Rozalia Pak¹, S.G. Pemberton¹, M.K. Gingras¹, F. Henk¹

(1) University of Alberta, Edmonton, AB

ABSTRACT: Reservoir Characterization of Burrow - Mottled Carbonates: an Example from the Ordovician Yeoman Formation, Southern Saskatchewan

Understanding small-scale heterogeneities is crucial for modeling fluid flow in a reservoir, especially when undertaking secondary and tertiary recovery schemes. Textural and chemical changes produced by the activities of burrowing and boring organisms can greatly affect primary porosity and permeability and thus affect subsequent diagenesis. Burrow fills may serve as preferential flow paths for diagenetic fluids. Studies have examined reservoir heterogeneity caused by burrowing and burrow related diagenetic fabrics in the Devonian Wabamun Formation (Alberta, Canada), the Cretaceous Shuaiba Formation (Qatar), and Jurassic Arab-D Formation (Saudi Arabia).

This relationship is being examined in the Ordovician Yeoman Formation (Lower Red River Formation) of Southern Saskatchewan. The Yeoman Formation is relatively uniform throughout the Williston Basin, but due to a complex diagenetic history, reservoir quality is highly variable. Core and thin sections were examined from several oil pools in order to determine the burrow fabrics and associated diagenetic features. A Pressure Decay Profile Permeameter was used to determine the permeability profiles of the cored intervals, and resolve the extent of reservoir heterogeneity. In some areas, valuable porosity was occluded by dolomitization, silicification or anhydrite cementation. Elsewhere, dolomitization of burrow fills and aureoles around burrows enhanced porosity and permeability. Some burrows were enlarged by dissolution, and were not occluded by anhydrite. Permeability measurements show that the variability in permeability can be observed even within several meters.

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