长源距定向电磁波测井仪器探测深度影响因素分析

Analysis of the Influence Factors on the Detection Depth of Long Spacing Directional Electromagnetic Logging Tools

探测深度是衡量测井仪器探测性能的核心指标。探测深度受源距、频率、地层电阻率和仪器对微弱信号的分辨能力等多种因素的影响。基于并矢格林函数理论,研究仪器探测深度与源距和地层电阻率的关系。根据仪器响应对地层电阻率的敏感性,提出将地层划分为双向敏感区、单向敏感区和不敏感区的方法,分析不同敏感区探测深度的变化规律。在双向敏感区,电阻率对比度越大探测深度越大;在单向敏感区,探测深度只随着敏感区电阻率变化;在同一不敏感区,即使地层电阻率对比度很大,探测深度很小甚至为零。搭建长源距定向测井缩比模型实验平台,研究不同电阻率对比度时仪器的响应特性,验证了不同敏感区探测深度变化规律的正确性。研究结果可为测井仪器线圈系设计提供理论依据。

The detection depth is the critical index to evaluate the performance of the logging tools.The detection depth is affected by various factors such as space,frequency,formation resistivity and resolution of weak signals.The relationship between the amplitude attenuation and main influence factors mentioned above is studied based on the dyadic Green's function method.The method of dividing the formation into double-sensitivity region,single-sensitivity region and non-sensitivity region is put forward according to the sensitivity of the response to the formation.The variation of the directional detection depth in different sensitive areas is analyzed.In the double-sensitivity region,the greater the contrast of resistivity,the greater the detection depth is.In the single-sensitivity region,the detection depth only changes with the resistivity of the sensitive region.In the same non-sensitivity region,the detection depth is small or zero even if the resistivity contrast is very large.The experiment platform of the scaled model for long space directional logging system was built.The experiments on the response characteristics of the tool to the formation with different resistivity contrast were carried out.The correctness of variations rules of the detection depth in different sensitivity region was verified.This study can provide a theoretical basis for the design of the coil system of the logging tools.