Abstract: Fractured Carbonate Reservoirs in the Foothills of the Canadian Rockies

COOPER, MARK
PanCanadian Petroleum, Calgary, Alberta, Canada

The foothills of the Canadian Rocky Mountains have been heavily explored for natural gas since the 1940s and contain a number of fields that produce sour gas from fractured carbonates. A typical play trend is located in the foothills of northeast British Columbia where the reservoirs are the Upper Triassic Pardonet and Baldonnel formations. The area is topographically difficult and structurally complex with a number of detachments that compartmentalize the deformation within distinct tectono-stratigraphic units. The British Columbia foothills are pervasively deformed by detachment and fault propagation folds, which contribute to typically poor-quality seismic imaging.

The traps are primarily fault propagation and detachment folds that detach in the shale-dominated lower Triassic. The structural style has been interpreted from stratigraphic data based on cuttings and wireline logs and detailed dip data provided by imaging tools. Fracturing is pervasive in the crest and forelimbs of the folds and enhances the tight primary reservoir quality to yield typical flow rates of 40 mmcf/day. The acquisition, processing, and interpretation of seismic data in this area are technically difficult and require careful analysis to yield good results. The integration of the seismic, well, and surface geology data is essential for the accurate definition of the highly fractured crestal portion of the structure, which is the preferred subsurface target.

A number of case studies illustrate the difficulty of drilling the crests of the structures and the common occurrence of sidetrack wells. Despite these difficulties the area has become a prolific gas production area in the last 10 years and continues to be an active exploration area. 

AAPG Search and Discovery Article #90927@1999-2000 AAPG Distinguished Lectures