CN114233275B - Well cementation quality evaluation method based on array acoustic logging time difference dispersion curve - Google Patents

Abstract

The invention discloses a cementing quality evaluation method based on array acoustic wave logging time difference dispersion curve: the array receiving probe receives logging waveforms with different source distances; the array acoustic wave logging waveform is modeled through complex exponential functions to obtain casing hole pattern waves The wavenumber-frequency distribution curve is obtained to obtain the transit time dispersion curve or the phase velocity dispersion curve; the real axis integration method is used to obtain the wave number-frequency distribution curve, transit time dispersion curve, and phase velocity dispersion curve of different water ring thicknesses at the I interface, as Wavenumber-frequency cementing interpretation standard chart, time difference-frequency cementing interpretation standard chart, phase velocity-frequency cementing interpretation standard chart; combined with the standard chart, determine the water ring thickness of the measured array acoustic wave logging waveform, and evaluate the cementing quality. Determine the serial groove of I interface in actual well logging. This invention evaluates the quality of cementing by utilizing the change patterns of the wave time difference dispersion curve and wave number frequency distribution curve of the casing hole mode in the 9-16kHz range of the medium and low frequency band in the casing hole with the thickness of the water ring.

Description

Cementing quality evaluation method based on array acoustic logging time difference and dispersion curve

Technical field

The present invention relates to the field of acoustic wave cementing quality logging, and more specifically, to a cementing quality evaluation method based on array acoustic wave logging time difference dispersion curve.

Background technique

Acoustic cementing quality logging has always used two source distances of 3 feet and 5 feet. The first wave amplitude of the acoustic logging waveform with a 3-foot source distance is used to evaluate the I-interface cementation quality of cementing. Density, the cementation quality of the cementing II interface (the interface between the formation and the cement sheath) is evaluated through formation waves. The basic principle comes from the reflection and transmission characteristics of plate waves and plane waves at different medium interfaces respectively: when there is a water ring on the I interface, the inside and outside of the casing wave are liquids, and the sound waves are reflected inside and outside the casing solid. To form plate waves, the greater the thickness of the water ring, the greater the amplitude of the plate waves. When the II interface is poorly cemented, less energy enters the formation through the II interface, and the reflected wave energy increases. When the II interface is well cemented, the amplitude of the sound wave sliding along the formation is large, and the amplitude of the formation wave propagating to the 5-foot receiving source distance is large. clear. These traditional sonic logging and cementing quality evaluation principles expand the casing along the circumferential direction and treat it as an infinite flat plate to analyze and interpret casing waves. This method only accounts for the propagation speed of the casing wave. The true source and amplitude characteristics of the casing wave are not revealed. In addition, the source distance design based on experiments has never questioned the velocity characteristics of the casing wave. It has always been believed that the casing wave is an acoustic wave propagating at a constant speed, and there is no analysis of the distribution of the mode waves that make up the casing wave in the frequency domain. The method and the composition of the casing wave waveform are analyzed in depth, especially the frequency characteristics of the casing wave and the distribution and source of the amplitude corresponding to the frequency characteristics. Since only the first wave amplitude of 3 inches of source distance is used to explain the I interface, can the waveforms of other source distances be used to judge the cementation quality of the I interface? Are the speeds of various mode waves included in the casing hole logging waveform related to the cementing quality of the cementing I interface? These questions have never been answered positively. There are more and more problems appearing in practical applications.

Contents of the invention

The purpose of this invention is to overcome the deficiencies in the prior art and propose a cementing quality evaluation method based on the array acoustic wave logging time difference dispersion curve, using the time difference dispersion curve, k-f distribution shape and phase velocity dispersion curve shape Calculate the thickness of the I interface water ring, and use the thickness of the water ring to evaluate the cementing quality.

The object of the present invention is achieved through the following technical solutions.

The present invention is a cementing quality evaluation method based on the array acoustic wave logging time difference dispersion curve, which utilizes the casing well mode wave time difference dispersion curve and wave number-frequency distribution curve in the casing hole response medium and low frequency band 9-16kHz range with the thickness of the water ring. The law of change evaluates the quality of cementing. The time difference of the cased hole mode wave is between the time difference of the formation shear wave and the time difference of the liquid in the well. It changes with the frequency; it includes the following processes:

1) The acoustic logging instrument is lowered into the casing well, and the transmitting probe generates vibration. The vibration propagates in the well liquid, casing, cement sheath, and formation in turn. In the well liquid, the array receiving probe receives logging waveforms with different source distances; where , the sonic logging instrument includes a transmitting probe and an array receiving probe composed of multiple receiving probes;

2) Use the array acoustic wave logging waveform to obtain the wave number-frequency distribution curve of the cased hole mode wave through complex exponential function modeling. The time difference dispersion curve is obtained by equaling the time difference to the wave number/frequency, or the phase velocity is obtained by equaling the phase velocity to the frequency/wave number. dispersion curve;

3) Using the real-axis integration method, the wavenumber-frequency distribution curve, time difference dispersion curve, and phase velocity dispersion curve of different water ring thicknesses at the I interface are obtained respectively, which are used as the standard chart for the interpretation of wavenumber-frequency cementing and time difference-frequency cementing respectively. Interpretation standard chart, phase velocity-frequency cementing interpretation standard chart;

4) Combined with the standard chart for wave number-frequency cementing interpretation, the standard chart for time difference-frequency cementing interpretation, and the standard chart for phase velocity-frequency cementing interpretation, the water ring thickness of the actually measured array acoustic wave logging waveform can be determined and the cementing bonding can be evaluated. The quality can also be used to determine the serious cross-grooving of the I interface in actual well logging; specifically, it includes the following situations:

Scenario 1: For the actually measured array acoustic logging waveform, the wavenumbers of different frequencies are obtained through complex exponential function modeling, and the wavenumber-frequency distribution curve of the cased hole mode wave is obtained; for the specified wavenumber, the wavenumber-frequency distribution curve is used to find the frequency , combined with the wavenumber-frequency cementing interpretation standard chart, use frequency to determine the thickness of the water ring, and evaluate the cementing quality; for a specified frequency, use the wavenumber-frequency distribution curve to find the wave number, combined with the wavenumber-frequency cementing interpretation standard chart, use the wavenumber Determine the thickness of the water ring and evaluate the cementing quality; convert the wave number-frequency distribution curve into a time difference and dispersion curve to obtain the shape of the time difference and dispersion curve. Take the frequencies corresponding to multiple specific time differences from the curve. The frequency value is consistent with the water The ring thickness is approximately in a linear relationship. Combined with the wave number-frequency cementing interpretation standard chart, the frequency is used to determine the water ring thickness and evaluate the cementing quality;

Scenario 2: Use the complex exponential function to model the actually measured array acoustic wave logging waveform to obtain the wave number-frequency distribution curve of the cased hole mode wave. Compared with the wave number-frequency cementing interpretation standard chart, the water ring corresponding to the closest curve The thickness is the actual measured water ring thickness at the casing hole I interface to evaluate the cementing quality; in addition, the distance between the actually measured wave number-frequency distribution curve and the wave number-frequency curve of different water ring thicknesses in the standard chart is calculated comprehensively, Take the water ring thickness corresponding to the curve with the smallest distance as the actual measured water ring thickness at the I interface of the casing well to evaluate the cementing quality;

The actual measured array acoustic wave logging waveform is modeled with a complex exponential function to obtain the time difference dispersion curve of the cased hole mode wave. Compared with the time difference-frequency cementing interpretation standard chart, the water ring thickness corresponding to the closest curve is the actual measured The thickness of the water ring at the I interface of the casing well is used to evaluate the cementing quality; in addition, the distance between the actual measured time difference and dispersion curve and the time difference and dispersion curve of different water ring thicknesses in the standard chart are comprehensively calculated, and the curve with the smallest distance is taken. The corresponding water ring thickness is the actual measured water ring thickness at the I interface of the casing well to evaluate the cementing quality;

Scenario 3: Using the wavenumber-frequency distribution curve when the water ring thickness is 0 in the standard chart for cementing interpretation as the benchmark curve, the wavenumber-frequency is obtained from the actually measured array acoustic logging waveform through the complex exponential function modeling method. The distribution curve is subtracted from the benchmark curve to obtain the differences at different frequencies. Add these differences and divide by the total number of added frequencies to obtain an engineering quantity. This engineering quantity has a monotonic relationship with the thickness of the water ring. Use this Cementing quality evaluation based on project quantities;

Taking the time difference dispersion curve when the water ring thickness is 0 in the time difference-frequency cementing interpretation standard chart as the benchmark curve, the time difference dispersion curve is obtained by using the complex exponential function modeling method for the actually measured array acoustic wave logging waveform, which is consistent with the benchmark curve. Subtract the curves to get the differences at different frequencies. Add these differences and divide by the total number of added frequencies to get another engineering quantity. This engineering quantity has a monotonic relationship with the thickness of the water ring. Use this engineering quantity to perform solidification Well quality assessment;

Scenario 4: Use the complex exponential modeling method for the actually measured array acoustic logging waveform to obtain the wavenumber-frequency distribution curves in the low-frequency and high-frequency bands. Compared with the inclined straight line whose slope is the sound velocity of the liquid in the casing hole, if there is a high slope If the wave number distribution is based on the slope of the inclined straight line of the liquid in the casing hole, and is continuous, forming a continuous curve, it is judged that the casing hole I interface is seriously cross-grooved;

For the actually measured array acoustic logging waveform, the complex exponential modeling method is used to obtain the low-frequency and high-frequency time difference dispersion curves. If there is a time difference distribution curve that is higher than the time difference of the liquid in the casing hole, and it is continuous, a time difference distribution curve is formed. The continuous time difference distribution curve indicates that the I interface of the casing well is severely cross-grooved.

The main frequency of the acoustic logging instrument in step 1) is consistent with the natural frequency of the liquid mode wave in the casing hole, and the frequency of the casing wave peak is located within the bandwidth of the receiving probe; the frequency of each receiving probe in the array receiving probe The frequency characteristics are consistent and the comprehensive sensitivity is consistent.

Step 2) Casing hole mode wave: When the cementation of the casing hole I interface is poor, there is a water ring between the casing and the cement sheath, and the shear stress on its boundary is 0. Multiple mode waves appear in the casing solid, all of which are Coupled with the mode wave in the well liquid, multiple casing hole mode waves are formed, whose speed changes with frequency. In sonic logging, the part whose speed is equal to the casing wave speed is collectively called casing wave; measured in the casing hole liquid The casing wave is composed of multiple casing well mode waves. The phase velocity of each casing well mode wave changes with the frequency. The change is small in a certain frequency range and is close to the casing wave speed. These frequency ranges are separated from each other and mutually exclusive. Independent, the amplitude versus frequency curve is disconnected, and the amplitude reaches a maximum value at or near the disconnection position; the amplitude of two adjacent, disconnected casing hole mode waves with a speed close to the casing wave speed varies with frequency. The change curves together form a complete casing wave spectrum peak and wave number peak; the time difference dispersion curve near the peak value is close to a constant, which is equal to the casing wave time difference, and the cementing quality is poor.

Compared with the existing technology, the beneficial effects brought by the technical solution of the present invention are:

Based on the mode wave distribution of the two-dimensional spectrum in the cased hole model, the patent of the invention makes full use of the influence of the water ring at the casing hole I interface on the phase velocity of each mode wave, and has sufficient theoretical basis. When using complex exponential modeling, the amplitude and phase information of each frequency band and each moment in the array acoustic logging waveform are fully utilized, and the I interface water ring thickness information contained in the waveform is fully utilized and mined. In particular, the I-interface water ring thickness information contained in the array acoustic logging waveform phase. The phase velocity versus frequency curve is used as the intermediate variable, which is similar to the velocity dispersion curve in surface wave exploration (with examples of successful application in formation shear wave exploration), and has a solid theoretical foundation.

The present invention utilizes most of the waveform information in the array acoustic logging waveform. Different from the evaluation of cementing quality based on the first wave amplitude of acoustic amplitude logging, the patent of this invention uses the phase information distributed in waveforms with different source distances to calculate the phase velocity (converting the amplitude and phase information into characteristic values through complex exponential modeling The imaginary part of to obtain the phase velocity). Convert cementing quality evaluation from single amplitude information to the joint use of velocity information at each frequency. The utilization of the I interface information contained in subsequent waves has been increased. In particular, the second Stoneley wave (mode wave) whose phase velocity is lower than the velocity of the liquid in the well is used to judge severe cross-trough conditions, and the waveform information located at the rear is directly used.

For sonic logging, phase velocity, that is, sonic time difference information, is the most important information. The thickness of the I interface water ring is shown by the change curve of phase velocity (the reciprocal of the phase velocity is the time difference) with frequency. This patent first theoretically discovered the relationship between the phase velocity curve and the thickness of the I interface water ring (or the time difference). The relationship between the dispersion curve and the I interface water ring thickness) was used as the standard curve and chart, and then the cementing quality evaluation method was established using this relationship.

The casing well is a cylindrical medium, in which the sound wave propagation law is based on the phase velocity of the cylindrical waveguide changing with frequency. Based on this, this is the most important feature of the patent of the present invention. This is the way in which the I-interface water ring thickness information unique to the cased hole sonic logging response is expressed. Improvements in cementing quality evaluation methods have led to changes in the structure of sonic logging instruments and changes in processing methods.

Evaluating the cementing quality of the cementing I interface from the speed change increases the perspective of observing the cementing quality. Starting from the full-wave waveform, the cementing quality information in the waveform is extracted, and the I-interface cementation information in the waveform is fully used.

The distribution curve or time difference dispersion curve on the f-k plane is used to calculate the water ring thickness. Pattern recognition and image recognition methods can be used to generate the water ring thickness. The acoustic time difference and dispersion curves of different water ring thicknesses are very different, so the judgment is more accurate and the solution is less.

Description of the drawings

Figure 1 is the two-dimensional amplitude spectrum of the liquid response in the well when there is a water ring (thickness 19mm) at the casing well I interface;

Figure 2 is the k-f distribution of the cased hole mode wave when there is a water ring (thickness 19mm) at the casing hole I interface;

Figure 3 is the two-dimensional amplitude spectrum of the liquid response in the well when there is a water ring (thickness 1 mm) at the casing well I interface;

Figure 4 is the k-f distribution of the cased hole mode wave when there is a water ring (thickness 1mm) at the casing hole I interface;

Figure 5 shows the k-f distribution of the cased hole mode wave when the I interface water ring thickness is 1mm and 19mm;

Figure 6 shows the k-f distribution of the casing well mode wave for four water ring thicknesses when there is a water ring at the casing well I interface;

Figure 7 is an enlarged result of Figure 6, showing the difference in k-f distribution of cased hole mode waves in the 9-20kHz range;

Figure 8 shows the k-f distribution of the casing well mode wave (0.4%) for four water ring thicknesses when there is a water ring at the casing well I interface;

Figure 9 is an enlargement of the low-frequency part of Figure 8. When there is a water ring at the casing hole I interface, the k-f distribution of the casing hole mode wave (0.4%) for four water ring thicknesses;

Figures 10, 11, and 12 are respectively examples of k-f distribution examples and time difference distributions of cased hole mode waves processed by actual logging waveforms at different depth points;

Figure 13 shows the distribution of time differences for four types of water ring thicknesses at the casing hole I interface (the maximum value is greater than 4% of the maximum amplitude of the two-dimensional spectrum);

Figure 14 is the time difference distribution of four water ring thicknesses at the casing hole I interface after the enlargement of Figure 13 (the maximum value is greater than 4% of the maximum amplitude of the two-dimensional spectrum);

Figures 15 and 16 are respectively examples of processing time difference and dispersion curves of different cased hole array acoustic logging waveforms;

Figure 17 shows the distribution of time differences for four types of water ring thicknesses at the casing hole I interface (the maximum value is greater than 1% of the maximum amplitude of the two-dimensional spectrum);

Figure 18 shows the distribution of time differences for four water ring thicknesses at the casing hole I interface (the maximum value is greater than 0.1% of the maximum amplitude of the two-dimensional spectrum);

Figure 19 is the time difference distribution of four water ring thicknesses at the casing hole I interface after enlarging the low frequency part of Figure 18 (the maximum value is greater than 0.1% of the maximum amplitude of the two-dimensional spectrum);

Figure 20 is a comparison of the actual logging waveforms of 7-inch casing wells and the processing results of time difference dispersion curves and distribution curves;

Figure 21 is the time difference distribution processed by the actual well logging waveform (right). The second Stoneley wave appears at the 800us/m position;

Figure 22 is the phase velocity distribution of the mode wave in the 7-inch casing hole when the I interface cementation is poor;

Figure 23 is the phase velocity distribution of the mode wave in the 7-inch casing well when the I interface cementation is poor (only the phase velocity changes with relatively large amplitude are drawn);

Figure 24 is a distribution diagram of the transit time dispersion curve at different I interface water ring thicknesses.

Detailed ways

Based on the basic characteristics of acoustic wave propagation in casing wells (liquid in the well, casing, cement sheath and formation) - two-dimensional spectrum, a casing well model with changes in the thickness of the water ring at the I interface (the interface between casing and cement sheath) is used to study casing. Regarding the acoustic wave propagation characteristics in the well, we found that the casing wave is composed of six casing well mode waves with similar speeds, and these mode waves are distributed in different frequency ranges. Related to the thickness of the I interface water ring are two adjacent mode waves, both of which reach maximum amplitudes at the frequency of the liquid mode wave in the well. The amplitude of the two mode waves changes with frequency together to form a casing wave. The spectrum peak determines the shape and amplitude of the casing wave. Since the shape and amplitude of the spectrum peak change with the thickness of the water ring, the attenuation coefficient (with source distance and time) and amplitude of the casing wave change with the thickness of the water ring. The speed of the casing wave is close to a constant and the speed value is constant.

During the above research process, we further theoretically discovered that: in addition to affecting the shape and amplitude of the casing wave spectrum peak, changes in the thickness of the I interface water ring also have a significant impact on the distribution curve of the mode wave in the k-f plane (i.e., phase velocity) , the thickness of the water ring leads to obvious differences in the distribution curves of different frequency intervals. After being converted into an acoustic wave phase velocity dispersion curve or an acoustic wave time difference dispersion curve, the shape of the curve is very different. Especially when the frequency is in the range of 9kHz-21kHz, the time difference dispersion curves caused by different water ring thicknesses are approximately equally spaced along the frequency. Therefore, the patent of the invention obtains the water ring thickness through the dispersion curve in this frequency range. The water ring thickness is Evaluate cementing quality.

The evaluation method described in the patent of the present invention is based on the casing hole acoustic wave propagation theory. Starting from the influence of the I interface water ring thickness on the full-frequency mode wave phase velocity in the casing hole response (analytical solution), the phase velocity changes with the I interface water The frequency range where the ring thickness changes most dramatically. The phase information in the cased hole mode wave and the change in the mode wave phase velocity caused by the thickness of the water ring under wellbore conditions are utilized. This is a method that uses the velocity characteristics of sound wave propagation in cylindrical interface media, and uses phase velocity or acoustic wave time difference to calculate the thickness of the I interface water ring and evaluate the cementing quality. Breaking through the traditional constraints of using only acoustic logging sound amplitude, it has a solid theoretical and experimental basis. It is a new cementing quality I based on the follow-up wave of the array acoustic logging waveform (contained cementing information) Interface evaluation methods.

The present invention is a cementing quality evaluation method based on the array acoustic wave logging transit time dispersion curve. It uses the casing hole mode wave transit time dispersion curve and the wave number-frequency distribution curve in the casing hole response in the medium and low frequency range to evaluate the cement quality evaluation method based on the change of the water ring thickness. Well cementation quality. The time difference of the cased hole mode wave is between the time difference of the formation shear wave and the time difference of the liquid in the well, and changes with frequency. The time difference dispersion curve of this casing hole mode wave uses a lower frequency range than the casing wave (19-30kHz), and is located in the low frequency range of 9-21kHz.

The patent of this invention utilizes the information on the I interface water ring thickness contained in the waveform behind the casing wave in the sonic logging waveform, and uses the phase velocity dispersion curve (or Calculate the water ring thickness of the cementing I interface by taking the reciprocal of the time difference dispersion curve), that is, using the water ring thickness information of the I interface included in the sonic logging waveform phase to evaluate the cementing quality.

From the two-dimensional spectrum of the response of the liquid in the well when there is a water ring at the casing hole I interface, it is found that poor cementation at the cementing I interface will cause casing waves. In addition, it will also lead to a casing hole mode with a speed much slower than the casing wave speed. The shape of the wave's phase velocity dispersion curve undergoes relatively large changes. This is the change in the root of the mode wave on the k-f plane in the solution of the cased hole model caused by the thickness of the I interface water ring. That is, given the value of frequency f, after the boundary conditions of the casing well are substituted, the wave number k of the mode wave that satisfies the boundary conditions changes with the thickness of the water ring. This change can be converted into phase velocity (f/k) or time difference (k/f), thereby obtaining the variation pattern of the phase velocity dispersion curve with the thickness of the water ring or the variation pattern of the phase velocity dispersion curve with the thickness of the water ring. Calculate the k-f curve and time difference dispersion curve of two types of casing commonly used on site (5.5 inches and 7 inches) with different water ring thicknesses. These curves are used as theoretical curves or charts to compare with the dispersion curves obtained from actual well logging waveforms to determine the thickness of the I interface water ring.

The phase velocity of these mode waves is slower than that of the casing wave, and the velocity changes with frequency. In the waveforms with different source distances, it is manifested as follows: multiple oscillation periods and long waveform occupation time. When processing the time difference or velocity dispersion curve from the actually measured array acoustic logging waveform, a relatively long window is required. Only by taking the waveform areas affected by these mode waves into the window can a relatively complete acoustic time difference and dispersion be obtained. Curved shape. When selecting the starting position of the window, you need to remove the casing wave and only retain the subsequent waveform of the casing wave.

Perform fft on the selected waveform in each well logging waveform to obtain the spectrum. Given the frequency, take out the spectrum of 8 source distance waveforms, use the complex exponential function to model the acoustic wave number k, and repeat the above steps for all frequencies to obtain the frequency. f-distribution curve of wave number k. The relationship between wave number, frequency and phase velocity is used to obtain the phase velocity dispersion curve (the change curve of phase velocity with frequency), and the reciprocal of the phase velocity is obtained to obtain the time difference dispersion curve. Use the wave number-frequency distribution curve or the time difference dispersion curve to obtain the I interface water ring thickness through the theoretical curve when the I interface water ring thickness is different, and evaluate the cementing quality with the water ring thickness.

The present invention is a cementing quality evaluation method based on array acoustic wave logging time difference dispersion curve. The specific implementation process is as follows:

The first step: lower the acoustic logging instrument into the casing well, and the transmitting probe generates vibration. The vibration propagates in the well liquid, casing, cement sheath, and formation in turn. In the well liquid, the array receiving probe receives logging waveforms with different source distances. . Among them, the sonic logging instrument includes a transmitting probe and an array receiving probe composed of multiple receiving probes. The main frequency of the sonic logging instrument is consistent with the natural frequency of the liquid mode wave in the casing hole, and the frequency of the peak value of the casing wave is within the bandwidth of the receiving probe. The frequency characteristics of each receiving probe in the array receiving probe are consistent, and the overall sensitivity is consistent.

Step 2: Use the array acoustic wave logging waveform to obtain the wave number-frequency distribution curve of the casing hole mode wave through complex exponential function modeling. The time difference dispersion curve is obtained by equaling the time difference to the wave number/frequency, or the phase velocity is equal to the frequency/wave number. Phase velocity dispersion curve.

Among them, casing hole mode waves: When the cementation of the casing hole I interface is poor, there is a water ring between the casing and the cement sheath, and the shear stress on its boundary is 0. Multiple mode waves appear in the casing solid along the z direction. Propagating at the casing wave speed, the coupled sound waves in the well liquid also move at the same speed along the z direction. They are coupled with the mode waves in the well liquid to form multiple casing well mode waves. Their speed changes with frequency. The sound wave In logging, the part whose speed is equal to the casing wave speed is generally called the casing wave; the casing wave measured in the liquid in the casing hole is composed of multiple casing hole mode waves, and the phase velocity of each casing hole mode wave varies with Frequency changes are small in a certain frequency range, close to the casing wave speed. These frequency ranges are separated from each other and independent of each other. The amplitude versus frequency curve is disconnected, and the amplitude reaches a maximum at or near the disconnection position. value; the change curves of amplitude and frequency of two adjacent, disconnected casing hole mode waves whose speed is close to the casing wave speed together form a complete casing wave spectrum peak and wave number peak. Its phase velocity is constant. The time difference within the frequency range of this spectrum peak is basically constant. If it is close to the casing wave time difference, the cementing quality will be poor. That is, the time difference dispersion curve near the peak value is close to a constant, which is equal to the casing wave time difference, and the cementing quality will be poor.

Step 3: Use the real-axis integration method to obtain the wavenumber-frequency distribution curve, time difference dispersion curve, and phase velocity dispersion curve of different water ring thicknesses at the I interface, respectively, as the wavenumber-frequency cementing interpretation standard chart and time difference-frequency Cementing interpretation standard chart, phase velocity-frequency cementing interpretation standard chart.

When there is a water ring at the interface of cementing quality cementation I, in addition to the occurrence of casing waves in the well liquid, the curve distribution shape of the relatively large amplitude casing hole mode wave on the wavenumber-frequency plane changes with the thickness of the water ring, which is converted into time difference dispersion. After the curve, the shape of the time difference dispersion curve changes with the thickness of the water ring. Use the real axis integration method to change the thickness of the water ring to obtain these two changing laws. These two changing laws are used as the wavenumber-frequency cementing interpretation standard chart and the time difference- Frequency cementing interpretation standard chart.

Step 4: Combining the standard chart for wave number-frequency cementing interpretation, the standard chart for time difference-frequency cementing interpretation, and the standard chart for phase velocity-frequency cementing interpretation, the water ring thickness of the actually measured array acoustic wave logging waveform can be determined, and the solid state can be evaluated. The quality of well cementation can also determine the serious cross-grooving of the I interface in actual well logging. Such as the following situations:

Scenario 1: For the actually measured array acoustic logging waveform, the wavenumbers of different frequencies are obtained through complex exponential function modeling, and the wavenumber-frequency distribution curve of the cased hole mode wave is obtained.

1) For a specified wave number, use the wave number-frequency distribution curve to find the frequency. Combined with the wave number-frequency cementing interpretation standard chart, use the frequency to determine the water ring thickness and evaluate the cementing quality.

2) For the specified frequency, use the wave number-frequency distribution curve to find the wave number, combine it with the wave number-frequency cementing interpretation standard chart, use the wave number to determine the thickness of the water ring, and evaluate the cementing quality.

3) Convert the wavenumber-frequency distribution curve into a time difference dispersion curve through the relationship between time difference and wave number (time difference is equal to wave number/frequency), and obtain the shape of the time difference dispersion curve (actually corresponding to the thickness of the water ring), and its shape changes with the thickness of the water ring. , the frequencies corresponding to multiple specific time differences can be obtained from the curve. The frequency value has an approximately linear relationship with the water ring thickness. Combined with the wave number-frequency cementing interpretation standard chart, the frequency is used to determine the water ring thickness and evaluate the cementing quality.

Scenario 2:

1) Use the complex exponential function to model the actually measured array acoustic wave logging waveform to obtain the wave number-frequency distribution curve of the cased hole mode wave. Compare it with the wave number-frequency cementing interpretation standard chart. The closest curve corresponds to the water ring thickness. It is the actual measured water ring thickness at the I interface of the casing hole to evaluate the cementing quality. The pattern recognition method can be used to identify the corresponding relationship between the wave number-frequency distribution curve of the actual logging waveform and the theoretical curve (wave number-frequency distribution curve of different water ring thicknesses at the I interface) in the standard chart for cementing interpretation, and obtain the I interface. The water ring thickness is used to evaluate the cementing quality. The image recognition method can also be used to identify the corresponding relationship between the wave number-frequency distribution curve of the actual logging waveform and the theoretical curve (wave number-frequency distribution curve of different water ring thicknesses at the I interface) in the standard chart of cementing interpretation to obtain I The thickness of the water ring at the interface is used to evaluate the cementing quality.

Comprehensively calculate the distance between the actually measured wave number-frequency distribution curve and the wave number-frequency curve of different water ring thicknesses in the standard chart, and take the water ring thickness corresponding to the curve with the smallest distance as the actually measured water ring at the casing well I interface. thickness to evaluate the cementing quality.

2) Use the complex exponential function to model the actually measured array acoustic wave logging waveform to obtain the time difference dispersion curve of the cased hole mode wave. Compared with the time difference-frequency cementing interpretation standard chart, the water ring thickness corresponding to the closest curve is The actual measured water ring thickness at the I interface of the casing well is used to evaluate the cementing quality. The pattern recognition method can be used to identify the corresponding relationship between the time difference and dispersion curve of the actual well logging waveform and the theoretical curve (the time difference and dispersion curve of the I interface with different water ring thicknesses) in the time difference-frequency cementing interpretation standard chart, and obtain the water value of the I interface. ring thickness to evaluate cementing quality. The image recognition method can also be used to identify the corresponding relationship between the time difference and dispersion curve of the actual well logging waveform and the theoretical curve in the time difference and frequency cementing interpretation standard chart (the time difference and dispersion curve of the I interface with different water ring thicknesses), and obtain the I interface. The thickness of the water ring is used to evaluate the cementing quality.

Comprehensively calculate the distance between the actual measured time difference and dispersion curve and the time difference and dispersion curve of different water ring thicknesses in the standard chart, and take the water ring thickness corresponding to the curve with the smallest distance as the actual measured water ring thickness at the casing well I interface. , to evaluate the cementing quality.

Scenario 3: Using the wavenumber-frequency distribution curve when the water ring thickness is 0 in the standard chart for cementing interpretation as the benchmark curve, the wavenumber-frequency is obtained from the actually measured array acoustic logging waveform through the complex exponential function modeling method. The distribution curve is subtracted from the reference curve to obtain the difference (wave number difference) at different frequencies. Add these differences and divide by the total number of added frequencies to obtain an engineering quantity (equivalent to the distribution curve and the thickness of the water ring: The area enclosed between the distribution curves of 0), this engineering quantity has a monotonic relationship with the thickness of the water ring, and this engineering quantity is used to evaluate the cementing quality.

Taking the time difference dispersion curve when the water ring thickness is 0 in the time difference-frequency cementing interpretation standard chart as the benchmark curve, the time difference dispersion curve is obtained by using the complex exponential function modeling method for the actually measured array acoustic wave logging waveform, which is consistent with the benchmark curve. Subtract the curves to get the differences at different frequencies. Add these differences and divide by the total number of added frequencies to get another engineering quantity (equivalent to the difference between the time difference dispersion curve and the dispersion curve with a water ring thickness of 0 The area enclosed by the gap), this engineering quantity has a monotonic relationship with the thickness of the water ring, and this engineering quantity is used to evaluate the cementing quality.

Scenario 4: Use the complex exponential modeling method to obtain the wave number-frequency distribution curve of the low-frequency band (0-9kHz) and high-frequency band (16-35kHz) for the actually measured array acoustic logging waveform, and the slope is the sound velocity of the liquid in the casing hole Compared with the oblique line (this is the second Stoneley wave, its speed is slower than the liquid speed, the time difference is large, and the corresponding slope is large), if there is a wave number distribution with a slope higher than the slope of the oblique line of the liquid in the casing hole, and it is continuous , forming a continuous curve, it is judged that the casing hole I interface is seriously cross-grooved.

For the actually measured array acoustic logging waveform, the complex exponential modeling method is used to obtain the time difference dispersion curves in the low frequency band (0-9kHz) and high frequency band (16-35kHz). If there is a time difference higher than that of the liquid in the casing hole (this If the time difference is close to the time difference distribution curve of the liquid (the reciprocal of the liquid acoustic wave propagation speed), and is continuous, forming a continuous time difference distribution curve, it is judged that the I interface of the casing well is seriously cross-channeled.

Severe cross-channeling can be judged by using the low-frequency (0-9kHz), low-speed mode wave (also called the second Stoneley wave) in the well liquid when severe cross-channeling occurs, and its phase velocity is lower than the sound speed of the well liquid. These waveforms are located after the well liquid wave and are serious cross-trough conditions contained in subsequent waveforms.

Note: The starting point of the cased hole mode wave's time difference dispersion (9-21kHz) curve is located at the shear wave velocity line or shear wave time difference line of the formation, which changes with the formation. When calculating the thickness of the water ring, it is necessary to first determine the shear wave time difference and normalize the k-f distribution curve (i.e., wave number-frequency distribution curve) or the shape of the time difference dispersion curve, and then the curve shape when the water ring thickness is 0 can be applied.

The principle of the present invention will be further explained below with reference to the accompanying drawings.

Figure 1 is the two-dimensional spectrum of the liquid response in the well calculated using a radial multi-layer model (cased well model) with a water ring (thickness 19mm) at the I interface of a 7-inch casing well. The abscissa is the frequency, the ordinate is the wave number, and the casing The two-dimensional spectrum of the response in the liquid in the tube well is only distributed in the white area, and the black part has no amplitude. Taking out the maximum value of the white part, Figure 2 is obtained, which is the distribution of all modes of waves in the liquid in the casing hole with an amplitude greater than 0.4% of the maximum amplitude.

If the thickness of the water ring at the I interface of the casing well is reduced to 1 mm, the two-dimensional amplitude spectrum of the response in the liquid in the well becomes as shown in Figure 3, which is quite different from Figure 1. The k-f distribution of the cased hole mode wave shown in Figure 4 is obtained by marking the maximum value position in Figure 3. This distribution is significantly different from Figure 2.

Figure 2 and Figure 4 are plotted together to obtain Figure 5, in which the thin line is the casing hole mode wave distribution when the water ring thickness is 1mm, and the thick line is the casing hole mode wave distribution when the water ring thickness is 19mm. The difference between the two is the theoretical basis for the patent of the present invention to use mode wave distribution to obtain the I interface water ring thickness and evaluate the cementing quality.

In order to further demonstrate the distribution of casing hole mode waves in k-f at different water ring thicknesses, Figure 6 adds the casing hole mode wave distribution of two water ring thicknesses of 5mm and 10mm. Different from Figures 2 and 4, the peak value of the maximum value Greater than 4% of the maximum peak value of the two-dimensional spectrum. At this time, it was found that the difference in the k-f distribution of the cased hole mode wave only appeared in the frequency range of 9-25kHz and the wave number in the range of 3-10. The k-f distribution of the cased hole mode wave in this range is enlarged to obtain Figure 7. The main difference in k-f distribution caused by different water ring thicknesses occurs in the range of 9-20kHz.

When the water ring thickness of the I interface is 19mm, 10mm, 5mm, etc., a second Stoneley wave with a speed lower than the sound speed of the liquid in the well appears in the range of 0-9kHz, as shown in the upper oblique arc in Figure 1 distributed. The k-f distribution of this wave is located above the oblique line (large slope) of the liquid velocity. Its velocity changes with frequency. It can be seen in all mode wave distributions with maximum amplitude greater than 0.4% of the maximum amplitude of the two-dimensional spectrum, as shown in Figure 8 Show. The low-frequency part is enlarged to obtain Figure 9. Since only this mode wave exists in the low-frequency part and is not coupled with other casing hole mode waves, it is easy to be measured. The patent of this invention uses the distribution of this mode wave to detect serious cross-tank situations. Because its speed is very slow, the time difference is large and clearly separated from other wave time differences, see Figure 21.

The cementing quality detection method based on the k-f distribution of the casing hole mode wave is: as shown in Figure 10(a), all the actual measurement waveforms are taken into the window, and the k-f distribution is obtained using the complex exponential modeling method, as shown in Figure 10(b) As shown in Figure 10(c), the time difference distribution is obtained using the k-f distribution. If there is a peak value in the time difference distribution greater than 700 microseconds/meter (the distribution on the right of 7 in Figure 10(c)), then the depth can be determined qualitatively. There is serious cross-channeling in the location. Figure 11 shows the actual logging waveform and processing results at another depth point. Figure 12 is the actual logging waveform and processing result of another depth point, and the time difference of the Stoneley wave is greater than 700 microseconds/meter. In Figure 10-12, the long straight line is the distribution of Stoneley waves obtained after processing, and the short straight line is the part of the dispersion curve. In actual casing wells, acoustic logging instruments can only measure part of the casing well mode wave shown in Figure 7. These local curves are used to determine the water ring thickness. The processed curve overlaps with the theoretical curve and is consistent with the water ring thickness. The coincidence of the k-f curves is the thickness of the water ring. Or as shown in Figure 11, given the wave number, obtain the frequency through the obtained local curve, use the theoretical curve to establish the relationship between the frequency corresponding to the given wave number and the thickness of the water ring, determine the thickness of the water ring through the frequency, and evaluate the cementing quality. You can also use a given frequency to find the wave number through the processed local curve, and use the theoretical curve to establish the corresponding relationship between the wave number of the given frequency and the thickness of the water ring, determine the thickness of the water ring, and evaluate the cementing quality.

The k-f distribution of cased hole mode waves caused by different water ring thicknesses can also be expressed as a time difference and dispersion curve. The shape of the time difference and dispersion curve is used to determine the water ring thickness of the I interface and evaluate the cementing quality.

Figure 13 is the time difference distribution curve of the cased hole mode wave at four different water ring thicknesses at the I interface. The amplitude of its maximum value is 4% of the maximum amplitude of the two-dimensional spectrum. Similarly, in the 10-20kHz range, the difference in the shape of the dispersion curve is very obvious. Figure 13 is enlarged to obtain Figure 14. Given a time difference (horizontal line), different frequencies can be obtained from the time difference curves of different water ring thicknesses. These frequencies correspond to the water ring thickness, and the water ring thickness can be obtained through the frequency value. Similarly, given a frequency (vertical line), 4 time differences can be obtained. These time differences correspond to the thickness of the water ring, and the thickness of the water ring can be obtained.

Figure 15 is an example of actual well logging waveform processing. Eight waveforms (a) are selected into the window and the time difference dispersion curve (b) is obtained using the complex exponential modeling method. The time difference distribution is obtained from the time difference dispersion curve, and the peak value of the time difference distribution is used to determine the time difference. Figure 16 is another example of actual well logging waveform processing. Compared with Figure 15, the frequency corresponding to a time difference of 400 microseconds/meter is different.

At low frequencies, starting from 0 frequency, the thickness of the water ring will cause the second Stoneley wave, whose amplitude is relatively small, and the time difference changes greatly with the thickness of the water ring. Figure 17 shows the mode wave time difference distribution of four water ring thicknesses when the maximum amplitude is greater than 1% of the maximum amplitude of the two-dimensional spectrum. Two mode waves appear above the horizontal line of 0.7ms/m, with a relatively large time difference at 0.88ms. The /m curve is the second Stoneley wave with a water ring thickness of 19mm. This wave also exists near 20-27kHz, and the time difference is close to the liquid time difference. Another discrete curve with a time difference close to 1ms/m is the second Stoneley wave when the water ring thickness is 10mm. Reduce the amplitude of the maximum value of the mode wave to 0.1% to obtain Figure 18. There are three curves above 0.7ms/m. Below 6kHz, the time difference is very different. After greater than 6kHz, the time difference begins to decrease, and finally tends to the liquid time difference in the well. .

The low-frequency part of Figure 8 is enlarged to obtain Figure 19. From the figure, we can see that in the range of 0 to 6 kHz, there are a total of four waves, the formation longitudinal wave, the shear wave, the time difference of the liquid in the well, and the second Stoneley wave with a relatively large time difference. Among them, the frequency distribution range of the second Stoneley is relatively large and is continuously distributed. The difference in time difference reflects the thickness of the water ring. This time difference can be used to determine the thickness of the water ring. Figure 20 shows the waveforms and time difference distribution processing results of two actual well logs. In the frequency range of 0-6kHz, the first picture has only one Stoneley wave distribution, with a time difference of 700us/m, and the second picture has a second Stoneley wave, with a time difference of 800us/m. The time difference between these two depth positions is relatively large.

Figure 21 is the result after the time difference distribution curve is expressed in color. Looking at the entire depth interval, the distribution and time difference of Stoneley waves change with depth, and the differences are very large. The frequency distribution interval is also very different. Near 2620, it is 700us/m. Near 2625, it splits into two time differences of 650 and 800us/m, and the second Stoneley wave appears. This second Stoneley wave is related to cementing quality. The time difference shown in Figure 19 reflects the water ring thickness at the I interface. Therefore, the time difference can be used to determine the water ring thickness. Because the amplitude and speed of the second Stoneley wave only appear when the thickness of the I interface water ring is relatively large. Therefore, this feature is mainly used to determine the situation of severe cross-tank. That is, the occurrence of such a second Stoneley wave can be used to determine that serious cross-tank has occurred.

The cased hole mode wave is represented by a phase velocity dispersion curve as shown in Figure 22. Only the phase velocity changes with relatively large amplitude (4% of the maximum amplitude of the two-dimensional spectrum) are plotted to obtain Figure 23. The same processing method as k-f distribution and moveout dispersion curve distribution. According to Figures 22 and 23, the shape of the phase velocity dispersion curve is obtained through complex exponential modeling. The shape of the phase velocity dispersion curve is used to determine the thickness of the water ring. The method is simultaneous difference. Distribution determination method. After the water ring thickness is determined, the water ring thickness is used to evaluate the cementing quality.

Figure 24 is a distribution diagram of the time difference dispersion curve at different I interface water ring thicknesses, corresponding to Figure 23. The thickness of the water ring changes, and the jet-lag dispersion curve changes.

The main invention of the patent of this invention is to first theoretically discover that the k-f distribution curve of the cased hole mode wave changes with the thickness of the water ring. This is a basic theoretical discovery based on the solution of the wave equation. It is an original innovation, combined with field application experimental experience, these results are verified, and the original technology is formed after comprehensive cementing quality evaluation methods.

The k-f distribution of cased hole mode waves is the most original theoretical innovation. On the basis of it, the variation rules of acoustic wave time difference dispersion curve and phase velocity dispersion curve with the thickness of water ring are derived. The shape of these curves changes with the thickness of the water ring, that is, the calculation of the thickness of the water ring is attributed to the shape of the dispersion curve. The dispersion curve is obtained through the array acoustic logging waveform, and the water ring thickness calculation method is established using the dispersion curve as an intermediate result. Using dispersion curves to develop I-interface water ring thickness information contained in well logging waveforms is the method innovation of this patent. The I interface water ring thickness information is distributed in the waveform, and the time difference dispersion curve is the carrier that carries the water ring thickness information. Convert the water ring thickness into a time difference dispersion curve and display it as a waveform. To process the waveform to obtain the water ring thickness, the dispersion curve needs to be obtained first. There are many curve shape identification methods based on dispersion curves. This patent mainly protects the method of calculating the thickness of the water ring using the shape of the transit time dispersion curve, k-f distribution shape and phase velocity dispersion curve.

Although the functions and working processes of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the above-mentioned specific functions and working processes. The above-mentioned specific implementations are only illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill can also make many forms without departing from the spirit of the present invention and the scope protected by the claims, and these all fall within the protection of the present invention.

Claims (3)

1. A well cementation quality evaluation method based on an array acoustic logging time difference dispersion curve is characterized in that a well cementation quality is evaluated by utilizing a time difference dispersion curve of a casing well mode wave in a response medium-low frequency range of 9-16kHz and a change rule of a wave number-frequency distribution curve along with the thickness of a water ring, wherein the time difference of the casing well mode wave is between the time difference of a stratum transverse wave and the time difference of a liquid in a well and changes along with the frequency; the method comprises the following steps:

1) Placing an acoustic logging instrument into a cased well, generating vibration by a transmitting probe, sequentially spreading the vibration in the liquid in the well, the casing, the cement sheath and the stratum, and receiving logging waveforms with different source distances by an array receiving probe in the liquid in the well; the acoustic logging instrument comprises a transmitting probe and an array receiving probe formed by a plurality of receiving probes;

2) Obtaining a wave number-frequency distribution curve of a cased well mode wave by using an array acoustic logging waveform through complex exponential function modeling, obtaining a time difference dispersion curve through time difference equal to wave number/frequency, or obtaining a phase velocity dispersion curve through phase velocity equal to frequency/wave number;

3) Respectively obtaining a wave number-frequency distribution curve, a time difference frequency dispersion curve and a phase velocity frequency dispersion curve of different water ring thicknesses of an interface I by using a real-axis integration method, wherein the wave number-frequency distribution curve, the time difference frequency dispersion curve and the phase velocity frequency dispersion curve are respectively used as a wave number-frequency well cementation interpretation standard plate, a time difference-frequency well cementation interpretation standard plate and a phase velocity-frequency well cementation interpretation standard plate;

4) The water ring thickness of the actually measured array acoustic logging waveform can be determined by combining the wave number-frequency well cementation interpretation standard plate, the time difference-frequency well cementation interpretation standard plate and the phase velocity-frequency well cementation interpretation standard plate, so that the well cementation quality can be evaluated, and the serious cross-slot of an I interface in the actual logging can be judged; the method specifically comprises the following situations:

case 1: obtaining wave numbers of different frequencies through complex exponential function modeling on actually measured array acoustic logging waveforms to obtain wave number-frequency distribution curves of cased well mode waves; for a designated wave number, calculating frequency by utilizing a wave number-frequency distribution curve, combining the wave number-frequency well cementation interpretation standard plate, determining the thickness of a water ring by using the frequency, and evaluating the well cementation quality; for the appointed frequency, calculating wave number by utilizing a wave number-frequency distribution curve, combining the wave number-frequency well cementation interpretation standard plate, determining the thickness of a water ring by using the wave number, and evaluating the well cementation quality; converting the wave number-frequency distribution curve into a time difference dispersion curve to obtain the shape of the time difference dispersion curve, taking frequencies corresponding to a plurality of specific time differences from the curve, wherein the frequency values and the water ring thickness are approximately in a linear relation, combining the wave number-frequency well cementation interpretation standard plate, determining the water ring thickness by using the frequencies, and evaluating the well cementation quality;

Case 2: modeling the actually measured array acoustic logging waveform by using a complex exponential function to obtain a wave number-frequency distribution curve of a cased well mode wave, comparing the wave number-frequency distribution curve with a wave number-frequency well cementation interpretation standard chart, wherein the water ring thickness corresponding to the closest curve is the water ring thickness of an actually measured cased well I interface, and evaluating the well cementation quality; in addition, comprehensively calculating the distances between the actually measured wave number-frequency distribution curve and wave number-frequency curves with different water ring thicknesses in a standard plate, taking the water ring thickness corresponding to the curve with the smallest distance as the actually measured water ring thickness of the sleeve well I interface, and evaluating the cementing quality;

modeling the actually measured array acoustic logging waveform by using a complex exponential function to obtain a time difference dispersion curve of a cased well mode wave, comparing the time difference dispersion curve with a time difference-frequency well cementation interpretation standard chart, wherein the water ring thickness corresponding to the closest curve is the water ring thickness of an actually measured cased well I interface, and evaluating the well cementation quality; in addition, comprehensively calculating the distance between the actually measured time difference dispersion curve and the time difference dispersion curves with different water ring thicknesses in the standard plate, taking the water ring thickness corresponding to the curve with the smallest distance as the actually measured water ring thickness of the sleeve well I interface, and evaluating the cementing quality;

Case 3: the wave number-frequency distribution curve when the water ring thickness is 0 in the wave number-frequency well cementation interpretation standard plate is taken as a reference curve, the wave number-frequency distribution curve is obtained by a complex exponential function modeling method for the actually measured array acoustic logging waveform, the wave number-frequency distribution curve is subtracted from the reference curve to obtain differences at different frequencies, the differences are added and divided by the total number of the added frequencies to obtain an engineering quantity, the engineering quantity and the water ring thickness are in monotone relation, and the well cementation quality evaluation is carried out by using the engineering quantity;

taking a time difference dispersion curve when the water ring thickness in a time difference-frequency well cementation interpretation standard plate is 0 as a reference curve, obtaining a time difference dispersion curve from an actually measured array acoustic logging waveform by a complex exponential function modeling method, subtracting the time difference dispersion curve from the reference curve to obtain differences at different frequencies, adding the differences, dividing the differences by the total number of the added frequencies to obtain another engineering quantity, wherein the engineering quantity has a monotonic relation with the water ring thickness, and carrying out well cementation quality evaluation by using the engineering quantity;

case 4: obtaining wave number-frequency distribution curves of a low frequency band and a high frequency band by a complex index modeling method for actually measured array acoustic logging waveforms, and judging that a cased well I interface is seriously jumped when the wave number distribution with the slope higher than that of a liquid inclined straight line in the cased well exists and is continuous and forms a continuous curve compared with the inclined straight line with the slope of the liquid acoustic velocity in the cased well;

The method comprises the steps of obtaining a low-frequency band and high-frequency band time difference dispersion curve by a complex exponential modeling method for actually measured array acoustic logging waveforms, and judging that the interface of the cased well I is seriously jumped if a time difference distribution curve higher than the time difference of liquid in the cased well exists and is continuous, so that a continuous time difference distribution curve is formed.

2. The method for evaluating the well cementation quality based on the time difference dispersion curve of the array acoustic logging according to claim 1, wherein the main frequency of the acoustic logging instrument in the step 1) is consistent with the natural frequency of the liquid mode wave in the cased well, and the frequency of the cased wave peak value is positioned in the bandwidth of the receiving probe; the frequency characteristics of each receiving probe in the array receiving probes are consistent, and the comprehensive sensitivity is consistent.

3. The method for evaluating the quality of well cementation based on the time difference dispersion curve of array acoustic logging according to claim 1, wherein in step 2), the cased well mode wave: when the interface cementing of the cased well I is poor, a water ring exists between the casing and the cement ring, the shear stress on the boundary is 0, a plurality of mode waves appear in the casing solid and are coupled with the mode waves in the liquid in the well to form a plurality of cased well mode waves, the speed of the mode waves changes along with the frequency, and the part of the acoustic logging, the speed of which is equal to the speed of the cased waves, is called as the cased wave; the casing wave measured in the liquid in the casing well consists of a plurality of casing well mode waves, the phase velocity of each casing well mode wave changes with frequency, the change of the phase velocity is small in a certain frequency interval and approaches to the casing wave velocity, the frequency intervals are mutually separated and independent, the amplitude changes along with the frequency, and the amplitude reaches a maximum value at or near the disconnection position; the two adjacent, disconnected, cased well mode wave amplitude curves with the frequency, which are close to the speed of the cased wave, are combined together to form a complete cased wave spectrum peak and wave number peak; the time difference dispersion curve near the peak is close to a constant and equal to the sleeve wave time difference, so that the well cementation quality is poor.