Structural and Geochemical Characterization of the Cretaceous Milk River Formation, Abbey and Lacadena Pools, Saskatchewan, Canada

Ridgley, J.L.¹ (1) U.S.Geological Survey, Lakewood, CO

The Cretaceous Milk River Formation in the contiguous Abbey and Lacadena (Abbey-Lacadena) gas pools, Saskatchewan, is composed of mudstone, siltstone, and very fine-grained sandstone that form stacked, upward-coarsening parasequences. Production is primarily from fine-grained, sandy reservoirs in two zones in the lower two-thirds of the formation. Commonly, reservoirs from both zones are perforated and commingled production is reported; when not combined, production is mostly from the lower zone. Thickness of the Milk River varies over short distances as a result of syndepositional movement on preexisting structures that created differential accommodation space during sedimentation. The Milk River in the Abbey- Lacadena pools has been folded into a composite “domal” structure, which is elongated both northwest and northeast.

Twenty-nine gas and 22 co-produced water samples were analyzed to determine (1) the origin of the gas and its genetic relation to co-produced water; and (2) the relative importance of reservoir distribution, past hydrologic flow, and structure on the spatial distribution of the composition and isotope chemistry of the gas and coproduced water. The gas origin is microbial. A cross plot of ¥Dwater versus ¥Dmethane indicates that, for most samples, the gas is in disequilibrium with the co-produced water and formed in the presence of isotopically heavier (¥Dwater) water rather than in the current aqueous environment. Gas and water geochemical and isotope data show no trends as a function of elevation. Rather, these data have a northeasternly orientation across the structure and are interpreted as indicating flow paths established prior to structural uplift.

AAPG Search and Discovery Article #90055©2006 AAPG Rocky Mountain Section Meeting, Billings, Montana