Diagenesis and related petrophysical characteristics of Ellenburger Group carbonates (Lower Ordovician), West Texas and southeastern New Mexico.
Item
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Title
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Diagenesis and related petrophysical characteristics of Ellenburger Group carbonates (Lower Ordovician), West Texas and southeastern New Mexico.
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Identifier
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AAI9029910
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identifier
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9029910
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Creator
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Amthor, Joachim Emil.
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Contributor
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Adviser: Gerald M. Friedman
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Date
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1990
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Language
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English
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Publisher
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City University of New York.
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Subject
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Geology | Geochemistry
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Abstract
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The distribution of major rock types and lithofacies in Ellenburger Group (Lower Ordovician) carbonate rocks from the deep subsurface (1.5 to 6.4 km) of West Texas and southeastern New Mexico indicate deposition as epicontinental platform carbonates, ranging from mixed clastic-carbonate deposits during an early marine phase to shallow subtidal to supratidal deposits during late stages of Ellenburger deposition.;Petrographic studies and X-ray analyses indicate that 90% of the studied samples were pervasively dolomitized. Seven dolomite-rock textures have been recognized and classified according to crystal-size distribution (unimodal or polymodal) and crystal-boundary shape (planar or nonplanar). Paragenetic relationships of the dolomite-rock textures indicate that Ellenburger carbonate rocks were subjected to a complex diagenetic history ranging from early shallow-subtidal dolomitization to late-diagenetic deep-burial dolomitization.;Electron-microprobe analyses of the dolomite-rock textures reveal characteristic differences in the distribution of major and minor elements. There was an increasing incorporation of iron and manganese into the lattice during progressive dolomitization. The geochemistry of the dolomite-rock textures correlates with the petrography: different dolomite-rock textures are also geochemically distinct.;Ellenburger dolostones were strongly modified during the post- Ellenburger unconformity by karst-related brecciation. Breccia types and associated deposits indicate a karst-related origin for most of the brecciation and fracturing observed in the Ellenburger cores. Karstification and dolomitization are closely related. Porosity and permeability pathways created by karst dissolution seem to have been of prime importance for the distribution of different dolomite types.;The integration of petrographic and geochemical data with petrophysical measurements obtained by high-pressure mercury porosimetry leads to recognition of nature and extent of micro-scale heterogeneity within the complex Ellenburger reservoir rocks. Dolomitization, leaching, and secondary porosity development are intimately associated in the Ellenburger carbonates.;Examination of various petrophysical parameters such as recovery efficiency, permeability, porosity, pore-throat size, and surface area reveal no simple relationships. Rocks of the karst lithofacies were modified more strongly during diagenesis than were rocks from the mottled dolomudstone/wackestone and the peloid-ooid-intraclast dolopackstone/grainstone lithofacies. Rocks from the latter lithofacies are characterized by petrophysical parameters which indicate that these rocks are good candidates for enhanced-oil recovery projects.;Using petrophysical parameters such as median throat-size, pore-throat size at 20% Hg-saturation, normalized pore-throat size, effective porosity, and minimum recovery efficiency, the petrophysical characteristics of the karst facies were examined. The results reflect the highly variable processes and diagenetic modifications that generated this facies, resulting in its heterogeneous nature.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
