--> A Paleobiological Approach to Modeling Giant Dolomite Reservoirs in Mississippian Outer Ramp Carbonates, Upper Midale Beds, Weyburn Oilfield, Saskatchewan

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A Paleobiological Approach to Modeling Giant Dolomite Reservoirs in Mississippian Outer Ramp Carbonates, Upper Midale Beds, Weyburn Oilfield, Saskatchewan

Abstract

A biogenic-diagenetic model for origin of giant reservoirs in outer ramp carbonates is proposed for Mississippian Upper Midale Beds, Weyburn Oilfield, Saskatchewan. This ichnology-based model is relevant for petroleum systems defined by both conformable and unconformable relationships between source and reservoir strata, representative of offshore areas on carbonate platforms. Mapping distribution patterns in bioturbated dolomudstones showing a distal-Cruziana ichnofossil assemblage, and associations with paleobiologically-influenced dolomites are useful in exploration. Since textural aspects of biogenic-diagenetic relationships in modified substrates provide information on influence of deposit-feeding activities and pelletization of mud, on dolomitization and fabric evolution in stable outer ramp settings, applications of ichnology for modeling reservoir development and characteristics require an upscaling of petrographic data. To understand origin of such reservoirs, genetic classification of burrow-fabrics and associated porosity-permeability relationships, and fluid dynamics linked to dolomitization in otherwise impermeable mudstones is necessary. Bioturbate textures reflect sedimentological manifestations of biotic processes in response to paleoecological dynamics; and, burrow-fabrics in local heterogeneities show deposit-feeding activities in response to distribution of organic matter, which link trophic resources and structure of benthic communities in marine mud. This study proposes an integrated approach to modeling petroleum systems. Such a model highlights the notion that biogenic recycling of organic matter significantly influences both diagenesis and kerogenesis in reservoir and source rocks, respectively. The new reservoir model consists of two components: a paleoecological classification of sedimentation rates is proposed for insights on paleoenvironmental constraints on biotic processes recorded in textural characteristics; and, an evaluation of local significance of organism-sediment interactions, where roles of organic matter in relation to oxygen levels, represent a common denominator in coupling of the reservoir and source rocks. Therefore, an integrated model on paleoecological-geochemical dynamics provides a framework that is consistent with the ichnofacies concept, and its large-scale geologic significance, including roles of bioturbate textures in the transition from diagenesis to kerogenesis in outer areas of the carbonate ramp.