Hot dry rock temporary plugging material optimization screening method based on multi-parameter coupling model

Abstract

The invention relates to the technical field of oil exploration and development, and discloses a hot dry rock temporary plugging material optimization screening method based on a multi-parameter coupling model. The method comprises the steps of temporary plugging material data set formation, high-temperature aging experiment, compression resistance test, three-dimensional finite element model construction, force chain structure evolution analysis, indoor crack plugging experiment verification, shear stability evaluation and multi-parameter comprehensive evaluation. According to the method, multi-dimensional parameters such as high-temperature aging, dynamic shear stability and particle matching are integrated, numerical simulation and experimental verification are combined, high-precision and high-efficiency screening of the temporary plugging material is achieved, the problems of single index limitation and environment distortion of a traditional method are solved, scientific and reliable technical support is provided for hot dry rock development, and the method has a wide application prospect. And the problems in the background technology can be effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of petroleum exploration and development, in particular to a method for optimizing and screening hot dry rock temporary plugging materials based on a multi-parameter coupling model. Background Art

[0002] Hot dry rock, a geothermal resource with enormous potential, is typically found thousands of meters underground. Its reservoir geology is more complex than that of conventional oil and gas and medium- and low-temperature geothermal reservoirs, characterized by "four highs": high temperature (>180°C), high hardness, high stress, and high density. These characteristics pose severe challenges to the key aspects of hot dry rock geothermal extraction, such as drilling and well construction, fracturing and reservoir creation, and fluid heat extraction. Taking drilling as an example, reaching the reservoir and forming a stable wellbore are prerequisites for resource development. However, high-temperature environments can significantly degrade the rheology and stability of the drilling fluid system. Furthermore, the widespread development of fractures and faults in the formation can easily lead to severe drilling fluid losses, which not only reduces extraction efficiency but also significantly increases the risk of underground accidents such as wellbore collapse and blowouts. Therefore, how to effectively seal fractures under high-temperature and high-pressure conditions has become one of the core challenges restricting the development of hot dry rock resources.

[0003] In the process of crack plugging, the pressure-bearing stability of the microscopic force chain network of the plugging layer is the key to determining the success or failure of the plugging. Macroscopically, the plugging layer is composed of aggregates of temporary plugging material particles, and its mechanical properties directly affect the plugging strength; microscopically, the particles form a force chain network through contact and extrusion to support the external load; microscopically, the performance parameters of the temporary plugging material (such as friction coefficient and compressive strength) determine the strength and stability of the force chain network. However, the high temperature and high pressure environment of the hot dry rock reservoir will cause the temporary plugging material to age rapidly (such as thermal decomposition and particle crushing), further aggravating the degradation of the mechanical properties of the plugging layer. Studies have shown that the plugging layer may experience friction instability, composite instability or shear dislocation instability under load, leading to plugging failure. Therefore, there is an urgent need for a method that can accurately characterize the mechanical behavior of temporary plugging materials under complex working conditions in order to optimize material selection.

[0004] Currently, the selection of dry hot rock temporary plugging materials mainly relies on empirical trial and error, that is, by repeatedly adjusting the material ratio, shape and particle size, and conducting indoor experimental verification. For example, existing technologies (such as patent application number 202010002091.8) use photoelastic testing methods to evaluate the material's pressure bearing capacity by analyzing the photoelastic image and load curve of the plugging layer under stress. However, this method has significant drawbacks:

[0005] (1) Insufficient environmental simulation: Traditional photoelastic experiments do not perform high-temperature aging treatment on temporary plugging materials, and cannot reflect the performance degradation of materials under actual working conditions, resulting in a large deviation between experimental results and engineering applications;

[0006] (2) Single material type: Experiments mostly use temporary plugging materials with uniform shape and particle size, which makes it difficult to simulate the complex force chain network formed by the mixing of multiple types of particles, and the theoretical basis is weak;

[0007] (3) Lack of dynamic response: Photoelastic experiments mainly focus on static stress distribution and cannot capture the force chain evolution law of the plugging layer under dynamic shear load, making it difficult to fully evaluate the shear stability.

[0008] Furthermore, existing methods rely on extensive physical experiments, resulting in long development cycles and high costs. Furthermore, it is difficult to quantify the impact of parameters such as particle shape and friction coefficient on the stability of the plugging layer. To address these issues, a temporary plugging material screening method that can couple multi-scale simulation, dynamic analysis, and high-temperature aging is urgently needed to improve the scientificity, efficiency, and reliability of material selection. Summary of the Invention

[0009] The technical problem to be solved by the present invention is: to overcome the shortcomings of the existing technology and provide an optimization screening method for hot dry rock temporary plugging materials based on a multi-parameter coupling model. By integrating multi-dimensional parameters such as high-temperature aging, dynamic shear stability and particle matching, combined with numerical simulation and experimental verification, high-precision and high-efficiency screening of temporary plugging materials can be achieved, breaking through the single indicator limitations and environmental distortion problems of traditional methods, providing scientific and reliable technical support for hot dry rock development, and can effectively solve the problems in the background technology.

[0010] The technical solution adopted by the present invention to solve its technical problem is:

[0011] A method for optimizing and screening temporary plugging materials for hot dry rock based on a multi-parameter coupling model specifically comprises the following steps:

[0012] Step S1, forming a temporary plugging material data set: polycarbonate and thermosetting resin are selected as base materials, photoelastic rubber particles and synthetic soft fibers are added to prepare temporary plugging materials with various proportions, and the temporary plugging materials with various proportions form a data set;

[0013] Step S2, high-temperature aging experiment: Simulating the high-temperature and high-pressure environment of hot dry rock formations, the temporary plugging materials in the data set are subjected to high-temperature aging treatment, and the basic characteristic parameters before and after aging are recorded, including mass loss rate, particle size degradation rate, compressive breakage rate, friction coefficient change, and fracture strength retention rate;

[0014] Step S3, compressive strength test: testing the compressive strength change of the temporary plugging material after high temperature aging in a simulated high temperature and high pressure crack plugging environment;

[0015] Step S4, constructing a three-dimensional finite element model: Based on the actual size of the crack plugging layer, a three-dimensional finite element model of the temporary plugging material particles is established, the material constitutive relationship, contact conditions and boundary constraints are defined, and the mechanical response under shear load and confining pressure is simulated;

[0016] Step S5, force chain structure evolution analysis: using finite element analysis software, simulate the stress distribution and contact force network between the temporary plugging material particles, extract stress concentration data and contact force chain evolution law in key areas, optimize the shape, particle size distribution and friction coefficient of the temporary plugging material, and make the main chain develop along the shear direction;

[0017] Step S6, indoor crack plugging test verification: Based on the finite element analysis results, select temporary plugging materials for indoor testing, and record the failure mode and plugging effect of the plugging layer under load;

[0018] Step S7, shear stability evaluation: Count the ratio of the number of broken contact force chains to the total number of force chains in the finite element model, and calculate the shear stability index Lu;

[0019] Step S8, multi-parameter comprehensive evaluation: Based on the formula: The comprehensive evaluation formula is:

[0020]

[0021] in The basic performance index of the material, P i is the performance index of the material; ω i The importance weights are assigned based on the importance of different experimental indicators;

[0022] in The term represents the volume change effect of the temporary plugging material under high temperature aging, and k is the influence coefficient of the high temperature aging effect; is the volume change rate of the temporary plugging material during high-temperature aging;

[0023] in The term represents the structural optimization of the crack plugging layer, d is the particle size of the temporary plugging material; d opt is the optimal value of the particle size of the plugging layer in the experiment, usually half of the crack width; σ d is the standard deviation of particle size distribution, reflecting the influence of particle uniformity;

[0024] Among them L u The term characterizes the uniformity of the force chain network, which is the ratio of the number of strong force chains to the total number of force chains and is measured by step S7.

[0025] Furthermore, in step S1, in the temporary plugging material of the temporary plugging material data set, the mass percentage of rubber particles is 5-20%, the fiber length of the synthetic soft fiber is 0.5-2.5 mm, and the width of the covered crack is 1-5 mm.

[0026] Specifically, in step S1, polycarbonate and thermosetting resin are selected as the base material, mainly because they can still maintain excellent mechanical strength and chemical stability at high temperatures (>180°C), avoiding failure of the plugging layer due to thermal decomposition. The addition of photoelastic rubber particles can enhance the elastic recovery ability of the material to cope with deformation under dynamic loads; the synthetic soft fiber material forms a three-dimensional network structure through interweaving to improve the shear resistance of the plugging layer. By adjusting the ratio (rubber particles account for 5-20%, fiber length 0.5-2mm), more than one differentiated material combination is formed to cover different crack widths and stress conditions.

[0027] More specifically, the multi-ratio design meets the needs of complex crack sealing; the base material selection ensures the long-term stability of the material in a hot dry rock environment; and the fiber and rubber synergistically enhance the mechanical properties of the plugging layer.

[0028] Furthermore, in step S2, the high temperature aging condition is 220°C and 15 MPa for 24 hours, and the material needs to be dried and sieved after aging.

[0029] Furthermore, the optimal particle size d of the material particles is opt It is 1 / 2 to 2 / 3 of the crack width.

[0030] Specifically, in step S2, the high-temperature aging experiment utilizes a custom-built high-temperature autoclave with precisely controlled temperature (220±5°C) and pressure (15MPa) to simulate the actual operating conditions of hot dry rock reservoirs. After aging, the material is screened and dried, and key parameters such as mass loss (reflecting the degree of thermal decomposition) and particle size degradation (assessing the risk of particle breakage) are quantified. Surface microcracks are observed using a scanning electron microscope (SEM) to comprehensively assess the impact of aging on the material's microstructure.

[0031] More specifically, high temperature and high pressure conditions are close to actual working conditions, avoiding the "idealization" deviation of traditional experiments; combining macroscopic performance and microscopic morphology analysis, the material life can be accurately predicted.

[0032] Furthermore, in step S3, the compressive strength test conditions are: under the conditions of a confining pressure of 3.0 MPa, a temperature of 200° C., and a pressure loading rate of 0.5 mm / min.

[0033] Specifically, in step S3, a triaxial compression tester was used to test the material at a confining pressure of 3.0 MPa and a temperature of 200°C, with a loading rate of 0.5 mm / min. The peak compressive strength and stress-strain curve were recorded. Materials with stable compressive properties were screened by comparing the data before and after aging (e.g., a compressive damage rate of ≤15% was considered acceptable).

[0034] More specifically, the triaxial test simulates the actual confining pressure of the crack, and the results are more valuable for engineering reference; it clarifies the threshold of the compressive damage rate and improves screening efficiency.

[0035] Furthermore, in step S4, establishing a three-dimensional finite element model includes the following steps:

[0036] Step S41: establishing a three-dimensional geometric model of temporary plugging material particles, including circular, conical, fan-shaped and polyhedron shapes;

[0037] Step S42: setting material properties, including elastic modulus, Poisson's ratio and friction coefficient, to define the contact mechanical behavior between particles;

[0038] Step S43: applying shear load and confining pressure boundary conditions to simulate the actual stress state of the hot dry rock formation;

[0039] Step S44: Obtain stress field, strain field and contact force chain distribution data through iterative calculation.

[0040] Specifically, in step S4, based on the actual crack size (such as width 2mm, length 50mm), a finite element tool is used to construct a particle model, covering shapes such as circular (diameter 1mm) and conical (bottom diameter 1.2mm, height 0.8mm); parameters such as elastic modulus (2-5GPa) and friction coefficient (0.3-0.6) are set, and shear load (5-10MPa) and confining pressure (1.5-3.0MPa) are applied, and the particle contact mechanical behavior is simulated through an explicit dynamics algorithm.

[0041] More specifically, the multi-shape particle model restores the real plugging scenario and flexibly adjusts the boundary conditions to adapt to the needs of different formations.

[0042] Furthermore, in step S5, the force chain structure evolution analysis includes the following steps:

[0043] Step S51: extracting the area in the finite element model where the contact force is greater than a set threshold as a strong force chain;

[0044] Step S52: Analyze the distribution direction, density, and continuity of the strength chain to evaluate its shear resistance;

[0045] Step S53: By adjusting the particle shape and particle size distribution, the main chain of the force chain network is optimized to develop along the shear direction, and the secondary chains are symmetrically distributed on both sides of the main chain.

[0046] Specifically, in step S5, the finite element post-processing module extracts regions where contact forces are greater than the average (force chains) and analyzes their distribution direction and density. For example, the main chain develops along the shear direction (horizontally), with secondary chains symmetrically distributed on both sides (angles of 30°-45°). By adjusting the particle shape (tapering to enhance shear resistance) and particle size distribution (the optimal particle size is 1 / 2-2 / 3 of the crack width), the continuity and stability of the force chain network are optimized.

[0047] Furthermore, in step S53, the specific method for optimizing the shape and particle size distribution of the temporary plugging material is: adjusting the shape of the temporary plugging material to a cone, prism or pyramid, so that the main chain is distributed along the shear direction, the secondary chains are symmetrically distributed on both sides of the main chain, and the angle between the main chain and the secondary chains is 30 to 45 degrees.

[0048] Furthermore, in step S6, the indoor experiment includes dynamic plugging simulation and pressurized leakage test, recording the breakthrough pressure, loss volume and bearing pressure data of the temporary plugging material, and comparing and verifying with the finite element analysis results.

[0049] Specifically, in step S6, during the dynamic plugging simulation, the preferred material was injected into a fracture model (2 mm width), and drilling fluid was circulated at a flow rate of 2 L / min. The breakthrough pressure (target ≥ 3.0 MPa) and loss (target ≤ 10%) of the temporary plugging material were recorded. During the pressurized leakage test, the confining pressure was gradually increased until the fracture ruptured, and the finite element predictions were compared with the actual failure mode (an error of < 5% was considered acceptable).

[0050] More specifically, ensure that the numerical simulation results are consistent with the actual project; clearly break through the pressure and loss thresholds to improve the reliability of material selection.

[0051] Furthermore, in step S7, the shear stability index Lu is defined as:

[0052]

[0053] Among them, L u When L<0.5, it is judged to be poor shear stability. u When <1, the shear stability was judged to be good.

[0054] The beneficial effects of the present invention are: the present invention has a reasonable design, a simple preparation method, and has the following advantages:

[0055] (1) The present invention achieves a leap from "experience-driven" to "data-driven" in temporary plugging material screening through the deep integration of finite element analysis, high-temperature aging experiments and multi-parameter models, solving the core defects of traditional methods in environmental simulation, dynamic response and efficiency, and providing reliable technical support for the efficient development of hot dry rock geothermal resources;

[0056] (2) The high-temperature autoclave of the present invention simulates the extreme environment of the hot dry rock reservoir, and combines nitrogen protection with performance testing after aging, so that the experimental results have a smaller deviation from the actual working conditions, which is significantly better than the traditional photoelastic experiment; This application extracts the evolution law of the force chain network under dynamic shear load based on finite element analysis, and defines the shear stability index L u , combined with critical instability conditions, the service life of the plugging layer under cyclic load is extended to 120 hours;

[0057] (3) The present invention constructs a multi-parameter comprehensive evaluation formula, integrates the basic material properties (compressive damage rate, etc.), high-temperature aging effect (volume change rate), particle size matching and force chain network stability, and scientifically quantifies the comprehensive performance of temporary plugging materials, avoiding the randomness and subjectivity of traditional trial and error methods; through numerical simulation, it quickly iterates particle shape, particle size and friction coefficient, reduces the number of physical experiments, and shortens the R&D cycle and cost;

[0058] (4) The present invention combines indoor verification experiments (dynamic plugging simulation, pressurized leakage test) to ensure that the finite element analysis results are consistent with the actual plugging effect, which is significantly better than traditional methods; it clarifies the optimal particle size range (1 / 2 to 2 / 3 of the crack width), provides standardized guidance for the design of temporary plugging materials, and enhances the long-term stability of the plugging layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0060] Figure 1 is a flow chart of the method of the present invention;

[0061] Figure 2 This is the stress-strain curve of the temporary plugging material with ratio 3. DETAILED DESCRIPTION

[0062] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0063] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular also includes the plural. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0064] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0065] Example 1

[0066] like Figure 1 The method for optimizing and screening temporary plugging materials of hot dry rock based on a multi-parameter coupling model is shown, and comprises the following steps:

[0067] (1) Step S1: forming a temporary plugging material data set, specifically:

[0068] Step S11: Substrate property analysis:

[0069] Polycarbonate: High-purity polycarbonate (PC) is selected, with a glass transition temperature (Tg) of 150°C and excellent creep resistance at high temperatures; elastic modulus 3.5GPa, Poisson's ratio 0.38, density 1.2g / cm 3 ;

[0070] Thermosetting resin: Epoxy resin (EP) is selected, and the temperature resistance after curing reaches 220°C. Elastic modulus 4.2GPa, Poisson's ratio 0.35, density 1.18g / cm 3 ;

[0071] Step S12: Enhanced component design:

[0072] Leak-proof rubber particles: Nitrile-butadiene rubber (NBR) particles are used, with a particle size distribution of 0.5 to 2 mm, accounting for 15%. They have an elastic modulus of 0.5 GPa and an elongation at break of >300%, which can buffer stress impacts under dynamic loads.

[0073] Synthetic soft fiber: Kevlar fiber is used, with a length of 1 to 3 mm and a diameter of 50 μm, accounting for 10%. It has a tensile strength of 3.5 GPa and a modulus of 70 GPa. It is interwoven into a three-dimensional mesh structure to enhance the shear resistance of the plugging layer.

[0074] Step S13, data set construction: according to the dynamic width of cracks (0.16-3.96 mm) and the crack-hole combination model, 6 ratios were designed (Table 1);

[0075] Table 1 Differentiated material ratios, requirements for covering different crack widths and stress conditions

[0076] serial number Rubber proportion (%) Fiber length (mm) Applicable crack width (mm) 1 5 0.5 1～2 2 10 1.0 2～3 3 15 1.5 3～4 4 20 2.0 4～5 5 12 0.8 1.5～2.5 6 18 2.5 3.5～4.5

[0077] (2) Step S2, high temperature aging experiment: simulate the high temperature and high pressure environment of dry hot rock formation, perform high temperature aging treatment on the temporary plugging materials in the data set, and record the basic characteristic parameters before and after aging, including mass loss rate, particle size degradation rate, compressive breakage rate, friction coefficient change and fracture strength retention rate; specifically:

[0078] Experimental equipment and conditions:

[0079] High-temperature autoclave: volume 5L, temperature control accuracy ±2°C, pressure range 0-30MPa (simulating 15MPa static rock pressure of hot dry rock reservoir);

[0080] Aging parameters: constant temperature of 220℃, pressure of 15MPa, for 24 hours, nitrogen is introduced to prevent oxidation;

[0081] Performance testing method:

[0082] 2.1. Calculation of mass loss rate: Use a precision balance (accuracy 0.1 mg) to measure the mass difference before and after aging and calculate:

[0083] The calculation shows that the average loss rate of PC-based materials is 4.2%, and that of EP-based materials is 2.8%;

[0084] 2.2. Particle size degradation rate: A laser particle size analyzer (Malvern Mastersizer 3000) was used to analyze the particle distribution before and after aging, and the breakage rate was calculated:

[0085] Calculations show that the rubber particle breakage rate is 8.5% and the fiber breakage rate is 12.3%;

[0086] 2.3. Micromorphology Analysis: Scanning electron microscopy (SEM, Hitachi SU8010) was used to observe surface cracks and fiber breakage.

[0087] Microcracks (length <10μm) appeared on the surface of PC-based materials, while the surface of EP-based materials was relatively intact. Local debonding occurred after fiber aging;

[0088] Screening criteria

[0089] a. Mass loss rate: ≤5%;

[0090] b. Rubber particle crushing rate: ≤15%;

[0091] c. Fiber breakage rate: ≤15%;

[0092] d. Micromorphology: Surface microcrack length is less than 20 μm, and there is no obvious debonding of the fibers;

[0093] The experimental data and screening results of each ratio are shown in Table 2:

[0094] Table 2 Experimental data and screening results of each ratio

[0095]

[0096]

[0097] Specific analysis, screening and elimination:

[0098] The rubber crushing rate of mix 4 was 18.7% (>15% threshold). The high rubber content resulted in excessive particle fragmentation, making it impossible to form a stable force chain network. The fiber breakage rate was 16.9% (>15% threshold). The fibers were too long (2.0 mm) and easily broke at high temperatures, weakening the three-dimensional network structure.

[0099] SEM observation of mix 4: debonding between the substrate and the fiber interface, dense surface cracks, and a high risk of overall material failure;

[0100] Eliminate ratio 4 and retain ratios 1, 2, 3, 5, and 6:

[0101] All meet the quality loss rate ≤ 5% (ratios 3 and 6 are close but not exceeding the standard);

[0102] Rubber crushing rate ≤ 15% (ratio 3 and 6 are 8.5% and 9.2%, respectively, meeting the requirements);

[0103] Fiber breakage rate ≤ 15% (ratios 3 and 6 are 12.3% and 13.5%, respectively, which are critical but acceptable);

[0104] SEM observation: micro-crack length is less than 20μm, the fiber main structure is intact, and there is no significant debonding phenomenon;

[0105] (3) Step S3: Compression test: Mixing ratios 1, 2, 3, 5, and 6 enter compression test;

[0106] Experimental setup:

[0107] Triaxial compression testing machine (GCTSRTX-3000): maximum confining pressure 50 MPa, temperature range -20 to 300°C, axial loading rate 0.001 to 10 mm / min.

[0108] Sample preparation: Temporary plugging material and drilling fluid (density 1.8g / cm 3 ) are mixed in a ratio of 1:1, injected into a mold (Φ25mm×50mm), and cured for 24 hours.

[0109] Test parameters:

[0110] The confining pressure was 3.0 MPa (simulating crack closure stress), the temperature was 200 °C, the loading rate was 0.5 mm / min, and the stress-strain curve was recorded until the specimen ruptured.

[0111] Result analysis:

[0112] Ratio 3 (rubber 15% + fiber 1.5mm) has a peak compressive strength of 45.3 MPa, a strain rate of 0.12, and a compressive failure rate of 11.7%.

[0113] Ratio 6 (18% rubber + 2.5mm fiber) was excluded because the stress concentration was caused by the excessive length of the fibers and the compressive strength was only 38.2MPa.

[0114] Key conclusions from step S3: Temporary plugging materials must balance compressive strength and toughness, with the optimal range being 15% to 18% rubber and 1 to 2 mm fiber length.

[0115] Figure 2 This is the stress-strain curve of the temporary plugging material with a ratio of 3. It can be seen from the figure that:

[0116] (a) Excellent compressive strength and bearing capacity: The compressive strength corresponding to the peak of the curve is 45.3 MPa, significantly higher than that of other mixes (e.g., Mix 6 is only 38.2 MPa). This indicates that Mix 3 can withstand higher confining pressure and shear loads under high temperature and high pressure environments, effectively supporting the crack sealing layer and preventing structural collapse caused by external pressure.

[0117] (b) Good toughness: The presence of a long plastic deformation phase (not complete brittle fracture) in the stress-strain curve, combined with a compressive failure rate of 11.7% (below the threshold of ≤15%), indicates that the material can absorb energy through plastic deformation before rupture, avoiding sudden failure. This toughness helps to cope with the repeated effects of dynamic loads (such as drilling fluid circulation impact) in hot dry rock reservoirs and extend the service life of the plugging layer.

[0118] (c) Moderate elastic modulus, balancing rigidity and adaptability: The slope (elastic modulus) of the curve in the initial stage reflects the rigidity of the material; the elastic modulus of mix 3 is 3.8 GPa, which ensures sufficient rigidity to maintain the stability of the plugging layer structure while avoiding brittle fracture caused by excessive rigidity. This property enables it to adapt to slight deformations of the crack wall and reduce the risk of stress concentration.

[0119] (d) Direct reflection of force chain network optimization: Combined with the force chain evolution analysis in step S5, the conical particles with a ratio of 3 and the optimal particle size (2 / 3 of the crack width) were designed to optimize the force chain network. The smooth rising segment and stable peak of the stress-strain curve may reflect the effective distribution of the main force chain along the shear direction, thereby improving the shear resistance of the material (shear stability index Lu = 0.28, in the "reserved" range).

[0120] (4) Step S4, multi-parameter coupling model construction, specifically including:

[0121] Step S41: Geometric model:

[0122] A fracture-cavity-fracture (FVF) model was constructed with a fracture length of 50 mm, a cavity diameter of 1000 mm, and a positive pressure difference of 10 MPa in the wellbore.

[0123] Plugging particle shape:

[0124] Conical particles: bottom diameter 1.2mm, height 0.8mm, cone angle 60° (enhanced shear resistance);

[0125] Irregular polygon: equivalent diameter 1.5mm, 5 to 7 sides, simulating the shape of natural particles;

[0126] Step S42: Material properties:

[0127] Elastic modulus: 3.8 GPa (average after aging), Poisson's ratio 0.36;

[0128] Friction coefficient: particle-particle 0.4, particle-crack wall 0.35 (corrected by aging experiments);

[0129] Step S43: Meshing and solver settings:

[0130] The unstructured mesh was generated using the finite element tool with a minimum element size of 0.1 mm and a global size factor of 0.5;

[0131] Explicit dynamics solver, time step 1e-6s, total duration 0.1s, output interval 1e-4s;

[0132] Step S44: Load and Constraint:

[0133] Shear load: 10 MPa (simulating positive wellbore pressure difference), applied normal to the fracture surface;

[0134] Confining pressure: 3.0 MPa (simulating horizontal formation stress), applied to the outer boundary of the model;

[0135] Symmetry constraint: set the symmetry plane along the crack centerline (X=0, Y=0);

[0136] Model verification in step S4:

[0137] Slit width increment data (slit width increment is 1.25 to 3.96 mm when the hole diameter is 1000 mm), simulation error is <5%;

[0138] (5) Step S5: force chain evolution and dynamic shear stability analysis, specifically including:

[0139] Step S51: Extracting strong chains:

[0140] The area with a contact force threshold > 5 MPa is defined as a strong force chain (accounting for 70% of the total contact force);

[0141] Use Python scripts to extract force chain data and visualize the distribution of strong force chains;

[0142] Step S52: Force chain optimization strategy:

[0143] Conical particles: The main force chain is distributed along the shear direction (X axis), with a density of 12 chains / mm 2 , the secondary chain symmetry angle is 40°±5°;

[0144] Particle size optimization: Adjust the particle equivalent diameter to 2 / 3 of the crack width (2.67 mm) to reduce local stress concentration (maximum stress dropped from 85 MPa to 62 MPa);

[0145] Step S53, shear stability index calculation:

[0146] Fracture force chain ratio Calculated Lu = 0.28;

[0147] The shear stability was judged to be good (Lu ≥ 0.5 was excellent);

[0148] Key conclusions from step S5:

[0149] The conical particles and optimal particle size design increase the continuity of the force chain network by 30% and significantly enhance the shear stability;

[0150] (6) Step S6, indoor crack sealing test verification, specifically including:

[0151] Experimental setup and process:

[0152] 6.1. Dynamic plugging simulation:

[0153] Crack model: steel crack plate (width 4 mm, length 200 mm), surface roughness Ra = 6.3 μm;

[0154] Drilling fluid circulation: density 1.8g / cm 3 , flow rate 2L / min, last for 30 minutes, record the bridge position of temporary plugging material;

[0155] 6.2. Pressurized leakage test:

[0156] Gradually increase the confining pressure (0→10MPa, step size 1MPa), and record the plugging layer fracture pressure and drilling fluid loss;

[0157] Experimental results:

[0158] Breakthrough pressure: 3.5MPa (target ≥3.0MPa), the plugging layer will partially fail at 8MPa;

[0159] Loss: 7.2% (target ≤ 10%), 2.8% error from finite element prediction;

[0160] Failure Mode Analysis:

[0161] SEM showed that the failure area was mainly debonding at the fiber-substrate interface (fiber surface treatment process needs to be optimized);

[0162] (7), Step S7, shear stability evaluation:

[0163] Indicator calculation and optimization:

[0164] Contact force chain statistics: 1,532 total force chains, 429 fracture force chains (Lu = 0.28);

[0165] Optimization direction: Increase the fiber content to 12%, improve the interface bonding strength, and increase Lu to 0.35;

[0166] (8) Step S8: Multi-parameter comprehensive evaluation: Based on the formula:

[0167]

[0168] After importing the data:

[0169]

[0170] Weight distribution: compressive strength (ω1=0.3), high temperature aging (ω2==0.2), particle size matching (ω3==0.3), shear stability (ω4==0.2);

[0171] Conclusion: The comprehensive score is 0.89 (out of 1.0), and the ratio 3 (rubber 15% + fiber 1.5mm) is the best.

[0172] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for optimizing and screening temporary plugging materials of hot dry rocks based on a multi-parameter coupling model, characterized by: The specific steps include: Step S1, forming a temporary plugging material data set: polycarbonate and thermosetting resin are selected as base materials, photoelastic rubber particles and synthetic soft fibers are added to prepare temporary plugging materials with various proportions, and the temporary plugging materials with various proportions form a data set; Step S2, high-temperature aging experiment: Simulating the high-temperature and high-pressure environment of hot dry rock formations, the temporary plugging materials in the data set are subjected to high-temperature aging treatment, and the basic characteristic parameters before and after aging are recorded, including mass loss rate, particle size degradation rate, compressive breakage rate, friction coefficient change, and fracture strength retention rate; Step S3, compressive strength test: testing the compressive strength change of the temporary plugging material after high temperature aging in a simulated high temperature and high pressure crack plugging environment; Step S4, constructing a three-dimensional finite element model: Based on the actual size of the crack plugging layer, a three-dimensional finite element model of the temporary plugging material particles is established, the material constitutive relationship, contact conditions and boundary constraints are defined, and the mechanical response under shear load and confining pressure is simulated; Step S5, force chain structure evolution analysis: using finite element analysis software, simulate the stress distribution and contact force network between the temporary plugging material particles, extract stress concentration data and contact force chain evolution law in key areas, optimize the shape, particle size distribution and friction coefficient of the temporary plugging material, and make the main chain develop along the shear direction; Step S6, indoor crack plugging test verification: Based on the finite element analysis results, select temporary plugging materials for indoor testing, and record the failure mode and plugging effect of the plugging layer under load; Step S7, shear stability evaluation: Count the ratio of the number of broken contact force chains to the total number of force chains in the finite element model, and calculate the shear stability index Lu; Step S8, multi-parameter comprehensive evaluation: Based on the formula: The comprehensive evaluation formula is: in The basic performance index of the material, P i is the performance index of the material; ω i The importance weights are assigned based on the importance of different experimental indicators; in The term represents the volume change effect of the temporary plugging material under high temperature aging, and k is the influence coefficient of the high temperature aging effect; is the volume change rate of the temporary plugging material during high-temperature aging; in The term represents the structural optimization of the crack plugging layer, d is the particle size of the temporary plugging material; d opt is the optimal value of the particle size of the plugging layer in the experiment, usually half of the crack width; σ d is the standard deviation of particle size distribution, reflecting the influence of particle uniformity; Among them L u The term characterizes the uniformity of the force chain network, which is the ratio of the number of strong force chains to the total number of force chains and is measured by step S7.

2. The method for optimizing and screening hot dry rock temporary plugging materials based on a multi-parameter coupling model according to claim 1, characterized in that: In step S1, in the temporary plugging material of the temporary plugging material data set, the mass percentage of rubber particles is 5-20%, the fiber length of the synthetic soft fiber is 0.5-2.5 mm, and the width of the crack covered is 1-5 mm.

3. The method for optimizing and screening hot dry rock temporary plugging materials based on a multi-parameter coupling model according to claim 2, characterized in that: In step S2, the high temperature aging condition is 220°C and 15 MPa for 24 hours. After aging, the material needs to be dried and sieved for particle size.

4. The method for optimizing and screening hot dry rock temporary plugging materials based on a multi-parameter coupling model according to claim 3, characterized in that: The optimal particle size d of the material particles opt It is 1 / 2 to 2 / 3 of the crack width.

5. The method for optimizing and screening hot dry rock temporary plugging materials based on a multi-parameter coupling model according to claim 1, characterized in that: In step S3, the compressive strength test conditions are: under the conditions of a confining pressure of 3.0 MPa, a temperature of 200° C., and a pressure loading rate of 0.5 mm / min.

6. The method for optimizing and screening hot dry rock temporary plugging materials based on a multi-parameter coupling model according to claim 1, characterized in that: In step S4, establishing a three-dimensional finite element model includes the following steps: Step S41: establishing a three-dimensional geometric model of temporary plugging material particles, including circular, conical, fan-shaped and polyhedron shapes; Step S42: setting material properties, including elastic modulus, Poisson's ratio and friction coefficient, to define the contact mechanical behavior between particles; Step S43: applying shear load and confining pressure boundary conditions to simulate the actual stress state of the hot dry rock formation; Step S44: Obtain stress field, strain field and contact force chain distribution data through iterative calculation.

7. The method for optimizing and screening hot dry rock temporary plugging materials based on a multi-parameter coupling model according to claim 1, characterized in that: In step S5, the force chain structure evolution analysis includes the following steps: Step S51: extracting the area in the finite element model where the contact force is greater than a set threshold as a strong force chain; Step S52: Analyze the distribution direction, density, and continuity of the strength chain to evaluate its shear resistance; Step S53: By adjusting the particle shape and particle size distribution, the main chain of the force chain network is optimized to develop along the shear direction, and the secondary chains are symmetrically distributed on both sides of the main chain.

8. The method for optimizing and screening hot dry rock temporary plugging materials based on a multi-parameter coupling model according to claim 7, characterized in that: In step S53, the specific method for optimizing the shape and particle size distribution of the temporary plugging material is: adjusting the shape of the temporary plugging material to a cone, prism or pyramid, so that the main chain is distributed along the shear direction, the secondary chains are symmetrically distributed on both sides of the main chain, and the angle between the main chain and the secondary chains is 30-45 degrees.

9. The method for optimizing and screening hot dry rock temporary plugging materials based on a multi-parameter coupling model according to claim 1, characterized in that: In step S6, the indoor experiment includes dynamic plugging simulation and pressurized leakage test, recording the breakthrough pressure, loss volume and bearing pressure data of the temporary plugging material, and comparing and verifying with the finite element analysis results.

10. The method for optimizing and screening hot dry rock temporary plugging materials based on a multi-parameter coupling model according to claim 1, characterized in that: In step S7, the shear stability index Lu is defined as: Among them, L u When L<0.5, it is judged to be poor shear stability. u When <1, the shear stability was judged to be good.

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