A method for casing cement sheath second interface reflected wave azimuthal imaging and cement annulus medium property inversion

Abstract

This invention discloses a method for azimuth imaging of the second interface of cement sheath in casing wells and for inverting the properties of the cement sheath medium. This invention utilizes a common-center-point superposition and other reflection wave imaging method to extract and image the reflection waves from the second interface of the cement sheath. When the reflected waves cannot be clearly observed in the original data, this processing method significantly enhances the reflected wave signal. The arrival time of the reflected waves is reliably picked up through the reflection wave imaging map. Combined with the annular medium impedance calculated from the casing imaging logging, the sound velocity and thickness of the cement or fluid in the annular medium, as well as the casing eccentricity, are inverted. This invention can achieve azimuth reflection wave imaging of the second interface of the cement sheath, invert the thickness and velocity of the cement sheath medium in different azimuths, and also provides a method for calculating the casing eccentricity.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field exploration and development technology. Background Technology

[0002] Azimuth reflection imaging of the second interface of the cement sheath in casing wells is crucial for inverting the thickness and velocity of the cement sheath medium, and is also a key step in calculating casing eccentricity. This is urgently needed in the field and has significant implications for deep and ultra-deep cementing design and cement packer performance evaluation. Currently, there are few reports in domestic and international literature on this research. The only existing findings are observations of reflected waves from the outer interface of the cement sheath in full-wave logging data, but no reports on methods for extracting these reflected waves or the imaging results. Summary of the Invention

[0003] The purpose of this invention is to provide a method for azimuth imaging of the second interface of the cement sheath in casing wells and inversion of the properties of the cement sheath cavity medium, so as to solve the technical problems of azimuth reflection imaging of the second interface of the cement sheath, inversion of the thickness and velocity of the cement sheath cavity medium in different azimuths based on the post-casing imaging logging data, and to provide a method for calculating casing eccentricity.

[0004] To achieve the above-mentioned objectives, the technical method steps employed in this invention are as follows:

[0005] (1) Perform back-casing imaging logging and caliper logging within the depth range;

[0006] (2) Select the 36 near and far waveform data received by the back-to-back imaging logging oblique incidence mode and preprocess them respectively, and combine them into a recording format of 1 transmitter and 2 receiver array acoustic logging. The waveform data received by the receiver includes direct curved Lamb waves (hereinafter referred to as direct waves) and reflected waves from the outside of the cement sheath.

[0007] (3) Apply median filtering or F_K filtering to the above 36 waveform data sets to remove or suppress the direct waves propagating along the bushing, and obtain the reflected waves on the outside of the cement ring.

[0008] (4) The processing results of step (3) are shifted to obtain the reflected wave image of the outer side of the cement ring;

[0009] (5) The reflected wave image is made clearer by imaging filtering (e.g., one-dimensional or two-dimensional wavenumber filtering, enhancement processing, etc.). The next step will further extract the arrival time of the reflected wave based on the image to obtain the actual sound velocity of the cement.

[0010] (6) Perform gray-level transformation on the reflected wave image and perform piecewise linear transformation to enhance the useful signal and reduce noise. Obtain the gray-level histogram of the image. Select the gray-level threshold of the envelope based on the gray-level histogram. Compare the mean value of the selected region with the gray-level threshold. If the mean value of the region is greater than the gray-level threshold, then the center position of the region is the arrival time of the reflected wave.

[0011] (7) Repeat steps (3) to (6) to obtain the arrival time curves T of the reflected waves received by the 36 remote receivers as the well depth varies. trab (i), i = 1, 2, 3, ..., 36;

[0012] (8) Perform Hilbert transform on the far-received waveforms in 36 azimuths within the measurement depth range, and extract the peak value of the direct curved Lamb wave packet in each of the 36 azimuths as a function of depth, up to time T. direct (i), i = 1, 2, 3, ..., 36;

[0013] (9) Select the depth segment corresponding to the far-receiving acoustic system at a certain depth within the measurement depth range, and obtain the average impedance Z_ave(i) and gas-liquid-solid phase statistics of the back-end medium in 36 azimuths of the depth segment corresponding to the far-receiving acoustic system, i=1,2,3,…,36. If the solid content of the back-end medium inverted in a certain azimuth exceeds 50%, the density of the back-end medium is selected as the cement density den_cement, which is a known parameter; otherwise, the fluid density den_fluid is selected, which can be taken as 1.0 g / cm³. 3 The method for obtaining the impedance of the medium and the gas-liquid-solid phase state after casing is the conventional processing method for post-casing imaging logging.

[0014] (10) See the schematic diagram of the propagation path from transmitter to remote receiver. Figure 1 As shown, the arrival times of the reflected waves and direct waves extracted from 36 azimuths are subtracted to obtain the travel time of the reflected waves in the annular medium (which can be cement or fluid) between the casing and the formation, as shown in formula (1). Formula (1) takes solid cement as an example for the annular medium. By solving formula (1), the transverse wave velocity V of the cement behind the casing at a certain azimuth can be obtained. cement (i) and thickness TH(i), V cement The initial value of (i) is Z_ave(i) / den_cement / 1.56. If the medium behind the cover in a certain direction is fluid, then the speed of sound V fluid The initial value is Z_ave(i) / den_fluid;

[0015]

[0016] In formula (1) V casingThe propagation velocity of the curved Lamb wave excited in the casing under the oblique incidence mode of post-casing imaging logging can be obtained by dividing the distance between the near and far receivers by the arrival time difference of the straight curved Lamb wave received by the two receivers. trav When the reflected wave arrives, T direct It is when the direct wave arrives;

[0017] (11) The annular thickness TH(i) of 36 directions can be obtained by using formula (1). The maximum and minimum values ​​in TH(i) are selected and it is determined whether the maximum and minimum values ​​are 180 degrees apart. If not, the selected directions are finely adjusted in the vicinity so that the two selected directions are 180 degrees apart.

[0018] (12) Sum the maximum and minimum thicknesses determined in step (11) and add them to the outer diameter of the casing to obtain the well diameter value obtained by this method. Compare this well diameter value with the well diameter logging value at the midpoint of the current depth receiving acoustic system. If the error is greater than 2 mm, repeat steps (10) and (11) and adjust the annulus thickness by changing the sound velocity of the annulus medium until the error between the inverted well diameter value and the well diameter logging value is less than 2 mm.

[0019] (13) The maximum and minimum annular thicknesses TH for two orientations 180 degrees apart i and TH i+18 If TH i >TH i+18 Then the eccentricity of the casing Ecc = (TH i -TH i+18 ) / (TH i +TH i+18 Otherwise, Ecc = (TH) i+18 -TH i ) / (TH i +TH i+18 The eccentricity D is:

[0020] D = Ecc × (TH) i +TH i+18 ) / 2.0 (2)

[0021] (14) Repeat steps (9) to (13) to obtain the casing eccentricity, eccentricity and annular velocity imaging diagrams of the measurement interval as a function of depth.

[0022] (15) Using the obtained annular thickness between the casing and the formation at 36 different depth positions, a stereoscopic image of the casing's three-dimensional centering degree as varying with depth was obtained, see [reference]. Figure 4 As shown.

[0023] The advantages and positive effects of this invention are as follows:

[0024] For the first time, a method for extracting and imaging reflected waves from the second interface of a cement sheath was achieved using a common center point superposition equal reflection wave imaging method. This method was developed based on the original data (see...). Figure 2 When the reflected wave cannot be clearly observed, this processing method significantly enhances the reflected wave signal, see... Figure 3 As shown. The arrival time of the reflected wave was reliably captured using the reflected wave imaging map. Combined with the annular medium impedance calculated from the casing imaging logging, the sound velocity and thickness of the annular medium (cement or fluid), as well as the casing eccentricity, were inverted. (See...) Figure 4 As shown, this lays the foundation for imaging of the casing and annular medium. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the propagation path of the reflected wave from the second interface of the cement ring (the interface between cement and the formation).

[0026] Figure 2 Waveform diagram of the original recording of post-casing imaging logging;

[0027] Figure 3 Reflected wave imaging diagram;

[0028] Figure 4 Image of the inverted cement ring thickness and sleeve eccentricity.

[0029] Numbered in the diagram: 1. Receiver, 2. Transmitter, 3. Sleeve, 4. Cement, 5. Ground. Detailed Implementation

[0030] This invention extracts the reflected wave from the outer interface of the cement sheath by recording the full-wave waveform with a casing imaging logging instrument, thereby realizing the inversion of the thickness and velocity of the cement sheath medium in different orientations. It also provides a method for calculating casing eccentricity.

[0031] The specific steps are as follows:

[0032] (1) Perform back-casing imaging logging and caliper logging in the depth range;

[0033] (2) Select the 36 near and far waveform data received by the back-to-back imaging logging oblique incidence mode and preprocess them respectively, and combine them into a recording format of 1 transmitter and 2 receiver array acoustic logging. The waveform data received by the receiver includes direct curved Lamb waves (hereinafter referred to as direct waves) and reflected waves from the outside of the cement sheath.

[0034] (3) Apply median filtering or F_K filtering to the above 36 waveform data sets to remove or suppress the direct waves propagating along the bushing, and obtain the reflected waves on the outside of the cement ring.

[0035] (4) The processing results of step (3) are shifted to obtain the reflected wave image of the outer side of the cement ring;

[0036] (5) The reflected wave image is made clearer by imaging filtering (e.g., one-dimensional or two-dimensional wavenumber filtering, enhancement processing, etc.). The next step will further extract the arrival time of the reflected wave based on the image to obtain the actual sound velocity of the cement.

[0037] (6) Perform gray-level transformation on the reflected wave image and perform piecewise linear transformation to enhance the useful signal and reduce noise. Obtain the gray-level histogram of the image. Select the gray-level threshold of the envelope based on the gray-level histogram. Compare the mean value of the selected region with the gray-level threshold. If the mean value of the region is greater than the gray-level threshold, then the center position of the region is the arrival time of the reflected wave.

[0038] (7) Repeat steps (3) to (6) to obtain the arrival time curves T of the reflected waves received by the 36 remote receivers as the well depth varies. trav (i), i = 1, 2, 3, ..., 36;

[0039] (8) Perform Hilbert transform on the far-received waveforms in 36 azimuths within the measurement depth range, and extract the peak value of the direct curved Lamb wave packet in each of the 36 azimuths as a function of depth, up to time T. direct (i), i = 1, 2, 3, ..., 36;

[0040] (9) Select the depth segment corresponding to the far-receiving acoustic system at a certain depth within the measurement depth range, and obtain the average impedance Z_ave(i) and gas-liquid-solid phase statistics of the back-end medium in 36 azimuths of the depth segment corresponding to the far-receiving acoustic system, i=1,2,3,…,36. If the solid content of the back-end medium inverted in a certain azimuth exceeds 50%, the density of the back-end medium is selected as the cement density den_cement, which is a known parameter; otherwise, the fluid density den_fluid is selected, which can be taken as 1.0 g / cm³. 3 The method for obtaining the impedance of the medium and the gas-liquid-solid phase state after casing is the conventional processing method for post-casing imaging logging.

[0041] (10) See the schematic diagram of the propagation path from transmitter to remote receiver. Figure 1 As shown, the arrival times of the reflected waves and direct waves extracted from 36 azimuths are subtracted to obtain the travel time of the reflected waves in the annular medium (which can be cement or fluid) between the casing and the formation, as shown in formula (1). Formula (1) takes solid cement as an example for the annular medium. By solving formula (1), the transverse wave velocity V of the cement behind the casing at a certain azimuth can be obtained. cement (i) and thickness TH(i), V cement The initial value of (i) is Z_ave(i) / den_cement / 1.56. If the medium behind the cover in a certain direction is fluid, then the speed of sound V fluid The initial value is Z_ave(i) / den_fluid;

[0042]

[0043] In formula (1) V casing The propagation velocity of the curved Lamb wave excited in the casing under the oblique incidence mode of post-casing imaging logging can be obtained by dividing the distance between the near and far receivers by the arrival time difference of the straight curved Lamb wave received by the two receivers. trav When the reflected wave arrives, T direct It is when the direct wave arrives;

[0044] (11) Using formula (1), the annular thickness TH(i) of 36 directions can be obtained by inversion. The maximum and minimum values ​​in TH(i) are selected and it is determined whether the directions of the maximum and minimum values ​​are 180 degrees apart. If not, the selected directions are finely adjusted in the vicinity so that the two selected directions are 180 degrees apart.

[0045] (12) Sum the maximum and minimum thicknesses determined in step (11) and add them to the outer diameter of the casing to obtain the well diameter value obtained by this method. Compare this well diameter value with the well diameter logging value at the midpoint of the current depth receiving acoustic system. If the error is greater than 2 mm, repeat steps (10) and (11) and adjust the annulus thickness by changing the sound velocity of the annulus medium until the error between the inverted well diameter value and the well diameter logging value is less than 2 mm.

[0046] (13) For the maximum and minimum annular thicknesses THi and THi+18, which are 180 degrees apart in orientation, if THi > THi+18, then the eccentricity of the casing Ecc = (THi - THi+18) / (THi + THi+18), otherwise Ecc = (THi+18 - THi) / (THi + THi+18), and the eccentricity D is:

[0047] D = Ecc × (TH) i +TH i+18 ) / 2.0 (2)

[0048] (14) Repeat steps (9) to (13) to obtain the casing eccentricity, eccentricity and annular velocity imaging diagrams of the measurement interval as a function of depth.

[0049] (15) Using the obtained annular thickness between the casing and the formation at 36 different depth positions, a stereoscopic image of the casing's three-dimensional centering degree as varying with depth was obtained, see [reference]. Figure 4 As shown.

Claims

1. A method for azimuth imaging of the second interface reflection wave and inversion of the cement sheath cavity properties in a casing well, comprising the following steps: (1) Perform back-casing imaging logging and caliper logging in the depth range; (2) Select the 36 near and far waveform data received by the back-to-back imaging logging oblique incidence mode and preprocess them respectively, and combine them into a recording format of 1 transmitter and 2 receiver array acoustic logging. The waveform data received by the receiver includes direct curved Lamb waves and reflected waves from the outside of the cement sheath. (3) Apply median filtering or F_K filtering to the above 36 near and far waveform data sets to remove or suppress the straight curved Lamb wave propagating along the sleeve, and obtain the reflected wave on the outside of the cement ring. (4) The processing results of step (3) are shifted to obtain the reflected wave image of the outer side of the cement ring; (5) The reflected wave image is made clearer by imaging filtering. The following steps will further extract the arrival time of the reflected wave based on the image to obtain the actual sound velocity of the cement. (6) Perform gray-level transformation on the reflected wave image and perform piecewise linear transformation to enhance the useful signal and reduce noise. Obtain the gray-level histogram of the image. Select the gray-level threshold of the envelope based on the gray-level histogram. Compare the mean value of the selected region with the gray-level threshold. If the mean value of the region is greater than the gray-level threshold, then the center position of the region is the arrival time of the reflected wave. (7) Repeat steps (3) to (6) to obtain the arrival-time curves of the reflected waves received by the 36 remote receivers as the well depth varies. ; (8) Perform Hilbert transform on the far-received waveforms in 36 azimuths within the measurement depth range, and extract the peak arrival times of the direct curved Lamb wave packets in the 36 azimuths that vary with depth. , ; (9) Select the depth segment corresponding to the far-receiving acoustic system at a certain depth in the measurement depth range, and obtain the average value Z_ave(i) of the back dielectric impedance and the statistical value of the gas-liquid-solid phase state in 36 directions of the depth segment corresponding to the far-receiving acoustic system. If the solid content of the backfill medium in a certain orientation exceeds 50%, the density of the backfill medium should be selected as the cement density (den_cement), which is a known parameter; otherwise, the fluid density (den_fluid) should be selected, which can be taken as 1.0 g / cm³. 3 The method for obtaining the impedance of the medium and the gas-liquid-solid phase state after casing is the conventional processing method for post-casing imaging logging. (10) On the propagation path from the transmitter to the receiver, the arrival times of the reflected waves extracted from 36 azimuths and the direct curved Lamb waves are subtracted to obtain the travel time of the reflected waves in the annular medium between the casing and the formation, as shown in Formula (1). Formula (1) takes solid cement as the annular medium as an example. By solving Formula (1), the transverse wave velocity of the cement behind the casing at a certain azimuth can be obtained. and thickness , The initial value is Z_ave(i) / den_cement / 1.

56. If the medium behind the cover at a certain direction is fluid, then the speed of sound... The initial value is Z_ave(i) / den_fluid; (1) In formula (1) The propagation speed of the curved Lamb wave excited in the casing in the oblique incidence mode of the post-casing imaging logging can be obtained by dividing the distance between the near and far receivers by the arrival time difference of the straight curved Lamb wave received by the two receivers. When the reflected wave arrives, When a straight, curved Lamb wave arrives; (11) The annular thickness in 36 directions can be obtained by using formula (1). Select Find the maximum and minimum values ​​in the range and determine whether the directions of the maximum and minimum values ​​differ by 180 degrees. If not, make a slight adjustment to the selected direction in the vicinity so that the two selected directions differ by 180 degrees. (12) Sum the maximum and minimum thicknesses determined in step (11) and add them to the outer diameter of the casing to obtain the well diameter value obtained by this method. Compare this well diameter value with the well diameter logging value at the midpoint of the current depth receiving acoustic system. If the error is greater than 2 mm, repeat steps (10) and (11) and adjust the annulus thickness by changing the sound velocity of the annulus medium until the error between the inverted well diameter value and the well diameter logging value is less than 2 mm. (13) The maximum and minimum annular thicknesses TH for two orientations 180 degrees apart i and TH i+18 In contrast, if TH i >TH i+18 Then the eccentricity of the casing, Ecc = (TH i -TH i+18 ) / (TH i +TH i+18 Otherwise, Ecc = (TH) i+18 -TH i ) / (TH i +TH i+18 The eccentricity D is: D=Ecc×(TH i +TH i+18 ) / 2.0 (2) (14) Repeat steps (9) to (13) to obtain the casing eccentricity, eccentricity and annular velocity imaging diagrams of the measurement interval as a function of depth. (15) Using the annular thickness between the casing and the formation in 36 azimuths that vary with depth, a stereoscopic image of the casing’s three-dimensional centering degree varies with depth is obtained.

2. The method for azimuth imaging of the second interface reflection wave and inversion of the cement sheath spatial properties in a casing well according to claim 1, characterized in that, The imaging filtering process in step (5) includes one-dimensional and two-dimensional wavenumber filtering and enhancement processing.

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