A method and device for evaluating compact reservoir compressibility based on rock scratch characteristics

Abstract

This specification relates to the field of oil and gas field development technology, and provides a method and apparatus for evaluating the compressibility of tight reservoirs based on rock scratch characteristics. The method includes: placing a target tight rock sample in a scratch testing instrument, performing multiple scratch tests based on a preset cutter width and loading rate, and recording the scratch test data generated in each scratch test, wherein the scratch test data includes cutter tangential force, scratch depth, and cutter displacement; calculating uniaxial compressive strength and fracture toughness based on the cutter tangential force, cutter width, and scratch depth obtained from the last scratch test; calculating fracture density based on the cutter displacement and cutter tangential force obtained from the last scratch test; calculating a compressibility index based on the uniaxial compressive strength, fracture toughness, and fracture density; and evaluating the compressibility of the target tight rock sample based on the compressibility index. This specification embodiment can improve the efficiency and accuracy of tight reservoir compressibility evaluation.

Description

Technical Field

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

[0002] Significant breakthroughs have been achieved in the exploration and development of unconventional oil and gas resources in recent years, becoming a crucial pillar for increasing reserves and production. Tight oil and gas, as one of the important unconventional resources, occupies a significant position in oil and gas production. Tight reservoirs mainly refer to reservoirs with low permeability, such as sandstone, carbonate rocks, mixed sedimentary rocks, tuff, and shale. Due to their low porosity and permeability, and poor seepage capacity, tight reservoirs require large-scale volumetric fracturing to form complex fracture networks, thereby improving reservoir connectivity and achieving efficient development. Compressibility assessment refers to the reservoir's ability to form complex fracture networks during fracturing development. Field experience shows that when tight reservoirs have good compressibility, complex fracture networks are easily generated during fracturing, resulting in relatively high production capacity of the oil and gas wells after fracturing; conversely, when tight reservoirs have poor compressibility, the reservoir rocks are prone to plastic deformation during fracturing, making it difficult to form complex fracture networks, resulting in relatively low production capacity of the oil and gas wells after fracturing. Determining whether reservoirs can form complex fracture networks under hydraulic fracturing conditions, i.e., conducting quantitative evaluation of compressibility, is of great significance for selecting sweet spots in engineering, optimizing hydraulic fracturing, assessing post-fracturing productivity, and developing economic benefits.

[0003] The core of tight reservoir compressibility assessment lies in accurately quantifying rock mechanical properties and damage characteristics. Traditional methods largely rely on destructive core experiments, such as uniaxial compression and three-point bending. These methods suffer from limitations such as high sampling costs, long testing cycles, and limited parameters, making it difficult to efficiently obtain multi-dimensional evaluation indicators. Consequently, the evaluation results deviate significantly from the actual fracturing effects. Therefore, there is an urgent need to develop a non-destructive, efficient, and multi-mechanical parameter quantitative assessment method for tight reservoir compressibility in the laboratory, which can solve the problems of low efficiency, high sampling costs, limited parameters, and poor accuracy in existing compressibility assessment methods. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, the purpose of the embodiments in this specification is to provide a method and apparatus for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, so as to solve the problem of low efficiency and accuracy in the evaluation of the compressibility of tight reservoirs in the prior art.

[0005] To solve the above-mentioned technical problems, the specific technical solutions of the embodiments in this specification are as follows:

[0006] On the one hand, embodiments of this specification provide a method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, the method comprising:

[0007] The target dense rock sample is placed in the scratch testing instrument, and multiple scratch tests are conducted based on the preset cutter head width and loading rate. The scratch test data generated in each scratch test are recorded, including the cutter head tangential force, scratch depth and cutter displacement.

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

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

[0010] The compressibility index is calculated based on the uniaxial compressive strength, fracture toughness, and crack density.

[0011] The compressibility of the target dense rock sample is evaluated based on the compressibility index.

[0012] Furthermore, the calculation of the uniaxial compressive strength based on the tangential force, cutter width, and scratch depth obtained from the last scratch test includes:

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

[0014]

[0015] Where UCS represents uniaxial compressive strength, F S represents the tangential force of the cutter head, w represents the width of the cutter head, and d represents the depth of the scratch.

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

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

[0018]

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

[0020] Furthermore, the calculation of crack density based on the tool displacement and tangential force of the tool tip obtained from the last scratch test includes:

[0021] The total length of the scratch is calculated based on the tool displacement.

[0022] Determine the number of times the absolute value of the fluctuation amplitude of the tangential force of the cutting head exceeds the 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 scratch length and the number of fluctuations, including:

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

[0026]

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

[0028] Furthermore, the calculation of the compressibility index based on the uniaxial compressive strength, fracture toughness, and crack density includes:

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

[0030]

[0031] Wherein, FI represents the compressibility index, and UCS and K... C CD represents the uniaxial compressive strength, fracture toughness, and crack density of the last scratch test, respectively, and UCS represents the crack density. max K Cmin CD max denoted as the maximum uniaxial compressive strength, minimum fracture toughness, and maximum crack density in multiple scratch tests, respectively. a represents the weighting coefficient of uniaxial compressive strength, b represents the weighting coefficient of fracture toughness, and g represents the weighting coefficient of crack density.

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

[0033] The target dense rock sample was subjected to scratch tests according to the preset initial number of tests, and the tangential force of the cutter head and the scratch depth were recorded for each scratch test.

[0034] The first coefficient of variation and the second coefficient of variation were calculated based on the tangential force of the cutting head and the scratch depth in each scratch test.

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

[0036] If so, then terminate the scratch test;

[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 based on the tangential force of the cutter 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.

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

[0039] Determine whether there are any abnormal data in the tool tip tangential force, scratch depth, and tool displacement of each scratch test;

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

[0041] On the other hand, embodiments of this specification provide a device for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, the device comprising:

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

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

[0045] The third calculation module is used to calculate the compressibility index based on the uniaxial compressive strength, fracture toughness and crack density.

[0046] The evaluation module is used to evaluate the compressibility of the target tight rock sample based on the compressibility index.

[0047] In another aspect, embodiments of this specification also provide a computer device, including a memory, a processor, and a computer program stored in the memory, wherein the computer program, when executed by the processor, performs instructions of any of the methods described above.

[0048] Using the above technical solution, the tight reservoir compressibility evaluation method based on rock scratch characteristics provided in this specification simulates multiple fracture initiation and propagation during fracturing by conducting multiple scratch tests on target tight rock samples. Compared to traditional uniaxial compression tests that only reflect initial failure strength, the multiple scratch test data in this specification effectively reflect the entire process of rock from initial damage to stable failure, more closely resembling real rock fracturing scenarios. By integrating three core parameters—uniaxial compressive strength, fracture toughness, and fracture density—and constructing a compressibility index as a comprehensive evaluation indicator, compressibility is evaluated. This avoids the one-sidedness of existing methods that only use a single brittleness index for compressibility evaluation, improving the accuracy of compressibility evaluation. Furthermore, compared to uniaxial compression, three-point bending, and other testing methods, the scratch test in 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 rocks, and shale, as well as low-permeability conventional oil and gas reservoirs, providing efficient quantitative support for engineering fracturing design.

[0049] The above description is merely an overview of some embodiments of the technical solutions in this specification. In order to better understand the technical means of some embodiments of this specification and to implement them in accordance with the content of the specification, and to make the above and other objects, features and advantages of the embodiments of this specification more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments or prior art of this specification, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 The diagram illustrates the steps of a method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, as described in some embodiments of this specification.

[0052] Figure 2(a) shows a schematic diagram of the plastic rock-breaking mode in a scratch test in some embodiments of this specification;

[0053] Figure 2(b) shows a schematic diagram of the brittle rock-breaking mode in the scratch test in some embodiments of this specification;

[0054] Figure 3 This specification shows schematic diagrams illustrating the steps of performing multiple scratch tests based on a preset blade width and loading rate in some embodiments of this specification;

[0055] Figure 4This specification illustrates schematic diagrams of the steps for calculating crack density in some embodiments;

[0056] Figure 5 This specification shows schematic diagrams illustrating the variation curves of normal stress and tangential stress in scratch tests in some embodiments of this specification;

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

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

[0059] Explanation of symbols in the attached drawings:

[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. Drive mechanism;

[0069] 710. Input / Output Module;

[0070] 712. Input devices;

[0071] 714. Output devices;

[0072] 716. Presentation equipment;

[0073] 718. Graphical User Interface;

[0074] 720. Network interface;

[0075] 722. Communication link;

[0076] 724. Communication bus. Detailed Implementation

[0077] The technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. Based on the embodiments in this specification, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this specification.

[0078] It should be noted that the terms "first," "second," etc., used in this specification, claims, and the foregoing drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, apparatus, product, or device that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or 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, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties. Furthermore, the acquisition, storage, use, and processing of data in the technical solutions described in the embodiments of this application all comply with relevant regulations.

[0080] To address the aforementioned issues, this specification provides an embodiment of a method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics. Figure 1 This diagram illustrates the steps of a method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, as provided in the embodiments of this specification. This specification provides the operational steps of the method described in the embodiments or flowcharts, but based on conventional or non-inventive labor, more or fewer operational steps may be included. The order of steps listed in the embodiments is merely one possible execution order among many and does not represent the only possible execution order. In actual system or device products, the methods shown in the embodiments or drawings can be executed sequentially or in parallel. Specifically, as shown in the attached diagrams... Figure 1 As shown, the method may include:

[0081] S101: Place the target dense rock sample inside the scratch testing instrument, perform multiple scratch tests based on the preset cutter head width and loading rate, and record the scratch test data generated in each scratch test, wherein the scratch test data includes the cutter head tangential force, scratch depth and cutter displacement;

[0082] S102: Based on the tangential force, cutter width, and scratch depth obtained from the last scratch test, the uniaxial compressive strength and fracture toughness are calculated.

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

[0084] S104: The compressibility index is calculated based on the uniaxial compressive strength, fracture toughness and crack density.

[0085] S105: Evaluate the compressibility of the target tight rock sample based on the compressibility index.

[0086] Using the above technical solution, the tight reservoir compressibility evaluation method based on rock scratch characteristics provided in this specification simulates multiple fracture initiation and propagation during fracturing by conducting multiple scratch tests on target tight rock samples. Compared to traditional uniaxial compression tests that only reflect initial failure strength, the multiple scratch test data in this specification effectively reflect the entire process of rock from initial damage to stable failure, which is more in line with real shale fracturing scenarios. By integrating three core parameters—uniaxial compressive strength, fracture toughness, and fracture density—and constructing a compressibility index as a comprehensive evaluation index, compressibility is evaluated. This avoids the one-sidedness of existing methods that only use a single brittleness index for compressibility evaluation, thus improving the accuracy of compressibility evaluation. Furthermore, compared to uniaxial compression, three-point bending, and other testing methods, the scratch test in 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, 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 fracturing 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 fracturing mode occurs at shallow cutting depths, where the rock is sheared before the cutter. In this mode, rock breakage mainly depends on uniaxial compressive strength. As shown in Figure 2(b), the brittle fracturing mode occurs at deeper cutting depths, where the cutter briefly creates cracks that propagate to the rock surface in front of the cutter. In this mode, rock breakage mainly depends on fracture toughness. Tight reservoirs are unique due to their low porosity and permeability physical properties and highly heterogeneous mechanical behavior. Because of different mineral compositions or structural defects within them, brittle fracture occurs locally during the scratching process, while plastic deformation occurs in other areas. In high-hardness, low-toughness rock regions (such as quartz-rich areas), sudden fracture occurs under the action of a cutting tool, resulting in fragmented spalling and brittle failure. In low-strength, high-plasticity regions (such as clay-rich areas), energy is dissipated through continuous deformation, producing ductile scratches and resulting in plastic failure. Therefore, tight reservoir rocks exhibit alternating brittle and plastic failure patterns in scratch tests. Existing tests such as uniaxial compression and three-point bending are usually based on data from a single location, which is insufficient to reflect the spatial heterogeneity of reservoir rocks. Furthermore, they focus only on a single mechanical parameter, lacking comprehensive analysis of multiple parameters, making it difficult to fully assess the compressibility of the rock. The embodiments in this specification consider the dynamic alternation of two rock-breaking modes in scratch testing. The rock fragmentation under these two modes depends on uniaxial compressive strength and fracture toughness, respectively. Therefore, the embodiments in this specification comprehensively analyze three parameters—uniaxial compressive strength, fracture toughness, and fracture density—to comprehensively assess the compressibility of tight reservoir rocks, thereby improving the accuracy of tight reservoir rock compressibility evaluation.

[0088] In some embodiments of this specification, the dense rock sample can be a standard cylindrical rock core with a diameter of 25 mm and a length of 50 mm. Obtaining a core cylinder of this size typically involves a drilling process to extract the original rock core from the underground rock, and then cutting it into standard-sized cylindrical samples using specialized cutting equipment in the laboratory or on-site. During the cutting process, it is necessary to ensure the surface smoothness and flatness of the core to facilitate subsequent testing and analysis. The φ25mm×50mm standard core cylinder, due to its moderate size, is suitable for permeability testing, porosity analysis, observation of rock microstructure, 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] The target dense rock sample is fixed on the stage of the scratch testing instrument. The cutter head is adjusted to be perpendicular to the rock surface, and the cutter head width ω (mm) and initial loading rate are set. The scratch testing instrument is then controlled to perform scratching operations on the rock surface at a constant rate. In some embodiments of this specification, the cutter head width ω is set to 5 mm and the initial loading rate to 0.1 mm / s. The following scratch test data are recorded simultaneously: cutter head tangential force F S (Unit: N), scratch depth d (unit: mm), and tool displacement l (unit: mm). The tangential force of the tool tip is the horizontal resistance exerted by the rock on the tool tip as it cuts through the rock, reflecting the rock's ability to resist shear failure. The scratch depth is the vertical depth to which the tool tip penetrates 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 crack density.

[0090] The goal of the scratch test is to induce a stable failure state in the rock sample through repeated scratching, thereby obtaining representative mechanical parameters to evaluate the compressibility of the rock sample. In some embodiments of this specification, reference is made to... Figure 3 The multiple scratch tests based on a preset blade width and loading rate include:

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

[0092] S302: The first coefficient of variation, the second coefficient of variation, and the third coefficient of variation are calculated based on the tangential force of the tool tip, the scratch depth, and the tool displacement in 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 so, 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 based on the tool tip tangential force, scratch depth and 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.

[0096] Understandably, when a rock sample is first scratched, the tangential force is relatively large due to the intact surface. As the number of scratches increases, the surface gradually breaks down, damage accumulates, and the tangential force and scratch depth gradually decrease and stabilize. When the test data from multiple consecutive scratch tests—namely, the tangential force, scratch depth, and tool displacement—stabilize, it indicates that the rock sample has reached a stable failure state, and subsequent tests have negligible impact on the results; at this point, the test can be stopped. Because different rock samples have different properties, the number of scratch tests required varies. For example, harder rocks may require more scratches to produce sufficient damage, while softer rocks may require fewer. Therefore, for dense rock samples, scratch tests can be performed with a preset initial number of tests, and then the stability of the test data can be used to determine whether additional tests should be conducted to bring the rock sample to a stable failure state. In some embodiments of this specification, the initial number of tests is set to 3. That is, the target dense rock sample is first subjected to 3 scratch tests. Then, the coefficients of variation for the cutter head tangential force, scratch depth, and cutter displacement are calculated based on the results of the 3 scratch tests. The coefficients of variation are used to quantify the dispersion of the test data and determine 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 coefficients of variation are calculated using the following formula:

[0097]

[0098] Where CV represents the coefficient of variation, m represents the mean, and s represents the standard deviation. In some embodiments of this specification, the threshold for the coefficient of variation is set to 5%. In other embodiments, other thresholds can be set according to actual accuracy requirements. If, after three tests, the coefficients of variation for the tangential force, scratch depth, and tool displacement are all less than 5%, it indicates that the target dense rock sample has reached a stable failure state, and the test can be terminated. If the coefficient of variation for any one of the test parameters is greater than 5%, it indicates that the dispersion of the data from these three tests is high, and the dense rock sample has not yet reached a stable failure state. Therefore, scratch tests need to be continued. In some embodiments of this specification, the number of tests is increased according to a preset step size. For example, if the test step size is set to 2, then two more scratch tests are performed on the target dense rock sample, and the coefficients of variation for each parameter are recalculated based on the data from the five tests. The scratch test is terminated when the coefficients of variation for each parameter are all less than 5%.

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

[0100] Determine whether there are any abnormal data in the tool tip tangential force, scratch depth, and tool displacement of each scratch test;

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

[0102] This can be understood as a measure to avoid significant anomalies in experimental data due to equipment malfunction or operational errors during the experiment, which could affect the accuracy of subsequent mechanical parameter calculations. Specifically, it addresses experimental data that deviates significantly from the laws of rock mechanics or the expectations of the experimental design, including physically unreasonable values ​​such as scratch depth d < 0 or tangential force F. S Outliers include those with a value <0, those whose deviation from the mean of other data exceeds a preset error range, and abrupt changes in continuous stable data, such as a sudden and significant drop in tangential force. In this specification, embodiments 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 IQR method can be applied to detect outliers. For abrupt changes in continuous stable data, the parameter change rate of adjacent tests can be calculated; if it exceeds a threshold, it can be determined to be abnormal. Using the above rules, anomalies are detected in the test data. If anomalies are found, they are deleted, and the order of the remaining scratch tests is re-determined based on the scratch test time. For example, if anomalies are detected in the data of the third test after four scratch tests on a target dense rock sample, the data of the third test is deleted, and the original order of the fourth scratch test is adjusted to the third. In other embodiments, if the number of valid test data is less than 3 after deletion, scratch tests need to be added 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 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 would affect the subsequent evaluation of compressibility.

[0103] In the initial scratch test, the rock sample's surface is undamaged, requiring the cutting tool to overcome high initial strength. As the number of scratches increases, cumulative damage (such as microcrack propagation and plastic deformation) gradually forms on the rock surface, and the tangential force and scratch depth gradually stabilize. The final scratch test is conducted after the rock sample surface damage has stabilized, typically corresponding to the state of most severe rock damage and the most complete failure mode. The test data at this stage better reflects the actual response of the rock under fracturing stress (such as the ease of crack propagation), and the stable values ​​of tangential force and scratch depth characterize the rock's ultimate fracturability. Therefore, the data from the final test in the stable stage more closely approximates the dynamic process of crack propagation 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 tangential force, cutter width, and scratch depth obtained from the last scratch test, including:

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

[0106]

[0107] Where UCS represents uniaxial compressive strength, F S Let represent the tangential force of the cutter head, w represent the cutter head width, d represent the scratch depth, e represent the specific work of crushing, and E represent the specific energy of crushing. In the scratch test, the tangential force drives the cutter to do work, and its energy is consumed in crushing the rock. Therefore, the specific work e corresponding to the cutting point of the cutter head in the scratch test is the uniaxial compressive strength of the rock sample.

[0108] In some embodiments of this specification, the fracture toughness is calculated based on the tangential force, cutter 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 F represents fracture toughness. S represents the tangential force of the cutter head, w represents the width of the cutter head, and d represents the depth of the scratch.

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

[0113] S401: The total length of the scratch is calculated based on the tool displacement.

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

[0115] S402: Determine the number of fluctuations in the absolute value of the tangential force fluctuation amplitude of the cutter head that exceed the preset value during the scratch test.

[0116] like Figure 5 As shown, when a tool cuts across a rock surface, the rock is subjected to a combination of shear stress and normal stress. The initiation or propagation of cracks leads to a sudden release of internal stress, a process that significantly affects the real-time measurement of the tangential force. This dynamic process creates characteristic peaks and valleys in the tangential force signal amplitude. By statistically analyzing the number of times the tangential force signal amplitude exceeds a preset value, the degree of development of micro-cracks within the rock can be reflected. During the scratching process, the tangential force abruptly changes when the tool encounters a crack; the more fluctuations, the higher the crack density. In some embodiments of this specification, the median tangential force F is used... s Based on this, the amplitude of the cutter head tangential force signal is within the upper and lower limits. and The number of fluctuations, or the number of fluctuations N, can be expressed as:

[0117]

[0118] in, For multiple scratch tests, F S The median, M is the total number of sampling points in the scratch test, F s,i Let be the tangential force value of the cutter head at the i-th sampling point, 1 (.) This is an indicator function that takes the value 1 if the condition within the parentheses is met, and 0 otherwise.

[0119] S403: The crack density is calculated based on the total length of the scratches and the number of fluctuations.

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

[0121]

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

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

[0124]

[0125] Wherein, FI represents the compressibility index, and UCS and K... C CD represents the uniaxial compressive strength, fracture toughness, and crack density of the last scratch test, respectively, and UCS represents the crack density. max K Cmin CD max These represent the maximum uniaxial compressive strength, minimum fracture toughness, and maximum fracture density, respectively, in multiple scratch tests. 'a' represents the uniaxial compressive strength weighting coefficient, 'b' represents the fracture toughness weighting coefficient, and 'g' represents the fracture density weighting coefficient. In some embodiments of this specification, 'a', 'b', and 'g' are set according to the rock properties; the specific values ​​of 'a', 'b', and 'g' may differ for rocks with different properties. If the rock is more sensitive to changes in uniaxial compressive strength during fracturing, the uniaxial compressive strength weighting coefficient can be set larger.

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

[0127] In some embodiments of this specification, tight reservoirs can be divided into three sweet spot regions: Class I (high compressibility), Class II (medium compressibility), and Class III (low compressibility) based on the compressibility index. Differentiated fracturing process parameter optimization schemes are formulated accordingly. The specific parameter ranges of 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. The compressive strength of medium-strength rocks is lower than that of high-strength rocks, and there are more brittle minerals inside. When compressed, they are prone to fracture along the fractures. Moreover, 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. The high fracture density means that there are a large number of prefabricated weak surfaces inside the rock. When compressed, the 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 in combination with the application experience of experts in related fields. For example, when FI reaches 0.7, the energy consumption during the rock breaking 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 aforementioned method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, 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 embodiments of this specification, combined with necessary implementation hardware. Based on the same innovative concept, the devices in one or more embodiments provided in this specification are as described in the following embodiments. Since the implementation schemes and methods for solving the problem by the devices are similar, the implementation of specific devices in the embodiments of this specification can refer to the implementation of the aforementioned method, and repeated details will not be repeated. As used below, the terms "unit" or "module" can refer to a combination of software and / or hardware that performs a predetermined function. Although the devices described in the following embodiments are preferably implemented in software, hardware implementation, or a combination of software and hardware, is also possible and contemplated.

[0133] Specifically, Figure 6 This is a schematic diagram of the module structure of one embodiment of a tight reservoir compressibility evaluation device based on rock scratch characteristics provided in this specification. (Refer to...) Figure 6 As shown in the embodiments of this specification, a tight reservoir compressibility evaluation device based on rock scratch characteristics includes:

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

[0135] The first calculation module 602 is used to calculate the uniaxial compressive strength and fracture toughness based on the tangential force, cutter 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 tool tip tangential force obtained from the last scratch test;

[0137] The third calculation module 604 is used to calculate the compressibility index based on the uniaxial compressive strength, fracture toughness and crack density.

[0138] Evaluation module 605 is used to evaluate the compressibility of the target tight rock sample based on the compressibility index.

[0139] The beneficial effects obtained by the apparatus provided in the embodiments of this specification are consistent with the beneficial effects obtained by the methods described above, and will not be repeated here.

[0140] Reference Figure 7As shown, based on the aforementioned method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, one embodiment of this specification also provides a computer device 702, wherein the above-described method operates 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 kind of information, such as code, settings, data, etc. Non-limitingly, for example, the memory 706 may include any type of RAM, any type of ROM, flash memory, hard disk, optical disk, etc. More generally, any memory can use any technology to store information. Further, any memory can provide volatile or non-volatile retention of information. Further, any memory may represent a fixed or removable component of the computer device 702. In one case, when the processor 704 executes associated instructions stored in any memory or combination of memories, the computer device 702 can perform any operation of the associated instructions. The computer device 702 also includes one or more drive mechanisms 708 for interacting with any memory, such as a hard disk drive mechanism, an optical disk drive mechanism, etc.

[0141] Computer device 702 may also include an input / output module 710 (I / O) for receiving various inputs (via input device 712) and providing various outputs (via output device 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 device 712, and output device 714 may be omitted, and the device may function solely as a computer device within a network. 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] Communication link 722 can be implemented in any way, such as via a local area network, a wide area network (e.g., the Internet), a point-to-point connection, or any combination thereof. 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, for example Figures 1 to 4 In addition to the method shown, embodiments of this specification also provide a computer-readable storage medium storing a computer program that, when executed by a processor, performs the steps of the above-described method.

[0144] This specification also provides computer-readable instructions, wherein when a processor executes the instructions, the program therein causes the processor to perform the following: Figures 1 to 4 The method shown.

[0145] This specification also provides a computer program product, including at least one instruction or at least one program segment, wherein the at least one instruction or the at least one program segment is loaded and executed by a processor to achieve the following: Figures 1 to 4 The method shown.

[0146] It should be understood that in the various embodiments of this specification, the sequence number of each process does not imply 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 related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this specification generally indicates that the preceding and following related objects have an "or" relationship.

[0148] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this specification can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of each example have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this specification.

[0149] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing 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, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the couplings or direct couplings or communication connections shown or discussed may be indirect couplings or communication connections through some interfaces, devices, or units, or they may be electrical, mechanical, or other forms of connection.

[0151] The units described as separate components may or may not be physically separate. 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 can be selected to achieve the purpose of the embodiments described in this specification, depending on actual needs.

[0152] Furthermore, the functional units in the various embodiments of this specification can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0153] If the integrated unit is implemented as 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, in essence, 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. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this specification. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0154] This specification uses specific embodiments to illustrate the principles and implementation methods of this specification. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this specification. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this specification. Therefore, the content of this specification should not be construed as a limitation of this specification.

Claims

1. A method for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, characterized in that, The method includes: The target dense rock sample is placed in the scratch testing instrument, and multiple scratch tests are conducted based on the preset cutter head width and loading rate. The scratch test data generated in each scratch test are recorded, including the cutter head tangential force, scratch depth and cutter displacement. Based on the tangential force, cutter width, and scratch depth obtained from the last scratch test, the uniaxial compressive strength and fracture toughness were calculated. The crack density is calculated based on the tool displacement and tangential force of the tool tip obtained from the last scratch test; wherein, the total scratch length is calculated based on the tool displacement; the number of fluctuations in the absolute value of the tangential force fluctuation amplitude exceeding a preset value during the scratch test is determined; and the crack density is calculated based on the total scratch length and the number of fluctuations. The compressibility index is calculated based on the uniaxial compressive strength, fracture toughness, and crack density. The compressibility of the target tight rock sample is evaluated based on the compressibility index; Based on the uniaxial compressive strength, fracture toughness, and crack density, the compressibility index is calculated, including: The compressibility index is calculated using the following formula: ； in, FI Indicates the compressibility index. UCS , K C , CD These represent the uniaxial compressive strength, fracture toughness, and crack density of the last scratch test, respectively. , , These represent the maximum uniaxial compressive strength, minimum fracture toughness, and maximum crack density, respectively, in multiple scratch tests. This represents the weighting coefficient for uniaxial compressive strength. This represents the fracture toughness weighting coefficient. This represents the crack density weighting coefficient.

2. The method according to claim 1, characterized in that, The uniaxial compressive strength is calculated based on the tangential force, cutter width, and scratch depth obtained from the last scratch test, including: The uniaxial compressive strength is calculated using the following formula: ； in, Indicates uniaxial compressive strength. Indicates the tangential force of the cutter head. Indicates the width of the cutter head. Indicates the depth of the scratch.

3. The method according to claim 1, characterized in that, Based on the tangential force, cutter width, and scratch depth obtained from the last scratch test, the fracture toughness is calculated, including: The fracture toughness is calculated using the following formula: ； in, Indicates fracture toughness. Indicates the tangential force of the cutter head. Indicates the width of the cutter head. Indicates the depth of the scratch.

4. The method according to claim 1, characterized in that, The crack density is calculated based on the total scratch length and the number of fluctuations, including: The crack density is calculated using the following formula: ； in, CD Indicates crack density. N This indicates the number of times the absolute value of the fluctuation amplitude of the cutting head's tangential force exceeded the preset value during the scratch test. L This indicates the total length of the scratch.

5. The method according to claim 1, characterized in that, The multiple scratch tests based on the preset blade width and loading rate include: The target dense rock sample was subjected to scratch tests according to the preset initial number of tests, and the tangential force of the cutter head, the scratch depth and the tool displacement were recorded for each scratch test. The first coefficient of variation, the second coefficient of variation, and the third coefficient of variation were calculated based on the tangential force of the cutting head, the scratch depth, and the tool displacement in each scratch test. 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; If so, then terminate the scratch test; 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 based on the cutting head tangential force, scratch depth, and cutting 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.

6. The method according to claim 5, characterized in that, After recording the tangential force, scratch depth, and tool displacement for each scratch test, the method also includes: Determine whether there are any abnormal data in the tool tip tangential force, scratch depth, and tool displacement of each scratch test; If so, delete the abnormal data and re-determine the order of the remaining scratch tests according to the scratch test time.

7. A device for evaluating the compressibility of tight reservoirs based on rock scratch characteristics, characterized in that, The device includes: The test module is used to place the target dense rock sample inside the scratch test instrument, perform multiple scratch tests based on the preset cutter head width and loading rate, and record the scratch test data generated in each scratch test, wherein the scratch test data includes the cutter head tangential force, scratch depth and cutter displacement; The first calculation module is used to calculate the uniaxial compressive strength and fracture toughness based on the tangential force, cutter 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 tool tip tangential force obtained from the last scratch test; wherein, the total scratch length is calculated based on the tool displacement; the number of fluctuations in the absolute value of the tool tip tangential force fluctuation amplitude exceeding a preset value is determined; and the crack density is calculated based on the total scratch length and the number of fluctuations. The third calculation module is used to calculate the compressibility index based on the uniaxial compressive strength, fracture toughness, and crack density; wherein, the third calculation module calculates the compressibility index using the following formula: ； in, FI Indicates the compressibility index. UCS , K C , CD These represent the uniaxial compressive strength, fracture toughness, and crack density of the last scratch test, respectively. , , These represent the maximum uniaxial compressive strength, minimum fracture toughness, and maximum crack density, respectively, in multiple scratch tests. This represents the weighting coefficient for uniaxial compressive strength. This represents the fracture toughness weighting coefficient. This represents the crack density weighting coefficient; The evaluation module is used to evaluate the compressibility of the target tight rock sample based on the compressibility index.

8. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method as described in any one of claims 1 to 6.

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