Method for measuring anisotropy of acoustic velocity and resistivity of stratified shale

Abstract

The invention discloses a method for measuring acoustic velocity and resistivity anisotropy of stratified shale. The method comprises the following steps: 1, acquiring a rock core sample; 2, arranging a marker line on the rock core sample, and arranging two groups of acoustoelectric transceiving probes on the side surface of the rock core sample; 3, overlapping the marker line and the axis of a group of acoustoelectric transceiving probes to serve as an initial orientation, placing a top column on the rock core sample, and then applying triaxial stress to the rock core sample; 4, measuring the resistance and the acoustic velocity of the rock core sample in the initial orientation; 5, rotating the rock core sample for multiple times, repeating the steps 3 and 4, and measuring the resistance and sound wave speed of each group of acoustoelectric receiving and transmitting probes at each angle; 6, calculating the average resistance and the average acoustic velocity of the rock core sample at each angle; and 7, calculating the resistivity anisotropy coefficient and the sound wave anisotropy coefficient of the rock core sample at each angle. The technical problems that in the prior art, the number of measurement directions is small, a large number of samples are consumed, and the influence of lithology heterogeneity is obvious are solved.

Description

Technical Field

[0001] The invention relates to the technical field of rock physics experiments, and in particular to a method for measuring acoustic wave velocity and resistivity anisotropy of stratigraphic shale. Background Art

[0002] Rock acoustic velocity and resistivity are important physical information in the field of geophysics. Measuring rock acoustic velocity and resistivity under laboratory conditions is an important means of geophysical research and the basis for quantitative evaluation of mineral resources such as oil and gas. The acoustic velocity and resistivity of unconventional reservoirs such as shale have strong anisotropy, that is, the acoustic velocity and resistivity measured in different directions are different, which makes it difficult to evaluate mineral resources. Therefore, it is necessary to measure the anisotropy of the acoustic velocity and resistivity of formation rocks under laboratory conditions.

[0003] There are two main types of experimental measurement methods for anisotropy of formation acoustic velocity and resistivity:

[0004] like Figure 1 As shown in the figure, the first type is to process cubic rock samples and measure the acoustic wave velocity and resistivity of the rock samples in three directions, namely, X, Y, and Z. However, the limitation of this type of method is that the sample can be measured in a limited number of directions, and the acoustic wave velocity and resistivity can only be measured in three directions, and the relative position relationship of the three directions is fixed.

[0005] like Figure 2 As shown, the second type is to drill conventional plunger cores (cylindrical cores with a diameter of 1 inch) in different directions on outcrop rocks or full-diameter cores, and then put the plunger cores taken from different directions into conventional clamps for measurement of acoustic wave velocity and resistivity. This type of scheme can flexibly select the direction of measurement, and the number can be set arbitrarily. However, it has two main disadvantages: on the one hand, a large number of cores are consumed, and the cost is high for downhole coring samples. On the other hand, the acoustic wave velocity and resistivity in different directions are measured on different core samples. When the lithology of the formation rock is highly heterogeneous, the lithology of different samples is quite different (for example, there may be sporadic pyrite distribution in shale, and the content of pyrite in different plunger samples may be significantly different). Therefore, the differences caused by lithological heterogeneity in the final measurement results may mask the anisotropy caused by factors such as bedding direction.

[0006] In addition, the patent document with publication number CN107037129A discloses a rock anisotropy measuring clamp and a measuring method thereof, which mainly includes a base, a guide rail, a slider, a propulsion part, a fixing part, a pressure gauge and an acoustic wave receiving device. An angle adjustment device and an angle pointer are provided on the propulsion part, and a displacement scale is provided on the base. It can measure the acoustic anisotropy characteristics of the core at different angles, and can more realistically reflect the physical response of the rock in the actual formation. However, this prior art requires that the axial direction of the cylindrical core and the axial direction of the acoustic wave probe be kept consistent during measurement, that is, when measuring rock anisotropy based on this prior art, at any angle, the propagation direction of the acoustic wave is always consistent with the axial direction of the cylindrical sample. And, if Figure 3 As shown in the figure, the prior art changes the vibration direction of the transverse wave of the sound wave in the rock core by adjusting the angle, but does not change the propagation direction of the sound wave in the rock core. For the longitudinal wave measurement of the sound wave, this technology will fail, because the propagation direction and vibration direction of the longitudinal wave are both axial to the rock core, and changing the angle will not change the propagation path of the sound wave, so the final measurement result cannot effectively reflect the rock and anisotropy. Summary of the invention

[0007] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art, and provide a method for measuring the acoustic wave velocity and resistivity anisotropy of layered shale. During measurement, the present invention can change the propagation direction of the acoustic wave in the core sample by adjusting the angle of the core sample, so that the acoustic wave velocity and resistivity anisotropy can be measured from multiple directions on the same core sample, which can not only effectively reflect the differences in the propagation of the acoustic wave in the rock along different directions, but also solve the technical problems in the prior art of few measurement directions, high sample consumption and obvious influence of lithology heterogeneity.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] A method for measuring acoustic velocity and resistivity anisotropy of stratified shale, characterized by comprising the following steps:

[0010] Step 1: Obtain a cylindrical core sample from the stratified shale and ensure that the anisotropy of the rock physical parameters can be reflected on the end surface of the core sample;

[0011] Step 2: Place the core sample on the measuring seat, set a mark line through the center of the circle on the top surface of the core sample, and then set two sets of mutually perpendicular acoustic and electric transceiver probes on the side of the core sample, each set of acoustic and electric transceiver probes includes acoustic and electric transmitting probes and acoustic and electric receiving probes symmetrically arranged on both sides of the core sample, and the axis of each set of acoustic and electric transceiver probes intersects perpendicularly with the axis of the core sample;

[0012] Step 3: overlap the marking line with the axis of one set of acoustic and electric transceiver probes as the initial orientation, place a top column on the top surface of the core sample, and apply triaxial stress to the core sample from the X, Y, and Z directions through the top column and the two sets of acoustic and electric transceiver probes;

[0013] Step 4: Use two sets of acoustic and electrical transceiver probes to measure the core sample, and obtain the resistance and acoustic wave velocity when the axis overlaps the marking line, and obtain the resistance and acoustic wave velocity when the axis is perpendicular to the marking line;

[0014] Step 5: Remove the triaxial stress, remove the top column and the acoustic and electrical transceiver probes, and then rotate the core sample several times. Repeat steps 3 and 4 after each rotation to obtain the resistance and acoustic wave velocity of each set of acoustic and electrical transceiver probes at various angles.

[0015] Step 6: Based on the resistance and acoustic wave velocity measured by the two sets of acoustic and electrical transceiver probes at the same angle relative to the marker line, the average resistance and average acoustic wave velocity of the core sample at each angle are calculated respectively;

[0016] Step 7: Calculate the resistivity anisotropy coefficient of the core sample at each angle based on the average resistance at each angle and the average resistance when the acoustic and electrical transceiver probe is perpendicular to the marking line, and calculate the acoustic anisotropy coefficient of the core sample at each angle based on the average acoustic wave velocity at each angle.

[0017] In step 6, the resistivity anisotropy coefficient is calculated as:

[0018]

[0019] Among them, α 电( θ) is the resistivity anisotropy coefficient of the core sample at angle θ, r(θ) is the average resistivity of the core sample at angle θ, and r 90 is the average resistivity of the core sample when the acoustic and electrical transceiver probe is perpendicular to the marker line, R(θ) is the average resistance of the core sample at angle θ, and R 90 is the average resistance of the core sample when the acoustic and electrical transceiver probe is perpendicular to the marking line, and K is the constant of the core sample.

[0020] In step 6, the calculation method of the acoustic anisotropy coefficient is:

[0021]

[0022] Among them, α 声( θ) is the acoustic anisotropy coefficient of the core sample at angle θ, V(θ) is the average acoustic velocity of the core sample at angle θ, and V 0is the average acoustic velocity of the core sample when the axis overlaps the marker line, Δt(θ) is the time difference taken by the acoustic signal of the core sample at angle θ from the acoustic-electric transmitting probe to the acoustic-electric receiving probe, Δt 0 It is the time difference of the acoustic wave signal from the acoustic and electrical transmitting probe to the acoustic and electrical receiving probe when the axis of the core sample overlaps with the marking line, and D is the diameter of the core sample.

[0023] In step 1, the axis of the core sample is parallel to the bedding plane of the layered shale.

[0024] In step 2, the measuring seat includes a circular base plate and four limit cards evenly fixed on the base plate, the four limit cards are distributed at 90 degrees to each other, and the distances between the four limit cards and the center of the base plate are equal and equal to the radius of the core sample.

[0025] In step 2, the inner sides of the limit cards are all arc surfaces with a curvature radius equal to the core radius.

[0026] In step 2, any acoustic and electrical transmitting probe / acoustic and electrical receiving probe is located between two adjacent limit cards, and the acoustic and electrical transmitting and receiving probe and the limit card are placed at 45 degrees to each other.

[0027] In step 2, a plurality of straight lines passing through the center of the circle with equal angles are engraved on the base plate.

[0028] In step 2, the angle of the straight line passing through the center of the circle on the base plate is 10°-20°.

[0029] In step 3, the outer diameter of the top column is smaller than the outer diameter of the core sample.

[0030] The advantages of adopting the present invention are:

[0031] 1. Compared with the prior art, the present invention can reduce the sampling consumption of core samples, and can measure the anisotropy of acoustic waves and resistivity from multiple directions on a core sample, which greatly reduces the number of rock samples required for the experiment and reduces the sampling consumption. Overall, compared with the traditional prior art, the present invention can obtain richer and more accurate acoustic wave velocity and resistivity anisotropy information based on fewer core samples, which is more practical and innovative. In addition, the measurement results of the present invention can reflect the anisotropic differences in the propagation velocity of acoustic waves in different directions, and are applicable to both longitudinal waves and transverse waves.

[0032] 2. The present invention improves the accuracy of the experimental results, because the rock physical responses in different directions obtained in the experiment are all from the same sample, and the obtained anisotropy coefficient is hardly affected by the lithological heterogeneity of the sample. The existing technology uses different core samples to measure the anisotropy coefficient of rock physical responses in different directions, which is easily affected by the differences in the mineral composition of the samples.

[0033] 3. The orientation of the experiment of the present invention is flexible and changeable. During the experiment, the core can be placed at will according to the experimenter's idea to obtain different measurement orientations, and it can be adjusted at any time. The azimuth that can be examined by the prior art is determined at the time of sampling, which is fixed and immutable, and has poor flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the structure of measuring rock anisotropy based on a cubic core in the prior art;

[0035] Figure 2 It is a schematic diagram of the structure of measuring rock anisotropy using several plunger cores in the prior art;

[0036] Figure 3 A schematic diagram of the direction of sound wave propagation during measurement using the prior art;

[0037] Figure 4 It is a flowchart of the present invention;

[0038] Figure 5 is a schematic diagram of a core sample in the present invention;

[0039] Figure 6 It is a schematic diagram of the structure of the measuring seat in the present invention;

[0040] Figure 7 It is a schematic diagram of the structure of the present invention during measurement;

[0041] Figure 8 It is a plane schematic diagram of the propagation direction of the sound wave during measurement of the present invention;

[0042] Fig. 9 It is a three-dimensional schematic diagram of the propagation direction of sound waves during measurement of the present invention;

[0043] Fig.10 This is a graph showing the resistivity anisotropy coefficient, longitudinal wave and shear wave anisotropy coefficient of the core sample changing with angle during measurement.

[0044] The markings in the figure are: 1. core sample, 2. base plate, 3. limit card, 4. top column, 5. acoustic and electric transceiver probe, 6. straight line through the center of the circle. DETAILED DESCRIPTION

[0045] Example 1

[0046] like Figure 4 As shown, this embodiment provides a method for measuring the acoustic velocity and resistivity anisotropy of stratified shale, which includes the following steps:

[0047] Step 1: Drill a 1.5-inch (or other size) cylindrical core sample from a full-diameter core or outcrop of stratified shale and ensure that the anisotropy of the rock physical parameters is reflected on the end face of the core sample. For example, Figure 5 As shown in Figure 2, for layered anisotropic shale, the axial direction of the core sample should be parallel to the bedding plane of the layered shale.

[0048] Step 2: Set up a non-conductive measuring seat, place the core sample on the measuring seat, and set a mark line through the center of the circle on the top surface of the core sample. For stratified shale, it is recommended that the mark line be parallel to the bedding plane, or that the mark line be consistent with the wellbore orientation of the horizontal well in the target layer of the study area.

[0049] Then, two groups of mutually perpendicular acoustic and electric transceiver probes are arranged on the sides of the core sample, each group of acoustic and electric transceiver probes includes an acoustic and electric transmitting probe and an acoustic and electric receiving probe, and the acoustic and electric transmitting probe and the acoustic and electric receiving probe of each group of acoustic and electric transceiver probes are symmetrically arranged on both sides of the core sample, and the axis of the acoustic and electric transmitting probe in each group of acoustic and electric transceiver probes coincides with the axis of the acoustic and electric receiving probe, and the axes of both intersect with the axis of the core sample at right angles.

[0050] It should be noted that the four acoustic and electric probes (two acoustic and electric transmitting probes and two acoustic and electric receiving probes) in the two groups of acoustic and electric transmitting and receiving probes are distributed at 90 degrees to each other. Between the acoustic and electric transmitting probes and the acoustic and electric receiving probes, the acoustic and electric transmitting probes generate acoustic wave pulse signals, and the time difference from the acoustic wave emission to the acoustic and electric receiving probes receiving the acoustic wave signals is measured and recorded. Based on the ratio of the core diameter to the recorded time difference, the acoustic wave velocity of the core sample in this direction can be obtained. In addition, the resistance measurement can be directly measured by an impedance analyzer to obtain the resistance between the acoustic and electric transmitting probe and the acoustic and electric receiving probe.

[0051] Step 3: Rotate the core sample and overlap the marking line with the axis of one set of acoustic and electric transceiver probes as the initial orientation, then place a top column on the top surface of the core sample, the outer diameter of which is smaller than the outer diameter of the core sample; after placing the top column, apply triaxial stress to the core sample from the X, Y, and Z directions through the top column and two sets of acoustic and electric transceiver probes.

[0052] Step 4: Measure the core sample using two sets of acoustic and electrical transceiver probes to obtain the resistance and acoustic wave velocity when the axis overlaps the marking line, and the resistance and acoustic wave velocity when the axis is perpendicular to the marking line.

[0053] Since two groups of acoustic and electric transceiver probes are provided in this embodiment, two resistance values ​​and two sound wave velocity values ​​can be measured in the initial orientation, specifically, the resistance value and the sound wave velocity value when the axis of one group of acoustic and electric transceiver probes overlaps with the marking line, and the resistance value and the sound wave velocity value when the axis of the other group of acoustic and electric transceiver probes is perpendicular to the marking line.

[0054] Step 5: Remove the triaxial stress, remove the top column and the acoustic and electric transceiver probes, and then rotate the core sample several times. Repeat steps 3 and 4 after each rotation to obtain the resistance and acoustic wave velocity of each set of acoustic and electric transceiver probes at various angles.

[0055] This step is based on two sets of acoustic and electric transceiver probes. After each rotation of the core sample, two resistance values ​​and two acoustic wave velocity values ​​can also be measured. Since the two sets of acoustic and electric transceiver probes are perpendicular to each other, it is only necessary to rotate the core sample 90 degrees to change the overlap of the marking line with the axis of the first set of acoustic and electric transceiver probes to overlap with the second set of acoustic and electric transceiver probes. At the same time, the marking line will be perpendicular to the first set of acoustic and electric transceiver probes. The rotation process from 90-180 degrees will repeat the rotation process of 0-90 degrees. Therefore, in the actual measurement process, the core sample is rotated multiple times, each time by 10-30 degrees. Of course, according to actual needs, each rotation can also be 5 degrees, 45 degrees or other angles.

[0056] Step 6: Based on the resistance and acoustic wave velocity measured by the two sets of acoustic and electrical transceiver probes at the same angle relative to the marking line, calculate the average resistance and average acoustic wave velocity of the core sample at each angle.

[0057] It should be noted that the average resistance in this step is calculated based on the resistance measured by the two groups of acoustic and electric transceiver probes at the same angle relative to the marking line, and the average acoustic wave velocity is calculated based on the acoustic wave velocity measured by the two groups of acoustic and electric transceiver probes at the same angle relative to the marking line. For example, when the core sample is rotated 30 degrees, the angle of the first group of acoustic and electric transceiver probes relative to the marking line is 30 degrees, and the angle of the second group of acoustic and electric transceiver probes relative to the marking line is 60 degrees. At this time, the first group of acoustic and electric transceiver probes measure the resistance and acoustic wave velocity at 30 degrees, and the second group of acoustic and electric transceiver probes measure the resistance and acoustic wave velocity at 60 degrees. After rotating the core sample 30 degrees again, the angle of the first group of acoustic and electric transceiver probes relative to the marking line is 60 degrees, and the angle of the second group of acoustic and electric transceiver probes relative to the marking line is 30 degrees. At this time, the first group of acoustic and electric transceiver probes measure the resistance and acoustic wave velocity at 60 degrees, and the second group of acoustic and electric transceiver probes measure the resistance and acoustic wave velocity at 30 degrees. Then the average resistance at 30 degrees is calculated by averaging the resistance at 30 degrees measured by the first group of acoustic and electric transceiver probes and the resistance at 30 degrees measured by the second group of acoustic and electric transceiver probes. The average resistance at 60 degrees is calculated by averaging the resistance at 60 degrees measured by the first group of acoustic and electric transceiver probes and the resistance at 60 degrees measured by the second group of acoustic and electric transceiver probes. The average sound wave velocity at 30 degrees is calculated by averaging the sound wave velocity at 30 degrees measured by the first group of acoustic and electric transceiver probes and the sound wave velocity at 30 degrees measured by the second group of acoustic and electric transceiver probes. The average sound wave velocity at 60 degrees is calculated by averaging the sound wave velocity at 60 degrees measured by the first group of acoustic and electric transceiver probes and the sound wave velocity at 60 degrees measured by the second group of acoustic and electric transceiver probes. Based on this, the accuracy of the measurement results can be effectively improved.

[0058] Step 7: Calculate the resistivity anisotropy coefficient of the core sample at each angle based on the average resistance at each angle and the average resistance when the acoustic and electrical transceiver probe is perpendicular to the marking line, and calculate the acoustic anisotropy coefficient of the core sample at each angle based on the average acoustic wave velocity at each angle.

[0059] In actual measurement, the direction of sound wave propagation is Figure 8 , 9 As shown, this is different from the prior art Figure 3 The acoustic wave propagation method shown is completely different, so the present invention can obtain richer and more accurate acoustic wave velocity and resistivity anisotropy information based on fewer core samples, and the measurement results can also reflect the anisotropic differences in the acoustic wave propagation velocity in different directions, which is applicable to both longitudinal waves and shear waves.

[0060] Example 2

[0061] Based on Example 1, this example further defines the calculation method of the resistivity anisotropy coefficient and the calculation method of the acoustic anisotropy coefficient. Specifically,

[0062] For the resistivity anisotropy coefficient, although the core sample is not a medium with uniform cross section in the measurement direction, the shape of the rock in all directions is exactly the same, so the resistivity r and resistor R It can be expressed as r =KR. When the size and shape of the contact surface between the electrode and the core sample, as well as the size and shape of the core sample are fixed, K is a constant. Therefore, the resistivity anisotropy coefficient can be directly obtained from the measured resistance, and its calculation method is:

[0063]

[0064] Among them, α 电 (θ) is the resistivity anisotropy coefficient of the core sample at angle θ, r(θ) is the average resistivity of the core sample at angle θ, and r 90 is the average resistivity of the core sample when the acoustic and electrical transceiver probe is perpendicular to the marker line, R(θ) is the average resistance of the core sample at angle θ, and R 90 is the average resistance of the core sample when the acoustic and electrical transceiver probe is perpendicular to the marking line, and K is the constant of the core sample.

[0065] Similarly, the calculation method of the acoustic anisotropy coefficient is:

[0066]

[0067] Among them, α 声( θ) is the acoustic anisotropy coefficient of the core sample at angle θ, V(θ) is the average acoustic velocity of the core sample at angle θ, and V 0 is the average acoustic velocity of the core sample when the axis overlaps the marker line, Δt(θ) is the time difference taken by the acoustic signal of the core sample at angle θ from the acoustic-electric transmitting probe to the acoustic-electric receiving probe, Δt 0 It is the time difference of the acoustic wave signal from the acoustic and electrical transmitting probe to the acoustic and electrical receiving probe when the axis of the core sample overlaps with the marking line, and D is the diameter of the core sample.

[0068] Example 3

[0069] like Figure 4 As shown, this embodiment provides a method for measuring the acoustic velocity and resistivity anisotropy of stratified shale, which includes the following steps:

[0070] Step 1: Drill a 1.5-inch (or other size) cylindrical core sample from a full-diameter core or outcrop of stratified shale and ensure that the anisotropy of the rock physical parameters is reflected on the end face of the core sample. For example, Figure 5As shown in Figure 2, for layered anisotropic shale, the axial direction of the core sample should be parallel to the bedding plane of the layered shale.

[0071] Step 2: Set up a non-conductive measuring seat, place the core sample on the measuring seat, and set a mark line through the center of the circle on the top surface of the core sample. For stratified shale, it is recommended that the mark line be parallel to the bedding plane, or that the mark line be consistent with the wellbore orientation of the horizontal well in the target layer of the study area.

[0072] Then, two groups of mutually perpendicular acoustic and electric transceiver probes are arranged on the sides of the core sample, each group of acoustic and electric transceiver probes includes an acoustic and electric transmitting probe and an acoustic and electric receiving probe, and the acoustic and electric transmitting probe and the acoustic and electric receiving probe of each group of acoustic and electric transceiver probes are symmetrically arranged on both sides of the core sample, and the axis of the acoustic and electric transmitting probe in each group of acoustic and electric transceiver probes coincides with the axis of the acoustic and electric receiving probe, and the axes of both intersect with the axis of the core sample at right angles.

[0073] like Figure 6 As shown, the measuring seat in this embodiment includes a circular base plate and four limit cards evenly fixed on the base plate, the four limit cards are distributed at 90° to each other, and the four limit cards are at equal distances from the center of the base plate and are equal to the radius of the core sample. Any acoustic electric transmitting probe / acoustic electric receiving probe is located between two adjacent limit cards, and the four acoustic electric probes (two acoustic electric transmitting probes and two acoustic electric receiving probes) and the four limit cards are placed at 45° to each other. In addition, in order to better limit the core sample, this embodiment also sets the inner side of the limit card to an arc surface with a curvature radius equal to the core radius.

[0074] Step 3: If Figure 7 As shown, the core sample is rotated, and the marking line is overlapped with the axis of one set of acoustic and electric transceiver probes as the initial orientation, and then a top column is placed on the top surface of the core sample, and the outer diameter of the top column is smaller than the outer diameter of the core sample; after the top column is placed, triaxial stress is applied to the core sample from the X, Y, and Z directions respectively through the top column and the two sets of acoustic and electric transceiver probes.

[0075] Step 4: Measure the core sample using two sets of acoustic and electrical transceiver probes to obtain the resistance and acoustic wave velocity when the axis overlaps the marking line, and the resistance and acoustic wave velocity when the axis is perpendicular to the marking line.

[0076] Step 5: Remove the triaxial stress, remove the top column and the acoustic and electric transceiver probes, and then rotate the core sample several times. Repeat steps 3 and 4 after each rotation to obtain the resistance and acoustic wave velocity of each set of acoustic and electric transceiver probes at various angles.

[0077] Step 6: Calculate the average resistance and average acoustic wave velocity of the core sample at each angle based on the resistance and acoustic wave velocity measured by the two sets of acoustic and electrical transceiver probes at the same angle relative to the marker line. The calculation method is the same as that in Example 2 and will not be repeated here.

[0078] Step 7: Calculate the resistivity anisotropy coefficient of the core sample at each angle based on the average resistance at each angle and the average resistance when the acoustic and electrical transceiver probe is perpendicular to the marking line, and calculate the acoustic anisotropy coefficient of the core sample at each angle based on the average acoustic wave velocity at each angle.

[0079] Example 4

[0080] like Figure 4 As shown, this embodiment provides a method for measuring the acoustic velocity and resistivity anisotropy of stratified shale, which includes the following steps:

[0081] Step 1: Drill a 1.5-inch (or other size) cylindrical core sample from a full-diameter core or outcrop of stratified shale and ensure that the anisotropy of the rock physical parameters is reflected on the end face of the core sample. For example, Figure 5 As shown in Figure 2, for layered anisotropic shale, the axial direction of the core sample should be parallel to the bedding plane of the layered shale.

[0082] Step 2: Set up a non-conductive measuring seat, place the core sample on the measuring seat, and set a mark line through the center of the circle on the top surface of the core sample. For stratified shale, it is recommended that the mark line be parallel to the bedding plane, or that the mark line be consistent with the borehole orientation of the horizontal well of the target layer in the study area. Then set up two sets of mutually perpendicular acoustic and electric transceiver probes on the side of the core sample, each set of acoustic and electric transceiver probes includes an acoustic and electric transmitting probe and an acoustic and electric receiving probe, and the acoustic and electric transmitting probe and the acoustic and electric receiving probe of each set of acoustic and electric transceiver probes are symmetrically arranged on both sides of the core sample, and the axis of the acoustic and electric transmitting probe in each set of acoustic and electric transceiver probes coincides with the axis of the acoustic and electric receiving probe, and the axes of both intersect perpendicularly with the axis of the core sample.

[0083] like Figure 6 As shown, the measuring seat in this embodiment includes a circular base plate and four limit cards evenly fixed on the base plate, the four limit cards are distributed at 90° to each other, and the four limit cards are at equal distances from the center of the base plate and are equal to the radius of the core sample. Any acoustic electric transmitting probe / acoustic electric receiving probe is located between two adjacent limit cards, and the four acoustic electric probes (two acoustic electric transmitting probes and two acoustic electric receiving probes) and the four limit cards are placed at 45° to each other. In addition, in order to better limit the core sample, this embodiment also sets the inner side of the limit card to an arc surface with a curvature radius equal to the core radius.

[0084] Step 3: If Figure 7 As shown, the core sample is rotated, and the marking line is overlapped with the axis of one set of acoustic and electric transceiver probes as the initial orientation, and then a top column is placed on the top surface of the core sample, and the outer diameter of the top column is smaller than the outer diameter of the core sample; after the top column is placed, triaxial stress is applied to the core sample from the X, Y, and Z directions respectively through the top column and the two sets of acoustic and electric transceiver probes.

[0085] Step 4: Measure the core sample using two sets of acoustic and electrical transceiver probes to obtain the resistance and acoustic wave velocity when the axis overlaps the marking line, and the resistance and acoustic wave velocity when the axis is perpendicular to the marking line.

[0086] Step 5: Remove the triaxial stress, remove the top column and the acoustic and electric transceiver probes, and then rotate the core sample several times. Repeat steps 3 and 4 after each rotation to obtain the resistance and acoustic wave velocity of each set of acoustic and electric transceiver probes at various angles.

[0087] Step 6: Calculate the average resistance and average acoustic wave velocity of the core sample at each angle based on the resistance and acoustic wave velocity measured by the two sets of acoustic and electrical transceiver probes at the same angle relative to the marker line. The calculation method is the same as that in Example 2 and will not be repeated here.

[0088] Step 7: Calculate the resistivity anisotropy coefficient of the core sample at each angle based on the average resistance at each angle and the average resistance when the acoustic and electrical transceiver probe is perpendicular to the marking line, and calculate the acoustic anisotropy coefficient of the core sample at each angle based on the average acoustic wave velocity at each angle.

[0089] In step 2 of this embodiment, in order to facilitate the adjustment of the angle of the core when placing the core, so as to achieve accurate measurement of different azimuth angles, this embodiment also engraves a number of equally distributed through-center straight lines on the base plate, and the angle between each two adjacent through-center straight lines is 10°-20°, but preferably 15°. Of course, this angle is only used for reference when rotating the core sample, and it can also be other angles.

[0090] Example 5

[0091] The applicant also verified the present invention by the method described in Example 4, as follows:

[0092] The applicant obtained a layer of rational shale cylindrical sample from a well in the Sichuan Basin. The sample diameter is 1.5 inches. Parallel bedding planes can be seen on the end face of the cylinder. The method described in the present invention is used to measure the acoustic wave and resistivity anisotropy of the sample. During the measurement, the three-axis pressure is set to 1Mpa, the measurement angle interval is 10°, and a marking line parallel to the bedding plane is drawn on the end face through the center of the circle. After measurement, Fig.10 The resistivity anisotropy coefficient, longitudinal wave and shear wave anisotropy coefficient of the core samples vary with angle as shown in the table below.

[0093]

[0094] Depend on Fig.10 As can be seen from the above table, at the initial angle, that is, when the rotation angle is 0°, the longitudinal and transverse wave velocities of the sample are the largest, and the resistivity is the smallest, because the propagation speed of sound waves along the bedding is the fastest, and the resistivity is the smallest in the direction along the bedding. When the rotation angle is 90°, the longitudinal and transverse wave velocities of the sample are the smallest, and the resistivity is the largest, because the propagation speed of sound waves perpendicular to the bedding is the slowest, and the resistivity is the largest in the direction perpendicular to the bedding. Therefore, the anisotropy coefficients of the longitudinal and transverse wave velocities decrease from 1 as the rotation angle increases from 0° to 90°, and eventually decay to 0.787 and 0.740, respectively; the resistivity anisotropy coefficient increases from 0.135 to 1 as the rotation angle increases from 0° to 90°. The experimental rules are consistent with the theoretical cognition of rock physics, confirming the correctness and feasibility of the present invention.

[0095] The above description is only a specific implementation mode of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other alternative features that are equivalent or have similar purposes; all the disclosed features, or all the steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A method for measuring the acoustic velocity and resistivity anisotropy of stratified shale, characterized in that The following steps are involved: Step 1: Obtain a cylindrical core sample from the stratified shale and ensure that the anisotropy of the rock physical parameters can be reflected on the end surface of the core sample; Step 2: Place the core sample on the measuring seat, set a mark line through the center of the circle on the top surface of the core sample, and then set two sets of mutually perpendicular acoustic and electric transceiver probes on the side of the core sample, each set of acoustic and electric transceiver probes includes acoustic and electric transmitting probes and acoustic and electric receiving probes symmetrically arranged on both sides of the core sample, and the axis of each set of acoustic and electric transceiver probes intersects perpendicularly with the axis of the core sample; Step 3: overlap the marking line with the axis of one set of acoustic and electric transceiver probes as the initial orientation, place a top column on the top surface of the core sample, and apply triaxial stress to the core sample from the X, Y, and Z directions through the top column and the two sets of acoustic and electric transceiver probes; Step 4: Use two sets of acoustic and electrical transceiver probes to measure the core sample, and obtain the resistance and acoustic wave velocity when the axis overlaps the marking line, and obtain the resistance and acoustic wave velocity when the axis is perpendicular to the marking line; Step 5: Remove the triaxial stress, remove the top column and the acoustic and electrical transceiver probes, and then rotate the core sample several times. Repeat steps 3 and 4 after each rotation to obtain the resistance and acoustic wave velocity of each set of acoustic and electrical transceiver probes at various angles. Step 6: Based on the resistance and acoustic wave velocity measured by the two sets of acoustic and electrical transceiver probes at the same angle relative to the marker line, the average resistance and average acoustic wave velocity of the core sample at each angle are calculated respectively; Step 7: Calculate the resistivity anisotropy coefficient of the core sample at each angle based on the average resistance at each angle and the average resistance when the acoustic and electrical transceiver probe is perpendicular to the marking line, and calculate the acoustic anisotropy coefficient of the core sample at each angle based on the average acoustic wave velocity at each angle.

2. The method for measuring acoustic velocity and resistivity anisotropy of stratigraphic shale according to claim 1, characterized in that: In step 6, the resistivity anisotropy coefficient is calculated as: Among them, α 电( θ) is the resistivity anisotropy coefficient of the core sample at angle θ, r(θ) is the average resistivity of the core sample at angle θ, and r 90 is the average resistivity of the core sample when the acoustic and electrical transceiver probe is perpendicular to the marker line, R(θ) is the average resistance of the core sample at angle θ, and R 90 is the average resistance of the core sample when the acoustic and electrical transceiver probe is perpendicular to the marking line, and K is the constant of the core sample.

3. A method for measuring acoustic velocity and resistivity anisotropy of stratigraphic shale according to claim 1 or 2, characterized in that: In step 6, the calculation method of the acoustic anisotropy coefficient is: Among them, α 声 (θ) is the acoustic anisotropy coefficient of the core sample at angle θ, V(θ) is the average acoustic velocity of the core sample at angle θ, V0 is the average acoustic velocity of the core sample when the axis overlaps with the marking line, Δt(θ) is the time difference taken for the acoustic signal of the core sample at angle θ to travel from the acoustic-electric transmitting probe to the acoustic-electric receiving probe, Δt0 is the time difference taken for the acoustic signal of the core sample to travel from the acoustic-electric transmitting probe to the acoustic-electric receiving probe when the axis overlaps with the marking line, and D is the diameter of the core sample.

4. The method for measuring acoustic velocity and resistivity anisotropy of stratigraphic shale according to claim 1, characterized in that: In step 1, the axis of the core sample is parallel to the bedding plane of the layered shale.

5. The method for measuring acoustic velocity and resistivity anisotropy of stratigraphic shale according to claim 1, characterized in that: In step 2, the measuring seat includes a circular base plate and four limit cards evenly fixed on the base plate, the four limit cards are distributed at 90 degrees to each other, and the distances between the four limit cards and the center of the base plate are equal and equal to the radius of the core sample.

6. The method for measuring acoustic velocity and resistivity anisotropy of stratigraphic shale according to claim 5, characterized in that: In step 2, the inner sides of the limit cards are all arc surfaces with a curvature radius equal to the core radius.

7. The method for measuring acoustic velocity and resistivity anisotropy of stratigraphic shale according to claim 5, characterized in that: In step 2, any acoustic and electrical transmitting probe / acoustic and electrical receiving probe is located between two adjacent limit cards, and the acoustic and electrical transmitting and receiving probe and the limit card are placed at 45 degrees to each other.

8. The method for measuring acoustic velocity and resistivity anisotropy of stratigraphic shale according to claim 1, characterized in that: In step 2, a plurality of straight lines passing through the center of the circle with equal angles are engraved on the base plate.

9. The method for measuring acoustic velocity and resistivity anisotropy of stratigraphic shale according to claim 8, characterized in that: In step 2, the angle of the straight line passing through the center of the circle on the base plate is 10°-20°.

10. The method for measuring acoustic velocity and resistivity anisotropy of stratigraphic shale according to claim 1, characterized in that: In step 3, the outer diameter of the top column is smaller than the outer diameter of the core sample.

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