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Abstract

A detailed palynologic, sedimentologic, and mineralogic investigation of the Robulus L No. 2 and the Robulus L No. 5 sands in cores from Texaco well No. 6 of Vermilion Block 31, offshore Louisiana, confirms that the units were deposited in the middle to outer part of the continental shelf during the early Miocene Epoch. The co-occurrence of the dinocysts, Hystrichosphaeropsis obscura and Lejeunecysta hyalina, further restricts the cored intervals to the Burdigalian Age. Variations in the abundances of Polysphaeridium zoharyi, Lingulodinium machareophorum, Tuberculodinium vancampoae, and terrestrial organic matter indicate the sediments are mixtures of marine and estuarine debris accumulating in the neritic zone.Five lithofacies and seven palynofacies are recognized. Current-structured, medium-grained sandstone containing abundant terrestrial organic matter and shell fragments (lithofacies B) forms the best potential reservoirs. Original high clay content and bioturbation restrict the permeability of other lithofacies and, hence, their producing potential. The Robulus L No. 2 is a better producer because lithofacies B is more abundant. Sandstones of this lithofacies often exhibit porosities between 15-28 percent and permeabilities as high as 2000 md because of their coarser grain size and the dissolution of shell fragments. In the Texaco No. 6 well, there is a clear relationship between original characteristics of the sediments, diagenesis, and hydrocarbon production.

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