ABSTRACT: Winnipegosis Buildups of the Hitchcock Area, S.E. Saskatchewan, Canada: A Case History

MARTINDALE, BILL, UGUR ERKMAN,* DARRYL F. METCALFE, and EDWARD B. POTTS, Home Oil Company Limited, Calgary, Alberta, Canada

This case study describes the sedimentology, diagenetic history, seismic configuration, geochemistry, and productivity of four separate Winnipegosis build-ups in the Hitchcock area of southeast Saskatchewan. Buildups are totally dolomitized, vary from 57 to 63 m thick, and average 25 hectares in area. Build-ups were located using 2-D seismic but their overall configuration and the well locations were based on a subsequent 3-D survey.

The lower 40 to 50 m of each buildup consists of steeply dipping, porous peloid and codiacean algal packstones and grainstones. The overlying interval is dominated by chaetetids and is locally bound by "stromatolitic" algae and fenestrate bryozoans. An in situ framework of red algae, colonial corals, fenestrate bryozoa, and stromatolitic algae represents the final phase of organic reef growth. Buildups are capped by planar laminated or highly contorted calcretes. Laminar, nodular, and brecciated dolomitic anhydrite (Whitkow Anhydrite) overlies the build-ups and acts as a seal to entrapped hydrocarbons. Buildups were initiated as a series of shoals that were stabilized by early marine fibrous cements. Emergence and subaerial erosion terminated reef growth and produced a capping calcret crust and a network of solution pores and cavities, which were subsequently infilled by mudstones of vadose origin. Dolomitization occurred by seepage reflux of marine waters during shallow burial.

Euxinic mudstones in basinal areas are organic rich and thermally mature. Their geochemical "signature" matches that of Winnipegosis oils in the area. To 1 September 1991, four wells in the Hitchcock area had cumulatively flowed 66,136 cubic meters of oil.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)