随钻电磁波电阻率前探测特性分析

Analysis of Looking Ahead Characteristics of Electromagnetic Propagation Resistivity While Drilling

随钻电磁波电阻率前探测测井技术能够预测钻头前方的地质构造和流体分布,具有描述较大范围的储层构造、预估钻井风险等能力。采用镜像法原理,以井眼垂直于地层界面为例,分别对轴向天线和三轴天线进行分析。探讨轴向天线系统收发距离、轴向天线收发距离比例、三轴天线收发距离等不同因素对前探测能力影响以及2种天线系统对不同电阻率对比度边界的响应。计算分析表明,三轴天线的前探测能力优于轴向天线;前探测能力随着发射天线到接收天线距离的增加而增强;电阻率对比度越大前探测响应越明显,且相同电阻率对比度条件下,仪器在高电阻率地层中探测低电阻率地层边界的能力强于仪器在低电阻率地层中探测高电阻率地层边界的能力。

The technology of looking ahead resistivity logging while drilling can predict the geological structure and fluid distribution in ahead of the bit,and has the ability to describe the reservoir structures in a large range and predict drilling risks.This paper adopts the principle of mirror method to analyze the axial antenna and the triaxial antenna respectively by taking the borehole perpendicular to the stratum interface as an example.The influence of different factors on looking ahead capability are discussed,such as the transmission and reception distance of the axial antenna system,the ratio of the transmission and reception distance of the axial antenna,and the transmission and reception distance of the tri-axis antenna,the response of the two antenna systems to the bed boundary in different resistivity contrast is also analyzed in this paper.The result of calculation shows that the looking ahead capability of the triaxial antenna is better than the axial antenna;the looking ahead capability increases as the distance between the transmitting antenna and the receiving antenna increases;the greater the formation resistivity contrast,the more obvious looking ahead response,and under the same resistivity contrast condition the boundary detection response of the instrument located in the high resistance layer is better than in the low resistance layer.