Summary

Marine muddy sandstones of the Cardium Formation is the most active light tight oil play in western Canada, with production from the new multistage horizontal wells exceeding 120,000 bbl/d. Cardium sandstones contain one of largest oil accumulations in the Western Canada Sedimentary Basin, which have been exploited since the mid 1950's. Since 2008 the play has been revitalized with activity mainly focused around the halo area of legacy pools, targeting low porosity and permeability muddy, intensely bioturbated sandstone reservoirs.

This study presents a pore to depositional sequence scale reservoir characterization of the unconventional type low permeability, intensely bioturbated offshore to transitional offshore reservoir facies. The characteristics of the eastern and western Pembina halo play areas are presented and contrasted. Although they contain similar sedimentary facies they have very different reservoir properties due to differences in burial depth and thereby diagenesis, compaction, cementation, pore characteristics and reservoir pressure. Facies belt and thereby reservoir fairway widths of offshore deposits are often portrayed as being 10s of km wide, however mapping within a 5th order high resolution sequence stratigraphic framework shows that the offshore facies belts within the Pembina area are commonly less than a few km wide. Thus, a horizontal well drilled perpendicular to shoreline orientation might be landed in different reservoir facies. The 5th order sequences form in west Pembina part of a 3th order falling stage systems tract, characterized by basinward shift of facies. In contrast, the sequences in the eastern Pembina halo area form part of a late lowstand to early transgressive 3 order systems tract. Reservoir properties of intensely bioturbated reservoirs are poorly characterized by routine core analysis due to their highly heterogeneous character. In this study, detailed core observations were complemented with thin section, SEM analysis, mercury (MICP) data of the various micro facies, i.e. muddy matrix versus sandy borrow fill. Full core diameter CT scanning were used to characterize the 3-D connectivity of the sandstone beds and sandstone filled borrows for each reservoir facies. Due to the small scale and discontinuous of the sandstones, routine plug and full diameter core analysis often underestimate the flow capacity of such intensely bioturbated reservoirs, where sand filled borrow provides flow pathways in 3-D.

URTeC 1619723

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