Cynthia L. Riediger¹, Patrick Stevenson², B. Kim Manzano¹

(1) University of Calgary, Calgary, AB
(2) Husky Oil, Calgary, AB

ABSTRACT: Integration of Petroleum Geochemical Data and Tectonic History: The Key to Understanding Jurassic to Lower Cretaceous Petroleum Systems in Southern Alberta and Northern Montana

Oils from Jurassic to Lower Cretaceous reservoirs in southern Alberta and northern Montana display a wide range of oil quality (i.e. 19 to 40° API gravity, sulphur contents ranging from 0.7 to over 4 wt %). Organic geochemical data indicate that the main factor governing this oil quality variation relates to differences in the source rock geochemistry of two effective Upper Paleozoic source rocks, resulting in the generation and pooling of two distinct oil families. Biomarker geochemistry reveals that oils assigned to oil family E (API <25°; S>2.0 wt %) were derived from the Devonian-Mississippian Exshaw Formation, whereas the better quality oils in oil family M (non-degraded oils exhibit API values >37°; sulphur values vary from 0.7 to 1.4 wt %) are tentatively correlated to the Mississippian Banff Formation. Cross-formational flow of family E and M oils into Jurassic to Lower Cretaceous reservoirs likely occurred via NW-SE trending normal and re-activated high angle reverse faults, and by incision of Cretaceous channels into older Jurassic and Mississippian carrier beds. Understanding the observed spatial overlap in the distribution of the two oil families requires knowledge of (a) source rock distribution and maturity, (b) timing of hydrocarbon generation, (c) the complicated regional stratigraphic relationships (particularly in the Cretaceous), and (d) the location and nature of faults and other structural features along inferred flow pathways. Integration of petroleum geochemical data with stratigraphic and structural data is paramount for understanding these complex petroleum systems.

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