Determination of saturation exponent in shaly formation

Archie formula is important for calculating water saturation of the reservoir, but it is only applicable to pure sandstone reservoirs. In the shaly formation,it is nonlinear relationship between the logarithm of the resistivity index and the logarithm of water saturation. The saturation exponent changes with resistivity index, with different changes under different pore structure and shale conditions. According to capillary tube theory,statistical theory,integration principle and volume model method,the relationship among saturation exponent, shale content, the parameters of pore structure and the resistivity index in shaly formation is derived, and the saturation exponent of shaly formation under different condition is determined.