Supercritical CO2 phase change rock breaking radius control method

Abstract

The invention discloses a supercritical CO2 phase change rock breaking radius control method, and relates to the technical field of rock breaking, a rock mass crack radius prediction model is established by combining a one-dimensional explosion gas expansion theory, and when a CO2 phase change fracturing method is used for replacing a traditional explosion method, a rock mass crack radius prediction model is established. According to the method, the rock breaking radius in the actual blasting process can be accurately simulated and estimated according to the blasting parameters, so that after the amplification database is established, the appropriate rock breaking parameters can be selected according to the target rock breaking radius, and the rock breaking radius is controlled by selecting the rock breaking parameters. And a technical support is provided for a supercritical CO2 phase change fracturing technology.

Description

Technical Field

[0001] The present invention relates to the field of rock breaking technology, and in particular to a method for controlling the rock breaking radius of supercritical CO2 phase change. Background Art

[0002] Supercritical CO2 phase change fracturing is a physical rock breaking technology that uses high-voltage current to stimulate liquid CO2 to quickly achieve liquid-gas phase change at a certain pressure and temperature, and the volume instantly expands 600 times, thereby generating strong physical pressure to break the rock. It is generally believed that rock fracture is the result of the combined effect of high-pressure shock waves and rapid gas expansion generated after supercritical CO2 phase change. However, due to the uncertainty of the expansion pressure of high-pressure gas, the rock breaking radius generated by this technology cannot be accurately calculated, resulting in the inability to grasp the safe distance when constructing adjacent buildings. Therefore, further experiments are needed to conduct theoretical research.

[0003] There are still three problems in the existing technology for calculating rock breaking radius: first, the current calculation of rock breaking radius mainly considers the rock breaking pressure of the shock wave, and less considers the effect of gas expansion pressure on the expansion of cracks; second, there is a lack of a calculation formula for the crack expansion radius under the action of supercritical CO2 phase change gas expansion pressure; third, there is a lack of in-depth analysis of the influencing parameters of the rock breaking radius of supercritical CO2 phase change gas expansion pressure, and it is impossible to control the rock breaking radius generated by the construction using this technology. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a supercritical CO2 phase change rock breaking radius control method which provides theoretical guidance for CO2 phase change cracking technology during construction.

[0005] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0006] A supercritical CO2 phase change rock breaking radius control method is provided, which comprises the following steps:

[0007] S1: Based on the one-dimensional explosion gas expansion theory, a rock crack radius prediction model is established:

[0008]

[0009] Where Y is the geometric correction factor, R2 is the initial crack length, σ cd is the uniaxial dynamic compressive strength of rock, σ td is the uniaxial dynamic tensile strength of rock; R1 is the radius of the initial crushing zone of the rock mass, and p3 is the initial expansion pressure of CO2;

[0010] S2: Conduct supercritical CO2 phase change rock breaking and acoustic wave detection tests, collect rock breaking radius and corresponding blasting parameters to obtain a data set, and use the data set to train the rock crack radius prediction model;

[0011] S3: amplify the data set to obtain an amplified data set;

[0012] S4: searching in the augmented data set according to the target rock breaking radius to obtain several blasting parameter groups; calculating the costs corresponding to the several blasting parameter groups, and taking the blasting parameter group with the lowest cost as the optimal blasting parameter group.

[0013] Furthermore, step S3 is specifically as follows:

[0014] A11: Perform regression analysis on the blasting parameters and the rock breaking radius to obtain the regression model of each blasting parameter and the rock breaking radius;

[0015] A12: Based on the Bayesian model averaging method, the regression models obtained in step A11 are fused to obtain a fused regression equation;

[0016] A13: Determine the value range of each blasting parameter, evenly select values ​​within the value range, and obtain several parameter combinations;

[0017] A14: Several parameter combinations are introduced into the fusion regression model to obtain the corresponding rock breaking radius, which is then integrated to obtain an augmented database.

[0018] Furthermore, step S4 also includes verification of the blasting data group, and the blasting parameter group with the lowest cost is input into the rock crack radius prediction model to obtain the predicted rock breaking radius. When the difference between the predicted rock breaking radius and the target rock breaking radius is greater than 5%, the blasting parameter group is discarded, and among the several blasting parameter groups retrieved, the blasting parameter group with the closest cost to the discarded one is further verified until the difference between the predicted rock breaking radius and the target rock breaking radius is less than or equal to 5%, and the corresponding blasting parameter group is output as the optimal blasting parameter group.

[0019] Furthermore, the blasting parameters include the initial expansion pressure of CO2, the initial crack length and the uniaxial dynamic compressive strength of the rock.

[0020] The beneficial effects of the present invention are:

[0021] The present invention establishes a rock crack radius prediction model by combining the one-dimensional explosion gas expansion theory. When CO2 phase change fracturing is used to replace the traditional blasting method, the rock breaking radius in the actual blasting process can be accurately simulated and estimated according to the blasting parameters. Therefore, after the establishment of the amplified database, the appropriate rock breaking parameters can be selected according to the target rock breaking radius. By selecting the rock breaking parameters, the rock breaking radius can be controlled. This provides technical support for supercritical CO2 phase change fracturing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a comparison of the acoustic wave velocity of rocks before and after supercritical CO2 phase change fracturing;

[0023] Figure 2 It is a line graph of the rock wave velocity change rate before and after supercritical CO2 phase change fracturing;

[0024] Figure 3 Schematic diagram of rock damage range after supercritical CO2 phase transformation cracking. DETAILED DESCRIPTION

[0025] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0026] A supercritical CO2 phase change rock breaking radius control method, comprising the following steps:

[0027] S1: Based on the one-dimensional explosion gas expansion theory, a rock crack radius prediction model is established:

[0028]

[0029] Where Y is the geometric correction factor, R2 is the initial crack length, σ cd is the uniaxial dynamic compressive strength of rock, σ td is the uniaxial dynamic tensile strength of rock; R1 is the radius of the initial crushing zone of the rock mass, and p3 is the initial expansion pressure of CO2;

[0030] The derivation principle of the rock crack radius prediction model is as follows:

[0031] S1.1. Calculate the initial peak pressure after supercritical CO2 phase change using the punching shear failure formula;

[0032]

[0033] Where: P0 is the pressure when the energy dissipation plate is destroyed, MPa; d0 is the thickness of the energy dissipation plate, mm; D is the clamping diameter of the energy dissipation plate, mm; σ s It is the shear strength of the material, generally 0.6 to 0.7 times the tensile strength, MPa.

[0034] S1.2. Considering the incident stress amplification effect on the wall of the fracture-causing hole, calculate the incident stress on the hole wall in the case of coupled buried fracture-causing pipe;

[0035]

[0036] Where, P2 is the hole wall pressure, MPa; d g and d t are the diameters of the fracture tube and fracture hole respectively, and n is the pressure increase multiple. In this embodiment, n is 6.

[0037] S1.3. Calculate the radius of the initial crushing zone and the initial crack length of the rock mass produced by the supercritical CO2 phase change shock wave according to the Mises criterion;

[0038]

[0039] Where R is the radius of the crack hole, m; σ cd and σ td are the uniaxial dynamic compressive strength and uniaxial dynamic tensile strength of rock, MPa; shock wave attenuation coefficient α=2+μ d / (1+μ d ); coefficient b = μ d / (1+μ d ); μ d is the dynamic Poisson's ratio.

[0040] S1.4. Introduce the one-dimensional explosive gas expansion theory to describe the high-pressure gas expansion pressure generated by supercritical CO2 phase change. The relationship between pressure and time is:

[0041]

[0042] Where: t is time; z is the distance that the CO2 high-pressure gas moves along the axial direction of the fracture hole, that is, the depth of the fracture hole; C0 is the flow rate of the high-pressure gas, m / s; that is:

[0043]

[0044] Where: ρ0 is the initial density of high pressure gas, kg / m 3 .

[0045] Combining equations (3) and (6) yields the flow rate and time when the high-pressure CO2 gas fills the crack-causing pores and the initial cracks. Substituting them into equation (5) yields the initial expansion pressure p3 of the high-pressure gas.

[0046] S1.5. Assuming that the gas does not leak after filling the cracks and decays to the original rock stress at the edge of the cracks, the pressure decay law of CO2 high-pressure gas in the cracks is described on this basis:

[0047] p(r)=p3exp(-κ(r-R1))(7);

[0048] Where: κ is the attenuation coefficient of gas pressure, which can be expressed as:

[0049] κ=(lnp3-lnσ td ) / (R2-R1)(8);

[0050] S1.6. Taking the stress intensity factor at the crack tip equal to the rock fracture toughness as the boundary condition, solve the rock breaking radius under the combined action of supercritical CO2 phase change shock wave and high-pressure gas:

[0051] As the pressure of CO2 high-pressure gas continues to decay, under the combined effect of gas expansion pressure and ground stress, the stress intensity factor at the crack tip also changes, and its change pattern with distance is:

[0052]

[0053] Where: Y is the geometric correction factor;

[0054] According to linear elastic fracture mechanics, when the stress intensity factor K at the fracture point is I The leading edge is equal to or greater than the corresponding rock fracture toughness K IC , the crack will extend radially at this point, so the extension condition is as follows:

[0055]

[0056] Based on the above conditions, the calculation formula for the rock crack radius under the combined action of supercritical CO2 phase change induced shock wave and high-pressure gas under coupled stress conditions, that is, the rock crack radius prediction model, can be obtained as follows:

[0057]

[0058] S2: Conduct supercritical CO2 phase change rock breaking and acoustic wave detection tests, collect rock breaking radius and corresponding blasting parameters to obtain a data set, and use the data set to train the rock crack radius prediction model;

[0059] When implementing it, the following steps are taken:

[0060] S2.1. According to the test plan, a rock drill is used to drill holes in the rock formation to obtain a fracturing hole with a hole diameter of 0.09 m and a hole depth of 5 m and an acoustic wave test hole with a hole diameter of 0.09 m and a hole depth of 6 m; four acoustic wave test holes are set, which are 0.5 m, 1.5 m, 2.5 m and 3.5 m away from the fracturing hole respectively, and the four test holes are named hole 1, hole 2, hole 3 and hole 4 in sequence;

[0061] S2.2. Use an ohmmeter to check the circuit connectivity of each fracture-causing pipe. If the circuit connectivity is good, perform hole burying operation. At the same time, use stone powder or sand to fill the gap between the fracture-causing pipe and the fracture hole to prevent the pipe from flying;

[0062] S2.3, use QL-PZ03 type filling machine to transport the liquid CO2 stored in QL-PZ06 type liquid storage tank to the fracturing tube buried in the fracturing hole through the filling hose, so that each fracturing tube is filled with liquid CO2;

[0063] S2.4. Before starting fracturing, clean water is injected into each sonic test hole as a coupling agent, and then the sonic data of the rock mass before the test is recorded using an RSM-SY5 sonic tester and a "one-transmit, two-receive" probe.

[0064] S2.5. After all inspections are completed, detonation is completed. After ensuring that all personnel have safely evacuated, rotate the detonator switch to perform CO2 phase change cracking. After cracking, repeat the sonic wave test operation and record the wave velocity changes.

[0065] S2.6. Analyze the changes in the acoustic wave velocity signal before and after rock breaking, and use the wave velocity change rate and the critical value of the damage variable to analyze the rock breaking range.

[0066] The results are as follows Figure 1-3 As shown, Figure 1 The comparison diagram of rock acoustic wave velocity before and after supercritical CO2 phase change fracturing; Figure 1 It can be seen that the wave velocity of the rock mass before and after fracturing fluctuates nonlinearly, and in each test hole, the wave velocity after fracturing is less than the wave velocity before fracturing. This is because cracks are generated in the rock mass after blasting, the elastic modulus decreases, and the propagation speed of the sound wave decreases accordingly. In the vertical direction, the wave velocity after fracturing gradually approaches the wave velocity before fracturing with the increase of hole depth, and eventually there is a trend of overlap, indicating that the rate of change of wave velocity decreases with the increase of hole depth, and the degree of damage to the rock mass is also reduced accordingly. In the horizontal direction, with the increase of the distance of the acoustic wave test hole, the wave velocity before and after fracturing is attenuated. Further processing of the acoustic wave velocity before and after rock damage detection can obtain the wave velocity change rate, which is expressed as follows:

[0067]

[0068] D=1-(1-η) 2 (13);

[0069] Where η is the wave velocity change rate, %; c0 and c are the acoustic wave test velocities before and after rock fracturing, km / s. D is the damage variable. The "SL47-2020 Technical Specifications for Excavation and Construction of Rock Foundations for Hydraulic Structures" proposes that the wave velocity change rate η = 10% is the critical value of rock damage, and the corresponding damage variable D = 0.19.

[0070] Figure 2 This is a curve of rock velocity changes before and after supercritical CO2 phase change fracturing. Figure 2It can be seen that with the increase of the depth of the test hole, the velocity change rate shows a nearly linear decreasing trend. In addition, with the increase of the hole spacing, the depth corresponding to the maximum velocity change rate of each test hole gradually decreases, and the depth of the minimum velocity change rate gradually increases, which indicates that while the rock fracture radius increases, the fracture depth is constantly decreasing. When the fracture radius reaches the maximum value, the fracture depth will become zero.

[0071] Figure 3 Schematic diagram of rock mass damage range before and after supercritical CO2 fracturing. Figure 3 It can be seen that the damage range in the depth direction and horizontal direction is 5.74 meters and 4.3 meters respectively. The final damage range of the rock mass is defined by the critical damage arc of D = 0.19, the ground and the straight line where the fracture tube is located, and it appears as a flat funnel shape in three-dimensional space, which is similar to the rock breaking effect of traditional explosive blasting.

[0072] The rock crack radius prediction model is trained based on the database obtained in the above manner. In this embodiment, the geometric correction factor Y=1.12;

[0073] S3: Amplify the data set to obtain an amplified data set; specifically:

[0074] A11: Perform regression analysis on the blasting parameters and the rock breaking radius to obtain the regression model of each blasting parameter and the rock breaking radius; the blasting parameters include the initial expansion pressure of CO2, the initial crack length and the uniaxial dynamic compressive strength of the rock.

[0075] A12: Based on the Bayesian model averaging method, the regression models obtained in step A11 are fused to obtain a fused regression equation;

[0076] A13: Determine the value range of each blasting parameter, evenly select values ​​within the value range, and obtain several parameter combinations;

[0077] A14: Several parameter combinations are introduced into the fusion regression model to obtain the corresponding rock breaking radius, which is then integrated to obtain an augmented database.

[0078] S4: searching in the augmented data set according to the target rock breaking radius to obtain several blasting parameter groups; calculating the costs corresponding to the several blasting parameter groups, and taking the blasting parameter group with the lowest cost as the optimal blasting parameter group.

[0079] Step S4 also includes verification of the blasting data group, inputting the blasting parameter group with the lowest cost into the rock crack radius prediction model to obtain the predicted rock breaking radius, and when the difference between the predicted rock breaking radius and the target rock breaking radius is greater than 5%, the blasting parameter group is discarded, and among the several blasting parameter groups retrieved, the blasting parameter group with the closest cost to the discarded one is further verified until the difference between the predicted rock breaking radius and the target rock breaking radius is less than or equal to 5%, and the corresponding blasting parameter group is output as the optimal blasting parameter group.

Claims

1. A supercritical CO2 phase change rock breaking radius control method, characterized in that: The steps include: S1: Based on the one-dimensional explosion gas expansion theory, a rock crack radius prediction model is established: Where Y is the geometric correction factor, R2 is the initial crack length, σ cd is the uniaxial dynamic compressive strength of rock, σ td is the uniaxial dynamic tensile strength of rock; R1 is the radius of the initial crushing zone of the rock mass, and p3 is the initial expansion pressure of CO2; S2: Conduct supercritical CO2 phase change rock breaking and acoustic wave detection tests, collect rock breaking radius and corresponding blasting parameters to obtain a data set, and use the data set to train the rock crack radius prediction model; S3: amplify the data set to obtain an amplified data set; S4: searching in the augmented data set according to the target rock breaking radius to obtain several blasting parameter groups; calculating the costs corresponding to the several blasting parameter groups, and taking the blasting parameter group with the lowest cost as the optimal blasting parameter group.

2. The supercritical CO2 phase change rock breaking radius control method according to claim 1 is characterized in that: The step S3 is specifically as follows: A11: Perform regression analysis on the blasting parameters and the rock breaking radius to obtain the regression model of each blasting parameter and the rock breaking radius; A12: Based on the Bayesian model averaging method, the regression models obtained in step A11 are fused to obtain a fused regression equation; A13: Determine the value range of each blasting parameter, evenly select values ​​within the value range, and obtain several parameter combinations; A14: Several parameter combinations are introduced into the fusion regression model to obtain the corresponding rock breaking radius, which is then integrated to obtain an augmented database.

3. The supercritical CO2 phase change rock breaking radius control method according to claim 1 is characterized in that: The step S4 also includes verification of the blasting data group, inputting the blasting parameter group with the lowest cost into the rock crack radius prediction model to obtain the predicted rock breaking radius, and when the difference between the predicted rock breaking radius and the target rock breaking radius is greater than 5%, the blasting parameter group is discarded, and among the several blasting parameter groups retrieved, the blasting parameter group with the closest cost to the discarded one is further verified until the difference between the predicted rock breaking radius and the target rock breaking radius is less than or equal to 5%, and the corresponding blasting parameter group is output as the optimal blasting parameter group.

4. The supercritical CO2 phase change rock breaking radius control method according to any one of claims 1 to 3, characterized in that: The blasting parameters include the initial expansion pressure of CO2, the initial crack length and the uniaxial dynamic compressive strength of the rock.

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