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UBC Theses and Dissertations

Stratigraphic, depositional and diagenetic controls on reservoir development, Upper Devonian Big Valley Formation, southern Alberta Colborne, Jacqueline

Abstract

The Upper Devonian Big Valley Formation in southern Alberta is a 10-m thick carbonate succession, unconformably overlain by organic-rich source rocks of the Exshaw Formation. The Exshaw Formation is part of a global continuum of mudrocks deposited under anoxic conditions, representing a distinct interval in Earth’s climatic, terrestrial and marine evolution, and the generation of prolific hydrocarbon source rocks worldwide. This thesis summarizes the stratigraphic, depositional and diagenetic controls on reservoir development of the Big Valley Formation and its relationship to the Exshaw Formation. Data analyses involved stratigraphic top picks and regional correlations in an 84 well-log database, core study, seismic interpretation, petrographic and carbon isotope analyses and petrophysical measurements. The availability of more core and wireline data as a result of recent exploration led to refining of the stratigraphic framework in the study area. The Big Valley Formation is redefined in this study to consist of two informal units: upper (open-marine) and lower hydrocarbon-bearing (peritidal) units. Based on lithofacies analyses, the peritidal unit more appropriately fits with the Big Valley Formation, rather than its current assignment to the underlying Stettler Formation. The peritidal unit consists of four lithofacies: subtidal shoal peloidal packstone-grainstone, mid-to-high intertidal microbial laminite and laminated dolomudstone and a local intraclastic breccia-laminite related to tidal drainage channels. Each lithofacies is laterally discontinuous, variably dolomitized and ranges from 0.5-to-2.0-m thick. iii In some areas the Big Valley Formation is up to 25-m thick, with >4-m of shoal deposits that have excellent reservoir properties. Thickened Big Valley areas are underlain by thinned evaporite beds, and have a similar orientation as an underlying NNW/SSE structural lineament. This relationship suggests basement-controlled high-angle block faulting and/or salt dissolution and collapse of underlying Devonian evaporite beds during Big Valley deposition. The complex interplay between deposition and diagenesis has influenced reservoir quality. Dolomitized peloidal packstone-grainstones have high intercrystalline porosity (>5%) and permeability values (>0.20 md). Reservoir potential of the microbial laminites is dependent on dolomitization and lack of anhydrite cement. Non-reservoir lithofacies show low petrophysical properties (

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