ABSTRACT: Regional Flow and Geochemical Processes in an Uplifted Foreland Basin: Mannville Group, Western Canada Sedimentary Basin

ABERCROMBIE, HUGH J., and GRANT FULLMER, Geological Survey of Canada, Calgary, Alberta, Canada

The Lower Cretaceous Mannville Group of the Western Canada sedimentary basin (WCSB) was deposited in the foreland basin that developed in response to Mid-Jurassic through Early Tertiary terrane accretion at the western margin of North America. Mannville Group rocks are recognized across the WCSB and contain significant quantities of oil and gas, as well as giant bitumen deposits. Regional mapping of structure, water and gas compositions, oil viscosities, and hydraulic potential of the Upper and Lower Mannville across the WCSB has been done using available and recently acquired digital water compositions. In the east, where meteoric incursion has initiated biodegradation of oil, Mannville reservoirs largely contain heavy oil and bitumen; carbon dioxide partial pressure (pCO2) is elevat d and formation water salinity is less than 20 g/L TDS. To the west, Mannville oils are lighter, pCO2 is lower, and formation waters have greater than 60 g/L TDS. The coincident geographic variations in water, gas, and oil compositions imply that an "interface" between westerly (downdip) flowing meteoric water and easterly (updip) flowing deep formation waters exists at present. The high salinity of deep Mannville waters in the west suggests that extensive meteoric flushing at depth has never occurred. This in turn suggests that the "interface" between meteoric and deep formation waters may have persisted over geologic time.

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