基于时域有限差分法的随钻声波测井仪隔声体隔声效果的数值模拟

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

随钻测井环境下,钻铤纵模式波会严重干扰地层纵波的测量,因此需要使用隔声体来减弱钻铤波对地层纵波测量的干扰。采用圆柱坐标系下的交错网格技术,自行开发了一种可用于设计随钻声波测井仪器隔声体的三维时域有限差分程序。利用该程序数值模拟采用不同结构的隔声体时,硬地层井眼中的随钻单极子声波测井响应,并对这几种不同结构的隔声体性能进行评价。结果表明:采用不同结构的隔声体,对钻铤纵模式波的时延量和隔声量存在很大差异;与其他结构隔声体相比,周期性交错排列的凹槽结构的隔声体在测量地层纵波速度时具有较好的效果。

Under logging while drilling （LWD） environment, the collar extensional wave would seriously disturb the measurement of formation compressional wave. Tbere（ore, 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.