Fracturing engineering dessert evaluation method based on mechanical parameter test of rock debris indentation while drilling

Abstract

The invention discloses a fracturing engineering dessert evaluation method based on a while-drilling rock debris indentation mechanical parameter test. The fracturing engineering dessert evaluation method comprises the following steps: S1, obtaining a while-drilling rock debris sample; s2, processing the rock debris sample while drilling into a casting body sheet; s3, acquiring micro-mechanical parameters of each test point; s4, obtaining macromechanical parameters of the rock debris sample; s5, core triaxial mechanical parameters of reservoir rock are obtained; s6, establishing relevance between micromechanical parameters of the while-drilling debris sample and triaxial mechanical parameters of the rock core, and correcting the micromechanical parameters obtained by a subsequent indentation method to obtain rock mechanical parameters of different well depths of the horizontal well section; S7, respectively carrying out weighted average treatment on the obtained rock mechanical parameters, and proposing a fracturing index; and S8, according to the fracturing indexes, a K-clustering analysis method is adopted, and the horizontal section stratums are classified and evaluated according to the three types of reservoir stratums. The horizontal well mechanical parameter testing and reservoir compressibility evaluation method is formed through the fracturing indexes, and a traditional reservoir evaluation method mainly based on geology is changed.

Description

Technical Field

[0001] The present invention belongs to the technical field of rock mechanics parameter testing, and particularly relates to a method for evaluating sweet spots in fracturing engineering based on indentation mechanical parameter testing of cuttings while drilling. Background Art

[0002] Conventional rock mechanics parameters need to take cores for uniaxial or triaxial mechanical tests to obtain mechanical parameters. Generally, coring is not carried out in the horizontal section of a horizontal well. Without core materials, the conventional method is to conduct mechanical parameter tests through cores in the vertical well section. However, when the reservoir heterogeneity is strong, the mechanical characteristics and physical properties at different depth positions in the horizontal well section are different. How to conduct continuous mechanical parameter tests in the horizontal well section, obtain the variation characteristics of reservoir rock mechanical characteristics in different well sections, and carry out the optimization and evaluation of engineering geological sweet spots in the horizontal well section is a very meaningful work, which has important guiding significance for optimizing horizontal well fracturing stages, fracture parameter design, and fracturing transformation plan optimization.

[0003] Cuttings are the drilling products of each well and are the first-hand data of reservoir rocks obtained intuitively. Using cuttings while drilling to conduct continuous mechanical parameter tests in the horizontal well section is an effective technical means, which is crucial for improving the evaluation and optimization of sweet spots in horizontal wells and enhancing the pertinence of fracturing plans.

[0004] The prior art, such as the invention patent with the publication (announcement) number: CN109063232A, discloses a method for evaluating sweet spots in shale gas well reservoirs, including the following steps: extracting logging density ρ, shear wave travel time Δts, and longitudinal wave travel time Δtp data from the logging data of the pilot well; fitting the above data to obtain the relationship between the density, longitudinal wave travel time, and shear wave travel time of the pilot well; inputting the fitted relationship of the shear wave travel time into the in-situ stress profile calculation software, and at the same time importing the longitudinal wave travel time Δtp and density ρ data to calculate the shear wave travel time data of the well; through the obtained shear wave travel time data, combining with the well diameter and natural gamma-ray logging data, and then using the in-situ stress profile calculation software to obtain the rock mechanics parameters of the shale gas horizontal well. This evaluation method calculates the shear wave travel time of the shale gas well, combines with the well diameter and natural gamma-ray logging to obtain the rock mechanics parameters of the shale gas horizontal well, and the calculation results have general accuracy and cannot reflect the differences in reservoir mechanical properties.

[0005] The invention patent with authorization announcement number: CN112179770B discloses a method for evaluating the uniaxial compressive strength of shale based on the micro-nano indentation test of rock chips, including: collecting rock chips of the target shale reservoir, using a three-ion beam cutter to process the surface of the rock chip samples to make the surface smooth and high-quality cross-section; conducting rock chip micro- or nano-indentation tests on the processed rock chip samples to obtain multiple sets of indentation test load-displacement curves; and then calculating the uniaxial compressive strength of shale in the shale reservoir. This evaluation method obtains the shale mechanical parameters of shale horizontal wells through the micro-nano indentation test of shale rock chips, and the experimental method and experimental conditions are simple.

[0006] "Prediction of Tight Sandstone Sweet Spots Based on Hybrid Deep Learning Network" (Geophysical Prospecting for Petroleum, 2021 Issue 06) Based on the spatial distribution characteristics and data distribution characteristics of logging data and seismic data, a hybrid deep learning network structure suitable for prediction of tight reservoir sweet spots was created in a targeted manner. This method predicts geological sweet spots based on logging and seismic data, without considering the evaluation of fracturing engineering sweet spots. SUMMARY OF THE INVENTION

[0007] The purpose of the present invention is to provide a method for evaluating the sweet spot of a fracturing project based on the mechanical parameter test of drilling cuttings indentation to overcome the above technical defects.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] The present invention discloses a method for evaluating the sweet spot of a fracturing project based on mechanical parameter testing of cuttings indentation while drilling, comprising the following steps:

[0010] S1. Obtain cuttings samples while drilling;

[0011] S2. Processing the drilling cuttings samples into casting thin slices;

[0012] S3. Carry out indentation method mechanical parameter test experiment on rock samples after rock chip processing, i.e. casting thin slices, to obtain the micromechanical parameters of each test point;

[0013] S4. Analyze the content of different mineral components in the rock cuttings sample, and calculate the macroscopic mechanical parameters of the rock cuttings sample in combination with the microscopic mechanical parameters obtained in step S4;

[0014] S5. Carry out core triaxial rock mechanics parameter test experiments to obtain the core triaxial mechanical parameters of reservoir rocks;

[0015] S6. Establish the correlation between the micromechanical parameters of the drilling debris samples and the triaxial mechanical parameters of the core, and correct the micromechanical parameters obtained by the subsequent indentation method to obtain the rock mechanical parameters of different well depths in the horizontal well section;

[0016] S7. Perform weighted average processing on the rock mechanics parameters obtained in step S6 respectively, and obtain the fracturing index according to the processing results;

[0017] S8. According to the size of the fracturing index, adopt the K-clustering analysis method to classify and evaluate the horizontal section formation according to three types of reservoirs.

[0018] As a further optimization scheme, the method for processing the cuttings samples taken while drilling into cast thin sections in step S2 is: Select the cuttings samples taken while drilling in the horizontal well at certain interval distances along the starting and ending depths of the horizontal well section, and process the selected samples into cast thin sections with a thickness of 8 mm through the embedding method.

[0019] It should be further noted that the selected interval distance is determined according to the lithology change situation. When the lithology changes rapidly, the interval distance is reduced; when the lithology changes slowly, the interval distance becomes larger.

[0020] As a further optimization scheme, the method for carrying out the indentation method mechanical parameter test experiment on the cast thin sections in step S3 is: Select a rectangular area on the surface of the cast thin section, and then select an indentation lattice within this rectangular area to conduct static nano-indentation tests on the cuttings cast thin sections on the G200X micro-nano mechanical property test platform to obtain the microscopic mechanical parameters of each measuring point. The microscopic mechanical parameters include hardness H, elastic modulus E, fracture toughness K, and brittleness index B.

[0021] Furthermore, the size of the indentation lattice should be smaller than the minimum particle size of the cuttings samples. Select cuttings at different depths and measure the particle size under an optical microscope. Determine the size of the indentation lattice selected for the experiment according to the particle size of the cuttings samples as a plane of (100 - 250) μm × (100 - 250) μm, and carry out (100 - 400) × (100 - 400) indentation lattice mechanical parameter tests, that is, (100 - 400) × (100 - 400) indentation mechanical parameter tests, effectively covering a single mineral monomer of the cuttings thin section.

[0022] Preferably, during the static nano-indentation test, the maximum indentation depth ≥ 80 m and the displacement resolution ≥ 0.004 nm.

[0023] It is worth mentioning that when the mechanical test load of the cuttings cast thin section indentation method is greater than 40 mN and the indentation depth is greater than 1200 nm, the indentation test hardness of the cuttings is relatively stable and the modulus parameter is basically stable. Therefore, the cuttings indentation experiment parameters are determined as: test load 50 mN, indentation depth 2000 nm.

[0024] As a further preferred solution, the method for calculating the macroscopic mechanical parameters of the cuttings sample by analyzing the contents of different mineral components in the cuttings sample in step S4 and combining the microscopic mechanical parameters obtained in step S4 is as follows: determining the contents of different mineral components in the cuttings sample through X-ray diffraction analysis, combining the microscopic mechanical parameters obtained in step S4, using the deconvolution method to obtain the distribution ratio (i.e., volume fraction) of different mineral components in the macroscopic mechanical properties, and then calculating the macroscopic mechanical parameters of the cuttings sample by using the homogenization method according to the ratio of different minerals in the macroscopic mechanical properties; the macroscopic mechanical parameters include hardness H hom , elastic modulus E hom , fracture toughness K hom , brittleness index B hom .

[0025] The formula for calculating the macroscopic mechanical parameters of the cuttings sample by using the homogenization method is as follows:

[0026]

[0027]

[0028]

[0029]

[0030] In the formula, H hom , E hom , K hom , B hom are the macroscopic hardness, elastic modulus, fracture toughness, and brittleness index respectively;

[0031] c j is the volume fraction of the j-th mineral, and J is the number of mineral types.

[0032] are the average hardness, average elastic modulus, average fracture toughness, and average brittleness index of the j-th mineral respectively.

[0033] As a further preferred solution, the core triaxial rock mechanics parameter test experiment in step S5 refers to conducting a triaxial compression mechanics test experiment on the formation core identical to the cuttings sample taken while drilling to obtain the core triaxial mechanics parameters, and the core triaxial mechanics parameters include the reservoir rock hardness H 岩心 , elastic modulus E 岩心 , fracture toughness K 岩心 , brittleness index B 岩心 .

[0034] As a further preferred solution, the specific method for establishing the correlation between the micro-mechanical parameters of the cuttings samples while drilling and the triaxial mechanical parameters of the core, and calibrating the indentation mechanical parameters to obtain the rock mechanical parameters at different well depths in the horizontal well section is as follows: Based on the test results of the triaxial rock mechanical parameters of the core in step S5, calibrate the test results of the indentation method mechanical parameters in step S3, establish the correlation between the micro-mechanical parameters obtained from the cuttings indentation experiment while drilling and the triaxial rock mechanical parameters, and correct the micro-mechanical parameters obtained by the subsequent indentation method through the triaxial mechanical parameters of the core, so as to obtain the macroscopic mechanical parameters at different well depths in the horizontal well section, including rock hardness H i , elastic modulus E i , fracture toughness K i , brittleness index B i .

[0035] The elastic modulus affects the crack propagation pattern. Perform weighted average processing on the elastic modulus E i to obtain the mean-normalized elastic modulus Hardness and fracture toughness affect the difficulty of hydraulic fracture initiation and propagation. Perform weighted average processing on hardness H i and fracture toughness K i respectively to obtain the normalized hardness normalized fracture toughness The brittleness index characterizes the difficulty of forming a complex fracture network. Perform weighted average processing on the brittleness index B i to obtain the normalized brittleness index Considering the normalized elastic modulus normalized hardness normalized fracture toughness and normalized brittleness index Propose a fracture index calculation formula, and the fracture index calculation formula is as follows:

[0036] As a further preferred solution, according to the size of the fracture index, adopt the K-clustering analysis method to divide the formation in the horizontal section into three categories: The fracture index FI of the type I reservoir is > 1.0, the fracture index FI of the type II reservoir is 0.4 - 1.0, and the fracture index FI of the type III reservoir is < 0.4. The order of the compressibility sweet spots of the reservoir is: type I > type II > type III.

[0037] Adopting the above technical solutions, the present invention has the following beneficial effects:

[0038] (1) Through the cast thin sections made from cuttings samples, carry out the test of the indentation method mechanical parameters to obtain the continuous mechanical parameters of different well sections, meeting the continuous horizontal well mechanical property evaluation under the condition of no core in the horizontal well.

[0039] (2) By conducting triaxial rock mechanics parameter tests and comparing the results with the mechanical parameter results obtained by the indentation method, the corresponding relationship of mechanical parameters under the two methods is established, and the obtained mechanical parameter data is more accurate.

[0040] (3) By using elastic modulus, hardness, fracture toughness, and brittleness index, the fracturing index is proposed. Based on the fracturing index, a method for testing mechanical parameters of horizontal wells and evaluating reservoir compressibility is formed, which changes the traditional reservoir evaluation method mainly based on geology.

[0041] The above description is only an overview of the technical solution of the present invention. In order to understand the technical means of the present invention more clearly and implement it according to the content of the specification, the following describes the preferred embodiments of the present invention in detail with reference to the accompanying drawings. Description of the Drawings

[0042] Figure 1 is a flowchart of a fracturing engineering sweet spot evaluation method based on in-situ cuttings indentation mechanical parameter testing;

[0043] Figure 2 is a reservoir compressibility evaluation and grading curve graph based on in-situ cuttings indentation mechanical parameter testing.

[0044] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Detailed Embodiments

[0045] The content of the present invention can be further understood by combining the following detailed description of the preferred implementation methods of the present invention and the included embodiments. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. If the definition of a specific term disclosed in the prior art is inconsistent with any definition provided in the present invention, the definition provided in the present invention shall prevail.

[0046] In a typical embodiment of the present application, referring to Figure 1 , a fracturing engineering sweet spot evaluation method based on in-situ cuttings indentation mechanical parameter testing is provided, including the following steps:

[0047] S1. Obtain in-situ cuttings samples;

[0048] S2. Process the in-situ cuttings samples into cast thin sections;

[0049] S3. Conduct indentation method mechanical parameter testing experiments on the rock samples after cutting processing, that is, cast thin sections, to obtain the microscopic mechanical parameters of each test point;

[0050] S4. Analyze the contents of different mineral components in the cuttings samples, and calculate the macroscopic mechanical parameters of the cuttings samples by combining with the microscopic mechanical parameters obtained in step S4;

[0051] S5. Conduct a core triaxial rock mechanics parameter test experiment to obtain the core triaxial mechanical parameters of the reservoir rocks;

[0052] S6. Establish the correlation between the microscopic mechanical parameters of the cuttings samples while drilling and the core triaxial mechanical parameters, and correct the microscopic mechanical parameters obtained by the subsequent indentation method, so as to obtain the rock mechanical parameters at different well depths in the horizontal well section;

[0053] S7. Perform weighted average processing on the rock mechanical parameters obtained in step S6 respectively, and obtain the fracturing index according to the processing results;

[0054] S8. According to the size of the fracturing index, adopt the K-clustering analysis method to classify and evaluate the horizontal section formation into three types of reservoirs.

[0055] As a preferred implementation, the method for processing the cuttings samples while drilling into casting thin sections in step S2 is as follows: Select the cuttings samples while drilling in the horizontal well according to a certain interval distance (such as at intervals of 5 meters, 10 meters, 20 meters, 30 meters, etc.) along the starting and ending depths of the horizontal well section, and make a casting thin section with a thickness of 8 mm by the embedding method, that is, putting the cuttings samples into resin for embedding. The surface needs to be polished to meet the surface roughness requirements of nano-indentation testing.

[0056] It should be further noted that the selected interval distance is determined according to the lithology change situation. If the lithology changes rapidly, the interval distance is reduced; if the lithology changes slowly, the interval distance is increased.

[0057] As a further preferred scheme, the method for conducting the indentation method mechanical parameter test experiment on the casting thin section in step S3 is as follows: Select a rectangular area on the surface of the casting thin section, and then select an indentation lattice in this rectangular area to conduct a static nano-indentation test on the cuttings casting thin section on the G200X micro-nano mechanical property test platform to obtain the microscopic mechanical parameters of each measuring point. The microscopic mechanical parameters include hardness H, elastic modulus E, fracture toughness K, and brittleness index B.

[0058] Furthermore, the size of the indentation lattice should be smaller than the minimum particle size of the cuttings samples. Select cuttings at different depths and measure the particle size under an optical microscope. Determine the size of the indentation lattice selected for the experiment according to the particle size of the cuttings samples as a plane of (100 - 250) μm × (100 - 250) μm, and conduct (100 - 400) × (100 - 400) indentation lattice mechanical parameter tests, that is, (100 - 400) × (100 - 400) indentation mechanical parameter tests, effectively covering a single mineral monomer of the cuttings thin section.

[0059] Preferably, during the static nano-indentation test, the maximum indentation depth ≥ 80 m, and the displacement resolution ≥ 0.004 nm.

[0060] As a further preferred solution, the method for analyzing the content of different mineral components in the cuttings sample in step S4 and calculating the macroscopic mechanical parameters of the cuttings sample in combination with the microscopic mechanical parameters obtained in step S4 is as follows:

[0061] Determine the content of different mineral components in the cuttings sample by X-ray diffraction analysis. Combine the microscopic mechanical parameters obtained in step S4, and use the deconvolution method to obtain the distribution ratio of different mineral components in the macroscopic mechanical properties. Then, calculate the macroscopic mechanical parameters of the cuttings sample by using the homogenization method according to the ratio of different minerals in the macroscopic mechanical properties; the macroscopic mechanical parameters include hardness H hom 、elastic modulus E hom 、fracture toughness K hom 、brittleness index B hom 。

[0062] As a further preferred solution, the triaxial rock mechanical parameter test experiment of the core in step S5 refers to performing a triaxial compression mechanical test experiment on the formation core identical to the cuttings sample taken while drilling to obtain the triaxial mechanical parameters of the core. The triaxial mechanical parameters of the core include the hardness H of the reservoir rock 岩心 、elastic modulus E 岩心 、fracture toughness K 岩心 、brittleness index B 岩心 。

[0063] As a further preferred solution, the specific method for establishing the correlation between the microscopic mechanical parameters of the cuttings sample taken while drilling and the triaxial mechanical parameters of the core in step S6 and correcting the indentation mechanical parameters to obtain the rock mechanical parameters at different well depths in the horizontal well section is as follows: Based on the test results of the triaxial rock mechanical parameters of the core in step S5, calibrate the test results of the indentation method mechanical parameter test experiment in step S3, establish the correlation between the microscopic mechanical parameters obtained from the cuttings indentation experiment taken while drilling and the triaxial rock mechanical parameters, and correct the microscopic mechanical parameters obtained by the subsequent indentation method by the triaxial mechanical parameters of the core, so as to obtain the macroscopic mechanical parameters at different well depths in the horizontal well section, including rock hardness H i 、elastic modulus E i 、fracture toughness K i 、brittleness index B i 。

[0064] As an even further preferred solution, the specific method for performing weighted average processing on the rock mechanical parameters obtained in step S6 and obtaining the fracturing index according to the processing results is as follows: One by one, for rock hardness H i 、elastic modulus E i, fracture toughness K i and brittleness index B i are subjected to weighted average processing to respectively obtain the normalized elastic modulus normalized hardness normalized fracture toughness normalized brittleness index According to the normalized elastic modulus normalized hardness normalized fracture toughness and normalized brittleness index a calculation formula for the fracturing index is proposed, and the calculation formula for the fracturing index is:

[0065] As a further preferred solution, according to the size of the fracturing index, using the K-clustering analysis method, the horizontal section formation can be divided into three categories: for Class I reservoirs, the fracturing index FI > 1.0; for Class II reservoirs, the fracturing index FI is 0.4 - 1.0; for Class III reservoirs, the fracturing index FI < 0.4. The order of the favorable sweet spots of reservoir fracturability is: Class I > Class II > Class III.

[0066] The present invention will be further described below in conjunction with embodiments:

[0067] For a carbonate horizontal well, a fracturing engineering sweet spot evaluation method based on in-situ cuttings indentation mechanical parameter testing is carried out.

[0068] According to a fracturing engineering sweet spot evaluation method based on in-situ cuttings indentation mechanical parameter testing, it includes the following steps:

[0069] Step 1) Obtain in-situ cuttings in the horizontal well section, and take a cuttings sample every 10 meters;

[0070] Step 2) Select in-situ cuttings in the horizontal well and prepare them by the embedding method. Put the cuttings into the resin for embedding to make a casting thin slice with a thickness of 8 mm, and through surface polishing treatment, meet the surface roughness requirements for nanoindentation testing;

[0071] Step 3) Use the G200X micro / nano mechanical property testing platform to carry out the indentation method mechanical parameter testing experiment on the rock samples after cutting. Select a rectangular area on the surface of the cutting samples, select the indentation lattice size within the area for micro-nano mechanical testing, and obtain the micro-hardness, elastic modulus, fracture toughness, and brittle force parameters of each test point. Among them, the indentation lattice size should be smaller than the minimum particle size of the cutting samples. Select cutting samples with different depths, measure the particle size under an optical microscope, and determine that the indentation lattice size should be less than 1065μm according to the particle size of the cutting samples. The selected indentation lattice size for the experiment is a plane of 200μm×200μm, and carry out the mechanical parameter testing of 50×50 indentation lattice, that is, 2500 times of indentation mechanical parameter testing (test load 50mN, indentation depth 2000nm), effectively covering a single mineral monomer of the cutting thin section:

[0072] Step 4) Determine the content of different mineral components in the cutting samples by X-ray diffraction analysis. Combine the micro-mechanical parameters obtained in Step S4, and use the deconvolution method to obtain the distribution ratio (i.e., volume fraction) of different mineral components in the macroscopic mechanical properties. Then, use the homogenization method to calculate according to the ratio of different minerals in the macroscopic mechanical properties to obtain the macroscopic hardness H hom , elastic modulus E hom , fracture toughness K hom , brittle index B hom ;

[0073] The formula for calculating the macroscopic mechanical parameters of the cutting samples by the homogenization method is:

[0074]

[0075]

[0076]

[0077]

[0078] In the formula, H hom , E hom , K hom , B hom are the macroscopic hardness, elastic modulus, fracture toughness, and brittle index respectively;

[0079] c j is the volume fraction of the j-th mineral, and J is the number of mineral types;

[0080] are the average hardness, average elastic modulus, average fracture toughness, and average brittle index of the j-th mineral respectively;

[0081] Step 5) Conduct triaxial rock mechanics parameter test experiments through vertical well coring, that is, conduct triaxial compression mechanics test experiments on the formation core identical to the cuttings rock samples taken while drilling, and obtain the triaxial mechanical parameters of the core, including the rock hardness H of the reservoir rock 岩心 , elastic modulus E 岩心 , fracture toughness K 岩心 , brittleness index B 岩心 ;

[0082] Step 6) Based on the triaxial rock mechanics parameter test experiments of the core, obtain the rock hardness H of the reservoir rock 岩心 , elastic modulus E 岩心 , fracture toughness K 岩心 , brittleness index B 岩心 , and compare them with the homogenized hardness H hom , elastic modulus E hom , fracture toughness K hom , brittleness index B hom obtained from the cuttings indentation experiment, establish the correlation between the micro-mechanical parameters obtained from the cuttings indentation experiment while drilling and the triaxial rock mechanics parameters, and correct the micro-mechanical parameters obtained by the subsequent indentation method through the triaxial mechanical parameters of the core, so as to obtain the macro-mechanical parameters at different well depths in the horizontal well section, including rock hardness H i , elastic modulus E i , fracture toughness K i , brittleness index B i

[0083] Step 7) Perform weighted average processing on the rock hardness H i , elastic modulus E i , fracture toughness K i and brittleness index B i respectively to obtain the normalized elastic modulus normalized hardness normalized fracture toughness normalized brittleness index According to the normalized elastic modulus normalized hardness normalized fracture toughness and normalized brittleness index propose the calculation formula for the fracturing index

[0084] Step 8) According to the magnitude of the fracturing index, adopt the K-clustering analysis method to divide the horizontal section formation into three categories, as Figure 2 shown. The average fracturing index of the Class 1 reservoir in this well is 1.12, with the best compressibility. The average fracturing index of the Class 2 reservoir is 0.65, with better compressibility. The average fracturing index of the Class 3 reservoir is 0.27, with poor compressibility.

[0085] The reservoir compressibility sweet spots are ranked as: Class 1 > Class 2 > Class 3.

[0086] The present invention conducts scratch method mechanical parameter tests on cuttings while drilling to obtain continuous mechanical parameters of different well sections, and forms a continuous mechanical profile of horizontal wells and a reservoir compressibility evaluation method.

[0087] The above are only the preferred embodiments of the present invention, which are merely illustrative of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for evaluating sweet spots in fracturing engineering based on mechanical parameter testing of cuttings indentation while drilling, characterized in that: The following steps are involved: S1. Obtaining drilling cuttings samples; S2. Processing the drilling cuttings samples into casting thin slices; S3. Conduct indentation method mechanical parameter test experiments on rock samples after rock chip processing, i.e., casting thin slices, to obtain micromechanical parameters of each test point; S4. Analyze the contents of different mineral components in the rock cuttings sample, and calculate the macroscopic mechanical parameters of the rock cuttings sample in combination with the microscopic mechanical parameters obtained in step S4; S5. Carry out core triaxial rock mechanics parameter test experiments to obtain core triaxial mechanical parameters of reservoir rocks; S6. Establish the correlation between the micromechanical parameters of the drilling debris sample and the triaxial mechanical parameters of the core, and correct the micromechanical parameters obtained by the subsequent indentation method to obtain the rock mechanical parameters of different well depths in the horizontal well section; S7. Perform weighted average processing on the rock mechanical parameters obtained in step S6, and obtain a fracturing index based on the processing results; S8. According to the size of the fracturing index, the K-cluster analysis method is used to classify and evaluate the horizontal section strata into three types of reservoirs.

2. The method for evaluating the sweet spot of a fracturing project based on mechanical parameter testing of drilling cuttings indentation according to claim 1, characterized in that: The method S2 for processing the drilling cuttings samples into casting slices is as follows: selecting the drilling cuttings samples of the horizontal well at a certain interval along the starting and ending depths of the horizontal well section, and processing the selected samples into 8 mm thick casting slices by the inlay method.

3. The method for evaluating the sweet spot of a fracturing project based on mechanical parameter testing of drilling cuttings indentation according to claim 1, characterized in that: The method for conducting the indentation method mechanical parameter testing experiment of the casting thin slice in S3 is: select a rectangular area on the surface of the casting thin slice, and then select an indentation point array in the rectangular area to perform a static nano-indentation test on the rock chip casting thin slice on the G200X micro-nano mechanical performance testing platform to obtain the micro-mechanical parameters of each measuring point, and the micro-mechanical parameters include hardness H, elastic modulus E, fracture toughness K, and brittleness index B.

4. The method for evaluating the sweet spot of a fracturing project based on mechanical parameter testing of drilling cuttings indentation according to claim 3, characterized in that: The indentation lattice size should be smaller than the minimum particle size of the rock cuttings sample. Rock cuttings of different depths are selected and the particle size is measured under an optical microscope. The indentation lattice size selected for the experiment is determined to be a plane of (100-250) μm×(100-250) μm according to the particle size of the rock cuttings sample. A (100-400)×(100-400) indentation lattice mechanical parameter test is carried out, i.e., (100-400)×(100-400) times of indentation mechanical parameter test is carried out, which effectively covers the individual mineral monomers of the rock cuttings slices.

5. The method for evaluating the sweet spot of a fracturing project based on mechanical parameter testing of drilling cuttings indentation according to claim 3, characterized in that: The maximum indentation depth during the static nano-indentation test is ≥80m, and the displacement resolution is ≥0.004nm.

6. The method for evaluating the sweet spot of a fracturing project based on mechanical parameter testing of drilling cuttings indentation according to claim 1, characterized in that: The method of analyzing the contents of different mineral components in the rock cuttings sample in step S4 and calculating the macroscopic mechanical parameters of the rock cuttings sample in combination with the microscopic mechanical parameters obtained in step S4 is as follows: The content of different mineral components in the rock cuttings sample is determined by X-ray diffraction analysis. Combined with the micromechanical parameters obtained in step S4, the deconvolution method is used to obtain the distribution ratio of different mineral components in macromechanical properties. Then, the macromechanical parameters of the rock cuttings sample are calculated using a homogenization method according to the ratio of different minerals in macromechanical properties. The macromechanical parameters include hardness H hom , elastic modulus E hom , fracture toughness K hom , Brittleness Index B hom .

7. The method for evaluating the sweet spot of a fracturing project based on mechanical parameter testing of cuttings while drilling according to claim 1, characterized in that: The core triaxial rock mechanics parameter test experiment in step S5 refers to performing a triaxial compression mechanics test experiment on the same formation core as the drilling cuttings sample to obtain the core triaxial mechanical parameters. The core triaxial mechanical parameters include the reservoir rock hardness H 岩心 , elastic modulus E 岩心 , fracture toughness K 岩心 , Brittleness Index B 岩心 .

8. The method for evaluating the sweet spot of a fracturing project based on mechanical parameter testing of cuttings while drilling as claimed in claim 1, characterized in that: The step S6 establishes the correlation between the micromechanical parameters of the drilling debris sample and the triaxial mechanical parameters of the core, corrects the indentation mechanical parameters, and thus obtains the rock mechanical parameters of different well depths in the horizontal well section. The specific method is: based on the test results of the triaxial rock mechanical parameters of the core in step S5, calibrate the test results of the mechanical parameters test by the indentation method in step S3, establish the correlation between the micromechanical parameters obtained by the drilling debris indentation experiment and the triaxial rock mechanical parameters, and correct the micromechanical parameters obtained by the subsequent indentation method by the triaxial mechanical parameters of the core, so as to obtain the macromechanical parameters of different well depths in the horizontal well section, including the rock hardness H. i , elastic modulus E i , fracture toughness K i , Brittleness Index B i .

9. The method for evaluating the sweet spot of a fracturing project based on mechanical parameter testing of drilling cuttings indentation according to claim 8, characterized in that: In step S7, the rock mechanical parameters obtained in step S6 are respectively subjected to weighted average processing, and the specific method for obtaining the fracturing index according to the processing results is: i , elastic modulus E i , fracture toughness K i and brittleness index B i Perform weighted average processing to obtain the normalized elastic modulus Normalized hardness Normalized fracture toughness Normalized brittleness index According to the normalized elastic modulus Normalized hardness Normalized fracture toughness and normalized fragility index A calculation formula for the fracturing index is proposed, which is:

10. The method for evaluating the sweet spot of a fracturing project based on mechanical parameter testing of cuttings while drilling as claimed in claim 1, characterized in that: According to the size of the fracturing index, the K-cluster analysis method is used to divide the horizontal strata into three categories: Class I reservoir fracturing index FI>1.0, Class II reservoir fracturing index FI is 0.4-1.0, Class III reservoir fracturing index FI<0.4, and the reservoir compressibility sweet spots are ranked as follows: Class I>Class II>Class III.

Images