Micro-seismic monitoring method for hard rock roadway advanced hydraulic fracture expansion range

Abstract

The invention provides a micro-seismic monitoring method for an advanced hydraulic fracture expansion range of a hard rock roadway, and belongs to the technical field of comprehensive mechanized tunneling of hard rock roadways. The technical problem of misalignment of detector layout in a traditional monitoring scheme is solved. According to the technical scheme, the method comprises the steps of S1, determining physical and mechanical parameters of a to-be-tunneled rock S2, an active seismic source calibration test is carried out, and micro-seismic signals are collected; s3, establishing a hard rock roadway stress wave amplitude attenuation model; s4, determining an attenuation distance; s5, determining the drilling depth; s6, designing a hard rock roadway advanced hydraulic fracture micro-seismic monitoring detector arrangement scheme; and S7, realizing accurate monitoring of the position and the scale of the constructed three-dimensional total space. The method has the beneficial effects that the hydraulic fracturing microseismic signal attenuation distance of the hard rock mass to be excavated in the hard rock roadway is determined by combining the rock mass mechanical parameters, the hydraulic fracturing energy and the initial amplitude conversion coefficient of the microseismic signal.

Description

Technical Field

[0001] The present invention relates to the technical field of comprehensive mechanized excavation of hard rock tunnels, and in particular to a microseismic monitoring method for an advanced hydraulic fracture expansion range in a hard rock tunnel. Background Art

[0002] The total annual mileage of coal mine tunnels in my country has exceeded 13,000 km, of which coal tunnels account for approximately 80% and rock tunnels for approximately 20%. In coal tunneling operations, because the uniaxial compressive strength of the coal mass is generally below 20 MPa, tunneling equipment has low cutting resistance, allowing construction efficiency to be maintained at a high level of 8 to 15 m / day. In stark contrast, in rock tunneling operations, particularly in hard rock formations with uniaxial compressive strength exceeding 60 MPa, conventional tunneling equipment faces technical challenges such as insufficient cutting power and severe tool wear, particularly due to geological characteristics such as high rock integrity coefficient (RQD>75%) and strong inter-particle bonding. This results in a sharp drop in construction efficiency to 3 to 5 m / day.

[0003] To address the technical need for improving the efficiency of hard rock tunneling, the use of hydraulic fracturing technology has been proposed to pre-treat the rock mass to be excavated, transforming its structural properties and optimizing its hard rock cutting performance. Precisely characterizing the spatial expansion morphology of hydraulic fractures, which increases the speed of hard rock tunneling, provides a decision-making basis for real-time control of the hydraulic fracture expansion trajectory. This is a key technical prerequisite for achieving hydraulic fracturing to improve the efficiency of hard rock tunneling.

[0004] Currently, downhole hydraulic fracturing monitoring primarily relies on a grid-like arrangement of geophones within boreholes, a common practice in the oil and gas industry. However, due to the rapid energy attenuation and short propagation distance of hydraulic fracturing microseismic signals, the geophone placement in traditional monitoring schemes is irrational, leading to missed detection of hydraulic fracture microseismic signals and wasted monitoring resources. Based on this, a microseismic monitoring method for advanced hydraulic fracture expansion in hard rock tunnels based on active source calibration is proposed, enabling precise sensing of the hydraulic fracture expansion range in hard rock tunnels. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems in the background technology and provide a microseismic monitoring method for the expansion range of advanced hydraulic fractures in hard rock tunnels.

[0006] The technical idea of ​​the present invention is: by conducting active source calibration tests, the wave field attenuation characteristics of elastic waves in hard rock tunnel formations are studied, the quantitative attenuation relationship between the amplitude of microseismic stress waves and the propagation distance is established, the stress distribution characteristics of the rock mass to be excavated are analyzed, and the reasonable monitoring distance of the microseismic signal of hydraulic fracturing of the microseismic detector is obtained by combining the hydraulic fracturing construction parameters, the mechanical parameters of the hard rock mass to be excavated and the energy loss coefficient, and the optimal spatial configuration scheme of the detector array is determined to solve the problem of inaccurate detector layout in the traditional monitoring scheme caused by the fast energy attenuation and short propagation distance of the microseismic signal during the hydraulic pre-fracture of the hard rock mass to be excavated, so as to realize accurate perception of the expansion range of hydraulic fractures in hard rock tunnels.

[0007] In order to achieve the above-mentioned object of the invention, the present invention adopts a technical solution specifically comprising: a microseismic monitoring method for the extension range of advanced hydraulic fractures in hard rock tunnels, comprising the following steps:

[0008] S1. Use field investigation, borehole observation, and laboratory testing to understand the original rock stress conditions at the hard rock tunnel excavation working face and determine the physical and mechanical parameters of the rock mass to be excavated.

[0009] S2. Select an area in the hard rock tunnel to be excavated, conduct an active source calibration test, and rationally distribute detectors in the monitoring area to synchronously collect microseismic signals;

[0010] S3. By fitting the calibration shot experimental data, a stress wave amplitude attenuation model for hard rock tunnels is established, and the conversion coefficient between calibration shot energy and initial amplitude is calculated;

[0011] S4. determining the attenuation distance of the hydraulic fracturing microseismic signal of the microseismic geophone;

[0012] S5. Determine the drilling depth for hydraulic fracturing of the rock mass to be excavated in the hard rock roadway;

[0013] S6. Design a layout plan for microseismic monitoring of hydraulic fractures in hard rock tunnels, with the number of geophones being z, where z ≥ 2.

[0014] S7, extracting stress longitudinal wave signals from the hydraulic fracture microseismic signals of z three-component geophones in the head section of the hard rock tunnel and the receiving hole, and calculating the propagation distance of the longitudinal wave in the surrounding rock;

[0015] Take z detectors as the center of the circle, s1, s2...s z Make z spheres with a radius of , and the intersection of the z spheres is the microseismic source point of the hydraulic fracture in the hard rock mass to be excavated. By analyzing the reflected signals received by the detector, accurate monitoring of the three-dimensional spatial position and scale of the structure can be achieved.

[0016] Furthermore, the specific contents of step S2 are as follows:

[0017] S2.1. Arrange geophones in the middle of the tunnel side, with the distance between each geophone and the blasting point increasing in sequence. Connect the geophones, microseismic signal acquisition instrument, and computer in sequence, and start the microseismic monitoring software to conduct a test acquisition to verify that the signal acquisition system is operating normally.

[0018] S2.2. On the basis of ensuring the safety of the blasting process, calculate the explosion energy. The calculation formula is as follows:

[0019] E b =Q·e (1)

[0020] Among them, E b is the explosion energy, Q is the charge mass, and e is the specific energy of the explosive;

[0021] S2.3. Calculate the propagation velocity v of the longitudinal stress wave in the rock mass based on the arrival time and distance of the longitudinal stress wave. p .

[0022] Furthermore, the specific contents of step S3 are as follows:

[0023] S3.1. Export the calibration shot microseismic waveform signal collected by each geophone from the microseismic acquisition software. Analyze the waveform data recorded by each sensor, use the peak value of the waveform signal as the amplitude, and establish an amplitude attenuation mathematical model:

[0024]

[0025] Among them, A is the microseismic amplitude, x is the distance between the detector and the earthquake source, γ is the attenuation coefficient, and A b is the initial amplitude of the fitted calibration gun;

[0026] S3.2. Fit the calibration experimental data and solve the square of the initial amplitude and attenuation coefficient γ, a mathematical model of stress wave amplitude attenuation in the rock mass of a hard rock tunnel to be excavated is established;

[0027] S3.3. Calculate the conversion coefficient n between the calibration gun energy and the initial amplitude. The calculation formula is as follows:

[0028] n=E b / A b (3)

[0029] Among them, E b is the explosion energy, A b is the initial amplitude of the fitted calibration gun.

[0030] Furthermore, the specific contents of step S4 are as follows:

[0031] S4.1. Determine the maximum injection pressure and injection flow rate through rock mechanics parameters and stress field analysis;

[0032] S4.11. The hydraulic fracturing injection flow rate is directly determined by the performance of the high-pressure water pump. The initial fracture initiation pressure is accurately calculated through rock mechanics parameters and stress field analysis. This initiation pressure serves as the core parameter to guide the selection of high-pressure pump units. The maximum injection pressure must exceed the theoretical initiation pressure:

[0033] P c =min{(3-λ)q0+R t , (3λ-1)q0+R t} (4)

[0034] P max =P c (5)

[0035] Among them, P c is the crack initiation pressure; q0 is the plumb bob stress; λ is the lateral stress coefficient; R t is the tensile strength of rock mass, P max is the maximum water injection pressure;

[0036] S4.12. Select a high-pressure pump with a rated pressure based on the cracking pressure, and determine the rated flow rate of the selected high-pressure pump;

[0037] S4.2. Calculate the hydraulic fracturing energy Ehy of the rock mass to be excavated in the hard rock tunnel using the following formula:

[0038] Ehy=α·q·Pmax(6)

[0039] Wherein, α is the energy loss coefficient, q is the hydraulic fracturing injection flow rate;

[0040] S4.3. Calculate the initial amplitude A of the hydraulic fracturing microseismic vibration according to formulas (3) and (6). hy , the calculation formula is as follows:

[0041]

[0042] Among them, E hy Hydraulic fracturing fracture energy, initial amplitude conversion coefficient n;

[0043] S4.4. Calculate the hydraulic fracturing microseismic signal attenuation distance L based on the microseismic signal attenuation law during hydraulic fracturing. hy , the calculation formula is as follows:

[0044]

[0045] Among them, L hy is the attenuation distance of hydraulic fracturing microseismic signals, A b is the initial amplitude of the calibration gun to be fitted, A hy Initial amplitude of hydraulic fracturing microseismic events.

[0046] Furthermore, the specific content of step S5 is:

[0047] S5.1. After the excavation working face is affected by mining, three characteristic zones will form in the rock mass in front of it: from near to far, the pressure relief zone, the concentrated stress zone, and the original rock stress zone;

[0048] S5.2. Determination of hydraulic fracturing scope: The fracturing construction points shall be arranged at a depth exceeding the pressure relief zone;

[0049] S5.3. The drilling depth L can be obtained by the limit equilibrium theory. K :

[0050]

[0051] Among them, N f is the rock stress concentration coefficient, f is the rock layer friction coefficient, m is the roadway height, d is the average density of the overlying rock layer, H is the burial depth, K is the stress concentration coefficient, N g N is the ratio coefficient between drilling depth and limit equilibrium zone width, g The value range is between 1.6 and 1.8.

[0052] Furthermore, step S6 includes the following steps:

[0053] S6.1 Select z = 6 and install two three-component geophones, numbered T1 and T2, at the tunneling head section. The geophone positions change with the tunneling head section.

[0054] S6.2. Arrange receiving holes symmetrically on both sides of the tunnel roof, drilling at a distance of 0.2 to 0.8 m from the tunnel wall, with an elevation angle of 20 to 60° along the borehole axis and a designed depth of 10 to 50 m. Hydraulically install two sets of three-component geophones, 5.0 to 30 m apart, starting 1 m from the bottom of the hole. Number them: T3, T4, T5, and T6.

[0055] S6.3, with the four geophones in the double receiving hole and the two geophones in the head section as the center of the sphere, construct the monitoring radius L hy Spherical space model, l1~l6 are the intersection lines between the corresponding numbered detector sphere and the rock mass, and the length of the rock mass to be excavated, L, is covered by them. w , represents the effective monitoring range of the layout scheme for hydraulic fracture microseismic signals;

[0056] S6.4, take an integer d, when d·L K <L w <(d+1)·L KAfter the hard rock to be excavated is cracked by hydraulic fracturing in d fracturing holes, the receiving holes are rearranged symmetrically on both sides of the tunnel roof.

[0057] Furthermore, the specific content of step S7 is:

[0058] The stress longitudinal wave signal is extracted from the hydraulic fracture microseismic signals of six three-component geophones in the head section and receiving hole of the hard rock tunnel. The travel time t of the reflected longitudinal wave received by the geophone is used to extract the stress longitudinal wave signal. p1 , t p2 , t p3 , t p4 , t p5 , t p6 and the surrounding rock longitudinal wave propagation velocity v p Calculate the distance s of the surrounding rock longitudinal wave propagation i =t pi ·v p ;

[0059] Six spheres are made with the six geophones as the center and s1, s2, s3, s4, s5 and s6 as the radius. The intersection of the six spheres is the microseismic source point of the hydraulic fracture in the hard rock mass to be excavated. By analyzing the reflected signals received by the geophones, accurate monitoring of the three-dimensional spatial position and scale of the structure can be achieved.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] 1. The present invention provides a method for converting energy and initial amplitude of microseismic signals. Through active source calibration experiments, a theoretical model of rock stress wave amplitude attenuation is established. Combining waveform data analysis and mathematical fitting, the method achieves quantitative characterization of the propagation law of microseismic signals in the rock mass to be excavated in hard rock tunnels.

[0062] 2. The present invention provides a method for determining the reasonable monitoring distance of hydraulic fracturing microseismic signals, which combines the rock mechanical parameters, hydraulic fracturing fracture energy and the initial amplitude conversion coefficient of the microseismic signal to determine the attenuation distance of hydraulic fracturing microseismic signals in hard rock tunnels.

[0063] 3. The present invention provides a solution for the arrangement of microseismic detectors for monitoring hydraulic fractures in advance in hard rock tunnels. This solution solves the problem of inaccurate arrangement of detectors in traditional monitoring solutions caused by the rapid energy attenuation and short propagation distance of microseismic signals during the hydraulic pre-fracture process of hard rock masses to be excavated, thereby achieving accurate perception of the expansion range of hydraulic fractures in hard rock tunnels.

[0064] 4. The present invention discloses a microseismic monitoring method for the expansion range of hydraulic fractures in hard rock tunnels. By conducting active source calibration tests, the wave field attenuation characteristics of elastic waves in hard rock tunnel formations are studied, and the attenuation quantitative relationship between the amplitude of microseismic stress waves and the propagation distance is established. The stress distribution characteristics of the rock mass to be excavated are analyzed, and combined with the hydraulic fracturing construction parameters, the mechanical parameters of the hard rock mass to be excavated and the energy loss coefficient, the reasonable monitoring distance of the microseismic signal of the hydraulic fracturing detector is obtained, and the optimal spatial configuration scheme of the detector array is determined. The method solves the problem of inaccurate detector layout in traditional monitoring schemes caused by the rapid energy attenuation and short propagation distance of microseismic signals in the hydraulic pre-fracture process of the hard rock mass to be excavated, and realizes the accurate perception of the expansion range of hydraulic fractures in hard rock tunnels. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0066] Figure 1 Schematic diagram of the active source calibration test.

[0067] Figure 2 Schematic diagram of hydraulic fracturing drilling depth and fracturing points.

[0068] Figure 3 Schematic diagram of the effective monitoring range of the designed scheme for hydraulic fracture microseismic signals.

[0069] Figure 4 Schematic diagram of precise positioning of microseismic signals. DETAILED DESCRIPTION

[0070] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. Of course, the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0071] In an embodiment, the present invention provides a microseismic monitoring method for the extension range of advanced hydraulic fractures in hard rock tunnels, the specific contents of which are as follows:

[0072] (1) Using methods such as field investigation, borehole observation, and laboratory testing, the original rock stress conditions of the hard rock tunnel excavation working face are understood and the physical and mechanical parameters of the rock mass to be excavated are determined.

[0073] (2) First, select an area in the hard rock tunnel to be excavated that does not affect normal production work and conduct an active source calibration test, such as Figure 1 , and reasonably distribute the detection devices in the monitoring area to synchronously collect microseismic signals.

[0074] A detector is arranged in the middle of the tunnel wall, and the distance between each detector and the blasting point increases successively. After the detector, microseismic signal acquisition instrument and computer are connected in sequence, the microseismic monitoring software is started to conduct trial acquisition to verify that the signal acquisition system is operating normally.

[0075] On the basis of ensuring the safety of the blasting process, the explosion energy is calculated by the charge amount. The calculation formula is as follows:

[0076] E b =Q·e (1)

[0077] Among them, E b is the explosion energy, MJ; Q is the charge mass, kg; e is the specific energy of the explosive, MJ / kg.

[0078] According to the on-site measurement, the charge amount is 1.0 kg, the stress wave specific energy of the explosive is 0.54 MJ / kg, and E b =1×0.54=0.54MJ.

[0079] Calculate the propagation velocity v of the stress wave in the rock mass based on the arrival time and distance of the stress wave p ; According to the on-site measured arrival time and distance, we can know through calculation that v p =3852m / s.

[0080] (3) By fitting the calibration shot experimental data, a stress wave amplitude attenuation model for hard rock tunnels was established, and the conversion coefficient n between the calibration shot energy and the initial amplitude was calculated.

[0081] The calibration shot microseismic waveform signal collected by each detector is exported from the microseismic acquisition software. The waveform data recorded by each sensor is analyzed. The peak value of the waveform signal is used as the amplitude, and an amplitude attenuation mathematical model is established.

[0082]

[0083] Among them, A is the microseismic amplitude, x is the distance between the detector and the earthquake source, γ is the attenuation coefficient, and A b is the initial amplitude of the fitted calibration gun;

[0084] According to the experimental data of the amplitude of microseismic waveform signal of each geophone and the distance from the earthquake source, γ and A are calculated by formula (2). b Perform fitting calibration to obtain the initial amplitude A b =810mv and attenuation coefficient γ = 25.67, a mathematical model of stress wave amplitude attenuation in the hard rock tunnel to be excavated is established.

[0085] And the conversion coefficient n between the calibration gun energy and the initial amplitude is calculated according to formula (3):

[0086] n=Eb / A b (3)

[0087] Calculate the conversion coefficient n=E between the calibration gun energy and the initial amplitude b / A b =0.54 / 810=0.6e -4 .

[0088] (4) Reasonable monitoring distance L of microseismic geophone hydraulic fracturing microseismic signal hy Sure:

[0089] During the expansion of hydraulic fractures, the energy of microseismic events generated by the fracture of hard rock is relatively low. When the stress waves excited by these microseismic activities propagate in the rock medium, their amplitude will be significantly attenuated due to geometric diffusion, medium absorption and scattering. Therefore, in order to accurately monitor the expansion range of hydraulic fractures, it is necessary to determine the attenuation distance L of the microseismic signal of hydraulic fracturing in the hard rock mass to be excavated in the hard rock tunnel. hy .

[0090] ① Determine the maximum injection pressure and injection flow rate through rock mechanics parameters and stress field analysis;

[0091] The hydraulic fracturing water injection rate is directly determined by the performance of the high-pressure water pump. In the hydraulic fracturing operation of hard rock, the equipment selection must follow the "demand-oriented" technical logic. The initial crack initiation pressure is accurately calculated through rock mechanical parameters and stress field analysis. This critical value will serve as the core parameter to guide the selection of high-pressure pump units. The maximum water injection pressure must cover the theoretical initiation pressure.

[0092] P c =min{(3-λ)q0+R t ,(3λ-1)q0+R t} (4)

[0093] P max =P c (5)

[0094] Among them, P c is the crack initiation pressure; q0 is the plumb bob stress; λ is the lateral stress coefficient; R t is the tensile strength of rock mass; P max is the maximum water injection pressure;

[0095] According to the field measurements, the plumb bob stress q0 = 12.5 MPa; the lateral stress coefficient λ = 1.2; the rock mass tensile strength R t =404Mpa, so from formula (4) we can get:

[0096] P c=min{(3-1.2)·12.5+4.4, (3·1.2-1)·12.5+4.4}=2639Mpa;

[0097] The fracturing pressure is determined to be 26.9 MPa, so a high-pressure pump with a rated fracturing pressure of 40 MPa can be selected. The rated flow rate of the selected high-pressure pump is determined to be q = 6 m 3 / h.

[0098] ②Calculate the hydraulic fracturing energy E of the rock mass to be excavated in the hard rock tunnel hy

[0099] E hy =α·q·P max (6)

[0100] Among them, α is the energy loss coefficient, which is 0.8; q is the hydraulic fracturing injection velocity, m 3 / h;

[0101] From formula (6), we can get the hydraulic fracturing energy E hy =0.8×26.9e6×6=0.129MJ.

[0102] ③ According to formulas (3) and (6), calculate the initial amplitude A of the hydraulic fracturing microseismic vibration hy :

[0103]

[0104] Determine the initial amplitude A of hydraulic fracturing microseismic vibration hy =0.129 / 0.6e -4 =193.7mv.

[0105] ④ Based on the attenuation law of microseismic signals during hydraulic fracturing, the hydraulic fracturing microseismic signal attenuation distance L is determined by the following steps: hy :

[0106]

[0107] Determine the hydraulic fracturing microseismic attenuation distance L hy =25.67×ln(810 2 / 193.7 2 )=73.5m.

[0108] (5) Hydraulic fracture drilling depth L of the rock mass to be excavated in the hard rock tunnel K Sure:

[0109] After the excavation working face is affected by mining, three characteristic areas will be formed in the rock mass in front of it: from near to far, the pressure relief zone, the concentrated stress zone and the original rock stress zone;

[0110] Hydraulic fracturing range determination: the pressure relief zone produces a large number of fractures due to stress release, if hydraulic fracturing is implemented in this area, high-pressure water is easy to leak to the working face through the existing fractures, so the fracturing construction point should be arranged at a position beyond the depth of the pressure relief zone; the stress concentration zone can effectively constrain the expansion direction of the fractures formed by hydraulic fracturing, so that the fracture network develops more orderly and penetrates the rock mass to be excavated, thereby realizing the weakening of the rock mass structure and improving the pre-fracturing effect, so this area is the best action range of hydraulic fracturing.

[0111] The drilling depth L can be obtained by the limit equilibrium theory K :

[0112]

[0113] Wherein, N f is the stress concentration coefficient of the rock stratum; f is the stratified friction coefficient of the rock stratum; m is the height of the roadway, unit m; d is the average density of the overburden rock stratum, unit kg / m 3 ; H is the buried depth, unit m; K is the stress concentration coefficient; N g is the ratio coefficient of the drilling depth and the width of the limit equilibrium zone, the value range is between 1.6 and 1.8;

[0114] According to the field measurement, the stratified friction coefficient of the rock stratum is 0.15, the height of the roadway is 4.3 m, the stress concentration coefficient is 3.5, the average density of the overburden rock stratum is 3000 kg / m 3 , the buried depth is 540 m, and the tensile strength of the rock is 4.4 Mpa. According to the width of the limit equilibrium zone and the coefficient N g (the value range is between 1.2 and 1.8), the value of N g is 1.7, for example Figure 2 , the drilling depth of the hydraulic fracture cracking of the rock mass to be excavated in the hard rock roadway can be obtained as follows:

[0115]

[0116] (6) According to the previous field measurement data, the reasonable monitoring distance L hy is usually greater than the drilling length L K , and the arrangement scheme of the advanced hydraulic fracture microseismic monitoring detector in the hard rock roadway is designed as follows:

[0117] ① Two three-component detectors (numbered: T1, T2) are installed at the heading section of the roadway, and the detector position changes with the heading section of the roadway.

[0118] ② Receiver holes were symmetrically arranged on both sides of the tunnel roof, 0.5 m from the tunnel wall, with the drilling axis elevation angle of 45°. The designed receiving hole depth was 16 m (to avoid the impact zone of the hydraulic fracturing crack and minimize environmental noise interference). Two groups of three-component geophones were hydraulically installed starting from 1 m from the bottom of the hole, with a group spacing of 5.0 m (numbered as T3, T4, T5, T6).

[0119] ③ With the four geophones in the double receiving hole and the two geophones in the head section as the sphere center, construct the monitoring radius L hy The spherical space model (l1~l6 are the intersection lines between the corresponding numbered detector sphere and the rock mass), and the length of the rock mass to be excavated, L, is covered by them. w , represents the effective monitoring range of the layout scheme for hydraulic fracture microseismic signals;

[0120] ④ Take an integer d, when d·L K <L w <(d+1)·L K After the hard rock to be excavated is cracked by hydraulic fracturing in d fracturing holes, the receiving holes are rearranged symmetrically on both sides of the tunnel roof.

[0121] (7) Extract stress longitudinal wave signals from the hydraulic fracture microseismic signals of the six three-component geophones in the head section and receiving hole of the hard rock tunnel. According to the travel time t of the reflected longitudinal wave received by the geophone, p1 , t p2 , t p3 , t p4 , t p5 , t p6 and the surrounding rock longitudinal wave propagation velocity v p Calculate the distance s of the surrounding rock longitudinal wave propagation i =t pi ·v p ;

[0122] With the six geophones as the center and s1, s2, s3, s4, s5, and s6 as the radius, six spheres are made. The intersection of the six spheres is the microseismic source point of the hydraulic fracture in the hard rock mass to be excavated. By analyzing the reflected signals received by the geophones, the precise monitoring of the three-dimensional spatial position and scale of the structure is achieved. Figure 4 shown.

[0123] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A microseismic monitoring method for the extension range of advanced hydraulic fractures in hard rock tunnels, characterized in that: The steps include: S1. Use field investigation, borehole observation, and laboratory testing to understand the original rock stress conditions at the hard rock tunnel excavation working face and determine the physical and mechanical parameters of the rock mass to be excavated. S2. Select an area in the hard rock tunnel to be excavated, conduct an active source calibration test, and rationally distribute detectors in the monitoring area to synchronously collect microseismic signals; S3. By fitting the calibration shot experimental data, a stress wave amplitude attenuation model for hard rock tunnels is established, and the conversion coefficient between calibration shot energy and initial amplitude is calculated; S4. determining the attenuation distance of the hydraulic fracturing microseismic signal of the microseismic geophone; S5. Determine the drilling depth for hydraulic fracturing of the rock mass to be excavated in the hard rock roadway; S6. Design a layout plan for microseismic monitoring of hydraulic fractures in hard rock tunnels, with the number of geophones being z, where z ≥ 2. S7, extracting stress longitudinal wave signals from the hydraulic fracture microseismic signals of z three-component geophones in the head section of the hard rock tunnel and the receiving hole, and calculating the propagation distance of the longitudinal wave in the surrounding rock; Take z detectors as the center of the circle, s1, s2...s z Make z spheres with a radius of , and the intersection of the z spheres is the microseismic source point of the hydraulic fracture in the hard rock mass to be excavated. By analyzing the reflected signals received by the detector, accurate monitoring of the three-dimensional spatial position and scale of the structure can be achieved.

2. The microseismic monitoring method for the extension range of advanced hydraulic fractures in hard rock tunnels according to claim 1 is characterized in that: The specific contents of step S2 are as follows: S2.

1. Arrange geophones in the middle of the tunnel side, with the distance between each geophone and the blasting point increasing in sequence. Connect the geophones, microseismic signal acquisition instrument, and computer in sequence, and start the microseismic monitoring software to conduct a test acquisition to verify that the signal acquisition system is operating normally. S2.

2. On the basis of ensuring the safety of the blasting process, calculate the explosion energy. The calculation formula is as follows: AND b =Q·e (1) Among them, E b is the explosion energy, Q is the charge mass, and e is the specific energy of the explosive; S2.

3. Calculate the propagation velocity v of the longitudinal stress wave in the rock mass based on the arrival time and distance of the longitudinal stress wave. p .

3. The microseismic monitoring method for the extension range of advanced hydraulic fractures in hard rock tunnels according to claim 1 is characterized in that: The specific contents of step S3 are as follows: S3.

1. Export the calibration shot microseismic waveform signal collected by each geophone from the microseismic acquisition software. Analyze the waveform data recorded by each sensor, use the peak value of the waveform signal as the amplitude, and establish an amplitude attenuation mathematical model: Where A is the microseismic amplitude, x is the distance between the detector and the source, γ is the attenuation coefficient, and Ax is the initial amplitude of the fitted calibration shot; S3.

2. Fit the calibration experimental data and solve the square of the initial amplitude and attenuation coefficient γ, a mathematical model of stress wave amplitude attenuation in the rock mass of a hard rock tunnel to be excavated is established; S3.

3. Calculate the conversion coefficient n between the calibration gun energy and the initial amplitude. The calculation formula is as follows: m=E b / A b (3) Among them, E b is the explosion energy, A b is the initial amplitude of the fitted calibration gun.

4. The microseismic monitoring method for the extension range of advanced hydraulic fractures in hard rock tunnels according to claim 1 is characterized in that: The specific contents of step S4 are as follows: S4.

1. Determine the maximum injection pressure and injection flow rate through rock mechanics parameters and stress field analysis; S4.

11. The hydraulic fracturing injection flow rate is directly determined by the performance of the high-pressure water pump. The initial fracture initiation pressure is accurately calculated through rock mechanics parameters and stress field analysis. This initiation pressure serves as the core parameter to guide the selection of high-pressure pump units. The maximum injection pressure must exceed the theoretical initiation pressure: P c =min{(3-λ)q0+R t ,(3λ-1)q0+R t } (4) P max =P c (5) Among them, P c is the crack initiation pressure; q0 is the plumb bob stress; λ is the lateral stress coefficient; R t is the tensile strength of rock mass, P max is the maximum water injection pressure; S4.

12. Select a high-pressure pump with a rated pressure based on the cracking pressure, and determine the rated flow rate of the selected high-pressure pump; S4.

2. Calculation of hydraulic fracturing energy E for the rock mass to be excavated in a hard rock tunnel hy , the calculation formula is as follows: From hy =α·q·P max (6) Wherein, α is the energy loss coefficient, q is the hydraulic fracturing injection flow rate; S4.

3. Calculate the initial amplitude A of the hydraulic fracturing microseismic vibration according to formulas (3) and (6). hy , the calculation formula is as follows: Among them, E hy Hydraulic fracturing fracture energy, initial amplitude conversion coefficient n; S4.

4. Calculate the hydraulic fracturing microseismic signal attenuation distance L based on the microseismic signal attenuation law during hydraulic fracturing. hy , the calculation formula is as follows: Among them, L hy is the attenuation distance of hydraulic fracturing microseismic signals, A b is the initial amplitude of the calibration gun to be fitted, A hy Initial amplitude of hydraulic fracturing microseismic events.

5. The microseismic monitoring method for the extension range of advanced hydraulic fractures in hard rock tunnels according to claim 1 is characterized in that: The specific contents of step S5 are: S5.

1. After the excavation working face is affected by mining, three characteristic zones will form in the rock mass in front of it: from near to far, the pressure relief zone, the concentrated stress zone, and the original rock stress zone; S5.

2. Determination of hydraulic fracturing scope: The fracturing construction points shall be arranged at a depth exceeding the pressure relief zone; S5.

3. The drilling depth L can be obtained by the limit equilibrium theory. K : Among them, N f is the rock stress concentration coefficient, f is the rock layer friction coefficient, m is the roadway height, d is the average density of the overlying rock layer, H is the burial depth, K is the stress concentration coefficient, N g N is the ratio coefficient between drilling depth and limit equilibrium zone width, g The value range is between 1.6 and 1.

8.

6. The microseismic monitoring method for the extension range of advanced hydraulic fractures in hard rock tunnels according to claim 1, characterized in that: The step S6 comprises the following steps: S6.1 Select z = 6 and install two three-component geophones, numbered T1 and T2, at the tunneling head section. The geophone positions change with the tunneling head section. S6.

2. Arrange receiving holes symmetrically on both sides of the tunnel roof, drilling at a distance of 0.2 to 0.8 m from the tunnel wall, with an elevation angle of 20 to 60° along the borehole axis and a designed depth of 10 to 50 m. Hydraulically install two sets of three-component geophones, 5.0 to 30 m apart, starting 1 m from the bottom of the hole. Number them: T3, T4, T5, and T6. S6.3, with the four geophones in the double receiving hole and the two geophones in the head section as the sphere center, construct the monitoring radius L hy Spherical space model, l1~l6 are the intersection lines between the corresponding numbered detector sphere and the rock mass, and the length of the rock mass to be excavated, L, is covered by them. w , indicating the effective monitoring range of the layout scheme for hydraulic fracture microseismic signals; S6.4, take an integer d, when d·L K <L w <(d+1)·L K After the hard rock to be excavated is cracked by hydraulic fracturing in d fracturing holes, the receiving holes are rearranged symmetrically on both sides of the tunnel roof.

7. The microseismic monitoring method for the extension range of advanced hydraulic fractures in hard rock tunnels according to claim 6, characterized in that: The specific content of step S7 is: The stress longitudinal wave signal is extracted from the hydraulic fracture microseismic signals of six three-component geophones in the head section and receiving hole of the hard rock tunnel. The travel time t of the reflected longitudinal wave received by the geophone is used to extract the stress longitudinal wave signal. p1 , t p2 , t p3 , t p4 , t p5 , t p6 and the surrounding rock longitudinal wave propagation velocity v p Calculate the distance s of the surrounding rock longitudinal wave propagation i =t pi ·v p ; Six spheres are made with the six geophones as the center and s1, s2, s3, s4, s5 and s6 as the radius. The intersection of the six spheres is the microseismic source point of the hydraulic fracture in the hard rock mass to be excavated. By analyzing the reflected signals received by the geophones, accurate monitoring of the three-dimensional spatial position and scale of the structure can be achieved.

Images