Browsing by Subject "Hickory"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item A core-based assessment of the spatial relationship of small faults associated with a basement-controlled, large normal fault in the Hickory Sandstone(Texas A&M University, 2006-10-30) Graff, Mitchell CThis research characterized a system of small faults (displacement < 0.3 m) in seven closely-spaced continuous 2.4 inch (6.1 cm) diameter cores. Cores were obtained from central Texas, on the western edge of the Llano Uplift. Cores penetrate a dip-slip dominant, normal fault (Nobles Fault) with 18.3 m (60 ft) of stratigraphic throw. The spatial, geometric and kinematic attributes of small faults within the Nobles Fault system were characterized to explore potential cause-and-effect relationships. To quantify spatial distributions, a "density" measure based on individual small fault magnitude was utilized. Approximately half of the small faults in the core possessed no discernible offset markers; thus displacement amount for these faults could not be measured directly. Using a nonparametric method in which an alternating conditional expectation determined optimal transformations for the data, a statistically significant empirical correlation was established for faults with measurable gouge thickness, displacement, protolith mean grain size and sorting. Gouge thickness of small faults was found to be dependant upon the displacement amount of the small fault and the textural characteristics of the host protolith. The role of protolith lithology, proximity to crystalline basement, and structural position relative to the Nobles Fault system were examined to explain observed ubiquitous spatial distribution of small faults. Small faults were found to occur in clusters and the number of faults per foot only weakly correlates to the cumulative displacement of the corresponding faults. The amount of mudstone present is the dominant factor controlling small fault formation. Intervals with only minor quantities of mudstone have the largest number of faults per foot as well as largest associated cumulative displacement per foot. Frequency of occurrence of small faults near the basement is greater when compared to similar lithologies higher in the core. Intensity of small faults do not universally increase with proximity to large faults. To observe an increase in small faults, it is necessary to use a mean global cumulative displacement approach. Zones of greater than average cumulative displacement of small faults in close proximity to large faults were observed in zones that are compatible with faultfault interaction.Item Permeability characterization of shear zones in the Hickory sandstone member, Riley Formation, Texas(Texas A&M University, 2005-02-17) Nieto Camargo, Jorge EnriqueReservoir compartments, typical targets for new infill locations, are commonly created by faults that may reduce or enhanced permeabilities. Faults often contain narrow zones of intense shear comprised of geometrically complex elements that reduce permeability and compartmentalize blocks as a function of time and pressure. This thesis characterizes the permeability structure of shear zones and the relationship between fault permeability, host rock properties and the relative degree of deformation. The main objectives of this work are to (1) characterize the geometry and permeability of deformation elements within shear zones; (2) determine permeability anisotropy in shear zones according to fault characteristics and host lithology; and (3) develop a process to predict permeability anisotropy of faults in reservoirs using probabilistic approaches. The study results give a better understanding of fluid flow behavior of shear zones and their potential to create reservoir heterogeneity and compartmentalization. Fluid flow in a reservoir with faults is controlled by variables such as fault throw, shear-zone thickness, undeformed and deformed rock permeability and the geometry of all deformation elements. Methodology to predict permeability structure was developed using analytical and numerical simulation of selected core samples and laboratory measurements. We found useful relationships between permeability of the host rock and highly deformed elements according to the amount of throw of the fault. The high lateral continuity of the highly deformed elements and their predictable low permeability make these elements most important in controlling permeability in shale-free and low-shale shear zones created by low displacement (subseismic) faulting. Probe permeameter data is a precise, inexpensive and non-destructive source of permeability information that can be effectively incorporated in detailed models to investigate the effect of individual deformation elements in the whole shear zone permeability and their effect at the field scale.Item Stratal architecture and sedimentology of a portion of the Upper Cambrian Hickory Sandstone, central Texas, U.S.A.(2009-05-15) Perez Teran, Isaac AntonioFluvial and coastal depositional environments may have been quite different before the development of land plants in the late Silurian. Rapid drainage of terrestrial surfaces, flashy rivers with poorly stabilized banks, coarse sediment loads supplied to coasts from landscapes dominated by physical weathering, and the prevalence of epicontinental seas are expected to have altered depositional patterns and associated preserved Facies. Quarries in the Upper Cambrian Hickory Sandstone located in central Texas provide an exceptional opportunity to examine the sedimentology of deposits of this age in order to interpret sedimentary environments. During quarrying, vertical walls, one half-kilometer long and several tens of meters high, are blasted back a few tens of meters at a time and then the rubble excavated, exposing successive outcrops in walls that are perpendicular to the regional paleocurrent direction. The deposits are characterized by sheet-like bedsets dominated by unidirectional cross-stratified sandstones interpreted to have formed in coastal areas fed by bedload dominated rivers. Thinner heterolithic and clay beds locally separating cross-stratified bedsets are commonly bioturbated by marine organisms. Presence of tidal features, such as abundant mud drapes, concave-upward cross-stratification and sparse herringbone cross-stratification, also suggests marine influence during deposition. Detailed mapping of stratal geometry and Facies across these exposures shows a complex internal architecture that can be interpreted in terms of growth and superposition of bars within shallow fluvial channels and adjacent shallow marine areas along the coast. Detailed 3D reconstruction of bars and channels reveals a range of processes including growth, coalescence, and erosion of bars during channel migration, switching and filling of channel segments, and mouth bar growth as channelised flows decelerated seaward. Sedimentary Facies, stratal geometry and ichnofossils suggest that these deposits were formed in a braid-delta system fed by lowsinuosity bedload-dominated rivers. Basinal processes were controlled by the shallow epicontinental sea, dissipating wave action and strengthening tidal currents.