Source Rock Characterization of the Lower Cretaceous Ostracode Zone, Southern Alberta, Canada
Whitney M. Wheeler1, Nicholas B. Harris1, and David
C. Jennette2
1Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO
2E&P Technology, Apache Corporation, Houston, TX
The Lower Cretaceous Ostracode Zone in southern Alberta, Canada represents a potential source interval for hydrocarbons in Mannville reservoirs and has been characterized as a lacustrine to marginal marine environment. It is overlain, and often incised, by the Glauconitic Sandstone reservoir unit and, therefore, has variable presence and thickness across southern Alberta. In the study area (10-25W4, 14-28W4), oil is found updip of gas in Mannville reservoirs. A source rock study of the Ostracode Zone seeks to provide an explanation for this hydrocarbon distribution.
The Ostracode Zone was correlated in cores and logs from across the study area. Two units were distinguished: the Ostracode Limestone and the Upper Ostracode. The basal limestone unit consists of layers of ostracode and gastropod shells, while the overlying unit represents an overall coarsening upward succession that experienced wave influence. Potential source units are considered to be 2 to 5 meter shale intervals interbedded with cherty sandstones within the Upper Ostracode unit.
In addition to stratigraphic correlation across the study area, RockEval / TOC studies are to be completed on collected source rock samples. Results will provide kerogen type and maturity data for the source intervals, which will then be used to model hydrocarbon generation. Biomarker work will also be performed on a select number of source extracts and oil samples. Previous biomarker research has revealed a suite of compounds, denoted as “Q compounds,” that are unique to the Ostracode Zone. The presence of these compounds in the sampled units will qualitatively identify the contribution of hydrocarbons from the Ostracode Zone; however, due to mixing with oils from other sources a statistical evaluation may prove problematic.
AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas