Biogenically enhanced reservoir properties in the Medicine Hat gas field, Alberta, Canada

Abstract

Spot-minipermeametry and micro-CT analytical techniques were employed to evaluate the effect(s) of bioturbation on porosity and permeability distributions in reservoir facies of the highly prolific Medicine Hat gas field of Alberta, Canada. This study focuses on five cm-scale samples that occur at different stratigraphic positions and intersect discrete bioturbated horizons within the Medicine Hat Member. Spot-minipermeability results demonstrate that permeability in bioturbated sandstones is up to two orders of magnitude greater than those of the muddy matrix, thus corresponding to a dual-porosity fluid flow system. Graphing bioturbation intensity versus measured permeability indicates that burrows are well connected horizontally and provide flow conduits. Micro-CT models reveal that burrowed sandstones are isolated and planiform in character; rare interpenetrations from vertically oriented trace fossils serve to interconnect these hydraulically isolated strata. Results show that bioturbated sandstones possess reservoir properties comparable to those associated with laminated sandstones, yielding an anisotropic porous medium. Understanding the impact of trace fossils on porosity–permeability distributions in the Medicine Hat gas field can be used to identify potential reservoir from previously interpreted non-reservoir rock, and, ultimately, improve reserve estimations.