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Characterization of Transgressive Marginal Marine Reservoir Architecture and Heterogeneity and its Application in Enhanced Oil Recovery Optimization: An Example From the Tyler Formation, Dickinson Field, North Dakota

Abstract

The Morrowan-age Tyler Sandstone reservoir at Dickinson Field, North Dakota, is currently being redeveloped with ongoing studies being conducted to optimize future enhanced oil recovery (EOR). The field was discovered in 1958 and since 1973 has been in a successful waterflood program. Basic criteria indicate that the field is a strong candidate for CO2 EOR. These include successful waterflood performance with observed good well interconnectivity, appropriate reservoir depth (avg. 7900’) to achieve minimum miscible pressure and manage a flood, good reservoir quality (f = 1%-22%, avg. f = 14%; K = 0.01–3,000 mD, avg. K = 160 mD), favorable oil properties (34° API, 3 cP), good residual oil saturation to waterflood (avg. Sorw = 37%), and low residual oil saturation to miscible flooding (Sorm ∼ 7%). To design an optimal flood, a high-resolution reservoir characterization study has taken a second look at the reservoir's depositional environment and stratigraphic architecture, as well as sand body geometry, connectivity and heterogeneity using 56 cores and approximately 200 wireline logs. The Tyler reservoir in Dickinson field is composed of a series of vertically-stacked thin sandstones, each of which range from 0-15 feet in thickness. Based on core and log observations, the Tyler Sandstone is interpreted to have been deposited as part of a transgressive marginal marine system with reservoir-quality sands deposited both in wave-dominated shoreface and back-barrier tidal complex settings. Reservoir-quality sands were deposited in both depositional settings; however, shoreface sand bodies are observed to be more continuous, whereas more variability in physical properties is observed in the tidal complex sands. Lithofacies, characterized from core, were integrated with wireline log response and core petrophysical properties to provide a basis for static and dynamic geomodel construction. By identifying areas of increased reservoir heterogeneity and delineating sand body geometries, this study allows for areas of the field to be high-graded for CO2 EOR and helps improve the flood design.