Legacy seismic investigations of karst surfaces: Implications for heavy oil extraction from the Devonian Grosmont Formation, northeastern Alberta, Canada.

摘要

The Devonian Grosmont Formation in northeastern Alberta, Canada is the world's largest accumulation of heavy oil in carbonate rock with estimated bitumen in place of 64.5×109 m 3. At the studies location the eroded and buried surface of the Grosmont, referred here as the SubMannville uncoformity (SMU), was analyzed and interpret for a karsted surface. Results from legacy seismic data and available well log information were able to define the SMU as a mature karst surface within observable features such as dolines, karst valleys, karst plain and poljie and a ridge. The large scale topography of the ridge and poljie were geologically controlled by the underlying the Paleozoic rocks. Furthermore, the poljie was observed to contain the majority of the dolines in the area, noted to occur elsewhere. That said, dolines and karst valleys and other such dissolution features have the potential to erode the bitumen reservoir of the upper Grosmont members C and D. It is important for future oil prospectors to map and avoid areas such as the poljie, dolines and karst valley to increase certainty of reservoir presence.;A preliminary rock-physics model was developed for the Grosmont reservoir of a bitumen-saturated dolomite. Results suggest that elastic properties of the Grosmont reservoir are temperature-frequency dispersive. This implies that there is a potential to use time-lapse seismic to map and monitor heating of the reservoir.