4D rock and fluid properties analysis at the Weyburn Field, Saskatchewan

This paper presents an analysis of CO2 rock and fluid properties and 1D seismic modeling from the Weyburn Field, Saskatchewan. Dry frame properties of the Marly and Vuggy units were computed using data from ultrasonic core measurements, and the fluid physics of oil/brine/CO2 mixtures was analyzed using established empirical relations and a multi-phase compositional simulator. The complex properties of supercritical CO2 and miscible oil systems were taken into account for the range of reservoir pressures and fluid saturations expected at Weyburn. These dry rock and fluid properties were combined to obtain saturated P- and S-velocities and densities that were used directly in generating 1D synthetic seismograms from well logs modified to simulate production-related changes in pressure and saturation. It was found that pressure effects at Weyburn are at least as large as, and often larger than, saturation effects. 1D modeling results confirm the sensitivities of rock properties to pressure and saturation changes found in the rock physics analysis, but they also include the complexities of spatially varying properties and wavelet effects, which can significantly alter the seismic response. This analysis is an important first step in successfully implementing CO2 monitoring and verification for enhanced oil recovery and long-term sequestration.

► Rock and fluid properties were analyzed over a range of pressures and CO2 saturations.
► At Weyburn, pressure effects are at least as large as saturation effects.
► Pore pressure increases affect seismic properties more than pore pressure decreases.
► The complexities of CO2 fluid physics should be included in rock physics analyses.
► Rock physics analyses and 1D modeling show similar pressure and saturation effects.