An Outcrop Example of Large-scale Conglomeratic Intrusions Sourced from Deep-water Channel Deposits, Cerro Toro Formation, Magallanes Basin, Southern Chile
Published:January 01, 2007
Stephen M. Hubbard, Brian W. Romans, Stephan A. Graham, 2007. "An Outcrop Example of Large-scale Conglomeratic Intrusions Sourced from Deep-water Channel Deposits, Cerro Toro Formation, Magallanes Basin, Southern Chile", Sand Injectites: Implications for Hydrocarbon Exploration and Production, Andrew Hurst, Joseph Cartwright
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Large-scale vertical to subvertical clastic intrusions (as much as 67 m [219 ft] wide and >100 m [>330 ft] high) are present in Cretaceous strata (Cerro Toro Formation) of the Ultima Esperanza district, southern Chile. The injectites emanate from the margins of submarine-channel deposits that accumulated at water depths of 1000–2000 m (3300–6600 ft) in the Magallanes foreland basin. The remobilized sediment is very coarse, consisting of sandy matrix conglomerate, muddy matrix conglomerate, and poorly sorted sandstone. The injectite bodies sometimes bifurcate upward and are circular in plan view and, thus, are geometrically analogous in many respects to numerous injection features mapped seismically in the North Sea Basin.
The remobilization of coarse sediment was likely induced after the burial of the parent deposit to at least a few hundred meters. The controlling factors on injection are difficult to discern; however, it is probable that the highly energetic process involved gas charging of the source body and, potentially, a seismic event trigger associated with the uplift of the Patagonian Andes.
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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.