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New Insights Into the Permeability Barriers Between Submarine Channels and Their Levees, Eocene Brito Formation, Sandino Basin, Nicaragua


Many oil and gas fields in the deepwater Gulf of Mexico produce hydrocarbons from thin-bedded channel/levee reservoirs where one of the unknown parameters is the connectivity between the channel and the levee sediments. Often, the coarser and higher net/gross sandstones in the associated channel are water-wet and do not appear to be in pressure connection with the hydrocarbon-bearing levee sediments, as in the L reservoir at Ram Powell field (Viosca Knoll, Gulf of Mexico) . Possible explanations for pressure barriers between the channel and the levee could be a shale drape, debrite drape, slide or slumped zone, a zone of intense faulting or other type of permeability barrier. Deepwater channel/levee complexes of the Eocene Brito Formation are well-exposed along the cliffs of the Pacific coast of southwest Nicaragua. One particular outcrop at Playa Las Tablas shows a very sharp synsedimentary master fault at the outer boundary of a 40 meter thick zone of chaotic slides between the coarse channel-fill and the undisturbed levee sequences. The slide zone contains blocks of proximal levee sediments almost perpendicular to the levee sediments, providing an effective barrier to fluid migration between the levee and the channel. This also implies that the levee was deposited and then collapsed, creating a low and allowing the channel to prograde further basinward. The channel-fill consists of coarse pebbly-sandstone overlying a basal erosional contact with the underlying deformed levee sediments. The apparent random and relatively thin nature of the slide zone may mean that tortuous pathways for water or hydrocarbon migration may exist between the channel and the levee and that water breakthrough may occur in isolated locations where the slides are not as chaotic or the slide zone is a lot thinner.