Numerical and physical simulations of flexural Lamb wave in cased wells
The wide use of lightweight cement in the oil and gas wells makes it difficult to accurately and effectively evaluate cement bond quality using the acoustic-impedance-based logging method(e.g.,pulse-echo ultrasonic technique).Lamb waves have been used for cement evaluation because the wave propagation in casing is sensitive to layered media acoustic parameters and cementation condition.This paper investigates the relationships among flexural mode attenuation,cement acoustic properties,and bonding conditions between casing and cement using theoretical modeling and analyses.The results show that the flexural mode attenua-tion is sensitive to the condition of cementation between casing and lightweight cement and,in the presence of free pipe condition,to channel fluid thickness between casing and cement.Using the attenuation difference between bonding fluid and bonding solid outside of casing,it is possible to distinguish fluid and solid even when the two situations have similar acoustic impedance values.However,using flexural mode attenuation alone is not sufficient because one attenuation value may correspond to two different cement acoustic impedance values.For this situation it is helpful to use the attenuation-acoustic impedance cross plot to improve reliability of the lightweight cement evaluation.The analysis results can be used to provide a guideline for lightweight cement bond quality evaluation.
万方数据
维普
