Reservoir Delineation and Performance: Application of Sequence Stratigraphy and Integration of Petrophysics and Engineering Data, Aneth Field, Southeast Utah, U.S.A.
L. James Weber, Frank M. Wright, J. F. (Rick) Sarg, Ed Shaw, Leslie P. Harman, Jim B. Vanderhill, Don A. Best, 1995. "Reservoir Delineation and Performance: Application of Sequence Stratigraphy and Integration of Petrophysics and Engineering Data, Aneth Field, Southeast Utah, U.S.A.", Hydrocarbon Reservoir Characterization: Geologic Framework and Flow Unit Modeling, Emily L. Stoudt, Paul M. Harris
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Rock petrophysical data and production/performance (i.e., engineering) data from the McElmo Creek Unit of the Giant Aneth Field, southeastern Utah, were integrated into a reservoir architecture or stratigraphic layer model that is based on high-resolution sequence stratigraphy. The layer model describes the architecture of high-frequency depositional cyclicity. Nineteen layers (i.e., parasequences or depositional cycles) are described within the Middle Pennsylvanian Desert Creek and lower Ismay section at McElmo Creek. Time-slice mapping of these synchronous layers, and of the facies contained within the layers, provides the basis for predicting the distribution and continuity of reservoirs. Geologic maps and cross sections were constructed to illustrate facies distribution and predict reservoir quality and continuity. Facies and layering data, coupled with core analysis data and engineering performance analysis, contribute to the understanding of fluid pathways. Several examples are selected that relate reservoir performance to changes in facies.
At the field scale, porous and permeable facies stack to form a thick and areally extensive reservoir. Reservoir performance is related to the position of shallow-water facies along a platform-to-basin transect. High-resolution sequence stratigraphy provides architectural detail that permits mapping of successive stages of platform development. Field performance is improved in areas where injection and production wells are completed in platform algal buildup facies.
Facies heterogeneity and reservoir eompartmentalization occur within a synchronous, genetically related cycle of deposition. Production/performance anomalies are observed at the interwell scale in laterally discrete reservoirs. Geologic maps show the distribution of facies and are used to predict the occurrence of reservoir quality rock. Engineering maps are compared with geologic maps to identify wells or areas of the field that require remedial action.
Areas of improved reservoir performance are tied to diagenetic processes that crosscut depositional fabric. Basinally restricted fluids are interpreted to have flowed through porous and permeable rock along localized areas of the northern or windward margin of the carbonate platform, causing pervasive dolomitization. Cumulative oil production in these areas is much higher than for other areas of the field.
A reservoir characterization study of the McElmo Creek Unit was conducted by technologists with Mobil Exploration and Producing U.S., Inc. A synergistic approach led to an improved geologic model, but, more importantly, aspects of this study have been used to increase reserves, increase production, and decrease production costs on a $/barrel basis.
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This collection of papers presents documentation for (1) approaches to be taken in developing a geologic framework for explaining layering, heterogeneity, and compartmentalization of a reservoir; (2) the value of outcrop data in improving understanding of reservoir performance; (3) methods for integrating, analyzing, and displaying geologic, petrophysical rock property, and engineering data to be used during field evaluation, management, and simulation; (4) geostatistical approaches that are being used to characterize the spatial distribution of reservoir properties and augment geologic descriptions, and (5) methods of displaying quantitative models of reservoir properties and reservoir simulation in three dimensions.