Abstract：Laboratory induced polarization study arid field induced polarization experiments conducted over hydrocarbon traps show that the key geological reason why deep hydrocarbon trap results iri shallow induced polarizatiori (IP) anomaly is the shallow secondary-pyrite contaminated zone that overlies the hydrocarbon trap. Pyrite was formed because ferrite in shallow porous country rock combined with the sulphide which resulted from bacteria's oxidizing the hydrocarbon that rad migrated from deep hydrocarbon trap to the country rock. It is pointed out that low success rate of IP hydroearbon-trap detection in China mainly resuits from (1) the geological condition restriction on IP anomaly of hydrocarbon trap and (2) the interference due to the IP effect of freshwater-saturated formation. It is discussed how the effect of IP hydrocarbon-trap detection can be improved,The effects of hole casing and nearsurface pipes should be considered in IP experiment in oil-gas production area.
