Fluidization and Associated Soft-sediment Deformation in Eolian Sandstones: Hopeman Sandstone (Permian), Scotland, and Rotliegend, North Sea
Published:January 01, 2007
Ken Glennie, Andrew Hurst, 2007. "Fluidization and Associated Soft-sediment Deformation in Eolian Sandstones: Hopeman Sandstone (Permian), Scotland, and Rotliegend, North Sea", Sand Injectites: Implications for Hydrocarbon Exploration and Production, Andrew Hurst, Joseph Cartwright
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On the southern shore of the Moray Firth, Scotland, the foreshore and cliffs east of Hopeman Harbor display a wide variety of soft-sediment deformation structures formed in unconsolidated Late Permian eolian sands. These include flows of water-saturated sand containing rip-up clasts that overturned the underlying dune sand; dune bedding that is now vertical; subvertical pipes and swirls of partly dilated sand; sand dikes; widespread partial to complete homogenization of dune sand; and a vertical escape structure some 20 m (66 ft) high. The driving force behind the deformation is believed to be widespread heavy rain over the northern edge of the Grampian highlands, causing slumping of the southward-migrating dune sands and possibly slight local northward sliding subparallel to the regional top Devonian erosion surface; this could have induced major increases in internal hydrodynamic pressure. Because the pores in the dune sands were filled with air prior to flooding, some of the vertical deformation structures may have been formed by the upward escape of air through rain-dampened dune sand driven by the hydrodynamic increase in water pressure. Probable coeval deformation, but of a different style, has been seen in cores recovered from oil and gas fields of the central and southern North Sea.
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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.