A method of rock drillability classification

Abstract

The present application provides a kind of rock drillability grading method, comprising the following steps: step S1, carries out cutter penetration test, calculates rock drillability index;Step S2, establish the single factor calculation model of rock drillability index and each influencing factor of rock drillability;Step S3, the correlation analysis of each influencing factor of rock drillability is carried out two by two, and determines key influencing factor;Step S4, based on key influencing factor, establish the prediction model of rock drillability index;Step S5, establish the calculation model of rock drillability index and underground engineering rock mass quality index;Step S6, establish the rock drillability classification standard of Cretaceous and Jurassic strata.The method is based on the penetration load-penetration curve obtained from cutter penetration test, determines rock drillability index, provides evaluation index for rock drillability research, the evaluation index is clear in meaning, and the calculation method is simple, realizes the rock drillability of Cretaceous and Jurassic strata is predicted.

Description

Technical Field

[0001] This invention relates to the field of well drilling technology, and in particular to a method for classifying rock drillability. Background Technology

[0002] The method of forming a shaft using vertical shaft drilling rigs as the main equipment is called well drilling, or simply well drilling. Because vertical shaft drilling allows for unmanned underground construction, it has been widely used in coal mine vertical shaft construction. In recent years, an increasing number of extra-large mines with a capacity of over ten million tons have been initiated. The mining of deep coal resources in these areas requires the construction of vertical shafts. However, in Cretaceous and Jurassic strata, well drilling using the vertical shaft method is slow and suffers from severe cutter wear, significantly restricting the construction speed of well drilling in mining areas and causing huge economic losses. To improve the construction efficiency and economic benefits of well drilling in mining areas, it is necessary to evaluate the drillability of rocks at different depths in Cretaceous and Jurassic strata and provide theoretical guidance for the preliminary work of well drilling projects in mining areas, so as to flexibly adjust and optimize parameters during subsequent drilling.

[0003] In the field of well drilling engineering, rock drillability describes the ability of rock to resist fracturing during cutter rock breaking. It is a comprehensive performance index of formation anti-drilling capability and one of the important parameters for optimizing drilling parameters and selecting drill bits. Current research on rock drillability mainly focuses on oil drilling and TBM tunneling engineering in coal mines. In oil drilling, the rock drillability grade is predicted primarily based on sonic logging data, rock abrasiveness, hardness, plasticity coefficient, and compressive strength as the main influencing factors. In coal mine TBM construction engineering, the relationship between factors such as uniaxial compressive strength, rock integrity coefficient, rock hardness, brittleness coefficient, and abrasiveness and the rock penetration index is established to predict the excavability of the surrounding rock during TBM construction. Most of the aforementioned methods for evaluating rock drillability use field data as influencing factors and evaluation indicators. However, field data is difficult to obtain, and the influencing factors and evaluation indicators for rock drillability research in the fields of oil drilling and coal mine TBM engineering are not applicable to rock drillability research in Cretaceous and Jurassic formations.

[0004] In view of this, given the lack of research on rock drillability in the drilling field of Cretaceous and Jurassic formations, there is a need for a rock drillability classification method involving Cretaceous and Jurassic formations. Summary of the Invention

[0005] The purpose of this invention is to provide a method for classifying rock drillability, which enables the prediction of rock drillability in Cretaceous and Jurassic strata.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A rock drillability classification method for evaluating the drillability of Cretaceous and Jurassic rock formations includes the following steps:

[0008] Step S1: Conduct a cutter penetration test and calculate the rock drillability index;

[0009] Step S2: Establish a single-factor calculation model for the rock drillability index and various influencing factors of rock drillability;

[0010] Step S3: Perform pairwise correlation analysis on the various factors affecting rock drillability to identify key influencing factors;

[0011] Step S4: Establish a predictive model for the rock drillability index based on key influencing factors;

[0012] Step S5: Establish a calculation model for the rock drillability index and the rock mass quality index of underground engineering.

[0013] Step S6: Establish rock drillability classification standards for Cretaceous and Jurassic strata.

[0014] Furthermore, in the above-mentioned rock drillability classification method, in step S1, rock samples are collected from Cretaceous and Jurassic strata at depths of 10m to 50m from top to bottom. The confining pressure of the cutter penetration test is the same as the in-situ stress of the stratum where the rock sample is located. The ratio of the cutter teeth in the cutter penetration test to the cutting teeth of the well drilling cutter is 1:1. The penetration load-penetration curve of the rock sample is obtained through the cutter penetration test. Preferably, the length dimension of the rock sample is greater than or equal to 5 times the length dimension of the cutter in the cutter penetration test. Preferably, the loading rate of the cutter penetration test is 0.005mm / s or 0.001mm / s, and loading is stopped and unloaded when the rock sample is completely destroyed after a displacement of 15mm.

[0015] Furthermore, in the above-described rock drillability classification method, in step S1, the calculation model for the rock drillability index of the rock sample is as follows:

[0016] FBI = F NB / P B Formula 1

[0017] In Formula 1: FBI is the rock drillability index, kN·mm -1 ;F NB P represents the penetration load (KN) at which the rock sample experiences its first precession failure. B The cutter penetration depth, in mm, is the depth of the cutter when the rock sample experiences its first leap failure.

[0018] Furthermore, in the above-mentioned rock drillability classification method, in step S2, the influencing factors of rock drillability include the uniaxial compressive strength (UCS) of the rock and the rock mass integrity coefficient (K). V Rock hardness H Z The rock brittleness index B2 and rock abrasiveness CAI; the uniaxial compressive strength UCS of the rock can be measured by laboratory tests or calculated from the point load strength of the rock; the rock mass integrity factor K V The rock hardness H can be obtained from engineering geological surveys or calculated from the rock quality index RQD; Z The hardness is either Steinmann indentation hardness or Vickers indentation hardness; the formula for calculating the brittleness index B2 of the rock is:

[0019] B2=σ c / σ t Formula 2

[0020] In Formula 2, σ c The uniaxial compressive strength of rock is given by σ (MPa). t The tensile strength of the rock is given in MPa.

[0021] The rock abrasiveness CAI was measured using a rock abrasiveness servo instrument to perform a rock abrasiveness test.

[0022] Furthermore, in the above-mentioned rock drillability classification method, in step S2, the single-factor calculation model for the rock drillability index and each influencing factor of rock drillability is as follows:

[0023] FBI = a i exp(b i X i ) Formula 3

[0024] In Formula 3, FBI is the rock drillability index, X i (i = 1, 2, ..., 5) are the factors affecting rock drillability, a i (i = 1, 2, ..., 5) are the coefficients of the computational model, b i (i = 1, 2, ..., 5) are the regression coefficients of the factors affecting rock drillability.

[0025] Furthermore, in the aforementioned rock drillability classification method, a single-factor calculation model of the rock drillability index and various influencing factors of rock drillability is used to analyze the relationship between the rock drillability index (FBI), the uniaxial compressive strength (UCS), and the rock mass integrity coefficient (K). V The rock hardness H Z The correlation between the rock brittleness index B2 and the rock abrasiveness CAI.

[0026] Furthermore, in the above-mentioned rock drillability classification method, in step S3, pairwise correlation analysis is performed on each influencing factor of rock drillability. The pairwise correlation analysis eliminates possible collinear relationships between the influencing factors of rock drillability. The key influencing factors that have a significant impact on the rock drillability index FBI are determined by combining the magnitude of the coefficient of determination between the rock drillability index FBI and each influencing factor of rock drillability. The correlation analysis between the influencing factors of rock drillability is performed by MATLAB software, SPSS software, or ORIGIN software. The correlation analysis is achieved by establishing linear or nonlinear regression equations between the influencing factors of rock drillability.

[0027] Furthermore, in the above-mentioned rock drillability classification method, in step S4, the prediction model for the rock drillability index based on key influencing factors is as follows:

[0028] FBI = c0exp(c1X1 + c2X2 + ... + c n X n +c n+1 ) Formula 4

[0029] In Formula 4, FBI is the rock drillability index, c0 is the coefficient of the prediction model, and X... n (n = 1, 2, ..., 5) are the key influencing factors, c n (n=1,2,…,5) are the partial regression coefficients of the key influencing factors, c n+1 (n = 1, 2, ..., 5) is the constant term in the predictive model exponent.

[0030] Furthermore, in the above-mentioned rock drillability classification method, in step S5, the calculation model for the rock drillability index and the underground engineering rock mass quality index is as follows:

[0031] FBI=d0exp(d1[BQ]) Formula 5

[0032] In Formula 5, FBI is the rock drillability index, d0 is the coefficient of the calculation model, [BQ] is the rock mass quality index for underground engineering, and d1 is the regression coefficient of the rock mass quality index [BQ] for underground engineering.

[0033] Furthermore, in the above-mentioned rock drillability classification method, in step S6, based on the calculation model of the rock drillability index FBI and the underground engineering rock mass quality index [BQ], the rock drillability classification standard for Cretaceous and Jurassic strata is obtained. Based on the underground engineering rock mass quality index [BQ], the smaller the value of the underground engineering rock mass quality index [BQ], the smaller the rock drillability index FBI, and the higher the rock drillability; the larger the value of the underground engineering rock mass quality index [BQ], the larger the rock drillability index FBI, and the lower the rock drillability.

[0034] Analysis reveals that this invention discloses a method for classifying rock drillability. This method determines the rock drillability index based on the penetration load-penetration curve obtained from roller cutter penetration tests on rock samples from Cretaceous and Jurassic strata. This provides an evaluation index for rock drillability research, and the evaluation index has clear significance and a simple calculation method. This method uses single-factor regression analysis to evaluate the rock drillability index based on numerous factors influencing rock drillability, and it also considers the uniaxial compressive strength (UCS) and rock mass integrity coefficient (K) of the rock. V The method for predicting rock drillability index comprehensively considers influencing factors, which can be obtained from geological survey data and laboratory tests, making the acquisition process simple. This method is a rock drillability classification method based on the underground engineering rock mass quality index [BQ]. It does not require large equipment, has simple steps, a scientific calculation method, and reliable evaluation results. It is of great significance for optimizing drilling parameters and reducing drilling costs in Cretaceous and Jurassic formations. Attached Figure Description

[0035] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0036] Figure 1 This is a flowchart of a rock drillability classification method according to an embodiment of the present invention.

[0037] Figure 2 This is a penetration load-penetration curve diagram of a roller penetration test according to an embodiment of the present invention.

[0038] Figure 3 This is a graph showing the relationship between the rock drillability index (FBI) and the uniaxial compressive strength (UCS) of rock according to an embodiment of the present invention.

[0039] Figure 4 The rock drillability index FBI and the rock mass integrity coefficient K are shown in one embodiment of the present invention. V The curve relationship diagram.

[0040] Figure 5 The rock drillability index FBI and rock hardness H are shown in one embodiment of the present invention. Z The curve relationship diagram.

[0041] Figure 6 This is a graph showing the relationship between the rock drillability index FBI and the rock brittleness index B2 according to an embodiment of the present invention.

[0042] Figure 7 This is a graph showing the relationship between the rock drillability index (FBI) and the rock abrasiveness index (CAI) according to an embodiment of the present invention.

[0043] Figure 8 This is a graph showing the relationship between the rock drillability index (FBI) and the underground engineering rock mass quality index (BQ) according to an embodiment of the present invention. Detailed Implementation

[0044] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Various examples are provided by way of explanation and not by way of limitation. Indeed, those skilled in the art will recognize that modifications and variations can be made to the invention without departing from its scope or spirit. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the invention encompass such modifications and variations falling within the scope of the appended claims and their equivalents.

[0045] like Figures 1 to 8 As shown, according to an embodiment of the present invention, a rock drillability classification method is provided for evaluating the rock drillability of Cretaceous and Jurassic strata, such as... Figure 1 As shown, it includes the following steps:

[0046] Step S1: Conduct a cutter penetration test and calculate the rock drillability index.

[0047] Roller cutter penetration tests were conducted on rock samples under confining pressure conditions. The rock drillability index was calculated based on the test results. Rock samples were collected from Cretaceous and Jurassic strata at depths of 10m–50m (e.g., 10m, 15m, 20m, 25m, 30m, 35m, 40m, 45m, 50m) from top to bottom. The confining pressure of the roller cutter penetration test was the same as the in-situ stress of the strata containing the rock sample. The ratio of the cutter teeth in the roller cutter penetration test to those in well drilling was 1:1. The longitudinal dimension of the rock sample was greater than or equal to five times the longitudinal dimension of the cutter in the roller cutter penetration test to prevent boundary effects from influencing the test results. The loading rate of the roller cutter penetration test was 0.005mm / s or 0.001mm / s. Loading was stopped and unloaded when the rock sample reached a displacement of 15mm or complete failure. The penetration load-penetration curve of the rock sample was obtained through the roller cutter penetration test.

[0048] Preferably, the calculation model for the rock drillability index of the rock sample is as follows:

[0049] FBI = F NB / P B Formula 1

[0050] In Formula 1: FBI is the rock drillability index, kN·mm -1 ;F NB The penetration load at which the rock sample experiences its first precession failure is expressed in kN; P B The cutter penetration depth, in mm, is the first jump failure of the rock sample.

[0051] Step S2: Establish a single-factor calculation model for the rock drillability index and various influencing factors of rock drillability.

[0052] The factors influencing rock drillability in Cretaceous and Jurassic strata were identified, and a single-factor calculation model for the rock drillability index and each influencing factor was established to analyze the impact of each influencing factor on rock drillability.

[0053] Factors affecting rock drillability include the uniaxial compressive strength (UCS) of the rock and the rock mass integrity factor (K). V Rock hardness H Z Rock brittleness index B2 and rock abrasiveness CAI.

[0054] Preferably, the uniaxial compressive strength (UCS) of the rock can be measured by laboratory tests or calculated from the point load strength of the rock.

[0055] As shown in Table 1, the rock mass integrity coefficient K V It can be obtained from engineering geological surveys or calculated from the rock quality index RQD.

[0056] Table 1: Rock Quality Index (RQD) and Rock Mass Integrity Coefficient (K) V Correspondence table

[0057]

[0058] Rock hardness H Z It is either the Smithsonian indentation hardness or the Vickers indentation hardness.

[0059] The formula for calculating the rock brittleness index B2 is as follows:

[0060] B2=σ c / σ t Formula 2

[0061] In Formula 2, σ c σ is the uniaxial compressive strength of the rock, MPa; t denoted as σ, where σ is the tensile strength of the rock, expressed in MPa.

[0062] Rock abrasiveness (CAI) was measured using a rock abrasiveness servo instrument and the CERCHAR abrasiveness test.

[0063] Preferably, the single-factor calculation model for the rock drillability index and various influencing factors of rock drillability is as follows:

[0064] FBI = a i exp(b i X i ) Formula 3

[0065] In Formula 3, FBI is the rock drillability index, X i (i = 1, 2, ..., 5) are the factors affecting rock drillability, a i (i = 1, 2, ..., 5) are the coefficients of the computational model, b i (i = 1, 2, ..., 5) are the regression coefficients of the factors affecting rock drillability.

[0066] Using a single-factor calculation model (Formula 3) of the rock drillability index and various influencing factors of rock drillability, the relationship between the rock drillability index (FBI), the uniaxial compressive strength (UCS), and the rock mass integrity coefficient (K) is analyzed. V Rock hardness H Z The correlation between rock brittleness index B2 and rock abrasiveness CAI.

[0067] Step S3 involves performing pairwise correlation analysis on the various factors affecting rock drillability to identify key influencing factors.

[0068] Pairwise correlation analysis was performed on the various factors influencing rock drillability to eliminate potential collinear relationships among them. The key influencing factors with the greatest impact on the FBI were identified by combining the coefficients of determination between the FBI and the various factors. Correlation analysis among the factors was conducted using mathematical analysis software such as MATLAB, SPSS, or ORIGIN, achieving correlation analysis by establishing linear or nonlinear regression equations among the factors.

[0069] Step S4: Establish a prediction model for the rock drillability index based on key influencing factors.

[0070] The prediction model for the rock drillability index, based on key influencing factors, is as follows:

[0071] FBI = c0exp(c1X1 + c2X2 + ... + c n X n +c n+1 ) Formula 4

[0072] In Formula 4, FBI is the rock drillability index, c0 is the coefficient of the prediction model, and X... n (n = 1, 2, ..., 5) are the key influencing factors, c n (n=1,2,…,5) are the partial regression coefficients of the key influencing factors, c n+1 (n = 1, 2, ..., 5) is the constant term in the predictive model exponent.

[0073] The coefficients c0 and partial regression coefficients c0 and c10 are obtained by solving equation (4) using mathematical analysis software such as MATLAB, SPSS, or ORIGIN. n and constant term c n+1 .

[0074] Step S5: Establish a calculation model for the rock drillability index and the rock mass quality index of underground engineering.

[0075] The calculation model for the rock drillability index and the rock mass quality index of underground engineering is as follows:

[0076] FBI=d0exp(d1[BQ]) Formula 5

[0077] In Formula 5, FBI is the rock drillability index, d0 is the coefficient of the calculation model, [BQ] is the rock mass quality index for underground engineering, and d1 is the regression coefficient of the rock mass quality index [BQ] for underground engineering.

[0078] The rock mass quality index [BQ] for underground engineering is calculated according to the national standard "Classification Standard for Engineering Rock Mass" (GB / T 50218—2014):

[0079] [BQ]=BQ-100(K1+K2+K3) Formula 6

[0080] In Formula 6: [BQ] is the quality index of underground rock mass, BQ is the basic quality index of rock mass, K1 is the correction coefficient for the influence of groundwater, K2 is the correction coefficient for the influence of the occurrence of the main structural planes of underground rock mass, and K3 is the correction coefficient for the influence of the initial stress state; K1, K2, and K3 are taken according to the "Standard for Classification of Engineering Rock Mass" (GB / T 50218—2014);

[0081] Preferably, the basic quality index BQ of the rock mass is calculated according to the national standard "Classification Standard for Engineering Rock Mass" (GB / T 50218—2014):

[0082] BQ = 100 + 3R C +250K V Formula 7

[0083] In Formula 7: R C It is the saturated uniaxial compressive strength of rock, K V It is the rock mass integrity coefficient; R C K V The following conditions must be met during the calculation:

[0084] When R C >90K V At +30, with R C =90K V +30 and K V Substitute into the formula to calculate the BQ value;

[0085] When K V >0.04R C When +0.4, with K V =0.04R C +0.4 and R C Substitute the values ​​into the formula to calculate the BQ value.

[0086] Step S6: Establish rock drillability classification standards for Cretaceous and Jurassic strata.

[0087] Based on the calculation model of the rock drillability index (FBI) and the underground engineering rock mass quality index (BQ), the rock drillability classification standards for Cretaceous and Jurassic strata are obtained. According to the underground engineering rock mass quality index (BQ), the smaller the value of the underground engineering rock mass quality index (BQ), the smaller the rock drillability index (FBI) and the higher the rock drillability; the larger the value of the underground engineering rock mass quality index (BQ), the larger the rock drillability index (FBI) and the lower the rock drillability.

[0088] The rock drillability classification standard for Cretaceous and Jurassic strata is based on a calculation model of the rock drillability index (FBI) and the underground engineering rock mass quality index (BQ). The rock drillability index (FBI) is used as the classification index, and the standard is established according to the classification standard of the underground engineering rock mass quality index (BQ) in the "Engineering Rock Mass Classification Standard" (GB / T 50218—2014).

[0089] Example 1

[0090] A method for classifying rock drillability includes the following steps:

[0091] Step S1: Conduct a cutter penetration test and calculate the rock drillability index.

[0092] Rock samples of sandy mudstone were collected from the Jurassic strata at depths of 350 m, 400 m, 450 m, 500 m, 550 m, 600 m, 650 m, and 700 m from top to bottom. The rock samples measured 300 mm long × 150 mm wide × 150 mm high. Roller cutter penetration tests were conducted on the rock samples. Figure 2 As shown, the penetration load-penetration curve of the rock sample was obtained through the cutter penetration test. The rock drillability index (FBI) of the rock sample was calculated using the rock drillability index calculation model (Formula 1), and the results are shown in Table 2.

[0093] Table 2: Test Results of Factors Affecting Rock Drillability and Rock Drillability Index

[0094]

[0095]

[0096] Note: SN35-1 represents a rock sample of sandy mudstone at a depth of 350m in the Jurassic strata, and the sample number is 1.

[0097] Step S2: Establish a single-factor calculation model for the rock drillability index and various influencing factors of rock drillability.

[0098] The factors influencing rock drillability were identified, and a single-factor calculation model was established for the rock drillability index (FBI) and each influencing factor. The uniaxial compressive strength (UCS) and rock mass integrity coefficient (K) of the rock were also considered. V Rock hardness H Z The calculation results of the rock brittleness index B2 and the rock abrasion index CAI are shown in Table 2.

[0099] The correlation between the rock drillability index (FBI) and various influencing factors of rock drillability was analyzed using a single-factor calculation model (Formula 3). The relationship between the FBI and these influencing factors is shown in [reference needed]. Figures 3 to 7 As shown in Table 3, the single-factor calculation model of the rock drillability index (FBI) and various influencing factors of rock drillability is presented.

[0100] Table 3: Single-factor calculation model of rock drillability index (FBI) and various influencing factors of rock drillability

[0101]

[0102] Table 3 shows that the correlation between the rock drillability index (FBI) and various influencing factors of rock drillability, from highest to lowest, is: uniaxial compressive strength (UCS) > rock hardness (H). Z Rock mass integrity coefficient K V >Rock abrasiveness (CAI) >Rock brittleness index (B2).

[0103] The relationship between the rock drillability index (FBI) and various factors influencing rock drillability is as follows: the rock drillability index (FBI) is related to the uniaxial compressive strength (UCS) of the rock and the rock mass integrity coefficient (K). V Rock hardness H Z Both the rock abrasiveness index (CAI) and rock drillability index (FBI) are positively correlated, while the rock brittleness index (B2) and rock brittleness index (B2) are negatively correlated.

[0104] Step S3 involves performing pairwise correlation analysis on the various factors affecting rock drillability to identify key influencing factors.

[0105] Pairwise correlation analysis was conducted on the various factors affecting rock drillability to eliminate possible collinear relationships among them. The key factors with a significant impact on the rock drillability index FBI were determined by combining the coefficient of determination between the rock drillability index FBI and the various factors affecting rock drillability.

[0106] The correlation analysis of various factors affecting rock drillability, based on experiments, shows that the uniaxial compressive strength (UCS) of rock is related to the rock hardness (H). ZThe coefficient of determination between them is 0.853, indicating a collinearity problem; the rock brittleness index B2 and the rock mass integrity coefficient K... V The coefficient of determination between rock abrasiveness (CAI) and rock uniaxial compressive strength (UCS) is 0.731, indicating collinearity. The coefficient of determination between CAI and CAS is 0.725, also indicating collinearity. The coefficient of determination between CAI and CAS is related to rock hardness (H). Z The coefficient of determination between the two factors is 0.693, indicating collinearity. The coefficients of determination among other factors influencing rock drillability are less than 0.6, indicating no collinearity. The regression equations for the various factors influencing rock drillability are shown in Table 4. Combining the correlation between the rock drillability index (FBI) obtained in step S2 and each influencing factor, and eliminating collinearity among the factors, the factors with the larger coefficient of determination of the rock drillability index (FBI) are identified. The factors with larger coefficients are the uniaxial compressive strength (UCS) and the rock mass integrity coefficient (K). V As a key influencing factor in the multiple regression analysis of the rock drillability index (FBI) and rock drillability.

[0107] Table 4: Regression equations and coefficients of determination among various factors influencing rock drillability

[0108]

[0109] Step S4: Establish a prediction model for the rock drillability index based on key influencing factors.

[0110] The coefficients c0 and partial regression coefficients c0 and c2 were obtained by solving the rock drillability index prediction model (Equation 4) based on key influencing factors using SPSS software. n and constant term c n+1 Using the uniaxial compressive strength (UCS) of rock and the rock mass integrity factor (K) V The prediction model for the rock drillability index (FBI), a key influencing factor, is as follows:

[0111] FBI=2.917exp(0.025UCS+1.035K V +0.463) Formula 8

[0112] In Formula 8, FBI is the rock drillability index; UCS is the uniaxial compressive strength of the rock; K V It is the rock mass integrity coefficient.

[0113] The above uses the uniaxial compressive strength (UCS) of rock and the rock mass integrity factor (K) as examples. V The coefficient of determination R of the prediction model for the rock drillability index (FBI), a key influencing factor. 2 It is 0.96.

[0114] Step S5: Establish a calculation model for the rock drillability index and the rock mass quality index of underground engineering.

[0115] The coefficients d0 and regression coefficient d1 were obtained by solving the calculation model (Formula 5) of rock drillability index and underground engineering rock mass quality index using SPSS software, thus establishing a calculation model for rock drillability index FBI and underground engineering rock mass quality index [BQ].

[0116] FBI = 7.226exp(0.0054×[BQ]) Formula 9

[0117] In Formula 9, FBI is the rock drillability index, and [BQ] is the rock mass quality index for underground engineering.

[0118] The coefficient of determination R of the above-mentioned rock drillability index FBI and underground engineering rock mass quality index [BQ] calculation model. 2 It is 0.914.

[0119] The relationship between the rock drillability index (FBI) and the rock mass quality index (BQ) for underground engineering is shown in [reference needed]. Figure 8 As shown.

[0120] Step S6: Establish a classification standard for the drillability of Jurassic strata.

[0121] Based on the calculation model of rock drillability index FBI and underground engineering rock mass quality index [BQ], the rock drillability classification standard of sandy mudstone in Jurassic strata is obtained.

[0122] The rock drillability classification criteria for sandy mudstone in the Jurassic strata are shown in Table 5:

[0123] Table 5. Rock drillability classification standards for sandy mudstones in Jurassic strata.

[0124]

[0125]

[0126] Based on Table 5, it can be seen that the smaller the underground engineering rock mass quality index [BQ] of the sandy mudstone of the Jurassic strata, the smaller the rock drillability index FBI, and the higher the drillability of the sandy mudstone of the Jurassic strata; the larger the underground engineering rock mass quality index [BQ] of the sandy mudstone of the Jurassic strata, the larger the rock drillability index FBI, and the lower the drillability of the sandy mudstone of the Jurassic strata.

[0127] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0128] (1) This method uses the penetration load-penetration curve obtained by rolling cutter penetration test on rock samples from Cretaceous and Jurassic strata to determine the rock drillability index, providing an evaluation index for rock drillability research. The evaluation index has clear significance and the calculation method is simple.

[0129] (2) This method uses a single-factor regression analysis to evaluate the rock drillability index based on numerous factors affecting rock drillability, and evaluates the rock drillability index based on the uniaxial compressive strength (UCS) and rock mass integrity coefficient (K). V The prediction of rock drillability index takes into account a relatively comprehensive range of influencing factors, which can be obtained from geological exploration data and laboratory tests, making the method of obtaining the data simple.

[0130] (3) This method is a rock drillability classification method based on the underground engineering rock mass quality index [BQ]. It does not require large equipment, has simple steps, scientific calculation methods, and reliable evaluation results. It is of great significance for optimizing drilling parameters and reducing drilling costs in Cretaceous and Jurassic formations.

[0131] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for classifying rock drillability, used to evaluate the drillability of Cretaceous and Jurassic strata, characterized in that, Includes the following steps: Step S1: Conduct a cutter penetration test and calculate the rock drillability index; Step S2: Establish a single-factor calculation model for the rock drillability index and various influencing factors of rock drillability; Step S3: Perform pairwise correlation analysis on the various factors affecting rock drillability to identify key influencing factors; Step S4: Establish a predictive model for the rock drillability index based on key influencing factors; Step S5: Establish a calculation model for the rock drillability index and the rock mass quality index of underground engineering. Step S6: Establish rock drillability classification standards for Cretaceous and Jurassic strata.

2. The rock drillability classification method according to claim 1, characterized in that, In step S1, rock samples are collected from the Cretaceous and Jurassic strata at depths of 10m to 50m from top to bottom. The confining pressure of the cutter penetration test is the same as the in-situ stress of the strata where the rock sample is located. The ratio of the cutter teeth in the cutter penetration test to the cutter teeth of the well drilling cutter is 1:

1. The penetration load-penetration curve of the rock sample is obtained through the cutter penetration test.

3. The rock drillability classification method according to claim 2, characterized in that, The longitudinal dimension of the rock sample is greater than or equal to 5 times the longitudinal dimension of the cutter in the cutter penetration test.

4. The rock drillability classification method according to claim 2, characterized in that, The loading rate of the roller cutter penetration test is 0.005 mm / s or 0.001 mm / s. Loading is stopped and unloaded when the displacement reaches 15 mm or the rock sample is completely destroyed.

5. The rock drillability classification method according to claim 2, characterized in that, In step S1, the calculation model for the rock drillability index of the rock sample is as follows: In Formula 1: FBI is the rock drillability index. ; The penetration load, in kN, is the force at which the rock sample undergoes its first precession failure. The cutter penetration depth, in mm, is the depth of the cutter when the rock sample experiences its first leap failure.

6. The rock drillability classification method according to claim 1, characterized in that, In step S2, the factors affecting rock drillability include the uniaxial compressive strength (UCS) of the rock and the rock mass integrity coefficient. Rock hardness Rock brittleness index and rock abrasiveness CAI; The uniaxial compressive strength (UCS) of the rock can be obtained by indoor testing or by calculating the point load strength of the rock. The rock mass integrity coefficient It can be obtained from engineering geological surveys or calculated from the rock quality index RQD; rock hardness It is either the Smithsonian indentation hardness or the Vickers indentation hardness; The rock brittleness index The calculation formula is: In Formula 2, The uniaxial compressive strength of the rock, in MPa. The tensile strength of the rock is given in MPa. The rock abrasiveness CAI was measured using a rock abrasiveness servo instrument to perform a rock abrasiveness test.

7. The rock drillability classification method according to claim 1, characterized in that, In step S2, the single-factor calculation model for the rock drillability index and each influencing factor of rock drillability is as follows: In Formula 3, FBI is the rock drillability index. It is a factor affecting rock drillability. These are the coefficients of the calculation model. These are the regression coefficients corresponding to the factors affecting rock drillability.

8. The rock drillability classification method according to claim 6, characterized in that, The rock drillability index (FBI) was analyzed in relation to the uniaxial compressive strength (UCS) and the rock mass integrity coefficient using a single-factor calculation model of various influencing factors of rock drillability. The rock hardness The rock brittleness index The correlation between the rock abrasiveness (CAI) and the rock abrasiveness (CAI).

9. The rock drillability classification method according to claim 1, characterized in that, In step S3, pairwise correlation analysis is performed on each factor affecting rock drillability. The pairwise correlation analysis eliminates possible collinear relationships between the factors affecting rock drillability. The key factors affecting the rock drillability index FBI are determined by combining the magnitude of the coefficient of determination of each factor affecting rock drillability with the rock drillability index FBI. Correlation analysis among various factors affecting rock drillability is performed using MATLAB, SPSS, or ORIGIN software. This correlation analysis is achieved by establishing linear or nonlinear regression equations among these factors.

10. The rock drillability classification method according to claim 4, characterized in that, In step S4, the prediction model for the rock drillability index based on key influencing factors is as follows: In Formula 4, FBI is the rock drillability index. These are the coefficients of the prediction model. It is a key influencing factor. It is the partial regression coefficient of the key influencing factors. It is the constant term in the predictive model index.

11. The rock drillability classification method according to claim 1, characterized in that, In step S5, the calculation model for the rock drillability index and the quality index of underground engineering rock mass is as follows: In Formula 5, FBI is the rock drillability index. These are the coefficients of the calculation model; [BQ] is the rock mass quality index for underground engineering. It is the regression coefficient of the rock mass quality index [BQ] for underground engineering.

12. The rock drillability classification method according to claim 11, characterized in that, In step S6, based on the calculation model of the rock drillability index FBI and the underground engineering rock mass quality index [BQ], the rock drillability classification standards for Cretaceous and Jurassic strata are obtained. Based on the rock drillability classification standard of Cretaceous and Jurassic strata according to the underground engineering rock mass quality index [BQ], the smaller the value of the underground engineering rock mass quality index [BQ], the smaller the rock drillability index FBI, and the higher the rock drillability; the larger the value of the underground engineering rock mass quality index [BQ], the larger the rock drillability index FBI, and the lower the rock drillability.

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