Laboratory Ultrasonic Measurements on Cambrian Sands: Implications for Seismic Monitoring in Deep CO2 Sequestration Projects

Basal Cambrian sandstones lie directly above the crystalline craton in many of the basins of North America. Their depth and petrophysical characteristics make these formations prime zones for long term geological sequestration of CO2 Active source seismic monitoring to track evolution of CO2 plumes will generally be required. Full use of the seismic data, however, requires knowledge of how the seismic responses change with saturation state and effective stress. We have recently completed P and S wave velocity measurements on a suite of Cambrian sandstone cores from the Deadwood Formation in the Williston Basin, Saskatchewan. This contribution focuses on the experimental techniques developed to make measurements. Samples were subject to confining pressures up to 60 MPa, and pore fluid pressures up to 17 MPa under both inert N2 and distilled water saturations. P wave velocities at the highest confining pressures are largely insensitive to saturation state. In contrast, S-wave velocities show significant variation highlighting the influence of bulk saturated density. This difference between P- and S-wave behavior may need to be considered during development of seismic monitoring strategies.