Method and apparatus for obtaining in-situ stress direction using cylindrical samples

Abstract

This invention relates to the field of geological exploration technology and discloses a method and apparatus for obtaining the direction of in-situ stress using cylindrical samples. The method includes: acquiring a cylindrical core sample; determining the marker line of the cylindrical sample and attaching multiple strain gauges to the surface of the cylindrical sample based on the extension direction of the marker line; adding a coating to the surface of the cylindrical sample with the attached strain gauges to obtain a proportionally enlarged coated cylindrical sample; pressurizing the coated cylindrical sample and collecting strain data from the multiple strain gauges during the pressurization process; and calculating the direction of in-situ stress in the formation based on the collected strain data. This method, based on limitations on the length, height, and strain gauge attachment positions of the cylindrical core sample, collects strain data from the cylindrical core sample and combines this with resistivity core orientation technology to accurately obtain the direction of in-situ stress in the formation from the cylindrical core sample.

Description

Technical Field

[0001] This invention relates to the field of geological exploration technology, and in particular to a method and apparatus for obtaining the direction of geostress using cylindrical samples. Background Technology

[0002] Crustal stress is the stress existing in the Earth's crust. It is the force per unit area within the medium caused by rock deformation. It generally includes two parts: (1) stress caused by the weight of the overlying rock, which is caused by gravity and the centrifugal force of the Earth's rotation; (2) tectonic stress transmitted from adjacent blocks or the bottom. This stress refers to the part that differs from the standard state. In addition to the modern tectonic stress transmitted from adjacent blocks or the bottom, it also includes residual stress left over from past tectonic movements that has not been completely relaxed, as well as stress changes caused by nearby man-made projects (such as tunnels and mining faces). Tectonic stress directly reflects the driving force of crustal movement and is an important factor causing earthquakes. When excavating tunnels in areas with strong tectonic stress, the tunnel walls become free surfaces and are easily deformed, causing the tunnel to gradually shrink or collapse. Therefore, the study of crustal stress is of great significance. Crustal stress is the natural stress existing in the Earth's crust that has not been disturbed by engineering projects. It is also called the initial stress of the rock mass, absolute stress, or original rock stress. In a broad sense, it also refers to the stress within the Earth's body. It includes stresses generated by geothermal activity, gravity, changes in the Earth's rotation speed, and other factors.

[0003] The commonly used experimental process for evaluating geostress direction is to first conduct differential strain experiments to determine the magnitude of the maximum horizontal geostress, the minimum horizontal geostress, the magnitude of the vertical geostress, and the angle between the direction of the maximum horizontal principal stress and the marker line. The angle between the direction of the maximum horizontal geostress and the marker line is then combined with a resistivity method core orientation experiment to determine the geographical location of the core, thus determining the geographical location of the maximum horizontal principal stress.

[0004] Deep underground, rock cores are under compression due to in-situ stress, and the natural fractures they contain are closed. When the core is brought to the surface, the release of stress causes it to expand, resulting in numerous new microcracks. The degree of opening, density, and direction of these microcracks are related to the stress field of the original environment where the core was located, reflecting the underground stress field. Differential strain analysis (DSA) can be performed on the core under pressure in different directions to determine the spatial directions of the maximum and minimum principal stresses. The DSA test is based on the following assumptions: all microcracks are generated by the release of in-situ compressive stress and are aligned with the direction of the principal stress; if the formation is isotropic, then when a principal stress value can be obtained independently, the principal strain ratio can be used to obtain the in-situ stress value.

[0005] In the laboratory, when a rock sample is subjected to hydrostatic pressure, the microcracks that appear due to stress release will close first. After the cracks close, if loading continues, the resulting deformation is due to the deformation of the rock solid (skeletal compression). Figure 1 This is a typical curve showing the relationship between strain and pressure changes measured after loading a rock sample. The curve is divided into two parts. The first part is the strain caused by the combined effects of microcrack closure and rock skeleton compression. The second part has a smaller slope. The difference in slope between the two parts reflects the strain caused solely by microcrack closure. By distinguishing these deformations, the contribution of microcracks to directional deformation can be determined, thus allowing the determination of the direction of the maximum principal strain (i.e., the maximum principal stress). Typically, this is then compared with the results of resistivity method core orientation experiments to determine the geographical orientation of the core, thereby identifying the geographical location of the maximum horizontal principal stress.

[0006] The above method is currently the most commonly used geostress direction test in the oil and gas industry. It is effective for cubic samples. However, most rock cores in the world are obtained by drilling, meaning that most rock cores are cylindrical. If the above method is to be used to determine geostress, the rock core must be processed into a cube. Rock cores are taken from thousands of meters underground and are important physical geological data for the country, providing data support and services for resource and energy security, earth science research and geological disaster prevention. Core taking requires tens of millions of yuan in material and human resources, making each rock core extremely precious. If the cylindrical sample is processed into a cube, there are the following disadvantages: (1) The preparation cycle of wire-cut samples is long and the preparation equipment requires high precision; (2) Rock cores made into cubes cannot be subjected to subsequent analytical operations, including displacement experiments; (3) Once the sample is made, it is inconvenient to test the physical properties from other angles; (4) Destructive cutting increases economic costs, increases rock core loss, reduces work efficiency, and makes it inconvenient to preserve the sample.

[0007] Since 99% of rock cores are cylindrical, there is an urgent need for a method and apparatus to directly determine the direction of geostress using cylindrical samples, while ensuring the integrity and reliability of the data and without damaging the original shape of the samples. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a method, apparatus, equipment, and medium for obtaining the geostress direction using cylindrical samples. This method, based on limitations on the length, height, and strain gauge contact position of the cylindrical rock core sample, collects strain data from the cylindrical rock core sample and combines it with resistivity core orientation technology to accurately obtain the geostress direction of the cylindrical rock core in the formation.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for obtaining the direction of geostress using a cylindrical sample, comprising:

[0011] Obtain cylindrical core samples;

[0012] Determine the marking lines of the cylindrical sample, and attach multiple strain gauges to the surface of the cylindrical sample based on the extension direction of the marking lines;

[0013] A coating is added to the surface of a cylindrical sample with multiple strain gauges attached to it, resulting in a proportionally enlarged coated cylindrical sample.

[0014] A coated cylindrical sample was subjected to pressure treatment, and strain data of multiple strain gauges in the coated cylindrical sample were collected during the pressure treatment process;

[0015] Based on the collected strain data, the direction of in-situ stress in the formation of the coated cylindrical sample was calculated.

[0016] Furthermore, this includes: the end face radius of the cylindrical core sample is R, and the height is 2R.

[0017] Furthermore, a connecting cable is provided in the coating of the cylindrical coated sample, which connects the strain gauge to the stress sensor.

[0018] Furthermore, based on the collected strain data, the direction of in-situ stress in the formation of the coated cylindrical sample was calculated, including:

[0019] Based on the collected strain data, the corresponding strain components of the coated cylindrical sample were calculated.

[0020] Based on the values ​​of the strain components corresponding to the coated cylindrical sample, the values ​​of the principal strain corresponding to the coated cylindrical sample are calculated;

[0021] Based on the values ​​of the strain components and principal strains corresponding to the coated cylindrical sample, the direction vector corresponding to the principal strain is calculated.

[0022] Based on the principal strain direction vector corresponding to the coated cylindrical sample, and combined with the resistivity core orientation direction obtained by the resistivity core orientation method, the geostress direction of the coated cylindrical sample in the formation is calculated.

[0023] Secondly, the present invention also provides an apparatus for obtaining the direction of geostress using a cylindrical sample, comprising:

[0024] The acquisition module is used to acquire cylindrical rock core samples;

[0025] The determination module is used to determine the marking lines of the cylindrical sample and to attach multiple strain gauges to the surface of the cylindrical sample based on the extension direction of the marking lines.

[0026] The module is used to add a coating to the surface of a cylindrical sample with multiple strain gauges attached, resulting in a proportionally enlarged coated cylindrical sample.

[0027] The acquisition module is used to pressurize the coated cylindrical sample and acquire strain data from multiple strain gauges in the coated cylindrical sample during the pressurization process.

[0028] The calculation module is used to calculate the geostress direction of the coated cylindrical sample in the formation based on the collected strain data.

[0029] Furthermore, this includes: the end face radius of the cylindrical core sample is R, and the height is 2R.

[0030] Furthermore, a connecting cable is provided in the coating of the cylindrical coated sample, which connects the strain gauge to the stress sensor.

[0031] Furthermore, the computing module is also used for:

[0032] Based on the collected strain data, the corresponding strain components of the coated cylindrical sample were calculated.

[0033] Based on the values ​​of the strain components corresponding to the coated cylindrical sample, the values ​​of the principal strain corresponding to the coated cylindrical sample are calculated;

[0034] Based on the values ​​of the strain components and principal strains corresponding to the coated cylindrical sample, the direction vector corresponding to the principal strain is calculated.

[0035] Based on the principal strain direction vector corresponding to the coated cylindrical sample, and combined with the resistivity core orientation direction obtained by the resistivity core orientation method, the geostress direction of the coated cylindrical sample in the formation is calculated.

[0036] Thirdly, the present invention also provides an electronic device, comprising: a processor and a memory;

[0037] The processor is coupled with the memory;

[0038] The processor is used to read and execute programs or instructions stored in the memory, causing the device to perform the method as described in the first aspect.

[0039] Fourthly, the present invention also provides a computer-readable storage medium storing a computer program that, when executed by a processor, implements the method as described in the first aspect.

[0040] The technical solution provided by this invention has at least the following technical effects or advantages:

[0041] The technical solution of this invention obtains cylindrical core samples of a specified length and height, determines marker lines, and attaches strain gauges along the direction of the marker lines to collect precise strain data. Based on this strain data, the strain components of the cylindrical core sample are calculated. The magnitude and vector of the principal strain of the cylindrical core sample are then calculated using these strain components. Furthermore, combined with the resistivity core orientation obtained through the resistivity method, the direction of in-situ stress in the cylindrical core sample is calculated. This solution, based on limitations on the length, height, and strain gauge attachment positions of the cylindrical core sample, collects strain data from the cylindrical core sample and, combined with resistivity core orientation technology, can accurately determine the direction of in-situ stress in the cylindrical core sample within the formation.

[0042] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0043] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a schematic diagram of a typical curve showing the relationship between strain and pressure changes measured after loading a rock sample in the background technology of this invention.

[0045] Figure 2 This is a schematic flowchart of a method for obtaining the direction of geostress using a cylindrical sample in an embodiment of the present invention;

[0046] Figure 3 This is a schematic diagram of a cylindrical sample in an embodiment of the present invention;

[0047] Figure 4 This is a schematic diagram of attaching multiple strain gauges to a cylindrical sample in an embodiment of the present invention;

[0048] Figure 5 This is a perspective view of multiple strain gauges attached to a cylindrical sample in an embodiment of the present invention;

[0049] Figure 6 This is a top view of a strain gauge attached to a cylindrical sample in an embodiment of the present invention;

[0050] Figure 7This is a front view of a strain gauge being attached to a cylindrical sample in an embodiment of the present invention;

[0051] Figure 8 This is a side view of a strain gauge attached to a cylindrical sample in an embodiment of the present invention;

[0052] Figure 9 This is a schematic diagram of a cylindrical sample including an externally compressed rubber sleeve in an embodiment of the present invention;

[0053] Figure 10 This is a schematic diagram of a device for obtaining the direction of geostress using a cylindrical sample, according to an embodiment of the present invention.

[0054] Figure 11 This is a schematic diagram of the structure of an electronic device provided in an embodiment of the present invention. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, 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, 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.

[0056] Figure 2 This is a schematic flowchart of a method for obtaining the direction of geostress using a cylindrical sample according to an embodiment of the present invention. As shown in the figure, the method includes:

[0057] S101. Obtain cylindrical core samples;

[0058] During drilling, coring tools are used to obtain cylindrical core samples from the ground. These cylindrical core samples can also be simply referred to as cylindrical samples. When obtaining cylindrical samples, ensure that the end face radius of the cylindrical sample is R and the height is 2R. The value of the end face radius R can be specified according to actual needs.

[0059] S102. Determine the marking lines of the cylindrical sample, and attach multiple strain gauges to the surface of the cylindrical sample based on the extension direction of the marking lines.

[0060] Determine the x-axis, y-axis, and z-axis marker lines for the cylindrical sample; for example... Figure 3As shown, the z-axis is usually chosen along the axial direction of the cylinder, with the center of the end face as the origin; the x-axis is usually chosen as the direction passing through points on the core with special structures or that are easy to mark, or it can be marked manually on the core if no special marking is needed; the y-axis is perpendicular to the x-axis; the x-axis, origin, and y-axis form the XoY plane; the y-axis, origin, and z-axis form the YoZ plane; the z-axis, origin, and x-axis form the ZoX plane; the x-axis, y-axis, and z-axis form a three-dimensional space. Multiple strain gauges are attached to the surface of the cylindrical sample, such as... Figure 4 , Figure 5 As shown, strain gauge 1 is attached to the upper surface of the cylindrical sample along the x-axis; strain gauge 2 is attached to the lower surface of the cylindrical sample along the x-axis; strain gauge 3 is attached to the upper surface of the cylindrical sample along the y-axis; strain gauge 4 is attached to the lower surface of the cylindrical sample along the y-axis; strain gauges 5 and 6 are attached to the side surface of the cylindrical sample along the z-axis; strain gauge 7 is attached to the upper surface of the cylindrical sample at a 45° angle along both the x and y axes; strain gauge 8 is attached to the lower surface of the cylindrical sample at a 45° angle along both the x and y axes; strain gauges 9 and 10 are attached to the side surface of the cylindrical sample at a 45° angle along both the x and z axes; and strain gauges 11 and 12 are attached to the side surface of the cylindrical sample at a 45° angle along both the z and y axes. The length of the strain gauges can be selected according to actual needs, ensuring effective contact between the strain gauges and the surface of the cylindrical sample. Figure 6 This is a top view of a strain gauge attached to a cylindrical sample in an embodiment of the present invention; Figure 7 This is a front view of a strain gauge being attached to a cylindrical sample in an embodiment of the present invention; Figure 8 This is a side view of a strain gauge attached to a cylindrical sample in an embodiment of the present invention.

[0061] S103. Add a coating to the surface of a cylindrical sample with multiple strain gauges attached to it to obtain a coated cylindrical sample that is enlarged proportionally.

[0062] Multiple strain gauges on the surface of the cylindrical sample are connected to a stress sensor via connecting cables embedded in the coating. The connecting cables can be electrical wires.

[0063] S104. Pressurize the coated cylindrical sample and collect strain data from multiple strain gauges in the coated cylindrical sample during the pressurization process.

[0064] The pressurization process can be hydrostatic or other methods. It can be achieved using a triaxial stress testing device manufactured by GCTS, or other devices with pressurization capabilities. The stress sensor collects strain data from multiple strain gauges in the coated cylindrical sample in real time based on pressure changes during the pressurization process.

[0065] For example, strain data is as follows Figure 5The strain data collected by the 12 strain gauges shown can be represented as ε1, ε2, ε3, ε4, ε5, ε6, ε7, ε8, ε9, ε 10 ε 11 ε 12 ; Figure 9 This is a schematic diagram of a cylindrical sample including an externally compressed rubber sleeve in an embodiment of the present invention.

[0066] S105. Based on the collected strain data, calculate the direction of in-situ stress in the formation of the coated cylindrical sample;

[0067] (1) Based on the collected strain data, calculate the strain components corresponding to the cylindrical sample;

[0068] Based on the fundamental principles of elasticity, the strain analysis and calculation of a cylindrical sample considers six strain components and three principal strains. The formulas for calculating the six strain components corresponding to the cylindrical sample are as follows:

[0069]

[0070] Where, ε x Represents the normal strain in the X direction. ε represents the partial derivative of the displacement component u in the X direction; y This represents the normal strain in the Y direction. ε represents the partial derivative of the displacement component v in the Y direction; z This represents the normal strain in the Z direction. ε represents the partial derivative of the displacement component w in the Z direction; yz Represents the shear strain in the YoZ plane. This represents the partial derivative of the displacement component w in the Y direction. ε represents the partial derivative of the displacement component v in the Z direction; zx Represents the shear strain in the ZoX plane. This represents the partial derivative of the displacement component u in the Z direction. ε represents the partial derivative of the displacement component w in the X direction; xy Represents the shear strain in the XoY plane. This represents the partial derivative of the displacement component v in the X direction. The partial derivative of the displacement component u in the direction.

[0071] By substituting the strain data collected by the stress sensor into the calculation formula for the strain components, the values ​​of the strain components corresponding to the cylindrical sample are obtained. The six strain components can be further expressed as:

[0072]

[0073] Where, εx ε y ε z It is the normal strain in the X, Y, and Z directions, ε xy ε yz ε zx ε1, ε2, ε3, ε4, ε5, ε6, ε7, ε8, ε9, ε 10 ε 11 ε 12 This represents the strain data collected by multiple strain gauges attached to the surface of a cylindrical sample.

[0074] (2) Based on the values ​​of the strain components corresponding to the cylindrical sample, calculate the values ​​of the principal strains corresponding to the cylindrical sample;

[0075] To calculate the principal strains corresponding to the cylindrical sample, since the directions of the three principal strains of the cylindrical sample are orthogonal (i.e., their directions are perpendicular), their dot product is 0. Therefore, the magnitudes of the principal strains satisfy the solution of the following cubic equation:

[0076] ε 3 -I1ε 2 -I2ε 2 -I3=0

[0077] Where ε represents the strain component corresponding to the cylindrical sample; I1, I2, and I3 are the coefficients of the equation;

[0078]

[0079] The values ​​of the strain components corresponding to the cylindrical sample are substituted into the principal strain calculation equation to solve for the three principal strain values ​​ε. ii (i = 1, 2, 3 represent the subscripts indicating the three principal strains), i.e., ε 11 ε 22 ε 33 .

[0080] (3) Based on the values ​​of the strain components and the principal strain corresponding to the cylindrical sample, calculate the direction vector corresponding to the principal strain;

[0081] The formula for calculating the direction vector corresponding to the principal strain is:

[0082]

[0083] Where, ε ii Indicates the value of the principal strain; l i m i n i The direction vectors corresponding to the principal strains are represented by i = 1, 2, and 3, which represent the subscripts indicating the three principal strains.

[0084] In three-dimensional space, the sum of the squares of the direction vectors corresponding to the three principal strains of a cylindrical sample is equal to 1, that is, it satisfies formula l. i 2 +m i 2 +n i 2 =1. Solving this formula simultaneously with the formula for calculating the direction vector corresponding to the principal strain, we can finally obtain:

[0085]

[0086] Among them, l i m i n i It is the direction vector of the principal strain, and i = 1, 2, 3 represent the subscripts of the three principal strains respectively;

[0087] (4) Based on the principal strain direction vector corresponding to the cylindrical sample, and combined with the resistivity core orientation direction obtained by the resistivity core orientation method, the geostress direction of the cylindrical sample in the formation is calculated.

[0088] The angles between the three principal strain directions of the cylindrical sample and the X, Y, and Z axes of the coordinate system fixed on the cylindrical sample (i.e., relative to the marker lines) can be expressed as α. i β i γ i (i = 1, 2, 3).

[0089] Based on the above solution, the three principal strain direction vectors l i m i n i (i = 1, 2, 3), use the inverse cosine function to find the corresponding α. i β i γ i (i = 1, 2, 3) can be represented as:

[0090] α i =arccos l i ,β=arccosm i ,γ=arccosγ i ;

[0091] The angle obtained relative to the mark line is the principal strain direction corresponding to the cylindrical sample.

[0092] The resistivity core orientation method (which is an existing technology and will not be described in detail here) is used to obtain the resistivity core orientation direction of the cylindrical sample. This orientation direction is combined with the principal strain direction of the cylindrical sample to calculate the geostress direction of the cylindrical sample relative to the orientation of the marker line in the strata.

[0093] The technical solution of the present invention will be further explained below in conjunction with a differential strain measurement system:

[0094] The main components of a differential strain measurement system include: a hydraulic pump, a sensor control box and power control host, a pressure chamber, a computer control system, stress sensors, and connecting cables.

[0095] To ensure the accuracy of this method, the height of the cylindrical sample must be equal to its diameter during sample preparation.

[0096] A coated cylindrical sample, numbered YG-021-64, as described above, was obtained and placed in a pressure chamber. The sample was then connected to a stress sensor, the pressure chamber was sealed, and the hydraulic circuit was emptied using a hydraulic pump. Three cycles of pressurization / depressurization were performed, from 150 Psi to 10000 Psi and back to 150 Psi, recording the strain changes throughout the pressurization / depressurization process. The main interface of the computer control system's data acquisition software displays the voltage values ​​of the 12 channels corresponding to the 12 strain gauges in the coated cylindrical sample, and shows the voltage changes of the acquired strain gauges over time as an image. Table 1 shows the data acquired from the 12 strain gauges; DSA1-DSA12 are considered as ε... 1。。。 ε 12 The values ​​in Table 1 are the strain changes that occur when the applied pressure increases from 150 psi to 10000 psi. The strain gauge is essentially a resistor. When a resistor is stretched or compressed under stress, its resistance changes. The strain readings here are already converted data.

[0097] Table 1

[0098] aisle numerical values unit DSA1 +0.003625 E DSA2 +0.003526 E DSA3 -0.02991 E DSA4 -0.02927 E DSA5 -0.04276 E DSA6 -0.04274 E DSA7 -0.01293 E DSA8 -0.01304 E DSA9 -0.01165 E DSA10 -0.01098 E DSA11 -0.01058 E DSA12 -0.01044 E

[0099] Based on the strain data in Table 1 collected by the stress sensor, the direction of the in-situ stress of the cylindrical sample in the formation is calculated as follows:

[0100] (1) Based on the collected strain data, calculate the strain components corresponding to the cylindrical sample;

[0101] By substituting the strain data collected by the stress sensor into the calculation formula for the strain components, the values ​​of the strain components corresponding to the cylindrical sample are obtained. The six strain components can be further expressed as:

[0102] Normal strain in the X direction: εx =1 / 2(ε1+ε2)=0.5*(0.003975+0.004125)=0.004;

[0103] Normal strain in the Y direction: ε y =1 / 2(ε3+ε4)=0.5*(-0.0151-0.0153)=-0.0152;

[0104] Normal strain in the Z direction: ε z =1 / 2(ε5+ε6)=0.5*(-0.0151-0.0153)=-0.0152;

[0105] Shear strain in the XoY plane:

[0106] ε xy =1 / 2(ε7+ε8)-2 0.5 / 2(ε x +ε y )

[0107] =0.5*(-0.04107-0.04107)-1.414 / 2*(0.004-0.0152)

[0108] = -0.03315;

[0109] Shear strain in the ZoX plane:

[0110] ε zx =1 / 2(ε9+ε 10 )-20.5 / 2(ε z +ε x )

[0111] =0.5*(-0.04111-0.04109)-1.414 / 2*(-0.0152+0.004)

[0112] = -0.03318;

[0113] Shear strain in the YoZ plane:

[0114] ε yz =1 / 2(ε 11 +ε 12 )-2 0.5 / 2(ε y +ε z )

[0115] =0.5*(-0.024742--0.024742)-1.414 / 2*(-0.0152-0.0152)=0.003249615.

[0116] (2) Based on the values ​​of the strain components corresponding to the cylindrical sample, calculate the values ​​of the principal strains corresponding to the cylindrical sample;

[0117] To calculate the principal strains corresponding to the cylindrical sample, since the directions of the three principal strains of the cylindrical sample are orthogonal (i.e., their directions are perpendicular), their dot product is 0. Therefore, the magnitudes of the principal strains satisfy the solution of the following cubic equation:

[0118] ε 3 -I1ε 2 -I2ε 2 -I3=0

[0119] The coefficients of the equation are I1 = ε x +ε y +ε z =0.004 - 0.0152 - 0.0152 = -0.03;

[0120] The coefficients of the equation are I² = ε y ε z +ε z ε x +ε x ε y -1 / 4*(ε yz 2 +ε zx 2 +ε xy 2 )

[0121] =0.00035264-1 / 4(ε) yz 2 +ε zx 2 +ε xy 2 )

[0122] = -0.0002;

[0123] The coefficients of the equation are I3 = ε x ε y ε z -1 / 4*(ε x ε yz 2 +ε y ε zx 2 +ε z ε xy 2 )+1 / 4(ε yz +ε zx +ε xy )=9.2416E-07-1 / 4*(0.004*ε yz2 -0.0152ε zx 2 -0.0152ε xy 2 )+1 / 4(ε yz +ε zx +ε xy )=9.2416E-07-1 / 4*(0.004*0.00001056-0.0152*0.0022)

[0124] +1 / 4(0.003249615-0.03318-0.03315)=0;

[0125] Substituting the coefficients I1, I2, and I3 into the equation, we get ε. 3 +0.03ε 2 +0.0002ε=0, solve the equation, and the root of the equation is the value of the principal strain ε. ii The values ​​of the three principal strains are ε 11 =0,ε 22 =-0.01,ε 33 = -0.02.

[0126] (3) Based on the values ​​of the strain components and the principal strain corresponding to the cylindrical sample, calculate the direction vector corresponding to the principal strain;

[0127] The formula for calculating the direction vector corresponding to the principal strain is:

[0128]

[0129] Where, ε ii Indicates the value of the principal strain; l i m i n i The direction vectors corresponding to the principal strains are represented by i = 1, 2, and 3, which represent the subscripts indicating the three principal strains.

[0130] In three-dimensional space, the sum of the squares of the direction vectors corresponding to the three principal strains of a cylindrical sample is equal to 1, that is, it satisfies formula l. i 2 +m i 2 +n i 2 =1. Solving this formula simultaneously with the formula for calculating the direction vector corresponding to the principal strain, we can finally obtain:

[0131]

[0132] Among them, l i m i ni It is the direction vector of the principal strain, and i = 1, 2, 3 represent the subscripts of the three principal strains respectively;

[0133] The values ​​of the strain components and principal strains corresponding to the cylindrical sample obtained through the above calculations are as follows:

[0134] ε 11 =0,ε 22 =-0.01,ε 33 =-0.02

[0135] ε x =0.004m,ε y =-0.0152,ε z = -0.0152

[0136] ε xy =-0.03315,ε zx =-0.03318,ε yz =0.003249615

[0137] Substitute the values ​​of the strain components and the principal strain into the formula for calculating the direction vector corresponding to the principal strain to calculate the principal strain ε. 11 Corresponding direction vectors:

[0138] (0.004-0)l1-0.5*(-0.03315)m1+1 / 2*(-0.03318)n1=0

[0139] 0.5*(-0.03315)l1+(-0.01-0)m1+1 / 2*(0.003249615)n1=0

[0140] After sorting, we can obtain:

[0141] 0.004l1-0.16575m1=0.01659n1

[0142] -0.16575l1-0.01m1=-0.2207n1

[0143]

[0144] The calculation yielded:

[0145] I1 = 1.3356n1, m1 = 0.1320n1

[0146] Will I 1、 Substituting m1 into l1 2 +m1 2 +n1 2 =1, therefore:

[0147] 1.3356 2 n1 2 +0.1320 2 n1 2 +n1 2 =1

[0148] Solving for ε, we get 11 Corresponding direction vectors:

[0149] n1 = 0.5975,

[0150] I1 = 1.3356 * n1 = 0.7980

[0151] m1 = 0.1320 * n1 = 0.0789

[0152] That is, we get ε 11 The corresponding direction vectors are (0.7980, 0.0789, 0.5975).

[0153] Substitute the values ​​of the strain components and the principal strain into the formula for calculating the direction vector corresponding to the principal strain to calculate the principal strain ε. 22 Corresponding direction vectors:

[0154] (0.004+0.01)l2-0.5*0.03315m2-1 / 2*0.03318n2=0

[0155] 1 / 2(-0.03315)l2+(-0.0152+0.01)m2+1 / 2*0.003249615n1=0

[0156] After sorting, we can obtain:

[0157] 0.014*l2-0.16575m2=0.01659n2

[0158] -0.16575l2-0.0052*m2=-0.001624808n2

[0159]

[0160] The calculation yielded:

[0161] I² = 0.0129n², m² = -0.0991n²

[0162] Will I 1、 Substituting m1 into l1 2 +m1 2 +n1 2 =1, therefore:

[0163] 0.01292 n2 2 +(-0.0991) 2 n2 2 +n2 2 =1

[0164] Solving for ε, we get 22 Corresponding direction vectors:

[0165] n2 = 0.9950

[0166] I² = 0.0129

[0167] m2 = -0.0986

[0168] That is, we get ε 22 The corresponding direction vector is (0.0129, -0.0986, 0.9950).

[0169] Substitute the values ​​of the strain components and the principal strain into the formula for calculating the direction vector corresponding to the principal strain to calculate the principal strain ε. 33 Corresponding direction vectors:

[0170] (0.004+0.02)l3-0.5*0.3315m3-1 / 2*0.03318n3=0

[0171] 1 / 2(-0.03315)l3+(-0.0152+0.02)m3+1 / 2*0.003249615n3=0

[0172] L3 2 +m3 2 +n3 2 =1

[0173] After sorting, we can obtain:

[0174] 0.024*l³ - 0.16575m³ = 0.1659n³

[0175] -0.16575l3+0.0048*m3=-0.0016248n3

[0176]

[0177] The calculation yielded:

[0178] I3 = 0.0069n3, m3 = 0.0991n3

[0179] Will I 1、 Substituting m1 into l1 2 +m1 2 +n1 2 =1, therefore:

[0180] 0.0069 2 n3 2 +0.0991 2 n3 2 +n3 2 =1

[0181] Solving for ε, we get 33 Corresponding direction vectors:

[0182] n3 = 0.9951

[0183] I3 = 0.0069

[0184] m3 = -0.0986

[0185] That is, we get ε 33 The corresponding direction vector is (0.0069, -0.0986, 0.9951).

[0186] (4) Based on the principal strain direction vector corresponding to the cylindrical sample and the resistivity core orientation direction obtained by the resistivity core orientation method, the geostress direction of the cylindrical sample in the formation is calculated.

[0187] The angles between the three principal strain directions of the cylindrical sample and the X, Y, and Z axes of the coordinate system fixed on the cylindrical sample (i.e., relative to the marker lines) can be expressed as α. i β i γ i (i = 1, 2, 3).

[0188] Based on the above solution, the three principal strain direction vectors l i m i n i (i = 1, 2, 3), use the inverse cosine function to find the corresponding α. i β i γ i (i = 1, 2, 3) can be represented as:

[0189] α i =arccos l i ,β=arccosm i ,γ=arccosγ i ;

[0190] The angle obtained relative to the mark line is the principal strain direction corresponding to the cylindrical sample. The principal strain direction can be uniformly represented as α. * .

[0191] Resistivity core orientation was performed on the JYG-021-64 cylindrical sample (resistivity core orientation is an existing technique and will not be elaborated here). The orientation direction of the cylindrical sample was obtained by resistivity core orientation. This orientation direction, combined with the principal strain direction of the cylindrical sample, was used to calculate the geostress direction of the JYG-021-64 cylindrical sample in the formation relative to the marker line orientation. The calculation formula can be expressed as:

[0192] α * =β * +θ *

[0193] In the formula: α * The principal strain direction, degrees (°); β * Resistivity is the azimuth direction, in degrees (°); θ* is the direction of geostress relative to the orientation of the marker line, in degrees (°).

[0194] In geological research, the direction of the maximum principal stress in the horizontal direction is of greater interest. Therefore, by comparing the corresponding principal strain values ​​of cylindrical samples, the maximum principal strain corresponding to the maximum principal stress is determined to be ε. 33 The corresponding direction vector is (0.0069, -0.0986, 0.9951).

[0195] The maximum principal strain ε 33 The corresponding direction vectors (0.0069, -0.0986, 0.9951) are projected onto the XoY plane, and the maximum principal strain ε is obtained using inverse cosine. 33 The corresponding direction, namely:

[0196] α*=arccos(-0.0986 / (0.0069^2+(-0.0986)^2)^0.5)=176°.

[0197] A marker position D was selected within the JYG-021-64 cylindrical sample. Resistivity method core orientation was performed on the cylindrical sample, yielding a positioning direction of N 38.4°E. The maximum principal strain ε was then determined. 33 Substituting the direction and positioning direction into the formula above for calculating the direction of in-situ stress of the JYG-021-64 cylindrical sample in the formation, we obtain the direction of the maximum in-situ stress of the JYG-021-64 cylindrical sample in the formation as follows:

[0198] θ*=α*-β*=176°-38.4°=137.6°

[0199] The technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0200] The technical solution of this invention obtains cylindrical core samples of a specified length and height, determines marker lines, and attaches strain gauges along the direction of the marker lines to collect precise strain data. Based on this strain data, the strain components of the cylindrical core sample are calculated. The magnitude and vector of the principal strain of the cylindrical core sample are then calculated using these strain components. Furthermore, combined with the resistivity core orientation obtained through the resistivity method, the direction of in-situ stress in the cylindrical core sample is calculated. This solution, based on limitations on the length, height, and strain gauge attachment positions of the cylindrical core sample, collects strain data from the cylindrical core sample and, combined with resistivity core orientation technology, can accurately determine the direction of in-situ stress in the cylindrical core sample within the formation.

[0201] Figure 10 This is a schematic diagram of a device for obtaining the direction of geostress using a cylindrical sample, provided in an embodiment of the present invention. As shown in the figure, the device includes:

[0202] The acquisition module is used to acquire cylindrical rock core samples;

[0203] The determination module is used to determine the marking lines of the cylindrical sample and to attach multiple strain gauges to the surface of the cylindrical sample based on the extension direction of the marking lines.

[0204] The module is used to add a coating to the surface of a cylindrical sample with multiple strain gauges attached, resulting in a proportionally enlarged coated cylindrical sample.

[0205] The acquisition module is used to pressurize the coated cylindrical sample and acquire strain data from multiple strain gauges in the coated cylindrical sample during the pressurization process.

[0206] The calculation module is used to calculate the geostress direction of the coated cylindrical sample in the formation based on the collected strain data.

[0207] It should be noted that, for ease of explanation, Figure 10 For example, only the main modules of the device structure for obtaining the direction of geostress using a cylindrical sample are shown. In practical applications, the device may also include modules or components not shown in the figure; the device is not limited to the above-described module structure, but may also be other module structures that implement the above method embodiments.

[0208] Figure 11 The present invention provides a schematic diagram of the structure of an electronic device, as shown in the figure. The electronic device includes a processor and a memory.

[0209] The processor is used to read and execute programs and instructions stored in the memory, causing the electronic device to perform the above-described method embodiments.

[0210] It should be noted that, for ease of explanation, Figure 11 For illustrative purposes only, the main components of the electronic device are shown. In practical applications, the electronic device may also include components or parts not shown in the figures.

[0211] The present invention also provides a computer-readable storage medium storing a program or instructions, which, when read and executed by a computer, causes the computer to perform the above-described method embodiments.

[0212] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for obtaining the direction of geostress using a cylindrical sample, characterized in that, include: Obtain cylindrical core samples; Determine the marking lines of the cylindrical sample, and attach multiple strain gauges to the surface of the cylindrical sample based on the extension direction of the marking lines; A coating is added to the surface of a cylindrical sample with multiple strain gauges attached to it, resulting in a proportionally enlarged coated cylindrical sample. A coated cylindrical sample was subjected to pressure treatment, and strain data of multiple strain gauges in the coated cylindrical sample were collected during the pressure treatment process; Based on the collected strain data, the direction of in-situ stress in the formation of the coated cylindrical sample was calculated.

2. The method for obtaining the direction of geostress using a cylindrical sample according to claim 1, characterized in that, include: The cylindrical core sample has an end face radius of R and a height of 2R.

3. The method for obtaining the direction of geostress using a cylindrical sample according to claim 1, characterized in that, The coating of the cylindrical sample is provided with connecting cables, which connect the strain gauge to the stress sensor.

4. The method for obtaining the direction of geostress using a cylindrical sample according to any one of claims 1-3, characterized in that, The calculation of the geostress direction of the coated cylindrical sample in the formation based on the collected strain data includes: Based on the collected strain data, the corresponding strain components of the coated cylindrical sample were calculated. Based on the values ​​of the strain components corresponding to the coated cylindrical sample, the values ​​of the principal strain corresponding to the coated cylindrical sample are calculated; Based on the values ​​of the strain components and principal strains corresponding to the coated cylindrical sample, the direction vector corresponding to the principal strain is calculated. Based on the principal strain direction vector corresponding to the coated cylindrical sample, and combined with the resistivity core orientation direction obtained by the resistivity core orientation method, the geostress direction of the coated cylindrical sample in the formation is calculated.

5. A device for obtaining the direction of geostress using a cylindrical sample, characterized in that, include: The acquisition module is used to acquire cylindrical rock core samples; The determination module is used to determine the marking lines of the cylindrical sample and to attach multiple strain gauges to the surface of the cylindrical sample based on the extension direction of the marking lines. The module is used to add a coating to the surface of a cylindrical sample with multiple strain gauges attached, resulting in a proportionally enlarged coated cylindrical sample. The acquisition module is used to pressurize the coated cylindrical sample and acquire strain data from multiple strain gauges in the coated cylindrical sample during the pressurization process. The calculation module is used to calculate the geostress direction of the coated cylindrical sample in the formation based on the collected strain data.

6. The apparatus for obtaining the direction of geostress using a cylindrical sample according to claim 5, characterized in that, include: The cylindrical core sample has an end face radius of R and a height of 2R.

7. The apparatus for obtaining the direction of geostress using a cylindrical sample according to claim 5, characterized in that, The coating of the cylindrical sample is provided with connecting cables, which connect the strain gauge to the stress sensor.

8. The apparatus for obtaining the direction of geostress using a cylindrical sample according to any one of claims 5-7, characterized in that, The computing module is also used for: Based on the collected strain data, the corresponding strain components of the coated cylindrical sample were calculated. Based on the values ​​of the strain components corresponding to the coated cylindrical sample, the values ​​of the principal strain corresponding to the coated cylindrical sample are calculated; Based on the values ​​of the strain components and principal strains corresponding to the coated cylindrical sample, the direction vector corresponding to the principal strain is calculated. Based on the principal strain direction vector corresponding to the coated cylindrical sample, and combined with the resistivity core orientation direction obtained by the resistivity core orientation method, the geostress direction of the coated cylindrical sample in the formation is calculated.

9. An electronic device, characterized in that, include: Processor and memory; The processor is coupled to the memory; The processor is configured to read and execute the program or instructions stored in the memory, causing the device to perform the method as described in any one of claims 1-4.

10. A computer-readable storage medium, characterized in that, The device contains a computer program that, when executed by a processor, implements the method as described in any one of claims 1-4.

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