A three-dimensional in-situ stress measurement method based on core diameter radial strain observation

Abstract

The application discloses a three-dimensional in-situ stress measuring method based on core diameter radial strain observation, first obtains the maximum and minimum directions of the core diameter and the axial direction, marks and establishes X, Y and Z axis coordinate systems, then arranges six strain gauges on the core side walls corresponding to the X axis and the Y axis and the 45-degree line between the X axis and the Y axis, obtains the inelastic strain of the core on the X, Y and Z axes through the data of the strain gauges, and finally calculates the main stress size corresponding to the three-dimensional X, Y and Z axis directions according to the inelastic strain difference. The method is simple, economical and accurate, and only six strain gauges are needed to measure the in-situ stress, so that the test process is greatly simplified and convenient.

Description

Technical Field

[0001] This invention relates to the field of geotechnical mechanics measurement technology, and more specifically to a three-dimensional geostress measurement method based on radial strain observation of rock core diameter. Background Technology

[0002] In-situ stress is a general term for the internal stresses present in rock masses. This mechanical state of engineering rock masses not only exists objectively, but its magnitude and direction also vary from place to place. In-situ stress measurement, research, and applications have spread to rock engineering design and stability evaluation in various fields such as water conservancy and hydropower, mining engineering, oil and gas resource extraction, and transportation. In-situ stress is one of the essential basic data for rock mechanics, engineering design, and calculation analysis.

[0003] Among existing geostress measurement methods, the core stress relief method and the hydraulic fracturing method are the most widely used. The core stress relief method is currently the most commonly used geostress measurement method. In this method, after core placement, the rock core is removed from the surrounding geostress field, and the core undergoes elastic recovery. Geostress is calculated by measuring the elastic deformation. However, the core deformation method can only obtain stress differences in two directions from the rock core, and the stress difference at the same location is only obtained once, making it impossible to verify its accuracy experimentally. If geostress needs to be obtained from the core deformation method, the hydraulic fracturing method is required to obtain one of the stresses. Therefore, the stress relief method itself still has certain limitations in practical applications, especially in three-dimensional geostress measurement. Furthermore, combining the stress relief method with the hydraulic fracturing method results in high cost, complex processes, and large errors, making it difficult to meet practical needs.

[0004] Therefore, how to provide a simpler and more accurate method for measuring three-dimensional geostress is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a three-dimensional geostress measurement method based on radial strain observation of rock core diameter, which obtains the rock core geostress by combining elastic and inelastic deformation of the rock core.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A three-dimensional geostress measurement method based on radial strain observation of rock core diameter includes the following steps:

[0008] Rock cores were drilled, and the directions of maximum and minimum core diameter were experimentally determined. These directions were then marked and a coordinate system was established, with the direction of maximum core diameter defined as the X-axis and the direction representing the maximum horizontal principal stress S. H Direction; the minimum diameter of the rock core is along the Y-axis, which is also the direction of the maximum horizontal principal stress S. hDirection; the core's axial direction is the Z-axis direction, which is perpendicular to the principal stress S. V direction;

[0009] Step 2: Attach two transverse strain gauges (labeled 1-2) to the core sidewall corresponding to the negative Y-axis, and two transverse strain gauges (labeled 5-6) to the core sidewall corresponding to the positive X-axis. Attach one vertical strain gauge (labeled 3) to the core sidewall corresponding to the 45° angle between the positive X-axis and the negative Y-axis, and one vertical strain gauge (labeled 4) to the core sidewall corresponding to the 45° angle between the positive X-axis and the positive Y-axis. Obtain the differential strain of the core in the X, Y, and Z axes using the data from strain gauges 1-6. Specifically:

[0010]

[0011] Wherein, Δε1-Δε6 are the differential strains obtained by strain gauge measurement and calculation; Δε X , Δε Y , Δε Z S H Direction S h Direction and S V Differential strain in direction;

[0012] Step 3: Calculate the magnitude of the principal stresses:

[0013]

[0014] Where v is Poisson's ratio, Δε X , Δε Y , Δε Z S H Direction S h Direction and S V Differential strain in direction, γ i H is the unit weight of the i-th rock layer; i Height of the i-th rock layer.

[0015] Preferably, in step one, the directions of maximum and minimum core diameter are obtained by core diameter scanning.

[0016] Preferably, the differential strain calculation formula in step two is as follows:

[0017] Δε=ε(t2)-ε(t1);

[0018] Where ε(t1) is the strain measured by the strain gauge at time t1, and ε(t2) is the strain measured by the strain gauge at time t2.

[0019] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a three-dimensional geostress measurement method based on core diameter radial strain observation, which has the following beneficial effects:

[0020] After the rock core is removed, elastic deformation occurs instantaneously. Due to the different magnitudes of stress in the horizontal direction, the rock core undergoes different degrees of elastic deformation. By measuring the magnitude of this deformation, the direction of the in-situ stress is obtained. Based on this, the inelastic deformation is measured to obtain the magnitude of the in-situ stress. Compared with traditional methods such as hydraulic fracturing and ASR, this method is simple, economical, and accurate. Furthermore, two strain gauges in the same direction can verify the accuracy of the results. Only six strain gauges are needed to measure the in-situ stress, greatly simplifying and facilitating the testing process. Attached Figure Description

[0021] 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.

[0022] Figure 1 The graphs show the instantaneous deformation and time-dependent deformation curves of the rock core.

[0023] Figure 2 This is a schematic diagram showing the location of the core and strain gauges in this invention;

[0024] Figure 3 This is a flowchart of the method of the present invention. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] The magnitude of geostress can be obtained by measuring rock cores, and the methods for measuring geostress using rock cores vary, such as... Figure 1 As shown, two types of deformation occur after core drilling: one is immediate elastic deformation, such as... Figure 1 AB segment; one type is inelastic deformation, such as Figure 1 Section BC.

[0027] Core drilling is performed. After core extraction, the core undergoes deformation in section AB, transforming into an elliptical shape due to stress release. Then, the maximum and minimum diameter directions of the core are obtained through core diameter scanning, marked, and a coordinate system is established. The direction of maximum core diameter is the X-axis, representing the maximum horizontal principal stress S. H Direction; the minimum diameter of the rock core is along the Y-axis, which is also the direction of the maximum horizontal principal stress S. hDirection; the core's axial direction is the Z-axis direction, which is perpendicular to the principal stress S. V direction;

[0028] As attached Figure 2 As shown, two transverse strain gauges, labeled 1-2, are attached to the core sidewall corresponding to the negative Y-axis; two transverse strain gauges, labeled 5-6, are attached to the core sidewall corresponding to the positive X-axis; one vertical strain gauge, labeled 3, is attached to the core sidewall corresponding to the 45° angle between the positive X-axis and the negative Y-axis; and one vertical strain gauge, labeled 4, is attached to the core sidewall corresponding to the 45° angle between the positive X-axis and the positive Y-axis. The differential strain is obtained from the data of strain gauges 1-6. The differential strain calculation formula is as follows:

[0029] Δε=ε(t2)-ε(t1);

[0030] As attached Figure 1 As shown, ε(t1) is the strain measured by the strain gauge at time t1, and ε(t2) is the strain measured by the strain gauge at time t2;

[0031] Based on the above, the differential strain of the rock core along the X, Y, and Z axes is obtained as follows:

[0032]

[0033] Where Δε1-Δε6 are the differential strains calculated by strain gauge measurements, Δε X , Δε Y , Δε Z S H Direction S h Direction and S V Differential strain in direction;

[0034] pass Figure 1 As can be seen from the curve, the ratio S of the principal stresses... H / S V and S h / S V Specifically:

[0035]

[0036] That is, the magnitude of the principal stress:

[0037]

[0038] Among them, S H S h and S V These represent the maximum horizontal principal stress, the minimum horizontal principal stress, and the vertical principal stress, respectively; v is Poisson's ratio, and Δε... X , Δε Y , Δε Z SH Direction S h Direction and S V Differential strain in the direction, perpendicular principal stress S V γ can be obtained from the weight of the overlying part. i H is the unit weight of the i-th rock layer; i Height of the i-th rock layer.

[0039] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0040] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A three-dimensional geostress measurement method based on radial strain observation of rock core diameter, characterized in that, Includes the following steps: Step 1: Drill and core samples. Obtain the directions of maximum and minimum core diameter through experiments, mark them, and establish a coordinate system. The direction of maximum core diameter is the X-axis, and the direction of maximum horizontal principal stress S is the X-axis. H Direction; the minimum diameter of the rock core is along the Y-axis, which is also the direction of the minimum horizontal principal stress S. h Direction; the core's axial direction is the Z-axis direction, which is perpendicular to the principal stress S. V direction; Step 2: Attach two transverse strain gauges (labeled 1-2) to the core sidewall corresponding to the negative Y-axis, and two transverse strain gauges (labeled 5-6) to the core sidewall corresponding to the positive X-axis. Attach one vertical strain gauge (labeled 3) to the core sidewall corresponding to the 45° angle between the positive X-axis and the negative Y-axis, and one vertical strain gauge (labeled 4) to the core sidewall corresponding to the 45° angle between the positive X-axis and the positive Y-axis. Obtain the differential strain of the core in the X, Y, and Z axes using the data from strain gauges 1-6. Specifically: ； in, - These are the differential strains obtained by measurement and calculation using strain gauges. , , S H Direction S h Direction and S V Differential strain in direction; Step 3: Calculate the magnitude of the principal stresses: The ratio S of the principal stresses H / S V and S h / S V Specifically: ； in, Poisson's ratio, , , S H Direction S h Direction and S V Differential strain in direction, Let be the unit weight of the i-th rock layer; Height of the i-th rock layer; In step one, the maximum and minimum diameter directions of the rock core are obtained by scanning the rock core diameter.

2. The three-dimensional geostress measurement method based on radial strain observation of rock core diameter according to claim 1, characterized in that, The differential strain calculation formula mentioned in step two is as follows: ； in, The strain measured by the strain gauge at time t1, The strain was measured by the strain gauge at time t2.

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