CN-122014225-A - Ultra-soft stratum well cementation quality evaluation method

CN122014225ACN 122014225 ACN122014225 ACN 122014225ACN-122014225-A

Abstract

The invention discloses an ultra-soft stratum well cementation quality evaluation method, and relates to the technical field of geophysical well logging. Based on well condition data of a cased well, the invention obtains a cased well acoustic logging actual measurement waveform curve by carrying out array acoustic logging on a target well section, acquires a cased well acoustic logging theoretical full-wave waveform curve of a target well section under different cased well cementing conditions by matching with an ultra-soft stratum cased well acoustic logging simulation model, carries out waveform characteristic matching on the cased well acoustic logging actual measurement waveform curve and the cased well acoustic logging theoretical full-wave waveform curve respectively aiming at each depth point of the target well section, extracts full-wave waveform response characteristics under different cased well cementing conditions of the ultra-soft stratum, accurately evaluates the ultra-soft stratum cementing quality of the target well section, and generates an ultra-soft stratum cementing quality evaluation result diagram. The method effectively solves the problem of difficult evaluation of the cementing quality of the second cementing surface of the cement sheath in the casing well of the ultra-soft stratum, and realizes accurate evaluation of the cementing quality of the ultra-soft stratum.

Inventors

CHEN XUELIAN
ZHANG MAI
PAN JINLIN
HE CHANGSHENG
WU XUEMING
LI ZHIHUAN

Assignees

中国石油大学(华东)

Dates

Publication Date: 20260512
Application Date: 20260203

Claims (5)

1. The ultra-soft stratum well cementation quality evaluation method is characterized by comprising the following steps of: Step 1, selecting a target well section in a cased well, and performing array acoustic logging on the target well section by adopting a monopole acoustic source and a dipole acoustic source respectively to obtain a cased well acoustic logging actual measurement waveform curve, wherein the actual measurement waveform curve comprises a monopole acoustic source actual measurement full-wave waveform and a dipole acoustic source actual measurement full-wave waveform; Step 2, a cased well model is established according to well condition data of a target well section and is used for simulating the cementation condition of a cased well in an ultra-soft stratum, theoretical calculation is respectively carried out on various cased well cementation conditions by utilizing the ultra-soft stratum cased well acoustic logging simulation model, and a cased well acoustic logging theoretical full-wave waveform curve of the target well section is obtained, wherein the cased well acoustic logging theoretical full-wave waveform curve comprises a monopole acoustic source theoretical full-wave waveform curve and a dipole acoustic source theoretical full-wave waveform curve; Step 3, respectively carrying out waveform characteristic matching on the actual measurement waveform curve of the acoustic logging of the cased well and the theoretical full-wave waveform curve of the acoustic logging of the cased well aiming at each depth point of the target well section, extracting full-wave waveform response characteristics of the ultra-soft stratum under different cementing conditions, and carrying out ultra-soft stratum well cementation quality evaluation according to the extracted full-wave waveform response characteristics; and step 4, generating an ultra-soft stratum well cementation quality evaluation result graph according to the ultra-soft stratum well cementation quality evaluation result of the target well section.
2. The method for evaluating the cementing quality of the ultra-soft stratum according to claim 1, wherein in the step 2, a cased well model is established in a cylindrical coordinate system according to well condition data of a target well section, and the cased well model is used for simulating the cementing condition of the stratum and the casing, and comprises the casing and the stratum, wherein the stratum is an infinite solid medium, and wellbore fluid is arranged in the casing of the cased well model; The casing well cementation conditions are four types, namely, free casing, unconsolidated cement sheath first cementation surface, unconsolidated cement sheath second cementation surface and completely cementation cement sheath, wherein when the cement sheath is not arranged between the casing and the stratum, the situation of the free casing is simulated by arranging a fluid layer between the casing outer wall and the stratum, when the cement sheath is arranged between the casing and the stratum, the cementation interface between the cement sheath and the casing outer wall is the first cementation surface, the cementation interface between the cement sheath and the stratum is the second cementation surface, the situation of unconsolidation of the cement sheath first cementation surface is simulated by arranging a fluid layer between the cement sheath and the casing outer wall, the situation of complete cementation of the cement sheath is simulated by arranging a fluid layer between the cement sheath and the stratum, and the situation of close adhesion between the cement sheath inner wall and the stratum.
3. The method for evaluating the quality of ultra-soft stratum well cementation according to claim 2, wherein the response characteristics of the acoustic wave logging full wave waveform of the cased well are obtained by the acoustic wave logging simulation model of the cased well, and the response characteristics comprise a monopole acoustic source theoretical full wave waveform curve and a dipole acoustic source theoretical full wave waveform curve, and the expression is as follows: ; ; In the formula, A theoretical full-wave waveform of a monopole sound source; is the radius of the medium; is the axial distance; Time is; radial wave number; is the radius of the sound source; is the circumferential direction ordinal number when When corresponding to monopole sound source Corresponding to the dipole sound source; is the density of the wellbore fluid; Is frequency; The amplitude coefficient of sound waves propagating from outside to inside in the fluid medium in the sleeve; Is of the first kind A Bessel function; is the sound source coefficient; Is of the second kind A Bessel function; Is a spectral function of the sound source; Is a natural constant; Is an imaginary unit; Is the axial wave number; Theoretical full wave waveform curve for dipole sound source.
4. The method for evaluating the quality of ultra-soft stratum well cementation according to claim 1, wherein in the step 3, for each depth point of a target well section, the full-wave waveform measured by a monopole sound source is utilized to extract the sleeve wave velocity measured by the monopole sound source, the full-wave waveform measured by a dipole sound source is utilized to extract the sleeve bending wave velocity measured by the dipole sound source and the stratum bending wave dispersion curve, and the full-wave waveform response characteristic of sleeve well acoustic logging is obtained; And according to the sleeve wave speed measured by the monopole sound source, the sleeve bending wave speed measured by the dipole sound source and the dispersion curve of the stratum bending wave, carrying out ultra-soft stratum well cementation quality evaluation by combining the stratum transverse wave speed obtained from the target well section well condition data, and judging the well cementation condition of the sleeve well at each depth point to obtain an ultra-soft stratum well cementation quality evaluation result.
5. The method for evaluating the cementing quality of an ultra-soft stratum according to claim 4, wherein the determination basis of the cementing condition of the cased well is as follows: when the sleeve wave speed measured by the monopole sound source is 5386-5586 m/s, the sleeve bending wave speed measured by the dipole sound source is 1506-1606 m/s, the speed of the extracted stratum bending wave is greater than the stratum transverse wave speed when the frequency of the extracted stratum bending wave dispersion curve is greater than 5.85kHz, and the dispersion phenomenon exists in the frequency domain of 0-30 kHz, the actual measurement waveform curve of the sleeve well acoustic wave logging is consistent with the waveform characteristic of the theoretical full-wave waveform curve of the sleeve well acoustic wave logging when the first cementing surface of the cement sheath is unconsolidated, and the cementing condition of the sleeve well is judged to be that the first cementing surface of the cement sheath is unconsolidated; When the sleeve wave speed measured by the monopole sound source is 4671-4871 m/s, the sleeve bending wave speed measured by the dipole sound source is 1404-1500 m/s, the speed of the extracted stratum bending wave in the frequency domain of 0-30 kHz is smaller than the stratum transverse wave speed, the frequency dispersion phenomenon exists in the frequency domain of 0-10 kHz, and the waveform characteristics of the sleeve well acoustic logging actual measurement waveform curve are consistent with the waveform characteristics of the theoretical full wave waveform curve of the sleeve well acoustic logging when the second cementing surface of the cement sheath is unconsolidated, judging that the cementing condition of the sleeve well is unconsolidated by the second cementing surface of the cement sheath; When the sleeve wave speed measured by the monopole sound source is 4671-4871 m/s, the sleeve bending wave speed measured by the dipole sound source is 1404-1500 m/s, the extracted stratum bending wave frequency dispersion curve does not contain stratum bending waves, and the actual measurement waveform curve of the sleeve well acoustic wave well logging is consistent with the waveform characteristics of the theoretical full wave waveform curve of the sleeve well acoustic wave well logging when the cement sheath is completely cemented, judging that the sleeve well cementing condition is the cement sheath is completely cemented; When the sleeve wave speed measured by the monopole sound source is 5386-5586 m/s, the sleeve bending wave speed measured by the dipole sound source is 1404-1500 m/s, the speed of the extracted stratum bending wave is smaller than the stratum transverse wave speed when the frequency is larger than 10kHz, the phenomenon of frequency dispersion does not exist when the frequency is larger than 1kHz, the actual measurement waveform curve of the sleeve well acoustic wave logging is consistent with the waveform characteristics of the theoretical full wave waveform curve of the sleeve well acoustic wave logging when the sleeve is free, and the sleeve well cementing condition is judged to be the free sleeve.

Description

Ultra-soft stratum well cementation quality evaluation method Technical Field The invention relates to the technical field of geophysical well logging, in particular to an ultra-soft stratum well cementation quality evaluation method. Background With further deep sea oil and gas exploration and development, deep water oil and gas is receiving more and more attention. Because deep water shallow layer is buried in depth, rock particles are consolidated and loose, the longitudinal wave speed is lower than that of a conventional soft stratum, namely the longitudinal wave speed is higher than that of well mud, the transverse wave speed is lower than that of well mud, and particularly the situation that the stratum longitudinal wave speed is lower than that of the well mud can occur in a gas bearing stratum section is defined as an ultra-soft stratum. Acoustic logging is one of the primary techniques for well cementation quality evaluation, primarily for evaluating the quality of the bond between the casing and the cement (i.e., the first cementing surface) and between the cement and the formation (i.e., the second cementing surface). The acoustic logging response characteristics in the ultra-soft formation cased well are different from those of a conventional formation, and formation waves cannot be observed by the acoustic variable density logging adopted in the prior art, so that the well cementation quality evaluation difficulty of the second cementing surface is increased. Therefore, there is a need to define the acoustic logging response characteristics of cased wells in ultra-soft formations and provide a well cementation quality evaluation method suitable for ultra-soft formations. Disclosure of Invention In order to solve the defects in the prior art, the invention provides an ultra-soft stratum well cementation quality evaluation method, which is used for obtaining a cased well acoustic logging actual measurement waveform curve through array acoustic logging measurement, and the problem that the cementing quality of a cement sheath second interface in an ultra-soft stratum is difficult to evaluate in the current stage of variable density logging is effectively solved by utilizing the full-wave waveform response characteristic of the cased well acoustic logging actual measurement waveform curve and combining the cementing condition of a cement sheath first cementing surface and a cement sheath second cementing surface of the cased well acoustic logging theoretical full-wave waveform curve of each cementing condition of the cased well. The invention adopts the following technical scheme: a method for evaluating the well cementation quality of an ultra-soft stratum comprises the following steps: Step 1, selecting a target well section in a cased well, and performing array acoustic logging on the target well section by adopting a monopole acoustic source and a dipole acoustic source respectively to obtain a cased well acoustic logging actual measurement waveform curve, wherein the actual measurement waveform curve comprises a monopole acoustic source actual measurement full-wave waveform and a dipole acoustic source actual measurement full-wave waveform; Step 2, a cased well model is established according to well condition data of a target well section and is used for simulating the cementation condition of a cased well in an ultra-soft stratum, theoretical calculation is respectively carried out on various cased well cementation conditions by utilizing the ultra-soft stratum cased well acoustic logging simulation model, and a cased well acoustic logging theoretical full-wave waveform curve of the target well section is obtained, wherein the cased well acoustic logging theoretical full-wave waveform curve comprises a monopole acoustic source theoretical full-wave waveform curve and a dipole acoustic source theoretical full-wave waveform curve; Step 3, respectively carrying out waveform characteristic matching on the actual measurement waveform curve of the acoustic logging of the cased well and the theoretical full-wave waveform curve of the acoustic logging of the cased well aiming at each depth point of the target well section, extracting full-wave waveform response characteristics of the ultra-soft stratum under different cementing conditions, and carrying out ultra-soft stratum well cementation quality evaluation according to the extracted full-wave waveform response characteristics; and step 4, generating an ultra-soft stratum well cementation quality evaluation result graph according to the ultra-soft stratum well cementation quality evaluation result of the target well section. Preferably, in the step 2, a cased well model is established in a cylindrical coordinate system according to well condition data of a target well section, the cased well model is used for simulating the cementing condition of a stratum and a casing, and comprises the casing and the stratum, wherein the stratum is an infinite s