Abstract: Oil Quality Variations in Upper Jurassic and Lower Cretaceous Reservoirs in Southern Alberta

MANZANO, B. KIM, University of Calgary, Department of Geology and Geophysics, Calgary, Alberta

Oils produced from Ellis (Jurassic) and Mannville Group (Lower Cretaceous) reservoirs in southern Alberta, Canada (T1-40, R1-27W 4M) display a range of oil gravities from less than 15 degrees API (low gravity) to greater than 40 degrees API (high gravity). Low gravity oils tend to have higher sulfur contents and are of poorer quality from an economic standpoint than higher gravity, low sulfur oils. Thus understanding the causes and controls on the oil quality variations within and among fields impacts exploration strategy and prospect economics in this region, and will potentially provide a predictive tool for the discovery of higher value oil in southern Alberta. Furthermore, delineation of migration pathways may indicate exploration potential in areas that are currently underexplored.

There are several factors which determine the quality of a particular oil. These include variations in: (1) source rock kerogen composition, (2) thermal maturity of the source- (3) biodegradation- (4) water washing; and (5) gas deasphalting. Organic geochemical analysis of 275 oils from 66 fields in the study area suggest that different source rock kerogen composition and biodegradation are the two main factors controlling the variations in oil quality in the study area.

This study is the first comprehensive study of the petroleum geochemistry of Cretaceous oils in southern Alberta and will therefore significantly improve our understanding of petroleum systems in Western Canada.

AAPG Search and Discovery Article #90931©1998 AAPG Foundation Grants-in-Aid