Quantitative evaluation method and system for cementing quality of well cementation interface I of cased well

Abstract

The invention discloses a cased well cementing I interface cementing quality quantitative evaluation method and a cased well cementing I interface cementing quality quantitative evaluation system, a method for extracting an attenuation coefficient frequency dispersion curve corresponding to a real pole of a casing wave in a response function is designed according to an acoustic logging theoretical research result, and an array acoustic logging cementing quality detection method is invented by using the attenuation coefficient frequency dispersion curve. The main theoretical basis is as follows: a casing wave corresponds to a real pole when the well cementation quality of an interface I is poor, and the response of each frequency is a sine wave; and when the well cementation quality is good, the response of each frequency is attenuated sinusoidal oscillation corresponding to a complex pole. And respectively projecting the time difference frequency dispersion curve and the attenuation coefficient frequency dispersion curve to obtain time difference distribution and attenuation coefficient distribution. The characteristics of the concentration degree and the approximate constant of the frequency dispersion curve are represented as distributed peaks and extreme values, and the shapes and extreme values of the peaks intuitively reflect the well cementation quality. And identifying casing waves based on the time difference distribution curve, and quantitatively evaluating the well cementation quality by using the identified casing waves or the I interface equivalent water ring thickness.

Description

Technical Field

[0001] The present invention belongs to the technical field of special instruments for measuring formation physical parameters and lithology evaluation in cased wells during oil engineering logging operations, and relates to a method and system for quantitatively evaluating the cementing quality of the I interface in cased wells. Background Art

[0002] The evaluation of cementing quality in cased wells is crucial for the safe production of oilfields. The most commonly used method for evaluating cementing quality is acoustic logging. The first arrival amplitude measured at a source spacing of 3 feet and the full wave variable density measured at a source spacing of 5 feet are used to evaluate and identify the cementing quality of the I interface and II interface of the cementing respectively. This logging method is based on the sliding wave theory. A large number of studies have been conducted on the waveform characteristics of cased wells. For example, the characteristics of waveforms have been obtained by numerical methods, and the mode wave distribution of cased wells has been obtained by mode wave analysis. However, the relationship between the casing wave and the mode wave of the cased well has not been clarified as a whole, and the relationship between the logging casing wave and the mode wave of the cased well has not been established. Therefore, except for using the first arrival amplitude to reflect the cementing quality of the I interface of the cementing, no new curves and methods have been generated. Constrained by the response of simple harmonic waves with real frequencies (the basic method for studying the transient acoustic logging response), the response characteristics of the formation longitudinal wave have not been obtained in previous studies, and the fundamental difference between the formation longitudinal wave and the casing wave in cased wells has not been recognized. The sliding wave only explains the propagation path, while the cementing evaluation uses the waveform amplitude. Therefore, understanding the cased well response based on the sliding wave theory hinders people's understanding of the acoustic wave propagation characteristics of cased wells, makes it impossible to effectively extract the cementing quality information in the waveform, restricts the development of acoustic logging technology in cementing quality evaluation, and makes it impossible to form new acoustic logging technologies, discover and construct new logging curves. Summary of the Invention

[0003] The purpose of the present invention is to solve the problem in the prior art that the cementing quality information in the waveform cannot be effectively extracted, which restricts the development of acoustic logging technology in cementing quality evaluation, and to provide a method and system for quantitatively evaluating the cementing quality of the I interface in cased wells.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for quantitatively evaluating the cementing quality of the I interface in cased wells proposed by the present invention includes the following steps:

[0006] Extract the wave peaks of the array acoustic logging waveform, process the obtained waveform to obtain the complex wave number of the complex exponential function, and obtain the attenuation coefficient dispersion curve and the time difference dispersion curve based on the complex wave number;

[0007] Project the time difference dispersion curve onto the time difference axis, obtain the number of time difference frequency points in the time difference dispersion curve, and convert the time difference dispersion curve into a time difference distribution curve;

[0008] Project the attenuation coefficient dispersion curve onto the attenuation coefficient axis, obtain the number of attenuation coefficient frequency points in the attenuation coefficient dispersion curve, and convert the attenuation coefficient dispersion curve into an attenuation coefficient distribution curve;

[0009] Extract the peak position from the attenuation coefficient distribution curve to obtain the casing wave attenuation coefficient, and obtain the water ring thickness of the I interface based on the casing wave attenuation coefficient;

[0010] Identify the casing wave based on the time difference distribution curve, and realize the quantitative evaluation of the cementing quality of the I interface in the array acoustic logging through the identified casing wave and the water ring thickness of the I interface.

[0011] Preferably, use a windowing method with equal window width and determined slope to extract the wave peaks in front of the array acoustic logging waveform.

[0012] Preferably, perform FFT on each extracted waveform to obtain the spectrum, and use the Prony method or the improved matrix method to process each frequency to obtain the complex wave number of the complex exponential function.

[0013] Preferably, extract the real part of the complex wave number of the complex exponential function to obtain the attenuation coefficient at that frequency, and extract the imaginary part of the complex wave number of the complex exponential function to obtain the time difference;

[0014] Among them, when performing FFT on the phase corresponding to the imaginary part, perform a phase compensation of adding 2π. Divide the compensated phase by 2π and the probe spacing to obtain the wave number, and then divide by the frequency to obtain the time difference. Perform the above processing for each frequency to obtain the attenuation coefficient dispersion curve and the time difference dispersion curve respectively.

[0015] Preferably, utilize the characteristics that the time difference of the casing wave is close to a constant and continuously distributed along the frequency axis to realize the identification of the casing wave.

[0016] Preferably, the longer the frequency interval in which the casing wave is distributed, the sharper the peak.

[0017] Preferably, the sharper the peak, the more obvious the casing wave, and the worse the cementing quality.

[0018] A quantitative evaluation system for the cementing quality of the I interface in a cased well proposed by the present invention includes:

[0019] A dispersion curve acquisition module, which is used to extract the wave peaks of the array acoustic logging waveform, process the extracted waveforms to obtain the complex wave number of the complex exponential function, and obtain the attenuation coefficient dispersion curve and the time difference dispersion curve based on the complex wave number;

[0020] A first dispersion curve conversion module, which is used to project the time difference dispersion curve onto the time difference axis, obtain the number of time difference frequency points in the time difference dispersion curve, and convert the time difference dispersion curve into a time difference distribution curve;

[0021] A second dispersion curve conversion module, which is used to project the attenuation coefficient dispersion curve onto the attenuation coefficient axis, obtain the number of attenuation coefficient frequency points for each attenuation coefficient in the attenuation coefficient dispersion curve, and convert the attenuation coefficient dispersion curve into an attenuation coefficient distribution curve;

[0022] An I-interface water ring thickness acquisition module, which is used to extract the peak position from the attenuation coefficient distribution curve to obtain the casing wave attenuation coefficient, and obtain the I-interface water ring thickness based on the casing wave attenuation coefficient;

[0023] An I-interface cementing quality acquisition module, which is used to identify the casing wave based on the time difference distribution curve, and realize the quantitative evaluation of the cementing quality of the I-interface in array acoustic logging through the identified casing wave and the I-interface water ring thickness.

[0024] A computer device, including a memory and a processor, where the memory stores a computer program, and when the processor executes the computer program, it implements the steps of the method for quantitatively evaluating the cementing quality of the I-interface in a cased well.

[0025] A computer-readable storage medium, where the computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, it implements the steps of the method for quantitatively evaluating the cementing quality of the I-interface in a cased well.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] A method for quantitatively evaluating the cementing quality of the I-interface in a cased well proposed by the present invention designs a method for extracting the attenuation coefficient dispersion curve corresponding to the real poles of the casing wave in the response function according to the research results of acoustic logging theory, and invents a method for detecting the cementing quality of array acoustic logging using the attenuation coefficient dispersion curve. Its main theoretical basis is: when the cementing quality of the I-interface is poor, the casing wave corresponds to real poles, and the response at each frequency is a sine wave; when the cementing quality is good, it corresponds to complex poles, and the response at each frequency is a decaying sine oscillation. Projecting the time difference dispersion curve and the attenuation coefficient dispersion curve respectively can obtain the time difference distribution and the attenuation coefficient distribution. The concentration degree and the characteristic of being close to a constant of the dispersion curve are manifested as the peaks and extreme values of the distribution, and the shapes of these peaks and the extreme values intuitively reflect the cementing quality. Taking out the extreme value positions of the distribution respectively obtains the time difference and the attenuation coefficient of the casing wave. The casing wave is identified based on the time difference distribution curve. This attenuation coefficient has a monotonic relationship with the thickness of the equivalent water ring at the I-interface. The cementing quality is quantitatively evaluated using the identified casing wave or the thickness of the equivalent water ring at the I-interface.

[0028] A quantitative evaluation system for the bonding quality of the I interface in casing well cementing proposed by the present invention realizes the quantitative evaluation of the bonding quality of the I interface in array acoustic logging cementing by dividing the system into a dispersion curve acquisition module, a first dispersion curve conversion module, a second dispersion curve conversion module, an I interface water ring thickness acquisition module, and an I interface bonding quality acquisition module. The modular idea is adopted to make each module independent of each other, facilitating the unified management of each module. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 It is a flow chart of the method for quantitatively evaluating the bonding quality of the I interface in casing well cementing of the present invention.

[0031] Figure 2 It is a two-dimensional spectrogram in the well fluid of the casing well of the present invention.

[0032] Figure 3 It is the mode wave distribution and casing wave amplitude in the well fluid of the casing well of the present invention.

[0033] Figure 4 It is a graph showing the variation of the extreme value of the casing wave with frequency at different water ring thicknesses of the I interface of the present invention.

[0034] Figure 5 It is to obtain the attenuation coefficient by fitting the variation curve of the extreme value of the casing wave with frequency using a double-sided exponential function in the present invention.

[0035] Figure 6 It is the fitting result using a double-sided exponential function in the present invention, and it is a graph showing the monotonic variation relationship between the attenuation coefficient and the water ring thickness.

[0036] Figure 7 It is a graph of the waveform of array acoustic logging in the casing well of the present invention and the selection of its first wave (fixed window length and slope).

[0037] Figure 8 It is a time difference dispersion curve graph of the first wave waveform processing in the present invention.

[0038] Figure 9 It is a time difference distribution graph obtained by projecting the time difference dispersion curve onto the time difference axis in the present invention.

[0039] Figure 10 For the present invention Figure 7 It is an attenuation coefficient dispersion curve graph of the first wave waveform processing.

[0040] Figure 11 is the attenuation coefficient distribution map obtained by projecting the attenuation coefficient dispersion curve of the present invention. Figure 10

[0041] Figure 12 is the time difference and attenuation coefficient distribution map processed from the actual logging waveforms of the casing well of the present invention.

[0042] Figure 13 is the system diagram for quantitatively evaluating the cementing quality of the I interface in the casing well of the present invention. Detailed implementation manners

[0043] To make the objectives, 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 with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components of the embodiments of the present invention described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0044] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0045] It should be noted that: similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0046] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper", "lower", "horizontal", "inner", etc. are used to indicate the orientation or positional relationship, it is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the present invention is usually placed when in use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present invention. In addition, terms such as "first", "second", etc. are only used for distinguishing descriptions and cannot be construed as indicating or implying relative importance.

[0047] In addition, if the term "horizontal" appears, it does not mean that the component is required to be absolutely horizontal, but it can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but it can be slightly inclined.

[0048] In the description of the embodiments of the present invention, it should also be noted that unless otherwise clearly specified and limited, if the terms "set", "install", "connected", "connected" are used, they should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] The following further describes the present invention in detail with reference to the accompanying drawings:

[0050] A method for quantitatively evaluating the bonding quality of the I interface in cementing of cased wells proposed by the present invention, as Figure 1 shown, includes the following steps:

[0051] S1. Extract the wave peaks of the array acoustic logging waveform, process the extracted waveform to obtain the complex wave number of the complex exponential function, and obtain the attenuation coefficient dispersion curve and the time difference dispersion curve based on the complex wave number.

[0052] Use the windowing method with equal window width and determined slope to extract the wave peaks in front of the array acoustic logging waveform.

[0053] Perform FFT on each extracted waveform to obtain the spectrum, and use the Prony method or the improved matrix method to process each frequency to obtain the complex wave number of the complex exponential function.

[0054] S2. Project the time difference dispersion curve onto the time difference axis, obtain the number of time difference frequency points in the time difference dispersion curve, and convert the time difference dispersion curve into a time difference distribution curve.

[0055] Take the real part of the complex wave number of the complex exponential function to obtain the attenuation coefficient at this frequency, and take the imaginary part of the complex wave number of the complex exponential function to obtain the time difference.

[0056] Among them, when performing FFT on the phase corresponding to the imaginary part, perform a phase compensation of adding 2π. Divide the compensated phase by 2π and the probe spacing to obtain the wave number, and then divide by the frequency to obtain the time difference. Perform the above processing for each frequency to obtain the attenuation coefficient dispersion curve and the time difference dispersion curve respectively.

[0057] S3. Project the attenuation coefficient dispersion curve onto the attenuation coefficient axis, obtain the number of attenuation coefficient frequency points in the attenuation coefficient dispersion curve, and convert the attenuation coefficient dispersion curve into an attenuation coefficient distribution curve.

[0058] S4. Extract the peak position from the attenuation coefficient distribution curve to obtain the attenuation coefficient of the casing wave, and obtain the water ring thickness of the I interface based on the attenuation coefficient of the casing wave.

[0059] S5. Identify the casing wave based on the time difference distribution curve, and realize the quantitative evaluation of the cementing quality of the cementing interface I in array acoustic logging through the identified casing wave and the water ring thickness at the interface I.

[0060] Utilize the characteristics that the time difference of the casing wave is close to a constant and is continuously distributed in segments along the frequency axis to identify the casing wave.

[0061] The longer the frequency range in which the casing wave is distributed, the sharper the peak. The sharper the peak, the more obvious the casing wave, and the worse the cementing quality.

[0062] The following is a detailed description of this method:

[0063] The envelope of the casing wave reflects the spectral shape of its single peak. The liquid mode wave in the well is coupled with the casing wave, and a single peak is formed in the casing wave spectrum around the natural frequency. Its response is a decaying oscillation, and the envelope is decaying, which is fitted with an exponential function. In order to obtain this envelope, an array acoustic logging instrument must be used, with at least 4 receiving probes. The instrument is centered in the well with a centralizer for logging. Determine the source distance from the transmitting probe to the first receiving probe according to the envelope shape of the casing wave distributed along the well axis, ensure that all receiving probes are located in the decaying region of the casing wave distribution envelope, and the obtained attenuation coefficient is positive.

[0064] Based on the casing wave velocity determined by the casing and instrument dimensions, determine the starting position of the casing wave of the first source distance waveform from the actual logging waveform. Use the windowing method with equal window width and determined slope to extract the wave peaks in front of the array acoustic logging waveform. Perform FFT on each extracted waveform to obtain its spectrum. For each frequency, use the Prony method or the improved matrix method to process and obtain the complex wave number of the complex exponential function. Its real part corresponds to the attenuation coefficient, and the imaginary part corresponds to the time difference.

[0065] Extract the real part of the complex wave number to obtain the attenuation coefficient at this frequency, and extract the imaginary part to obtain the time difference. Among them, for the phase corresponding to the imaginary part, there is a loss of 2π in the part with relatively high frequencies during FFT, and 2π losses are accumulated successively as the frequency increases. Perform 2π phase compensation according to the actual situation. Divide the compensated phase by 2π and the probe spacing to obtain the wave number, and then divide by the frequency to obtain the time difference. Perform such processing for each frequency to obtain the attenuation coefficient dispersion curve and the time difference dispersion curve respectively.

[0066] When the first arrival wave taken is only the casing wave, the time difference dispersion curve obtained changes relatively little with frequency, approaching a constant. The time difference dispersion curve is a straight line or close to a straight line, and the attenuation coefficient also changes relatively little with frequency, approaching a straight line. Project the time difference dispersion curve onto the time difference axis, that is, count how many frequency points there are for each time difference in the processed time difference dispersion curve, and convert the time difference dispersion curve into a time difference distribution curve (the curve of the change of the statistical points with the time difference). The straight line segments in different frequency intervals of the time difference dispersion curve are all converted into peaks of the time difference distribution curve. The time difference distributions of the casing waves with the same time difference in different frequency intervals are superimposed together, increasing the peak value of the time difference distribution curve. The longer the frequency interval where the casing wave is distributed, the sharper the peak, and the more obvious the casing wave. At this time, a casing wave identification method is designed using the characteristics that the time difference of the casing wave is close to a constant and is continuously distributed along the frequency axis. As long as the casing wave exists, even if its amplitude is relatively small, due to its large distribution frequency range, the obtained peak of the time difference distribution is also equally sharp, and the accuracy of identifying the casing wave is relatively high. The existence of the casing wave indicates poor cementing quality at the cementing I interface. Therefore, identifying whether the casing wave exists is one of the keys to judging the cementing quality of the cased well.

[0067] Quantitatively evaluate the cementing quality of the cementing I interface using the attenuation coefficient dispersion curve of the casing wave. The attenuation coefficient dispersion curve obtained from the selected first arrival wave also has the characteristics of changing relatively little with frequency and being relatively constant when the first arrival wave is the casing wave, and the attenuation coefficient is close to a constant. Project the attenuation coefficient dispersion curve onto the attenuation coefficient axis, count how many frequencies there are for each attenuation coefficient in the processed attenuation coefficient dispersion curve, obtain the number of points corresponding to each attenuation coefficient, and convert the attenuation coefficient dispersion curve into an attenuation coefficient distribution curve of the change of the statistical points with the attenuation coefficient. The part of the attenuation coefficient dispersion curve close to the straight line segment is converted into the peak of the distribution curve, and the position of the peak corresponds to the attenuation coefficient of the straight line segment.

[0068] The above results are obtained by simulating the single-peak spectrum of the casing wave disconnected at the resonance frequency with the single-peak spectrum of exponential decay oscillation. The extreme amplitude of the casing wave changes with frequency at the resonance frequency, forming a disconnected single-peak distribution. This single-peak amplitude and shape are both monotonically related to the thickness of the water ring. CBL is the manifestation of the single-peak amplitude, and the attenuation coefficient obtained from the Prony method or the matrix method describes the shape of this disconnected single-peak. The spectrum of the exponential decay oscillation function is a continuous single-peak, and the attenuation coefficient is obtained by fitting its shape to the disconnected single-peak shape of the casing wave. CBL and the attenuation coefficient respectively describe the main characteristics such as the amplitude and shape of the casing wave spectrum.

[0069] The wider the region of the straight line distribution in the processed time difference dispersion curve, the larger the peak value of the time difference distribution after projection, the more concentrated the distribution, the more obvious the casing wave, and the worse the cementing quality; the larger the peak value of the attenuation coefficient distribution projected by the attenuation coefficient dispersion curve, the more concentrated the distribution, the more obvious the casing wave, and the worse the cementing quality.

[0070] The time difference at the peak position is taken from the time difference distribution curve to obtain the casing wave time difference, and the peak position is taken from the attenuation coefficient distribution curve to obtain the attenuation coefficient of the casing wave. Here, it is utilized that the casing wave is the real pole of the response function. When excited by a sinusoidal wave with a real frequency, there is a corresponding sinusoidal steady-state response. This response can exist in the well fluid of the cased well for a long time, forming a steady-state solution. Its response amplitude varies with frequency and reaches a maximum value at the natural frequency, corresponding to the extreme value of the response function and forming a resonance response. This is unique to the vibration mode of the casing and is the mode wave formed after countless reflections of the acoustic wave on the inner and outer walls of the casing. It is formed by the superposition of the casing waves excited countless times in the casing when the acoustic wave propagating radially in the well fluid is reflected countless times by the inner wall of the casing. Countless casing waves are periodically excited, propagate along the casing, and have the largest amplitude at the natural frequency, forming resonance. At other frequencies, there is no resonance and the amplitude is small, but there is still a steady-state solution, which is also a sinusoidal wave that varies continuously with time. This is because when the acoustic wave is reflected countless times on the inner and outer walls of the casing, the wave impedance difference between the casing and the fluid is large, the reflection coefficient is large, and the transmission coefficient is small. Most of the energy entering the casing accumulates in the casing wall thickness and very little leaks. When propagating along the well axis, it can maintain the energy required for sinusoidal oscillation through the excitation of countless reflected waves, forming a sinusoidal steady-state response and being able to exist in the well for a long time. The coupled wave of the well fluid also provides continuous excitation through this way of countless reflections, forming a steady-state solution.

[0071] The formation compressional wave leaks energy into the formation through transmission. The reflection coefficient of the well fluid is less than 1. When propagating along the well axis, its acoustic wave response amplitude attenuates both with the source distance and with time. The response of each frequency is a transient solution. In the response function, it is manifested as complex poles for both frequency and wavenumber.

[0072] When the I interface is poorly consolidated, there are water-filled microcracks at the I interface, which are equivalent to the water ring thickness. The outer wall of the casing is water and the shear stress is 0. The shear stress of the acoustic wave in the casing is all reflected. The vibration energy forms casing waves through countless reflections on the inner and outer walls of the casing. The casing wave has a disconnected single-peak spectrum at the natural frequency, and the corresponding attenuation coefficient varies little with frequency. There is a monotonic relationship between the equivalent water ring thickness at the I interface and the attenuation coefficient, corresponding to the relationship chart of the equivalent water ring thickness and the attenuation coefficient. Using this chart, the equivalent water ring thickness can be obtained from the attenuation coefficient to quantitatively evaluate the cementing quality.

[0073] When the cementing quality is good and there is complete bonding, when acoustic waves pass through the outer interface of the casing and come into direct contact with the cement sheath, the tangential stress is continuous, and the energy enters the cement sheath and the formation through the interface. The energy of the casing wave leaks into the cement sheath and the formation, and the amplitude of the casing wave is very small. The first wave of the logging waveform is mainly the formation longitudinal wave, corresponding to the complex poles of the response function. The response at each frequency is not a sinusoidal steady-state response. The time difference dispersion curve and the attenuation coefficient dispersion curve processed by the Prony method and the improved matrix method do not form a concentrated distribution. The distribution obtained by projecting onto the attenuation coefficient is uncertain, and the distributions obtained from different depth intervals of the well are not concentrated and cannot form a continuously varying curve, but instead jump back and forth.

[0074] When the bonding of the cementing I interface is poor, the casing wave corresponds to the real poles of the response function, and the response at each frequency is a sinusoidal steady-state solution. The frequency spectrum of the casing wave can be fitted with an exponential function, and the obtained attenuation coefficient does not change with frequency and is close to a constant. When the bonding is good, the casing wave becomes a complex pole with a large imaginary part and a very small amplitude. The attenuation coefficients fitted with the exponential function are not concentrated.

[0075] When both the casing wave and the formation longitudinal wave exist in the first wave of the logging waveform, multi-mode waves are processed, and the time difference and attenuation coefficient dispersion curves of multiple mode waves are obtained simultaneously. The time difference distributions of the two are close to a straight line; the attenuation coefficient dispersion curve of the casing wave is close to a straight line, and the attenuation coefficient forms a peak; the attenuation coefficient distribution of the formation longitudinal wave is not concentrated and does not form a peak.

[0076] Figure 2 It is the two-dimensional spectrum of the response of the fluid in the cased well. There is a 1-mm water ring on the interface between the casing and the cement sheath, simulating poor bonding of the cementing I interface. Since it is a fluid between the casing and the cement sheath, the shear stress is 0, and the shear stress of the casing solid is completely reflected at the outer interface of the casing, forming a casing wave propagating along the well axis. Its velocity is constant within the frequency range of logging. In the plane formed by the frequency f and the wave number k, it is a straight line with a slope equal to the time difference of the casing wave, and the extreme values of the response function are distributed along the straight line. The acoustic wave propagating radially in the well fluid is reflected when it reaches the inner wall of the casing, and the reflected wave will reach the inner wall of the casing again and be reflected when propagating radially. Countless reflections form natural frequencies and resonance responses, which are hyperbolas in the f-k plane, and the extreme values of the response function are distributed along the hyperbolas. When there is fluid in the casing, the hyperbola intersects with the straight line, and the shape of the extreme value of the response function changes at the intersection point. Connecting the straight line and the hyperbola forms a new continuous distribution, and both the hyperbola and the straight line are truncated. See Figure 2 The region where the lower hyperbola in the figure is truncated is located between the two straight lines.

[0077] When the sound source is excited in the well fluid, the extreme amplitude on the hyperbola is large. The mode wave in the casing couples to the well fluid through the inner wall of the casing to generate the casing wave, which follows the distribution after the hyperbola is truncated by the straight line. Among them, the response function forms an extreme value around the straight line of the casing wave, and the amplitude is larger closer to the intersection point. The extreme value distributions along the straight line on both sides of the intersection point form discontinuous single peaks. The spectra corresponding to these single peaks propagate at the casing wave velocity and are the real poles of the well fluid response function (a bivariate complex function), and each frequency corresponds to a sinusoidal steady-state solution. Therefore, signal processing methods (Prony and improved matrix methods) based on linear time-invariant systems can be used to process the first arrival wave. Fit its spectrum to obtain the time difference dispersion curve and the attenuation coefficient dispersion curve, and extract the casing wave information contained in the actual logging waveform. If there is a casing wave in the first arrival wave, there is a frequency interval where the time difference dispersion curve and the attenuation coefficient dispersion curve are close to constants. Among them, the constant value of the attenuation coefficient varies with the thickness of the water ring at the cementing I interface, and this attenuation coefficient is used to evaluate the cementing quality.

[0078] The distribution of the casing wave is located Figure 2 in the lowest discontinuous oblique straight line part of the two-dimensional spectrum of Figure 2 . To study the relationship between the cementing quality and the casing wave, the extreme values of the two-dimensional spectrum of Figure 3 are taken out to obtain Figure 3 . Among them, the thickest line at the bottom is the position of the extreme value distribution of the casing wave, and its distribution area along the casing wave line is large and is discontinuous at the intersection position with the hyperbola. The extreme values distributed along the casing wave line are taken out to obtain the Figure 4 curve. It reaches an extreme value and is discontinuous at the intersection point. The extreme value distributions on both sides of the intersection point together form a discontinuous single peak. The amplitude and shape of this peak change with the thickness of the water ring, as shown in

[0079] . On both sides of the peak, the curves are basically coincident with small differences, which do not reflect the cementing quality of the cement sheath; at the break point position, the amplitude difference is large and the shape difference is also large, which is the most sensitive to the cementing quality. Among them, the difference in amplitude is manifested in the amplitude of the casing wave, forming the CBL, which has been used for a long time. Because the amplitude is also affected by other factors, it has multiple solutions. This invention patent uses the difference in the spectrum shape of the casing wave to generate a new array acoustic logging curve to evaluate the cementing quality of the cement sheath. Figure 4 The inverse FFT is performed on the extreme amplitude curve (casing wave spectrum) in Figure 4The result of superimposing sine waves corresponding to the amplitudes of each frequency in the shown extreme amplitude curve.

[0080] Fitting with the unimodal continuous spectrum of the exponential function Figure 4 of the extreme value distribution to obtain Figure 5 the shown fitting result. From the continuous unimodal peak after fitting, the attenuation coefficient can be obtained. This attenuation coefficient does not change with frequency and is a constant within the entire frequency range. Because the spectrum of the exponential function:

[0081]

[0082] changes with the frequency f and reaches a maximum value at f0 to form a continuous unimodal peak. Its numerator A and attenuation coefficient α are both constants and do not change with frequency. After fitting the actually measured first wave waveform with the above spectrum, if there is a frequency range where the attenuation coefficient α is a constant, it indicates that the actually measured spectrum is close to the spectrum of the exponential function, and the actually measured waveform contains casing waves.

[0083] Using Figure 5 the shown fitting method to fit Figure 4 the discontinuous unimodal peaks of each water ring thickness shown to obtain the variation curve of the attenuation coefficient with the water ring thickness, as Figure 6 shown. This is a monotonically changing curve. It establishes a relationship chart between the attenuation coefficient and the water ring thickness. The water ring thickness can be obtained using the attenuation coefficient to quantitatively evaluate the cementing I interface.

[0084] Figure 7 is the actually measured logging waveform of a depth point. Using Figure 7 the shown oblique straight line as the starting position, taking out the first wave waveform with a fixed window width, and processing it with the improved matrix method to obtain Figure 8 the time difference dispersion curve shown. Among them, the time difference of the lower curve is close to a constant, and there are three discontinuous positions, which is consistent with the distribution characteristics of the lowest casing wave shown in Figure 3 . It is the time difference dispersion curve of the casing wave. The time difference distribution obtained by projecting the time difference dispersion curve onto the time difference axis is as Figure 9 shown. It reaches a maximum value at the casing wave time difference position, and the maximum value corresponds to 230, indicating that there are 230 frequencies whose time difference is the casing wave time difference. The casing wave time difference can be obtained from this maximum value. This distribution can also be used to judge whether the casing wave exists. When the I interface is poorly consolidated, the casing wave exists, and the frequency distribution interval of its time difference is relatively large. After projecting the time difference dispersion curve, the time difference distribution curve shows a maximum value at the casing wave time difference position, forming a sharp peak.

[0085] When processing the first wave waveform with the improved matrix method, the attenuation coefficient dispersion curve is also obtained simultaneously. Figure 10 It is obtained using Figure 7The attenuation coefficient dispersion curve obtained from the first arrival waveform shown. Compared with the travel time dispersion curve, it varies greatly with frequency. However, within the range of 14 - 20 kHz between two breakpoints, the attenuation coefficient is close to a straight line, and a peak appears in the distribution obtained by projecting the entire attenuation coefficient, as Figure 11 shown. The position corresponding to this peak is the attenuation coefficient of the casing wave. Representing the acoustic travel time distribution and attenuation coefficient distribution of all depth points in gray scale gives Figure 12 , where the leftmost one is the travel time distribution. The travel time of the casing wave varies little with depth and has a relatively large peak. The second trace from the left is the depth, and the third trace is the distribution of the attenuation coefficient, which is also relatively concentrated and forms a curve with depth. Taking the position of its maximum value gives the attenuation coefficient curve, as seen in the fourth trace, where there are two curves obtained by taking different window widths. Its variation with depth reflects the water ring thickness at the cementing I interface. They are the cementing information contained in the waveform shape of the array acoustic logging, obtained from the attenuation coefficient dispersion curves at various frequencies, and is a new cementing quality evaluation curve. It is based on the spectral peak where the casing wave is disconnected and obtained by means of signal processing methods such as exponential function modeling.

[0086] A quantitative evaluation system for the bonding quality of the cementing I interface in a cased well proposed by the present invention, as Figure 13 shown, includes a dispersion curve acquisition module, a first dispersion curve conversion module, a second dispersion curve conversion module, an I interface water ring thickness acquisition module, and an I interface bonding quality acquisition module;

[0087] The dispersion curve acquisition module is used to extract the wave peaks of the array acoustic logging waveform, process the extracted waveform to obtain the complex wave number of the complex exponential function, and obtain the attenuation coefficient dispersion curve and the travel time dispersion curve based on the complex wave number;

[0088] The first dispersion curve conversion module is used to project the travel time dispersion curve onto the travel time axis, obtain the number of travel time frequency points in the travel time dispersion curve, and convert the travel time dispersion curve into a travel time distribution curve;

[0089] The second dispersion curve conversion module is used to project the attenuation coefficient dispersion curve onto the attenuation coefficient axis, obtain the number of attenuation coefficient frequency points in the attenuation coefficient dispersion curve, and convert the attenuation coefficient dispersion curve into an attenuation coefficient distribution curve;

[0090] The I interface water ring thickness acquisition module is used to extract the peak position from the attenuation coefficient distribution curve to obtain the casing wave attenuation coefficient, and obtain the I interface water ring thickness based on the casing wave attenuation coefficient;

[0091] The I interface bonding quality acquisition module is used to identify the casing wave based on the travel time distribution curve, and realize the quantitative evaluation of the bonding quality of the cementing I interface of the array acoustic logging through the identified casing wave and the I interface water ring thickness.

[0092] The terminal device provided by an embodiment of the present invention includes: a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps in the above-mentioned method embodiments are implemented. Alternatively, when the processor executes the computer program, the functions of each module / unit in the above-mentioned device embodiments are implemented.

[0093] The computer program may be divided into one or more modules / units, and the one or more modules / units are stored in the memory and executed by the processor to complete the present invention.

[0094] The terminal device may be a computing device such as a desktop computer, a notebook, a palm computer, or a cloud server. The terminal device may include, but is not limited to, a processor and a memory.

[0095] The processor may be a central processing unit (CPU), or may also be other general-purpose processors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0096] The memory may be used to store the computer program and / or module, and the processor realizes various functions of the terminal device by running or executing the computer program and / or module stored in the memory, and by invoking the data stored in the memory.

[0097] If the modules / units integrated in the terminal device are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, to implement all or part of the processes in the above-described embodiment methods of the present invention, it can also be completed by instructing relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by a processor, the steps of the above-described method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in the form of source code, object code, executable file, or some intermediate form, etc. The computer-readable medium can include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic disk, optical disc, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electrical carrier signal, telecommunication signal, and software distribution medium, etc. It should be noted that the content included in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice within the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, the computer-readable medium does not include electrical carrier signals and telecommunication signals.

[0098] A method for quantitatively evaluating the cementing quality of the I interface in a cased well proposed by the present invention has the following advantages:

[0099] The acoustic wave propagating radially in the well fluid is reflected countless times on the wellbore to form the natural frequency of the wellbore. The extreme values of its response function are distributed along a hyperbola in the frequency-wavenumber plane; when the cementing of the I interface is poor, the mode wave of the casing itself has a constant propagation speed within the logging frequency range, and its extreme values are distributed along a straight line in the frequency-wavenumber plane; the hyperbola intersects with the straight line, and both the straight line and the hyperbola are truncated around the intersection point. The casing wave forms a discontinuous distribution along the straight line, and the extreme value of the function reaches a maximum value at the discontinuous point, forming a single peak. The amplitude and shape of this single peak change simultaneously with the equivalent water ring thickness of the I interface. The amplitude of the single peak affects the amplitude of the first arrival wave CBL. This invention patent utilizes the monotonic relationship between the shape of the single peak and the water ring thickness, and generates an attenuation coefficient dispersion curve through modern signal processing technology to quantitatively evaluate the cementing quality of the I interface.

[0100] The composition of the casing wave is mainly determined by the amplitude and shape of the discontinuous single peak spectrum around the natural frequency of the wellbore. Its speed is close to the casing wave speed and remains unchanged within the frequency range between two natural frequencies. After clearly understanding this natural law, select the corresponding modern signal processing method, fit the casing wave spectrum with the spectrum of a single peak with exponential decay oscillation shape, extract the cementing quality information in the casing wave waveform, and realize the quantitative evaluation of the cementing quality.

[0101] Modern signal processing methods are based on the theory of the response of linear time-invariant systems under simple harmonic excitation. First, it is required that the system responds to simple harmonic waves, that is, there is a sinusoidal steady-state response at each frequency. The casing wave corresponds to the real poles of the casing well response function and is distributed along a straight line with the slope of the casing wave time difference in the frequency-wavenumber plane. There is a sinusoidal steady-state solution at each frequency, meeting the conditions of a linear time-invariant system. Therefore, the spectrum of exponentially decaying oscillations is used to simulate the casing wave. The obtained attenuation coefficient changes relatively little with frequency and is close to a constant. After projecting onto the attenuation coefficient, a peak can be formed to obtain the attenuation coefficient distribution curve, which is unique to the casing wave and reflects the cementing quality. The worse the cementing quality of the I interface, the sharper the peak, and its distribution constitutes a distribution image for intuitively judging the cementing quality.

[0102] The formation compressional wave corresponds to the complex poles of the casing well response function. Both the frequency and wavenumber of the poles are complex numbers, and the poles are distributed in the four-dimensional space formed by the frequency complex plane and the wavenumber complex plane. The response function is a complex function of two variables, frequency and wavenumber. This complex function reaches an extreme value at the complex poles, and this extreme value is distributed along a straight line with the slope of the formation compressional wave time difference in the frequency-wavenumber plane. According to the residue theorem of complex functions, the response of a complex pole with a complex frequency itself is an oscillating decay with time. The formation compressional wave response is composed of the superposition of these decaying oscillations and is not composed of the superposition of non-decaying sinusoidal steady-state responses. Therefore, it does not meet the conditions of a linear time-invariant system. The attenuation coefficients obtained by the Prony method and the improved matrix method of modern signal processing do not change concentratedly with frequency, and no peak of the attenuation coefficient can be obtained after projection. Only the time difference dispersion curve can be obtained.

[0103] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A quantitative evaluation method for the cementing I interface bonding quality of a cased well, characterized in that, It includes the following steps: Extract the wave peaks of the array acoustic logging waveform, process the extracted waveform to obtain the complex wave number of the complex exponential function, and obtain the attenuation coefficient dispersion curve and the time difference dispersion curve based on the complex wave number; Project the time difference dispersion curve onto the time difference axis, obtain the number of time difference frequency points in the time difference dispersion curve, and convert the time difference dispersion curve into a time difference distribution curve; Project the attenuation coefficient dispersion curve onto the attenuation coefficient axis, obtain the number of attenuation coefficient frequency points in the attenuation coefficient dispersion curve, and convert the attenuation coefficient dispersion curve into an attenuation coefficient distribution curve; Extract the peak position from the attenuation coefficient distribution curve to obtain the casing wave attenuation coefficient, and obtain the water ring thickness of the I interface based on the casing wave attenuation coefficient; Identify the casing wave based on the time difference distribution curve, and realize the quantitative evaluation of the cementing quality of the I interface of the array acoustic logging through the identified casing wave and the water ring thickness of the I interface.

2. The quantitative evaluation method for the cementing I interface bonding quality of a cased well according to claim 1, characterized in that, Use the windowing method with equal window width and determined slope to extract the wave peaks in front of the array acoustic logging waveform.

3. The quantitative evaluation method for the cementing I interface bonding quality of a cased well according to claim 1, characterized in that, Perform FFT on each extracted waveform to obtain the frequency spectrum, and use the Prony method or the improved matrix method to process each frequency to obtain the complex wave number of the complex exponential function.

4. The quantitative evaluation method for the cementing I interface bonding quality of a cased well according to claim 1, characterized in that, Extract the real part of the complex wave number of the complex exponential function to obtain the attenuation coefficient at this frequency, and extract the imaginary part of the complex wave number of the complex exponential function to obtain the time difference; Among them, when performing FFT on the phase corresponding to the imaginary part, perform a phase compensation of adding 2π. Divide the compensated phase by 2π and the probe spacing to obtain the wave number, and then divide by the frequency to obtain the time difference. Perform the above processing on each frequency to obtain the attenuation coefficient dispersion curve and the time difference dispersion curve respectively.

5. The quantitative evaluation method for the cementing I interface bonding quality of a cased well according to claim 1, characterized in that, Utilize the characteristics that the time difference of the casing wave is close to a constant and is continuously distributed in segments along the frequency axis to identify the casing wave.

6. The quantitative evaluation method for the cementing I interface bonding quality of a cased well according to claim 1, characterized in that, The longer the frequency interval where the casing wave is distributed, the sharper the peak.

7. The quantitative evaluation method for the cementing I interface bonding quality of a cased well according to claim 6, characterized in that, The sharper the peak, the more obvious the casing wave, and the worse the cementing quality.

8. A quantitative evaluation system for the cementing I interface bonding quality of a cased well, characterized in that, It includes: A dispersion curve acquisition module, which is used to extract the wave peaks of the array acoustic logging waveform, process the extracted waveform to obtain the complex wave number of the complex exponential function, and obtain the attenuation coefficient dispersion curve and the time difference dispersion curve based on the complex wave number; A first dispersion curve conversion module, which is used to project the time difference dispersion curve onto the time difference axis, obtain the number of time difference frequency points in the time difference dispersion curve, and convert the time difference dispersion curve into a time difference distribution curve; A second dispersion curve conversion module, which is used to project the attenuation coefficient dispersion curve onto the attenuation coefficient axis, obtain the number of attenuation coefficient frequency points in the attenuation coefficient dispersion curve, and convert the attenuation coefficient dispersion curve into an attenuation coefficient distribution curve; An I interface water ring thickness acquisition module, which is used to extract the peak position from the attenuation coefficient distribution curve to obtain the casing wave attenuation coefficient, and obtain the water ring thickness of the I interface based on the casing wave attenuation coefficient; An I interface cementing quality acquisition module, which is used to identify the casing wave based on the time difference distribution curve, and realize the quantitative evaluation of the cementing quality of the I interface of the array acoustic logging through the identified casing wave and the water ring thickness of the I interface.

9. A computer device, including a memory and a processor, the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method for quantitatively evaluating the bonding quality of the casing well cementing I interface described in any one of claims 1 to 7.

10. A computer-readable storage medium, the computer-readable storage medium stores a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the method for quantitatively evaluating the bonding quality of the casing well cementing I interface described in any one of claims 1 to 7.

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