Collar Mode Wave Attenuation in Characteristics Acoustic Logging While Drilling and Isolator Design

Abstract

AbstractThe acoustic logging while drilling (LWD) technology has developed rapidly in recent years. A key technology of this method is the design of an acoustic isolator to suppress acoustic propagation along the drill pipe, such that the acoustic signals from formation can be effectively measured under the LWD conditions. In order to optimize the groove cutting technique commonly used for the LWD isolator design, we apply a 3D finite difference elastic‐wave modeling technique to simulate and analyze the acoustic response of a drill pipe before and after cutting grooves. Analyses of the simulation results reveal the relationship between in the collar's stop‐band characteristics (such as center frequency and width) and collar size, and that between collar wave attenuation and the width and depth of grooves. Based on the results, a new type of LWD acoustic isolator structure is designed, and the theoretical acoustic attenuation curves and the borehole response characteristics for typical soft and hard formation conditions are obtained. The in‐situ well test results indicate that the LWD acoustic tool with the new‐type acoustic isolator can suppress the interference of collar wave and acquire high‐quality waveforms and slownesss of compressional waves in formation.