A rapid measurement device and method for core acoustic wave velocity

Abstract

The present invention provides a rapid core acoustic wave velocity measurement device and method. This device integrates a length measurement device into the holder of a transmission-based ultrasonic measurement device. This device measures core length simultaneously with the acoustic wave propagation time, combining two separate experimental steps into one. This improves the efficiency and accuracy of core acoustic wave velocity measurements and effectively addresses the issue of length inaccuracy when measuring the acoustic wave velocity of irregular, loose, or fractured cores. Furthermore, an experimental method for analyzing the difference between maximum and minimum horizontal in-situ stresses in rock using radial acoustic wave velocity is proposed.

Description

Technical Field

[0001] The invention relates to the field of indoor rock physics experiments, and in particular to a device and method for quickly measuring core ultrasonic velocity. Background Art

[0002] Acoustic wave velocity is a key geophysical property of rock, closely related to geological parameters of oil and gas reservoirs, such as rock porosity, lithology, and fluid content. Dynamic elastic constants calculated from P- and S-wave velocities and density can be used to nondestructively analyze rock mechanical properties. This serves as the basis for geophysical exploration methods such as seismic and acoustic logging in oil and gas geological exploration. Measuring acoustic wave velocity in rock cores in the laboratory is a key tool for studying rock physical response mechanisms and logging and seismic interpretation methods, and is a common core analysis technique.

[0003] Currently, core acoustic wave velocity is measured in the laboratory using the transmission method. According to the current industry standard SY / T6351-2012, "Laboratory Measurement Specification for Acoustic Properties of Rock Samples," the measurement setup primarily consists of a pulse generator, a transmitting transducer, a sample holder, a receiving transducer, and an oscilloscope. The core is typically processed into a cylindrical shape. The core length (L) and the propagation time between the core and the transducer (zero delay t0) are first measured. The core is then loaded into the holder. The pulse generator transmits an electrical pulse to the transmitting transducer, which converts it into an ultrasonic wave. After the signal passes through the core, it is converted back into an electrical pulse in the receiving transducer. The oscilloscope receives and reads the first wave arrival time (t). The core acoustic wave propagation velocity is calculated by dividing the core length (L) by the time it takes the acoustic wave to propagate through the core (t-t0). Currently, all laboratory core acoustic wave velocity measurement devices use this method, but it has two issues: first, the core length measurement and the acoustic wave propagation time measurement are performed separately. Typically, the core length is measured first, followed by the acoustic velocity. These two methods are independent of each other, making them inefficient. Furthermore, when the core is irregular, it is difficult to ensure that the clamping points for length measurement and acoustic wave measurement are consistent, resulting in large errors in acoustic wave velocity measurements. Furthermore, when measuring acoustic wave velocity on a core, a certain amount of pressure is generally required to ensure good coupling. Pressure decreases the core length, and for oil sands and fractured rock samples, the length sometimes varies significantly. Calculating the acoustic wave propagation velocity based on the length measured without pressure can introduce errors.

[0004] When cores are retrieved from high-pressure underground, stress releases, creating microcracks. Horizontally, the direction of maximum stress release, the most cracks, and the slowest acoustic wave velocity occur in the direction of minimum stress. Conversely, the direction of minimum stress experiences the fastest acoustic wave velocity. Based on this principle, measuring the acoustic wave velocity along different diameters of full-diameter core samples is a common experimental method for analyzing in-situ stress. However, cores are often not perfectly cylindrical; their diameters vary in different directions. Using the same diameter to analyze acoustic velocity can lead to errors, affecting the results. Summary of the Invention

[0005] In response to the problems existing in the prior art, the present invention provides a device and method for quickly measuring the acoustic wave velocity of cores, which can simultaneously measure the core length and acoustic wave propagation time, eliminate the influence of the change in the length of the core during pressurization, reduce measurement errors, and improve the efficiency of laboratory core acoustic wave propagation velocity measurements.

[0006] The present invention is achieved through the following technical solutions:

[0007] A core acoustic wave velocity rapid measurement device, comprising a core acoustic wave velocity measurement device, a pressure measurement and control device, and a core length measurement device;

[0008] The core acoustic wave velocity measuring device includes a transmitting transducer, a receiving transducer, a signal generator and an oscilloscope;

[0009] The transmitting transducer and the receiving transducer are respectively arranged at the movable end and the fixed end of the clamp, the transmitting transducer and the receiving transducer are respectively connected to the signal generator and the oscilloscope, the oscilloscope is connected to the control unit, and the control unit is used to detect the speed of the ultrasonic wave. The core is clamped between the transmitting transducer and the receiving transducer;

[0010] The pressure measurement and control device includes a pressure device provided at the movable end of the clamp and a pressure detection device provided at the fixed end. During measurement, the pressure device end can move toward the pressure detection device end to apply axial pressure to the core, and the pressure value is measured by the pressure detection device.

[0011] The length measuring device is arranged on the holder and is used to measure the length of the core between the transmitting transducer and the receiving transducer.

[0012] Preferably, the length measuring device is a linear displacement sensor, a caliper or a micrometer.

[0013] Preferably, the pressure detection device is a pressure sensor or an electronic pressure gauge.

[0014] A measuring method of a core acoustic wave velocity rapid measuring device comprises the following steps:

[0015] Step 1: Place the transmitting transducer in contact with the receiving transducer and pressurize them to a specified pressure P. Record the measured value L1 of the length measuring device as 0, and the transmission time of the ultrasonic wave as t0.

[0016] Step 2: Place the core between the transmitting transducer and the receiving transducer of the holder and pressurize it to the specified pressure P. Record the measured value L2 of the length measuring device and obtain the first wave arrival time t.

[0017] Step 3: Determine the core acoustic wave velocity V based on the measured value L2 and the first wave arrival time t.

[0018] Preferably, the method for determining the core acoustic wave velocity in step 3 is as follows:

[0019] V=(L2-L1) / (t-t0)

[0020] A measurement method for a rapid core acoustic wave velocity measurement device for analyzing horizontal in-situ stress differences in a full-diameter core, comprising the following steps:

[0021] Step 1: Place the transmitting transducer in contact with the receiving transducer and pressurize them to a specified pressure P. Record the measured value L1 of the length measuring device as 0, and the transmission time of the ultrasonic wave as t0.

[0022] Step 2: Clamp the full-diameter core on the indexing plate, turn the angle to 0 degrees, and install it between the two transducers along the diameter direction;

[0023] Step 3: Pressurize to the specified pressure P, record the measured value L2 of the length measuring device, and obtain the first wave arrival time t;

[0024] Step 4: Turn the indexing plate to the set angle and measure the radial sound wave velocity at the set angle according to step 3;

[0025] Step 5: Measure the radial acoustic wave velocity of the core at every set angle according to steps 3 and 4 until 180 degrees, and obtain the radial acoustic wave velocity at each angle;

[0026] Step 6: Use the percentage of the difference between the maximum and minimum acoustic wave velocities to the average acoustic wave velocity at all angles to represent the magnitude of the horizontal stress difference in the core.

[0027] Compared with the prior art, the present invention has the following beneficial technical effects:

[0028] The present invention provides a rapid core acoustic wave velocity measurement device and method. A transducer, a length measuring device, a pressurizing device, and a pressure measuring device are provided on the clamp. The core length is measured while measuring the core acoustic wave propagation time, and the two separate experimental links are combined into one, which greatly improves the efficiency of core acoustic wave velocity measurement, ensures that the clamping position during length measurement and acoustic wave measurement are consistent, and can also eliminate the measurement error caused by the length change when the core is pressurized. It effectively solves the problem of inaccurate length measurement when measuring the acoustic wave velocity of irregular cores, loose cores, and cores with developed fractures. Due to the large error in velocity measurement, radial acoustic wave velocity stress analysis is currently only used to determine the relative direction of maximum and minimum horizontal stresses. The application of this technology can provide the diameter when measuring the acoustic wave in real time, thereby improving the accuracy of velocity measurement, and can further analyze the difference between maximum and minimum horizontal stresses, which is of great significance for analyzing the compressibility of formations. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1This is a schematic structural diagram of the device for rapid measurement of core acoustic wave velocity according to the present invention.

[0030] In the figure: 1 is the core to be tested; 2 is the ultrasonic transmitting or receiving transducer; 3 is the pressurizing device, 4 is the pressure monitoring device; 5 is the core length measuring device; 6 is the core holder; 7 is the signal generator; 8 is the oscilloscope; and 9 is the control unit. DETAILED DESCRIPTION

[0031] The present invention will be further described in detail below with reference to the accompanying drawings, which are intended to explain rather than limit the present invention.

[0032] See Figure 1 , a core acoustic wave velocity rapid measurement device, comprising a core acoustic wave velocity measurement device, a pressure measurement and control device and a core length measurement device;

[0033] A rock core acoustic wave velocity rapid measurement device comprises a conventional rock core acoustic wave velocity measurement system, a pressure measurement and control system and a rock core length measurement device.

[0034] The conventional core acoustic wave velocity measurement system includes a pulse signal generator, a transmitting and receiving transducer oscilloscope 8, and can realize the basic functions of the transmission method core acoustic wave velocity measurement: the signal generator 7 transmits an electric pulse to the transmitting transducer 2, the electric pulse is converted into an acoustic wave, passes through the core 1 to the receiving transducer 2, and is converted into an electric signal again, which is received by the oscilloscope 8. The signal generator 7 transmits a signal to the transmitting transducer 2 and simultaneously transmits a synchronization signal to the oscilloscope 8, so that the time it takes for the acoustic wave to pass through the core (1) can be read on the oscilloscope.

[0035] The pressure measurement and control system includes a pressure device 3 and a pressure monitoring device 4, which are integrated at both ends of the clamp 6 frame, with a transmitting and receiving transducer 2 installed in the middle. During measurement, the end of the pressure device 3 can move toward the end of the pressure detection device 4, thereby applying axial pressure to the core in the middle of the transducer 2, and the pressure is measured and recorded by the pressure detection device 4. The pressure monitoring device is connected to the transmitting (or receiving) transducer and is used to measure the pressure applied to the core when measuring the core length and the sound wave propagation time, and to ensure that the pressure is consistent with the pressure applied when measuring zero delay, thereby eliminating errors caused by different pressures. The pressure monitoring device can be mechanically read and recorded manually, or electronically read and recorded automatically.

[0036] The length measuring device 5 is integrated into the clamp 6, with the measuring end fixed to the pressurizing device 3 and moving with it toward the pressure detection device 4 during measurement. The length of the length measuring device 5 when the transmitting and receiving transducers 2 are connected is set to 0 scale. When measuring the acoustic wave velocity of the core 1, the length reading after clamping the core 1 is the length of the core 1.

[0037] The length measuring device is a vernier caliper, a screw ruler or a linear displacement sensor. The reading method can be mechanical manual reading or electronic automatic reading. In this example, electronic reading is adopted. The length measuring device 5 is connected to the control unit 9, and the length value is displayed and collected on the control unit.

[0038] A method for rapidly measuring core acoustic wave velocity comprises the following steps:

[0039] Step 1. Connect the test device according to the industry standard SY / T 6351-2012 "Laboratory Measurement of Acoustic Properties of Rock Samples";

[0040] Step 2: Drive the pressure block to make the transmitting transducer abut against the receiving transducer, and apply pressure to the specified pressure P. Record the measured value L1 of the length measuring device. At this time, the length is reset to zero. According to the industry standard SY / T 6351-2012 "Laboratory Measurement Specification for Acoustic Properties of Rock Samples", the zero delay t0 of the measurement system is measured.

[0041] Step 3: Place the core between the transmitting and receiving transducers in the holder and apply pressure to the specified pressure P. Record the length measurement value L2 and measure the first wave arrival time t according to the industry standard SY / T 6351-2012, "Laboratory Measurement Specification for Acoustic Properties of Rock Samples."

[0042] Step 4: Calculate the core acoustic wave velocity V based on the measured value L2 and the first ultrasonic wave arrival time t, and the core acoustic wave velocity at the specified pressure P can be obtained.

[0043] V=(L2-L1) / (t-t0)

[0044] Example 1

[0045] Core B is a 1.5-inch diameter plunger core. The lithology is zeolite conglomerate. Zeolite is a framework-structured mineral with high compressibility. In addition, the conglomerate has well-developed fractures at the edges. The acoustic wave velocity is very sensitive to pressure, and the first wave arrival times measured under different pressures vary greatly. Calculating the acoustic wave velocity under pressure using the length measured without pressure will result in a large error. The measurement device and method of the present invention effectively solve this problem. The specific implementation steps are as follows:

[0046] Step 1: Grind the end face B of the plunger core flat and perpendicular to the side face;

[0047] Step 2: Connect the test device according to the industry standard SY / T 6351-2012 "Laboratory Measurement of Acoustic Properties of Rock Samples";

[0048] Step 3: Place the transmitting transducer in contact with the receiving transducer and apply pressure to 1 MPa. Return the length measuring device to zero and measure the system zero delay t0 according to the industry standard SY / T 6351-2012, “Laboratory Measurement Specification for Acoustic Properties of Rock Samples.”

[0049] Step 4: Place core B between the two transducers, apply pressure to 1 MPa, and adjust the oscilloscope so that the first wave is clearly displayed;

[0050] Step 5: Collect the length measurement value L and the first wave arrival time t in the control unit, and calculate the core acoustic wave velocity V according to the formula V=L / (t-t0).

[0051] Example 2

[0052] Taking the radial acoustic wave velocity measurement of full-diameter core as an example, a rapid measurement method of core acoustic wave velocity is introduced.

[0053] Core A is a full-diameter core sample taken from a well, with a diameter of about 10 cm. The core sampling direction is perpendicular to the formation direction, and the acoustic wave velocity along different directions parallel to the formation needs to be measured to study the horizontal stress difference. Because the stress of the core is released after it is taken from the underground to the ground, microcracks are generated. The stress release is the most, the most cracks are generated, and the acoustic wave velocity is the slowest in the direction of the maximum horizontal stress; conversely, the acoustic wave velocity is the fastest in the direction of the minimum horizontal stress. According to this principle, the acoustic wave velocity of the full-diameter core along different diameter directions is measured to reflect the horizontal stress difference of core A. Since the surface of the core sample taken from the well is relatively rough, it needs to be polished before the acoustic wave is measured, but after polishing, the diameters at different angles will have length differences. The conventional measurement method of separating length measurement and acoustic wave measurement is inefficient and the length is prone to errors. The measuring device described in Example 1 is used to perform synchronous measurement of length and acoustic wave time difference, which effectively solves the above problems. The specific implementation steps are as follows:

[0054] Step 1: Grind the side of the full-diameter core A smooth;

[0055] Step 2: Connect the test device according to the industry standard SY / T 6351-2012 "Laboratory Measurement of Acoustic Properties of Rock Samples";

[0056] Step 3: Place the transmitting transducer in contact with the receiving transducer and apply pressure to 0.5 MPa. Return the length measuring device to zero and measure the system zero delay t0 according to the industry standard SY / T 6351-2012, “Laboratory Measurement Specification for Acoustic Properties of Rock Samples.”

[0057] Step 4: Clamp core A on the indexing plate, turn the angle to 0 degrees, and install core A between the two transducers along the diameter direction of core A;

[0058] Step 5: Increase the pressure to 0.5 MPa, collect the length measurement value L, measure the first wave arrival time t, and calculate the core acoustic wave velocity V according to the formula V = L / (t-t0), so as to obtain the core radial acoustic wave velocity V0 at 0 degrees;

[0059] Step 6: Turn the indexing plate angle to 15° and repeat steps 4 and 5 to obtain the radial acoustic wave velocity when the core is rotated 15°;

[0060] Step 7: Repeat steps 4-6, measuring the radial acoustic wave velocity of the core every 15 degrees until 180 degrees, to obtain the radial acoustic wave velocity of the core at various angles.

[0061] Step 8: Draw a graph to analyze the acoustic wave velocity values ​​at different angles (the horizontal axis is angle, the vertical axis is velocity). If there is a horizontal stress difference in the formation rock, the line connecting the scattered points will form a sine curve with a peak and a trough, representing the minimum and maximum horizontal stresses, respectively. The larger the peak-to-trough difference, the greater the horizontal stress difference. The percentage of the peak-to-trough difference to the average acoustic wave velocity at all angles can be used to represent the magnitude of the horizontal stress difference in the core.

[0062] The above content is only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A rapid measurement device for core acoustic wave velocity, characterized in that: It includes a core acoustic wave velocity measuring device, a pressure measurement and control device, and a core length measuring device; The core acoustic wave velocity measuring device includes a transmitting transducer, a receiving transducer, a signal generator and an oscilloscope; The transmitting transducer and the receiving transducer are respectively arranged at the movable end and the fixed end of the clamp, the transmitting transducer and the receiving transducer are respectively connected to the signal generator and the oscilloscope, the oscilloscope is connected to the control unit, and the control unit is used to detect the speed of the ultrasonic wave. The core is clamped between the transmitting transducer and the receiving transducer; The pressure measurement and control device comprises a pressure applying device (3) and a pressure detection device (4) respectively arranged at the movable end of the clamp; during measurement, the pressure applying device (3) can move toward the pressure detection device (4) to apply axial pressure to the core, and the pressure value is measured by the pressure detection device (4); The length measuring device (5) is arranged on the clamp (6) and is used to measure the length of the core between the transmitting transducer and the receiving transducer, and the clamping position of the length measuring device (5) is consistent with that of the core acoustic wave velocity measuring device; The length measuring device is a linear displacement sensor, a caliper or a micrometer; The measuring method of the core acoustic wave velocity rapid measuring device comprises the following steps: Step 1: Place the transmitting transducer in contact with the receiving transducer and pressurize them to a specified pressure P. Record the measured value L1 of the length measuring device as 0, and the transmission time of the ultrasonic wave as t0. Step 2: Place the core between the transmitting transducer and the receiving transducer of the holder and pressurize it to the specified pressure P. Record the measured value L2 of the length measuring device and obtain the first wave arrival time t. Step 3: Determine the core acoustic wave velocity V based on the measured value L2 and the first wave arrival time t.

2. A rapid core acoustic wave velocity measurement device according to claim 1, characterized in that: The pressure detection device (4) is a pressure sensor or an electronic pressure gauge.

3. The device for rapid measurement of core acoustic wave velocity according to claim 1, characterized in that: The method for determining the core acoustic wave velocity in step 3 is as follows: V = (L2-L1) / (t-t0).

4. A method for measuring a core acoustic wave velocity rapid measurement device according to any one of claims 1 to 3, used for analyzing horizontal stress differences in full-diameter cores, characterized in that: The following steps are involved: Step 1: Place the transmitting transducer in contact with the receiving transducer and pressurize them to a specified pressure P. Record the measured value L1 of the length measuring device as 0, and the transmission time of the ultrasonic wave as t0. Step 2: Clamp the full-diameter core on the indexing plate, turn the angle to 0 degrees, and install it between the two transducers along the diameter direction; Step 3: Pressurize to the specified pressure P, record the measured value L2 of the length measuring device, and obtain the first wave arrival time t; Step 4: Turn the indexing plate to the set angle and measure the radial sound wave velocity at the set angle according to step 3; Step 5: Measure the radial acoustic wave velocity of the core at every set angle according to steps 3 and 4 until 180 degrees, and obtain the radial acoustic wave velocity at each angle; Step 6: Use the percentage of the difference between the maximum and minimum acoustic wave velocities to the average acoustic wave velocity at all angles to represent the magnitude of the horizontal stress difference in the core.

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