This study uses VSP and well log data to analyze the AVO response of a subsurface gas-saturated carbonate zone. Analysis of the well log data show that the gas-saturated zone is dolomitized with a porosity as high as 18 %. The VSP data consist of three surveys; a zero-offset VSP; an offset VSP, and a multioffset VSP. The P-SV converted-wave reflections from the offset VSP and multioffset VSP were found to correlate well with the pure P-wave reflections from each VSP. Forward modeling was used to analyze the AVO response of the gas-saturated zone. It was found that there is extreme tuning in the reservoir zone, causing the combined AVO response of the layers within 1/2 of the seismic wavelength to be very complicated. It was also found that a better match of the forward model data with the field multioffset VSP data could be made by lowering the P-wave velocity in the reservoir zone.
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