Lower Cretaceous Geology and Heavy-Oil Potential of the Lloydminster Area

Abstract

ABSTRACT Lloydminster comprises the most southerly deposit of the Alberta-Saskatchewan, Mannville sand belt. Hydrocarbon entrapment is controlled in part by updip sand pinchout, but is related primarily to regional anticlinal closure associated with salt solution of the Middle Devonian Prairie Evaporite Formation. This area, with oil gravities ranging from 10 to 25 degrees API, differs from the rest of the heavy-oil belt in that it has demonstrated primary recovery. Mannville sedimentation in the Lloydminster area was influenced by paleotopography and structure on the pre-Cretaceous unconformity surface. Widespread emergence accompanying the Paleozoic unconformity resulted in nonmarine, mainly fluvial, deposition of the basal Dina clastic unit. Maximum marine incursion occurred during Sparky time, and the remainder of the Mannville comprises a complex intertonguing of nearshore, deltaic and alluvial facies. Widely developed channel-fill deposits in the uppermost Mannville over much of the area indicate a return to emergent conditions which were terminated with transgression and inundation by the Colorado Sea. Higher sand content in the northeastern part of the area, and mineralogy, indicate that sediment source was the Precambrian Shield. The Mannville sands of the Lloydminster area contain more than 16 billion barrels of oil in place. The reservoirs that have demonstrated primary production and were included in this estimate are the Colony, McLaren, Waseca, Sparky, GP, Lloydminster and Cummings sands. The Sparky is the most prolific producer; the Cummings and Colony units have been minor contributors to date.