BUNGE, ROBERT J., Colorado School of Mines, Dept. of Geophysics, Golden, CO

ABSTRACT: Analysis of a Fractured Reservoir, Weyburn Field, Saskatchewan

The Weyburn field of southeastern Saskatchewan was previously believed to be a structurally simple reservoir, with at most one direction of fracturing. Borehole images (3 EMIs and 1 FMS), recently analyzed in preparation for an upcoming CO₂ injection and seismic monitoring program, reveal at least 3 open fracture sets at the reservoir interval.

Static image thresholds were applied to one EMI log to define which fracture set dominates reservoir flow. It was discovered that all three sets contribute equally based on fracture aperture from electrical conductivity.

The three fracture sets are consistent within a regional wrench fault framework established in the U.S. portion of the Williston Basin. However, the current local stress field allowing extension, and three open mode fracture sets, must be explained by extensive salt dissolution. Seismic shows not only recurrent fault movement and salt dissolution beneath the reservoir, but further structural control on sedimentary processes throughout time.

AAPG Search and Discovery Article #90909©2000 AAPG Foundation Grants-in-Aid