Fluid detection in carbonate rocks by integrating well logs and seismic attributes

It has been well documented that the pre-stack seismic attributes can be an efficient tool for hydrocarbon exploration and pore fluid detection using techniques like Amplitude Versus Offset (AVO) analysis. These studies mainly focus on siliciclastics rather than carbonates as fluid effects in carbonate rocks can be masked by their complex pore structure. These fluid detection seismic attributes usually reside on a linear background model for P- and S-velocities of the water-saturated rocks, and any deviation from this trend is assigned to the possible pore fluid changes. This means that fake (or even missed) fluid effects can be detected in carbonate rocks if the fluid detection seismic attributes, which designed for siliciclastics, are used. This can mainly be related to the nonlinearity of background model in carbonates due to their varying pore structure. In this study, both well logs and seismic data from a carbonate sequence are used to show that the correlation between P- and S-velocities in water-saturated carbonates becomes more linear when considering P-velocity squared versus the product of the P- and S-velocities. Furthermore, this linear version is used for detecting the fluid anomalies, and being compared with other various fluid factors to highlight the gas saturated interval. The modified fluid attribute displays the gas-saturation brighter than the alternatives, although, in this case, all the studied indicators perform well and consistently.