Stephen M. Hubbard¹, Mark Thomas¹, John-Paul Zonneveld²

(1) Shell Canada Limited, Calgary, AB
(2) University of Calgary, Calgary, AB

ABSTRACT: The Geometry and Stacking Pattern of Fan Delta Sand Bodies in the Ostracode Zone, Alberta: Improved Subsurface Predictability Through Detailed Stratigraphic Analysis

In the Peace River region of central Alberta, fan delta sand bodies of the Lower Cretaceous Ostracode Zone represent an important component in the future development of the Peace River Oil Sands. The fan delta complex was sourced by a sand-dominated braided river system which incised resistant, Mississippian-aged carbonate highlands in the northern part of the study area. These braided rivers debouched directly from the confines of narrow canyons into a shallow, regionally mappable embayment. Five progradational fan delta lobes have been mapped, and comprise the main reservoir lithofacies association in the area. The fan delta succession spread out onto a regionally significant erosional unconformity. Paleotopography on this surface strongly influenced sediment distribution. Individual lobes are interpreted as parasequences, as lobe shifting was influenced primarily by relative sea-level fluctuations. From sand isolith maps of the individual parasequences, it is evident that delta lobes increased in size laterally as the system evolved.

The initial two parasequences consisted of fans dominated by fluvial processes. However, as successive parasequences prograded basinward, long-shore currents are interpreted to have had an increasingly significant influence on sediment distribution. Individual parasequences are typically 6-9 m thick, separated by flooding surfaces characterized by a pronounced landward shift in lithofacies. Stacking of multiple parasequences results in a cumulative sand thickness of up to 20 m. A significant ravinement surface truncates fan delta deposits of the Ostracode Zone, separating them from immediately overlying estuarine sediments of the Bluesky Formation.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado