Estimating elastic properties of sandstone reservoirs using well logs and seismic inversion

Maria Fernanda Quijada

Well logs and seismic data from a heavy oilfield in east-central Saskatchewan are analyzed to estimate the elastic properties of the reservoir facies. The sand-shale interface is characterized by a significant increase in S-wave velocities (Vs), from 800 to 1300 m/s, and almost no change in P-wave velocities. Within the target zone, density values lower than 2250 kg/m3 are diagnostic of sands. Reservoir sands from Assam, India also have an anomalous Vs response. Including prior lithological information is necessary to model accurate elastic parameters over the complete depth interval. Polarity changes at the reservoir levels and different frequency content of the PP and PS volumes significantly affect the registration and interpretation process. Productive channels are indicated by low-impedance zones, driven by the density decrease in the sands. The mudrock line consistently underestimates Vs values in sands, suggesting the Vs residual can generally be used as a sand indicator.