随钻电磁波电阻率测井联合反演方法及其应用

针对海上油气田高正压差井筒条件下随钻测井电阻率受钻井液低侵影响的问题,提出了随钻电磁波电阻率测井联合反演方法,设计了一种基于视电阻率曲线分离程度的反演初始值选取方案,通过反演可以获得原始地层电阻率和钻井液侵入深度。数值模拟结果显示,初始值选取精度满足工程应用需求,地层真电阻率和钻井液侵入深度参数反演相对误差小于0.5%。时间推移测井资料分别反演所得地层真电阻率一致,表明该方法稳定可靠。对中国南海西部东方区块随钻测井资料开展电阻率反演应用研究,结合反演成果开展了钻井液侵入规律统计,得到了钻井液侵入深度与地层孔隙度、渗透率、钻井液柱压力、钻井液浸泡时间及地层电性变化等参数的统计关系,其对钻井液侵入预测与评价具有参考价值。该电阻率联合反演方法可推广应用于其他海域随钻电磁波电阻率测井,对储层评价与储量计算具有重要意义。

Joint inversion method of electromagnetic wave resistivity logging while drilling and its application

In view of the fact that the electromagnetic wave resistivity logging while drilling(LWD) is affected by low invasion of drilling fluid under the condition of a shaft with positive high pressure difference in offshore oil and gas fields, a joint inversion method of electromagnetic wave resistivity logging while drilling was proposed in this study. Then a selection scheme of initial inversion value was designed based on the separation degree of apparent resistivity curves, so as to obtain the original formation resistivity and drilling-fluid invasion depth through inversion. Numerical simulation results show that the accuracy of initial value selection can meet the requirements of engineering application, and the relative errors of inversion parameters such as true formation resistivity and drilling fluid invasion depth are less than 0.5%. The true formation resistivity obtained through respective inversion of time-lapse logging data is consistent, proving that this method is steady and reliable. A resistivity inversion application study was carried out according to LWD data in western South China Sea. In combination with inversion results, the statistics were performed on drilling-fluid invasion laws to obtain the statistical relationship between drilling-fluid invasion depth and various parameters such as formation porosity, permeability, drilling-fluid column pressure, drilling-fluid soaking time and formation resistivity variation, etc., which provides a reference for the prediction and evaluation of drilling-fluid invasion. This joint resistivity inversion method can be applied to LWD in other seawaters, and has great significance to reservoir evaluation and reserve calculation.