Hydraulic fracturing parameter optimization method based on nanoindentation spatial heterogeneity map

Abstract

This invention discloses a method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps, relating to the field of coalbed methane extraction. The method includes: sampling and nanoindentation testing of the target coal seam to obtain load-displacement curves at each measuring point; analyzing and calculating the load-displacement curves at each measuring point to plot the heterogeneity map of the sampling points and the micromechanical spatial heterogeneity map of the entire coal seam; identifying the micromechanical spatial heterogeneity map of the entire coal seam; constructing a hydraulic fracturing design scheme based on the distribution information of the easily proliferating advantageous paths and difficult-to-proliferate disadvantageous paths of the fracturing fractures in the coal seam; and monitoring the fracture propagation range using resistivity tomography to dynamically adjust the fracturing parameters of the hydraulic fracturing design scheme. This invention generates micromechanical spatial heterogeneity maps using a nanoindentation instrument, characterizing the mechanical heterogeneity within coal and rock, saving trial-and-error costs in fracturing design, and reducing the blindness of fracturing.

Description

Technical Field

[0001] This invention relates to the field of coalbed methane extraction, and more specifically, to a method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps. Background Technology

[0002] Coalbed methane (CBM) is a high-quality clean energy source with significant extraction value. CBM primarily exists in the coal matrix through adsorption, with a smaller portion existing in free or dissolved states within the water in coal seam fractures. However, due to the low permeability of coal seams in my country, hydraulic fracturing technology is widely used for CBM extraction.

[0003] Due to the significant heterogeneity of coal, traditional hydraulic fracturing designs using uniform macroscopic mechanical parameters are unable to cope with the intense heterogeneity within coal seams. This results in suboptimal fracture morphology, weak fracture conductivity, and low single-well coalbed methane production. Therefore, to improve coalbed methane extraction efficiency and increase single-well coalbed methane production, it is urgent to seek optimized hydraulic fracturing parameter models and methods to meet the requirements of efficient coalbed methane extraction.

[0004] No effective solutions have yet been proposed to address the problems in the relevant technologies. Summary of the Invention

[0005] To address the problems in related technologies, this invention proposes a method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps, in order to overcome the aforementioned technical problems existing in existing related technologies.

[0006] Therefore, the specific technical solution adopted by the present invention is as follows: According to one aspect of the present invention, a method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps is provided, the method comprising: S1. Obtain geological data of the target coal seam, sample the target coal seam to obtain core samples; perform gridded nanoindentation tests on the core samples to obtain load-displacement curves at each measuring point; S2. Analyze and calculate the load-displacement curves of each measuring point, draw the heterogeneity map of the sampling points, and draw the micromechanical spatial heterogeneity map of the entire coal seam based on the heterogeneity map of the sampling points. S3. Identify the micromechanical spatial heterogeneity spectrum of the entire coal seam to obtain the advantageous paths and disadvantageous paths that are difficult to extend in the coal seam. S4. Based on the distribution information of the advantageous paths and disadvantageous paths that are difficult to extend in the coal seam, construct a targeted hydraulic fracturing design scheme. S5. Implement the hydraulic fracturing design scheme, and monitor the fracture propagation range using resistivity tomography technology; feed the monitoring data back to the computer in real time, and dynamically adjust the fracturing parameters of the hydraulic fracturing design scheme.

[0007] Furthermore, geological data of the target coal seam was obtained, and core samples were taken from the target coal seam. Gridded nanoindentation tests were performed on the core samples to obtain load-displacement curves at each measuring point, including: Before performing gridded nanoindentation tests on the core samples, the core samples were cut into several square coal samples of a predetermined size, the surface of the square coal samples was polished, and the polished square coal samples were cast in epoxy resin.

[0008] Furthermore, geological data of the target coal seam is obtained, and core samples are taken from the target coal seam. Gridded nanoindentation tests are performed on the core samples to obtain load-displacement curves for each measuring point. (The process also includes:) In the gridded nanoindentation test of the core sample, a target area was selected on the surface of the square coal sample; the mechanical parameters of the measuring points within the target area were tested, and the load-displacement curves of each measuring point were obtained.

[0009] Furthermore, the mechanical parameters of the measuring points within the target area are tested, including: There are 625 measuring points in the target area. Indentation experiments are performed on square coal samples based on the 625 measuring points, and the spacing between each measuring point is 10 μm.

[0010] Furthermore, the load-displacement curves at each measuring point are analyzed and calculated, and the heterogeneity map of the sampling points is plotted. Based on the heterogeneity map of the sampling points, the micromechanical spatial heterogeneity map of the entire coal seam is plotted, including: The load-displacement curves of each measuring point are calculated to obtain the fracture toughness of each measuring point; Statistical analysis of fracture toughness at each measuring point is performed, and the heterogeneity spectrum of the sampling points is output. Based on the heterogeneity maps of the sampling points, a micromechanical spatial heterogeneity map of the entire coal seam was drawn.

[0011] Furthermore, the load-displacement curves at each measuring point are calculated to obtain the fracture toughness at each measuring point, including: Based on the principle of energy conservation, the total energy generated during the nanoindentation test was analyzed to obtain the fracture energy, recoverable elastic energy, and irrecoverable plasticity. By integrating the relationship between load and displacement in the load-displacement curve, the sum of recoverable elastic energy and unrecoverable plastic energy is calculated. The total energy generated during the nanoindentation test is calculated based on the maximum indentation depth and the creep displacement during the holding phase. Based on the sum of recoverable elastic energy and non-recoverable plasticity, and the total energy generated during the nanoindentation test, the rate of change of fracture energy relative to the indenter contact projection surface is calculated to obtain the critical energy release rate. The fracture toughness at the current measuring point is calculated based on the critical energy release rate and the reduced modulus.

[0012] Furthermore, statistical analysis was performed on the fracture toughness at each measuring point, and the heterogeneity spectrum of the sampling points was output, including: The fracture toughness values ​​calculated from all measuring points are collected to form a mechanical property dataset for each measuring point. The normal analytical algorithm was used to perform fitting analysis on the mechanical performance dataset of each measuring point; Based on the fitting analysis results, statistical distribution parameters are extracted, and a heterogeneity map of the sampling points is generated according to the spatial location of each measuring point and the corresponding fracture toughness value.

[0013] Furthermore, by identifying the microscopic mechanical spatial heterogeneity spectrum of the entire coal seam, the advantageous paths for the propagation of hydraulic fracturing fractures and the disadvantageous paths for their propagation that are difficult to propagate were determined, including: The advantageous path that is easy to extend is a weak zone or a modulus abrupt change interface, which will promote the development and extension of hydraulic fracturing fractures; the disadvantageous path that is difficult to extend is a hard zone or a region with concentrated modulus, where hydraulic fracturing fractures will avoid development.

[0014] Furthermore, based on the distribution information of advantageous and disadvantageous paths for the easy propagation of hydraulic fracturing fractures in coal seams, targeted hydraulic fracturing design schemes are constructed, including: For hydraulic fracturing designs used in hard regions, the specific approach is to increase perforation density, raise the injection pressure of the fracturing injection pump, and increase the viscosity of the fracturing fluid to effectively support the identified weak fractures. For weak regions, the hydraulic fracturing design approach is to reduce perforation density, lower the injection pressure of the fracturing injection pump, and reduce the viscosity of the fracturing fluid to form a uniformly distributed fracture network.

[0015] Furthermore, the hydraulic fracturing design scheme is implemented, and resistivity tomography is used to monitor the fracture propagation range. The monitoring data is fed back to the computer in real time, and the fracturing parameters of the hydraulic fracturing design scheme are dynamically adjusted, including: When implementing a hydraulic fracturing design scheme, resistivity tomography is used to monitor the fracture propagation range. The monitoring data is fed back to the computer in a timely manner. The hydraulic fracturing design scheme is optimized by changing the pumping pressure of the fracturing injection pump, adjusting the perforation density, adjusting the proppant type, and adjusting the mixing ratio of proppant and water.

[0016] According to another aspect of the present invention, a hydraulic fracturing parameter optimization system based on nanoindentation spatial heterogeneity map is also provided. The system includes: a data acquisition and testing module, a micromechanical spatial heterogeneity map construction module, a path identification module, a fracturing scheme design module, and a fracturing scheme optimization module. The data acquisition and testing module is used to acquire geological data of the target coal seam, sample the target coal seam to obtain core samples, and perform gridded nanoindentation tests on the core samples to obtain load-displacement curves at each measuring point. The micromechanical spatial heterogeneity map construction module is used to analyze and calculate the load-displacement curves of each measuring point, draw the heterogeneity map of the sampling points, and draw the micromechanical spatial heterogeneity map of the entire coal seam based on the heterogeneity map of the sampling points. The path identification module is designed to identify the microscopic mechanical spatial heterogeneity of the entire coal seam, and ultimately obtain the advantageous paths that are easy to extend and the disadvantageous paths that are difficult to extend in the coal seam. The fracturing scheme design module will construct a targeted hydraulic fracturing design scheme based on the distribution information of the advantageous paths that are easy to expand and the disadvantageous paths that are difficult to expand in the coal seam. The fracturing scheme optimization module is responsible for executing the hydraulic fracturing design scheme. At the same time, it uses resistivity tomography to monitor the fracture propagation range and feeds the data obtained from the monitoring back to the computer in real time to dynamically adjust the fracturing parameters of the hydraulic fracturing design scheme.

[0017] By utilizing the above-mentioned technical solution of this invention, the present invention generates a microscopic mechanical spatial heterogeneity map using a nanoindenter, accurately characterizing the mechanical heterogeneity inside coal and rock, providing precise navigation for hydraulic fracturing, saving trial and error costs in fracturing design, and reducing the blindness of fracturing; at the same time, it uses resistivity tomography to monitor the propagation morphology of fracturing fractures in real time, optimizes the fracturing path, increases the complexity of the fracture network, and combines parallel fracturing parameter optimization schemes to form an alternating enhanced fracturing method. This method is accurate in prediction, efficient, low in cost, has good production increase effect, and has a wide range of applications. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a flowchart of a hydraulic fracturing parameter optimization method based on nanoindentation spatial heterogeneity maps according to an embodiment of the present invention; Figure 2 This is a connection system diagram of each component in the hydraulic fracturing parameter optimization method based on nanoindentation spatial heterogeneity map according to an embodiment of the present invention; Figure 3 These are the load-displacement curves obtained by nanoindentation testing at each measuring point in the hydraulic fracturing parameter optimization method based on nanoindentation spatial heterogeneity map according to an embodiment of the present invention. Figure 4 This is a heterogeneity map of sampling points in the hydraulic fracturing parameter optimization method based on nanoindentation spatial heterogeneity map according to an embodiment of the present invention; Figure 5 This refers to the micromechanical spatial heterogeneity map of the entire coal seam in the hydraulic fracturing parameter optimization method based on nanoindentation spatial heterogeneity map according to an embodiment of the present invention.

[0020] In the picture: 1. Square coal sample; 2. Load-displacement curves at each measuring point; 3. Heterogeneity map of the sampling point; 4. Micromechanical spatial heterogeneity map of the entire coal seam; 5. Computer; 6. Fracturing injection pump; 7. Fracturing fluid; 8. Propionate; 9. Valve 1; 10. Valve 2; 11. Sand mixer; 12. Packer; 13. Target coal seam; 14. Surrounding rock; 15. Perforation; 16. Electrode. Detailed Implementation

[0021] To further illustrate the various embodiments, the present invention provides accompanying drawings, which are part of the disclosure of the present invention. These drawings are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementation methods and the advantages of the present invention. The components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0022] According to embodiments of the present invention, a method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps is provided.

[0023] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments, such as... Figures 1-5 As shown, according to an embodiment of the present invention, a method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps is provided, the method comprising: S1. Obtain geological data of target coal seam 13 in surrounding rock 14, take samples of target coal seam 13 to obtain core samples; perform gridded nanoindentation test on core samples to obtain load-displacement curves 2 at each measuring point; It should be noted that the geological data for target coal seam 13 includes the coal mine planning and mining area plan, coal mining face design drawings, and other materials.

[0024] like Figure 3 As shown, this is the load-displacement curve obtained by nanoindentation testing in this invention. Figure 3 The horizontal axis represents displacement, and the vertical axis represents load. MP1-9 are the nanoindentation test data of 9 points out of 625 different test points of the coal sample, that is, the load-displacement curves of different points.

[0025] In this optional embodiment, geological data of the target coal seam 13 is obtained, and core samples are taken from the target coal seam 13. The core samples are then subjected to gridded nanoindentation testing to obtain load-displacement curves 2 at each measuring point, including: Before performing gridded nanoindentation tests on the core samples, the core samples were cut into several square coal samples 1 of a predetermined size. The surface of the square coal samples 1 was polished, and the polished square coal samples 1 were cast in epoxy resin.

[0026] Specifically, prior to the nanoindentation test, the sample was prepared into a square coal sample 1 measuring 15×15×10mm by cutting. The surface of the square coal sample 1 was meticulously polished with sandpaper to obtain a smooth and uniform surface, and then the square coal sample 1 was cast into epoxy resin.

[0027] In this optional embodiment, geological data of the target coal seam 13 in the surrounding rock 14 is obtained, and samples are taken from the target coal seam 13 to obtain core samples; gridded nanoindentation tests are performed on the core samples to obtain load-displacement curves 2 at each measuring point, which further includes: In the gridded nanoindentation test of the core sample, a target area was selected on the surface of the square coal sample 1; the mechanical parameters of the measuring points in the target area were tested, and the load-displacement curves of each measuring point were obtained.

[0028] In this optional embodiment, testing the mechanical parameters of the measuring points within the target area includes: There are 625 measuring points in the target area. Indentation experiments are performed on square coal samples based on the 625 measuring points, and the spacing between each measuring point is 10 μm.

[0029] Specifically, the peak load Pmax for different coal samples was set to 10-100mN.

[0030] S2. Analyze and calculate the load-displacement curves 2 of each measuring point, draw the heterogeneity map 3 of the sampling points, and draw the micromechanical spatial heterogeneity map 4 of the entire coal seam based on the heterogeneity map 3 of the sampling points. It needs to be explained that, for example Figure 4 As shown, this is the heterogeneity spectrum 3 of the sampling points in this invention. The moduli are sorted from high to low as red, yellow, green, and blue. Figure 4The horizontal and vertical axes represent length / distance, respectively, with X and Y representing the horizontal and vertical coordinates, in μm; Kc / (MPa·m) 0.5 In this context, Kc represents fracture toughness (MPa·m). 0.5 The units are 4. The distribution characteristics of the hard skeleton (high modulus, high hardness) and the weak structural plane (low modulus, low hardness) should be clearly identified in the micromechanical spatial heterogeneity map of the entire coal seam.

[0031] In this optional embodiment, the load-displacement curves 2 of each measuring point are analyzed and calculated, and the heterogeneity map 3 of the sampling points is plotted. Based on the heterogeneity map 3 of the sampling points, the micromechanical spatial heterogeneity map 4 of the entire coal seam is plotted, including: The load-displacement curves 2 at each measuring point are calculated to obtain the fracture toughness at each measuring point; Statistical analysis of fracture toughness at each measuring point was performed, and the heterogeneity spectrum of the sampling points was output. Based on the heterogeneity map of the sampling points 3, the micromechanical spatial heterogeneity map of the entire coal seam 4 was drawn.

[0032] In this optional embodiment, the load-displacement curves 2 of each measuring point are calculated to obtain the fracture toughness of each measuring point, including: Based on the principle of energy conservation, the total energy generated during the nanoindentation test was analyzed to obtain the fracture energy, recoverable elastic energy, and irrecoverable plasticity. By integrating the relationship between load and displacement in the load-displacement curve, the sum of recoverable elastic energy and unrecoverable plastic energy is calculated. The total energy generated during the nanoindentation test is calculated based on the maximum indentation depth and the creep displacement during the holding phase. Based on the sum of recoverable elastic energy and non-recoverable plasticity, and the total energy generated during the nanoindentation test, the rate of change of fracture energy relative to the indenter contact projection surface is calculated to obtain the critical energy release rate. The fracture toughness at the current measuring point is calculated based on the critical energy release rate and the reduced modulus.

[0033] Specifically, fracture toughness K c The calculation formula is as follows: U t = U c + U e + U P ; ; ; ; ; In the formula, U t This represents the total energy generated during the nanoindentation test. U c This refers to the energy required for fracture. U e It is recoverable elastic energy; U P It exhibits irreversible plasticity; h max This represents the maximum indentation depth. P For head load; d The differential symbol; h For displacement; h k This refers to the creep displacement during the load-holding phase. A c This represents the contact projection area of ​​the pressure head; G c The critical energy release rate in the indentation test; E r The reduced modulus represents the modulus resulting from the combined action of the indenter and the sample. K c This refers to fracture toughness.

[0034] In this optional embodiment, statistical analysis is performed on the fracture toughness at each measuring point, and the heterogeneity spectrum of the sampling points is output, including: The fracture toughness values ​​calculated from all measuring points are collected to form a mechanical property dataset for each measuring point. The normal analytical algorithm was used to perform fitting analysis on the mechanical performance dataset of each measuring point; Based on the fitting analysis results, statistical distribution parameters are extracted, and a heterogeneity map of the sampling points is generated according to the spatial location of each measuring point and the corresponding fracture toughness value.

[0035] Specifically, the mechanical properties of the core sample at different locations were estimated using the load-displacement curves obtained from nanoindentation at each measuring point. A normal analytical algorithm was used to statistically analyze the mechanical properties at different locations at the microscale. The optimal model based on the normal distribution curve was fitted as follows: ; In the formula, x To fit the values ​​of the mechanical properties in the model; μ This represents the average value of the distribution in the fitted model; σ This represents the standard deviation of the distribution in the fitted model.

[0036] S3. Identify the micromechanical spatial heterogeneity spectrum of the entire coal seam to obtain the advantageous paths and disadvantageous paths that are difficult to extend in the coal seam. It needs to be explained that, for example Figure 5 As shown in the diagram, the red areas represent hard zones where fracturing fractures typically avoid development, making them unfavorable paths for propagation. The blue areas represent soft zones where fracturing fractures typically develop and propagate, making them the most likely and advantageous paths for propagation.

[0037] In this optional embodiment, the micromechanical spatial heterogeneity spectrum of the entire coal seam is identified to obtain the advantageous paths and disadvantageous paths in the coal seam that are easy to propagate and difficult to propagate, including: The advantageous path that is easy to extend is a weak zone or a modulus abrupt change interface, which will promote the development and extension of hydraulic fracturing fractures; the disadvantageous path that is difficult to extend is a hard zone or a region with concentrated modulus, where hydraulic fracturing fractures will avoid development.

[0038] S4. Based on the distribution information of the advantageous paths and disadvantageous paths that are difficult to extend in the coal seam, construct a targeted hydraulic fracturing design scheme. In this optional embodiment, based on the distribution information of advantageous paths and disadvantageous paths in coal seams that are easy to propagate and difficult to propagate, a targeted hydraulic fracturing design scheme is constructed, including: For hydraulic fracturing designs used in hard regions, the specific approach is to increase perforation density, raise the injection pressure of the fracturing injection pump, and increase the viscosity of the fracturing fluid to effectively support the identified weak fractures. For weak regions, the hydraulic fracturing design approach is to reduce perforation density, lower the injection pressure of the fracturing injection pump, and reduce the viscosity of the fracturing fluid to form a uniformly distributed fracture network.

[0039] It should be explained that increasing the density of perforations 15 or increasing the pumping pressure of fracturing injection pump 6 in hard areas makes the flow direction of fracturing fluid 7 and the direction of fracture propagation match the predicted dominant path; and by adjusting valve 1 9 and valve 2 10, the proportion of proppant 8 mixed with fracturing fluid 7 in sand mixer 11 is increased; at the same time, the type and particle size of proppant 8 are optimized, using larger particle size and high hardness proppant, and adopting a fracturing mode of "high flow rate, high viscosity, large particle size proppant" to better support the identified weak fractures.

[0040] Reduce the density of perforations 15 or lower the pumping pressure of fracturing injection pump 6 in weak areas; and reduce the proportion of proppant 8 mixed with fracturing fluid 7 in sand mixer 11 by adjusting valve 19 and valve 210; adopt a "low-pressure, slow-speed" fracturing mode, without excessive energy, avoid excessive concentration, and allow fracturing fluid to preferentially seep and spread along soft thin layers, maximizing the communication of natural fractures, thereby naturally forming a fracture network; It should be explained that the packer 12 can adopt an existing conventional structure. Its main purpose is to seal different sections of the hydraulic fracturing borehole to form a closed space; thereby cooperating with the fracturing injection pump 6 to inject fracturing fluid to fracturing the target coal seam 13.

[0041] S5. Implement the hydraulic fracturing design scheme, and monitor the fracture propagation range using resistivity tomography technology; feed the monitoring data back to the computer in real time, and dynamically adjust the fracturing parameters of the hydraulic fracturing design scheme.

[0042] In this optional embodiment, a hydraulic fracturing design scheme is implemented, and resistivity tomography is used to monitor the fracture propagation range. The monitoring data is fed back to the computer in real time, and the fracturing parameters of the hydraulic fracturing design scheme are dynamically adjusted, including: The hydraulic fracturing design scheme is implemented, and resistivity tomography is used to monitor the fracture propagation range. The monitoring data is fed back to the computer in real time, and the hydraulic fracturing design scheme is optimized by changing the pumping pressure of the fracturing injection pump, the density of the perforation, adjusting the type of proppant, and adjusting the mixing ratio of proppant and water.

[0043] It should be explained that, by combining resistivity tomography technology with computer 5 and pre-arranged electrode 16, the system switches between power supply electrode pairs and measurement electrode pairs, and uses different electrode arrangements to perform measurements, obtaining the true three-dimensional resistivity distribution underground. Through time-delayed resistivity imaging, the diffusion range, direction, and fracture network morphology of the fracturing fluid can be seen intuitively and dynamically. Thus, by accurately realizing dynamic visualization monitoring of fracture morphology, fracturing parameters can be optimized.

[0044] It should be explained that, by combining resistivity tomography technology with computer 5 to determine the extent of fracture propagation, real-time data feedback is provided to optimize fracturing parameters. In areas where fracturing is not ideal, the fracture network is optimized by increasing the pumping pressure of fracturing injection pump 6 and increasing the density of perforations 15. Furthermore, the proportion of proppant 8 mixed with fracturing fluid 7 in the sand mixer 11 is increased based on feedback data to better support the fracture network. According to one embodiment of the present invention, a hydraulic fracturing parameter optimization system based on nanoindentation spatial heterogeneity mapping is also provided. This system includes: a data acquisition and testing module, a micromechanical spatial heterogeneity mapping construction module, a path identification module, a fracturing scheme design module, and a fracturing scheme optimization module. The data acquisition and testing module is used to acquire geological data of the target coal seam, sample the target coal seam to obtain core samples, and perform gridded nanoindentation tests on the core samples to obtain load-displacement curves at each measuring point. The micromechanical spatial heterogeneity map construction module is used to analyze and calculate the load-displacement curves of each measuring point, draw the heterogeneity map of the sampling points, and draw the micromechanical spatial heterogeneity map of the entire coal seam based on the heterogeneity map of the sampling points. The path identification module is designed to identify the microscopic mechanical spatial heterogeneity of the entire coal seam, and ultimately obtain the advantageous paths that are easy to extend and the disadvantageous paths that are difficult to extend in the coal seam. The fracturing scheme design module will construct a targeted hydraulic fracturing design scheme based on the distribution information of the advantageous paths that are easy to expand and the disadvantageous paths that are difficult to expand in the coal seam. The fracturing scheme optimization module is responsible for executing the hydraulic fracturing design scheme. At the same time, it uses resistivity tomography to monitor the fracture propagation range and feeds the data obtained from the monitoring back to the computer in real time to dynamically adjust the fracturing parameters of the hydraulic fracturing design scheme.

[0045] By utilizing the above-mentioned technical solution of this invention, the present invention generates a microscopic mechanical spatial heterogeneity map using a nanoindenter, accurately characterizing the mechanical heterogeneity inside coal and rock, providing precise navigation for hydraulic fracturing, saving trial and error costs in fracturing design, and reducing the blindness of fracturing; at the same time, it uses resistivity tomography to monitor the propagation morphology of fracturing fractures in real time, optimizes the fracturing path, increases the complexity of the fracture network, and combines parallel fracturing parameter optimization schemes to form an alternating enhanced fracturing method. This method is accurate in prediction, efficient, low in cost, has good production increase effect, and has a wide range of applications.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps, characterized in that, The method includes: S1. Obtain geological data of the target coal seam, sample the target coal seam to obtain core samples; perform gridded nanoindentation tests on the core samples to obtain load-displacement curves at each measuring point; S2. Analyze and calculate the load-displacement curves of each measuring point, draw the heterogeneity map of the sampling points, and draw the micromechanical spatial heterogeneity map of the entire coal seam based on the heterogeneity map of the sampling points. S3. Identify the micromechanical spatial heterogeneity spectrum of the entire coal seam to obtain the advantageous paths and disadvantageous paths that are easy to extend and difficult to extend of the hydraulic fracturing fractures in the coal seam. Specifically, the advantageous paths that are easy to extend are weak zones or modulus abrupt change interfaces, which will promote the development and extension of hydraulic fracturing fractures; the disadvantageous paths that are difficult to extend are hard zones or modulus concentration areas, which hydraulic fracturing fractures will avoid developing. S4. Based on the distribution information of the advantageous paths and disadvantageous paths of fracturing fractures in coal seams that are easy to extend and difficult to extend, construct targeted hydraulic fracturing design schemes. For the hydraulic fracturing design scheme used in hard areas, the specific approach is to increase the perforation density, increase the pumping pressure of the fracturing injection pump, and increase the viscosity of the fracturing fluid to effectively support the identified weak fractures. For weak areas, the hydraulic fracturing design scheme used is to reduce the perforation density, reduce the pumping pressure of the fracturing injection pump, and reduce the viscosity of the fracturing fluid to form a uniformly distributed fracture network. S5. Implement the hydraulic fracturing design scheme, and monitor the fracture propagation range using resistivity tomography technology; feed the monitoring data back to the computer in real time, and dynamically adjust the fracturing parameters of the hydraulic fracturing design scheme.

2. The method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps according to claim 1, characterized in that, The geological data of the target coal seam are obtained, and samples are taken from the target coal seam to obtain core samples; Mesh nanoindentation tests were performed on the core samples, and the load-displacement curves at each measuring point were obtained, including: Before performing gridded nanoindentation tests on the core samples, the core samples were cut into several square coal samples of a predetermined size, the surface of the square coal samples was polished, and the polished square coal samples were cast in epoxy resin.

3. The method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps according to claim 2, characterized in that, The geological data of the target coal seam are obtained, and samples are taken from the target coal seam to obtain core samples; Gridded nanoindentation tests were performed on the core samples, and the load-displacement curves at each measuring point were obtained, including: In the gridded nanoindentation test of core samples, a target area is selected on the surface of a square coal sample; The mechanical parameters of the measuring points within the target area are tested to obtain the load-displacement curves of each measuring point.

4. The method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps according to claim 3, characterized in that, The testing of the mechanical parameters of the measuring points within the target area includes: There are 625 measuring points in the target area. Indentation experiments are performed on square coal samples based on the 625 measuring points, and the spacing between each measuring point is 10 μm.

5. The method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps according to claim 1, characterized in that, The process of analyzing and calculating the load-displacement curves at each measuring point, plotting the heterogeneity map of the sampling points, and plotting the micromechanical spatial heterogeneity map of the entire coal seam based on the heterogeneity map of the sampling points includes: The load-displacement curves of each measuring point are calculated to obtain the fracture toughness of each measuring point; Statistical analysis of fracture toughness at each measuring point is performed, and the heterogeneity spectrum of the sampling points is output. Based on the heterogeneity maps of the sampling points, a micromechanical spatial heterogeneity map of the entire coal seam was drawn.

6. The method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps according to claim 5, characterized in that, The calculation of the load-displacement curves at each measuring point yields the fracture toughness at each measuring point, including: Based on the principle of energy conservation, the total energy generated during the nanoindentation test was analyzed to obtain the fracture energy, recoverable elastic energy, and irrecoverable plasticity. By integrating the relationship between load and displacement in the load-displacement curve, the sum of recoverable elastic energy and unrecoverable plastic energy is calculated. The total energy generated during the nanoindentation test is calculated based on the maximum indentation depth and the creep displacement during the holding phase. Based on the sum of recoverable elastic energy and non-recoverable plasticity, and the total energy generated during the nanoindentation test, the rate of change of fracture energy relative to the indenter contact projection surface is calculated to obtain the critical energy release rate. The fracture toughness at the current measuring point is calculated based on the critical energy release rate and the reduced modulus.

7. The method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps according to claim 5, characterized in that, The statistical analysis of fracture toughness at each measuring point, and the output of the heterogeneity spectrum of the sampling points, includes: The fracture toughness values ​​calculated from all measuring points are collected to form a mechanical property dataset for each measuring point. The normal analytical algorithm was used to perform fitting analysis on the mechanical performance dataset of each measuring point; Based on the fitting analysis results, statistical distribution parameters are extracted, and a heterogeneity map of the sampling points is generated according to the spatial location of each measuring point and the corresponding fracture toughness value.

8. The method for optimizing hydraulic fracturing parameters based on nanoindentation spatial heterogeneity maps according to claim 1, characterized in that, The hydraulic fracturing design scheme is implemented, and resistivity tomography technology is used to monitor the fracture propagation range. The monitoring data is fed back to the computer in real time, and the fracturing parameters of the hydraulic fracturing design scheme are dynamically adjusted, including: When implementing a hydraulic fracturing design scheme, resistivity tomography is used to monitor the fracture propagation range. The monitoring data is fed back to the computer in a timely manner. The hydraulic fracturing design scheme is optimized by changing the pumping pressure of the fracturing injection pump, adjusting the perforation density, adjusting the proppant type, and adjusting the mixing ratio of proppant and water.

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