Multi-scale crustal stress field non-uniformity spatial distribution characteristic characterization method and device

Abstract

The invention discloses a multi-scale crustal stress field non-uniformity spatial distribution characteristic characterization method and device. The method comprises the following steps: acquiring stress occurrence states of different crustal depths; acquiring deformation characteristics of different earth crust depths; calculating distribution characteristics of a crustal stress field by taking actually measured stress states, inversion stress states and deformation characteristics of different crustal depths as constraints; and according to the direction, magnitude, stress structure and deformation characteristics in the crustal stress field distribution characteristics, obtaining deep and shallow crustal stress correlation and non-uniformity characterization. By adopting the technical scheme provided by the invention, the crustal stress occurrence characteristics, the stress field non-uniformity distribution characteristics and the deep and shallow crustal stress field coupling can be comprehensively evaluated.

Description

Technical Field

[0001] The present invention belongs to the technical field of geomechanics, and particularly relates to a method and device for characterizing the spatial distribution characteristics of the non-uniformity of a multi-scale in-situ stress field. Background Art

[0002] The crustal stress is closely related to tectonic activities such as crustal deformation, faulting, earthquakes, and associated geological disasters. Revealing the current crustal stress state and its action law is of great significance for studying and solving major engineering geological problems such as the unstable sliding of faults, the regional crustal stability, and the surrounding rock stability during the planning and construction of major projects. For a long time, how to obtain a reliable current crustal stress state has been an urgent problem to be solved in various fields of earth science. Different requirements and conditions have given rise to different methods for obtaining in-situ stress, including in-situ stress observation based on cores and boreholes, and geological structure and geophysical inversion methods. With the emergence of earth system science as the guiding ideology for earth science research, the coupling relationship between deep-earth processes and surface processes has received increasing attention. Under the interaction of tectonic movements and in-situ stress, in addition to the continuity of the large-scale stress field controlled by plate movements, the non-uniformity of in-situ stress in spatial distribution is a common phenomenon. Both the stress direction and the stress magnitude show obvious local characteristics. Therefore, it is very important to reveal the distribution characteristics and occurrence states of the in-situ stress field at different scales. However, at present, the acquisition of the occurrence characteristics of crustal stress mainly uses a single method for constraint, either based on in-situ testing methods such as hydraulic fracturing method, borehole breakout method, stress relief method, etc., or based on focal mechanism solution method, numerical simulation method, etc. for tectonic stress field inversion, lacking a comprehensive evaluation method for the coupling and mutual 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 device for characterizing the spatial distribution characteristics of the non-uniformity of a multi-scale in-situ stress field.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for characterizing the spatial distribution characteristics of the non-uniformity of a multi-scale in-situ stress field includes:

[0006] Step S1, obtaining the occurrence states of stresses at different crustal depths;

[0007] Step S2, obtaining the deformation characteristics at different crustal depths;

[0008] Step S3, establishing a finite element model of the target area and calculating the stress field distribution with the measured stress state, inverted stress state, and deformation characteristics at different crustal depths as constraints, and obtaining the distribution characteristics of the crustal stress field;

[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 characterization of the correlation and non-uniformity of deep and shallow crustal stresses.

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

[0011] Preferably, in step S2, the deformation characteristics at different crustal depths are obtained by using surface deformation observation and seismic anisotropy research methods.

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

[0013] The present invention also provides a device for characterizing the non-uniform spatial distribution characteristics of a multi-scale crustal stress field, including:

[0014] A first acquisition module for acquiring the stress occurrence states at different crustal depths;

[0015] A second acquisition module for acquiring the deformation characteristics at different crustal depths;

[0016] A calculation module for establishing a finite element model of the target area and calculating the stress field distribution with the measured stress state, inverted stress state, and deformation characteristics at different crustal depths as constraints, and obtaining the crustal stress field distribution characteristics;

[0017] A processing module for obtaining the characterization of the correlation and non-uniformity of deep and shallow crustal stresses 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 by in-situ stress measurement methods and test methods based on boreholes, and obtain the inverted stress state by focal mechanism solution inversion methods.

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

[0020] Preferably, the stress field direction is characterized by the horizontal maximum principal stress direction; the stress field magnitude 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 judged based on the Anderson fault type and stress relationship; the shallow and deep crustal deformation characteristics are characterized by the horizontal maximum tensile strain rate - horizontal minimum principal stress - anisotropic fast wave direction.

[0021] It can effectively evaluate the multi-scale comprehensive analysis combining qualitative - semi-quantitative - quantitative of the crustal stress field. The horizontal scale includes the key positions of the site and the regional continuous scale, and the vertical scale ranges from the shallow surface layer of the crust to the upper crust and the middle and lower crust, which can comprehensively evaluate the occurrence characteristics of in-situ stress, the non-uniform distribution characteristics of the stress field, and the coupling of shallow and deep crustal stress fields. Brief Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0023] Figure 1 It is a schematic flow chart of the method for characterizing the non-uniform spatial distribution characteristics of the multi-scale crustal stress field. Detailed Embodiments

[0024] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

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

[0026] Embodiment 1:

[0027] As Figure 1 shown, the present invention provides a method for characterizing the non-uniform spatial distribution characteristics of the multi-scale crustal stress field, including:

[0028] Step S1, obtaining the in-situ stress occurrence state at different crustal depths;

[0029] Step S2, obtaining the 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 the constitutive relationship of the Maxwell body to describe the viscoelastic behavior of crustal deformation. With 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 distribution characteristics of the crustal stress field.

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

[0032] As an implementation manner of an embodiment of the present invention, in step S1, the stress state at different depths of the upper crust is obtained by methods such as in-situ stress measurement, and the stress state at different crustal depths is obtained by the focal mechanism solution inversion method.

[0033] Furthermore, the in-situ stress measurement method is used to obtain the shallow stress state: for the crustal shallow surface layer (generally less than 3 km), the in-situ test method based on boreholes (such as the hydraulic fracturing method) is used to obtain the in-situ stress magnitude and direction at different depths of a single borehole or a group of boreholes, and the in-situ stress occurrence state is quantitatively obtained.

[0034] The hydraulic fracturing method uses a pair of expandable rubber packer devices to seal a section of the borehole at the selected measurement depth, and then pumps fluid into the sealed section to pressurize it until cracks are generated around the borehole wall. During the fracturing process, the pressure-time change curve is recorded simultaneously. The fracture pressure P can be obtained from the measured curve. b , the instantaneous closure pressure P of the crack s , the pressure P when the crack reopens r . Then, the maximum and minimum horizontal principal stresses, vertical stress, and rock tensile strength can be calculated according to 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 according to the direction of the crack obtained by the impression packer.

[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 ois the pore pressure, γ is the bulk density of the overlying rock mass in the test section, and H is the thickness of the overlying rock mass in the test section.

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

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

[0042] As an implementation method of the embodiment of the present invention, in step S2, surface deformation observation and seismic anisotropy testing methods are used to obtain deformation characteristics at different crustal depths.

[0043] Furthermore, using GPS crustal deformation observation data, the multi-scale method based on spherical wavelets proposed by Tape et al. is used to calculate the continuous strain rate field and velocity field of the shallow crust, and the horizontal maximum tensile strain rate and the horizontal maximum compressive strain rate are obtained. First, the sphere is divided to generate discretized grid points. The discrete grid points obtained by the division are used as the central poles to construct wavelet functions of different scales. Then the observation data is expressed as a linear combination of the wavelet frame, and the wavelet coefficients are solved by the least squares method or other optimization methods. Finally, the solved wavelet coefficients are used for multi-scale analysis. By gradually refining or coarsening the scale, the distribution characteristics at different spatial resolutions can be extracted. The GPS velocity field on the sphere can be expressed as:

[0044]

[0045] in, and The three directions of vertical, north-south and east-west station speeds are represented in turn, θ is latitude and φ is longitude. The wavelet basis function is constructed using the unevenly distributed GPS speed on the earth's surface to describe the geophysical phenomena of different spatial scales and the characteristics of different noise sources.

[0046] The anisotropic characteristics of different depths of the crust are obtained using seismic waveform data, and the anisotropic parameters, the fast wave direction and the slow wave delay time, are obtained. Among them, the anisotropy of the upper crust is calculated using near-source shear wave splitting. Waveform records with a magnitude less than 4.0, an epicentral distance less than 25 km, an incident angle less than 45°, and a signal-to-noise ratio greater than 5.0 are selected. The anisotropy of the entire crust is calculated using the splitting parameters of the Pms wave of receiver functions. Waveform records of earthquake events with a magnitude greater than 5.0, an epicentral distance range of 30° - 90°, clear seismic phases, and a signal-to-noise ratio greater than 5.0 are selected. The P-wave receiver function is extracted using the time-domain deconvolution method. Stations with clear waveforms and a cos2θ variation characteristic in the radial receiver function are selected for splitting parameter calculation. The optimal splitting parameters are obtained by grid-searching for the maximum superposition amplitude of the Pms in the radial receiver function. Reasonable search steps for the fast wave direction and the delay time are set (such as 1 degree and 0.02 seconds), and the reference arrival time search range is 5 - 10 s.

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

[0048] As an implementation manner of an embodiment of the present invention, in step S3, the finite element method is used to simulate and calculate to obtain the crustal stress distribution characteristics. Constrained by the in-situ stress data at different depths, the rock mechanics data obtained in the laboratory, and the deformation data at different depths of the crust, a finite element model of the target area is established and the stress field distribution is calculated to obtain the continuous stress field distribution characteristics.

[0049] As an implementation manner of an embodiment of the present invention, in step S4, the stress field direction is characterized by the horizontal maximum principal stress direction; the stress field magnitude is characterized by the principal stress value, lateral pressure coefficient, stress accumulation parameter, and relative stress magnitude respectively; the type of stress structure is judged based on the Anderson fault type and stress relationship; the shallow and deep crustal deformation characteristics are characterized by the horizontal maximum tensile strain rate - horizontal minimum principal stress - anisotropic fast wave direction. Through the distribution characteristics of the stress field and deformation field at different depths, the coherent deformation characteristics of the shallow surface layer - upper crust - middle and lower crust of the crust are established, and its coupling and differences are revealed.

[0050] Embodiment 2:

[0051] The embodiment of the present invention also provides a device for characterizing the non-uniform spatial distribution characteristics of a multi-scale in-situ stress field, including:

[0052] The first acquisition module is used to acquire the stress occurrence states at different depths of the crust;

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

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

[0055] A processing module, which is used to obtain the correlation and non-uniformity characterization of the shallow and deep crustal stresses according to the stress field direction, the stress field magnitude, the stress structure, and the shallow and deep crustal deformation characteristics in the distribution characteristics of the crustal stress field.

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

[0057] As an implementation manner of the embodiment of the present invention, the second acquisition module is used to obtain the deformation characteristics at different crustal depths by using surface deformation observation and seismic anisotropy test methods.

[0058] As an implementation manner of the embodiment of the present invention, the stress field direction is characterized by the horizontal maximum principal stress direction; the stress field magnitude is respectively characterized by the principal stress value, the lateral pressure coefficient, the stress accumulation parameter and the relative stress magnitude; the type of the stress structure is judged according to the Anderson fault type and the stress relationship; the shallow and deep crustal deformation characteristics are characterized by the horizontal maximum tensile strain rate - the horizontal minimum principal stress - the fast wave direction of anisotropy.

[0059] The above embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for characterizing the spatial distribution characteristics of the inhomogeneity of multi-scale geostress fields, characterized in that: include: Step S1, obtaining stress occurrence states at different crustal depths; Step S2, obtaining 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, establishing a finite element model of the target area and calculating the stress field distribution to obtain the crustal stress field distribution characteristics; Step S4: According to the stress field direction, stress field magnitude, stress structure, and deep and shallow crust deformation characteristics in the crust stress field distribution characteristics, the deep and shallow crust stress correlation and heterogeneity characterization are obtained.

2. The method for characterizing the spatial distribution characteristics of the multi-scale geostress field heterogeneity according to claim 1, characterized in that: In step S1, the stress state at different depths of the upper crust is obtained by an in-situ geostress measurement method and a test method based on drilling and cores, and the stress state at the focal depth is obtained by an inversion method of focal mechanism solution.

3. The method for characterizing the spatial distribution characteristics of the multi-scale geostress field heterogeneity according to claim 2, characterized in that: In step S2, the deformation characteristics at different crustal depths are obtained by using methods such as surface deformation observation and seismic anisotropy.

4. The method for characterizing the spatial distribution characteristics of the multi-scale geostress field heterogeneity according to claim 3, characterized in that: In step S4, the stress direction is characterized by the horizontal maximum principal stress direction; the stress magnitude 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 deformation characteristics of deep and shallow crust are characterized by horizontal maximum tensile strain rate-horizontal minimum principal stress-anisotropic fast wave direction.

5. A device for characterizing the spatial distribution characteristics of the inhomogeneity of a multi-scale geostress field, characterized in that: include: The first acquisition module is used to obtain the stress distribution state at different crustal depths; The second acquisition module is used to obtain 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 based on the measured stress state, inverted stress state and deformation characteristics at different crustal depths, and obtain the crustal stress field distribution characteristics; The processing module is used to obtain the correlation and heterogeneity characterization of deep and shallow crust stress according to the stress field direction, stress field value, stress structure, and deep and shallow crust deformation characteristics in the crust stress field distribution characteristics.

6. The device for characterizing the spatial distribution characteristics of the multi-scale geostress field non-uniformity according to claim 5, characterized in that: The first acquisition module is used to obtain the stress state at different depths of the upper crust by an in-situ geostress measurement method and a test method based on drilling and cores, and to obtain the stress state at the focal depth by a focal mechanism solution inversion method.

7. The device for characterizing the spatial distribution characteristics of the multi-scale geostress field non-uniformity according to claim 6, characterized in that: The second acquisition module is used to obtain deformation characteristics at different crustal depths using surface deformation observations and seismic anisotropy methods.

8. The device for characterizing the spatial distribution characteristics of the multi-scale geostress field non-uniformity according to claim 7, characterized in that: The stress direction is characterized by the horizontal maximum principal stress direction; the stress magnitude 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 deformation characteristics of deep and shallow crust are characterized by horizontal maximum tensile strain rate-horizontal minimum principal stress-anisotropic fast wave direction.

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