Partial gas discrimination is a challenging problem because low and high gas saturation can result in very similar seismic AVO, bright spot, and velocity sag anomalies. This is typically explained using Gassmann's theory: i.e., (1) small amounts of gas in the pore space cause large decreases in rock incompressibility while further increasing gas content does not reduce rock incompressibility significantly, and (2) the shear modulus is not affected by nonviscous fluids in the rock pore space. In addition, rock bulk density varies gradually with water saturation, as predicted using the volume-average equation. Consequently, low-gas saturation reservoirs and high-gas saturation reservoirs...

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