Predicting Clearwater Formation Natural Fracture Intensity, Athabasca Oil Sands Area

Abstract

This research investigates the controls on natural fracture intensity observed in Clearwater Formation over townships 94-95, ranges 5-6, west of the fourth meridian. These potential controls include thickness variations of both Clearwater Formation and underlying Devonian age rocks, as well as the topography of the sub-Cretaceous unconformity. Fracture data were drawn from 30 boreholes, all of which have both core and image log essentially covering the full thickness of Clearwater Formation. Results show that Clearwater Formation thins to the north and does not appear to influence natural fracture intensity. Where Firebag Member of Waterways Formation thins and disappears to expose Slave Point Formation subcrop in northeast corner, no correlation is observed between fracture intensity values and Devonian age formation thickness. The relationship between natural fracture intensity and the underlying sub-Cretaceous unconformity is unclear. A map view of natural fracture intensity overlaid on the sub-Cretaceous unconformity surface indicates that some of the highest intensity values occur along the transition edge from topographically high to low areas. However, fracture intensity along the transition edge is variable. Some lower intensity values occur along this same edge. If the basin edge does influence fracture development, its relationship is statistical in nature and does not manifest as a one-to-one mapping.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016