A method and device for testing the natural frequency of small-sized cylindrical rocks

Abstract

The present invention relates to a method and device for testing the natural frequency of small-sized cylindrical rocks, comprising the following steps: preparing a standard cylindrical rock sample; performing vibration experiments on the rock sample at different frequencies, and detecting the rock sample vibration data using an axial strain gauge and a radial strain gauge; converting the rock sample vibration data detected by the axial strain gauge and the radial strain gauge into voltage peak-to-peak values ​​respectively; obtaining the axial strain and radial strain at different vibration frequencies based on the voltage peak-to-peak values; obtaining the volume strain at different vibration frequencies based on the axial strain and radial strain at different vibration frequencies; and obtaining the natural frequency of the rock sample based on the variation law of the volume strain. The present invention can test the natural frequency of the rock sample, which can approximately reflect the natural frequency of the rock. The rock can be subjected to acoustic vibration at this frequency, which is conducive to causing vibration damage to the shale rock, thereby increasing the microcracks in the rock, and improving the permeability of the shale, thereby effectively improving the shale oil and gas recovery rate.

Description

Technical Field

[0001] The present invention relates to the technical field of rock performance testing, and in particular to a method and device for testing the natural frequency of small-sized cylindrical rocks. Background Art

[0002] Unconventional oil and gas reservoirs have low porosity and permeability, requiring stimulation measures to achieve effective production. Currently, several researchers have proposed various stimulation methods, including hydraulic fracturing, high-energy gas fracturing, carbon dioxide fracturing, liquid nitrogen fracturing, oxidative fracturing, and electric heating fracturing. Others have also proposed using acoustic vibration to stimulate production in unconventional oil and gas reservoirs.

[0003] The effect of acoustic vibration is to use acoustic vibration to cause rock cracking. If the applied acoustic frequency is consistent with the natural frequency of the rock, the rock is prone to damage. However, there is no clear understanding of the natural frequency of rock. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a method and equipment for testing the natural frequency of small-sized cylindrical rocks.

[0005] The present invention is achieved through the following technical solutions:

[0006] The present application provides a method for testing the natural frequency of a small-sized cylindrical rock, comprising the following steps:

[0007] Prepare standard cylindrical rock samples;

[0008] Conduct vibration experiments of different frequencies on rock samples, and use axial and radial strain gauges to detect rock sample vibration data;

[0009] The rock sample vibration data detected by the axial strain gauge and the radial strain gauge are converted into peak-to-peak voltage respectively;

[0010] Based on the peak-to-peak voltage at different vibration frequencies, the axial strain and radial strain at different vibration frequencies are obtained;

[0011] Based on the axial strain and radial strain at different vibration frequencies, the volume strain at different vibration frequencies is obtained;

[0012] The natural frequency of the rock sample is obtained based on the changing law of volume strain.

[0013] The present application provides a testing device for the natural frequency of small-sized cylindrical rocks, comprising:

[0014] Rock sample clamping device, used to fix the rock sample to be tested;

[0015] A knocking device, used to knock and vibrate the rock sample to be tested;

[0016] A vibration control device, connected to the knocking device, for controlling the knocking device to knock the rock sample to be tested;

[0017] A vibration detection device, including an axial strain gauge and a radial strain gauge, is used to detect deformation data of the rock sample being tested;

[0018] a data acquisition device connected to the vibration detection device and used to collect signals from the vibration detection device;

[0019] The signal processing device is connected to the data acquisition device and is used to process the acquired data to obtain the natural frequency.

[0020] Compared with the prior art, this application has at least the following beneficial effects:

[0021] This application can test the natural frequency of small-sized cylindrical rocks, which can approximately reflect the natural frequency of the rock. The rock can be subjected to acoustic vibration at this frequency, which is beneficial to causing vibration damage to the shale rock, and then increasing the micro-cracks of the rock, which can improve the permeability of the shale, thereby effectively improving the shale oil and gas recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 Flowchart of the rock natural frequency testing method in the embodiment;

[0024] Figure 2 Schematic diagram of the installation of the vibration detection device in the embodiment;

[0025] Figure 3 Schematic diagram of a rock natural frequency testing device in an embodiment;

[0026] Figure 4 This is a graph showing the relationship between the axial strain and frequency of rock sample No. 1 in the embodiment;

[0027] Figure 5 This is a graph showing the relationship between radial strain and frequency of rock sample No. 1 in the embodiment;

[0028] Figure 6 This is a graph showing the relationship between strain and frequency of rock sample No. 1 in the embodiment;

[0029] Figure 7 This is a graph showing the relationship between strain and frequency of rock sample No. 1 in the embodiment;

[0030] Figure 8 This is a graph showing the relationship between strain and frequency of rock sample No. 2 in the embodiment. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments.

[0032] It should be noted that, in the absence of any conflict, the embodiments and features of the embodiments of the present invention can be combined with each other. It should be noted that the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to in conjunction with each other. For the device embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts can be referred to the partial description of the method embodiments.

[0033] In the description of the present invention, it should also be noted that, unless otherwise expressly specified or limited, the terms "disposed," "installed," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0034] like Figure 1 As shown, the method for testing the natural frequency of cylindrical rocks disclosed in this embodiment includes the following steps:

[0035] S1, collect geological data, well logging data, and seismic data of the study area;

[0036] S2, preparing standard cylindrical rock samples from the collected rock samples and measuring the length and diameter of the rock samples;

[0037] S3, perform acoustic wave measurement on the rock sample to obtain the longitudinal wave velocity and shear wave velocity of the rock sample, and select rock samples with similar acoustic wave velocity for experiment;

[0038] S4, attaching axial strain gauges and radial strain gauges to the surface of the rock sample to detect the transverse and longitudinal deformation data of the rock sample respectively;

[0039] In one possible design, Figure 2As shown, there are two radial strain gauges, and two sets of radial deformation data are collected and averaged to reduce errors. In particular, the axial strain gauge and radial strain gauge are attached to the middle of the rock sample surface, with the axial strain gauge located between the two radial strain gauges.

[0040] S5, such as Figure 3 As shown in the figure, the rock sample with the strain gauge attached is placed in the vibration equipment and clamped by the rock sample clamping device. The corresponding sine wave is emitted by the vibration control device to drive the knocking device to knock the rock sample. After the rock sample is vibrated, it will deform. The strain gauge on the surface of the rock sample will also deform. The deformation of the strain gauge will be converted into an electrical signal. The electrical signal is collected by the data acquisition device, and the signal processing device outputs the peak-to-peak voltage required for the test. The calculation formula of the peak-to-peak voltage is:

[0041]

[0042] In the above formula, U is the peak-to-peak voltage, V cc is the power supply level, K is the sensitivity coefficient of the semiconductor type strain gauge (120±5%); ε is the rock sample strain.

[0043] S6, the vibration frequency is changed in sequence by the vibration control device, and the strain gauges on the surface of the rock sample will reflect a series of deformation information in sequence;

[0044] S7, after obtaining the frequency and peak-to-peak voltage according to the above experimental results, the axial strain and radial strain information at different vibration frequencies can be obtained by formula (2) and formula (3), respectively. The radial strain is calculated as the average value of radial strain gauge 1 and radial strain gauge 2, as shown in Figure 4 and Figure 5 , and then use formula (4) to calculate the volume strain information of rock at different frequencies, such as Figure 6 shown.

[0045]

[0046]

[0047] ε t =ε ax +2ε rad (4)

[0048] In the above formula, ε t is the volume strain of the rock sample; ε ax is the axial strain; ε rad is the radial strain; K is the sensitivity coefficient of the semiconductor type strain gauge (120±5%), which is regarded as a constant of 120 in this embodiment; V cc is the power supply level, also considered a constant, 2V; U ax is the axial peak-to-peak value of the rock sample corresponding to the axial strain gauge; Urad1 、U rad2 are the radial peak-to-peak values ​​of the rock samples corresponding to the two radial strain gauges;

[0049] S8, for the vibration frequency and rock mass strain data, curve fitting was performed using Origin software, and the curve relationship between vibration frequency and rock mass strain was obtained as follows:

[0050]

[0051] In the above formula, y is the volume strain; y0 is the offset; A is the amplitude; W is the width; x c is the vibration center; x is the vibration frequency;

[0052] like Figure 7 、 Figure 8 As shown in this example, for rock sample No. 1, y0 is 0.00427, x c is 58.53009, w is 22.59315, A is 0.00192; for rock sample No. 2, y0 is 0.00406, x c = 61.31596, w = 37.58035, A = 0.00183. Substituting the vibration frequency and the above data into formula (5), the resonance frequency can be obtained by integrating the extreme value method. The natural frequency of rock sample No. 1 is calculated to be 58 Hz, and the natural frequency of rock sample No. 2 is 61 Hz.

[0053] When the excitation vibration frequency of the vibration control device is consistent with the natural frequency of the core, the core resonates. At this time, the deformation of the core is the largest, and the amplitude of the strain gauge signal on the core is the largest. The corresponding emission frequency can be regarded as the natural frequency of the rock.

[0054] like Figure 3 As shown, this embodiment discloses a testing device for the natural frequency of small-sized cylindrical rocks, which is used to implement the above-mentioned testing method. It mainly includes a carrying machine, a rock sample clamping device, a knocking device, a vibration control device, a vibration detection device, a data acquisition device and a signal processing device.

[0055] The rock sample clamping device is used to fix the rock sample to be tested;

[0056] The knocking device is used to knock and vibrate the rock sample to be tested;

[0057] A vibration control device, connected to the knocking device, for controlling the knocking device to knock the rock sample to be tested;

[0058] The vibration detection device includes an axial strain gauge and a radial strain gauge, which is used to detect the deformation data of the rock sample being tested and is placed in close contact with the rock sample being tested when in use;

[0059] The data acquisition device is connected to the vibration detection device and is used to collect signals from the vibration detection device;

[0060] The signal processing device is connected to the data acquisition device and is used for processing the data collected by the data acquisition device so as to obtain the natural frequency.

[0061] This application can test the natural frequency of rock samples, which can approximately reflect the natural frequency of the rock. The rock can be subjected to acoustic vibration at this frequency, which is beneficial to causing vibration damage to the shale rock, and then increasing the micro-cracks of the rock, which can improve the permeability of the shale, thereby effectively improving the shale oil and gas recovery rate.

[0062] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for testing the natural frequency of small-sized cylindrical rocks, characterized in that: The following steps are involved: Prepare standard cylindrical rock samples; Axial and radial strain gauges are placed close to the surface of the rock sample, and vibration experiments of different frequencies are performed on the rock sample. Specifically, the rock sample with the strain gauges attached is placed in the vibration equipment and clamped by the rock sample clamping device. The vibration control device emits a corresponding sine wave to drive the striking device to strike the rock sample, causing the rock sample to deform after being vibrated. Use axial strain gauges and radial strain gauges to detect rock sample vibration data; The rock sample vibration data detected by the axial strain gauge and the radial strain gauge are converted into peak-to-peak voltage respectively; Based on the peak-to-peak voltage at different vibration frequencies, the axial strain and radial strain at different vibration frequencies are obtained; Based on the axial strain and radial strain at different vibration frequencies, the volume strain at different vibration frequencies is obtained; The natural frequency of the rock sample is obtained based on the variation law of volume strain. The vibration frequency corresponding to the maximum volume strain is the natural frequency of the rock sample. The axial strain gauge and two radial strain gauges are pasted in the middle of the rock sample surface. The axial strain gauge is located between the two radial strain gauges. The calculation formula of the volume strain is: ； ； ； In the above formula, is the volume strain of the rock sample; is the axial strain of the rock sample; is the radial strain of the rock sample, is the sensitivity coefficient of semiconductor type strain gauge; is the power supply level; is the peak-to-peak axial voltage of the rock sample, 、 are the peak-to-peak values ​​of the radial voltage of the rock sample corresponding to the two radial strain gauges.

2. A testing device for the natural frequency of small-sized cylindrical rocks, characterized in that: Used to implement the test method according to claim 1, comprising: Rock sample clamping device, used to fix the rock sample to be tested; A knocking device, used to knock and vibrate the rock sample to be tested; A vibration control device, connected to the knocking device, for controlling the knocking device to knock the rock sample to be tested; A vibration detection device, including an axial strain gauge and a radial strain gauge, is used to detect deformation data of the rock sample being tested; a data acquisition device connected to the vibration detection device and used to collect signals from the vibration detection device; The signal processing device is connected to the data acquisition device and is used to process the acquired data to obtain the natural frequency.

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