R. Bunge

Colorado School of Mines, Golden, CO

ABSTRACT: Midale Reservoir Fracture Characterization Using Integrated Well and Seismic Data, Weyburn Field, Saskatchewan

The Weyburn field of southeastern Saskatchewan produces oil from the carbonate Midale beds of the Mississippian Charles Formation. This study was designed to characterize fractures of the Midale beds. Fractures were quantified using the available data, and structural mechanisms that caused fracturing were identified using compressional wave seismic data in an effort to predict spatial variation in fracture populations. Oriented cores and one borehole image log were used to quantify fracture height, aperture, density, and orientation. Five fracture sets were identified based on strike azimuth: 2 healed and 3 open. Previously only one set of open fractures was believed to exist at Weyburn. Using 2D and 3D compressional wave seismic data, multiple fracture mechanisms were identified. Patterns in seismic maps and fractures suggest that a left lateral shear system is responsible for creating the majority of the open fractures. Salt dissolution under the reservoir later provided a second fracture mechanism, and a means to open preexisting fracture sets. Analysis of the gamma ray logs from several horizontal wells suggests that small-scale faults with less than 5m of throw exist. FScan analysis of the seismic data (similar to coherency) revealed that these faults could not be detected or predicted using the seismic that is currently available. However, fractures in an oriented core located within one 3D survey showed that dominant fracture trends may be aligned with predominant structural edges detected by seismic.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado