基于介电测井和电阻率测井的致密砂岩储层饱和度联合反演方法

Joint Inversion of Saturation of Tight Sandstone Reservoirs Using Resistivity and Dielectric Logs

鄂尔多斯盆地三叠系延长组致密砂岩储层具有地层水矿化度变化大、孔隙结构复杂、泥质含量较高等特点,含油饱和度评价困难。然而,致密储层钻井液侵入较浅,且多频介电测井蕴含地层水矿化度等信息,为饱和度评价提供了有利条件。基于阵列感应电阻率曲线以及介电测井4种频率的介电常数曲线和电导率曲线,提出一种联合电阻率测井和介电测井信息反演储层含油饱和度的方法。根据储层性质选择模型构建目标函数,电阻率测井响应采用西门杜方程,介电测井1 GHz频率下测量的介电常数和电导率使用复折射率模型,20~500 MHz频率测量的介电常数和电导率采用泥质砂岩响应模型。利用粒子群优化算法对目标函数进行寻优反演,并构建实例检验算法。将该方法应用于目标储层,获得饱和度、水相曲折度指数、冲洗带矿化度及泥质频散项体积含量。结果显示理论测井响应曲线和实际测井曲线的相对误差小于10%,计算的含油饱和度与岩心分析、试油数据吻合较好,表明该方法反演的参数结果有效、可靠,具有推广应用价值。

The tight sandstone reservoirs of Yanchang formation of Triassic in Ordos basin are characterized by large variation of formation water salinity,complex pore structure,and high shale content,which makes it difficult to evaluate oil saturation.The shallow mud invasion in tight reservoir,and water salinity indicated by multi-frequency dielectric logs provide a feasible method for saturation evaluation.Based on the array induction resistivity logs and the permittivity and conductivity logs of dielectric logging at four frequencies,a joint inversion method for reservoir oil saturation by resistivity and dielectric logs is proposed.Response equations are chosen to construct the misfit function based on reservoir properties.Simandoux equation is used for resistivity log.Complex refractive index model is used for permittivity and conductivity measured from dielectric logging at 1 GHz,and shaly sandstone model is used for permittivity and conductivity from dielectric logging in 20~500 MHz frequency band.The particle swarm optimization(PSO)algorithm is used to optimize the objective function,and examples are constructed to test the algorithm.The method is applied to the target reservoir to obtain saturation,tortuosity index of water phase,salinity of flushing zone,and volume content of shale dispersive phase.The results show that the relative error between the synthetic log response and the measured log is less than 10%,which indicates that the inversion parameters of this method are effective and reliable.Furthermore,the calculated oil saturation is in good agreement with the core analysis and oil test data,which verifies the accuracy of the method.This method has the value of popularization and application.