Spectral ratios for the Pembina Cardium formation computed with virtual sources

Arnim B. Haase, Donald C. Lawton, Abdullah A. Alshuhail

Spectral ratios across the Pembina-Cardium formation are computed from surface source lines and down-hole receiver gathers by applying virtual source principles. It is found necessary to apply first-arrival wave package windowing to reduce ringing of these spectral ratios. There is an increase of attenuation across the reservoir layer for all three source line experiments following CO2 injection. This attenuation increase is confirmed by spherical wave modelling employing a multi-interface Sommerfeld integral algorithm and using monitor well-logs as well as fluid substitution derived perturbations of reservoir parameters. Spherical wave modelling also shows far-offset tuning across the reservoir when offsets are retained rather than applying virtual source methods. Alternate measures of CO2 injection effects are demonstrated by displaying time domain maximum amplitude differences as function of offset as well as plotting frequency domain magnitude spectral differences as function of frequency and offset.