ABSTRACT: Lateral Facies Variability and Impact on Reservoir Heterogeneity, Middle Triassic Doig Formation, Sinclair, Wembley, and Valhalla (East) Fields, Alberta, Canada

WITTENBERG, JOERG, and THOMAS F. MOSLOW, University of Alberta, Edmonton, Alberta, Canada

Sedimentological characterization of Doig Formation depositional facies is an important factor in determining the constraints on relative quality and heterogeneity of the reservoir sandstones. Detailed core evaluation is an essential tool in establishing reservoir quality trends in relatively narrow, anomalously thick sandstone bodies, which are characteristic of Doig Formation reservoirs. Four cored sequences through anomalously thick Doig sandstones in the Wembley, Sinclair, and Valhalla (East) Fields display significant lateral and vertical depositional and diagenetic discontinuities within the reservoir facies. Regionally, Doig sandstone reservoirs are characterized by a series of elongate and locally thick, strike-parallel sand bodies overlying a sequence of laminated marine shal s, siltstones, and fine-grained sandstones. Correlation of sedimentary facies within the anomalously thick sandstones to porosity and permeability values from analyzed core suggests that a number of facies and diagenetically defined porosity and permeability trends within each thick sandstone trend. Overall, porosity and permeability decreases from east to west in the thick sandstone bodies, in conjunction with the westward fining (increasing mud content) of depositional facies within the sandstones. Additionally there is a decrease in the abundance of bioclastic material, resulting in a reduction of biomoldic porosity toward the west. In a vertical section, diagenetic factors control reservoir quality to a great extent. The general decline in porosity and permeability being tied to an i crease in the abundance of poikilotopic anhydrite cement toward the top of the section. Similarly, the recognition of marine flooding surfaces in the vertical section has also shown that a marked decline in reservoir quality occurs in proximity to these surfaces. This diagenetic aspect associated with the flooding surfaces is primarily due to the variation in water chemistry accompanying the flooding event, or in the most extreme case, subaerial exposure at or near the flooding surface.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)