Method for obtaining rock compressive strength using drilling cuttings

Abstract

The present invention provides a method for obtaining rock compressive strength using drilling cuttings, the method comprising: obtaining the unconfined compressive strength of the core through an indoor uniaxial compression test; obtaining cuttings of a preset size from the rock corresponding to the core sample, and preparing multiple cuttings rock samples using the cuttings and epoxy resin glue; obtaining the indentation elastic modulus of the cuttings sample through a cuttings micron indentation test; establishing a rock and cuttings compressive strength relationship prediction model based on the unconfined compressive strength of the core and the indentation elastic modulus of the cuttings sample; and selecting different types of cores in different formations for experiments to verify the universality of the compressive strength relationship prediction model. The present invention simulates the formation drill bit rock breaking process to prepare corresponding cuttings, uses relevant mathematical models and data processing methods to explore the mathematical relationship between the relevant mechanical parameters of the core and the cuttings, establishes a mathematical relationship model between the mechanical parameters of the cuttings and the rock, and improves the accuracy of the microscopic mechanical properties research of the rock.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling, and in particular relates to a method for obtaining the compressive strength of rocks by utilizing drilling cuttings. Background Art

[0002] Based on the important role played by formation rock mechanical properties in the field of oil drilling, more and more experts and scholars are committed to pioneering and making progress in the study of formation rock mechanical properties, continuously carrying out research and experiments on rock mechanical properties, improving the research results system and applying it to the on-site drilling process. In the absence of drilling core or logging data, the evaluation of formation rock mechanical properties must make good use of drilling cuttings that are easily available and have sufficient sources on site. Based on the current research status at home and abroad, the technology or instruments for directly obtaining or measuring the microscopic mechanical properties of cuttings are not mature and accurate. Summary of the invention

[0003] The main purpose of the present invention is to propose a method for obtaining the compressive strength of rocks using drilling cuttings, aiming to solve the technical problem of low accuracy in directly obtaining or measuring the compressive strength of cuttings in the prior art.

[0004] In order to achieve the above object, the present invention provides a method for obtaining the compressive strength of rock using drilling cuttings, comprising the steps of:

[0005] The non-confining compressive strength of the core was obtained through indoor uniaxial compression tests;

[0006] Obtaining rock cuttings of a preset size from the rock corresponding to the core sample, and preparing a plurality of rock cutting samples using the rock cuttings and epoxy resin glue;

[0007] The indentation elastic modulus of rock cuttings samples was obtained through rock cuttings micro-indentation experiments;

[0008] A prediction model for the relationship between the compressive strength of rock and cuttings is established based on the unconfined compressive strength of the core and the indentation elastic modulus of the cuttings sample.

[0009] Different types of cores from different formations were selected for experiments to verify the universality of the compressive strength relationship prediction model.

[0010] In an embodiment of the present invention, the step of obtaining the non-confining pressure compressive strength of the core through an indoor uniaxial compression test comprises:

[0011] Select a core sample of a preset size from the formation rock, and heat-seal the core sample with a heat shrink tubing;

[0012] Placing the core sample in a confining pressure chamber and loading the core sample axially until the core sample is destroyed;

[0013] Real-time record of stress on the core sample during loading and drawing of stress-strain curve;

[0014] The compressive strength of the core sample is obtained according to the stress-strain curve.

[0015] In an embodiment of the present invention, the step of obtaining rock cuttings of a preset size from the rock corresponding to the core sample and preparing a plurality of rock cutting samples using the rock cuttings and epoxy resin glue comprises:

[0016] Using a hammer to crush the rock corresponding to the core sample and selecting a plurality of rock fragments of a preset particle size; wherein the preset particle size ranges from 6 to 10 mm;

[0017] Hydraulically cutting each of the rock fragments into cube-shaped rock fragments;

[0018] Multiple rock cuttings are stacked one by one from top to bottom in a cylindrical mold and wait for casting;

[0019] injecting epoxy resin bonding liquid into the cylindrical mold through a glass rod to solidify the rock cuttings;

[0020] The solidified rock chips are cut and polished to obtain rock chip samples.

[0021] In an embodiment of the present invention, the step of cutting and polishing the solidified rock cuttings to obtain rock cutting samples comprises:

[0022] removing the solidified rock cuttings from the cylindrical mold;

[0023] Cutting excess cement from the upper and lower surfaces of the rock cuttings to optimize the parallelism between the upper and lower surfaces of the rock cuttings;

[0024] The rock cuttings after cutting are polished to obtain rock cutting samples that meet the requirements.

[0025] In an embodiment of the present invention, the step of cutting off the excess cement on the upper and lower surfaces of the rock cuttings to optimize the parallelism between the upper and lower surfaces of the rock cuttings comprises:

[0026] Select four locations on the outer side wall of the cuttings and measure the heights of the four locations;

[0027] Control the height difference of the four positions within the preset range;

[0028] Use micrometer indentation instrument mechanical sensor to test the matching degree between sample and instrument sensor;

[0029] Determine whether the force on the instrument sensor is uniform;

[0030] When the force on the instrument sensor is uneven, repeat the above steps in sequence until the parallelism meets the preset requirements.

[0031] In an embodiment of the present invention, the step of obtaining the indentation elastic modulus of the rock chip sample through the rock chip micro-indentation experiment comprises:

[0032] Carrying out micrometer indentation tests on each of the rock cuttings samples for no less than 10 times and obtaining an indentation elastic modulus;

[0033] The multiple test values ​​of each rock chip sample are averaged to obtain the indentation elastic modulus of the rock chip sample.

[0034] In an embodiment of the present invention, the step of establishing a rock-cutting compressive strength relationship prediction model based on the unconfined compressive strength of the core and the indentation elastic modulus of the cuttings sample comprises:

[0035] The indentation elastic modulus of the rock cuttings sample is selected as the independent variable, the compressive strength without confining pressure of the core is selected as the dependent variable, and the scattered points are plotted in the same coordinate system;

[0036] Using different mathematical models to perform regression analysis on the above scattered points, and obtaining the linear correlation coefficients corresponding to the different mathematical models;

[0037] The mathematical model with the largest linear correlation coefficient is selected as the prediction model for the compressive strength of rock.

[0038] In an embodiment of the present invention, the indentation elastic modulus of the rock cuttings sample is obtained using the following calculation formula:

[0039]

[0040] in,

[0041] Where E is the indentation elastic modulus of the rock cuttings sample, E r represents the reduced elastic modulus, μ d represents the Poisson's ratio of the rock cuttings sample, μ i represents the Poisson's ratio of the indenter material, E i represents the modulus of the indenter material, C represents the contact flexibility, which is equal to the curve dh / dF (the inverse of the contact stiffness) when the test force is unloaded at the maximum test force, and A p Represents the contact projected area.

[0042] In an embodiment of the present invention, the prediction model of the compressive strength of the rock can be expressed by the following formula:

[0043] UCS=0.1099E 2 -3.0353E+60.55

[0044] Among them, UCS represents the compressive strength of rock, and E represents the indentation elastic modulus of rock cuttings.

[0045] In an embodiment of the present invention, the rock hammer includes a support frame, a rock cutting groove for placing rocks and located on the bottom end surface of the support frame, an impact hammer and a drill tooth. The impact hammer is hung on the top of the support frame through a connecting rod. The impact hammer is used to apply an impact force to the drill tooth to drive the drill tooth to move toward the rock, and the center lines of the drill tooth and the rock cutting groove coincide.

[0046] Through the above technical solution, the method for obtaining rock compressive strength by using drilling cuttings provided in the embodiment of the present invention has the following beneficial effects:

[0047] The unconfined compressive strength of the core is obtained through indoor uniaxial compression experiments; the rock cuttings of preset sizes are obtained from the rocks corresponding to the core samples, and multiple rock cutting samples are prepared using the rock cuttings and epoxy resin glue; the indentation elastic modulus of the rock cutting samples is obtained through the rock cutting micron indentation experiment; the rock and rock cutting compressive strength relationship prediction model is established based on the unconfined compressive strength of the core and the indentation elastic modulus of the rock cutting samples; different types of cores in different formations are selected for experiments to verify the universality of the compressive strength relationship prediction model. Based on this, the formation drill bit rock breaking process is simulated to prepare the corresponding rock cuttings, and the rock cutting sample micron indentation experiment is carried out to measure its indentation hardness and elastic modulus. According to the experimental data results and the core-related mechanical parameters, the mathematical relationship between the relevant mechanical parameters of the core and the rock cuttings is explored using relevant mathematical models and data processing methods, and the mathematical relationship model between the mechanical parameters of the rock cuttings and the rock is established, so that the mechanical properties of the formation rock can be studied more accurately according to the prediction model. Furthermore, the present invention can utilize rock cuttings (sand samples) on-site to evaluate the compressive strength of rocks while drilling, which has important practical significance for drill bit selection, parameter optimization, and formulation of various technical measures in drilling engineering.

[0048] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings are used to provide an understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention. In the accompanying drawings:

[0050] Figure 1 is a schematic flow chart of a method for obtaining rock compressive strength by using drilling cuttings according to an embodiment of the present invention;

[0051] Figure 2 It is a schematic diagram of a sub-process of one embodiment of the method for obtaining rock compressive strength by using drilling cuttings according to the present invention;

[0052] Figure 3 is a schematic diagram of a sub-flow chart of another embodiment of the method for obtaining rock compressive strength by using drilling cuttings according to the present invention;

[0053] Figure 4 is a schematic diagram of the structure of a hammer mill for preparing rock cuttings according to the present invention;

[0054] Figure 5 is an indentation load-displacement curve of one of the samples obtained in a micro-indentation experiment according to the present invention;

[0055] Figure 6 3 is a relationship diagram between the compressive strength obtained by the uniaxial compression test and the elastic modulus obtained by the micron indentation test according to the present invention.

[0056] Description of Reference Numerals

[0057] Label name Label name 1 Support frame 4 Connecting rod 2 Cuttings trough 5 Drilling teeth 3 Impact hammer 6 rock DETAILED DESCRIPTION

[0058] The specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0059] The method for obtaining the compressive strength of rock by using drilling cuttings according to the present invention is described below with reference to the accompanying drawings.

[0060] like Figure 1 As shown, in an embodiment of the present invention, a method for obtaining rock compressive strength using drilling cuttings is provided, comprising the steps of:

[0061] Step S10: obtaining the non-confining pressure compressive strength of the core through an indoor uniaxial compression test;

[0062] Step S20: obtaining rock cuttings of a preset size from the rock corresponding to the core sample, and preparing a plurality of rock cutting samples using the rock cuttings and epoxy resin glue;

[0063] Step S30: obtaining the indentation elastic modulus of the rock cuttings sample through a rock cuttings micron indentation experiment;

[0064] Step S40: establishing a prediction model for the relationship between the compressive strength of rock and rock cuttings based on the unconfined compressive strength of the core and the indentation elastic modulus of the rock cuttings sample;

[0065] Step S50: Select different types of cores in different strata to conduct experiments to verify the universality of the compressive strength relationship prediction model.

[0066] Among them, before conducting the rock chip micro-indentation experiment, the following five aspects are mainly considered.

[0067] (1) Selection of cores and cuttings: The mechanical parameters of the cores and cuttings obtained in the experiment must be consistent, relevant, and accurate.

[0068] (2) Preparation and selection of rock chips. Since the preparation of rock chips from cores is uncertain and accidental, how to prepare rock chips from cores and how to select rock chips for sample preparation are the keys to reducing experimental errors and ensuring experimental accuracy.

[0069] (3) The selection of the number of indentation points on the rock chip surface and the distribution of indentations in the micro-indentation experiment. In order to improve the indentation efficiency and experimental accuracy of the micro-indentation experiment, it is necessary to determine the arrangement of each indentation point on the surface of the rock chip sample, while the density distribution and position distribution of the indentation points on the sample surface are not affected by the thickness of the rock chip sample.

[0070] (4) The influence of the indentation load-displacement curve on the experimental results during the micro-indentation test.

[0071] (5) Study on the regularity of size effect of mechanical properties of cores and cuttings. Cores of different types and mechanical properties from different formations are selected for experiments. Cuttings samples are then prepared and tested to ensure the universality of the regularity results.

[0072] The present invention prepares corresponding rock cuttings by simulating the rock breaking process of a formation drill bit, carries out a micron indentation experiment of the rock cuttings sample to measure its indentation hardness and elastic modulus, analyzes and processes the experimental data results and the core-related mechanical parameters, and uses relevant mathematical models and data processing methods to explore the mathematical relationship between the relevant mechanical parameters of the core and the rock cuttings, and establishes a mathematical relationship model between the mechanical parameters of the rock cuttings and the rock, which lays a good foundation for the subsequent study of the mechanical properties of the formation rock, and greatly improves the accuracy of the determination of the compressive strength of the formation rock. In addition, the present invention can use rock cuttings (sand samples) on site to evaluate the compressive strength of the rock while drilling, which has important practical significance for the selection of drill bits, parameter optimization, and formulation of various technical measures in drilling engineering.

[0073] like Figure 2 As shown, in one embodiment, the step of obtaining the non-confining pressure compressive strength of the core through an indoor uniaxial compression test includes:

[0074] Step S11: selecting a core sample of a preset size from the formation rock, and using a heat shrink tubing to heat and plastic-seal the core sample;

[0075] Step S12: placing the core sample in a confining pressure chamber and loading the core sample axially until the core sample is destroyed;

[0076] Step S13: recording the stress of the core sample during the loading process in real time and drawing a stress-strain curve;

[0077] Step S14: Obtain the compressive strength of the core sample according to the stress-strain curve.

[0078] The uniaxial compression test is a rock mechanics test in which a standard core is subjected to unconfined axial pressure to cause it to fail. Through this experiment, the compressive strength and deformation of the core can be obtained, and then the corresponding elastic mechanical parameters, such as elastic modulus and Poisson's ratio, can be obtained through calculation. The experiment uses the rock mechanics triaxial stress test system of Changchun Chaoyang Experimental Instrument Co., Ltd. (a conventional stress test system equipment in the prior art). The test system consists of four parts: axial pressure control system, confining pressure control system, pore pressure control system and computer acquisition and control system; among them, a axial pressure control system: the axial pressure is provided by the LX-50 servo loading system. The axial pressure is controlled by strain or pressure servo through the computer control system. b confining pressure control system: the system is used to simulate the horizontal stress conditions in the well, and is composed of a φ45 servo loading system and a booster. The confining pressure change can be monitored by a pressure sensor and a pressure gauge, and the maximum confining pressure can be simulated to 70MPa. c pore pressure control system: the system simulates the pore pressure conditions in the well, and the pressure is provided by the LX-45 servo loading system. The pore pressure change can be monitored by pressure sensors and pressure gauges, and the maximum pore pressure can be simulated to 40MPa. d Computer acquisition and control system: When testing rock samples, various loading paths and test processes can be controlled in real time by computers. The computer automatically collects voltage signals through sensors and converts them into stress and displacement data and stores them in the computer. The relevant experimental steps and methods are as follows:

[0079] 1. Prepare the core as required, a cylinder with a ground radius of 25mm and a height of 50mm. Then put the heat shrink tube on the core to be tested and heat it to plastic seal the core sample.

[0080] 2. Clamp the strain gauge and place it in the confining pressure chamber without lowering the confining pressure cylinder. Then adjust the position of the strain sensor and the pressure head and close the safety door.

[0081] 3. Open the computer software, edit and adjust the computer control mode, protection mode, etc., set the experimental loading method, and start axially loading the core sample until the core is destroyed.

[0082] 4. During the experimental loading process, relevant data should be recorded at any time and the equipment and core conditions should be observed.

[0083] 5. After the core is destroyed, the relevant experimental data are exported, the stress-strain curve is drawn, and the relevant elastic mechanical parameters of the final core are calculated.

[0084] 6. Turn off the laboratory power, organize the equipment and tidy up the laboratory.

[0085] After indoor core experiments, this study selected 10 different cores. The test results of relevant mechanical parameters of the cores are shown in Table 1:

[0086] Table 1 Indoor core test results

[0087]

[0088]

[0089] like Figure 3 As shown, in another embodiment of the present invention, the step of obtaining rock cuttings of a preset size from the rock corresponding to the core sample and preparing a plurality of rock cutting samples using the rock cuttings and epoxy resin glue comprises:

[0090] Step S21: using a hammer to crush the rock corresponding to the core sample and selecting a plurality of rock fragments of a preset particle size; wherein the preset particle size ranges from 6 to 10 mm;

[0091] Step S22: hydraulically cutting each rock fragment into cube-shaped rock fragments;

[0092] Step S23: placing multiple rock cuttings in a cylindrical mold in layers from top to bottom to wait for casting;

[0093] Step S24: injecting epoxy resin bonding liquid into the cylindrical mold through the glass rod to solidify the rock cuttings;

[0094] Step S25: cutting and polishing the solidified rock cuttings to obtain rock cutting samples.

[0095] Requirements for cuttings sample preparation: With the continuous advancement of drilling technology, the cuttings collected at the drilling site generally show a trend of small particles and small particle sizes, with a particle size range of mainly 1-10mm. In order to simulate the situation of the on-site cuttings as much as possible, it is necessary to Figure 4 The hammer shown in the figure continuously simulates the process of downhole drill bit breaking rock on the core to produce corresponding rock chips. In addition, in the process of producing rock chips, it is not advisable to select rock chips with large or small particle sizes. Rock chips with moderate particle sizes should be selected to ensure the thickness and area of ​​the produced rock chip samples, which will not affect the indentation effect and avoid boundary effects. At the same time, it can also ensure that the size of the sample base meets the size requirements of the micron indenter. The specific value should be determined according to the indentation parameter setting and the distribution of the indentation points of the micron indenter experiment. The micron indenter used in the micron indenter experiment is a conventional device in the prior art. The indentation principle is well known to those skilled in the art and will not be described here one by one.

[0096] The prepared rock cuttings were subjected to fractal experiments. The rock cuttings of various particle sizes were sieved out using 0.8mm, 1mm, 2mm, 4mm, 6mm, 8mm, and 10mm sieves. To facilitate the preparation of rock cutting samples, rock cuttings of 6-10mm were selected for bonding as much as possible. The thickness and area of ​​the rock samples were based on not affecting the indentation effect, avoiding boundary effects, and being suitable for the sample base size. The specific values ​​were determined based on the indentation depth parameter setting and indentation point distribution of the indentation experiment. The micron indentation experiment required the use of epoxy resin glue to make the rock cuttings into small rock samples with a bottom radius of 20mm and a height of 20mm, as follows Figure 3 As shown, the experiment was carried out after the rock sample was polished and cut.

[0097] The hammer comprises a support frame 1, a rock chip slot 2 for placing rock 6 and located at the bottom end surface of the support frame 1, an impact hammer 3 and a drill tooth 5. The impact hammer 3 is hung on the top of the support frame 1 through a connecting rod 4, and the impact hammer 3 is used to apply an impact force to the drill tooth 5 to drive the drill tooth 5 to move toward the rock 6, and the center lines of the drill tooth 5 and the rock chip slot 2 coincide. When conducting an experiment, the rock 6 is placed in the rock chip slot 2, and a force is applied to the impact hammer 3 through an external driving force, so that the impact hammer 3 drives the drill tooth 5 to move toward the surface of the rock 6 and applies a drilling force to the rock 6, thereby achieving the crushing of the rock 6.

[0098] In an embodiment of the present invention, the steps of cutting and polishing the solidified rock cuttings to obtain rock cutting samples include:

[0099] removing the solidified rock cuttings from the cylindrical mold;

[0100] Cut away excess cement on the upper and lower sides of the cuttings to optimize the parallelism between the upper and lower sides of the cuttings;

[0101] Polish the cut rock chips to obtain rock chip samples that meet the requirements.

[0102] Specifically, the steps of cutting excess cement from the upper and lower surfaces of the cuttings to optimize the parallelism between the upper and lower surfaces of the cuttings include:

[0103] Select four locations on the outer side wall of the cuttings and measure the heights of the four locations;

[0104] Control the height difference of the four positions within the preset range;

[0105] Use micrometer indentation instrument mechanical sensor to test the matching degree between sample and instrument sensor;

[0106] Determine whether the force on the instrument sensor is uniform;

[0107] When the force on the instrument sensor is uneven, repeat the above steps in sequence until the parallelism meets the preset requirements.

[0108] Requirements for parallelism of cuttings samples, such as Figure 5 The indentation load-displacement curve (where the horizontal axis refers to displacement and the vertical axis refers to indentation load) measured by the micro-indentation test shown in the figure is the key to obtaining experimental data, so the parallelism of the test sample has high requirements. Take the first surface that has been ground and polished as the reference, and then polish the second surface to ensure that the two surfaces of the sample are flat and parallel. After grinding and polishing, a micrometer should be used to measure four positions around the rock sample. The difference should be controlled to be less than 100μm, and preferably less than 50μm. This will greatly improve the accuracy of the experimental data. In order to ensure that the parallelism of the horizontal surface of the sample meets the requirements, it is also necessary to use the micro-indentation instrument mechanical sensor to test the matching degree of the sample and the instrument sensor after polishing. If the sensor shows uneven force, the parallelism of the sample needs to be further optimized. (3) Indentation point distribution requirements. In order to ensure the accuracy of the micro-indentation test data, each sample should be tested at least 10 different indentation points. At the same time, since most rock samples are formed by a variety of mineral sediments cemented by a clay matrix, the rock surface will have different degrees of roughness. For smooth surfaces, a dot matrix layout should be used in the test area at a spacing of 50-100μm to conduct experiments; if the surface is relatively rough, manual point selection is required for testing.

[0109] In an embodiment of the present invention, the step of obtaining the indentation elastic modulus of the rock cuttings sample through the rock cuttings micron indentation experiment comprises:

[0110] Carry out micron indentation tests for no less than 10 times on each rock chip sample and obtain the indentation elastic modulus;

[0111] The multiple test values ​​of each rock chip sample were averaged to obtain the indentation elastic modulus of the rock chip sample.

[0112] The micro-indentation test objects are the corresponding rock cuttings samples prepared from 10 kinds of cores tested in uniaxial compression tests. The experimental mode adopts the form of uniaxial crushing samples, and micro-indentation tests are carried out on each experimental sample. A total of 10 rock cuttings samples were tested, and each rock cutting sample was subjected to 10-15 point indentation tests. A total of 145 micro-indentation tests were carried out, and 290 experimental data results were obtained. The specific data are shown in Table 2 (abnormal points have been removed).

[0113] Table 2 Micron indentation test data record

[0114]

[0115]

[0116]

[0117]

[0118]

[0119] Then, the data of the elastic modulus of the samples obtained from the micron indentation test were processed, some abnormal points were eliminated (which may be caused by the cementation or crystallization part tested in the rock cuttings), and then the average values ​​of the relevant mechanical parameters measured for each rock cutting sample were calculated to obtain the following experimental results, as shown in Table 3 for details.

[0120] Table 3 Results of rock sample micro-indentation test

[0121]

[0122] The calculation formula of heterogeneity coefficient V is: S represents the standard deviation of the data, and RMav represents the mean value of the data.

[0123] Furthermore, the steps of establishing a prediction model for the relationship between the compressive strength of rock and rock cuttings based on the unconfined compressive strength of the core and the indentation elastic modulus of the rock cuttings sample include:

[0124] The indentation elastic modulus of the rock cuttings sample was selected as the independent variable, the unconfined compressive strength of the core was selected as the dependent variable, and the scattered points were plotted in the same coordinate system;

[0125] Using different mathematical models to perform regression analysis on the above scattered points, and obtaining the linear correlation coefficients corresponding to the different mathematical models;

[0126] The mathematical model with the largest linear correlation coefficient is selected as the prediction model for the compressive strength of rock.

[0127] In an embodiment of the present invention, the indentation elastic modulus of the rock cuttings sample is calculated using the following formula:

[0128]

[0129] in,

[0130] Where E is the indentation elastic modulus of the rock cuttings sample, E r represents the reduced elastic modulus, μ d represents the Poisson's ratio of the rock cuttings sample, μ i represents the Poisson's ratio of the indenter material, E i represents the modulus of the indenter material, C represents the contact flexibility, which is equal to the curve dh / dF (the inverse of the contact stiffness) when the test force is unloaded at the maximum test force, and A p Represents the contact projected area.

[0131] According to the results of the uniaxial compression test in the core chamber and the micron indentation test results of the corresponding prepared cuttings, the following parameters were obtained through the analysis of the elastic modulus and compressive strength: Figure 5 As shown. Figure 5 The respective scattered points are regressed using different mathematical models. The data on the X-axis in the figure are independent variables, and the data on the Y-axis are dependent variables. Since there will be large errors when using a mathematical function for regression analysis, in order to improve the accuracy of the analysis and reduce errors, 5 different mathematical models such as straight line, polynomial function, exponential function, logarithmic function and power function are used for regression analysis. According to the theory of single-factor variance analysis in mathematical statistics, the correlation coefficient R2 is used as the judgment standard to verify the regression results, and the final linear correlation coefficients between them are obtained respectively, and the optimal results and curves are selected. The specific results are shown in Table 4 below.

[0132] Table 4 Fitting relationship between the compressive strength of the uniaxial compression test and the elastic modulus measured by the micro-indentation test

[0133]

[0134]

[0135] Note: In the table, x is the indentation elastic modulus measured by the micron indentation test, and y is the compressive strength measured by the uniaxial compression test.

[0136] It can be clearly seen that the compressive strength of the core has a good positive correlation with the indentation elastic modulus of the corresponding cuttings. The correlation coefficients of the five mathematical models are all above 0.75. The prediction model of the compressive strength of rock can be expressed by the following formula:

[0137] UCS=0.1099E 2 -3.0353E+60.55

[0138] Among them, UCS represents the compressive strength of rock, and E represents the indentation elastic modulus of rock cuttings.

[0139] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0140] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral one; it can be a mechanical connection, an electrical connection, or communication with each other; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0141] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0142] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for obtaining rock compressive strength using drilling cuttings, characterized in that: Includes steps: The compressive strength of core samples without confining pressure was obtained through indoor uniaxial compression test; Obtaining rock cuttings of a preset size from the rock corresponding to the core sample, and preparing a plurality of rock cutting samples using the rock cuttings and epoxy resin glue; The indentation elastic modulus of rock cuttings samples was obtained through rock cuttings micro-indentation experiments; A prediction model for the relationship between the compressive strength of rocks and cuttings is established based on the unconfined compressive strength of core samples and the indentation elastic modulus of cuttings samples. Different types of core samples from different formations were selected for experiments to verify the universality of the compressive strength relationship prediction model; The step of establishing a rock-cutting compressive strength relationship prediction model based on the no-confining-pressure compressive strength of the core sample and the indentation elastic modulus of the cuttings sample comprises: The indentation elastic modulus of the rock cuttings sample is selected as the independent variable, the compressive strength without confining pressure of the core sample is selected as the dependent variable, and the scattered points are plotted in the same coordinate system; Using different mathematical models to perform regression analysis on the above scattered points, and obtaining the linear correlation coefficients corresponding to the different mathematical models; The mathematical model with the largest linear correlation coefficient is selected as the prediction model for the compressive strength of rock; The prediction model of the compressive strength of the rock can be expressed by the following formula: UCS=0.1099E 2 -3.0353E+60.55 Among them, UCS represents the compressive strength of rock, and E represents the indentation elastic modulus of rock cuttings.

2. The method for obtaining rock compressive strength using drilling cuttings according to claim 1, characterized in that: The step of obtaining the non-confining pressure compressive strength of the core sample by indoor uniaxial compression test comprises: Select a core sample of a preset size from the formation rock, and heat-seal the core sample with a heat shrink tubing; Placing the core sample in a confining pressure chamber and loading the core sample axially until the core sample is destroyed; Real-time record of stress on the core sample during loading and drawing of stress-strain curve; The compressive strength of the core sample is obtained according to the stress-strain curve.

3. The method for obtaining rock compressive strength using drilling cuttings according to claim 1, characterized in that: The step of obtaining rock cuttings of a preset size from the rock corresponding to the core sample and preparing a plurality of rock cutting samples using the rock cuttings and epoxy resin glue comprises: Using a hammer to crush the rock corresponding to the core sample and selecting a plurality of rock fragments of a preset particle size; wherein the preset particle size ranges from 6 to 10 mm; Hydraulically cutting each of the rock fragments into cube-shaped rock fragments; Multiple rock cuttings are stacked one by one from top to bottom in a cylindrical mold and wait for casting; injecting epoxy resin bonding liquid into the cylindrical mold through a glass rod to solidify the rock cuttings; The solidified rock chips are cut and polished to obtain rock chip samples.

4. The method for obtaining the acoustic wave characteristics of formation rocks by using drilling cuttings according to claim 3, characterized in that: The step of cutting and polishing the solidified rock cuttings to obtain rock cutting samples comprises: removing the solidified rock cuttings from the cylindrical mold; Cutting excess cement from the upper and lower surfaces of the rock cuttings to optimize the parallelism between the upper and lower surfaces of the rock cuttings; The rock cuttings after cutting are polished to obtain rock cutting samples that meet the requirements.

5. The method for obtaining rock compressive strength using drilling cuttings according to claim 4, characterized in that: The step of cutting the excess cement on the upper and lower surfaces of the rock cuttings to optimize the parallelism between the upper and lower surfaces of the rock cuttings comprises: Select four locations on the outer side wall of the cuttings and measure the heights of the four locations; Control the height difference of the four positions within the preset range; Use micrometer indentation instrument mechanical sensor to test the matching degree between sample and instrument sensor; Determine whether the force on the instrument sensor is uniform; When the force on the instrument sensor is uneven, repeat the above steps in sequence until the parallelism meets the preset requirements.

6. The method for obtaining rock compressive strength using drilling cuttings according to claim 1, characterized in that: The step of obtaining the indentation elastic modulus of the rock chip sample through the rock chip micron indentation experiment comprises: Carrying out micrometer indentation tests on each of the rock cuttings samples for no less than 10 times and obtaining an indentation elastic modulus; The multiple test values ​​of each rock chip sample are averaged to obtain the indentation elastic modulus of the rock chip sample.

7. The method for obtaining rock compressive strength using drilling cuttings according to claim 6, characterized in that: The indentation elastic modulus of the rock cuttings sample is calculated using the following formula: in, Where E is the indentation elastic modulus of the rock cuttings sample, E r represents the reduced elastic modulus, μ d represents the Poisson's ratio of the rock cuttings sample, μ i represents the Poisson's ratio of the indenter material, E i represents the modulus of the indenter material, C represents the contact flexibility, which is equal to the curve dh / dF when the test force is unloaded at the maximum test force, that is, the inverse of the contact stiffness, A p Represents the contact projected area.

8. The method for obtaining rock compressive strength using drilling cuttings according to claim 3, characterized in that: The hammer includes a support frame, a rock cutting groove for placing rocks and located on the bottom end surface of the support frame, an impact hammer and a drill tooth. The impact hammer is hung on the top of the support frame through a connecting rod. The impact hammer is used to apply an impact force to the drill tooth to drive the drill tooth to move toward the rock, and the center lines of the drill tooth and the rock cutting groove coincide.

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