Electrical and Electromagnetic Methods
Since 1982, we have undertaken induced polarization research for oil exploration at more than 20 oil fields in different parts of China. Using the oil field in region K in northwest China as the main example, we examine in detail the mechanism of the cause of the IP anomaly over an oil reservoir. Based on the results of many different kinds of physical and chemical determinations and analysis, we conclude that the main geological factor which causes the IP anomaly is the pyrite mineralization distributed in the shallow layers over the oil reservoir. We infer that the pyrite mineralization is related closely to the diffusion or escape of the hydrocarbon substance from the oil reservoir. Along the vertical direction, the variation of the substance in the overburden layers has been investigated theoretically and practically. From these results we provide a preferable geological-geophysical model which describes the vertical variation of the material and of the ρs, Ms property of the overburden layers.