the height of 50mm in the prefabricated mould, and carrying out Brazilian splitting experiment on the test piece to obtain the tensile strength of the material. And (3) placing the sample in a mold for 24 hours, demolding, curing for 28 days under the conditions of standard constant temperature and constant humidity (the relative humidity is more than 95 percent and the temperature is 20 +/-1.5 ℃), and then polishing the surface of the test piece. And selecting a rock-like sample with mechanical property similar to that of the reservoir rock for a fracturing physical experiment. During the preparation process of the rock-like test piece, a miniature pressure box is prefabricated in the interior of the test piece in advance.
And step 3: sample drilling and drilling arrangement
Firstly, a core drill is used to drill holes with the diameter of 20mm and the depth of 180mm around the two sides of the center point of the test piece, the distance between the two holes and the center point of the test piece is the same and the two holes are symmetrical, and the layout schematic diagram of the holes in the embodiment is shown in fig. 2. And then cleaning debris such as rock debris and the like in the drilled hole by using a cleaning tool.
And 4, step 4: monitoring equipment installation
The 12 acoustic emission probes are arranged and mounted along the diagonal of the surface of the test piece 6, and fig. 4 is a schematic spatial arrangement diagram of the acoustic emission probes according to the embodiment. When the acoustic emission system is connected correctly, the threshold value is set to be 40 decibels, the sampling frequency is 1 megahertz, and parameters and waveforms of acoustic emission events are recorded. And the thermal imager is placed at the position 0.5m in front of the sample, forms an included angle of 45 degrees with the sample, is connected with the thermal image processing system, and monitors the temperature change of the sample by using an infrared thermal imaging technology. And arranging strain flowers and other measuring elements on the surface of the sample.
And 5: simulated ground stress loading
Square pressing plates are arranged around the test piece, and a soft rubber pad is arranged between the test piece and the pressing plates. And (3) setting the maximum horizontal principal stress to be 10MPa, the vertical principal stress to be 8MPa and the maximum horizontal principal stress to be 6MPa by combining the simulated ground stress loading condition of the fracturing experiment and the on-site actual stress condition of reservoir rock, and applying confining pressure to the periphery of the sample by using a ground stress loading and control system. Fig. 5 is a schematic diagram of the ground stress loading of the present embodiment.
Step 6: pack design under different fracturing modes
The different fracturing modes are divided into a fracturing mode of synchronous fracturing and a fracturing mode of sequential fracturing.
The fracturing mode of synchronous fracturing is to inject the expanding agent into two pre-drilled boreholes simultaneously.
The fracturing mode of sequential fracturing is that a pre-drilled drill hole is injected with a swelling agent, and after the swelling agent in the first drill hole reacts for 30min, 1h, 2h, 6h and 12h respectively, the swelling agent is injected into the other drill hole.
The slurry of the expanding agent is poured into the pre-drilled holes immediately after being mixed and stirred evenly.
And 7: experimental post-processing and data interpretation
And (5) finishing and maintaining the experimental equipment after the fracturing experiment is finished. And taking out the test piece, observing and evaluating the quantity and size of the collapsed rock debris, and calculating the fractal dimension and the fracture density as a part of image and acoustic emission data analysis and post-processing. And characterizing the fractal dimension and the crack density of the fracture surface to quantify the crack geometric shape and quantitatively describe the crack induction behavior. And recording the temperature change value of the sample obtained by the infrared thermal imaging technology, and analyzing the influence of the temperature on the fracturing effect of the reservoir rock in the reaction process of the expanding agent and the water. And analyzing the induced stress evolution law and rock mass deformation characteristics in the reservoir rock in the crack initiation and propagation process by utilizing the measuring elements such as the miniature pressure boxes, the strain rosettes and the like distributed in the sample and on the bottom surface. And recording parameters and waveforms of the acoustic emission events by using the acoustic emission probe, and positioning the actions of crack initiation, crack expansion and the like in real time. The crack propagation on the surface and inside of the model body was observed by adding a red tracer to the water. And recording, sorting and contrastively analyzing the detailed information about the fracture parameters obtained under different fracturing modes and other conditions by using a measuring element and equipment.
And 8: theoretical model validation and numerical model parameter calibration
Designing a corresponding fracturing physical experiment of the swelling agent by referring to the actual conditions of a theoretical model and a numerical model in a horizontal well section multi-cluster hydraulic fracturing experiment, comparing and verifying the obtained fracturing experiment result of the swelling agent with the simulation results of the theoretical model and the numerical model by adopting similar fracturing physical parameters, calibrating the theoretical model and the numerical model which do not accord with the experiment result, and finally determining the qualified theoretical model and the qualified numerical model.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. An experimental method for researching the rock fracturing multi-crack propagation rule by using a volume expansion material is characterized in that: the method comprises the following steps:
preparing a fracturing sample by adopting a rock-like material, and embedding a pressure sensor in the fracturing sample;
drilling two drill holes with the same diameter and depth around the central axis of the fracturing sample;
installing a plurality of acoustic emission probes along the diagonal line of the fracturing sample, and placing a thermal imager on one side of the fracturing sample;
arranging pressing plates around the fracturing sample, and applying confining pressure to the fracturing sample by using a ground stress loading and control system;
filling an expansion material into a drill hole of the fracturing sample, and performing a fracturing experiment;
and after the fracturing experiment is finished, carrying out experiment post-treatment and data arrangement.
2. The experimental method for researching the rock fracturing multi-fracture propagation law by using the volume expansion material as claimed in claim 1, is characterized in that: the rock-like material comprises the following components in parts by weight:
1 part of cement, 2-3 parts of sand, 0.4-0.6 part of water and 0.003-0.005 part of polycarboxylic acid water reducing agent.
3. The experimental method for researching the rock fracturing multi-fracture propagation law by using the volume expansion material as claimed in claim 1, is characterized in that: the fracturing sample is of a cubic structure.
4. The experimental method for researching the rock fracturing multi-fracture propagation law by using the volume expansion material as claimed in claim 1, is characterized in that: the pressure sensor is a miniature pressure cell.
5. The experimental method for researching the rock fracturing multi-fracture propagation law by using the volume expansion material as claimed in claim 1, is characterized in that: the ratio of the diameter of the drilled hole to the side length of the fracturing sample is 1:3-5, and the ratio of the depth of the drilled hole to the side length of the fracturing sample is 0.5-0.8: 1;
further, the ratio of the depth of the drilled hole to the side length of the fracturing sample is 0.7: 1;
further, after the drilling is finished, the method also comprises the step of cleaning rock debris remained in the drilled hole by using a cleaning tool.
6. The experimental method for researching the rock fracturing multi-fracture propagation law by using the volume expansion material as claimed in claim 1, is characterized in that: the thermal imager is arranged at a position of 0.4-0.6m on one side of the sample, and the included angle between the thermal imager and the sample is 40-50 degrees;
furthermore, the thermal imager is connected with the thermal image processing system. The temperature of the test sample was monitored for changes using infrared thermography.
7. The experimental method for researching the rock fracturing multi-fracture propagation law by using the volume expansion material as claimed in claim 1, is characterized in that: and a soft rubber pad is arranged between the fracturing sample and the pressing plate.
8. The experimental method for researching the rock fracturing multi-fracture propagation law by using the volume expansion material as claimed in claim 1, is characterized in that: filling an expansion material into a drilled hole of a fracturing sample, wherein the filling mode of the expansion material comprises sequential filling fracturing and synchronous filling fracturing when a fracturing experiment is carried out;
further, the expansion material is calcium oxide, ferric oxide, silicon dioxide or aluminum oxide;
further, the ambient temperature during the experiment was controlled at 18.5-21.5 ℃.
9. The experimental method for researching the rock fracturing multi-fracture propagation law by using the volume expansion material as claimed in claim 1, is characterized in that: and (3) processing data after the experiment, wherein the data at least comprises one of the following steps:
observing the geometric size and the number of the cracks, and evaluating the number and the size of the caving rock debris;
calculating fractal dimension and fracture density;
quantifying the geometric shape of the crack by representing the fractal dimension and the crack density of the fracture surface, and quantitatively describing the induction behavior of the crack;
analyzing the influence of temperature on the volume expansion fracturing effect of reservoir rock in the reaction process of the expanding agent and water by utilizing a sample temperature change value obtained by an infrared thermal imaging technology;
analyzing the induced stress evolution law and rock mass deformation characteristics in the reservoir rock in the crack initiation and propagation process by using measuring elements distributed in the sample and on the bottom surface;
recording parameters and waveforms of acoustic emission events by using an acoustic emission probe, and positioning the crack in real time;
and adding a red tracer into the water to observe the crack on the surface of the model body and the crack propagation condition inside the model body.
10. The experimental method for researching the rock fracturing multi-fracture propagation law by using the volume expansion material as claimed in claim 1, is characterized in that: the method also comprises the step of correcting the theoretical model and the numerical model by adopting the experimental data of the experimental method.
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