A method for characterizing the uniaxial compressive strength of rock while drilling

Abstract

The present invention belongs to the technical field of surrounding rock mechanical parameter measurement, and provides a method for characterizing the uniaxial compressive strength of rock while drilling. The method takes into account the inherent variation relationship between the parameters while drilling, and uses the index K which is only related to the UCS of the rock and is not affected by the change of drilling conditions. F‑D , characterize the UCS of rock, and then establish a rock uniaxial compressive strength while drilling characterization model that is less affected by working conditions, which solves the problem that the existing model is greatly affected by changes in drilling conditions to a certain extent. This model only needs to use three parameters: thrust, drilling speed, and rotation speed to predict the uniaxial compressive strength of rock; the constant coefficients a, b, and c in this model are only related to the drill bit. Therefore, the rock uniaxial compressive strength model obtained by calibrating the drill bit used in the engineering site through indoor tests can be used to guide the engineering site conveniently and quickly.

Description

Technical Field

[0001] The invention belongs to the technical field of surrounding rock mechanical parameter measurement and relates to a method for characterizing the uniaxial compressive strength of rock while drilling. Background Art

[0002] Drilling and blasting is an important part of mining production activities. Good blasting effect plays an important role in optimizing mining energy consumption and mining efficiency. Good blasting effect depends on the blasting design that matches the uniaxial compressive strength (UCS) of the rock. Traditional rock UCS measurement methods, such as coring, have limitations such as long measurement cycle and high cost, so only a small number of tests are carried out in specific areas. However, due to the spatial variability of rock mechanical properties, the coring method is difficult to accurately characterize the rock UCS within a specific spatial range, and new rock UCS measurement methods still need to be further developed.

[0003] As a pre-process for blasting, support and other projects, drilling is characterized by a large number of holes and close spacing. The application of measurement while drilling (MWD) technology can capture the thrust, torque, rotation speed, drilling speed and other drilling parameters during the drilling process. These drilling parameters are closely related to the mechanical properties of rocks. By establishing the relationship between the drilling parameters and the rock UCS, the real-time characterization of the rock UCS during the drilling process can be achieved. This method makes up for the limitations of traditional UCS measurement methods, such as long test cycles, small test quantities, and the inability to continuously measure along the drilling direction, and provides a new method for the fine characterization of the mechanical properties of rock masses.In order to use drilling parameters to characterize the UCS of rock, many researchers have proposed various rock strength models. For example, based on the energy balance principle, mechanical specific energy was proposed to characterize the uniaxial compressive strength of rock (TEALE R. The concept of specific energy in rock drilling [J]. International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1965, 2 (1): 57-73); based on the limit cutting balance, considering the friction between the drill bit and the rock, the unit volume cutting energy was derived to evaluate the uniaxial compressive strength of rock (WANG Q, GAO H, YU H, et al. Method for measuring rock mass characteristics and evaluating the grouting-reinforced effect based on digital drilling [J]. Rock Mechanics and Rock Engineering, 2019, 52 (3): 841-851); based on data analysis and dimensional balance principles, a new drillability index was proposed, and a rock uniaxial compressive strength model was established (KARASAWA H, OHNO T, KOSUGI M, et al. Methods to estimate the rock strength and tooth wear while drilling with roller-bits-Part 1: Milled-tooth bits[J].Journal of Energy Resources Technology,Transactions of the ASME,2002,124(3):125-132;YU B,ZHANG K,NIU G.Rock strength determination based on rock drillability index and drilling specific energy:numerical simulation using discrete element method[J].IEEE Access,2021,9:43923-43937).

[0004] However, it should be pointed out that the variables in the model, namely the drilling parameters, are not only related to the rock strength, but also to the drilling conditions. For example, when drilling the same rock, changing the thrust of the drill rig will cause the torque and drilling speed to change, which may cause the UCS calculated by the strength model to change significantly with the change of thrust, but UCS as an objective property of rock should not change. The reason for this problem may be that these models mainly focus on the relationship between the strength model and the rock UCS, ignoring the impact of changes in the drilling rig conditions on the strength model, which will lead to a large difference between the rock UCS calculated by the model and the true value of UCS under certain drilling conditions. Considering the changing relationship characteristics between the drilling parameters, establishing a quantitative relationship between this relationship characteristic and the rock UCS, and then proposing a new rock UCS characterization model may be one of the effective ways to solve this limitation of previous models. Summary of the invention

[0005] The present invention provides a method for characterizing the uniaxial compressive strength of rock while drilling. The method takes into account the inherent change relationship between the parameters while drilling, uses an indicator that is only related to the UCS of the rock and is not affected by changes in drilling conditions to characterize the UCS of the rock, and further establishes a method for characterizing the uniaxial compressive strength of rock while drilling that is less affected by the working conditions.

[0006] The technical solution of the present invention is a method for characterizing the uniaxial compressive strength of rock while drilling. The UCS model of the uniaxial compressive strength of rock is:

[0007] Where F is the thrust of the drill in the stable drilling stage, D is the penetration rate per revolution of the drill; a, b, and c are all constants related only to the performance of the drill bit.

[0008] Furthermore, the calculation formula for the penetration per revolution is: Where v is the drilling speed and N is the rotation speed.

[0009] Furthermore, the method for obtaining the constant a is as follows:

[0010] Step 1: Use the same drill bit to perform drilling tests on different types of rocks under different thrust settings to obtain the thrust and penetration data per revolution of the drilling rig at the stable drilling stage under the corresponding thrust settings;

[0011] Step 2: Using the thrust F obtained in step 1 as the ordinate and the penetration per revolution D as the abscissa, plot the drilling data of different types of rocks and perform linear fitting F=f+K F-D D, get the slope K of the fitting line for different types of rocks F-D and intercept f;

[0012] Step 3: Establish the slope K of the straight line F-DAnd the straight line fitting relationship of intercept f: f = aK F-D , obtain the constant a according to the fitting result.

[0013] Furthermore, the constants b and c are obtained as follows:

[0014] Establish the slope K of the fitting straight line between the uniaxial compressive strength of different types of rocks and the corresponding types of rocks F-D The exponential fitting relationship: UCS = bexp (cK F-D ), and obtain the constants b and c according to the fitting results.

[0015] Furthermore, there are no less than 3 types of rocks.

[0016] Further preferably, the different types of rocks include yellow sandstone, red sandstone, green sandstone, white sandstone, black sandstone, Shidao red granite, sesame white granite, sesame gray granite, yellow rust stone granite, and basalt.

[0017] Furthermore, drilling tests were conducted more than twice for each type of rock at different thrust settings.

[0018] The beneficial effects of the present invention are as follows: a method for characterizing the uniaxial compressive strength of rock while drilling is provided, which takes into account the inherent variation relationship between the parameters while drilling, and uses an index K which is only related to the UCS of the rock and is not affected by the change of drilling conditions. F-D , characterize the UCS of rock, and then establish a rock uniaxial compressive strength while drilling characterization model that is less affected by working conditions, which solves the problem that the existing model is greatly affected by changes in drilling conditions to a certain extent. This model only needs to use three parameters: thrust, drilling speed, and rotation speed to predict the uniaxial compressive strength of rock; the constant coefficients a, b, and c in this model are only related to the drill bit. Therefore, the rock uniaxial compressive strength model obtained by calibrating the drill bit used in the engineering site through indoor tests can be used to guide the engineering site conveniently and quickly. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is the relationship between rock thrust and penetration per revolution.

[0020] Figure 2 is the intercept f and the slope K F-D relationship.

[0021] Figure 3 is the rock uniaxial compressive strength UCS and slope K F-D relationship.

[0022] Figure 4Comparison between the predicted values ​​of rock strength models and the values ​​obtained from uniaxial compression tests: (a) Teale model; (b) Karasawa model; (c) Zhang model; (d) Wang model; (e) this model. DETAILED DESCRIPTION

[0023] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] Example

[0025] Through indoor rock mechanics tests, the uniaxial compressive strength (UCS) of yellow sandstone, red sandstone, green sandstone, white sandstone, black sandstone, Shidao red granite, sesame white granite, sesame gray granite, yellow rust stone granite and basalt were obtained.

[0026] This embodiment provides a method for characterizing the uniaxial compressive strength of rock while drilling, which is specifically implemented according to the following steps:

[0027] Step 1: Conduct a series of drilling tests under different thrust settings on the above different types of rocks to obtain the thrust, drilling speed and rotation speed data of the drilling rig in the stable drilling stage under the corresponding thrust settings; then use formula (1) to calculate the penetration per revolution:

[0028]

[0029] Where v is the drilling speed and N is the rotation speed.

[0030] Step 2: With thrust F as the ordinate and penetration per revolution D as the abscissa, plot the drilling data of each rock, and perform linear fitting according to formula (2) to obtain the slope K of the fitting line for different types of rocks. F-D and intercept f, the result is Figure 1 As shown;

[0031] F=f+K F-D D (2)

[0032] In the formula, F is the thrust, D is the penetration per revolution, K is F-D is the slope and f is the intercept.

[0033] Step 3: Substitute the intercept f and slope K in equation (2) F-D According to formula (3), the empirical fitting results are as follows: Figure 2 shown.

[0034] f=aK F-D (3)

[0035] In the formula, for the same drill bit, the coefficient a is a constant, from Figure 2 It can be seen that a is 0.54.

[0036] Step 4: Substitute f from equation (3) into equation (2) to obtain K expressed in terms of thrust and penetration per revolution: F-D :

[0037]

[0038] Step 5: Establish the relationship between rock uniaxial compressive strength and K F-D The relationship between thrust and penetration per revolution is used to obtain an empirical model of rock uniaxial compressive strength, thus realizing the while-drilling characterization of rock uniaxial compressive strength.

[0039] The uniaxial compressive strength of rock and the slope K F-D According to the functional relationship of formula (5), the fitting results are as follows: Figure 3 shown.

[0040] UCS=bexp(cK F-D ) (5)

[0041] Where UCS is the uniaxial compressive strength of rock. For the same drill bit, coefficients b and c are constants. Figure 3 It can be seen that b is 21.4253 and c is 0.18464.

[0042] The K in formula (4) F-D Substituting into formula (5), we can obtain the empirical model of rock uniaxial compressive strength expressed by thrust and penetration per revolution corresponding to the drill bit, as shown in the following formula:

[0043]

[0044] In order to verify the accuracy and reliability of the model, the Teale model (TEALE R. The concept of specific energy in rock drilling [J]. International Journal of Rock Mechanics and MiningSciences&Geomechanics Abstracts, 1965, 2(1): 57-73.) and the Wang model (WANG Q, GAO H, YU H, et al. Method for measuring rock mass characteristics and evaluating the grouting-reinforced effect based on digital drilling[J]. Rock Mechanics and Rock Engineering, 2019, 52(3):841-851.), Karasawa model (KARASAWA H, OHNO T, KOSUGIM, et al. Methods to estimate the rock strength and tooth wear while drilling with roller-bits-Part 1: Milled-tooth bits[J]. Journal of Energy Resources Technology, Transactions of the ASME,2002,124(3):125-132.), Zhang model (YU B, ZHANG K, NIU G. Rock strength determination based on rock drillability index and drilling specific energy: numerical simulation using discrete element method [J]. IEEE Access, 2021, 9: 43923-43937.) for comparison, such as Figure 4 As shown in the figure, the horizontal axis is the UCS uniaxial compression test value, the same horizontal axis represents the same type of rock, and the vertical axis is the UCS predicted value calculated using the strength model. Figure 4 ad) results show that the UCS prediction results (ordinate) of the same rock (same abscissa) under different drilling conditions are quite different, and this model ( Figure 4e) The predicted UCS values ​​under different drilling conditions are close and the differences are small, indicating that it has stronger adaptability to changes in drilling conditions. Figure 4 It can be seen that the fitting curve of this model is closer to the 1:1 line and has the highest determination coefficient, which means that the UCS prediction value is closer to the experimental value. In order to quantitatively evaluate the accuracy of the model, the mean absolute error and coefficient of variation of the prediction results were further compared. The calculation formulas of the mean absolute error and coefficient of variation are shown in formula (7) and formula (8):

[0045]

[0046]

[0047] In the formula, MAE is the mean absolute error, Cv is the coefficient of variation, is the average value of rock UCS prediction, f(x) is the rock UCS prediction, y is the rock UCS uniaxial compression test value, i is the drilling test number, and n is the total number of drilling tests.

[0048] MAE represents the average error between the predicted UCS value and the experimental value, reflecting the accuracy of the model. The MAE between the predicted UCS value and the experimental value of each rock under different drilling conditions is shown in Table 1. The results show that the average MAE of the existing models Teale model, Wang model, Karasawa model, and Zhang model for ten types of rocks are 32.34, 32.82, 57.05, and 48.52 MPa, respectively, and the average MAE of this model is 19.80 MPa.

[0049] Cv reflects the impact of drilling conditions on the UCS model, as shown in Table 2, but Cv cannot reflect the accuracy of the UCS prediction value. The combined MAE and Cv values ​​can better analyze the UCS prediction results. A comprehensive comparison of Tables 1 and 2 shows that the average Cv value (0.08) of the Karasawa model is the smallest, but the average MAE value is the largest, indicating that the predicted UCS is less affected by the drilling conditions, but the error with the true UCS is large. The average Cv value of the Wang model and the Teale model is the largest (0.22), but the average MAE value is small, indicating that the model is greatly affected by the drilling conditions, but the error with the true UCS is small. The average Cv value (0.16) and average MAE value of the Zhang model are in the middle of these comparison models, indicating that the model has moderate accuracy in predicting rock UCS and is moderately affected by drilling conditions. The average MAE and Cv (0.09) of this model are both at a low level, indicating that even if the drilling conditions change, the uniaxial compressive strength of the rock can still be predicted more accurately.

[0050] Table 1 Comparison of the average absolute error between the predicted and experimental values ​​of the uniaxial compressive strength of rocks with different strength models. Unit: MPa

[0051]

[0052]

[0053] Table 2 Comparison of coefficient of variation between predicted and experimental values ​​of uniaxial compressive strength of rocks with different strength models.

[0054]

Claims

1. A method for characterizing the uniaxial compressive strength of rock while drilling, characterized in that: The UCS model of uniaxial compressive strength of rock is: Where, F is the thrust of the drill in the stable drilling stage, D is the penetration per revolution of the drill; a, b, and c are all constants related only to the performance of the drill bit; The method for obtaining the constant a is as follows: Step 1: Use the same drill bit to perform drilling tests on different types of rocks under different thrust settings to obtain the thrust and penetration data per revolution of the drilling rig at the stable drilling stage under the corresponding thrust settings; Step 2: Using the thrust F obtained in step 1 as the ordinate and the penetration per revolution D as the abscissa, plot the drilling data of different types of rocks and perform linear fitting F=f+K F-D D, get the slope K of the fitting line for different types of rocks F-D and intercept f; Step 3: Establish the slope K of the straight line F-D And the straight line fitting relationship of intercept f: f = aK F-D , obtain the constant a according to the fitting result; The method for obtaining the constants b and c is as follows: Establish the uniaxial compressive strength of different types of rocks and the slope K of the fitting line of the corresponding type of rock F-D The exponential fitting relationship: UCS = bexp (cK F-D ), obtaining the constants b and c according to the fitting results; The calculation formula for the penetration per revolution is: Where v is the drilling speed and N is the rotation speed.

2. The method for characterizing the uniaxial compressive strength of rock while drilling according to claim 1, characterized in that: There are no less than 3 types of rocks mentioned.

3. The method for characterizing the uniaxial compressive strength of rock while drilling according to claim 1, characterized in that: The different types of rocks include yellow sandstone, red sandstone, green sandstone, white sandstone, black sandstone, Shidao red granite, sesame white granite, sesame gray granite, yellow rust stone granite and basalt.

4. The method for characterizing the uniaxial compressive strength of rock while drilling according to claim 1, characterized in that: For each type of rock, drilling tests were carried out more than twice under different thrust settings.

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