Abstract:

Although the majority of in situ oil sands schemes in Alberta do not encounter significant reservoir containment problems, there have been documented occurrences of fluid releases because of compromised caprock seals. The Energy Resources Conservation Board recognized the need for a greater understanding of the caprock and a project to characterize the geological and geomechanical factors was initiated. The objective of this project is to characterize the units above and below bitumen zones to determine which geological factors may affect the quality of the caprock seal. Mapping of the Cretaceous strata focuses on the spatial extent and thickness of the lower Clearwater shale unit overlying the McMurray Formation reservoir. Mapping of the underlying Devonian strata is targeted at better understanding the potential effects of salt dissolution and collapse of overlying strata on the integrity of the caprock seal. In addition, this project examined the stress regime above the in situ operations in the study area to evaluate the effects the operations would have on the stress regime quality of the caprock seal. Initial numerical model results demonstrated that stress reduction above an in situ operation may lead to the creation of vertical fractures if the fracture gradient is exceeded.

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