A method to evaluate reservoirs and estimate saturation by dynamic responses of dual-induction logging tools

The invasion of drilling mud–filtrate into a reservoir is a dynamic process. Formation-resistivity profiles are therefore invasion-time dependent. The dynamic response model for resistivity logs is established and solved by numerical methods. The present model gives more physical understanding to the invasion process than the conventional step model does. The dynamic resistivity responses are sensitive to the variations of formation–water saturation, hence an effective method to evaluate reservoirs is suggested by history matching the dynamic dual-induction logging readings. Field examples are illustrated that distinguish oil reservoirs, water zones, and oil/water zones, as well as define the oil–water interface by the responses of induction logs at different logging times after drilling.