Rock brittleness index determination method and related equipment

Abstract

The invention provides a rock brittleness index determination method and related equipment. The method comprises the following steps: performing a triaxial compression test on a rock to obtain a stress-strain curve; and determining the rock brittleness index based on the stress-strain curve. According to the scheme, the stress-strain curve can be obtained based on the rock triaxial compression test, the curve can reflect the energy evolution characteristics of the whole process from deformation starting to damage of the rock under the action of external force, and then the brittleness evaluation index is established. The method can comprehensively consider the brittleness influence factors of lithology, diagenesis, confining pressure, pore pressure and the like of the rock, and can continuously measure the brittleness change trend of the rock in the whole range from ideal plasticity to ideal brittleness. And furthermore, the accuracy of the determination result of the rock brittleness index is effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration reservoir evaluation, and more specifically, to a rock brittleness index determination method, a rock brittleness index determination device, an electronic device and a storage medium. Background Art

[0002] Brittleness characterizes the ability of rock to resist inelastic deformation before failure and to self-maintain macroscopic failure after failure. In the process of oil and gas exploration and development, brittleness is an important parameter for evaluating the degree of development of natural fractures and predicting the effect of hydraulic fracturing. The more brittle a reservoir is, the easier it is to develop natural tectonic fractures, and the easier it is to form a complex fracture system during hydraulic fracturing. Therefore, conducting rock brittleness evaluation is of great guiding significance for the efficient exploration and development of oil and gas resources.

[0003] At present, the brittleness evaluation methods of rocks mainly include mineral composition method, rock mechanics parameter method, compressive and tensile strength method, hardness and fracture toughness method, and internal friction angle method. Existing research results ignore some important factors affecting brittleness or lack sufficient physical basis, making it difficult to accurately reflect the brittle characteristics of rocks.

[0004] Therefore, a new technical solution is urgently needed to solve the above technical problems. Summary of the invention

[0005] A series of simplified concepts are introduced in the Summary of the Invention, which will be further described in detail in the Detailed Description of the Invention. The Summary of the Invention does not mean to attempt to define the key features and essential technical features of the claimed technical solution, nor does it mean to attempt to determine the scope of protection of the claimed technical solution.

[0006] In a first aspect, the present invention provides a method for determining a rock brittleness index, comprising:

[0007] Triaxial compression tests are performed on rocks to obtain stress-strain curves;

[0008] Based on the stress-strain curve, the rock brittleness index is determined.

[0009] Optionally, triaxial compression tests are performed on the rock to obtain stress-strain curves, including:

[0010] Process the rock to be tested into a cylindrical rock sample;

[0011] Applying a preset confining pressure and a preset pore pressure to the cylindrical rock sample;

[0012] A gradually increasing axial pressure is applied to the cross section of the cylindrical rock sample until the rock sample breaks, so as to obtain a stress-strain curve in the process of gradually increasing axial pressure.

[0013] Optionally, the method further comprises:

[0014] Based on the line shape of the stress-strain curve between two specific points, the yield strength point, peak strength point and residual strength point of the rock are determined on the stress-strain curve, wherein the specific two points include: a point where the axial strain is zero and a yield strength point, a yield strength point and a peak strength point, and a peak strength point and a residual strength point.

[0015] Optionally, the method further comprises:

[0016] Based on the stress-strain curve, the principal stress difference and axial strain of the rock at the yield strength point, peak strength point and residual strength point are determined.

[0017] Optionally, the method further comprises:

[0018] The elastic modulus of the rock is determined based on the principal stress difference and axial strain at the yield strength point.

[0019] Optionally, based on the stress-strain curve, a rock brittleness index is determined, including:

[0020] Determining a first energy based on the principal stress difference at the peak strength point and the elastic modulus of the rock;

[0021] determining a second energy based on the principal stress difference, the axial strain, and the axial strain at the peak strength point of the stress-strain curve;

[0022] Based on the first energy and the second energy, a pre-peak brittleness index is determined.

[0023] Optionally, based on the stress-strain curve, a rock brittleness index is determined, including:

[0024] The third energy is determined based on the principal stress difference and axial strain of the stress-strain curve, the principal stress difference and axial strain of the peak strength point, the principal stress difference and axial strain of the residual strength point, and the elastic modulus of the rock;

[0025] Determine the fourth energy based on the principal stress difference and axial strain of the stress-strain curve, the principal stress difference and axial strain at the peak strength point, the axial strain at the residual strength point, and the elastic modulus of the rock;

[0026] determining a post-peak brittleness index based on the third energy and the fourth energy;

[0027] The rock brittleness index is determined based on the pre-peak brittleness index and the post-peak brittleness index.

[0028] In the second aspect, a device for determining a rock brittleness index is also proposed, comprising:

[0029] Curve acquisition module, used to perform triaxial compression test on rock to obtain stress-strain curve;

[0030] The brittleness index determination module is used to determine the rock brittleness index based on the stress-strain curve.

[0031] In a third aspect, an electronic device is also proposed, comprising a processor and a memory, wherein the memory stores computer program instructions, and when the computer program instructions are executed by the processor, they are used to execute the rock brittleness index determination method as described above.

[0032] In a fourth aspect, a storage medium is also proposed, on which program instructions are stored, and the program instructions are used to execute the rock brittleness index determination method as described above when running.

[0033] According to the above scheme, based on the triaxial compression test of rock, a stress-strain curve can be obtained, which can reflect the energy evolution characteristics of the whole process from the beginning of deformation to destruction of rock under the action of external force, and then establish a brittleness evaluation index. Therefore, the brittleness influencing factors of rock, such as lithology, diagenesis, confining pressure, pore pressure, etc., can be comprehensively considered, and the brittleness change trend of rock from ideal plasticity to ideal brittleness can be continuously measured. In addition, the accuracy of the rock brittleness index determination result is effectively improved.

[0034] Other advantages, objectives and features of the rock brittleness index determination method of the present invention will be reflected in part through the following description, and in part will be understood by those skilled in the art through research and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present specification. Also, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0036] Figure 1 A schematic flow chart of a method for determining a rock brittleness index according to an embodiment of the present invention is shown;

[0037] Figure 2 A schematic diagram of a stress-strain curve of a rock sample according to an embodiment of the present invention is shown;

[0038] Figure 3 A schematic block diagram of a device for determining a rock brittleness index according to an embodiment of the present invention is shown;

[0039] Figure 4 A schematic block diagram of an electronic device according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0040] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments.

[0041] According to a first aspect of the present invention, the present invention provides a method for determining a rock brittleness index. Figure 1 A schematic flow chart of a rock brittleness index determination method 100 according to an embodiment of the present invention is shown. The method 100 may include the following steps:

[0042] Step S110, performing a triaxial compression test on the rock to obtain a stress-strain curve.

[0043] For example, a rock sample with appropriate conditions can be selected to perform a triaxial compression test in a laboratory using a triaxial compression instrument. A person skilled in the art can understand the working principle of the triaxial compression instrument, which will not be elaborated in detail here. After the triaxial compression test is performed on the rock, the corresponding stress-strain curve can be obtained. Figure 2 FIG. 2 shows a schematic diagram of a stress-strain curve of a rock sample according to an embodiment of the present invention. Figure 2 As shown in the figure, the ordinate of the curve represents the principal stress difference of the rock, and the abscissa represents the axial strain of the rock. Among them, there are three special points: the yield strength point, the peak strength point, and the residual strength point. The principal stress difference and the corresponding axial strain of these three points can be read out according to the curve.

[0044] Step S120, determining the rock brittleness index based on the stress-strain curve.

[0045] For example, based on Figure 2 The stress-strain curve shown can be used to obtain multiple rock brittleness evaluation indicators, and the rock brittleness index can be determined based on these rock brittleness evaluation indicators.

[0046] According to the above scheme, based on the triaxial compression test of rock, a stress-strain curve can be obtained, which can reflect the energy evolution characteristics of the whole process from the beginning of deformation to destruction of rock under the action of external force, and then establish a brittleness evaluation index. Therefore, the brittleness influencing factors of rock, such as lithology, diagenesis, confining pressure, pore pressure, etc., can be comprehensively considered, and the brittleness change trend of rock from ideal plasticity to ideal brittleness can be continuously measured. In addition, the accuracy of the rock brittleness index determination result is effectively improved.

[0047] Optionally, step S110 of performing a triaxial compression test on the rock to obtain a stress-strain curve may include:

[0048] Step S111, processing the rock to be tested into a cylindrical rock sample.

[0049] Preferably, the rock to be tested can be processed into a cylindrical rock sample. In this embodiment, the diameter of the processed rock sample can be 2.500 cm and the length can be 5.864 cm.

[0050] Step S112, applying a preset confining pressure and a preset pore pressure to the cylindrical rock sample.

[0051] For example, after obtaining the cylindrical rock sample, a predetermined confining pressure and pore pressure may be applied to the rock sample. In one embodiment, the preset confining pressure may be 25 MPa, and the pore pressure may be 15 MPa. By applying the confining pressure and pore pressure to the rock sample, the actual underground environment of the rock sample can be simulated in the laboratory, providing a reliable guarantee for the accuracy of the brittleness index determination.

[0052] Step S113, applying a gradually increasing axial pressure to the cross section of the cylindrical rock sample until the rock sample breaks, so as to obtain a stress-strain curve in the process of gradually increasing axial pressure.

[0053] For example, axial pressure can be applied to two cross sections of a cylindrical rock sample and gradually increased until the rock sample breaks, and the stress-strain curve of the rock sample during the change of axial pressure can be obtained. It can be understood that the two cross sections of the rock sample are the upper and lower circular cross sections of the cylinder. As mentioned above, the stress-strain curve uses the principal stress difference as the ordinate and the axial strain as the abscissa, and the stress-strain curve is used to characterize the relationship between the principal stress difference and the axial strain corresponding to the rock. Among them, the principal stress difference is the difference between the axial pressure and the confining pressure per unit area of ​​the circular cross section of the cylindrical rock sample.

[0054] The stress-strain curve obtained under the above scheme can accurately simulate the deformation process and energy evolution process of rock under the action of external forces in a real underground environment, providing a reliable guarantee for determining the rock brittleness index.

[0055] Optionally, the method may also include: based on the line shape of the stress-strain curve between two specific points, the yield strength point, peak strength point and residual strength point of the rock can be determined on the stress-strain curve, wherein the specific two points include: a point where the axial strain is zero and a yield strength point, a yield strength point and a peak strength point, and a peak strength point and a residual strength point.

[0056] Exemplarily, in one embodiment, the stress-strain curve is a straight line between the point where the axial strain is zero and the yield strength point, which can indicate that during this process, the rock only has elastic deformation, and the principal stress difference increases with the increase of the axial strain. Optionally, the stress-strain curve is a curve between the yield strength point and the peak strength point, which can indicate that during this process, the rock has elastic deformation and plastic deformation, and the principal stress difference increases with the increase of the axial strain. Optionally, the stress-strain curve is a curve between the peak strength point and the residual strength point, which can indicate that during this process, the rock has elastic deformation and plastic deformation, and the principal stress difference decreases with the increase of the axial strain. Therefore, it can be determined that the yield strength point is the dividing point from the straight line to the curve of the stress-strain curve; the peak strength point is the point where the principal stress difference increases to the maximum value with the increase of the axial strain; the residual strength point is the point where the principal stress difference decreases to the minimum value with the increase of the axial strain. Furthermore, it can be read on the stress-strain curve that the principal stress difference of the yield strength point of the rock under predetermined experimental conditions is 45.9MPa, and the axial strain is 2.50×10 -3 ; The principal stress difference at the peak strength point is 111.7MPa, and the axial strain is 11.70×10 -3 ; The principal stress difference at the residual strength point is 82.3MPa, and the axial strain is 22.80×10 -3 .

[0057] Optionally, the method may further include: determining the elastic modulus of the rock based on the principal stress difference and the axial strain at the yield strength point.

[0058] For example, the elastic modulus of rock can be calculated according to the following formula 1: Where E represents the elastic modulus of rock, in MPa, σ a Indicates the principal stress difference at the yield strength point, in MPa, ε a It represents the axial strain at the yield strength point, dimensionless. It can be understood that the elastic modulus of rock can reflect the size of the principal stress difference required to produce a unit axial strain. According to the above, the principal stress difference and axial strain at the yield strength point are substituted into the above formula 1 to calculate the elastic modulus of rock to be 18.36×10 3 MPa.

[0059] Optionally, step S120 of determining the rock brittleness index based on the stress-strain curve may include:

[0060] Step S121, determining the first energy based on the principal stress difference at the peak strength point and the elastic modulus of the rock.

[0061] Exemplarily, the first energy may be calculated according to the following formula 2: Among them, W eb It represents the elastic strain energy provided by the axial pressure difference within the unit volume of the rock at the peak strength point, that is, the first energy, with a unit of 10 6 J / m 3 , σ b The principal stress difference at the peak strength point is expressed in MPa. Substituting the principal stress difference at the peak strength point and the elastic modulus of the rock into the above formula 2, the first energy is calculated to be 0.33978×10 6 J / m 3 .

[0062] Step S122, determining the second energy based on the principal stress difference, the axial strain and the axial strain at the peak strength point of the stress-strain curve.

[0063] Exemplarily, the second energy may be calculated according to the following formula 3: Among them, W d It represents the energy provided by the axial pressure difference within the unit volume of the rock between the point where the axial strain is zero and the peak strength point, that is, the second energy, with a unit of 10 6 J / m 3 , ε b The second energy is calculated by substituting the principal stress difference, axial strain and axial strain of the stress-strain curve into the above formula 3 to obtain 0.91172×10 6 J / m 3 .

[0064] Step S123, determining a pre-peak brittleness index based on the first energy and the second energy.

[0065] Exemplarily, the pre-peak brittleness index may be calculated according to the following formula 4: Among them, B pre It represents the pre-peak brittleness index, and the unit is %. Substituting the first energy and the second energy into the above formula 4, it can be calculated that the pre-peak brittleness index is 37.3%.

[0066] Optionally, step S120 of determining the rock brittleness index based on the stress-strain curve may include:

[0067] Step S124, determining the third energy based on the principal stress difference and axial strain of the stress-strain curve, the principal stress difference and axial strain of the peak strength point, the principal stress difference and axial strain of the residual strength point, and the elastic modulus of the rock.

[0068] Exemplarily, the third energy may be calculated according to the following formula 5: Among them, W f It represents the fracture energy released per unit volume of rock from the peak strength point to the residual strength point, that is, the third energy, with a unit of 10 6 J / m 3 , ε c represents the axial strain at the residual strength point, dimensionless, σ c The principal stress difference at the residual strength point is expressed in MPa. Substituting the principal stress difference and axial strain of the stress-strain curve, the principal stress difference and axial strain at the peak strength point, the principal stress difference and axial strain at the residual strength point, and the elastic modulus of the rock into the above formula 5, the third energy can be calculated to be 1.24080×10 6 J / m 3 .

[0069] Step S125, determining the fourth energy based on the principal stress difference and axial strain of the stress-strain curve, the principal stress difference and axial strain of the peak strength point, the axial strain of the residual strength point, and the elastic modulus of the rock.

[0070] Exemplarily, the fourth energy may be calculated according to the following formula 6: Among them, W g It represents the sum of the energy provided by the axial pressure difference in the rock unit volume from the peak strength point to the residual strength point and the elastic strain energy provided by the axial pressure difference in the rock unit volume at the peak strength point, that is, the fourth energy, with the unit of 10 6 J / m 3 Substituting the principal stress difference and axial strain of the stress-strain curve, the principal stress difference and axial strain at the peak strength point, the axial strain at the residual strength point, and the elastic modulus of the rock into the above formula 6, the fourth energy can be calculated to be 1.42526×10 6 J / m 3 .

[0071] Step S126, determining a post-peak brittleness index based on the third energy and the fourth energy.

[0072] Exemplarily, the post-peak brittleness index may be calculated according to the following formula 7: Among them, B post It represents the post-peak brittleness index, and its unit is %. Substituting the third energy and the fourth energy into the above formula 7, it can be calculated that the post-peak brittleness index is 87.1%.

[0073] Step S127, determining the rock brittleness index based on the pre-peak brittleness index and the post-peak brittleness index.

[0074] Exemplarily, the rock brittleness index may be calculated according to the following formula 8: Wherein, B represents the rock brittleness index, and the unit is %. Substituting the pre-peak brittleness index and the post-peak brittleness index into the above formula 8, it can be calculated that the rock brittleness index is 62.2%.

[0075] According to the second aspect of the present invention, a device for determining a rock brittleness index is also proposed. Figure 3 FIG. 3 is a schematic block diagram of a rock brittleness index determination device 300 according to an embodiment of the present invention. Figure 3 As shown, the apparatus 300 may include:

[0076] The curve acquisition module 310 is used to perform a triaxial compression test on the rock to obtain a stress-strain curve;

[0077] The brittleness index determination module 320 is used to determine the rock brittleness index based on the stress-strain curve.

[0078] According to a third aspect of the present invention, an electronic device is also provided. Figure 4 FIG. 4 shows a schematic block diagram of an electronic device 400 according to an embodiment of the present invention. Figure 4 As shown, the electronic device 400 includes a processor 410 and a memory 420, wherein the memory 420 stores computer program instructions, and the computer program instructions are used by the processor 410 to execute the rock brittleness index determination method as described above when the processor 410 is running.

[0079] According to a fourth aspect of the present invention, a storage medium is also provided, on which program instructions are stored, and the program instructions are used to execute the rock brittleness index determination method as described above when running. The storage medium may include, for example, a storage component of a tablet computer, a hard disk of a computer, a read-only memory (ROM), an erasable programmable read-only memory (EPROM), a portable compact disk read-only memory (CD-ROM), a USB memory, or any combination of the above storage media. The computer-readable storage medium may be any combination of one or more computer-readable storage media.

[0080] A person skilled in the art may understand the specific details and beneficial effects of the rock brittleness index determination device, electronic device and storage medium by reading the above description of the rock brittleness index determination method, which will not be described here for the sake of brevity.

[0081] In the several embodiments provided in the present application, it should be understood that the disclosed devices and / or equipment can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0082] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0083] In addition, each functional unit in each embodiment of the present application may be integrated into one processing unit, or each unit may exist physically separately, or two or more units may be integrated into one unit. The above-mentioned integrated unit may be implemented in the form of hardware or in the form of software functional units.

[0084] 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 the present application 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 to enable a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the various embodiments of the present application. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (Read-Only Memory, ROM), random access memory (Random Access Memory, RAM), disk or optical disk and other media that can store program codes.

[0085] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for determining a rock brittleness index, characterized in that: include: Performing a triaxial compression test on the rock to obtain a stress-strain curve; Based on the stress-strain curve, the rock brittleness index is determined.

2. The method for determining the rock brittleness index according to claim 1, characterized in that: The triaxial compression test is performed on the rock to obtain a stress-strain curve, including: Process the rock to be tested into a cylindrical rock sample; applying a preset confining pressure and a preset pore pressure to the cylindrical rock sample; A gradually increasing axial pressure is applied to the cross section of the cylindrical rock sample until the rock sample breaks, so as to obtain the stress-strain curve in the process of gradually increasing the axial pressure.

3. The method for determining rock brittleness index according to claim 1 or 2, characterized in that: The method further comprises: Based on the line shape of the stress-strain curve between two specific points, the yield strength point, peak strength point and residual strength point of the rock are determined on the stress-strain curve, wherein the two specific points include: a point where the axial strain is zero and the yield strength point, the yield strength point and the peak strength point, and the peak strength point and the residual strength point.

4. The method for determining the rock brittleness index according to claim 3, characterized in that: The method further comprises: Based on the stress-strain curve, the principal stress difference and the axial strain of the rock at the yield strength point, the peak strength point and the residual strength point are determined.

5. The method for determining rock brittleness index according to claim 4, characterized in that: The method further comprises: The elastic modulus of the rock is determined based on the principal stress difference and the axial strain at the yield strength point.

6. The method for determining rock brittleness index according to claim 5, characterized in that: Determining the rock brittleness index based on the stress-strain curve includes: Determining a first energy based on the principal stress difference at the peak strength point and the elastic modulus of the rock; determining a second energy based on a principal stress difference, an axial strain, and an axial strain at a peak strength point of the stress-strain curve; Based on the first energy and the second energy, a pre-peak brittleness index is determined.

7. The method for determining rock brittleness index according to claim 6, characterized in that: Determining the rock brittleness index based on the stress-strain curve includes: Determining a third energy based on the principal stress difference and the axial strain of the stress-strain curve, the principal stress difference and the axial strain of the peak strength point, the principal stress difference and the axial strain of the residual strength point, and the elastic modulus of the rock; Determining a fourth energy based on the principal stress difference and the axial strain of the stress-strain curve, the principal stress difference and the axial strain of the peak strength point, the axial strain of the residual strength point, and the elastic modulus of the rock; determining a post-peak brittleness index based on the third energy and the fourth energy; The rock brittleness index is determined based on the pre-peak brittleness index and the post-peak brittleness index.

8. A device for determining rock brittleness index, characterized in that: include: A curve acquisition module, used for performing a triaxial compression test on the rock to obtain a stress-strain curve; The brittleness index determination module is used to determine the rock brittleness index based on the stress-strain curve.

9. An electronic device, characterized in that: It comprises a processor and a memory, wherein the memory stores computer program instructions, and the computer program instructions are used by the processor to execute the rock brittleness index determination method as described in any one of claims 1 to 7 when the processor is running.

10. A storage medium having program instructions stored thereon, wherein the program instructions are used to execute the method for determining the rock brittleness index according to any one of claims 1 to 7 when running.

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