Fuping Zhu1,
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