Method and device for evaluating compressibility of tight reservoir based on rock scratch characteristics

Abstract

The embodiment of the invention relates to the technical field of oil and gas field development, and provides a tight reservoir compressibility evaluation method and device based on rock scratch characteristics, and the method comprises the following steps: placing a target tight rock sample in a scratch test instrument, and carrying out multiple times of scratch tests based on a preset tool bit width and a loading rate, recording scratch test data generated in each scratch test, wherein the scratch test data comprises cutter head tangential force, scratch depth and cutter displacement; according to the tool bit tangential force, the tool bit width and the scratch depth obtained in the last scratch test, the uniaxial compressive strength and the fracture toughness are calculated; calculating the crack density according to the cutter displacement and the cutter bit tangential force obtained in the last scratch test; calculating to obtain a compressibility index according to the uniaxial compressive strength, the fracture toughness and the crack density; and evaluating the compressibility of the target compact rock sample according to the compressibility index. According to the embodiment of the invention, the efficiency and accuracy of compressibility evaluation of the tight reservoir can be improved.

Description

Technical Field

[0001] The embodiments of this specification relate to the technical field of oil and gas field development, and in particular to a method and device for evaluating the compressibility of tight reservoirs based on rock scratch characteristics. Background Art

[0002] The exploration and development of unconventional oil and gas resources has made significant breakthroughs in recent years, becoming a crucial pillar for increasing reserves and production. Tight oil and gas, as one of the key unconventional resources, plays a crucial role in oil and gas production. Tight reservoirs primarily refer to low-permeability sandstones, carbonate rocks, mixed sedimentary rocks, tuffs, and shales. Due to their low porosity and permeability, as well as poor flow capacity, tight reservoirs require large-scale volume fracturing to create complex fracture networks and improve reservoir connectivity for efficient development. Fracturability evaluation refers to the reservoir's ability to form a complex fracture network during fracturing. Field experience shows that when tight reservoirs have good fracturability, complex fracture networks are easily generated during fracturing, resulting in relatively high well productivity. When tight reservoirs have poor fracturability, plastic deformation of the reservoir rock during fracturing makes it less likely to form a complex fracture network, resulting in relatively low well productivity. Clarifying whether a reservoir can form a complex fracture network under hydraulic fracturing conditions, that is, conducting quantitative evaluation of its compressibility, is of great significance for engineering sweet spot selection, hydraulic fracturing optimization, post-fracturing production capacity evaluation, and economic benefit development.

[0003] The core of tight reservoir compressibility evaluation lies in how to accurately quantify the mechanical properties and damage characteristics of the rock. Traditional methods rely heavily on core destructive tests, such as uniaxial compression and three-point bending. These testing methods have limitations such as high sampling loss, long test cycles, and single parameters. This makes it difficult to efficiently obtain multi-dimensional evaluation indicators, resulting in large deviations between the evaluation results and the actual fracturing effect. Therefore, there is an urgent need to develop a non-destructive, efficient, and multi-mechanical parameter evaluation method for quantitative evaluation of tight reservoir compressibility in the laboratory. This method can address the problems of low efficiency, high sampling loss, single parameters, and poor accuracy in existing compressibility evaluation methods. Summary of the Invention

[0004] In view of the above problems in the prior art, the purpose of the embodiments of this specification is to provide a method and device for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, so as to solve the problems of low efficiency and accuracy in the prior art in evaluating the compressibility of tight reservoirs.

[0005] In order to solve the above technical problems, the specific technical solutions of the embodiments of this specification are as follows:

[0006] In one aspect, an embodiment of this specification provides a method for evaluating the compressibility of a tight reservoir based on rock scratch characteristics, the method comprising:

[0007] Placing the target dense rock sample in a scratch testing instrument, performing multiple scratch tests based on a preset cutter head width and loading rate, and recording scratch test data generated by each scratch test, wherein the scratch test data includes cutter head tangential force, scratch depth, and tool displacement;

[0008] The uniaxial compressive strength and fracture toughness were calculated based on the blade tangential force, blade width, and scratch depth obtained from the last scratch test.

[0009] The crack density was calculated based on the tool displacement and tool head tangential force obtained from the last scratch test;

[0010] Calculating a compressibility index based on the uniaxial compressive strength, fracture toughness, and crack density;

[0011] The compressibility of the target dense rock sample is evaluated according to the compressibility index.

[0012] Furthermore, the uniaxial compressive strength is calculated based on the cutter head tangential force, cutter head width and scratch depth obtained from the last scratch test, including:

[0013] The uniaxial compressive strength is calculated using the following formula:

[0014]

[0015] Among them, UCS represents the uniaxial compressive strength, F S represents the tangential force of the blade, w represents the width of the blade, and d represents the scratch depth.

[0016] Furthermore, the fracture toughness is calculated based on the blade tangential force, blade width, and scratch depth obtained from the last scratch test, including:

[0017] The fracture toughness is calculated using the following formula:

[0018]

[0019] Among them, K C Indicates fracture toughness, F S represents the tangential force of the blade, w represents the width of the blade, and d represents the scratch depth.

[0020] Furthermore, the crack density is calculated based on the tool displacement and the tool head tangential force obtained from the last scratch test, including:

[0021] Calculating the total length of the scratch according to the tool displacement;

[0022] Determine the number of times the absolute value of the fluctuation amplitude of the cutting head tangential force exceeds a preset value during the scratch test;

[0023] The crack density is calculated based on the total length of the scratches and the number of fluctuations.

[0024] Furthermore, the crack density is calculated based on the total length of the scratches and the number of fluctuations, including:

[0025] The crack density is calculated using the following formula:

[0026]

[0027] Wherein, CD represents the crack density, N represents the number of times the absolute value of the fluctuation amplitude of the tool head tangential force exceeds the preset value in the scratch test, and L represents the total scratch length.

[0028] Furthermore, the compressibility index is calculated based on the uniaxial compressive strength, fracture toughness and crack density, including:

[0029] The compressibility index is calculated using the following formula:

[0030]

[0031] Among them, FI represents the compressibility index, UCS, K C , CD represent the uniaxial compressive strength, fracture toughness and crack density of the last scratch test, respectively, UCS max , K Cmin 、CD max They represent the maximum uniaxial compressive strength, minimum fracture toughness and maximum crack density in multiple scratch tests, respectively; a represents the weight coefficient of uniaxial compressive strength, b represents the weight coefficient of fracture toughness, and g represents the weight coefficient of crack density.

[0032] Furthermore, the multiple scratch tests based on the preset blade width and loading rate include:

[0033] Performing a scratch test on the target dense rock sample according to a preset number of initial tests, and recording the cutter head tangential force and scratch depth of each scratch test;

[0034] The first coefficient of variation and the second coefficient of variation are calculated based on the tangential force of the tool head and the scratch depth of each scratch test;

[0035] Determining whether the first coefficient of variation and the second coefficient of variation are both less than a preset threshold;

[0036] If so, the scratch test is terminated;

[0037] If not, the number of tests is increased according to the preset step size, and the steps of calculating the first coefficient of variation and the second coefficient of variation according to the tangential force of the tool head and the scratch depth of each scratch test are repeated until the first coefficient of variation and the second coefficient of variation are both less than the preset threshold value.

[0038] Furthermore, after recording the cutter head tangential force, scratch depth and tool displacement of each scratch test, the method further includes:

[0039] Determining whether there is abnormal data in the tool head tangential force, scratch depth, and tool displacement of each scratch test;

[0040] If so, the abnormal data is deleted and the order of the remaining scratch tests is re-determined according to the scratch test time.

[0041] On the other hand, an embodiment of this specification provides a device for evaluating the compressibility of a tight reservoir based on rock scratch characteristics, the device comprising:

[0042] A test module is used to place a target dense rock sample in a scratch test instrument, perform multiple scratch tests based on a preset cutter head width and loading rate, and record scratch test data generated by each scratch test, wherein the scratch test data includes cutter head tangential force, scratch depth, and tool displacement;

[0043] The first calculation module is used to calculate the uniaxial compressive strength and fracture toughness based on the cutter head tangential force, cutter head width and scratch depth obtained from the last scratch test;

[0044] The second calculation module is used to calculate the crack density based on the tool displacement and the cutter head tangential force obtained from the last scratch test;

[0045] a third calculation module, configured to calculate a compressibility index based on the uniaxial compressive strength, fracture toughness, and crack density;

[0046] An evaluation module is used to evaluate the compressibility of the target dense rock sample according to the compressibility index.

[0047] On the other hand, an embodiment of this specification further provides a computer device, including a memory, a processor, and a computer program stored in the memory, wherein when the computer program is run by the processor, the computer program executes instructions of any one of the above methods.

[0048] Using the above technical solution, the embodiments of this specification provide a method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics. By conducting multiple scratch tests on target tight rock samples to simulate the multiple initiation and expansion of cracks during fracturing, compared to traditional uniaxial compression tests that only reflect the initial failure strength, the multiple scratch test data of the embodiments of this specification can effectively reflect the entire process of rock damage from initial damage to stable failure, more closely matching the actual rock fracturing scenario. By integrating three core parameters: uniaxial compressive strength, fracture toughness, and crack density, and constructing a compressibility index as a comprehensive evaluation indicator to evaluate compressibility, this method avoids the one-sidedness of existing methods that only use a single brittleness index to evaluate compressibility, thereby improving the accuracy of compressibility evaluation. Moreover, compared to test methods such as uniaxial compression and three-point bending, the scratch test of the embodiments of this specification is low-cost and requires less testing time for rock samples, thereby improving the efficiency of compressibility evaluation. It is applicable to unconventional reservoirs such as tight sandstone, carbonate rock, shale, and low-permeability conventional oil and gas reservoirs, providing efficient quantitative support for engineering fracturing design.

[0049] The above description is only an overview of the technical solutions of some embodiments of this specification. In order to more clearly understand the technical means of some embodiments of this specification, they can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the embodiments of this specification more obvious and easy to understand, the following specifically cites preferred embodiments and provides detailed descriptions in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of this specification. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0051] Figure 1 A schematic diagram showing the steps of a method for evaluating the compressibility of a tight reservoir based on rock scratch characteristics in some embodiments of this specification is shown;

[0052] FIG2( a ) is a schematic diagram showing a plastic rock breaking mode in a scratch test in some embodiments of this specification;

[0053] FIG2( b ) shows a schematic diagram of a brittle rock breaking mode in a scratch test in some embodiments of this specification;

[0054] Figure 3 A schematic diagram showing the steps of performing multiple scratch tests based on a preset tool tip width and loading rate in some embodiments of this specification is shown;

[0055] Figure 4A schematic diagram of the steps for calculating crack density in some embodiments of this specification is shown;

[0056] Figure 5 Schematic diagram of the curve showing the change of normal stress and tangential stress in the scratch test in some embodiments of this specification;

[0057] Figure 6 A schematic diagram of the structure of a tight reservoir compressibility evaluation device based on rock scratch characteristics in some embodiments of this specification is shown;

[0058] Figure 7 A schematic structural diagram of a computer device in this specification is shown.

[0059] Description of the accompanying symbols:

[0060] 601, test module;

[0061] 602. First calculation module;

[0062] 603. Second calculation module;

[0063] 604, third calculation module;

[0064] 605, evaluation module;

[0065] 702. Computer equipment;

[0066] 704, processor;

[0067] 706. Memory;

[0068] 708, driving mechanism;

[0069] 710, input / output module;

[0070] 712. Input devices;

[0071] 714. Output device;

[0072] 716. Presentation equipment;

[0073] 718. Graphical User Interface;

[0074] 720, network interface;

[0075] 722, communication link;

[0076] 724. Communication bus. DETAILED DESCRIPTION

[0077] The following will be combined with the drawings in the embodiments of this specification to clearly and completely describe the technical solutions in the embodiments of this specification. Obviously, the embodiments described are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this specification.

[0078] It should be noted that the terms "first," "second," and the like in this specification, the claims, and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of this specification described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product, or device comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, products, or devices.

[0079] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, storage, and display, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties. The acquisition, storage, use, and processing of data in the technical solutions described in the embodiments of this application comply with relevant regulations.

[0080] In order to solve the above problems, the present invention provides a method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics. Figure 1 This is a schematic diagram of the steps of a method for evaluating the compressibility of a tight reservoir based on rock scratch characteristics provided in an embodiment of this specification. This specification provides method operation steps as described in the embodiment or flow chart, but may include more or fewer operation steps based on conventional or non-creative work. The order of steps listed in the embodiment is only one way of executing the steps among many, and does not represent the only execution order. When the actual system or device product is executed, it can be executed in the order or in parallel according to the method shown in the embodiment or the accompanying drawings. Specifically, Figure 1 As shown, the method may include:

[0081] S101: placing a target dense rock sample in a scratch testing instrument, performing multiple scratch tests based on a preset cutter head width and loading rate, and recording scratch test data generated by each scratch test, wherein the scratch test data includes cutter head tangential force, scratch depth, and tool displacement;

[0082] S102: Calculate the uniaxial compressive strength and fracture toughness based on the blade tangential force, blade width, and scratch depth obtained from the last scratch test;

[0083] S103: Calculate the crack density based on the tool displacement and the tool head tangential force obtained from the last scratch test;

[0084] S104: Calculating a compressibility index based on the uniaxial compressive strength, fracture toughness, and crack density;

[0085] S105: Evaluate the compressibility of the target dense rock sample according to the compressibility index.

[0086] Using the above technical solution, the present invention provides a method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics. By conducting multiple scratch tests on target tight rock samples to simulate the multiple initiation and expansion of cracks during fracturing, the scratch test data from the present invention effectively reflects the entire process from initial damage to stable failure, compared to traditional uniaxial compression tests that only reflect the initial failure strength. This method is more suitable for real-world shale fracturing scenarios. By integrating three core parameters, uniaxial compressive strength, fracture toughness, and crack density, and constructing a compressibility index as a comprehensive evaluation indicator to evaluate compressibility, it avoids the one-sidedness of existing methods that use only a single brittleness index for compressibility evaluation, thereby improving the accuracy of compressibility evaluation. Furthermore, compared to uniaxial compression, three-point bending, and other testing methods, the scratch test in the present invention is low-cost and requires less testing time for rock samples, thereby improving the efficiency of compressibility evaluation. It is applicable to unconventional reservoirs such as tight sandstone, shale, and carbonate rocks, as well as low-permeability conventional oil and gas reservoirs, providing efficient quantitative support for engineering fracturing design.

[0087] The rock breaking mode (plastic or brittle) during the scratching process is directly related to its mechanical response. The core mechanism is that at the same cutting depth, the spatial heterogeneity of local matrix parameters (such as mineral composition, porosity, and cementation strength) leads to significant differences in the mechanical response of different regions of the rock. As shown in Figure 2(a), the plastic breaking mode occurs at shallow cutting depths, where the rock is sheared ahead of the cutter. In this mode, rock fragmentation is primarily determined by uniaxial compressive strength. As shown in Figure 2(b), the brittle breaking mode occurs at deep cutting depths, where the cutter is short, generating cracks that propagate toward the rock surface ahead of the cutter. In this mode, rock fragmentation is primarily determined by fracture toughness. Tight reservoirs are unique in their low porosity and low permeability physical properties and highly heterogeneous mechanical behavior. Due to varying mineral compositions or structural defects within the rock, brittle fracture occurs locally during the scratching process, while plastic deformation occurs elsewhere. In rock areas with high hardness and low toughness (such as quartz-rich areas), sudden fractures occur under the action of the tool, forming fragmented peeling, which causes brittle failure. In areas with low strength and high plasticity (such as clay-rich areas), energy is dissipated through continuous deformation, resulting in ductile scratches, which causes plastic failure. Therefore, tight reservoir rocks will show a pattern of alternating brittle and plastic failure in scratch tests. Existing tests such as uniaxial compression and three-point bending are usually based on data from a single position, which makes it difficult to reflect the spatial heterogeneity of reservoir rocks, and only focus on a single mechanical parameter. There is a lack of comprehensive analysis of multiple parameters, making it difficult to comprehensively evaluate the compressibility of rocks. The embodiments of this specification take into account the dynamic alternation of two rock breaking modes in rocks during scratches, and the rock crushing under the two rock breaking modes depends on the uniaxial compressive strength and fracture toughness, respectively. Therefore, the embodiments of this specification comprehensively evaluate the compressibility of tight reservoir rocks by comprehensively analyzing the three parameters of uniaxial compressive strength, fracture toughness and crack density, thereby improving the accuracy of the evaluation of the compressibility of tight reservoir rocks.

[0088] In some embodiments of this specification, the dense rock sample can be a standard core cylindrical rock sample with a diameter of 25 mm and a length of 50 mm. Obtaining a core cylinder of this size usually involves a drilling process to extract the original core from the underground rock, and then cutting it into a cylindrical sample of standard size using professional cutting equipment in the laboratory or on-site. During the cutting process, it is necessary to ensure the surface finish and flatness of the core to facilitate subsequent testing and analysis. Due to its moderate size, the standard core cylinder of φ25mm×50mm is suitable for experiments such as permeability testing, porosity analysis, rock microstructure observation, and compressibility testing. Through these tests, the oil storage capacity, permeability and microstructural characteristics of the rock can be understood, providing a scientific basis for the evaluation and exploitation of oil and gas resources.

[0089] Fix the target dense rock sample on the stage of the scratch tester, adjust the cutter head to be perpendicular to the rock surface, set the cutter head width ω (mm) and the initial loading rate, and control the scratch tester to scratch the rock surface at a constant rate. In some embodiments of this specification, the cutter head width ω is set to 5mm and the initial loading rate is set to 0.1mm / s. The following scratch test data are also recorded simultaneously: cutter head tangential force F S (unit: N), scratch depth d (unit: mm), and tool displacement l (unit: mm). The cutter head tangential force is the horizontal resistance exerted by the rock on the cutter head when the cutter head cuts through the rock, reflecting the rock's ability to resist shear failure. The scratch depth is the vertical depth of the cutter head into the rock, reflecting the rock's deformation capacity under normal load and is directly related to the rock's hardness and fracture toughness. The tool displacement reflects the scratch length and can therefore be used to calculate the crack density.

[0090] The goal of the scratch test is to make the rock sample reach a stable failure state through multiple scratches, so as to obtain representative mechanical parameters and use these mechanical parameters to evaluate the compressibility of the rock sample. Figure 3 The multiple scratch tests based on the preset blade width and loading rate include:

[0091] S301: performing a scratch test on the target dense rock sample according to a preset number of initial tests, and recording the cutter head tangential force, scratch depth, and tool displacement of each scratch test;

[0092] S302: Calculating a first coefficient of variation, a second coefficient of variation, and a third coefficient of variation based on the tool head tangential force, the scratch depth, and the tool displacement of each scratch test;

[0093] S303: Determine whether the first coefficient of variation, the second coefficient of variation, and the third coefficient of variation are all less than a preset threshold;

[0094] S304: If yes, terminate the scratch test;

[0095] S305: If not, increase the number of tests according to the preset step size, and repeat the steps of calculating the first coefficient of variation, the second coefficient of variation and the third coefficient of variation according to the tool head tangential force, the scratch depth and the tool displacement of each scratch test, until the first coefficient of variation, the second coefficient of variation and the third coefficient of variation are all less than the preset threshold value.

[0096] It is understandable that when a rock sample is first scratched, the tangential force is relatively large because the rock sample surface is intact. As the number of scratches increases, the rock sample surface gradually breaks and damage accumulates, and the tangential force and scratch depth gradually decrease and tend to stabilize. When the test data of multiple consecutive scratch tests, namely the cutter head tangential force, scratch depth, and tool displacement, tend to be stable, it indicates that the rock sample has reached a stable failure state. The impact of subsequent tests on the results can be ignored, and the test can be stopped at this time. Due to the different properties of different rock samples, the number of scratch tests for different rock samples is also different. For example, harder rocks may require more scratches to produce sufficient damage, while softer rocks may require fewer scratches. Therefore, for the target dense rock sample, the scratch test can be performed according to the preset initial number of tests. Then, based on the stability of the test data, it can be determined whether the number of tests should be increased to allow the rock sample to reach a stable failure state. In some embodiments of this specification, the initial number of tests is set to 3, that is, three scratch tests are first performed on the target dense rock sample, and then the coefficient of variation of the cutter head tangential force, scratch depth, and tool displacement are calculated based on the cutter head tangential force, scratch depth, and tool displacement of the three scratch tests. The coefficient of variation is used to quantify the degree of dispersion of the test data and judge the stability of the test parameters. The smaller the coefficient of variation, the more stable the test data. In some embodiments of this specification, the coefficient of variation is calculated using the following formula:

[0097]

[0098] Wherein, CV represents the coefficient of variation, m represents the mean, and s represents the standard deviation. In some embodiments of this specification, the threshold value of the coefficient of variation is set to 5%. In other embodiments, the remaining threshold values can be set according to the actual accuracy requirements. If after 3 tests, the coefficients of variation of the cutter head tangential force, scratch depth and tool displacement are all less than 5%, it indicates that the target dense rock sample has reached a stable destruction state, and the test can be terminated at this time. If the coefficient of variation of one of the test parameters is greater than 5%, it indicates that the discrete degree of the 3 test data is high, and the dense rock sample has not yet reached a stable destruction state, so the scratch test needs to be continued. In some embodiments of this specification, the number of tests is increased according to the preset step size. For example, the step size of the number of tests is set to 2, that is, the target dense rock sample is subjected to 2 scratch tests, and the respective coefficients of variation are recalculated based on the 5 test data until the coefficients of variation of each parameter are less than 5%, and then the scratch test is terminated.

[0099] In some embodiments of this specification, after recording the cutter head tangential force, scratch depth, and tool displacement of each scratch test, the method further includes:

[0100] Determining whether there is abnormal data in the tool head tangential force, scratch depth, and tool displacement of each scratch test;

[0101] If so, the abnormal data is deleted and the order of the remaining scratch tests is re-determined according to the scratch test time.

[0102] It can be understood that in order to avoid the problem that the test data are obviously abnormal due to equipment abnormality or operation error during the test, which affects the accuracy of subsequent mechanical parameter calculation, that is, the test data that deviates significantly from the rock mechanical behavior law or the test design expectation, including physically unreasonable values, such as scratch depth d<0, tangential force F S <0, outliers whose mean deviation from other data exceeds a preset error range, and sudden changes in continuous stable data, such as a sudden and significant drop in tangential force. The embodiments of this specification perform anomaly detection and processing on the test data before determining that the rock sample has reached a stable failure state. In some embodiments, physical anomalies can be detected by setting a physical rationality threshold, such as a normal scratch depth d>0. If d<0 is detected in a certain test, the data can be determined to be abnormal. In other embodiments, the 3σ principle or the IQR method can be applied to detect outliers. For sudden changes in continuous stable data, the parameter change rate of adjacent tests can be calculated. If it exceeds the threshold, it can be determined to be an anomaly. The test data is detected for anomalies using the above rules. If an anomaly is found, it is deleted and the order of the remaining scratch tests is re-determined based on the test scratch test time. For example, after four scratch tests on the target dense rock sample, if the data of the third test is detected to be abnormal, the data of the third test is deleted and the order of the original fourth scratch test is adjusted to the third. In other embodiments, if the number of valid test data after deletion is less than 3, additional scratch tests are required to meet the minimum number of tests (3). In this way, by eliminating abnormal data caused by equipment failure or operational errors, the reliability of the test data is improved, and the misjudgment of the rock sample reaching a stable failure state due to the use of abnormal data is avoided, which may affect the subsequent evaluation of compressibility.

[0103] In the initial scratch test of the rock sample, since the rock surface is undamaged, the cutter head needs to overcome a relatively high initial strength. As the number of scratches increases, cumulative damage (such as microcrack expansion and plastic deformation) gradually forms on the rock surface, and the tangential force and scratch depth gradually tend to be stable. The final scratch test is the last round of scratching after the damage on the rock sample surface tends to be stable. It usually corresponds to the state where the rock damage is the most severe and the failure mode is the most complete. The test data at this time can better reflect the actual response of the rock under fracturing stress (such as the difficulty of crack expansion). The stable values of the tangential force and scratch depth can represent the ultimate fracturing ability of the rock. Therefore, the last test data in the stable stage is closer to the dynamic process of crack expansion during fracturing and can be used to calculate uniaxial compressive strength, fracture toughness and crack density.

[0104] In some embodiments of this specification, the uniaxial compressive strength is calculated based on the blade tangential force, blade width, and scratch depth obtained from the last scratch test, including:

[0105] The uniaxial compressive strength is calculated using the following formula:

[0106]

[0107] Among them, UCS represents the uniaxial compressive strength, F S represents the tangential force on the cutter head, w represents the cutter head width, d represents the scratch depth, e represents the specific work of crushing, and E represents the specific energy of crushing. The tangential force in a scratch test pushes the cutter to perform work, and its energy is consumed in crushing the rock. Therefore, the specific work of crushing, e, corresponding to the cutter head's cutting point in the scratch test, is the rock sample's uniaxial compressive strength.

[0108] In some embodiments of this specification, the fracture toughness is calculated based on the blade tangential force, blade width, and scratch depth obtained from the last scratch test, including:

[0109] The fracture toughness is calculated using the following formula:

[0110]

[0111] Among them, K C Indicates fracture toughness, F S represents the tangential force of the blade, w represents the width of the blade, and d represents the scratch depth.

[0112] In some embodiments of this specification, the crack density is calculated based on the tool displacement and the tool head tangential force obtained from the last scratch test, including:

[0113] S401: Calculating the total scratch length according to the tool displacement.

[0114] In some embodiments of the present specification, the total scratch length is calculated based on the integral of the tool displacement.

[0115] S402: Determine the number of times that the absolute value of the fluctuation amplitude of the cutting head tangential force exceeds a preset value during the scratch test.

[0116] like Figure 5 As shown, when the tool passes through the rock surface, the rock is locally subjected to the combined effects of shear stress and normal stress. The initiation or expansion of cracks will cause the sudden release of stress inside the material. This process will significantly affect the real-time measurement value of the tangential force. This dynamic process will form characteristic fluctuation peaks and valleys in the tangential force signal amplitude. By counting the number of times the fluctuation amplitude of the cutter head tangential force signal exceeds the preset value, the degree of development of microcracks inside the rock can be reflected. During the scratching process, the tangential force will suddenly change when the tool encounters a crack. The more fluctuations there are, the higher the crack density. In some embodiments of this specification, the median tangential force of the cutter head is F~ s As a benchmark, the amplitude of the cutter head tangential force signal is within the upper and lower limits. and The number of times, that is, the number of fluctuations N can be expressed as:

[0117]

[0118] in, F in multiple scratch tests S The median value of M is the total number of sampling points in the scratch test, and F is the median value of s,i is the tangential force value of the cutter head at the i-th sampling point, 1 (.) It is an indicator function, which takes the value 1 when the condition in the brackets is met, and takes the value 0 otherwise.

[0119] S403: Calculate the crack density according to the total length of the scratches and the number of fluctuations.

[0120] In some embodiments of this specification, the crack density is calculated based on the total scratch length and the number of fluctuations using the following formula:

[0121]

[0122] Wherein, CD represents the crack density, N represents the number of times the absolute value of the fluctuation amplitude of the tool head tangential force exceeds the preset value in the scratch test, and L represents the total scratch length.

[0123] In some embodiments of this specification, the compressibility index is calculated based on the uniaxial compressive strength, fracture toughness, and crack density using the following formula:

[0124]

[0125] Among them, FI represents the compressibility index, UCS, K C , CD represent the uniaxial compressive strength, fracture toughness and crack density of the last scratch test, respectively, UCS max , K Cmin 、CD max where a represents the maximum uniaxial compressive strength, minimum fracture toughness, and maximum crack density, respectively, during multiple scratch tests. a represents the uniaxial compressive strength weighting factor, b represents the fracture toughness weighting factor, and g represents the crack density weighting factor. In some embodiments of this specification, a, b, and g are set based on rock properties. The specific values of a, b, and g may vary for rocks of different properties. If the rock is more sensitive to changes in uniaxial compressive strength during fracturing, the uniaxial compressive strength weighting factor may be set larger.

[0126] It is understandable that uniaxial compressive strength can reflect the ability of rock to resist fracturing damage. Fracture toughness characterizes the ability of rock to resist crack extension. The lower the fracture toughness, the easier it is for cracks to extend and the less energy required for fracturing. Fracture density indicates the degree of development of natural cracks within the rock. The higher the fracture density, the easier it is for natural cracks to be activated during fracturing and form a complex fracture network, thereby improving the fracturing effect. In formula (6), UCS / UCS max It represents the normalized compressive strength. The larger the value, the higher the brittle fracture potential. Cmin / K C It represents the reciprocal of the normalized fracture toughness. The larger the value, the smaller the crack propagation resistance. max It represents the normalized fracture density. The larger the value, the more developed the natural fracture network. Therefore, the higher the compressibility index, the better the rock compressibility.

[0127] In some embodiments of this specification, tight reservoirs can be divided into three sweet spots according to the compressibility index: Class I (high compressibility), Class II (medium compressibility), and Class III (low compressibility). Differentiated fracturing process parameter optimization plans are formulated accordingly. The specific parameter ranges for the above three types of tight reservoirs are shown in Table 1.

[0128] Table 1

[0129]

[0130] As can be seen from Table 1, for Class I (high compressibility), FI > 0.7, which characterizes medium strength (150 Mpa < UCS < 250 MPa), low toughness (Kc < 1.5 MPa·m1 / 2), and high fracture density (CD > 8 fractures / cm); for Class II (medium compressibility), 0.4 < FI < 0.7, corresponding to high strength (UCS > 250 MPa), medium toughness (1.5 MPa·m1 / 2 < Kc < 2.5 MPa·m1 / 2), and medium fracture density (5 fractures / cm < CD < 8 fractures / cm); for Class III (low compressibility), FI < 0.4, reflecting low strength (UCS < 150 MPa), high toughness (Kc > 2.5 MPa·m1 / 2), and low fracture density (CD < 5 fractures / cm). High compressibility requires that the rock is prone to generating a complex fracture network when compressed. When UCS > 250 MPa, the rock has extremely high compressive strength. High-strength rocks are often accompanied by medium toughness. During fracturing, shear fractures dominated by plastic deformation are likely to occur, resulting in a decrease in fracture propagation efficiency. Therefore, high-strength rocks have medium compressibility. Medium-strength rocks have a lower compressive strength than high-strength rocks and contain more brittle minerals inside. They are prone to cracking along fractures when compressed. Medium-strength rocks are often accompanied by low toughness and high fracture density. Low toughness indicates that the rock is brittle, and fractures are prone to rapid propagation when compressed, reducing the overall strength and increasing compressibility. High fracture density means that there are a large number of prefabricated weak surfaces inside the rock. When compressed, energy is concentrated on fracture propagation rather than resisting external forces, thus greatly enhancing compressibility. Therefore, rocks with medium strength + low toughness + high fracture density have the highest compressibility.

[0131] In some embodiments of this specification, through indoor tests on a large number of rock samples, the compressibility performance of rocks under different compressibility indices is tested, and the threshold ranges of the above three types of compressibility are determined by combining the application experience of experts in related fields. For example, when FI reaches 0.7, the energy consumption during the rock fragmentation process is significantly reduced, and the productivity of the gas well after fracturing is relatively high. Therefore, it can be used as the starting point for high compressibility.

[0132] Based on the above-mentioned method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, an embodiment of this specification also provides a corresponding device for evaluating the compressibility of tight reservoirs based on rock scratch characteristics. The device may include a system (including a distributed system), software (application), module, component, server, client, etc. using the method described in the embodiment of this specification and combined with the necessary implementation hardware. Based on the same innovative concept, the device in one or more embodiments provided in the embodiment of this specification is as described in the following embodiments. Since the implementation scheme and method for solving the problem of the device are similar, the implementation of the specific device in the embodiment of this specification can refer to the implementation of the aforementioned method, and the repetitions will not be repeated. As used below, the term "unit" or "module" can be a combination of software and / or hardware that implements a predetermined function. Although the device described in the following embodiments is preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceived.

[0133] Specifically, Figure 6 This is a schematic diagram of the module structure of an embodiment of a tight reservoir compressibility evaluation device based on rock scratch characteristics provided in this specification. Figure 6 As shown, the embodiment of this specification provides a tight reservoir compressibility evaluation device based on rock scratch characteristics, including:

[0134] A test module 601 is configured to place a target dense rock sample in a scratch test instrument, perform multiple scratch tests based on a preset cutter head width and loading rate, and record scratch test data generated by each scratch test, wherein the scratch test data includes cutter head tangential force, scratch depth, and tool displacement;

[0135] A first calculation module 602 is configured to calculate the uniaxial compressive strength and fracture toughness based on the cutter head tangential force, cutter head width, and scratch depth obtained from the last scratch test;

[0136] The second calculation module 603 is used to calculate the crack density based on the tool displacement and the tool head tangential force obtained from the last scratch test;

[0137] A third calculation module 604 is configured to calculate a compressibility index based on the uniaxial compressive strength, fracture toughness, and crack density;

[0138] The evaluation module 605 is configured to evaluate the compressibility of the target dense rock sample according to the compressibility index.

[0139] The beneficial effects achieved by the device provided in the embodiments of this specification are consistent with the beneficial effects achieved by the above-mentioned method and will not be repeated here.

[0140] Reference Figure 7As shown, based on the above-described method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, one embodiment of this specification further provides a computer device 702, wherein the above-described method is executed on the computer device 702. The computer device 702 may include one or more processors 704, such as one or more central processing units (CPUs), each of which may implement one or more hardware threads. The computer device 702 may also include any memory 706 for storing any type of information, such as code, settings, data, etc. For example, without limitation, the memory 706 may include any one or more combinations of the following: any type of RAM, any type of ROM, a flash memory device, a hard disk, an optical disk, etc. More generally, any memory may use any technology to store information. Furthermore, any memory may provide volatile or non-volatile retention of information. Furthermore, any memory may represent a fixed or removable component of the computer device 702. In one embodiment, when the processor 704 executes associated instructions stored in any memory or combination of memories, the computer device 702 may perform any operation of the associated instructions. The computer device 702 also includes one or more drive mechanisms 708 for interacting with any storage, such as a hard disk drive mechanism, an optical disk drive mechanism, and the like.

[0141] The computer device 702 may also include an input / output module 710 (I / O) for receiving various inputs (via input devices 712) and for providing various outputs (via output devices 714). A specific output mechanism may include a presentation device 716 and an associated graphical user interface (GUI) 718. In other embodiments, the input / output module 710 (I / O), input devices 712, and output devices 714 may not be included, and the computer device 702 may simply be a computer device in a network. The computer device 702 may also include one or more network interfaces 720 for exchanging data with other devices via one or more communication links 722. One or more communication buses 724 couple the components described above together.

[0142] The communication link 722 may be implemented in any manner, for example, via a local area network, a wide area network (e.g., the Internet), a point-to-point connection, etc., or any combination thereof. The communication link 722 may include any combination of hardwired links, wireless links, routers, gateway functions, name servers, etc., governed by any protocol or combination of protocols.

[0143] Corresponding to Figures 1 to 4 In addition to the method shown, an embodiment of this specification also provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the above method are executed.

[0144] The embodiment of this specification also provides a computer-readable instruction, wherein when the processor executes the instruction, the program therein causes the processor to execute the following Figures 1 to 4 The method shown.

[0145] The embodiment of this specification also provides a computer program product, including at least one instruction or at least one program, which is loaded and executed by a processor to implement the following Figures 1 to 4 The method shown.

[0146] It should be understood that in the various embodiments of this specification, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this specification.

[0147] It should also be understood that in the embodiments of this specification, the term "and / or" is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. Furthermore, the character " / " in this specification generally indicates that the associated objects are in an "or" relationship.

[0148] Those skilled in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed in this specification can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the above description has generally described the composition and steps of each example according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this specification.

[0149] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0150] In the several embodiments provided in this specification, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are merely illustrative. For example, the division of the units is merely a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the mutual coupling or direct coupling or communication connection shown or discussed can be an indirect coupling or communication connection through some interfaces, devices or units, or can be an electrical, mechanical or other form of connection.

[0151] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the embodiments of this specification.

[0152] In addition, the functional units in the various embodiments of this specification may be integrated into a single processing unit, or each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0153] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this specification is essentially or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for enabling a computer device (which can be a personal computer, server, or network device, etc.) to execute all or part of the steps of the method described in each embodiment of this specification. The aforementioned storage medium includes: various media that can store program codes, such as a USB flash drive, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk.

[0154] Specific embodiments are used in this specification to illustrate the principles and implementation methods of this specification. The description of the above embodiments is only used to help understand the methods and core ideas of this specification. At the same time, for those skilled in the art, based on the ideas of this specification, there will be changes in the specific implementation methods and application scope. In summary, the contents of this specification should not be understood as limiting this specification.

Claims

1. A method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, characterized in that: The method comprises: Placing the target dense rock sample in a scratch testing instrument, performing multiple scratch tests based on a preset cutter head width and loading rate, and recording scratch test data generated by each scratch test, wherein the scratch test data includes cutter head tangential force, scratch depth, and tool displacement; The uniaxial compressive strength and fracture toughness were calculated based on the blade tangential force, blade width, and scratch depth obtained from the last scratch test. The crack density was calculated based on the tool displacement and tool head tangential force obtained from the last scratch test; Calculating a compressibility index based on the uniaxial compressive strength, fracture toughness, and crack density; The compressibility of the target dense rock sample is evaluated according to the compressibility index.

2. The method according to claim 1, characterized in that The uniaxial compressive strength is calculated based on the blade tangential force, blade width, and scratch depth obtained from the last scratch test, including: The uniaxial compressive strength is calculated using the following formula: Among them, UCS represents the uniaxial compressive strength, F S represents the tangential force of the blade, w represents the width of the blade, and d represents the scratch depth.

3. The method according to claim 1, characterized in that The fracture toughness is calculated based on the blade tangential force, blade width, and scratch depth obtained from the last scratch test, including: The fracture toughness is calculated using the following formula: Among them, K C Indicates fracture toughness, F S represents the tangential force of the blade, w represents the width of the blade, and d represents the scratch depth.

4. The method according to claim 1, wherein The crack density is calculated based on the tool displacement and the tool head tangential force obtained from the last scratch test, including: Calculating the total length of the scratch according to the tool displacement; Determine the number of times the absolute value of the fluctuation amplitude of the cutting head tangential force exceeds a preset value during the scratch test; The crack density is calculated based on the total length of the scratches and the number of fluctuations.

5. The method according to claim 4, characterized in that The crack density is calculated based on the total length of the scratches and the number of fluctuations, including: The crack density is calculated using the following formula: Wherein, CD represents the crack density, N represents the number of times the absolute value of the fluctuation amplitude of the tool head tangential force exceeds the preset value in the scratch test, and L represents the total scratch length.

6. The method according to claim 1, characterized in that The compressibility index is calculated based on the uniaxial compressive strength, fracture toughness and crack density, including: The compressibility index is calculated using the following formula: Among them, FI represents the compressibility index, UCS, K C , CD represent the uniaxial compressive strength, fracture toughness and crack density of the last scratch test, respectively, UCS max , K Cmin 、CD max They represent the maximum uniaxial compressive strength, minimum fracture toughness and maximum crack density in multiple scratch tests, respectively; a represents the weight coefficient of uniaxial compressive strength, b represents the weight coefficient of fracture toughness, and g represents the weight coefficient of crack density.

7. The method according to claim 1, characterized in that The multiple scratch tests based on the preset blade width and loading rate include: Performing a scratch test on the target dense rock sample according to a preset number of initial tests, and recording the cutter head tangential force, scratch depth, and tool displacement of each scratch test; The first coefficient of variation, the second coefficient of variation and the third coefficient of variation are calculated based on the tool head tangential force, the scratch depth and the tool displacement of each scratch test; Determining whether the first coefficient of variation, the second coefficient of variation, and the third coefficient of variation are all less than a preset threshold; If so, the scratch test is terminated; If not, the number of tests is increased according to the preset step size, and the steps of calculating the first coefficient of variation, the second coefficient of variation and the third coefficient of variation respectively according to the tool head tangential force, the scratch depth and the tool displacement of each scratch test are repeated until the first coefficient of variation, the second coefficient of variation and the third coefficient of variation are all less than the preset threshold value.

8. The method according to claim 7, characterized in that After recording the cutter head tangential force, scratch depth and tool displacement of each scratch test, the following steps are also included: Determining whether there is abnormal data in the tool head tangential force, scratch depth, and tool displacement of each scratch test; If so, the abnormal data is deleted and the order of the remaining scratch tests is re-determined according to the scratch test time.

9. A device for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, characterized in that: The device comprises: A test module is used to place a target dense rock sample in a scratch test instrument, perform multiple scratch tests based on a preset cutter head width and loading rate, and record scratch test data generated by each scratch test, wherein the scratch test data includes cutter head tangential force, scratch depth, and tool displacement; The first calculation module is used to calculate the uniaxial compressive strength and fracture toughness based on the cutter head tangential force, cutter head width and scratch depth obtained from the last scratch test; The second calculation module is used to calculate the crack density based on the tool displacement and the cutter head tangential force obtained from the last scratch test; a third calculation module, configured to calculate a compressibility index based on the uniaxial compressive strength, fracture toughness, and crack density; An evaluation module is used to evaluate the compressibility of the target dense rock sample according to the compressibility index.

10. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the method according to any one of claims 1 to 8 is implemented.

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