Browsing by Subject "Diagenesis -- Permian Basin (Tex. and N.M.)"
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Item Clay diagenesis of the source rocks from the Permian Basin(Texas Tech University, 1990-08) Sivalingam, SivagnanamThe main objective of this study is to investigate the transformation of illite/smectite mixed layer clay during burial diagenesis. Shales of Atokan and Wolfcampian ages from the Northwestern Shelf, Delaware Basin, Midland Basin and Southern Shelf were examined, using X-ray diffraction and analytical electron microscopy. The illite/smectite (I/S) particles in Atokan shales are less mature, consist of a mixture of random, RO and Rl ordered phases with about 45 to 70% illite. The Wolfcampian shales contain R3 ordered phases with greater than 70% illite component. As diagenesis progresses, there is a gradual shift in the basal reflection towards 10 A, decrease in cation exchange capacity, change in particle morphology from a cornflake to a platy habit, change in texture of the aggregates from a smooth subrounded aggregate to a domained subrounded aggregate and an increase in both tetrahedral and octahedral substitution. The octahedral charge is largely created by Mg substitution for Al and the tetrahedral charge by Al for Si. The Atokan shales, which have a higher percentage of smectite, octahedral Al and Fe and interlayer water within the I/S particles show a higher catalytic property than the mature Wolfcampian shales. Based on this study a transformation-recrystallization mechanism is proposed for the conversion of smectite to illite in the coarse particles. Transformation involves partial dissolution, diffusion and substitution of ions. True mixed-layering occurs at the early stages of diagenesis as indicated by the lattice fringes and the reflections at 17 A and 26-30 A in Atokan shales. As diagenesis progresses, subgrains or packets of discrete illites are formed. These packets grow and eventually coalesce and form platy illite particles. A neoformationrecrystallization mechanism is proposed for epitaxial growths on clay aggregates. Generally, as diagenesis progresses, iron-rich carbonates and Fe-chlorite are precipitated and illite/smectite mixed-layers transform into illite or illite/chlorite particles depending on whether K- or Fe and Mg-rich pore fluids are present, respectively. Availability of K"*" ions and permeability of shales are more important factors controlling illitization than depth, temperature or age.Item Depositional environments and diagenesis of the lower San Andres Formation(Texas Tech University, 1976-08) Barone, William EdwardNot availableItem Depositional Environments and Diagenesis of the Lower San Andres Formation, Roosevelt and Quay counties, New Mexico(Texas Tech University, 1978-05) Muir, Nancy JeanNot Available.Item Depositional environments and diagenesis of the Magutex Ellenburger Field, Andrews County, Texas(Texas Tech University, 1989-05) Sciscoe, JamesNot availableItem Sedimentology, petrography, and diagenesis of selected Paleozoic source rocks from the Permian Basin(Texas Tech University, 1990-12) Trabelsi, Ali M. S.Sedimentological and paleontological investigations of the Upper Devonian Woodford, Pennsylvanian (Missourian), and Permian (Wolfcampian) shales from the Permian Basin of west Texas and southeastern New Mexico indicate that these shales were deposited in deep-water environments, whereas the Atokan shales were deposited in a shallow-water open shelf environment. Woodford, and Wolfcampian shales were deposited as hemipelagic sediments in environments having little wave and current action, while Canyon shales were deposited by turbidity currents and are associated with submarine fan facies. Integrated sedimentological, paleontological and geochemical data indicate that these Paleozoic shale sequences were accumulated in stratified water columns and anoxic to near-anoxic conditions prevailed during their deposition. Hence, large amounts of marine organic matter are preserved in these shales, as indicated by the relatively high total organic content (TOC) values. TOC for all shales exceeds 5 wt% and reaches up to 26 wt%. Shales are classified as, lutite, granolutite, granopackite, and compackite. Lutite is a clay-supported rock with less than 10% grains, whereas granolutite is a claysupported rock with more than 10% grains. Granopackite is a grain-supported rock, having a texture in which grains are in contact and detrital clay is dispersed among the grains. Compackite is characterized by a grain-supported fabric, but the grains are separated by clay platelets which have been bent and distorted owing to compaction. Canyon turbiditic shales exhibit much more shale rock type diversity than any of the Woodford, Atokan, and Wolfcampian hemipelagites. Appreciable amounts of diagenetic minerals were precipitated in these shales. Framboidal and cubic pyrite and silica are common minerals in all shale sequences. Dolomite, calcite, ferroan dolomite and ferroan calcite are abundant in Wolfcampian shales and significant amounts of ferroan dolomite occur in Woodford silty black shales. Celestite and anhydrite were detected only in the Wolfcampian shales from the Delaware Basin and siderite is only found in the Canyon shales. The significance of abundant authigenic minerals in these shales, is that they occur early, possibly before hydrocarbon generation, hence producing a very impermeable medium which would obstruct migrating pore fluids and/or oil. Clay-mineral diagenesis (conversion of illite smectite mixed layers to illite) appears to partially have influenced the diagenesis or precipitation of the authigenic nonclay minerals in these shales, and played an important role in the evolution of ferroan calcite and ferroan dolomite in Woodford and Wolfcampian shales. Petrographic analyses of the studied (Woodford, Atokan, Canyon, and Wolfcampian) shales, in conjunction with examination of geophysical density and porosity logs (FDC and CNL) indicate that some shales are compacted, while others are less compacted. Compacted shales are characterized by low densities, contain flattened palynomorphs and shale fabrics compressed around sand grains, bioclasts, and pyrite and phosphatic nodules. Less compacted shales (Wolfcampian shales) contain appreciable amounts of diagenetic minerals which resulted in differential cementation of these shales, increasing their density and arresting compaction.