Ultrasonic Lamb wave logging well wall acoustic interface reverse time migration imaging method

Abstract

The invention discloses an ultrasonic Lamb wave well wall acoustic interface reverse time migration imaging method comprising the following steps: calculating a theoretical frequency dispersion curve, carrying out phase interpolation on original data, and expanding original detector data into array waveform data; establishing an initial density, longitudinal wave and transverse wave velocity model of the target area; forward extrapolation is carried out on the sound source wave field, and a forward extrapolation wave field is stored; inverting the time axis, performing reverse time extrapolation on the receiver wave field, and storing a reverse time extrapolation wave field; solving an envelope line of a forward extrapolation wave field and an extrapolation wave field; applying a zero-delay cross-correlation time consistency imaging condition to obtain a reverse time migration imaging result; and performing imaging denoising on the result, and enhancing the imaging result of the high-frequency acoustic interface. According to the method, the ultrasonic Lamb oblique incidence waveform offset can be classified to the real position, the imaging illusion caused by Lamb wave frequency dispersion is suppressed, the acoustic interface imaging results between the casing and the cement and between the cement and the stratum are obtained, and a powerful guarantee is provided for evaluating the well cementation quality.

Description

technical field [0001] The invention relates to the technical field of cementing quality evaluation, in particular to a reverse-time migration imaging method of an ultrasonic Lamb wave logging borehole wall acoustic interface. Background technique [0002] The exploitation of oil and gas, geothermal and groundwater, the construction of gas storage, and the storage of carbon dioxide all require casings to be placed in the wellbore, and cement is injected between the casing and the well wall to ensure the integrity of the wellbore and realize interlayer and Hydraulic isolation. The annular space between the rock wall of an oil and gas well and the steel casing in the well is usually filled with different types of cement for well wall protection and isolation between rock layers at different depths. In this structure, damages such as casing corrosion and quality problems of cement bonding outside the pipe will have a significant impact on the production of oil and gas wells. ...

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Problems solved by technology

[0004] However, in practical applications, the conventional ultrasonic Lamb data processing method is difficult to provide complete information on the second and third acoustic interfaces of the borehole wall, and can only qualitatively judge the attenuation information of the casing medium, which mainly has the following two problems:

[0005] 1) The eccentricity of the casing or the instrument will affect the amplitude of the leaked A0 reflection wave at the cement-formation interface, and the cement-formation interface cannot be directly observed from the waveform data;

[0006] 2) The complex downhole environment makes it impossible for us to perform time-position conversion through obliquely incident ultrasonic Lamb wave data, and it is difficult to convert the leaked A0 reflected wave signal in the time domain to its distance from the well axis. The A0 reflected wave cannot converge, and the well Accurate location of wall-acoustic interface (borehole wall and cement, cement and formation)

[0008] However, the leaked A0 mode waves produced by the oblique incidence of ultrasonic Lamb waves have a certain dispersion. Directly using conventional reverse time migration and imaging conditions will produce interface imaging artifacts at multiple positions, and the reflected waves and diffracted waves cannot be shifted and homing.

In addition, the current ultrasonic Lamb wave logging adopts oblique incidence single-shot-double-receive technology, and each depth point only contains the measurement waveform results of the far and near two geophones, and the reverse time migration algorithm cannot be used

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