Richard L. Gibson1,
Joel S. Watkins1,
Sung H. Yuh1
(1) Texas A&M University, College Station, TX
Abstract: Rpp/Rps to discriminate commercial gas reservoirs from non-commercial reservoirs
The discrimination of commercial from non-commercial gas reservoirs is a challenging problem. We propose a new hydrocarbon indicator based on differences in P (P-P) and converted wave (P-SV) reflection coefficients. This can help distinguish between the two cases when using multicomponent seismic data. Rpp and Rps are defined as the change in the P-P and P-SV reflection coefficient as gas saturation increases from 100% water saturation, respectively. Using the Zoeppritz and Gassmann's equations, we compute reflection coefficients for a range of examples to demonstrate that the ratio Rpp/Rps, the new hydrocarbon indicator, behaves quite differently for high and low gas saturations. Synthetic multicomponent seismic data also proved Rpp/Rps as an effective hydrocarbon indicator. Rpp/Rps significantly reduces the ambiguity for partial gas discrimination using P-P or P-SV data separately.
For all three classes of gas sands, the ratio provides a useful discriminant. Gas saturation is qualitatively indicated by differences in the change of Rpp/Rps with near and intermediate offsets for low and high gas saturation. High and low gas saturation is also quantitatively indicated by Rpp/Rps values at these offset; it shows negative values for high gas saturation, but either much more negative or positive values for low gas saturation
The application of this approach does not require inversion or knowledge of petrophysical parameters other than compressional- and shear-wave velocities, which are used for P-P and P-SV seismic correlation. It does require some information on P-P and P-SV from water saturated portions of the reservoir.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana