双自然电位测井方法在水淹层评价中的应用

在完井测井时，采用替换井内泥浆，改变泥浆矿化度方法测2次自然电位曲线，即换泥浆前测1次，换泥浆后再测1次，由于改变了泥浆矿化度，也就改变了自然电位曲线幅度，在资料解释时，利用2个自由电位方程，求解出2个地层参数，即地层水矿化度和阳离子交换量，再应用地层电阻率和孔隙度曲线，按韦克斯曼－史密茨方程计算地层含水饱和度，因为在计算中地层水电阻率是按求出的地层水矿化度计算的，用求出的阳离子交换量进行了粘土影响校正，故计算的地层含水饱和度较为准确了，然后，应用地层水矿化度变化和层含水饱和度数值来判定油层是否水淹及确定水淹级别，水淹层的含油饱和度即是其剩余油饱和度，在辽河油田进行了2口井实验，取得了较好地质效果，该测井方法适用于所有能够测量自然电位的砂泥岩油田。

Application of Dual SP Logging in Waterflooded Zones

In completion logging, spontaneous potential logging was run twice by replacing mud in wells and changing the mud salinity, or run before changing the salinity and run again after changing the salinity. The height of spontaneous potential logs varies due to the variation of mud salinity. From the two spontaneous potential equations two formation parameters, i.e., formation water salinity and cation exchange capacity, are gained. The formation water saturation is obtained from Maxsman-Smith equation using formation resistivity and porosity. Because the formation water resistivity is obtained from the gained formation salinity and clay effect is corrected with the gained cation exchange capacity, the formation water saturation is accurate. Whether the oil layer is waterflooded or not, its flooded levels were determined from formation water salinity and formation water saturation. So, the oil saturation in water-flooded zone is residual oil saturation. Log interpretations of 2 wells in Liaohe Oilfield prove that dual SP logging is better and more applicable to sand-shale oilfield where spontaneous potential log can be run.