Sound isolation numerical simulation on isolator of logging while drilling sonic tool using finite difference time-domain method

Under logging while drilling(LWD) environment,the collar extensional wave would seriously disturb the measurement of formation compressional wave.Therefore,the collar wave must be suppressed by isolator in order to measure the formation arrival. Based on staggered grid technique in cylindrical coordinates,a 3D finite-difference time-domain(FDTD) scheme was developed for simulation of isolator for LWD sonic tool.Sonic logging responses of monopole wave in the borehole of fast formation were simulated.The performances of several different isolators with complex geometrical structures were evaluated.The monopole waves for a fast formation were provided for LWD tools when the tools have different isolators.Simulation results show that for the isolators with different structures,the time delay and sound isolation for the collar extensional wave vary widely.A type of isolator with staggered cyclical grooves has better performance than any other isolator.