Facies Controls on Early Diagenesis: Wilcox Group, Texas Gulf Coast
S. A. Stonecipher, J. A. May, 1990. "Facies Controls on Early Diagenesis: Wilcox Group, Texas Gulf Coast", Prediction of Reservoir Quality Through Chemical Modeling, Indu D. Meshri, Peter J. Ortoleva
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In the Paleocene-Eocene Wilcox Group of the Texas Gulf Coast, early diagenetic patterns appear to be related to factors such as original water chemistry, sediment texture, detrital composition, and organic content which were, in turn, related directly or indirectly to depositional environment. Rapid lateral and vertical changes in depositional environments produced markedly different early diagenetic patterns in sand units only a few feet or even inches apart.
One of the most important controls was the chemistry of the original pore waters. Flushing by fresh meteoric water produced early mica-derived kaolinite. Fresh, but anoxic, water resulted in abundant siderite. Saline marine pore waters typically led to the development of chlorite rims. Reducing or mildly reducing marine waters yielded pyrite or glauconite. Mixing of fresh and marine waters resulted in chamosite/berthierine ooids or illite, depending on oxygen content.
These patterns suggest that lateral and vertical variations in diagenetic facies defined on the basis of sediment texture, detrital composition, and early authigenic cements can be used to complement, and test, traditional sedimentologic methods of interpreting depositional environment.
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Prediction of reservoir quality ahead of the drill is one of the most complex problems facing exploration geologists, especially when they are exploring in frontier basins, where rock and water data are minimal or non existent. Although useful descriptive models of diagenesis have existed in the past, they cannot be applied in the areas where rock and water data do not exist. This volume comes out of a 1987 conference oand contains 10 chapters that document the substantial progress made toward the goal of modeling reservoir quality. One facet of chemical modeling, namely porosity prediction, is the thrust of this book. However, chemical modeling has contributed heavily in the field of environmental geochemistry, nuclear waste disposal, and in the thermal recovery of heavy oil and the like, thus one such chapter is included in this memoir.