A New Approach to 3-D Geological Modeling of Complex Sand Injectite Reservoirs: The Alba Field, United Kingdom Central North Sea
Published:January 01, 2007
P. N. Fretwell, W.Gordon Canning, J. Hegre, R. Labourdette, M. Sweatman, 2007. "A New Approach to 3-D Geological Modeling of Complex Sand Injectite Reservoirs: The Alba Field, United Kingdom Central North Sea", Sand Injectites: Implications for Hydrocarbon Exploration and Production, Andrew Hurst, Joseph Cartwright
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Alba is a heavy oil (19 –20° API) field discovered in 1984 and brought on production in 1994. The oil is reservoired within middle Eocene turbiditic sands deposited within hemipelagic background argillaceous sediments. Alba sands have been subjected to postdepositional remobilization and sand injection on a field- wide scale. Sand geometries are highly complex. Prediction of sand-shale lithology from the Alba field four-component Ocean Bottom Cable seismic data set is refined through detailed horizontal and vertical well-seismic integration. Reservoir sands are subdivided into remobilized or injected and depositional facies in all wells by recognition in cores and/or logging-while-drilling response and by elastic impedance seismic character. An abundance of multiple horizontal well sidetrack data (commonly in the same vertical plane) in the Alba field allows the construction of facies cross sections against a seismic impedance data backdrop with some confidence. A new, threedimensional (3-D) geomodeling software is used that can directly include these facies cross sections as constraints on geomodeling, in addition to conventional well and seismic data constraints. This allows a degree of geological interpretation to be imposed and supported with outcrop analogs within the uncertainties of the available data. Numerous equiprobable 3-D cellular geomodel possibilities are created that differentiate remobilized or injected reservoir facies from depositional reservoir facies. The impacts of facies variability on production profiles are tested in a streamline reservoir simulator at the geological model scale.
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Sand Injectites: Implications for Hydrocarbon Exploration and Production
Sand injectites are described in scientific literature as an increasingly common occurrence in hydrocarbon reservoirs, in particular in deep-water clastic systems, where they are known to influence reserves distribution and recovery. Seismically-detectable injected sand bodies constitute targets for exploration and development wells and, subseismic sand bodies provide excellent intra-reservoir flow units that create field-wide vertical communication through depositionally extensive, low-permeability units. As sand injectites form permeable conduits in otherwise low-permeability units they facilitate the expulsion of basinal fluids; hence they act both as a seal risk and mitigate timing and rate of hydrocarbon migration. Injected sand bodies form intrusive traps, which are distinct from structural or stratigraphic traps. Included in this publication are 10 chapters on subsurface examination of sand injectites, 1 chapter on theoretical considerations, and 13 outcrop analogs in reservoirs across the world. Captured in this volume is at least a taste of the global and stratigraphic distribution of sand injectites, and an attempt to introduce readers to sand injectites and their significance in the context of hydrocarbon exploration and production. The book is not intended as a complete review of the field-based literature, but emphasizes high quality case studies from the surface and subsurface. The geographic scope of the book is large, and illustrates the diversity of geological settings in which these fascinating and economically significant features are found.