随钻声波测井钻铤模式波衰减规律研究与隔声体设计

LWD acoustic color mode wave attenuation character research and isolator design

随钻声波测井技术近年来发展很快,这门技术的关键技术之一是随钻仪器的隔声设计,以保证在随钻条件下有效地测量地层的声波信号.针对普遍采用的刻槽隔声技术,本文利用三维有限差分弹性波场模拟对钻铤刻槽前、后的声波响应进行了数值模拟和理论研究.通过模拟结果的理论分析给出了钻铤波固有阻带分布规律与钻铤尺寸关系和钻铤波衰减频段与刻槽宽度、深度的关系.在此基础上,设计了一种随钻声波测井隔声体结构,给出了理论声衰减曲线和典型地层井孔中的响应特征.现场实验井测试结果表明,本文没计的隔声体结构有效地消除了钻铤直达波的干扰,能够测量到高质量地层纵波的波形和时差.

The acoustic logging while drilling （LWD） technology has undergone a rapid development in recent years. A key technology of the LWD acoustic measurement 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 analyse 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 stopband characteristics （suches 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 LWD acoustic isolator structure is designed, and the theoretical acoustic attenuation curve and the borehole response characteristics for typical soft and hard formation conditions are obtained. The field experiment well test results indicate that an LWD acoustic tool with the new-type acoustic isolator can suppress the interfere of collar wave and measure a high quality formation eompressional-wave data and slowness.