Tight Gas Reservoirs of the Western Canada Deep Basin

Thomas F. Moslow¹ and Brian A. Zaitlin^2
1Midnight Oil Exploration Ltd., Calgary, AB, Canada
²Prospect Generation Services, Suncor Energy Inc., Calgary, AB, Canada

The prolific Deep Basin parallels the western edge or structural "foredeep" of the Western Canada Sedimentary Basin (WCSB)and forms a regionally extensive area of hydrocarbon-saturated, abnormally pressured, thermally mature, Mesozoic to Paleozoic rocks characterized by multiple, stacked, “permeability challenged” gas and oil reservoirs characterized by little to no water production. This Deep Basin fairway has produced >10 TCF of gas with up to 1750 TCF OGIP, and remains relatively undrilled by American standards.

The initial Deep Basin reservoirs in the Elmworth-Wapiti area targeted aggradationally-stacked Lower Cretaceous high permeability shoreface conglomerates encased within lower reservoir quality “tight” sandstones, siltstones, organic shales and coals. Until recently, these “sweetspots” of High Permeability Basin Centered Gas (HP-BCG), have been the traditional reservoir targets.

Exploration over the last 30 years has expanded both the aerial extent of the Deep Basin parallel to the overthrust belt, and stratigraphically, to include Devonian carbonates through Mesozoic fluvial and paralic siliciclastics. In the late 1980’s and into the 1990’s exploration in the Deep Basin began to focus on interbedded HP-BCG systems and lower-permeability (Kmax <1 md) basin-centered gas systems (LP-BCGS), resulting in the exploitation of dual-transmissivity reservoirs, analogous to plays occurring in the US Rocky Mountains. However, the WCSB has predominately undergone only tectonic compression and subsequent unroofing since late Jurassic, restricting fracture permeability in clastic reservoirs to isolated zones of basin suturing and subsequent transpressional motion. An understanding of resulting tectonics, pore-geometry and multi-phase permeability in interbedded HP - LP-BCG systems is key to realizing the enormous gas potential of the Deep Basin.

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