Methods and apparatus for characterizing the spatial distribution characteristics of non-uniform geostress fields at multiple scales

Abstract

This invention discloses a method and apparatus for characterizing the spatial distribution characteristics of non-uniformity of multi-scale geostress fields, comprising: acquiring stress occurrence states at different crustal depths; acquiring deformation characteristics at different crustal depths; calculating crustal stress field distribution characteristics using measured stress states, inverted stress states, and deformation characteristics at different crustal depths as constraints; and obtaining the correlation and non-uniformity characterization of deep and shallow crustal stresses based on the direction, magnitude, stress structure, and deformation characteristics in the crustal stress field distribution characteristics. Using the technical solution of this invention, it is possible to comprehensively evaluate geostress occurrence characteristics, stress field non-uniformity distribution characteristics, and the coupling between deep and shallow crustal stress fields.

Description

Technical Field

[0001] This invention belongs to the field of geomechanics technology, and in particular relates to a method and apparatus for characterizing the non-uniform spatial distribution characteristics of multi-scale geostress fields. Background Technology

[0002] Crustal stress is closely related to tectonic activities such as crustal deformation, faulting, and earthquakes, as well as associated geological hazards. Revealing the current state of crustal stress and its mechanisms is crucial for addressing major engineering geological issues such as fault instability and slippage, regional crustal stability, and the stability of surrounding rock during the planning and construction of major engineering projects. For a long time, obtaining reliable current crustal stress data has been a pressing issue in various fields of Earth science. Different needs and conditions have led to different methods for obtaining in-situ stress data, including core and borehole-based in-situ stress observations and methods based on geological structures and geophysical inversion. With Earth system science becoming the guiding principle of Earth science research, the coupling relationship between deep and surface processes has received increasing attention. Under the interaction of tectonic movements and in-situ stress, apart from the large-scale stress field continuity controlled by plate tectonics, the spatial heterogeneity of in-situ stress distribution is a widespread phenomenon. Stress direction and stress values ​​exhibit significantly different local characteristics. Therefore, revealing the distribution characteristics and occurrence state of the in-situ stress field at different scales is extremely important. However, the acquisition of crustal stress characteristics currently mainly relies on single-method constraints, or on in-situ testing methods such as hydraulic fracturing, borehole collapse, and stress relief, or on source mechanism solutions and numerical simulations to invert tectonic stress fields. There is a lack of comprehensive evaluation methods for coupling and feedback processes at different depths. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a method and apparatus for characterizing the non-uniform spatial distribution characteristics of multi-scale geostress fields.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for characterizing the non-uniform spatial distribution of multi-scale geostress fields, comprising:

[0006] Step S1: Obtain the stress occurrence state at different crustal depths;

[0007] Step S2: Obtain deformation characteristics at different crustal depths;

[0008] Step S3: Using the measured stress state, inverted stress state and deformation characteristics at different crustal depths as constraints, establish a finite element model of the target area and calculate the stress field distribution to obtain the crustal stress field distribution characteristics;

[0009] Step S4: Based on the stress field direction, stress field magnitude, stress structure, and deep and shallow crustal deformation characteristics in the crustal stress field distribution characteristics, obtain the correlation and non-uniformity characterization of deep and shallow crustal stress.

[0010] Preferably, in step S1, the stress state at different depths of the upper crust is obtained by in-situ stress measurement method and test method based on borehole and core, and the stress state at the focal depth is obtained by focal mechanism solution inversion method.

[0011] As a preferred option, in step S2, surface deformation observation and seismic anisotropy research methods are used to obtain deformation characteristics at different crustal depths.

[0012] Preferably, in step S4, the stress field direction is characterized by the direction of the maximum horizontal principal stress; the stress field magnitude is characterized by the principal stress value, lateral pressure coefficient, stress accumulation parameter and relative stress magnitude; the stress structure type is determined based on the Anderson fault type and stress relationship; the deep and shallow crustal deformation characteristics are characterized by the direction of the maximum horizontal tensile strain rate - minimum horizontal principal stress - anisotropic fast wave.

[0013] The present invention also provides a device for characterizing the spatial distribution characteristics of non-uniformity of multi-scale geostress fields, comprising:

[0014] The first acquisition module is used to acquire the stress occurrence state at different crustal depths;

[0015] The second acquisition module is used to acquire deformation characteristics at different crustal depths;

[0016] The calculation module is used to establish a finite element model of the target area and calculate the stress field distribution by using measured stress state, inverted stress state and deformation characteristics at different crustal depths as constraints, and to obtain the crustal stress field distribution characteristics.

[0017] The processing module is used to obtain the correlation and non-uniformity of crustal stress based on the stress field direction, stress field magnitude, stress structure, and deep and shallow crustal deformation characteristics in the crustal stress field distribution characteristics.

[0018] Preferably, the first acquisition module is used to obtain the measured stress state at different crustal depths using in-situ stress measurement methods and borehole-based testing methods, and to obtain the inverted stress state using the focal mechanism solution inversion method.

[0019] Preferably, the second acquisition module is used to obtain deformation characteristics at different crustal depths by utilizing surface deformation observation and seismic anisotropy testing methods.

[0020] As a preferred approach, the stress field direction is characterized by the direction of the maximum horizontal principal stress; the stress field magnitude is characterized by the principal stress value, lateral pressure coefficient, stress accumulation parameter, and relative stress magnitude; the stress structure type is determined based on the Anderson fault type and stress relationship; and the deformation characteristics of the deep and shallow crust are characterized by the direction of the maximum horizontal tensile strain rate, the minimum horizontal principal stress, and the anisotropic fast wave.

[0021] It can effectively evaluate the crustal stress field through a multi-scale comprehensive analysis combining qualitative, semi-quantitative, and quantitative methods. The lateral scale includes key locations on the site and continuous regional scales, while the vertical scale extends from the shallow crust to the upper and middle crust. It can comprehensively evaluate the characteristics of geostress occurrence, the non-uniform distribution of the stress field, and the coupling between the deep and shallow crustal stress fields. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 A flowchart illustrating the method for characterizing the non-uniform spatial distribution of multi-scale geostress fields. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1:

[0027] like Figure 1 As shown, this invention provides a method for characterizing the spatial distribution characteristics of non-uniform geostress fields at multiple scales, including:

[0028] Step S1: Obtain the stress occurrence state at different crustal depths;

[0029] Step S2: Obtain deformation characteristics at different crustal depths;

[0030] Step S3: Establish a three-dimensional geomechanical model that conforms to the actual geological structure, fault geometry, and wave velocity structure characteristics of the target area. Use Maxwell's volume constitutive relation to describe the viscoelastic behavior of crustal deformation. Use measured stress state, inverted stress state, and deformation characteristics at different crustal depths as constraints to establish a finite element model of the target area and calculate the stress field distribution to obtain the crustal stress field distribution characteristics.

[0031] Step S4: Based on the stress field direction, stress field magnitude, stress structure, and deep and shallow crustal deformation characteristics in the crustal stress field distribution characteristics, obtain the correlation and non-uniformity characterization of deep and shallow crustal stress.

[0032] As one embodiment of the present invention, in step S1, the stress state at different depths of the upper crust is obtained by in-situ stress measurement and other methods, and the stress state at different depths of the crust is obtained by source mechanism solution inversion method.

[0033] Furthermore, in-situ stress measurement methods are used to obtain shallow stress states: for the shallow crustal stress field (generally less than 3km), borehole-based in-situ testing methods (such as hydraulic fracturing) are used to obtain the magnitude and direction of stress at different depths of a single borehole or a group of boreholes, and to quantitatively obtain the stress occurrence state.

[0034] Hydraulic fracturing utilizes a pair of expandable rubber packers to seal a section of borehole at a selected measurement depth. Fluid is then pumped in to pressurize the sealed section until cracks are generated around the borehole wall. The pressure-time curve is recorded simultaneously during fracturing. The fracturing pressure P can be obtained from the measured curve. b The instantaneous closing pressure P of the crack s The pressure P that causes the crack to reopen r Then, the maximum and minimum horizontal principal stresses, vertical stresses, and tensile strength of the rock can be calculated using relevant formulas. If the induced crack is vertical, i.e., parallel to the vertical pressure, the direction of the maximum horizontal stress can be determined based on the direction of the crack obtained from the impression tool.

[0035] σ H =3P s -P r -P o

[0036] T = P b -P r

[0037] σ h =P s

[0038] σ v =γH

[0039] Among them, P oγ is the pore pressure, H is the unit weight of the overlying rock mass of the test section, and H is the thickness of the overlying rock mass of the test section.

[0040] To obtain the stress state of the upper crust using borehole and core-based testing methods: Since current in-situ geostress measurement methods can only obtain data at depths of 3 kilometers, to quantitatively obtain the geostress state of the deep upper crust, it is necessary to use borehole and core-based methods, including borehole collapse / induced tensile fracture method and viscoelastic strain recovery method, to obtain the magnitude and direction of geostress at different depths of a single borehole or a group of boreholes, and to quantitatively obtain the geostress occurrence state.

[0041] Furthermore, the inverted stress state is obtained using focal mechanism solution inversion methods: using natural earthquakes or induced earthquakes, focal mechanism solution inversion methods (such as CAP, HASH, and BABO methods) are used to obtain focal mechanism solution data. Based on the amount of data, the study area is divided into several precise grids (such as 0.5°×0.5°). Using stress field inversion methods (MSATSI and StressInverse methods), the stress tensor and tectonic stress field characteristics within each grid partition at different depths are obtained.

[0042] As one embodiment of the present invention, in step S2, the deformation characteristics of different crustal depths are obtained by using surface deformation observation and seismic anisotropy testing methods.

[0043] Furthermore, using GPS crustal deformation observation data, the multi-scale method based on spherical wavelets proposed by Tape et al. was employed to calculate the continuous strain rate and velocity fields in the shallow crustal layer, obtaining the maximum horizontal tensile strain rate and the maximum horizontal compressive strain rate. First, the sphere was partitioned to generate discretized grid points. Wavelet functions at different scales were constructed using these discrete grid points as the central poles. Then, the observation data was represented as a linear combination of wavelet frames, and the wavelet coefficients were solved using the least squares method or other optimization methods. Finally, multi-scale analysis was performed using the solved wavelet coefficients. By progressively refining or coarsening the scale, distribution characteristics at different spatial resolutions could be extracted. The GPS velocity field on the sphere can be represented as:

[0044]

[0045] in, and The three directions of station velocity—vertical, north-south, and east-west—are represented sequentially, with θ representing latitude and φ representing longitude. Wavelet basis functions are constructed using the non-uniformly distributed GPS velocities on the Earth's surface to describe geophysical phenomena at different spatial scales and the characteristics of different noise sources.

[0046] Seismic waveform data was used to obtain anisotropic characteristics at different depths of the crust, acquiring anisotropic parameters such as fast wave direction and slow wave delay time. Upper crustal anisotropy was calculated using near-field shear wave splitting, selecting waveform records with magnitude less than 4.0, epicentral distance less than 25 km, incident angle less than 45°, and signal-to-noise ratio greater than 5.0. Whole-crustal anisotropy was calculated using Pms wave splitting parameters from receiver functions, selecting waveform records of seismic events with magnitude greater than 5.0, epicentral distances ranging from 30° to 90°, clear phases, and a signal-to-noise ratio greater than 5.0. The P-wave receiver function was extracted using time-domain deconvolution. Stations with clear waveforms and radial receiver functions exhibiting cos²θ variation characteristics were selected for splitting parameter calculation. Optimal splitting parameters were obtained by grid search using the maximum amplitude of the superimposed radial receiver function Pms wave. Reasonable fast wave direction and delay time search step sizes (e.g., 1 degree and 0.02 seconds) were set, with a reference arrival time search range of 5-10 seconds.

[0047] Furthermore, based on the obtained maximum horizontal tensile strain rate and maximum horizontal compressive strain rate, the anisotropic parameters fast wave direction and slow wave delay time, and the crustal tectonic stress field distribution, the deformation characteristics of the crust at different depths are obtained.

[0048] In one embodiment of the present invention, step S3 involves using the finite element method to simulate and calculate the characteristics of crustal stress distribution. Using stress data at different depths, rock mechanics data obtained in the laboratory, and crustal deformation data at different depths as constraints, a finite element model of the target region is established, and the stress field distribution is calculated to obtain the characteristics of continuous stress field distribution.

[0049] In one embodiment of the present invention, in step S4, the stress field direction is characterized by the direction of the maximum horizontal principal stress; the stress field magnitude is characterized by the principal stress value, lateral pressure coefficient, stress accumulation parameter, and relative stress magnitude; the stress structure type is determined based on the Anderson fault type and stress relationship; the deformation characteristics of the deep and shallow crust are characterized by the direction of the maximum horizontal tensile strain rate - minimum horizontal principal stress - anisotropic fast wave. By analyzing the distribution characteristics of stress and deformation fields at different depths, a coherent deformation characteristic of the shallow crust - upper crust - middle and lower crust is established, revealing their coupling and differences.

[0050] Example 2:

[0051] This invention also provides a device for characterizing the spatial distribution characteristics of non-uniformity of multi-scale geostress fields, comprising:

[0052] The first acquisition module is used to acquire the stress occurrence state at different crustal depths;

[0053] The second acquisition module is used to acquire deformation characteristics at different crustal depths;

[0054] The calculation module is used to establish a finite element model of the target area and calculate the stress field distribution by using measured stress state, inverted stress state and deformation characteristics at different crustal depths as constraints, and to obtain the crustal stress field distribution characteristics.

[0055] The processing module is used to obtain the correlation and non-uniformity of crustal stress based on the stress field direction, stress field magnitude, stress structure, and deep and shallow crustal deformation characteristics in the crustal stress field distribution characteristics.

[0056] Preferably, the first acquisition module is used to obtain the measured stress state at different crustal depths using in-situ stress measurement methods and borehole-based testing methods, and to obtain the inverted stress state using the focal mechanism solution inversion method.

[0057] As one embodiment of the present invention, the second acquisition module is used to obtain deformation characteristics at different crustal depths by utilizing surface deformation observation and seismic anisotropy testing methods.

[0058] As one embodiment of the present invention, the stress field direction is characterized by the direction of the maximum horizontal principal stress; the stress field magnitude is characterized by the principal stress value, lateral pressure coefficient, stress accumulation parameter and relative stress magnitude; the stress structure type is determined based on the Anderson fault type and stress relationship; the deep and shallow crustal deformation characteristics are characterized by the direction of the maximum horizontal tensile strain rate - minimum horizontal principal stress - anisotropic fast wave.

[0059] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for characterizing the spatial distribution characteristics of non-uniform geostress fields at multiple scales, characterized in that, include: Step S1: Obtain the stress occurrence state at different crustal depths; Step S2: Obtain deformation characteristics at different crustal depths; Step S3: Using the measured stress state, inverted stress state and deformation characteristics at different crustal depths as constraints, establish a finite element model of the target area and calculate the stress field distribution to obtain the crustal stress field distribution characteristics; Step S4: Based on the stress field direction, stress field magnitude, stress structure, and deep and shallow crustal deformation characteristics in the crustal stress field distribution characteristics, obtain the stress correlation and non-uniformity characterization of deep and shallow crust. In step S1, the stress state at different depths of the upper crust is obtained by in-situ stress measurement method and test method based on borehole and core, and the stress state at the focal depth is obtained by focal mechanism solution inversion method. In step S2, surface deformation observation and seismic anisotropy methods are used to obtain deformation characteristics at different crustal depths; In step S4, the stress direction is characterized by the direction of the maximum horizontal principal stress; the stress value is characterized by the principal stress value, the lateral pressure coefficient, the stress accumulation parameter, and the relative stress magnitude; the type of stress structure is determined based on the Anderson fault type and stress relationship. The characteristics of crustal deformation at both shallow and deep depths are characterized by the horizontal maximum tensile strain rate, the horizontal minimum principal stress, and the anisotropic fast wave direction.

2. A device for characterizing the spatial distribution characteristics of non-uniformity of multi-scale geostress fields, characterized in that, include: The first acquisition module is used to acquire the stress occurrence state at different crustal depths; The second acquisition module is used to acquire deformation characteristics at different crustal depths; The calculation module is used to establish a finite element model of the target area and calculate the stress field distribution by using measured stress state, inverted stress state and deformation characteristics at different crustal depths as constraints, and to obtain the crustal stress field distribution characteristics. The processing module is used to obtain the correlation and non-uniformity of deep and shallow crustal stress based on the stress field direction, stress field magnitude, stress structure, and deep and shallow crustal deformation characteristics in the crustal stress field distribution characteristics. The first acquisition module is used to obtain the stress state at different depths of the upper crust using in-situ stress measurement methods and borehole and core testing methods, and to obtain the stress state at the focal depth using the focal mechanism solution inversion method. The second acquisition module is used to obtain deformation characteristics at different crustal depths by utilizing surface deformation observation and seismic anisotropy methods. The stress direction is characterized by the direction of the maximum horizontal principal stress; the stress value is characterized by the principal stress value, lateral pressure coefficient, stress accumulation parameter, and relative stress magnitude; the type of stress structure is determined based on the Anderson fault type and stress relationship. The characteristics of crustal deformation at both shallow and deep depths are characterized by the horizontal maximum tensile strain rate, the horizontal minimum principal stress, and the anisotropic fast wave direction.

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