Abstract

Sandstone bodies of the Middle Triassic Doig Formation are composed of well sorted sublithic- to quartz arenites and bioclastic packstones to grainstones deposited in a shoreface environment. These south-southeast trending sandstone bodies were tilted into the Peace River Basin as a result of periodic reactivation of the Dawson Creek Graben Complex and subsequent sediment loading over the southern portion of the reservoir trend. Effective porosity is primarily intergranular in the reservoir sandstone facies, and significant moldic and intragranular porosity is developed in the coquina facies at the West Stoddart and Cache Creek fields. Average porosity ranges from 6.5–9.4% for the sandsone lithofacies and 4.9–8.6% for the coquina lithofacies. Pore-occluding cements are mainly calcite in the northwestern, and dolomite and anhydrite in the southeastern, reservoirs. Sandstone bodies with only minor interstitial calcite have undergone extensive porosity loss due to compaction and authigenic quartz precipitation. A Doig sandstone exploration fairway is identified, based on the following: production, thermal maturity, core analysis data, structural and depositional models, and diagenesis.

Reservoir quality and production from Doig Formation sandstone bodies in the Peace River area of Western Canada are impacted significantly by the preservation of intergranular porosity and fractures and by the distribution of early calcite cement. Bioclastic grainstones and packstones and calcareous mudstones were the likely source of calcite for early cements. Diagenetic events along the northwest-southeast reservoir trend include the precipitation of calcite in the near surface and shallow burial realm, the formation of fractures and faults in cemented intervals, and the dissolution of cements and framework grains in three identifiable episodes. Multiple dissolution phases during diagenesis created secondary moldic, intragranular, and intergranular porosity. The formation of open fractures during early diagenesis enhanced both the secondary porosity and the permeability of the West Stoddart and Cache Creek Doig pools. Production data from the Valhalla, Sinclair, West Stoddart, Cache Creek, and Buick Creek fields reflects the control of diagenesis on porosity and permeability.

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