The Potential for Gas Storage in Bioturbated Media in the Upper Cretaceous Alderson Member – Hatton Gas Pool, SW-Saskatchewan Canada

The Upper Cretaceous Alderson Member of western Canada is an example of a giant gas-play that revolves around low permeability, gas-prone, non-associated reservoirs. The fields contained within this play produce from shallow zones (less than ~600m) from thin bedded, fine-grained sand within muddy units. In many cases the productive zones are interbedded with, or are, the source rock. Such intervals can be laterally extensive and continuous.

Due to their fine-grained nature, sedimentary facies within the Alderson Member have been difficult to interpret. Various studies have suggested deep through shallow-water affinities for the deposit. We show that the ichnological assemblages are dominated by common Planolites, Phycosiphon, and escape traces along with rare Asterosoma, Schaubcylindrichnus, Schaubcylindrichnus freyi, Scolicia, Arenicolites, Thalassinoides, Chondrites, Zoophycos, and Helminthopsis. The trace fossil assemblage represents the Cruziana Ichnofacies and is interpreted to represent relatively shallow-water sedimentation in quiescent settings.

The presence of sand-rich burrows within otherwise fine-grained media, suggests that burrow fabrics within the Alderson Member enhance the storativity and deliverability of gas. Using porosimetry and minipermeametry, we assess the impact of burrow volume and connectivity on reservoir behaviour. Hg Porosimetry show that the pore-throat distribution of bioturbated media is similar to interlaminated silt and sand. The bioturbated zones can be several meters thick and thus represent an estimable part of the deliverable resource. Moreover, burrow permeability is one to two orders of magnitude higher than matrix permeability. The impact of the permeability depends on the size of burrows and the burrowing intensity in a given unit.