A method for measuring non-uniformity of a casing based on ultrasonic Lamb waves

Abstract

The application discloses a casing anisotropy measurement method based on ultrasonic Lamb waves. The application simulates by constructing an ultrasonic Lamb wave logging simulation model, respectively obtains the relationship between ultrasonic Lamb wave attenuation values, reflection amplitude values and casing corrosion degrees, then places the ultrasonic Lamb wave sound system in a preset target well section for actual measurement, obtains far and near waveform data and reflection waveform data, processes to obtain the envelope curves of the far and near waveforms and the reflection, calculates the casing corrosion degree value by using the reflection amplitude and casing corrosion degree relationship, determines the ultrasonic Lamb wave attenuation value after casing corrosion by using the ultrasonic Lamb wave attenuation value and casing corrosion degree relationship, combines the ultrasonic Lamb wave attenuation value of the casing without corrosion, determines the ultrasonic Lamb wave attenuation amount, calculates the difference value between the far and near waveform attenuation values and the ultrasonic Lamb wave attenuation amount, and obtains the real ultrasonic Lamb wave attenuation value. The application eliminates the influence of casing anisotropy on ultrasonic Lamb wave attenuation, and realizes accurate measurement of casing anisotropy.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geophysical logging, in particular to a casing anisotropy measurement method based on ultrasonic Lamb waves. BACKGROUND

[0002] The cementing quality evaluation is a key link in the production of oil and gas wells. The ultrasonic Lamb wave cementing quality evaluation method evaluates the state of the post-casing medium by calculating the attenuation of the near and far Lamb waves and combining the impedance measured by the resonance wave, but in the actual production process, when the casing is corroded and the axial absence of cement behind the casing causes the casing well to change non-uniformly, it will affect the attenuation value calculated by the measured waveforms, thereby affecting the judgment of the gas-liquid-solid state of the post-casing medium.

[0003] Therefore, it is urgent to propose a casing anisotropy measurement method based on ultrasonic Lamb waves, which obtains the reflected wave generated by the non-uniform interface of the casing well, further processes and eliminates the influence of the non-uniformity of the casing well on the attenuation of the Lamb wave, and improves the accuracy of the cementing quality evaluation. SUMMARY

[0004] In order to solve the problem that the ultrasonic Lamb wave evaluation of the post-casing medium is easily affected by the non-uniformity of the casing well at the present stage, the present application proposes a casing anisotropy measurement method based on ultrasonic Lamb waves, which uses the full-wave waveforms measured by the near and far receivers in the ultrasonic Lamb wave sound system and the reflected wave waveforms measured by the ultrasonic Lamb wave sound source transmitter, and realizes the accurate determination of the non-uniformity of the casing by quantitatively calculating the true attenuation value of the ultrasonic Lamb wave, effectively eliminating the influence of the casing non-uniformity on the attenuation calculation of the ultrasonic Lamb wave.

[0005] The present application adopts the following technical solutions:

[0006] A casing anisotropy measurement method based on ultrasonic Lamb waves, comprising the following steps:

[0007] Step 1: According to the structure characteristics of the ultrasonic Lamb wave sound system and the casing well, an ultrasonic Lamb wave logging simulation model including an ultrasonic Lamb wave sound system model and a casing well model is constructed;

[0008] Step 2: The casing non-uniformity change simulation is carried out by using the ultrasonic Lamb wave logging simulation model, the full-wave waveforms measured by the near and far receivers and the reflected wave waveforms measured by the ultrasonic Lamb wave sound source transmitter under different casing corrosion degrees are simulated by changing the casing thickness at the same depth in the ultrasonic Lamb wave logging simulation model, and the waveform data of the ultrasonic Lamb wave sound system model under different casing corrosion degrees are obtained;

[0009] Step 3, compare the full waveforms measured by the near and far receivers before and after the casing corrosion, and analyze the influence of the casing heterogeneity change on the full waveforms;

[0010] Step 4, according to the waveform data measured by the near and far receivers under different casing corrosion degrees, calculate the ultrasonic Lamb wave attenuation values under different casing corrosion degrees, obtain the change rule of the ultrasonic Lamb wave attenuation with the casing corrosion degree, and determine the relationship between the ultrasonic Lamb wave attenuation value and the casing corrosion degree; then, according to the reflected wave waveform measured by the ultrasonic Lamb wave sound source transmitter under different casing corrosion degrees, select the peak value of the reflected wave waveform envelope by Hilbert transform on the reflected wave waveform, obtain the reflected wave amplitude value under different casing corrosion degrees, obtain the change rule of the reflected wave amplitude with the casing corrosion degree, and determine the relationship between the reflected wave amplitude value and the casing corrosion degree;

[0011] Step 5, preset a target well section, set multiple casing thicknesses in the target well section, and gradually reduce the casing thicknesses from top to bottom to represent the gradually increasing casing corrosion degree, and set the material parameters of the casing and the structural parameters of the ultrasonic Lamb wave sound system in the target well section according to the setting parameters of the ultrasonic Lamb wave logging simulation model in step 1;

[0012] Step 6, place the ultrasonic Lamb wave sound system in the target well section for measurement, obtain the far and near waveform data and the reflected wave waveform data at the measurement depth, perform recursive average filtering on the far and near waveforms and the reflected wave waveform, remove the direct current component of the zero drift in the reflected wave waveform after recursive average filtering and perform Hilbert transform to obtain the envelope curve of the reflected wave; perform Hilbert transform on the far and near waveforms after recursive average filtering to obtain the envelope curves of the far and near waveforms;

[0013] Step 7, according to the envelope curve of the reflected wave, calculate the casing corrosion degree value by using the relationship between the reflected wave amplitude value and the casing corrosion degree, then substitute it into the relationship between the ultrasonic Lamb wave attenuation value and the casing corrosion degree to obtain the ultrasonic Lamb wave attenuation value after the casing corrosion, combine the ultrasonic Lamb wave attenuation value before the casing corrosion to determine the ultrasonic Lamb wave attenuation amount ΔAtt before and after the casing corrosion; according to the Lamb wave envelope peak values of the far and near waveform envelope curves, calculate the far and near waveform attenuation values Att0; according to the difference between the far and near waveform attenuation values Att0 and the ultrasonic Lamb wave attenuation amount ΔAtt, determine the real ultrasonic Lamb wave attenuation value Att1 at the measurement depth;

[0014] Step 8, repeat steps 6-7 to complete the measurement of the entire target well section by using the ultrasonic Lamb wave sound system, and obtain the real ultrasonic Lamb wave attenuation values at each depth of the target well section to complete the non-uniformity measurement of the casing.

[0015] Preferably, the ultrasonic Lamb wave acoustic system model is centrally arranged in the casing well model, and the ultrasonic Lamb wave acoustic system model is sequentially and obliquely arranged from top to bottom with an ultrasonic Lamb wave acoustic source transmitter, a near receiver and a far receiver, wherein the ultrasonic Lamb wave acoustic source transmitter adopts a self-emission and self-reception probe with emission and reception functions, is used to excite the acoustic source and receive the reflected waveforms, and the near receiver and the far receiver are both used to measure the full-wave waveforms; the incidence angle of the ultrasonic Lamb wave acoustic source transmitter is the same as the receiving angle of the near receiver and the far receiver.

[0016] The casing well model comprises a formation and a casing, and the casing is filled with a wellbore medium; and the material parameters of the casing well model are set according to the actual situation of the casing well to be simulated.

[0017] Preferably, the source distance of the near receiver is set to 25 cm, and the source distance of the far receiver is set to 35 cm; and the incidence angle of the ultrasonic Lamb wave acoustic source transmitter is set to 33°-38°, so as to excite the A0 mode Lamb wave at the critical angle of shear of the casing.

[0018] Preferably, the ultrasonic Lamb wave attenuation value calculation formula is as follows:

[0019]

[0020] In the formula, Att is the ultrasonic Lamb wave attenuation value, dB·m -1 ; RR is the distance between the near receiver and the far receiver, m; Amp f is the direct Lamb wave envelope peak value obtained by Hilbert transform of the full-wave waveform measured by the far receiver; and Amp n is the direct Lamb wave envelope peak value obtained by Hilbert transform of the full-wave waveform measured by the near receiver.

[0021] The relationship between the ultrasonic Lamb wave attenuation value and the casing corrosion degree is as follows:

[0022]

[0023] In the formula, ct is the casing corrosion degree value; A and B are ultrasonic Lamb wave attenuation fitting coefficients.

[0024] The relationship between the reflected wave amplitude value and the casing corrosion degree is as follows:

[0025] Ramp=C×(5.4×ct 6 -14.5×ct 5 +16.8×ct 4 -8.6×ct+2×ct 2 -0.09×ct) (3)

[0026] In the formula, Ramp is a reflected wave amplitude value; C is an energy coefficient of an ultrasonic Lamb wave sound source transmitter.

[0027] Preferably, the recursive average filtering process is:

[0028] The initial value of the preset mean value parameter N1 is created as a zero vector Z(N1, 1) and is used as a sliding filter queue.

[0029] According to the waveform data, the first N1 measurement values X(1:N1, 1) in the waveform data are selected as the values of the first N1 output points of the zero vector, and the output values Z(1:N1, 1) of the sliding filter queue are determined.

[0030] The moving sliding filter queue is moved by one measurement point along the waveform data to obtain updated waveform data measurement values X(2:N1+1) and is moved into the sliding filter queue, and the arithmetic mean value of the sliding filter queue is calculated as the filtered data of the first N1 measurement values X(1:N1, 1) in the waveform data, and the above steps are repeated until the recursive filtering process reaches the last measurement point of the waveform data.

[0031] Preferably, the ultrasonic Lamb wave sound source transmitter in the ultrasonic Lamb wave sound system is also optimized, and the performance improvement of the ultrasonic Lamb wave sound source transmitter is verified.

[0032] The filter control module is added to the receiving circuit of the ultrasonic Lamb wave sound source transmitter, the filter control module is set as a band-pass filter, an MFB type second-order multi-stage negative feedback Butterworth narrow-band filter circuit is cascaded, including a first-stage filter and a second-stage filter, and the bandwidth, center frequency, gain and transfer function of the first-stage filter and the second-stage filter are set respectively.

[0033] The visual simulation tool simulink is used for simulation, the reflected wave waveform data of the ultrasonic Lamb wave sound system is input into the receiving circuit of the ultrasonic Lamb wave sound source transmitter before and after optimization respectively, the waveform images before and after filtering are obtained through simulation, the denoising effect of the ultrasonic Lamb wave sound source transmitter after optimization is compared and analyzed, and the performance of the ultrasonic Lamb wave sound source transmitter after optimization is verified.

[0034] Preferably, the center frequency of the first-stage filter is set as 187 kHz, and the center frequency of the second-stage filter is set as 334 kHz.

[0035] The present application has the following beneficial effects:

[0036] The application provides a casing anisotropy measurement method based on ultrasonic Lamb waves, solves the problem that, in the process of ultrasonic Lamb wave logging, non-uniform interfaces are formed due to non-uniform changes of casing corrosion, and the transmission of ultrasonic Lamb waves in the casing encounters non-uniform interfaces to cause the emission wave to have a long influence range and the near receiver to have an attenuation measurement precision problem.

[0037] Meanwhile, the application also optimizes the ultrasonic Lamb wave sound source transmitter used in the casing anisotropy measurement method based on ultrasonic Lamb waves, increases a filter control module in the receiving circuit of the ultrasonic Lamb wave sound source transmitter, utilizes an MFB type second-order multi-stage negative feedback Butterworth narrowband filter circuit cascade to combine a negative feedback link and an amplification link to realize a filter function, cooperates with the cascade structure to effectively reduce the influence of low-frequency noise and high-frequency noise in the reflected wave data on the measurement of the emission wave waveform data of the ultrasonic Lamb wave sound source transmitter, improves the de-noising performance of the ultrasonic Lamb wave sound source transmitter, and provides a basis for accurately mastering the waveform data of the reflected wave. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 Fig. 1 is a structural schematic diagram of an ultrasonic Lamb wave logging simulation model.

[0039] Figure 2 Fig. 2 is a schematic diagram of the ultrasonic Lamb wave logging simulation model used for simulating different casing corrosion degrees.

[0040] Figure 3 Fig. 3 is a waveform diagram measured by a near receiver and a far receiver in the ultrasonic Lamb wave sound system model before and after casing corrosion.

[0041] Figure 4 Fig. 4 is a curve of ultrasonic Lamb wave attenuation changing with casing corrosion degrees.

[0042] Figure 5 Fig. 5 is a reflected wave waveform measured by the ultrasonic Lamb wave sound source transmitter under different casing corrosion degrees.

[0043] Figure 6 Fig. 6 is a curve of reflected wave amplitude changing with casing corrosion degrees.

[0044] Figure 7 Fig. 7 is a waveform processing schematic diagram of the reflected wave received by the ultrasonic Lamb wave sound source transmitter in the non-uniform casing well.

[0045] Figure 8A flow chart for the casing anisotropy measurement method based on ultrasonic Lamb waves.

[0046] Figure 9 A schematic diagram of the ultrasonic Lamb wave sound source transmitter receiving circuit after optimization.

[0047] Figure 10 A schematic diagram of the basic MFB type narrow band pass filter circuit.

[0048] Figure 11 A Bode plot of the filter circuit characteristics of the filter control module.

[0049] Figure 12 A filter control module receiving circuit simulation result diagram; in the diagram, (a) is a schematic diagram of the filter control module receiving circuit structure, and (b) is a filter control module receiving circuit simulation result diagram.

[0050] In the diagram, 1 is an ultrasonic Lamb wave sound source transmitter, 2 is a near receiver, 3 is a far receiver, 4 is a casing, 5 is a wellbore medium, and θ is an incident angle. DETAILED DESCRIPTION

[0051] The specific embodiments of the present application will be further described below in combination with the accompanying drawings:

[0052] The present application proposes a casing anisotropy measurement method based on ultrasonic Lamb waves, which comprises the following steps:

[0053] Step 1: According to the structure characteristics of the ultrasonic Lamb wave sound system and the casing well, an ultrasonic Lamb wave logging simulation model including an ultrasonic Lamb wave sound system model and a casing well model is constructed, as shown in the following figure. Figure 1

[0054] The ultrasonic Lamb wave sound system model is centrally arranged in the casing well model, and the ultrasonic Lamb wave sound system model is sequentially and obliquely arranged from top to bottom with an ultrasonic Lamb wave sound source transmitter 1, a near receiver 2 and a far receiver 3, wherein the ultrasonic Lamb wave sound source transmitter 1 adopts a self-emission and self-reception probe with emission and reception functions, is used for exciting the sound source and receiving the Lamb wave (i.e. the reflected wave form), the near receiver 2 and the far receiver 3 are both used for measuring the full wave form, the source distance of the near receiver is set to 25 cm, the source distance of the far receiver is set to 35 cm, the spacing RR between the near receiver 2 and the far receiver 3 is 10 cm, the incident angle of the ultrasonic Lamb wave sound source transmitter is the same as the receiving angle of the near receiver and the far receiver, the incident angle of the ultrasonic Lamb wave sound source transmitter is set to 33°-38° to reach the shear critical angle of the steel casing, excite the A0 mode Lamb wave and receive it at the same angle.

[0055] ​The casing well model includes a formation and a casing 4 filled with wellbore medium, and material parameters of the casing well model are set according to actual conditions of the casing well to be simulated.

[0056] In this embodiment, the casing is a steel casing, and the wellbore medium 5 filled in the casing is water. Material parameters of the casing well model in this embodiment are shown in Table 1.

[0057] Table 1 Material parameters of the casing well model

[0058]

[0059] Step 2: Simulate casing non-uniformity change by using the ultrasonic Lamb wave logging simulation model. The casing thickness at the same depth in the ultrasonic Lamb wave logging simulation model is changed to represent the corrosion degree of the casing, as shown in FIG. 2. The casing corrosion degree is more serious, and the casing thickness is smaller. In this embodiment, the original casing thickness is D, and the casing thickness at the same depth in the ultrasonic Lamb wave logging simulation model is reduced from D to 0 at intervals of 0.1D. The ultrasonic Lamb wave logging simulation model is simulated under different casing thickness conditions to obtain the full-wave waveform measured by the near receiver and the far receiver and the reflected wave waveform measured by the ultrasonic Lamb wave sound source transmitter under different casing corrosion degrees, and waveform data of the ultrasonic Lamb wave sound system model under different casing corrosion degrees are obtained. Figure 2 Step 3: Compare the full-wave waveforms measured by the near receiver and the far receiver before and after casing corrosion, as shown in FIG. 3. It is found that the time of the waveforms measured by the near receiver and the far receiver after casing corrosion is delayed, and the waveform amplitude is smaller. Therefore, when the data processing is performed during the ultrasonic Lamb wave logging, the non-uniformity change caused by casing corrosion has a great influence on the waveform, and the non-homogeneity change of the casing seriously interferes with the processing result of the ultrasonic Lamb wave logging waveform data.

[0060] Figure 2 Figure 3

[0061] Step 4: Calculate the ultrasonic Lamb wave attenuation value under different casing corrosion degrees according to the waveform data measured by the near receiver and the far receiver under different casing corrosion degrees. The calculation formula is as follows:

[0062]

[0063] In the formula, Att is the ultrasonic Lamb wave attenuation value, the unit is dB·m -1 ; RR is the distance between the near receiver and the far receiver, the unit is m; Amp f is the direct Lamb wave envelope peak value obtained by Hilbert transform of the full-wave waveform measured by the far receiver; Amp n ​​​The direct Lamb wave envelope peak value obtained after the full wave waveform measured by the near receiver is subjected to Hilbert transform.

[0064] The Hilbert transform process is as follows:

[0065]

[0066] In the formula, y(t) is the convolution calculation result; x(τ) is the integrated function; and h(t-τ) is the convolution kernel function.

[0067] The Hilbert transform is actually the result of convolution of the original signal x(τ) and a signal, which is According to the convolution formula, the following can be obtained:

[0068]

[0069] In the formula, x(t) is the input waveform data; t is time; The convolution kernel function used in the Hilbert transform is as follows: The convolution value of x(t) and is i; and z(t) is the Hilbert transform result.

[0070] According to the ultrasonic Lamb wave attenuation values under different casing corrosion degrees, the change rule of the ultrasonic Lamb wave attenuation with the casing corrosion degree is obtained, as shown in Figure 4 The fitting analysis determines the relationship between the ultrasonic Lamb wave attenuation value and the casing corrosion degree as follows:

[0071] The relationship between the ultrasonic Lamb wave attenuation value and the casing corrosion degree is as follows:

[0072]

[0073] In the formula, ct is the casing corrosion degree value; A and B are ultrasonic Lamb wave attenuation fitting coefficients, in the embodiment, the value of the ultrasonic Lamb wave attenuation fitting coefficient A is 100, and the value of the ultrasonic Lamb wave attenuation fitting coefficient B is 10 5 .

[0074] After the casing is corroded, when the ultrasonic Lamb wave propagates in the casing, the reflection wave is generated due to the change of the internal interface, the reflection wave path is as shown in the green path in Figure 2 , the reflection wave waveform measured by the ultrasonic Lamb wave sound source transmitter under different casing corrosion degrees is analyzed, as shown in Figure 5 It is found that the amplitude of the reflection wave received by the ultrasonic Lamb wave sound source transmitter is different when the casing corrosion degree is different, so that it is determined that the higher the casing corrosion degree is, the greater the amplitude of the reflection wave waveform is.

[0075] According to the reflected waveforms measured by the ultrasonic Lamb wave sound source transmitter under different casing corrosion degrees, the peak values of the envelope of the reflected waveforms are selected by Hilbert transform, the reflected wave amplitude values under different casing corrosion degrees are obtained, it is found that the reflected wave amplitude value increases with the increase of the casing corrosion degree, and thus the change rule of the reflected wave amplitude with the casing corrosion degree is obtained, as shown in FIG. 2. Figure 6 The fitting analysis determines that the relationship between the reflected wave amplitude value and the casing corrosion degree is as follows:

[0076] Ramp = C × (5.4 × ct 6 -14.5 × ct 5 + 16.8 × ct 4 -8.6 × ct + 2 × ct 2 -0.09 × ct) (3)

[0077] In the formula, Ramp is the reflected wave amplitude value; C is the energy coefficient of the ultrasonic Lamb wave sound source transmitter, and the energy coefficient C of the ultrasonic Lamb wave sound source transmitter in the embodiment is 100.

[0078] Step 5, a target well section is preset, the casing thicknesses at different depth sections in the target well section are different, the original casing thickness is D, the casing thickness is reduced from D to 0 according to the interval of 0.1D from top to bottom, which is used to represent that the casing corrosion degree gradually increases, and the material parameters of the casing in the target well section and the structural parameters of the ultrasonic Lamb wave sound system are set according to the setting parameters of the ultrasonic Lamb wave logging simulation model in step 1.

[0079] Step 6, the ultrasonic Lamb wave sound system is placed in the target well section for measurement, the far and near waveform data and the reflected waveform data at the measurement depth are obtained, the recursive average filtering is performed on the far and near waveforms and the reflected waveform, the direct current component of the zero drift in the reflected waveform after the recursive average filtering is removed and the Hilbert transform is performed, and the envelope curve of the reflected wave is obtained, as shown in FIG. 3. Figure 7 At the same time, the Hilbert transform is performed on the far and near waveforms after the recursive average filtering, and the envelope curves of the far and near waveforms are obtained.

[0080] In the embodiment, the recursive average filtering process is as follows:

[0081] The original waveform of the reflected waveform data X(N, 1) in the embodiment is shown by the black waveform curve in FIG. 4. Figure 7 It can be observed that there are many noise interferences in the reflected original waveform curve, the recursive average filtering method needs to be used for filtering processing on the original waveform curve of the reflected wave, the interference of the periodic clutter existing in the ultrasonic Lamb wave sound source transmitter circuit is removed, and the smoothness of the reflected waveform is improved.

[0082] The initial value of the preset mean value parameter N1 is 4, a zero vector Z(N1, 1) with a length of N1 is created and used as a sliding filter queue.

[0083] According to the waveform data, the first N1 measurement values in the waveform data are selected as the values of the first N1 output points of the zero vector, that is, X(1:N1, 1) is input to Z(1:N1, 1).

[0084] The sliding filter queue is moved by one measurement point along the waveform data, the updated waveform data measurement value X(2:N1+1) is obtained and moved into the sliding filter queue, the arithmetic mean value of the sliding filter queue is calculated as the filtered data of the first N1 measurement values X(1:N1, 1) in the waveform data, and the above steps are repeated until the recursive filtering processing reaches the last measurement point of the waveform data, that is, Z(1:N1, 1) = X(j+1:N1+j, 1), j is the serial number of the data point, j = 1, 2, 3, …, N-N1, and the filtered reflected wave waveform is obtained, as shown in the middle red waveform curve in FIG. 2. Figure 7 As compared with the reflected wave waveform before the filtering processing, it is found that the noise filtering effect of the recursive average filtering is obvious, the waveform smoothness is high, but there is a zero point drift phenomenon.

[0085] Therefore, the direct current component of the zero point drift in the reflected wave waveform after the recursive average filtering is further removed, and the blue waveform curve in FIG. 2 is obtained. Figure 7 After the Hilbert transform is continuously performed, the reflected wave envelope curve shown in the green waveform curve in FIG. 2 is obtained. Figure 7

[0086] Step 7, according to the envelope curve of the reflected wave, the casing corrosion degree value is calculated by using formula (3), and then substituted into formula (2) to obtain the ultrasonic Lamb wave attenuation value after the casing corrosion, combined with the ultrasonic Lamb wave attenuation value before the casing corrosion, the ultrasonic Lamb wave attenuation amount ΔAtt before and after the casing corrosion is determined, at the same time, according to the Lamb wave envelope peak values of the far and near waveform envelope curves, the far and near waveform attenuation values Att0 are calculated, according to the difference between the far and near waveform attenuation values Att0 and the ultrasonic Lamb wave attenuation amount ΔAtt, the real ultrasonic Lamb wave attenuation value Att1 at the measurement depth is determined, that is, Att1 = Att0-ΔAtt.

[0087] Step 8, steps 6 to 7 are repeated, and the ultrasonic Lamb wave acoustic system is used to complete the measurement of the entire target well section, and the real ultrasonic Lamb wave attenuation value at each depth of the target well section is obtained by processing, and the non-uniform measurement of the casing is completed.

[0088] ​When the casing anisotropy measurement method based on ultrasonic Lamb wave proposed in the embodiment is applied to the actual casing well anisotropy measurement, as shown in Figure 8 the ultrasonic Lamb wave sound system is placed in the casing well to measure the target well section, the near receiver of the ultrasonic Lamb wave sound system is used to measure the full wave waveform, and the reflection wave waveform is measured by the ultrasonic Lamb wave sound source transmitter, so as to obtain the far and near waveform data and the reflection wave waveform data. The far and near waveforms and the reflection wave waveform are recursively averaged and filtered, the direct current component of the zero drift in the reflection wave waveform after recursive average filtering is removed, and Hilbert transform is performed, so as to obtain the envelope curve of the reflection wave. According to the envelope curve of the reflection wave, the casing corrosion degree value is calculated by formula (3), and then substituted into formula (2) to calculate the ultrasonic Lamb wave attenuation value after casing corrosion. Combined with the ultrasonic Lamb wave attenuation value before casing corrosion, the ultrasonic Lamb wave attenuation amount ΔAtt before and after casing corrosion is determined. At the same time, according to the Lamb wave envelope peak value of the far and near waveform envelope curves, the far and near waveform attenuation values Att0 are calculated. According to the difference between the far and near waveform attenuation values Att0 and the ultrasonic Lamb wave attenuation amount ΔAtt, the real ultrasonic Lamb wave attenuation value Att1 at the measurement depth is determined, the measurement of the casing anisotropy of the target well section is completed, and the accurate evaluation of the casing corrosion degree at different depths is realized.

[0089] At the same time, in order to improve the measurement accuracy of the casing anisotropy measurement method based on ultrasonic Lamb wave, the ultrasonic Lamb wave sound source transmitter in the ultrasonic Lamb wave sound system is optimized, and the performance improvement of the ultrasonic Lamb wave sound source transmitter is verified.

[0090] In the embodiment, in order to ensure that the reflection wave information can be accurately obtained, the original reflection wave data measured by the ultrasonic Lamb wave sound source transmitter in the ultrasonic Lamb wave sound system is subjected to frequency spectrum analysis, and it is found that the noise is located in the frequency band below 150 kHz and above 350 kHz. Therefore, a filter control module is added to the receiving circuit of the ultrasonic Lamb wave sound source transmitter in the ultrasonic Lamb wave sound system, and a band-pass filter is used to eliminate the low-frequency noise and high-frequency noise in the reflection wave data measured by the ultrasonic Lamb wave sound source transmitter.

[0091] The filter control module, as shown in Figure 9 adopts MFB type second-order multi-stage negative feedback Butterworth narrow-band filter circuit cascade, including a first filter and a second filter, and realizes the filtering function through the negative feedback link and the amplification link, and cooperates with the cascade structure to improve the performance of the filter control module.

[0092] The filter control module is provided with a first-stage filter and a second-stage filter connected in series, each filter adopts a basic MFB type narrow-band filter circuit as shown in Figure 10 Table 2 shows the filter parameters.

[0093] Table 2 shows the filter parameters.

[0094]

[0095] Figure 11 The Bode diagram of the filter circuit of the filter control module in the embodiment is shown in Figure 10 It can be seen that the center frequency of the amplitude-frequency characteristic curve is at 250 kHz, and the phase-frequency characteristic is basically linear in the passband range, that is, the filter control module can meet the requirement of eliminating low-frequency noise and high-frequency noise in the measured reflected wave data of the ultrasonic Lamb wave sound source transmitter.

[0096] The simulation is performed by using a visual simulation tool simulink, as shown in Figure 12 (a) shows the reflected wave waveform data measured by the ultrasonic Lamb wave sound system input into the ultrasonic Lamb wave sound source transmitter receiving circuit before and after optimization, respectively, and the waveform images before and after filtering are obtained by simulation, and the denoising effect of the ultrasonic Lamb wave sound source transmitter after optimization is compared and analyzed, and it is found that Figure 12 (b) shows the filtered waveform on the lower side compared with the measured waveform on the upper side before filtering, and the noise is obviously filtered out, thereby verifying the performance of the ultrasonic Lamb wave sound source transmitter after optimization.

[0097] Of course, the above description is not a limitation of the present application, and the present application is not limited to the above examples, and the changes, modifications, additions or replacements made by the person skilled in the art within the essential scope of the present application should also belong to the protection scope of the present application.

Claims

1. A method for measuring anisotropy of a casing based on ultrasonic Lamb waves, characterized by, The method comprises the following steps: Step 1, according to the ultrasonic Lamb wave acoustic system and the structural characteristics of the cased well, an ultrasonic Lamb wave logging simulation model comprising an ultrasonic Lamb wave acoustic system model and a cased well model is constructed; Step 2, the cased non-homogeneous change simulation is performed by using the ultrasonic Lamb wave logging simulation model, the full-wave waveforms measured by the near and far receivers under different cased corrosion degrees are simulated by changing the cased thickness at the same depth in the ultrasonic Lamb wave logging simulation model, and the waveform data of the ultrasonic Lamb wave acoustic system model under different cased corrosion degrees are obtained; Step 3, the influence of the cased non-homogeneous change on the full-wave waveforms is analyzed by comparing the full-wave waveforms measured by the near and far receivers before and after the cased corrosion; Step 4, the ultrasonic Lamb wave attenuation values under different cased corrosion degrees are calculated according to the waveform data measured by the near and far receivers under different cased corrosion degrees, the change rule of the ultrasonic Lamb wave attenuation with the cased corrosion degree is obtained, and the relationship between the ultrasonic Lamb wave attenuation value and the cased corrosion degree is determined; the reflection wave amplitude values under different cased corrosion degrees are obtained by selecting the peak values of the reflection wave envelope through Hilbert transform on the reflection waveforms measured by the ultrasonic Lamb wave source transmitter under different cased corrosion degrees, the change rule of the reflection wave amplitude with the cased corrosion degree is obtained, and the relationship between the reflection wave amplitude value and the cased corrosion degree is determined; Step 5, a target well section is preset, a plurality of cased thicknesses are arranged in the target well section, the cased thicknesses decrease from top to bottom to represent that the cased corrosion degree gradually increases, and the material parameters of the cased well and the structural parameters of the ultrasonic Lamb wave acoustic system in the target well section are set according to the setting parameters of the ultrasonic Lamb wave logging simulation model in step 1; Step 6, the ultrasonic Lamb wave acoustic system is placed in the target well section for measurement, the far and near waveform data and the reflection wave waveform data at the measurement depth are obtained, the recursive average filtering is performed on the far, near and reflection waveforms, the direct current component of the reflection wave after the recursive average filtering is removed, and the Hilbert transform is performed to obtain the envelope curve of the reflection wave; the Hilbert transform is performed on the far and near waveforms after the recursive average filtering to obtain the envelope curves of the far and near waveforms; Step 7, the cased corrosion degree value is calculated by using the relationship between the reflection wave amplitude value and the cased corrosion degree according to the envelope curve of the reflection wave, the ultrasonic Lamb wave attenuation value after the cased corrosion is calculated by substituting the cased corrosion degree value into the relationship between the ultrasonic Lamb wave attenuation value and the cased corrosion degree, the ultrasonic Lamb wave attenuation amount ΔAtt before and after the cased corrosion is determined in combination with the ultrasonic Lamb wave attenuation value when the cased well is not corroded, the far and near waveform attenuation values Att0 are calculated according to the Lamb wave envelope peak values of the far and near waveform envelope curves, and the ultrasonic Lamb wave real attenuation value Att1 at the measurement depth is determined according to the difference between the far and near waveform attenuation values Att0 and the ultrasonic Lamb wave attenuation amount ΔAtt. Step 8, repeating step 6 to step 7, using ultrasonic Lamb wave sound system to complete the measurement of the whole target well section, and processing to obtain the real attenuation value of ultrasonic Lamb wave at each depth of the target well section, and completing the non-uniform measurement of the casing.

2. The ultrasonic Lamb wave based casing anisotropy measurement method of claim 1, wherein, The ultrasonic Lamb wave sound system model is centrally arranged in the casing well model, and the ultrasonic Lamb wave sound system model is sequentially and obliquely arranged from top to bottom with an ultrasonic Lamb wave sound source transmitter, a near receiver and a far receiver, wherein the ultrasonic Lamb wave sound source transmitter adopts a self-emission and self-reception probe with emission and reception functions, is used for exciting the sound source and receiving the reflected wave form, and the near receiver and the far receiver are both used for measuring the full wave form; the incidence angle of the ultrasonic Lamb wave sound source transmitter is the same as the receiving angle of the near receiver and the far receiver. The casing well model includes a formation and a casing, and the casing is filled with wellbore medium; the material parameters of the casing well model are set according to the actual situation of the casing well to be simulated.

3. The ultrasonic Lamb wave based casing anisotropy measurement method of claim 2, wherein, The source distance of the near receiver is set to 25 cm, the source distance of the far receiver is set to 35 cm, the incidence angle of the ultrasonic Lamb wave sound source transmitter is set to 33°-38°, and the A0 mode of Lamb wave is excited to reach the shear critical angle of the casing.

4. The ultrasonic Lamb wave based casing anisotropy measurement method of claim 1, wherein, The ultrasonic Lamb wave attenuation value calculation formula is: In the formula, Att is the ultrasonic Lamb wave attenuation value, with unit of dB·m -1 ; RR is the distance between the near receiver and the far receiver, with unit of m; Amp f is the direct Lamb wave envelope peak value of the full wave waveform measured by the far receiver after Hilbert transform; Amp n is the direct Lamb wave envelope peak value of the full wave waveform measured by the near receiver after Hilbert transform; The relationship between the ultrasonic Lamb wave attenuation value and the casing corrosion degree is: In the formula, ct is the casing corrosion degree value; A and B are both ultrasonic Lamb wave attenuation fitting coefficients; The relationship between the reflected wave amplitude value and the casing corrosion degree is: Ramp = C x (5.4 x ct 6 -14.5 x ct 5 +16.8 x ct 4 -8.6 x ct + 2 x ct 2 -0.09 x ct) (3) In the formula, Ramp is the reflected wave amplitude value; C is the energy coefficient of the ultrasonic Lamb wave sound source transmitter.

5. The ultrasonic Lamb wave based casing anisotropy measurement method of claim 1, wherein, The recursive average filtering process is: The initial value of the preset mean value parameter N1 is set, a zero vector Z(N1, 1) is created and used as a sliding filter queue; According to the waveform data, the first N1 measurement values X(1:N1, 1) in the waveform data are selected as the values of the first N1 output points of the zero vector, and the output value Z(1:N1, 1) of the sliding filter queue is determined; The moving sliding filter queue is moved by one measurement point along the waveform data to obtain updated waveform data measurement values X(2:N1+1) and move them into the sliding filter queue, the arithmetic mean value of the sliding filter queue is calculated as the filtered data of the first N1 measurement values X(1:N1, 1) in the waveform data, and the above steps are repeated until the recursive filtering process reaches the last measurement point of the waveform data.

6. The ultrasonic Lamb wave based casing anisotropy measurement method of claim 1, wherein, The ultrasonic Lamb wave sound source transmitter in the ultrasonic Lamb wave sound system is also optimized, and the performance improvement of the ultrasonic Lamb wave sound source transmitter is verified; The filter control module is added to the receiving circuit of the ultrasonic Lamb wave sound source transmitter, the filter control module is set as a band-pass filter, an MFB type second-order multi-stage negative feedback Butterworth narrow-band filter circuit is cascaded, including a first filter and a second filter, and the bandwidth, center frequency, gain and transfer function of the first filter and the second filter are set respectively. The simulation is carried out by using a visual simulation tool simulink, the reflection wave waveform data measured by the ultrasonic Lamb wave sound system is input into the ultrasonic Lamb wave sound source transmitter receiving circuit before and after optimization respectively, the waveform images before and after filtering are obtained by simulation, the denoising effect of the ultrasonic Lamb wave sound source transmitter after optimization is compared and analyzed, and the performance of the ultrasonic Lamb wave sound source transmitter after optimization is verified.

7. The ultrasonic Lamb wave based casing anisotropy measurement method of claim 6, wherein, The center frequency of the first stage filter is set to 187 kHz, and the center frequency of the second stage filter is set to 334 kHz.

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