Ground stress relative change analysis method and system

Abstract

The invention discloses a ground stress relative change analysis method and system. The method comprises the following steps: S1, acquiring piezomagnetic ground stress monitoring data; s2, obtaining additional stress through a least square method according to the piezomagnetic ground stress monitoring data; and S3, obtaining the current stress according to the change of the additional stress. By adopting the technical scheme of the invention, the relative change rule of the stress field can be effectively obtained, and the mutual relation between the regional stress field activity and the earthquake is disclosed.

Description

Technical Field

[0001] The present invention belongs to the technical field of crustal stress monitoring, and in particular relates to a method and system for analyzing relative changes in crustal stress. Background Art

[0002] The development and occurrence of earthquakes are essentially related to the changes in the crustal stress field. The significance of studying earthquake activity by measuring the relative changes in ground stress is obvious, and it is also an idea proposed by Mr. Li Siguang to achieve earthquake prediction. At present, the dynamic change observation technology of crustal stress-strain field can be summarized as "deep drilling, multi-component, wide-band". Comprehensive observation of multiple parameters of rock mass stress and deformation is carried out in a deep hole, which is convenient for comparison and verification of data quality. The accumulation of crustal strain field is accurately recorded in a period of seconds to months, and their amplitude and rate change characteristics are studied. The process of accumulation and release of crustal structural deformation energy is understood, and its relationship with tectonic activities and earthquake occurrence is explored.

[0003] In 1991, Wang Lianjie and Pan Lizhou published a monograph entitled "Ground Stress Measurement and Its Application in Engineering", which systematically discussed the basic theory, measurement methods and instruments of ground stress measurement, and gave examples of engineering applications. Since my country began to explore earthquake prediction using borehole stress-strain observation technology, there have been many successful cases. Although a mature theoretical system has not yet been formed, and it also contains a large amount of experience and speculation, the phenomenon of repeated and stable appearance of various precursor features before earthquakes is encouraging. It may reveal some internal and essential things related to the source process, which is worthy of in-depth study. However, the current analysis method of observation data is not perfect enough to reveal the relationship between regional stress field activity and earthquakes. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method and system for analyzing relative changes in ground stress, which can effectively obtain the relative change law of the stress field and reveal the relationship between regional stress field activity and earthquakes.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A method for analyzing relative changes in ground stress, comprising:

[0007] Step S1, obtaining piezomagnetic geostress monitoring data;

[0008] Step S2, obtaining additional stress by least square method according to the piezomagnetic geostress monitoring data;

[0009] Step S3, obtaining the current stress according to the change of the additional stress.

[0010] Preferably, in step S1, the piezomagnetic geostress monitoring data is acquired by a piezomagnetic geostress monitoring probe; wherein, the measuring elements of the piezomagnetic geostress monitoring probe in four different directions are arranged in sequence at an interval of 45°.

[0011] Preferably, in step S2, the stress component of the additional stress is obtained according to the piezomagnetic in-situ stress monitoring data, namely:

[0012]

[0013] Where i = 1, 2, 3, 4,

[0014] The maximum principal stress for calculating additional stress is:

[0015] The minimum principal stress for calculating additional stress is:

[0016] Calculate the maximum principal stress σ of the additional stress H With σ x The angle γ is:

[0017] Preferably, in step S3, the measured ground stress value at the depth closest to the installation depth of the piezomagnetic ground stress monitoring probe is taken as the initial stress state, and the change of the additional stress is superimposed to obtain the current stress.

[0018] The present invention also provides a system for analyzing relative changes in ground stress, comprising:

[0019] The piezomagnetic stress monitoring instrument is used to obtain piezomagnetic ground stress monitoring data;

[0020] The data processing and analysis device is used to obtain additional stress through the least square method based on the piezomagnetic geostress monitoring data; and to obtain the current stress based on the change of the additional stress.

[0021] Preferably, the piezomagnetic stress monitoring instrument obtains piezomagnetic geostress monitoring data through a piezomagnetic geostress monitoring probe; wherein, the measuring elements of the piezomagnetic geostress monitoring probe in four different directions are arranged in sequence at a 45° interval.

[0022] Preferably, the additional stress is obtained by the data processing and analysis device as follows:

[0023] According to the piezomagnetic in-situ stress monitoring data, the stress component of the additional stress is obtained, namely:

[0024]

[0025] Where i = 1, 2, 3, 4,

[0026] The maximum principal stress for calculating additional stress is:

[0027] The minimum principal stress for calculating additional stress is:

[0028] Calculate the maximum principal stress σ of the additional stress H With σ x The angle γ is:

[0029] Preferably, the data analysis device is used to use the measured ground stress value at the depth closest to the installation depth of the piezomagnetic ground stress monitoring probe as the initial stress state, and superimpose the change of additional stress to obtain the current stress.

[0030] The present invention obtains additional stress by the least square method based on the piezomagnetic stress monitoring data; obtains the current stress based on the change of the additional stress; the present invention realizes the rapid analysis and automatic output of the piezomagnetic stress monitoring data, and can quickly obtain the stress evolution process; at the same time, it realizes the correlation analysis of the relative change of stress and the correlation with seismic activity, especially the change of stress before and after a strong earthquake, including pre-earthquake abnormal change, co-seismic stress change and post-earthquake adjustment process. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0032] Figure 1 It is a flow chart of the method for analyzing relative changes in ground stress of the present invention;

[0033] Figure 2 Schematic diagram of the arrangement of the piezomagnetic stress monitoring probes in four different directions. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] Embodiment 1:

[0037] like Figure 1 As shown, an embodiment of the present invention provides a method for analyzing relative changes in ground stress, including:

[0038] Step S1, obtaining piezomagnetic geostress monitoring data;

[0039] Step S2, obtaining additional stress by least square method according to the piezomagnetic geostress monitoring data;

[0040] Step S3, obtaining the current stress according to the change of the additional stress.

[0041] As an implementation of an embodiment of the present invention, in step S1, the piezomagnetic in-situ stress monitoring data is obtained by a piezomagnetic in-situ stress monitoring probe; wherein the four measuring elements in different directions of the piezomagnetic in-situ stress monitoring probe are arranged in sequence at intervals of 45°, such as Figure 2 shown.

[0042] As an implementation method of the present invention, based on the deformation of the borehole under the plane stress state of elastic mechanics, the ground stress borehole is regarded as a circular hole in an infinite thin plate. What we are concerned about is the radial displacement μ of the hole wall displacement during the deformation of the borehole under the action of external force. Assume that there is a circular hole in an infinite elastic thin plate, and the thin plate is subjected to a uniformly distributed tensile force in a certain direction at infinity, with an intensity of σ H , and a uniformly distributed tensile force perpendicular to it, with an intensity of σ h The displacement of a point A on the hole wall can be expressed as follows:

[0043]

[0044] Where E is the elastic modulus of the infinite elastic thin plate; a is the drilling radius; α is σ H The angle to point A is positive if it is counterclockwise and negative if it is clockwise. It is stipulated that the displacement direction μ away from the hole center takes a positive value, and vice versa takes a negative value. Further, we can get:

[0045]

[0046] According to the principal stress σ H , σ h With stress component σ x , σ y , τ xy Relationship:

[0047]

[0048] make

[0049] 1+2cos2θ i =C 1θi

[0050] 1-2cos2θ i =C 2θi

[0051] 4sin2θ i =C 3θi

[0052] i=1,2……n

[0053] where γ is σ x to H The angle of θ is σ x Angle to the measuring element.

[0054] The above formula can be rewritten as:

[0055]

[0056] make

[0057]

[0058] According to the least squares method, a set of solutions that can minimize the sum of squares of residual errors (i.e., the deviations between the observed values ​​and the regression line) is found from many possible solutions. This set of solutions is the most reliable and closest to the true value of the measured stress at that point. When it is the most reliable solution, it must satisfy the following conditions:

[0059] Aσ=G

[0060] in:

[0061]

[0062] σ=[σ x σ y τ xy ] T

[0063]

[0064] Right now:

[0065] σ=A -1 G

[0066] Further, in step S2, the stress component of the additional stress is obtained according to the piezomagnetic in-situ stress monitoring data, namely:

[0067]

[0068] Where i = 1, 2, 3, 4,

[0069] The maximum principal stress for calculating additional stress is:

[0070] The minimum principal stress for calculating additional stress is:

[0071] Calculate the maximum principal stress σ of the additional stress H With σ x The angle γ is:

[0072] As an implementation method of the embodiment of the present invention, in step S3, the measured ground stress value at the depth closest to the installation depth of the piezomagnetic ground stress monitoring probe is used as the initial stress state, and the change of the additional stress is superimposed to obtain the current stress.

[0073] Furthermore, the measured ground stress value at the depth closest to the installation depth of the monitoring probe is taken as the initial stress value σ H1 , σ h1 , β1, which is the direction of the maximum principal stress, the minimum principal stress and the maximum principal stress, and let σ H1 The angle between the x-axis and the x-axis is γ1. According to the two-dimensional plane stress tensor conversion formula, the stress component σ in the rectangular coordinate system xoy can be calculated: x0 , σ y0 , τ xy0 .

[0074]

[0075] Let Δσ x Δτ xy Δσ y is the change of additional stress, the stress component σ of the current stress, x ,σ, y , τ, xy :

[0076]

[0077] Then according to σ, x ,σ, y , τ, xy , calculate the maximum principal stress σ of the current stress, H , minimum principal stress σ, h and the maximum principal stress σ, H With σ, x The included angle γ, and the direction of the maximum principal stress β, =π / 2-γ,.

[0078] The present invention can quickly obtain additional stress and current stress, and then analyze the correlation between the relative change of ground stress and seismic activity.

[0079] Embodiment 2:

[0080] The embodiment of the present invention also provides a system for analyzing relative changes in geostress, including: a piezomagnetic stress monitoring instrument and a data processing and analysis device; selecting a suitable location in a tectonic activity area or an engineering area to perform vertical hole drilling, selecting a complete section to install a piezomagnetic stress monitoring instrument based on the core and well logging, installing the piezomagnetic geostress monitoring probe of the piezomagnetic stress monitoring instrument in the borehole of the crustal rock mass so that the measuring element is well coupled with the borehole rock wall, and continuously recording the geostress data output by the measuring element. The geostress data is sent to the data processing and analysis device in real time through the GPS transmission system. Among them, the piezomagnetic stress monitoring instrument is used to obtain piezomagnetic geostress monitoring data; the data processing and analysis device is used to obtain additional stress by the least squares method based on the piezomagnetic geostress monitoring data; and at the same time, the current stress is obtained according to the change of the additional stress.

[0081] As an implementation method of an embodiment of the present invention, the piezomagnetic stress monitoring instrument obtains piezomagnetic geostress monitoring data through a piezomagnetic geostress monitoring probe; wherein, the measuring elements of four different directions of the piezomagnetic geostress monitoring probe are arranged in sequence at an interval of 45°.

[0082] As an implementation method of the embodiment of the present invention, the additional stress is obtained by the data processing and analysis device as follows:

[0083] According to the piezomagnetic in-situ stress monitoring data, the stress component of the additional stress is obtained, namely:

[0084]

[0085] Where i = 1, 2, 3, 4,

[0086] The maximum principal stress for calculating additional stress is:

[0087] The minimum principal stress for calculating additional stress is:

[0088] Calculate the maximum principal stress σ of the additional stress H With σ x The angle γ is:

[0089] As an implementation method of an embodiment of the present invention, the data analysis device is used to use the measured ground stress value at the depth closest to the installation depth of the piezomagnetic ground stress monitoring probe as the initial stress state, and superimpose the change of additional stress to obtain the current stress.

[0090] Taking a monitoring station as an example, the four-component piezomagnetic stress sensor monitoring probe is first calibrated. The first is indoor calibration, which converts the instrument frequency reading into stress reading. The second is reference value calibration. In addition to the monitoring elements in different directions, the piezomagnetic stress monitoring probe is also equipped with a suspended element. The element is suspended and not in direct contact with the hole wall. Its value fluctuation is affected by external non-stress factors and serves as a reference value for calibration. After that, the change of the four-component monitoring data can be obtained. Since the stress monitoring data records the relative change value during the monitoring time, it is called additional stress. According to the above basic theory, the change of the additional stress state can be obtained through the stress monitoring data of the station. If the current stress field change characteristics are to be obtained, in-situ absolute ground stress measurement (such as hydraulic fracturing ground stress measurement) is required after the drilling is completed and before the monitoring instrument is installed. The measured ground stress value at the depth closest to the installation depth of the monitoring probe is taken as the initial stress state, and the additional stress change is superimposed, which is called the current stress state. If the monitoring time is long enough, the stress evolution diagram of the monitoring station can be obtained. The stress evolution diagram can be used to interpret the stress changes during the monitoring period, whether compression is accumulated or tension is released, whether the direction of the principal stress axis is deflected, etc. These are of great significance for further research on tectonic stress fields, fault activities and earthquakes.

[0091] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for analyzing relative changes in ground stress, characterized in that: include: Step S1, obtaining piezomagnetic geostress monitoring data; Step S2, obtaining additional stress by least square method according to the piezomagnetic geostress monitoring data; Step S3, obtaining the current stress according to the change of the additional stress.

2. The method for analyzing relative changes in ground stress according to claim 1, characterized in that: In step S1, the piezomagnetic geostress monitoring data is obtained by using a piezomagnetic geostress monitoring probe; wherein, the measuring elements of the piezomagnetic geostress monitoring probe in four different directions are arranged in sequence at an interval of 45°.

3. The method for analyzing relative changes in ground stress according to claim 2, characterized in that: In step S2, the stress component of the additional stress is obtained according to the piezomagnetic in-situ stress monitoring data, namely: Where i = 1, 2, 3, 4, The maximum principal stress for calculating additional stress is: The minimum principal stress for calculating additional stress is: Calculate the maximum principal stress σ of the additional stress H With σ x The angle γ is:

4. The method for analyzing relative changes in ground stress according to claim 3, characterized in that: In step S3, the measured ground stress value at the depth closest to the installation depth of the piezomagnetic ground stress monitoring probe is taken as the initial stress state, and the change of the additional stress is superimposed to obtain the current stress.

5. A system for analyzing relative changes in ground stress, characterized in that: include: The piezomagnetic stress monitoring instrument is used to obtain piezomagnetic ground stress monitoring data; The data processing and analysis device is used to obtain additional stress through the least square method based on the piezomagnetic geostress monitoring data; and to obtain the current stress based on the change of the additional stress.

6. The ground stress relative change analysis system according to claim 5, characterized in that: The piezomagnetic stress monitoring instrument obtains piezomagnetic geostress monitoring data through a piezomagnetic geostress monitoring probe; wherein, the four measuring elements in different directions of the piezomagnetic geostress monitoring probe are arranged in sequence at a 45° interval.

7. The ground stress relative change analysis system according to claim 6, characterized in that: The additional stress obtained by the data processing and analysis device is as follows: According to the piezomagnetic in-situ stress monitoring data, the stress component of the additional stress is obtained, namely: Where i = 1, 2, 3, 4, The maximum principal stress for calculating additional stress is: The minimum principal stress for calculating additional stress is: Calculate the maximum principal stress σ of the additional stress H With σ x The angle γ is:

8. The ground stress relative change analysis system according to claim 7, characterized in that: The data analysis device is used to take the measured ground stress value at the depth closest to the installation depth of the piezomagnetic ground stress monitoring probe as the initial stress state, and superimpose the change of additional stress to obtain the current stress.

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