Method for inverting cased well micro-ring thickness

Abstract

A method for inverting the thickness of a cased well microring comprises the steps that post-casing scanning imaging logging, CBL / VDL logging and borehole diameter logging are conducted in a depth interval, wave crests and wave troughs of direct bending type Lamb waves received by far and near receivers in 36 directions of post-casing scanning imaging logging of each depth point are extracted, the thickness of a cement annulus is obtained according to the borehole diameter and the outer diameter of a casing, and the thickness of the cement annulus is calculated according to the thickness of the cement annulus. According to the thickness of the annulus and reflected wave arrival time in far and near waveforms recorded by post-casing scanning imaging logging, the shear wave speed of cement is estimated, and according to the shear wave speed and the shear wave speed of the cement, the relation between the thickness of the micro-ring and the attenuation difference value when the micro-ring and the cementing are good is established through an analytical calculation method. And according to the attenuation difference value, the accurate fluid micro-ring thickness of the processing interval can be obtained through inversion. By combining post-casing scanning imaging logging and CBL / VDL logging information, the accurate micro-ring thickness between the casing and the cement interface is accurately calculated, evaluation of the cased well cementation quality and the cement packing capacity is achieved, the defect that the micro-ring cannot be judged only by means of an acoustic amplitude curve is overcome, and the accuracy of well cementation is improved. And important technical support is provided for safe development and production of an oil field.

Description

Technical Field

[0001] The invention belongs to the field of oil and gas field exploration and development, and relates to a method for inverting micro-annulus thickness through post-casing scanning imaging logging and CBL / VDL logging data. Background Art

[0002] When there is a liquid-filled microring between the casing and the cement sheath, the casing wave amplitude of CBL / VDL logging is significantly enhanced. However, when the cement sheath is poorly bonded, the casing wave amplitude is also very strong. Therefore, it is difficult to determine whether there is a microring downhole only by the casing wave amplitude.

[0003] The attenuation of the curved Lamb wave in the post-casing scanning imaging logging is relatively large when there is a microring behind the casing, especially when conventional cement is bonded behind the casing. If the cement is well bonded, the attenuation of the curved Lamb wave is very low, and the presence of microrings will significantly increase its attenuation. When lightweight cement is bonded behind the casing, the presence of microrings will slightly reduce the attenuation compared to when the cement is well bonded. Although the combination of CBL / VDL and post-casing scanning imaging logging can identify downhole microrings, the calculation of microring thickness has not yet been reported in the literature. Summary of the invention

[0004] In view of the problems existing in the background technology, the present invention aims to establish a method for calculating the thickness of the micro-ring, which provides important parameters for reliably evaluating the sealing capacity of the cement ring. Specifically, the following inversion method is proposed:

[0005] A method for inverting the microannulus thickness of a cased well comprises the following steps:

[0006] (1) Perform post-casing scanning imaging logging, CBL / VDL logging and caliper logging in the depth interval;

[0007] (2) Extract the peaks and troughs of the direct bending Lamb waves received by the near and far receivers at 36 azimuths of the post-scanning imaging logging at each depth point, and calculate the attenuation value α at 36 azimuths of this depth point using formula (1): i , i=1~36

[0008]

[0009] In formula (1), l is the distance between the near and far detectors, T i+18 and T i is the amplitude of the near and far detectors, and max and min represent the peak and trough.

[0010] (3) If the cement density is greater than or equal to 1.80 g / cm 3 , and continue with steps (4) to (9).

[0011] (4) Select a well section where the relative amplitude of the casing wave is between 30% and 60% and the attenuation of the curved Lamb wave of the post-casing scanning imaging logging is above 80 dB / m. This section is the micro-ring section.

[0012] (5) Count the average value of the well section attenuation in step (4), and the calculation formula is formula (2), where m is the depth point;

[0013]

[0014] In formula (2), α i,n Indicates the attenuation value at the nth depth and the ith direction

[0015] (6) Determine the section in the whole well where the casing wave relative amplitude is less than 5% and the attenuation value is less than 80 dB / m. This section is the section with good bonding. Use formula (2) to calculate the average value of attenuation when the bonding is good.

[0016] (7) Subtract the average attenuation value in step (6) from the average attenuation value in step (5) to obtain the difference in attenuation between the micro-annular section and the well-cemented section;

[0017] (8) Obtain cement annulus thickness based on the wellbore diameter and casing outer diameter, and estimate cement shear wave velocity based on annulus thickness and the arrival time of reflected waves in the near and far waveforms recorded by post-casing scanning imaging logging; or measure the longitudinal and shear wave velocities of cement in the well in the laboratory;

[0018] (9) establishing the relationship between the micro-ring thickness and the attenuation difference between the micro-ring and the well-bonded state by an analytical calculation method based on the longitudinal and transverse wave velocities of the cement, and inverting the micro-ring thickness based on the attenuation value in step (7);

[0019] (10) If the cement density is less than 1.8 g / cm 3 , and continue with steps (11) to (16).

[0020] (11) Select the section where the casing wave relative amplitude is less than 15% and the bending Lamb wave attenuation of the whole well is the highest. This is the section with good cement bonding. Use formula (2) to calculate the average value of the bending Lamb wave attenuation.

[0021] (12) Select a well section where the casing wave relative amplitude is between 40% and 70% and the bending Lamb wave attenuation is reduced by 10 dB / m to 20 dB / m compared with the well section with good cement bonding. This is the micro-ring section. Use formula (2) to calculate the average value of the bending Lamb wave attenuation.

[0022] (13) Subtract the average attenuation value in step (12) from the average attenuation value in step (11) to obtain the difference in attenuation between the micro-ring section and the well-cemented well section;

[0023] (14) Obtain cement annulus thickness based on the wellbore diameter and casing outer diameter, and estimate cement shear wave velocity based on annulus thickness and arrival time of reflected waves in near and far waveforms recorded by post-casing scanning imaging logging; or

[0024] The longitudinal and shear wave velocities of the cement in this well were measured in the laboratory;

[0025] (15) establishing the relationship between the micro-ring thickness and the attenuation difference between the micro-ring and the well-bonded state by an analytical calculation method based on the longitudinal wave and shear wave velocities of the cement, and inverting the micro-ring thickness based on the attenuation difference in step (13);

[0026] (16) The cementing quality and the sealing capacity of the cement sheath are further evaluated based on the micro-annulus thickness inverted in step (9) or (15).

[0027] The present invention discloses a method for inverting the micro-annulus thickness of a cased well. The method adopts the attenuation difference between a fluid annulus model and a complete cementation model for the first time to calculate the micro-annulus thickness of a cased well. The method can realize accurate evaluation of the cementing quality and cement isolation capacity of the cased well, and makes up for the drawback that the existence of the micro-annulus cannot be judged by relying solely on the acoustic amplitude curve. The method provides important technical support for the safe development and production of oil fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] A more complete understanding of the present invention and its attendant advantages and features will be more readily appreciated by reference to the following detailed description taken in conjunction with the accompanying drawings, in which:

[0029] Figure 1 The present invention is a flow chart of the method for inverting the micro-annulus thickness of a cased well.

[0030] Figure 2 These are the measured data of CBL / VDL and post-casing imaging logging of a certain well in the present invention.

[0031] Figure 3 It is the azimuthal attenuation ATT measured by the post-casing imaging logging in the present invention and the calculated attenuation average value at each depth.

[0032] Figure 4 It is a phase velocity dispersion curve calculated based on the measured wellbore parameters in the present invention when there are fluid rings of different thicknesses behind the casing.

[0033] Figure 5 This is the relationship curve between the micro-ring thickness and the attenuation difference (the attenuation difference between good bonding and the micro-ring model) at a frequency of 165 kHz in the present invention. DETAILED DESCRIPTION

[0034] The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings.

[0035] The following examples are only provided to illustrate the present invention and are not intended to limit the embodiments of the present invention.

[0036] In actual operation, changes and modifications can be made as needed based on the following description, but obvious changes or modifications derived from the spirit of the present invention are still within the scope of protection of the present invention.

[0037] like Figure 1 The method for inverting the microannulus thickness of a cased well shown includes the following steps:

[0038] (1) Perform post-casing scanning imaging logging, CBL / VDL logging and caliper logging in the depth interval;

[0039] (2) Extract the peaks and troughs of the direct bending Lamb waves received by the near and far receivers at 36 azimuths of the post-scanning imaging logging at each depth point, and calculate the attenuation value α at 36 azimuths of this depth point using formula (1): i , i=1~36

[0040]

[0041] In formula (1), l is the distance between the near and far detectors, T i+18 and T i is the amplitude of the near and far detector, max

[0042] and min represent peaks and troughs.

[0043] Figure 2 is the curved Lamb wave data of CBL / VDL and post-casing scanning imaging logging of a certain well, where CBL and VDL are the relative amplitude and density map results of CBL / VDL logging, WFN and WFF are the waveforms received by post-casing scanning imaging logging with source distances of 25 cm and 35 cm respectively, and is the first of the 36 waveforms received in azimuth. According to step (2), the attenuation in different azimuths is calculated, and the result is: Figure 2 ATT in.

[0044] (3) If the cement density is greater than or equal to 1.80 g / cm 3 , and continue with steps (4) to (9).

[0045] (4) Select a well section where the relative amplitude of the casing wave is between 30% and 60% and the attenuation of the curved Lamb wave of the post-casing scanning imaging logging is above 80 dB / m. This section is the micro-ring section.

[0046] (5) Count the average value of the well section attenuation in step (4), and the calculation formula is formula (2), where m is the depth point;

[0047]

[0048] In formula (2), α i,n Indicates the attenuation value at the nth depth and the ith direction

[0049] (6) Determine the section in the whole well where the casing wave relative amplitude is less than 5% and the attenuation value is less than 80 dB / m. This section is the section with good bonding. Use formula (2) to calculate the average value of attenuation when the bonding is good.

[0050] (7) Subtract the average attenuation value in step (6) from the average attenuation value in step (5) to obtain the difference in attenuation between the micro-annular section and the well-cemented section;

[0051] (8) Obtain cement annulus thickness based on the wellbore diameter and casing outer diameter, and estimate cement shear wave velocity based on annulus thickness and the arrival time of reflected waves in the near and far waveforms recorded by post-casing scanning imaging logging; or measure the longitudinal and shear wave velocities of cement in the well in the laboratory;

[0052] According to steps (3) and (6), the CBL curve can be used to divide the layer into two layers, I and II. The relative amplitude of layer I is between 30% and 60%, which is a micro-ring segment, and the relative amplitude of layer II is less than 5%, which is a well-bonded segment. Figure 3 The value at the middle casing collar (curve peak value) is calculated according to step (5) formula (2) to calculate the average value of the attenuation in the two boxes. The calculation results for zone I and zone II are approximately 106.4 dB / m and 74.8 dB / m. According to step (7), the attenuation difference between the well-bonded section and the micro-annulus section is 31.6 dB / m. The casing size and well diameter will be recorded during the construction operation, thereby obtaining the cement annulus thickness in step (8). The acoustic parameters of cement are based on the data measured in the laboratory. Based on the above parameters, the fluid-casing-cement well-bonded model and the fluid-casing-fluid-cement micro-annulus model are established.

[0053] (9) establishing the relationship between the micro-ring thickness and the attenuation difference between the micro-ring and the well-bonded state by an analytical calculation method based on the longitudinal and transverse wave velocities of the cement, and inverting the micro-ring thickness based on the attenuation value in step (7);

[0054] According to step (9), the phase velocity dispersion curves when there are fluid rings of different thicknesses behind the casing are calculated using an analytical method: Figure 4 , select the attenuation value of 165kHz (within the box interval) and draw the relationship curve between the micro-ring thickness and the attenuation difference (the attenuation difference between the well-bonded and micro-ring models) Figure 5 ,exist Figure 5 It can be determined that the micro-ring thickness corresponding to the attenuation difference of 31.6dB / m is about 0.25mm. Figure 2 The thickness of the microannulus in the middle zone I is about 0.25 mm.

[0055] (10) If the cement density is less than 1.8 g / cm 3 , and continue with steps (11) to (16).

[0056] (11) Select the section where the casing wave relative amplitude is less than 15% and the bending Lamb wave attenuation of the whole well is the highest. This is the section with good cement bonding. Use formula (2) to calculate the average value of the bending Lamb wave attenuation.

[0057] (12) Select a well section where the casing wave relative amplitude is between 40% and 70% and the bending Lamb wave attenuation is reduced by 10 dB / m to 20 dB / m compared with the well section with good cement bonding. This is the micro-ring section. Use formula (2) to calculate the average value of the bending Lamb wave attenuation.

[0058] (13) Subtract the average attenuation value in step (12) from the average attenuation value in step (11) to obtain the difference in attenuation between the micro-ring section and the well-cemented well section;

[0059] (14) Obtain cement annulus thickness based on the wellbore diameter and casing outer diameter, and estimate cement shear wave velocity based on annulus thickness and arrival time of reflected waves in near and far waveforms recorded by post-casing scanning imaging logging; or measure the longitudinal and shear wave velocities of cement in the well in the laboratory;

[0060] (15) establishing the relationship between the micro-ring thickness and the attenuation difference between the micro-ring and the well-bonded state by an analytical calculation method based on the longitudinal wave and shear wave velocities of the cement, and inverting the micro-ring thickness based on the attenuation difference in step (13);

[0061] (16) The cementing quality and the sealing capacity of the cement sheath are further evaluated based on the micro-annulus thickness inverted in step (9) or (15).

[0062] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that within the spirit and principles of the present invention, the technical solutions described in the aforementioned embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents. However, these modifications or replacements do not deviate from the protection scope of the present invention.

Claims

1. A method for inverting the microannulus thickness of a cased well, comprising the following steps: (1) Perform post-casing scanning imaging logging, CBL / VDL logging and caliper logging in the depth interval; (2) Extract the peaks and troughs of the direct bending Lamb waves received by the near and far receivers at 36 azimuths of the post-scanning imaging logging at each depth point, and calculate the attenuation value α at 36 azimuths of this depth point using formula (1): i , i=1~36 In formula (1), l is the distance between the near and far detectors, T i+18 and T i is the amplitude of the near and far detectors, and max and min represent the peak and trough. (3) If the cement density is greater than or equal to 1.80 g / cm 3 , and continue with steps (4) to (9). (4) Select a well section where the relative amplitude of the casing wave is between 30% and 60% and the attenuation of the curved Lamb wave of the post-casing scanning imaging logging is above 80 dB / m. This section is the micro-ring section. (5) Count the average value of the well section attenuation in step (3), and the calculation formula is formula (2), where m is the depth point; In formula (2), α i,n Indicates the attenuation value at the nth depth and the i-th direction. (6) Determine the section in the whole well where the casing wave relative amplitude is less than 5% and the attenuation value is less than 80 dB / m. This section is the section with good bonding. Use formula (2) to calculate the average value of attenuation when the bonding is good. (7) Subtract the average attenuation value in step (6) from the average attenuation value in step (5) to obtain the difference in attenuation between the micro-annular section and the well-cemented section; (8) Obtain cement annulus thickness based on the wellbore diameter and casing outer diameter, and estimate cement shear wave velocity based on annulus thickness and the arrival time of reflected waves in the near and far waveforms recorded by post-casing scanning imaging logging; or measure the longitudinal and shear wave velocities of cement in the well in the laboratory; (9) establishing the relationship between the micro-ring thickness and the attenuation difference between the micro-ring and the well-bonded state by an analytical calculation method based on the longitudinal and transverse wave velocities of the cement, and inverting the micro-ring thickness based on the attenuation value in step (6); (10) If the cement density is less than 1.8 g / cm 3 , and continue with steps (11) to (16). (11) Select the section where the casing wave relative amplitude is less than 15% and the bending Lamb wave attenuation of the whole well is the highest. This is the section with good cement bonding. Use formula (2) to calculate the average value of the bending Lamb wave attenuation. (12) Select a well section where the casing wave relative amplitude is between 40% and 70% and the bending Lamb wave attenuation is reduced by 10 dB / m to 20 dB / m compared with the well section with good cement bonding. This is the micro-ring section. Use formula (2) to calculate the average value of the bending Lamb wave attenuation. (13) Subtract the average attenuation value in step (12) from the average attenuation value in step (11) to obtain the difference in attenuation between the micro-ring section and the well-cemented well section; (14) Obtain cement annulus thickness based on the wellbore diameter and casing outer diameter, and estimate cement shear wave velocity based on annulus thickness and arrival time of reflected waves in near and far waveforms recorded by post-casing scanning imaging logging; or measure the longitudinal and shear wave velocities of cement in the well in the laboratory; (15) establishing the relationship between the micro-ring thickness and the attenuation difference between the micro-ring and the well-bonded state by an analytical calculation method based on the longitudinal wave and shear wave velocities of the cement, and inverting the micro-ring thickness based on the attenuation difference in step (13); (16) The cementing quality and the sealing capacity of the cement sheath are further evaluated based on the micro-annulus thickness inverted in step (11) or (15).

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