Paleogeography, Burial History, Porosity Development and 35 Years of Production History From the Middle Devonian Slave Point Formation at Slave Field, Near the Peace River Arch, Alberta

Abstract

Cores from Slave Field recover Precambrian granite basement. During the Middle Devonian, the Peace River Arch was an expanse of granite highlands flanked by alluvial plains. Slave Field cores show granite basement overlain by variable thicknesses of alluvial Granite-Wash sand, followed by marine carbonate sediment of the Givetian-age Slave Point Formation. The paleo-topographic surface formed by hills and valleys on the irregular granite surface forms the major control on the types of carbonate facies that overlie basement. In topographic lows, alluvial Granite Wash sand is relatively thick above basement, and the first carbonate sediments deposited by incipient marine onlap are laminated peritidal muds. As marine-onlap continued, the higher flanks of granite hills were flooded by deeper-marine carbonate facies types that contain fossils including the stick-shaped stromatoporoid Amphipora as well as tabular and bulbous stromatoporoids. These fossils are particularly susceptible to dissolution during burial diagenesis, and the reservoir quality of the Slave Point Formation is directly related to presence or absence of these soluble components. The final phase of marine onlap resulted in deposition of a “death assemblage” of crinoid-brachiopod floatstone above a firm-ground on top of the shallow-marine Slave Point platform. There is no evidence of karsting on the top of the Slave Point platform. During burial, the paragenetic sequence progressed from dolomite-replacement of lime-mud matrix, but not fossils which remained calcium carbonate, followed by stylolites and associated compaction fractures, followed by dissolution of calcite fossils but not dolomite-mud matrix, followed by precipitation of coarse vug-lining saddle dolomite, followed by very coarse crystalline late calcite cement, and ultimately oil-migration into the moldic-porosity system. Shale compaction curves and bottom-hole temperatures constrain the basin model, and show that potential source rocks are immature at Slave field; the oil has migrated from deeper kitchens to the southwest. Maximum burial depth is estimated at about 3000 meters, followed by about 1500 meters of tectonic uplift beginning in the Cretaceous. Maximum temperature at base Slave Point is estimated to be about 100 degrees C. The field has produced over 11.4 million barrels of oil. Core data combined with 35 years of production statistics convey lessons that are relevant to ongoing exploration and production in the region.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016