The Influence of Bioturbation from the Resource Quality of Low Permeability Gas Charged Reservoirs - A Case Study from the Upper Cretaceous Alderson Member, Southwestern Saskatchewan, Canada

Ryan T. Lemiski¹, Murray Gingras¹, George Pemberton¹, and Jussi Hovikoski^2
1Univeristy of Alberta, Edmonton, AB, Canada
²University of Turku, Turku, Finland

Although burrow-associated permeability is evident in the rock record, it receives little scientific scrutiny. This may be due to the scalar nature of permeability and that the permeability of geological media is a bulk character at the reservoir scale. However, the bulk permeability of sediment dominated by small, macroscopic heterogeneities, such as worm burrows, is exceedingly difficult to observe, assess, and numerically model. Overlooking the potential impact of biogenic structures within a rock body can lead to inaccurate assessments of the permeability characteristics of a sedimentary rock and possibly the non-recognition of permeability streaks within a hydrocarbon reservoir. The impact of burrow-hosted porosity and permeability is especially important in gas-prone reservoirs where slight variations in burrow morphology, distribution and infill can have dramatic effects on the storativity and deliverability of hydrocarbons.

The upper Cretaceous Alderson Member (Lea Park Formation) of western Canada is an example of a giant low permeability gas-play. Within the Alderson the productive zones are interbedded with the source rock. The gas present within these zones is biogenic in origin and may have been generated recently. Spot permeability measurements and capillary pressure tests—conducted on hand samples and full diameter core—from the Hatton Gas Pool, show improved porosity and permeability in association with very small, highly interconnected burrows. In general burrow permeability is slightly enhanced over matrix permeability. Typical burrow fabric permeabilities ranged from 0.23 - 30.4 millidarcy while matrix permeability values were on the order of 0.020 - 0.06 millidarcy. Capillary pressure tests show an increased modality of very fine sand over silt in some ichnogenera, especially in burrows associated with the genus Phycosiphon.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas