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.