"Western Geco" as a part of Schlumberger has the techniques to find out easily between Gas/Oil and water content formations........
CSEM - Controlled Source Electro Magnetic .....a new tool for risk reduction
Applications: The primary application of CSEM is the identification and characterization of units that are more resistive than the surrounding rocks. Typically, a potential reservoir is identified with seismic data and CSEM used to analyze its resistivity, taking advantage of the resistivity contrast between oil- or gas-saturated rocks and those with a significant water content The transformation from resistivity to geology, and finally pore fluid content, is an interpretive process that requires careful interpretation and integration of the CSEM data with seismic data and local well control.