Variations in Sediment Extrusion in Basin-floor, Slope, and Delta-front Settings: Sand Volcanoes and Extruded Sand Sheets from the Namurian of County Clare, Ireland
Published:January 01, 2007
R. Jonk, B. T. Cronin, A. Hurst, 2007. "Variations in Sediment Extrusion in Basin-floor, Slope, and Delta-front Settings: Sand Volcanoes and Extruded Sand Sheets from the Namurian of County Clare, Ireland", Sand Injectites: Implications for Hydrocarbon Exploration and Production, Andrew Hurst, Joseph Cartwright
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An outcrop and microtextural study of sand volcanoes from the Namurian of County Clare is presented. Sand volcanoes occur on top of mud-rich slumps that are interpreted to have loaded the sediment pile and caused rapid compaction and fluid expulsion from the underlying units. Fluids migrated into the most permeable sand-rich bodies in the slump, and fluidized grains were then extruded at the sediment-water interface. In some cases, a laterally extensive extrusive sheet of silt and sand developed, with volcanoes located at focused sites of sediment expulsion. From microtextural studies, several (geologically short-lived) episodes of sediment and fluid expulsion are recognized as distinct, normally graded silt to sand-size beds separated by clay-rich beds. The clay-rich beds may either represent background sedimentation between expulsion events or may have been part of the extruding fluidized sediment itself.
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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.