岩芯电容率特征研究及其在流体识别中的应用

CHARACTERISTICS OF PERMITTIVITY OF CORES AND ITS APPLICATION IN FLUIDS IDENFICATION

由于频散影响因素多,产生机理不清,并且测井时其实部和虚部的计算存在错误,导致了"实部不实,虚部不虚"的结果,制约了复电阻率测井技术在油田的应用和发展。对油田大量岩芯的实验测量发现,地层的电容率信号对油气的响应更显著:NaCl溶液的电容随着测量极板距离的增加按负平方关系减小;随着溶液浓度的增加按平方关系增加;随着频率的增加按负幂指数规律减小。NaCl溶液电阻率和电容率对比发现,相同条件下,电容率的变化率比电阻率明显,从而证明了地层电容率比电阻率对地层压力、孔隙度、流体矿化度和饱和度等地层参数响应更敏感。基于这样一个发现,仿照阿尔奇公式,建立了以电容率为核心参数的含水率和矿化度计算公式,进而识别流体类型。油田双侧向电阻率测井实际资料证明,利用电容率信号可以更好地识别地层流体。

Complex electrical well logging has been widely used in many oilfields.It is a powerful method for the low-resistivity,water-flooded and residual oil zone.However,frequency dispersion and incorrecte calculation of the real and image part of complex resistivity are the main reasons that restrict its development.The principle of complex resistivity logging are studied in this paper,and it is found that permittivity of the rocks and formation fluids have more distinguished response than resistivity of them.The previous experiments have been proved that the permittivity decreased with the distance square between two poles.Based on the results of the experiments,the new equations to calculate the saturation and salinity of formation water have been established,in addition,a circute that used to detect capacitivity is designed.The new method has been shown available for identifing the fluid by the oilfield data.