Large Scale Meandering Channel Processes and Product: New Insights From McMurray Formation Type Section

Abstract

The Lower Cretaceous McMurray Formation Type Section is located 5km downstream from the confluence of the Athabasca and Clearwater rivers and extends 2 km along the east bank of the Athabasca River. This outstanding, up to 80 m thick exposure has been visited by many geologists, but remains poorly documented in literature. The outcrop is comprised of four distinct stratigraphic units. The focus of this report is on heterogeneities observed across the large-scale (35m thick) channel deposit. Since oil-saturated, this outcrop also presents an unparalleled portal for reservoir studies. Data was acquired through detailed two-dimensional outcrop mapping recorded on high resolution photographs and scaled photo-montages, line-drawing of various geological contacts interpreted on both outcrops and images, and integrating detailed (cm-dm) bed-by-bed logging along selected outcrop exposures. Mapping and line drawings were further assisted by the collection of paleo-flow indicators. These data were coupled with core descriptions from drill holes behind the outcrop which allowed for 3D visualization. Point bar evolution is interpreted based on nature (geometry) of contacts, geometric relationship of mapped architectural elements, facies changes between architectural elements, and paleo-current indicators. Detailed mapping revealed numerous enigmatic features commonly not associated with point bar processes and architecture that include: (1) five types of breccia not associated with channel lag deposits; (2) a variety of mud occurrences in high-energy bottom-channel deposits; (3) encased channel shaped features within the mid-to-upper point-bar deposits (interpreted as short lived chute and rill channels); and (4) paleo-current reversals. Observations of detailed reservoir architecture from the Type Section provides a basis for characterizing dynamic interplay of deposition and erosion of channel deposits on various time scales; new insights for point-bar facies models; and more fulsome understanding of the impact of facies heterogeneities on reservoir oil-charge and in-reservoir fluid migration.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015