Rock elastic modulus measurement method and system based on cyclic loading and unloading

Abstract

The present specification relates to the technical field of rock physics, and provides a rock elastic modulus measurement method and system based on cyclic loading and unloading. The method comprises: preparing a rock sample; determining indentation point arrays of the rock sample; performing cyclic loading and unloading on each indentation point in the indentation point arrays to obtain load-depth relationship data of each indentation point; calculating the elastic modulus of each indentation point according to the load-depth relationship data of each indentation point; and calculating the elastic modulus of the rock sample according to the elastic modulus of each indentation point. Through the embodiment of the present specification, the efficiency, convenience and accuracy of rock elastic modulus measurement can be improved.

Description

Technical Field

[0001] This specification relates to the field of rock physics technology, and in particular to a method and system for measuring the elastic modulus of rocks based on cyclic loading and unloading. Background Technology

[0002] Accurately obtaining the mechanical parameters of rock formations is an important prerequisite for the efficient development of deep oil and gas resources. Conventional methods involve drilling to extract rock cores and then conducting laboratory experiments to obtain mechanical parameters such as the elastic modulus of the rock. However, in deep and complex rock formation environments, the difficulty of drilling to extract rock cores increases, and the probability of the obtained rock cores developing fractures or even breaking due to high pressure and high temperature is greatly increased. This leads to increased errors in the experimental results of the rock's elastic modulus and other mechanical parameters, and may even make it impossible to conduct experiments.

[0003] Therefore, there is an urgent need for a method to measure the elastic modulus of rocks that can measure the elastic modulus of rocks on-site without requiring the rock to be intact, while improving the efficiency, convenience and accuracy of rock elastic modulus measurement. Summary of the Invention

[0004] Given the current low efficiency, convenience, and accuracy of rock elastic modulus measurement, this scheme is proposed to overcome or at least partially solve the above problems.

[0005] On the one hand, the purpose of some embodiments of this specification is to provide a method for measuring the elastic modulus of rock based on cyclic loading and unloading, the method comprising:

[0006] Preparation of rock samples;

[0007] Determine the indentation lattice of the rock sample;

[0008] By cyclically loading and unloading each indentation point in the indentation point array, the relationship data between the load and the indentation depth of each indentation point is obtained.

[0009] Calculate the elastic modulus of each indentation point based on the relationship between the load and the indentation depth at each indentation point;

[0010] The elastic modulus of the rock sample is calculated based on the elastic modulus of each indentation point.

[0011] Further, the preparation of the rock sample includes:

[0012] Obtain the rock to be tested;

[0013] Cut the rock to be tested so that the rock to be tested has a pair of parallel planes with overlapping projections;

[0014] Use sandpaper to polish the surface;

[0015] The rock sample was obtained by cleaning and drying the rock to be tested with anhydrous alcohol.

[0016] Furthermore, the cutting of the rock to be tested further includes:

[0017] When the size of the rock to be tested is smaller than a first threshold, the rock to be tested is encapsulated in thermosetting plastic.

[0018] Cut the encapsulated rock to be tested so that the encapsulated rock has a pair of parallel planes with overlapping projections.

[0019] Further, determining the indentation lattice of the rock sample includes:

[0020] The spacing between the indentation points is determined; the spacing between the indentation points is greater than a second threshold.

[0021] According to the rock type of the rock sample, a corresponding spherical indenter is matched from a preset spherical indenter matching table;

[0022] Using the spherical indenter, the rock sample is plotted with points at the indentation point spacing to determine the indentation point lattice of the rock sample.

[0023] Further, the step of cyclically loading and unloading each indentation point in the indentation point array to obtain the relationship data between the load and the indentation depth of each indentation point includes:

[0024] Based on the rock type of the rock sample, the corresponding maximum and minimum loads are matched from a preset load matching table;

[0025] With a first displacement rate, each of the pressing points is traversed as a selected point, and the spherical indenter is controlled to uniformly load the selected point;

[0026] Once the load reaches the maximum load, the load is maintained.

[0027] After the load holding period ends, the spherical indenter is controlled to unload the selected point at a uniform speed with a first displacement rate until the load reaches the minimum load and unloading stops.

[0028] Record the time and load corresponding to the uniform loading process, the load holding process, and the uniform unloading process;

[0029] The corresponding indentation depth is calculated based on the first displacement rate and the time.

[0030] Based on the indentation depth and the load, a set of data relating the load and indentation depth at the selected point is obtained.

[0031] Repeat the uniform loading process, the load holding process, and the uniform unloading process to obtain multiple sets of data on the relationship between the load and the indentation depth at the selected point.

[0032] Further, the step of calculating the elastic modulus of each indentation point based on the relationship data between the load and the indentation depth at each indentation point includes:

[0033] Based on the relationship data between the load and the indentation depth at each indentation point, a fitting curve of the relationship between the load and the indentation depth at each indentation point is obtained;

[0034] By fitting a curve to the relationship between load and indentation depth at each indentation point, the elastic contact stiffness of the corresponding indentation point and the contact area between the spherical indenter and the indentation point are calculated using the following formula:

[0035] Where, P = a(hh) f ) b ;

[0036] A=πα 2 Where α=πDh c ,

[0037] Where P is the fitted curve of the relationship between load and indentation depth, h is the indentation depth of the spherical indenter at the indentation point, a and b are both fitting parameters, and h f The residual depth of the indentation point after unloading, S is the elastic contact stiffness of the indentation point, and h is the residual depth of the indentation point after unloading. max h represents the maximum indentation depth of the spherical indenter at the indentation point. c Where α is the contact depth, D is the contact radius between the spherical indenter and the indentation point, A is the contact area between the spherical indenter and the indentation point, and ε is the geometric shape parameter of the spherical indenter.

[0038] Based on the elastic contact stiffness and the contact area, the reduced modulus and elastic modulus of the corresponding indentation point are calculated using the following formula:

[0039]

[0040]

[0041] Among them, E r E is the reduced modulus of the indentation point. ind v is the elastic modulus of the spherical indenter. ind For the spherical indenter, v s E represents the Poisson's ratio of the rock sample. s This is the elastic modulus at the indentation point.

[0042] On the other hand, some embodiments of this specification also provide a rock elastic modulus measurement system based on cyclic loading and unloading, the system comprising:

[0043] A rock sample preparation unit, used for preparing rock samples;

[0044] An indentation lattice determination unit is used to determine the indentation lattice of the rock sample;

[0045] The data acquisition unit is used to perform cyclic loading and unloading on each pressing point in the pressing point array to obtain the relationship data between the load and the pressing depth of each pressing point.

[0046] The indentation point elastic modulus calculation unit is used to calculate the elastic modulus of each indentation point based on the relationship data between the load and the indentation depth of each indentation point.

[0047] The rock sample elastic modulus calculation unit is used to calculate the elastic modulus of the rock sample based on the elastic modulus of each indentation point.

[0048] On the other hand, some embodiments of this specification also provide a computer device, including a memory, a processor, and a computer program stored in the memory, which, when run by the processor, executes instructions for the methods described above.

[0049] On the other hand, some embodiments of this specification also provide a computer storage medium having a computer program stored thereon, which, when run by the processor of a computer device, executes instructions for the methods described above.

[0050] On the other hand, some embodiments of this specification also provide a computer program product, which includes a computer program that, when run by the processor of a computer device, executes instructions for the methods described above.

[0051] Some embodiments of this specification provide one or more technical solutions, which have at least the following technical effects:

[0052] The embodiments in this specification first prepare rock samples. The rock samples are prepared from rock specimens. The rock specimens do not need to be complete large rock blocks; they can also be rock fragments. When the rock specimen is a rock fragment, it is encapsulated in thermosetting plastic before cutting. When the rock specimen is a complete large rock block, cutting begins directly. After cutting, grinding is performed, and the grinding mesh accuracy is required to be much lower than the nanometer level, which is highly feasible. After the rock specimen is prepared, a spherical indenter is used to determine the indentation point lattice. The spacing between the indentation points is selected to ensure that the indentation plastic zone does not overlap. Then, the spherical indenter is used to cyclically load and unload the indentation points one by one. Each loading and unloading process uses the same uniform displacement rate. The indentation depth is calculated based on the uniform displacement rate and time, and the corresponding load is recorded. There is a load holding time between loading and unloading, thus obtaining multiple sets of load-indentation depth relationship data for each indentation point. Finally, the elastic modulus of each indentation point is calculated based on the data of eliminating abnormal relationships, and the average value is taken to calculate the elastic modulus of the rock specimen. This allows for convenient, accurate, and efficient measurement of the rock elastic modulus with lower requirements for the state of the rock specimen and the experimental environment.

[0053] 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 some embodiments of this specification more apparent and understandable, specific implementation methods of some embodiments of this specification are given below. Attached Figure Description

[0054] To more clearly illustrate some embodiments or technical solutions in the prior art of this specification, the accompanying drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments recorded in this specification. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort. In the drawings:

[0055] Figure 1 A flowchart of a rock elastic modulus measurement method based on cyclic loading and unloading is shown in some embodiments of this specification;

[0056] Figure 2 This is a schematic diagram illustrating the steps for preparing rock samples in some embodiments of this specification;

[0057] Figure 3 This is a schematic diagram illustrating the steps of encapsulating the rock to be tested in some embodiments of this specification;

[0058] Figure 4 This is a schematic diagram illustrating the steps for determining the indentation lattice of a rock sample in some embodiments of this specification;

[0059] Figure 5 This is a schematic diagram illustrating the steps for obtaining the relationship data between the load and the indentation depth at each indentation point in some embodiments of this specification;

[0060] Figure 6 This is a schematic diagram illustrating the relationship between time and load during the loading and unloading process in some embodiments of this specification;

[0061] Figure 7a and Figure 7b This is a schematic diagram illustrating the relationship between load and indentation depth during loading and unloading processes in some embodiments of this specification;

[0062] Figure 8 This is a schematic diagram of the structure of a rock elastic modulus measuring device based on cyclic loading and unloading in some embodiments of this specification;

[0063] Figure 9 This is a schematic diagram of the computer device structure provided in some embodiments of this specification.

[0064] [Explanation of Labels in the Attached Image]

[0065] 81. Rock Sample Preparation Unit;

[0066] 82. Press-in lattice to determine the unit;

[0067] 83. Data Acquisition Unit;

[0068] 84. Calculation unit for elastic modulus at the indentation point;

[0069] 85. Rock sample elastic modulus calculation unit;

[0070] 902. Computer equipment;

[0071] 904, Processor;

[0072] 906. Memory;

[0073] 908. Drive mechanism;

[0074] 910. Input / output interfaces;

[0075] 912. Input devices;

[0076] 914. Output devices;

[0077] 916. Presentation equipment;

[0078] 918. Graphical User Interface;

[0079] 920. Network interface;

[0080] 922. Communication link;

[0081] 924. Communication bus. Detailed Implementation

[0082] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in some 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 some embodiments of this specification, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this specification.

[0083] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings herein are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such use of 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 non-exclusive inclusion; for example, a process, method, apparatus, product, or device that includes 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. It should be noted that the acquisition, storage, use, and processing of data in the technical solutions of this application comply with the relevant provisions of national laws and regulations.

[0084] Figure 1 This is a flowchart illustrating a method for measuring the elastic modulus of rock based on cyclic loading and unloading, as provided in an embodiment of the present invention. This specification provides the operational steps of the method described in the embodiments or flowchart, but based on conventional or non-inventive methods, 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 flowchart... Figure 1 As shown, the method may include:

[0085] S101: Preparation of rock samples;

[0086] S102: Determine the indentation lattice of the rock sample;

[0087] S103: Perform cyclic loading and unloading on each pressing point in the pressing point array to obtain the relationship data between the load and the pressing depth of each pressing point;

[0088] S104: Calculate the elastic modulus of each indentation point based on the relationship data between the load and the indentation depth of each indentation point;

[0089] S105: Calculate the elastic modulus of the rock sample based on the elastic modulus of each indentation point.

[0090] The embodiments in this specification first prepare rock samples. The rock samples are prepared from rock specimens. The rock specimens do not need to be complete large rock blocks; they can also be rock fragments. When the rock specimen is a rock fragment, it is encapsulated in thermosetting plastic before cutting. When the rock specimen is a complete large rock block, cutting begins directly. After cutting, grinding is performed, and the grinding mesh accuracy is required to be much lower than the nanometer level, which is highly feasible. After the rock specimen is prepared, a spherical indenter is used to determine the indentation point lattice. The spacing between the indentation points is selected to ensure that the indentation plastic zone does not overlap. Then, the spherical indenter is used to cyclically load and unload the indentation points one by one. Each loading and unloading process uses the same uniform displacement rate. The indentation depth is calculated based on the uniform displacement rate and time, and the corresponding load is recorded. There is a load holding time between loading and unloading, thus obtaining multiple sets of load-indentation depth relationship data for each indentation point. Finally, the elastic modulus of each indentation point is calculated based on the data of eliminating abnormal relationships, and the average value is taken to calculate the elastic modulus of the rock specimen. This allows for convenient, accurate, and efficient measurement of the rock elastic modulus with lower requirements for the state of the rock specimen and the experimental environment.

[0091] Specifically, in some embodiments, the elastic modulus refers to the stress divided by the strain in that direction under uniaxial stress. In simple terms, when an external force is applied to an elastic body, the body undergoes a shape change, usually called deformation. The elastic modulus is a physical quantity describing the elasticity of a material. During the elastic deformation stage, the stress and strain of a material are directly proportional, and the proportionality coefficient of this function is called the elastic modulus. The elastic modulus is an important performance parameter for engineering materials, and the elastic modulus of rocks is one of the important physical and mechanical properties of rocks. The elastic modulus of rocks varies depending on the type, composition, grain size, water content, and pore size of the rock. Accurately obtaining the elastic modulus of rocks is an important prerequisite for oil and gas extraction. Traditional methods for measuring the elastic modulus of rock cores involve loading and unloading the rock sample using uniaxial compression tests. However, these methods have high requirements for the experimental environment, the integrity of the rock sample, and its size. Furthermore, the extracted rock cores are not always intact, and transporting the extracted rock cores to the relevant laboratory for elastic modulus measurement significantly increases the manpower, material costs, and time required. Therefore, this patent differs from the traditional uniaxial compression method by cyclically loading and unloading the compression points on the rock sample. Under the premise of calculating the elastic modulus of the rock from a macroscopic perspective, this method achieves convenient, accurate, and efficient measurement of the rock's elastic modulus with lower requirements for the state of the rock sample and the experimental environment.

[0092] See attached document Figure 2 In some embodiments, the preparation of the rock sample may include:

[0093] S210: Obtain the rock to be tested;

[0094] S220: Cut the rock to be tested so that the rock to be tested has a pair of parallel planes with overlapping projections;

[0095] S230: Use sandpaper to polish the surface;

[0096] S240: The rock to be tested is cleaned and dried using anhydrous alcohol to obtain the rock sample.

[0097] Specifically, in some embodiments, the rock core refers to a cylindrical rock sample taken from a hole using a ring core drill bit and other core-taking tools according to the needs of geological exploration work or engineering. It is an important physical geological data for studying and understanding underground geological conditions. The rock to be tested comes from the rock core and is used to measure the elastic modulus. To measure the elastic modulus, the rock to be tested first needs to be pretreated to obtain the target rock sample. The pretreatment process begins by cutting the rock to have a pair of parallel planes with coincident projections. For example, the rock can be cut into a cuboid, with opposite faces of the cuboid satisfying the requirement of parallelism and coincident projections. Then, the cut rock is polished with sandpaper on the planes. For example, a metallographic polishing machine can be used, selecting sandpaper of grits of 180, 400, 800, 1200, and 2000 respectively. The purpose of polishing is to reduce the surface roughness of the planes, further reducing the error of the final measurement result. The higher the sandpaper grit, the higher the polishing accuracy, but the longer the polishing time. Theoretically, the polishing time should double each time the sandpaper grit is increased. However, given that the rock sample in some embodiments of this invention has a large indentation depth, the requirement for polishing accuracy is much smaller than nanometer level, making actual experimental measurement more convenient and efficient. Therefore, the polishing time is adjusted by increasing the sandpaper grit each time. The relationship between sandpaper grit and polishing time is shown in Table 1.

[0098] Table 1. Schematic diagram of the relationship between sandpaper grit and polishing time.

[0099] Sandpaper grit 180 400 800 1200 2000 Polishing time / min 5 8 11 14 17

[0100] After grinding, some impurities will remain on the rock surface. These impurities can be removed by cleaning with anhydrous alcohol and drying, and finally the target rock sample can be obtained.

[0101] See attached document Figure 3 In some embodiments, cutting the rock to be tested may further include:

[0102] S310: When the size of the rock to be tested is smaller than the first threshold, the rock to be tested is encapsulated in thermosetting plastic;

[0103] S320: Cut the encapsulated rock to be tested so that the encapsulated rock to be tested has a pair of parallel planes with overlapping projections.

[0104] It can be understood that, in some embodiments, when cores are obtained using coring tools, the cores are not always as intact as expected. In the case of breakage, the rock to be tested is a rock fragment rather than a complete and sufficiently large rock block. In this case, thermosetting plastics, such as epoxy resin and acrylic resin, are used to encapsulate the rock fragments. The thermosetting plastics play a fixing role and have a certain hardness. The encapsulated rock to be tested is then subjected to the same cutting, grinding, cleaning and drying processes to obtain a rock sample of rock fragments.

[0105] See attached document Figure 4 In some embodiments, determining the indentation lattice of the rock sample may include:

[0106] S410: Determine the spacing between the pressing points; the spacing between the pressing points is greater than a second threshold.

[0107] S420: Match the corresponding spherical indenter from the preset spherical indenter matching table according to the rock type of the rock sample;

[0108] S430: Using the spherical indenter, the rock sample is plotted with points at the indentation point spacing to determine the indentation point lattice of the rock sample.

[0109] It can be understood that, in some embodiments, selecting a spherical indenter can ensure the accuracy of elastic modulus measurement. Selecting other indenters, such as conical indenters (e.g., Bodeichte indenters, Vickers indenters), will cause plastic deformation or even macroscopic fracture of the rock sample under a small load. Plastic deformation is a type of deformation that cannot be recovered on its own, and once it occurs, it will seriously affect the subsequent measurement of the rock's elastic modulus. In some embodiments, when a φ2.5mm spherical indenter is used and the maximum load does not exceed 300N, the rock will not exhibit plastic deformation. Furthermore, determining the indentation point lattice requires determining the indentation point spacing. If the spacing is too small, the plastic zone beneath the spherical indenter will overlap, affecting the measurement results of the rock's elastic modulus. If the spacing is too large, the error may increase. Typically, the indentation point spacing needs to be at least 10 times the indentation depth. In some embodiments, when using a φ2.5mm spherical indenter and with a maximum load not exceeding 300N, the plastic zone beneath the φ2.5mm spherical indenter is smaller than the indenter diameter, and the indentation depth does not exceed 0.2mm. Considering operational and observational difficulties, a 4mm indentation point spacing can be chosen. It should be noted that the elastic modulus varies among different rock types, and the selected spherical indenter and indentation point spacing may differ accordingly.

[0110] See attached document Figure 5 In some embodiments, the step of cyclically loading and unloading each indentation point in the indentation point array to obtain the relationship data between the load and the indentation depth of each indentation point may include:

[0111] S510: Match the corresponding maximum and minimum loads from a preset load matching table according to the rock type of the rock sample;

[0112] S520: Using a first displacement rate, traverse each of the pressing points as selected points, and control the spherical indenter to uniformly load the selected points;

[0113] S530: Load holding is performed after the load reaches the maximum load;

[0114] S540: After the load holding period ends, the spherical indenter is controlled to unload the selected point at a uniform speed with a first displacement rate until the load reaches the minimum load and unloading stops.

[0115] S550: Records the time and load corresponding to the uniform loading process, load holding process, and uniform unloading process;

[0116] S560: Calculate the corresponding indentation depth based on the first displacement rate and the time;

[0117] S570: Based on the indentation depth and the load, obtain a set of load-indentation depth relationship data at the selected point;

[0118] S580: Repeat the uniform loading process, the load holding process, and the uniform unloading process to obtain multiple sets of data on the relationship between the load and the indentation depth at the selected point.

[0119] In some embodiments, after the spacing between the indentation points and the spherical indenter have been determined, a universal electronic testing machine is used to perform cyclic loading and unloading tests on each point in the indentation point array using the spherical indenter. The universal electronic testing machine can be used for force measurement tests such as tensile, compression, bending, shearing, peeling, and tearing with a maximum load of 5kN. The load sensor accuracy is 10. -3 N, the displacement sensor accuracy is 10. -4 mm, meeting the accuracy requirements for cyclic loading and unloading of the indentation points in the rock sample.

[0120] Specifically, before cyclically loading and unloading each indentation point, the corresponding maximum and minimum loads need to be matched from a preset load matching table according to the rock type. The maximum load ensures that no plastic hysteresis loop occurs when cyclically loading and unloading the indentation point. The process of determining the maximum load is as follows: an experiment is conducted on the prepared rock sample, and the load is gradually increased from 50N, 100N, 150N, 200N, 250N, to 300N. As the maximum load increases, according to the changing trend of the elastic-plastic zone below the indenter, the elastic modulus successively shows three processes: increasing, becoming flat, and slightly decreasing. The load corresponding to the stage where the elastic modulus becomes flat is taken as the maximum load, thereby obtaining the preset load matching table. In some embodiments, the minimum load is one-tenth of the maximum load. Then, the loading and unloading displacement rates, holding times, etc., are set. These settings are required to balance experimental efficiency and measurement accuracy. In some embodiments, the sensing head of the displacement sensor is placed on a disk above the spherical indenter and fixed with a strong magnet. The rock sample is then placed between the stage of the electronic universal testing machine and the spherical indenter, with the spherical indenter directly facing the indentation point. This indentation point is used as the selected point, and the spherical indenter is controlled to uniformly load the selected point at a first displacement rate. When the load reaches the maximum load, the load is held. After the load holding is completed, the spherical indenter is also controlled to uniformly unload the selected point at the same first displacement rate until the load reaches the minimum load. Simultaneously, the electronic universal testing machine collects and records the corresponding time and load data during the uniform loading process, the load holding process, and the uniform unloading process. Figure 6 An exemplary embodiment is shown.

[0121] The indentation depth at each moment is calculated by multiplying the first displacement rate by the time. This indentation depth is also the displacement of the spherical indenter. Based on the indentation depth and the load, a set of load-indentation depth relationship data at the selected point can be obtained. By repeating the uniform loading process, the load holding process, and the uniform unloading process, multiple sets of load-indentation depth relationship data at the selected point are obtained. The load-indentation depth relationship data at the selected point can be determined by taking the average value. By selecting each indentation point in the indentation point array, the load-indentation depth relationship data for each indentation point in the indentation point array can be obtained.

[0122] Further, calculating the elastic modulus of each indentation point based on the relationship data between the load and the indentation depth at each indentation point may include:

[0123] Based on the relationship data between the load and the indentation depth at each indentation point, a fitting curve of the relationship between the load and the indentation depth at each indentation point is obtained;

[0124] By fitting a curve to the relationship between load and indentation depth at each indentation point, the elastic contact stiffness of the corresponding indentation point and the contact area between the spherical indenter and the indentation point are calculated using the following formula:

[0125] Where, P = a(hh) f ) b ;

[0126] A=πα 2 Where α=πDh c ,

[0127] Where P is the fitted curve of the relationship between load and indentation depth, h is the indentation depth of the spherical indenter at the indentation point, a and b are both fitting parameters, and h f The residual depth of the indentation point after unloading, S is the elastic contact stiffness of the indentation point, and h is the residual depth of the indentation point after unloading. max h represents the maximum indentation depth of the spherical indenter at the indentation point. c Where α is the contact depth, D is the contact radius between the spherical indenter and the indentation point, A is the contact area between the spherical indenter and the indentation point, and ε is the geometric shape parameter of the spherical indenter.

[0128] Based on the elastic contact stiffness and the contact area, the reduced modulus and elastic modulus of the corresponding indentation point are calculated using the following formula:

[0129]

[0130]

[0131] Among them, E r E is the reduced modulus of the indentation point. ind v is the elastic modulus of the spherical indenter. ind For the Poisson's ratio of the spherical indenter, v s E represents the Poisson's ratio of the rock sample. s This is the elastic modulus at the indentation point.

[0132] It can be understood that, in some embodiments, given that the unloading curve in the loading and unloading experiment of the rock sample is nonlinear, using linear fitting would lead to large errors and dispersion in the final elastic modulus measurement results. Furthermore, in traditional indentation experiments, due to creep and mineral particle breakage mechanisms, the initial segment of the unloading curve often has a high slope (this is even more pronounced in rock loading and unloading experiments under large loads). Therefore, a nonlinear fitting method is used to fit the load-indentation depth curve based on the relationship data between the load and indentation depth of the indentation lattice, such as... Figure 7a and Figure 7b As shown in the exemplary embodiment, the elastic contact stiffness of the corresponding indentation point and the contact area between the spherical indenter and the indentation point are then calculated according to the following formula using a fitted curve of the relationship between the load and the indentation depth at each indentation point:

[0133] Where, P = a(hh) f ) b ;

[0134] A=πα 2 Where α=πDh c ,

[0135] Where P is the fitted curve of the relationship between load and indentation depth, h is the indentation depth of the spherical indenter at the indentation point, a and b are both fitting parameters, and h f The residual depth of the indentation point after unloading, S is the elastic contact stiffness of the indentation point, and h is the residual depth of the indentation point after unloading. max h represents the maximum indentation depth of the spherical indenter at the indentation point. cLet α be the contact depth, D be the diameter of the spherical indenter, A be the contact area between the spherical indenter and the indentation point, and ε be the geometric parameters of the spherical indenter. It should be noted that in some embodiments, the geometric parameters of the spherical indenter are typically taken as 0.75. When determining the fitting curve of the relationship between the load and the indentation depth, the first 20% is often discarded to ensure accuracy. The difference between the maximum indentation depth and the contact depth lies in their starting points for measurement. The starting point for measuring the maximum indentation depth is the location of the indentation point before loading and unloading by the spherical indenter. The starting point for measuring the contact depth is the point with the shortest vertical distance among all contact points between the spherical indenter and the indentation point before loading and unloading by the spherical indenter.

[0136] Finally, based on the elastic contact stiffness and the contact area, the reduced modulus and elastic modulus of the corresponding indentation point are calculated using the following formulas:

[0137]

[0138]

[0139] Among them, E r E is the reduced modulus of the indentation point. ind ν is the elastic modulus of the spherical indenter. ind ν is the Poisson's ratio of the spherical indenter. s E represents the Poisson's ratio of the rock sample. s This is the elastic modulus at the indentation point.

[0140] Specifically, in some embodiments, Poisson's ratio refers to the ratio of transverse normal strain to axial normal strain when a material is subjected to uniaxial tension or compression, also known as the transverse deformation coefficient. The Poisson's ratio of the spherical indenter and the Poisson's ratio of the rock sample are obtained in advance through measurement. Based on the calculated reduced modulus of each indentation point, the elastic modulus corresponding to each indentation point is calculated using the Poisson's ratio of the spherical indenter and the Poisson's ratio of the rock sample. The median, upper quartile, and lower quartile are calculated based on the multiple elastic moduli obtained at this time. The absolute value of 1.5 times the difference between the upper quartile and the lower quartile is taken as the upper bound of the error. Data exceeding the upper bound of the error is regarded as abnormal elastic modulus data. The mean of all elastic modulus data after deleting abnormal elastic modulus data is calculated as the final rock sample modulus measurement result, thereby realizing the measurement of the macroscopic elastic modulus of rock through a small number of indentation points.

[0141] Furthermore, a specific embodiment will be used to illustrate the method for measuring the elastic modulus of rock based on cyclic loading and unloading. However, it is worth noting that this embodiment is only for better illustrating the present invention and does not constitute an improper limitation of the present invention.

[0142] S1, a tight sandstone core from a block in the Tarim Oilfield was selected as the rock sample to be tested. The rock sample was reddish-brown in appearance, with good integrity and homogeneity, and no obvious cracks. To facilitate measurement, it was first cut into 50×50×20mm cuboid samples for cyclic loading and unloading tests. In order to reduce the influence of rock roughness on the elastic modulus measurement results, the rock sample was polished with 180, 400, 800, 1200 and 2000 grit sandpaper using a BUEHLER MetaServ 250 metallographic polishing machine. In order to improve the measurement accuracy, the rock sample was cleaned with anhydrous alcohol and dried after polishing, thus completing the preparation of the rock sample.

[0143] S2. To determine the indentation lattice, the spacing between the indentation points must first be determined. To avoid mutual interference between the indentation points, the spacing should be more than 10 times the maximum indentation depth. In the preliminary test on dense sandstone, spherical indenters with a maximum load between 50N and 300N were used for the indentation test, and the maximum indentation depth was within 0.2mm. Therefore, the spacing between the indentation points should be greater than 2mm. Selecting a lattice spacing of 4mm can avoid mutual interference between the indentation points and facilitate experimental operation and observation.

[0144] S3. Select any one of the pressing points in the pressing point array as the selected point. Use a WANCE503A electronic universal testing machine to perform 10 cycles of loading and unloading pressing on the selected point. Displacement control is used during loading and unloading. The maximum load is set to 50N, the minimum load is 10N, and the loading and unloading rates are 0.03mm / min. After loading to the maximum load, the load is held for 10s. After the load holding time ends, the load is unloaded at a constant speed until the minimum load is reached, and then the loading state is entered again. This cycle is repeated 10 times to obtain 10 sets of load and displacement relationship data for the selected point. The average of the 10 sets of load and displacement relationship data for the selected point is taken as the final load and displacement relationship data for the selected point. Repeat the cyclic loading and unloading pressing test for each pressing point in the pressing point array to obtain the final load and displacement relationship data for each pressing point.

[0145] S4. Based on the final load and displacement relationship data of each indentation point obtained in S3, the load-displacement curve is obtained using a nonlinear fitting formula. Then, the elastic modulus of the rock is calculated based on the load-displacement curve, and abnormal rock elastic modulus is removed.

[0146] The elastic modulus results of the rock samples are shown in Table 2. For the same indentation point, the rock elastic modulus changes with the increase of the number of indentations. The error of the rock elastic modulus obtained by the cyclic loading and unloading indentation method is within 15%. The increased data volume from multiple indentations helps to reduce measurement errors and improve the accuracy of rock elastic modulus measurement. The formula for calculating the error can be:

[0147]

[0148] Where err is the error, E u E is the elastic modulus measured by a traditional uniaxial compression test. i The elastic modulus is the value obtained through embodiments of the present invention.

[0149] Table 2. Schematic diagram of rock elastic modulus measurement results under cyclic loading and unloading.

[0150]

[0151] It should be noted that although the operation of the method of the present invention has been described in a specific order in the above embodiments and figures, this does not require or imply that the operations must be performed in that specific order, or that all the operations shown must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one step, and / or one step may be broken down into multiple steps.

[0152] Corresponding to the above-described method for measuring the elastic modulus of rock based on cyclic loading and unloading, some embodiments of this specification also provide a system for measuring the elastic modulus of rock based on cyclic loading and unloading. (Refer to...) Figure 8 As shown, in some embodiments, a rock elastic modulus measurement system based on cyclic loading and unloading may include:

[0153] Rock sample preparation unit 81 is used to prepare rock samples;

[0154] Indentation lattice determination unit 82 is used to determine the indentation lattice of the rock sample;

[0155] Data acquisition unit 83 is used to perform cyclic loading and unloading on each pressing point in the pressing point array to obtain the relationship data between the load and the pressing depth of each pressing point;

[0156] The indentation point elastic modulus calculation unit 84 is used to calculate the elastic modulus of each indentation point based on the relationship data between the load and the indentation depth of each indentation point.

[0157] The rock sample elastic modulus calculation unit 85 is used to calculate the elastic modulus of the rock sample based on the elastic modulus of each indentation point.

[0158] For ease of description, the above system is described by dividing it into various functional units. Of course, in implementing this specification, the functions of each unit can be implemented in one or more software and / or hardware components.

[0159] 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 the embodiments of this specification are all information and data authorized and agreed upon by the user and fully authorized by all parties.

[0160] Embodiments of this specification also provide a computer device. For example... Figure 9 As shown, in some embodiments of this specification, the computer device 902 may include one or more processors 904, such as one or more central processing units (CPUs) or graphics processing units (GPUs), each of which may implement one or more hardware threads. The computer device 902 may also include any memory 906 for storing information of any kind, such as code, settings, data, etc. In one specific embodiment, a computer program is stored on the memory 906 and can run on the processor 904. When the computer program is run by the processor 904, it can execute instructions of the methods described in any of the above embodiments. Without limitation, for example, the memory 906 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 902. In one case, when the processor 904 executes associated instructions stored in any memory or combination of memories, the computer device 902 can perform any operation of the associated instructions. The computer device 902 also includes one or more drive mechanisms 908 for interacting with any memory, such as a hard disk drive mechanism, an optical disk drive mechanism, etc.

[0161] Computer device 902 may also include an input / output interface 910 (I / O) for receiving various inputs (via input device 912) and providing various outputs (via output device 914). A specific output mechanism may include a presentation device 916 and an associated graphical user interface 918 (GUI). In other embodiments, the input / output interface 910 (I / O), input device 912, and output device 914 may be omitted, and the device may function solely as a computer device within a network. Computer device 902 may also include one or more network interfaces 920 for exchanging data with other devices via one or more communication links 922. One or more communication buses 924 couple the components described above together.

[0162] Communication link 922 can be implemented in any way, such as via a local area network (LAN), a wide area network (WAN) (e.g., the Internet), a point-to-point connection, or any combination thereof. Communication link 922 may include any combination of hardwired links, wireless links, routers, gateway functions, name servers, etc., governed by any protocol or combination of protocols.

[0163] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), computer-readable storage media, and computer program products according to some embodiments of this specification. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processor to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processor, create a mechanism for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0164] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processor to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0165] These computer program instructions may also be loaded onto a computer or other programmable data processor, causing a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable device for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0166] In a typical configuration, a computer device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0167] Memory may include non-persistent storage in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0168] Computer-readable media, including both permanent and non-permanent, removable and non-removable media, can store information using any method or technology. Information can be computer-readable instructions, data structures, program modules, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by computer equipment. As defined in this specification, computer-readable media does not include transient media, such as modulated data signals and carrier waves.

[0169] Those skilled in the art will understand that the embodiments of this specification can be provided as methods, systems, or computer program products. Therefore, the embodiments of this specification can take the form of entirely hardware embodiments, entirely software embodiments, or embodiments combining software and hardware aspects. Furthermore, the embodiments of this specification can take the form of computer program products implemented on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0170] The embodiments described in this specification can be described in the general context of computer-executable instructions, such as program modules, that are executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform a specific task or implement a specific abstract data type. The embodiments of this specification can also be practiced in distributed computing environments where tasks are performed by remote processors connected via a communication network. In distributed computing environments, program modules can reside in local and remote computer storage media, including storage devices.

[0171] 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 document generally indicates that the preceding and following related objects have an "or" relationship.

[0172] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to interchangeably. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0173] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the embodiments of this specification. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0174] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for measuring the elastic modulus of rock based on cyclic loading and unloading, characterized in that, The method includes: Preparation of rock samples; Using a spherical indenter matched to the rock sample, a dot matrix is ​​plotted on the rock sample with an indentation point spacing, thereby determining the indentation point lattice of the rock sample. Based on the maximum and minimum loads of the rock sample, cyclic loading and unloading are performed on each indentation point in the indentation point array to obtain multiple sets of load-indentation depth relationship data for each indentation point. Each loading and unloading operation for each indentation point in the indentation point array includes: controlling the spherical indenter to uniformly load the selected point until the maximum load is reached, and then maintaining the load; after the load maintenance ends, controlling the spherical indenter to uniformly unload the selected point until the minimum load is reached, recording the load and indentation depth during the loading process. Calculate the elastic modulus of each indentation point based on the relationship between the load and the indentation depth at each indentation point; The elastic modulus of the rock sample is calculated based on the elastic modulus of each indentation point.

2. The method according to claim 1, characterized in that, The preparation of the rock sample includes: Obtain the rock to be tested; Cut the rock to be tested so that the rock to be tested has a pair of parallel planes with overlapping projections; Use sandpaper to polish the surface; The rock sample was obtained by cleaning and drying the rock to be tested with anhydrous alcohol.

3. The method according to claim 2, characterized in that, The cutting of the rock to be tested further includes: When the size of the rock to be tested is smaller than a first threshold, the rock to be tested is encapsulated in thermosetting plastic. Cut the encapsulated rock to be tested so that the encapsulated rock has a pair of parallel planes with overlapping projections.

4. The method according to claim 1, characterized in that, The process of determining the spacing between the indentation points and the matching spherical indenter for the rock sample includes: The spacing between the indentation points is determined; the spacing between the indentation points is greater than a second threshold. Based on the rock type of the rock sample, a corresponding spherical indenter is matched from a preset spherical indenter matching table.

5. The method according to claim 1, characterized in that, The process of determining the maximum and minimum loads of the rock sample includes: matching the corresponding maximum and minimum loads from a preset load matching table according to the rock type of the rock sample; Controlling the spherical indenter to uniformly load the selected point until the maximum load includes: traversing each indentation point as a selected point at a first displacement rate, and controlling the spherical indenter to uniformly load the selected point until the load reaches the maximum load; Controlling the spherical indenter to unload the selected point at a uniform speed until the minimum load is reached includes: controlling the spherical indenter to unload the selected point at a uniform speed with a first displacement rate until the load reaches the minimum load and then stopping the unloading; The recording of load and indentation depth during the loading process includes: Record the time and load corresponding to the uniform loading process, the load holding process, and the uniform unloading process; The corresponding indentation depth is calculated based on the first displacement rate and the time. Based on the indentation depth and the load, a set of load-indentation depth relationship data is obtained at the selected point.

6. The method according to claim 1, characterized in that, The step of calculating the elastic modulus of each indentation point based on the relationship between the load and the indentation depth at each indentation point includes: Based on the relationship data between the load and the indentation depth at each indentation point, a fitting curve of the relationship between the load and the indentation depth at each indentation point is obtained; By fitting a curve to the relationship between load and indentation depth at each indentation point, the elastic contact stiffness of the corresponding indentation point and the contact area between the spherical indenter and the indentation point are calculated using the following formula: ,in, ; ,in, , ; Where P is the fitted curve of the relationship between load and indentation depth. Let a and b be the indentation depth of the spherical indenter at the indentation point, where a and b are both fitting parameters. S represents the residual depth of the indentation point after unloading, and S represents the elastic contact stiffness of the indentation point. This represents the maximum indentation depth of the spherical indenter at the indentation point. For contact depth, Let be the contact radius between the spherical indenter and the indentation point, and D be the diameter of the spherical indenter. The contact area between the spherical indenter and the indentation point. These are the geometric parameters of the spherical indenter; Based on the elastic contact stiffness and the contact area, the reduced modulus and elastic modulus of the corresponding indentation point are calculated using the following formula: ； ； in, The reduced modulus of the indentation point. The elastic modulus of the spherical indenter. Poisson's ratio for the spherical indenter The Poisson's ratio of the rock sample. This is the elastic modulus at the indentation point.

7. A rock elastic modulus measurement system based on cyclic loading and unloading, characterized in that, include: A rock sample preparation unit, used for preparing rock samples; The indentation lattice determination unit is used to use a spherical indenter matched to the rock sample to plot points on the rock sample with an indentation point spacing, thereby determining the indentation lattice of the rock sample. The data acquisition unit is used to perform cyclic loading and unloading on each indentation point in the indentation point array according to the maximum and minimum loads of the rock sample, and obtain multiple sets of load-indentation depth relationship data for each indentation point. The loading and unloading process for each pressing point in the pressing point array includes: controlling the spherical indenter to uniformly load the selected point until the maximum load is reached and then holding the load; after the load holding is completed, controlling the spherical indenter to uniformly unload the selected point until the minimum load is reached, and recording the load and pressing depth during the loading process; The indentation point elastic modulus calculation unit is used to calculate the elastic modulus of each indentation point based on the relationship data between the load and the indentation depth of each indentation point. The rock sample elastic modulus calculation unit is used to calculate the elastic modulus of the rock sample based on the elastic modulus of each indentation point.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory, characterized in that, When the computer program is run by the processor, it executes the instructions of the method according to any one of claims 1-6.

9. A computer storage medium having a computer program stored thereon, characterized in that, When the computer program is run by the processor of the computer device, it executes the instructions of the method according to any one of claims 1-6.

10. A computer program product, characterized in that, The computer program product includes a computer program that, when executed by a processor, performs instructions according to any one of claims 1-6.

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