随钻电阻率测井的环境影响校正主次因素分析

Analysis of The Primary and Secondary Environmental Effects Correction on LWD Resistivity Log

环境影响校正是随钻电阻率测井资料精细解释与应用中的重要问题。分析了随钻电阻率测井中井眼、围岩、地层倾角(或井斜角)、地层各向异性及泥浆侵入等环境因素对测井结果的影响及其校正方法。在大斜度井、水平井中采集随钻电阻率测井数据,当地层倾角或井斜角比较大时受地层各向异性影响最为明显;当目的层为薄油气层时需要考虑围岩影响;当钻速较低、测井仪器离钻头较远、岩层暴露时间较长时需要考虑泥浆侵入的影响。推导出地层视电阻率与垂直层界面方向的电阻率、平行层界面方向的电阻率的关系式,并给出了随钻电阻率测井环境影响主次因素判释流程图。依据校正公式和数值逼近迭代方法及所编制的主次因素分析与自动校正程序处理了某油田的多口井随钻电阻率测井资料,认为井斜角和各向异性导致实测的电阻率值增高,通过校正提高了随钻测井解释的精度和准确性。

Correction of environmental effects is very important in the log interpretation for resistivity logging while drilling. Special emphyasis is given to the analysis of the primary and secondary environmental effects such as well borehore, shoulder bed, formation dip（deviation angle） , formation anisotropy and mud-filtrate invasion. Data acquisition of resistivity logging while drilling in high-angle and horizontal （HA/HZ） wells is considerable affected by formation anisotropy when formation dip/deviation angle is bigger, affected by shoulder beds in thinedded gas formation as interest zone, affected by mud-filtrate invasion at low drilling velocity. Empirical relation of the formation apparent resistivity, the vertical interface resistivity and the parallel interface resistivity are derived. The flow chart is established and dedicated to users in order to distinguish the primary and secondary environmental factors. According to the derived corresponding correction formula , the numerical approximating iteration method and the relevant processing programs for analysing the primary and secondary environmental effects, the resistivity well logging curves while drilling are processed and corrected, the practical cases show that deviation angle and formation anisotropy can result in increasing resistivities.