Deep shale brittleness evaluation method based on energy evolution, electronic equipment and medium

Abstract

The invention discloses a deep shale brittleness evaluation method based on energy evolution, electronic equipment and a medium. The method comprises the following steps: collecting basic parameters of a target stratum, and determining key parameters; carrying out a total stress-strain triaxial compression experiment according to the key parameters to obtain a total stress-strain curve of the rock core; dividing the total stress-strain curve, and respectively calculating the strain energy density related to the rock; and calculating the mineral brittleness index of the rock according to the key parameters and the strain energy density. According to the method, mineral components and energy evolution in the whole rock deformation-damage process are considered at the same time, and the brittleness characteristics of deep shale can be better reflected.

Description

Technical Field

[0001] The present invention relates to the field of reservoir transformation, and more specifically, to a deep shale brittleness evaluation method based on energy evolution, electronic equipment and medium. Background Art

[0002] In recent years, the development technology of shale gas reservoirs in shallow marine facies with a depth of 3,500 meters has gradually matured, and deep shale gas will be the focus of future exploration and development. At present, the maximum vertical depth of a shale gas well in southeastern Sichuan Basin is as high as 6,600 meters. Compared with shallow shale reservoirs, deep shale formations have greater burial depth, higher stress and higher temperature. Revealing the brittle characteristics of deep shale is the key to the optimization design of deep shale gas well fracturing.

[0003] At present, the existing brittleness evaluation methods are roughly divided into: mineral content brittleness evaluation method, elastic mechanical parameter brittleness evaluation method, and energy evolution brittleness evaluation method. The mineral content brittleness evaluation method cannot reflect the impact of complex stress state changes on rock brittle failure and does not consider the brittleness differences caused by other factors such as diagenesis. The elastic mechanical parameter method ignores regional differences through statistics and has limitations. At present, the energy evolution method is considered to be one of the most reliable methods for evaluating rock brittleness, which reflects the energy evolution characteristics of rocks during the brittle process. The disadvantage is that the weight coefficient of each energy uses an average weight, and does not consider the differences in energy evolution characteristics caused by different mineral components.

[0004] At present, there is still a need to develop a deep shale brittleness evaluation method based on energy evolution.

[0005] The information disclosed in the background technology section of the present invention is only intended to deepen the understanding of the general background technology of the present invention, and should not be regarded as acknowledging or suggesting in any form that the information constitutes the prior art already known to those skilled in the art. Summary of the invention

[0006] The present invention proposes a deep shale brittleness evaluation method, electronic equipment and medium based on energy evolution, which simultaneously considers the mineral components and the energy evolution of the entire rock deformation-destruction process, and can better reflect the brittle characteristics of deep shale.

[0007] In a first aspect, the present disclosure provides a method for evaluating the brittleness of deep shale based on energy evolution, comprising:

[0008] Collect basic parameters of target formation and determine key parameters;

[0009] Carry out a total stress-strain triaxial compression test according to the key parameters to obtain a total stress-strain curve of the core;

[0010] The total stress-strain curve is divided, and the strain energy density related to the rock is calculated respectively;

[0011] The mineral brittleness index of the rock is calculated according to the key parameters and the strain energy density.

[0012] Preferably, the key parameters include ground stress, formation pressure, formation temperature, and the content of brittle minerals and non-brittle minerals in the target formation core.

[0013] Preferably, carrying out a total stress-strain triaxial compression test to obtain a total stress-strain curve of the core includes:

[0014] The experimental samples were sealed with heat shrink tubes;

[0015] Use external heating sheet to heat the hydraulic oil;

[0016] When heated to the target experimental temperature, the temperature is maintained constant, and the confining pressure and axial stress are simultaneously applied to the confining pressure design value;

[0017] The sample is continuously loaded by displacement control until failure, and the changes of load and deformation with time during the failure process are recorded throughout the process to obtain the full stress-strain curve.

[0018] Preferably, the rock-related strain energy density includes the mechanical energy density of the pre-peak external load input, the pre-peak accumulated elastic energy density, the energy density dissipated in the pre-peak stage, the mechanical energy density of the post-peak external load input, and the residual elastic energy density inside the rock sample.

[0019] Preferably, the mechanical energy density of the pre-peak external load input is:

[0020]

[0021] in, is the mechanical energy density of the external load input before the peak, σ a is the axial stress of the specimen, σ c is the confining pressure of the specimen, ε a is the axial strain of the specimen, ε ap is the axial strain of the specimen when the stress reaches the peak value, ε vp is the volume strain of the sample when the stress reaches the peak value;

[0022] The elastic energy density accumulated before the peak is:

[0023]

[0024] in, is the elastic energy density accumulated before the peak, σ p is the peak stress borne by the specimen, E is Young's elastic modulus, and ν is Poisson's ratio;

[0025] The energy density dissipated in the pre-peak stage is:

[0026]

[0027] in, It is the energy density dissipated by the pre-peak sample due to crack closure, friction, rock deformation and damage.

[0028] Preferably, the mechanical energy density of the post-peak external load input is:

[0029]

[0030] in, is the mechanical energy density of the post-peak external load input, ε vr is the volume strain of the sample when the stress is at residual stress; ε ar is the axial residual strain of the specimen when the stress is at residual stress;

[0031] The residual elastic energy density inside the rock sample is:

[0032]

[0033] in, is the residual elastic energy density inside the rock sample.

[0034] Preferably, calculating the mineral brittleness index of the rock according to the key parameter and the strain energy density includes:

[0035] The pre-peak brittleness index and the post-peak brittleness index are calculated according to the contents of brittle minerals and non-brittle minerals in the target formation core, and then the mineral brittleness index is calculated.

[0036] Preferably, the pre-peak brittleness index is:

[0037]

[0038] Among them, B pre is the pre-peak brittleness index, c brit is the brittle mineral content, c inbrit It is the non-brittle mineral content of the rock;

[0039] The post-peak brittleness index is:

[0040]

[0041] Among them, B post is the post-sewing brittleness index;

[0042] The mineral brittleness index is:

[0043] BI=B pre ×Bpost (8)

[0044] Among them, BI is the mineral brittleness index.

[0045] In a second aspect, an embodiment of the present disclosure further provides an electronic device, the electronic device comprising:

[0046] A memory storing executable instructions;

[0047] A processor runs the executable instructions in the memory to implement the deep shale brittleness evaluation method based on energy evolution.

[0048] In a third aspect, the embodiments of the present disclosure further provide a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the deep shale brittleness evaluation method based on energy evolution.

[0049] Its beneficial effects are:

[0050] Based on the rock brittleness evaluation method based on energy evolution, the present invention introduces mineral components as the weight of energy distribution for the first time, and establishes a rock brittleness evaluation method based on mineral content component weights and energy evolution. This method simultaneously considers the energy evolution of mineral components and the entire rock deformation-destruction process, and can better reflect the brittle characteristics of deep shale.

[0051] The methods and apparatus of the present invention have other features and advantages that will be apparent from, or will be described in detail in, the accompanying drawings and subsequent detailed descriptions incorporated herein, which together serve to explain the specific principles of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0053] Figure 1 A schematic diagram showing a full stress-strain curve of rock failure and energy evolution during the process according to an embodiment of the present invention is shown.

[0054] Figure 2 A flow chart showing the steps of a method for evaluating deep shale brittleness based on energy evolution according to an embodiment of the present invention.

[0055] Figure 3A schematic diagram of a full stress-strain curve of a core obtained by triaxial compression at a confining pressure of 60 MPa and a temperature of 180° C. according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0056] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited to the embodiments set forth herein.

[0057] The present invention provides a deep shale brittleness evaluation method based on energy evolution, comprising:

[0058] Collect basic parameters of target formation and determine key parameters;

[0059] Carry out full stress-strain triaxial compression test based on key parameters to obtain full stress-strain curve of the core;

[0060] The total stress-strain curve is divided and the rock-related strain energy density is calculated respectively;

[0061] The mineral brittleness index of rock is calculated based on key parameters and strain energy density.

[0062] In one example, the key parameters include ground stress, formation pressure, formation temperature, and the contents of brittle minerals and non-brittle minerals in the target formation core.

[0063] In one example, a full stress-strain triaxial compression test is carried out to obtain the full stress-strain curve of the core including:

[0064] The experimental samples were sealed with heat shrink tubes;

[0065] Use external heating sheet to heat the hydraulic oil;

[0066] When heated to the target experimental temperature, the temperature is maintained constant, and the confining pressure and axial stress are simultaneously applied to the confining pressure design value;

[0067] The sample is continuously loaded with displacement control until failure. The changes of load and deformation over time during the failure process are recorded throughout the process to obtain the full stress-strain curve.

[0068] In one example, the rock-related strain energy density includes the mechanical energy density of the pre-peak external load input, the elastic energy density accumulated before the peak, the energy density dissipated in the pre-peak stage, the mechanical energy density of the post-peak external load input, and the residual elastic energy density inside the rock sample.

[0069] In one example, the mechanical energy density of the pre-peak external load input is:

[0070]

[0071] in, is the mechanical energy density of the external load input before the peak, σ a is the axial stress of the specimen, σ c is the confining pressure of the specimen, ε a is the axial strain of the specimen, ε ap is the axial strain of the specimen when the stress reaches the peak value, ε vp is the volume strain of the sample when the stress reaches the peak value;

[0072] The elastic energy density accumulated before the peak is:

[0073]

[0074] in, is the elastic energy density accumulated before the peak, σ p is the peak stress borne by the specimen, E is Young's elastic modulus, and ν is Poisson's ratio;

[0075] The energy density dissipated in the pre-peak stage is:

[0076]

[0077] in, It is the energy density dissipated by the pre-peak sample due to crack closure, friction, rock deformation and damage.

[0078] In one example, the mechanical energy density of the post-peak external load input is:

[0079]

[0080] in, is the mechanical energy density of the post-peak external load input, ε vr is the volume strain of the sample when the stress is at residual stress; ε ar is the axial residual strain of the specimen when the stress is at residual stress;

[0081] The residual elastic energy density inside the rock sample is:

[0082]

[0083] in, is the residual elastic energy density inside the rock sample.

[0084] In one example, the calculation of the mineral brittleness index of rock based on key parameters and strain energy density includes:

[0085] The pre-peak brittleness index and the post-peak brittleness index are calculated according to the contents of brittle minerals and non-brittle minerals in the core of the target formation, and then the mineral brittleness index is calculated.

[0086] In one example, the pre-peak fragility index is:

[0087]

[0088] Among them, B pre is the pre-peak brittleness index, c brit is the brittle mineral content, c inbrit It is the non-brittle mineral content of the rock;

[0089] The post-peak brittleness index is:

[0090]

[0091] Among them, B post is the post-sewing brittleness index;

[0092] The mineral brittleness index is:

[0093] BI=B pre ×B post (8)

[0094] Among them, BI is the mineral brittleness index.

[0095] Specifically, key parameters of the target formation, such as ground stress, formation pressure, formation temperature, and mineral content components of the target formation core, are obtained, and the contents of brittle minerals and non-brittle minerals are listed separately; key parameters of the target formation include maximum horizontal principal stress, minimum horizontal principal stress, original formation pressure, formation temperature, the content of each mineral component, and the contents of brittle minerals and non-brittle minerals are distinguished.

[0096] Carry out total stress-strain triaxial compression experiment to obtain the total stress-strain curve of the core:

[0097] First, the experimental samples were sealed with heat shrink tubes; second, the hydraulic oil was heated at a heating rate of 0.5℃ / min using an external heating plate; third, when heated to the target experimental temperature, the constant temperature was maintained for 2 hours to ensure uniform heating of the rock samples; then, the confining pressure and axial stress were applied simultaneously at a loading rate of 0.05MPa / s to the design value of the confining pressure; finally, the sample was continuously loaded with displacement control at a rate of 0.002mm / s until it was destroyed, and the computer recorded the changes in load and deformation over time during the destruction process.

[0098] Figure 1 A schematic diagram showing a full stress-strain curve of rock failure and energy evolution during the process according to an embodiment of the present invention is shown.

[0099] like Figure 1 As shown in the figure, the stress-strain curve is divided, and the strain energy density before the peak and after the crack of the rock failure curve is calculated respectively:

[0100] The total work done by the pre-peak external load and the accumulated elastic energy can be expressed as formula (1) and formula (2).

[0101] The energy dissipated in the pre-peak stage can be expressed as formula (3). The rock sample continues to fail after the fracture, and the external load continues to do work, which can be expressed as formula (4).

[0102] The elastic energy accumulated before the peak is continuously released with the macroscopic fracture of the rock sample. When the rock sample is completely broken and the deviatoric stress is equal to the residual stress, the residual elastic energy inside the rock sample can be expressed as formula (5).

[0103] According to the content of brittle minerals and non-brittle minerals in the core, and the strain energy density of each part before and after the peak of the total stress-strain curve, the specific steps for calculating the mineral brittleness index of the rock are as follows:

[0104] The pre-peak brittleness index can be expressed as formula (6), and the post-peak brittleness index can be expressed as formula (7). Taking into account the influence of pre-peak and post-peak, the product method is used to obtain the final brittleness index BI as formula (8).

[0105] The present invention also provides an electronic device, which includes: a memory storing executable instructions; and a processor running the executable instructions in the memory to implement the above-mentioned deep shale brittleness evaluation method based on energy evolution.

[0106] The present invention also provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the deep shale brittleness evaluation method based on energy evolution is implemented.

[0107] To facilitate understanding of the solutions and effects of the embodiments of the present invention, four specific application examples are given below. Those skilled in the art should understand that the examples are only for facilitating understanding of the present invention, and any specific details thereof are not intended to limit the present invention in any way.

[0108] Example 1

[0109] Figure 2 A flow chart showing the steps of a method for evaluating deep shale brittleness based on energy evolution according to an embodiment of the present invention.

[0110] like Figure 2As shown, the deep shale brittleness evaluation method based on energy evolution includes: step 101, collecting basic parameters of the target formation and determining key parameters; step 102, conducting a total stress-strain triaxial compression experiment according to the key parameters to obtain the total stress-strain curve of the core; step 103, dividing the total stress-strain curve and calculating the strain energy density related to the rock respectively; step 104, calculating the mineral brittleness index of the rock according to the key parameters and the strain energy density.

[0111] Collect the basic parameters of the target formation, including the effective minimum principal stress, the original formation temperature, and the content of each mineral component, and use this to divide the content of brittle minerals and non-brittle minerals. Carry out a total stress-strain triaxial compression experiment to obtain the total stress-strain curve of the core.

[0112] The experimental samples were sealed with heat shrink tubes; the hydraulic oil was heated at a heating rate of 0.5℃ / min using an external heating plate; when heated to the target experimental temperature, the constant temperature was maintained for 2 hours to ensure uniform heating of the rock sample; then, the confining pressure and axial stress were applied simultaneously at a loading rate of 0.05MPa / s to the design value of the confining pressure; the sample was continuously loaded using displacement control at a rate of 0.002mm / s until it was destroyed, and the computer recorded the changes in load and deformation over time during the destruction process.

[0113] After obtaining the full stress-strain curve during the core failure process, the total work done by the pre-peak external load and the accumulated elastic energy are calculated using equations (1) and (2), respectively, and the dissipated energy in the pre-peak stage is calculated using equation (3); then, the work done by the post-fracture external load is calculated using equation (4), and the residual elastic energy inside the rock after the sample is completely destroyed is calculated using equation (5). According to the brittle mineral and non-brittle mineral content of the core, the strain energy density of each part given by equations (1)-(5) is used, and equations (6)-(8) are used to calculate the pre-peak brittleness index, post-fracture brittleness index, and final brittleness index.

[0114] Taking the parameters of an ultra-deep formation in southeastern Sichuan and the formation core as an example, the parameters are shown in Table 1.

[0115] Table 1 Main parameters of staged fracturing horizontal wells and their reservoirs

[0116] Parameter name Numeric unit Effective minimum horizontal principal stress 82.3 MPa Formation temperature 177.5 ℃ Brittle mineral content 63.5 ％ Non-brittle mineral content 36.5 ％

[0117] Figure 3 A schematic diagram of a full stress-strain curve of a core obtained by triaxial compression at a confining pressure of 60 MPa and a temperature of 180° C. according to an embodiment of the present invention is shown.

[0118] Table 1 Data combination Figure 3The stress-strain curve of the core is used to calculate the characteristic parameters and strain energy density of each part during the failure process, as shown in Table 2. The brittleness index before the peak is calculated to be 0.91, the brittleness index after the fracture is 0.58, and finally the brittleness index is calculated to be 0.53.

[0119] Table 2 Characteristic parameters of stress-strain curve and strain energy density of each part

[0120]

[0121]

[0122] Example 2

[0123] The present disclosure provides an electronic device, which includes: a memory storing executable instructions; a processor running the executable instructions in the memory to implement the above-mentioned deep shale brittleness evaluation method based on energy evolution.

[0124] An electronic device according to an embodiment of the present disclosure includes a memory and a processor.

[0125] The memory is used to store non-temporary computer-readable instructions. Specifically, the memory may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may, for example, include random access memory (RAM) and / or cache memory (cache), etc. The non-volatile memory may, for example, include read-only memory (ROM), hard disk, flash memory, etc.

[0126] The processor may be a central processing unit (CPU) or other forms of processing units having data processing capabilities and / or instruction execution capabilities, and may control other components in the electronic device to perform desired functions. In one embodiment of the present disclosure, the processor is used to run the computer-readable instructions stored in the memory.

[0127] Those skilled in the art should be able to understand that in order to solve the technical problem of how to obtain a good user experience, the present embodiment may also include well-known structures such as a communication bus and an interface, and these well-known structures should also be included in the protection scope of the present disclosure.

[0128] For detailed description of this embodiment, reference may be made to the corresponding descriptions in the aforementioned embodiments, which will not be repeated here.

[0129] Example 3

[0130] An embodiment of the present disclosure provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the deep shale brittleness evaluation method based on energy evolution.

[0131] According to the computer-readable storage medium of the embodiment of the present disclosure, non-transitory computer-readable instructions are stored thereon. When the non-transitory computer-readable instructions are executed by a processor, all or part of the steps of the above-mentioned methods of each embodiment of the present disclosure are executed.

[0132] The above-mentioned computer-readable storage media include, but are not limited to: optical storage media (e.g., CD-ROM and DVD), magneto-optical storage media (e.g., MO), magnetic storage media (e.g., magnetic tape or mobile hard disk), media with built-in rewritable non-volatile memory (e.g., memory card) and media with built-in ROM (e.g., ROM box).

[0133] Those skilled in the art should understand that the purpose of the above description of the embodiments of the present invention is only to exemplarily illustrate the beneficial effects of the embodiments of the present invention, and is not intended to limit the embodiments of the present invention to any given examples.

[0134] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A deep shale brittleness evaluation method based on energy evolution, characterized in that: include: Collect basic parameters of target formation and determine key parameters; Carry out a total stress-strain triaxial compression test according to the key parameters to obtain a total stress-strain curve of the core; The total stress-strain curve is divided, and the strain energy density related to the rock is calculated respectively; The mineral brittleness index of the rock is calculated according to the key parameters and the strain energy density.

2. The deep shale brittleness evaluation method based on energy evolution according to claim 1, wherein: The key parameters include ground stress, formation pressure, formation temperature, and the content of brittle minerals and non-brittle minerals in the target formation core.

3. The deep shale brittleness evaluation method based on energy evolution according to claim 1, wherein: Carry out full stress-strain triaxial compression test to obtain full stress-strain curve of core including: The experimental samples were sealed with heat shrink tubes; Use external heating sheet to heat the hydraulic oil; When heated to the target experimental temperature, the temperature is maintained constant, and the confining pressure and axial stress are simultaneously applied to the confining pressure design value; The sample is continuously loaded by displacement control until failure, and the changes of load and deformation with time during the failure process are recorded throughout the process to obtain the full stress-strain curve.

4. The deep shale brittleness evaluation method based on energy evolution according to claim 1, wherein: The strain energy density related to rock includes the mechanical energy density of external load input before the peak, the elastic energy density accumulated before the peak, the energy density dissipated in the pre-peak stage, the mechanical energy density of external load input after the peak, and the residual elastic energy density inside the rock sample.

5. The deep shale brittleness evaluation method based on energy evolution according to claim 4, wherein: The mechanical energy density of the pre-peak external load input is: in, is the mechanical energy density of the external load input before the peak, σ a is the axial stress of the specimen, σ c is the confining pressure of the specimen, ε a is the axial strain of the specimen, ε ap is the axial strain of the specimen when the stress reaches the peak value, ε vp is the volume strain of the sample when the stress reaches the peak value; The elastic energy density accumulated before the peak is: in, is the elastic energy density accumulated before the peak, σ p is the peak stress borne by the specimen, E is Young's elastic modulus, and ν is Poisson's ratio; The energy density dissipated in the pre-peak stage is: in, It is the energy density dissipated by the pre-peak sample due to crack closure, friction, rock deformation and damage.

6. The deep shale brittleness evaluation method based on energy evolution according to claim 4, wherein: The mechanical energy density of the post-peak external load input is: in, is the mechanical energy density of the post-peak external load input, ε vr is the volume strain of the sample when the stress is at residual stress; ε ar is the axial residual strain of the specimen when the stress is at residual stress; The residual elastic energy density inside the rock sample is: in, is the residual elastic energy density inside the rock sample.

7. The deep shale brittleness evaluation method based on energy evolution according to claim 2, wherein: Calculating the mineral brittleness index of rock according to the key parameters and the strain energy density includes: The pre-peak brittleness index and the post-peak brittleness index are calculated according to the contents of brittle minerals and non-brittle minerals in the target formation core, and then the mineral brittleness index is calculated.

8. The deep shale brittleness evaluation method based on energy evolution according to claim 7, wherein: The pre-peak brittleness index is: Among them, B pre is the pre-peak brittleness index, c brit is the brittle mineral content, c inbrit It is the non-brittle mineral content of the rock; The post-peak brittleness index is: Among them, B post is the post-sewing brittleness index; The mineral brittleness index is: BI=B pre ×B post (8) Among them, BI is the mineral brittleness index.

9. An electronic device, characterized in that: The electronic device comprises: A memory storing executable instructions; A processor, wherein the processor runs the executable instructions in the memory to implement the deep shale brittleness evaluation method based on energy evolution as described in any one of claims 1-8.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the deep shale brittleness evaluation method based on energy evolution described in any one of claims 1 to 8 is implemented.

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