Browsing by Subject "Geology -- Texas -- Gulf Region"
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Item Depositional setting, structural style, and sandstone distribution in three geopressured geothermal areas, Texas Gulf Coast(University of Texas at Austin. Bureau of Economic Geology, 1983) Winker, C. D.Three areas in the Texas Gulf Coastal Plain were studied using electric logs and seismic reflection data to interpret their depositional and structural history and to compare their potential as geopressured-geothermal reservoirs. The Cuero study area, on the lower Wilcox (upper Paleocene) growth-fault trend, is characterized by closely and evenly spaced, subparallel, down-to-the-basin growth faults, relatively small expansion ratios, and minor block rotation. Distributary-channel sandstones in the geopressured lower Wilcox Group of the South Cook fault block appear to be the best geothermal aquifers in the Cuero area. The Blessing study area, on the lower Frio (Oligocene) growth-fault trend, shows wider and more variable fault spacing and much greater expansion ratios and block rotation, particularly during early Frio time. Thick geopressured sandstone aquifers are laterally more extensive in the Blessing area than in the Cuero area. The Pleasant Bayou study area, like the Blessing area, is on the Frio growth-fault trend, and its early structural development was similar; rapid movement of widely spaced faults resulted in large expansion ratios and major block rotation. However, a late-stage pattern of salt uplift and withdrawal complicated the structural style. Thick geopressured lower Frio sandstone aquifers are highly permeable and laterally extensive, as in the Blessing area. In all three areas, geopressured aquifers were created where early, rapid movement along down-to-the-basin growth faults juxtaposed shallow-water sands against older shales, probably deposited in slope environments. Major transgressions followed the deposition of reservoir sands and probably also influenced the hydraulic isolation that allowed the buildup of abnormal pressures. Of the three areas, the Pleasant Bayou area has the best potential for geothermal energy production because of larger fault block area, greater thickness and lateral continuity of individual sandstones, and higher formation temperatures and pressures.Item Lower Miocene (Fleming) depositional episode of the Texas coastal plain and continental shelf : structural framework, facies, and hydrocarbon resources(University of Texas at Austin. Bureau of Economic Geology, 1986) Galloway, William E.The Fleming Group and its basinward equivalents constitute the stratigraphic record of one of the major Cenozoic depositional episodes of the northern Gulf Coast Basin. The depositional sequence representing the episode is bounded above by the Amphistegina B shale and below by the Anahuac shale. Initially, lower Miocene (Oakville) progradation advanced across the broad submerged shelf platform constructed during earlier Frio deposition. When outbuilding reached the Frio paleocontinental margin, the rate slowed as large-scale growth faulting created a narrow lower Miocene expansion zone. The later portion of the lower Miocene episode, generally equivalent to the Lagarto Formation, was characterized by long-term shoreline stability and retreat punctuated by local, temporary progradation.In South Texas, the lower Miocene depositional framework includes the Santa Cruz fluvial system and the North Padre delta system. The bed-load fluvial complex fed a wave-dominated delta, constructing a broadly convex deltaic headland across the foundered Frio Norias delta system. Extensive wave reworking and longshore transport of sand and mud nourished a broad barrier island/ lagoon and strandplain complex that extended along the central and much of the northeastern Texas coast. This well-known barrier/strandplain system was bounded updip by a coastal plain traversed by numerous, small, intrabasinal streams. Near the present Sabine River, westernmost deposits of a continental-scale mixed-load fluvial and equivalent delta system extend beneath the Texas Coastal Plain and shelf from the Miocene depocenter in Louisiana. Here, the early phase of lower Miocene progradation was also complicated by the incision and filling of numerous submarine gorges.Lower Miocene reservoirs have produced nearly 4 billion barrels of oil equivalent of petroleum from nine identified plays in the Texas Coastal Plain and shelf. The most prolific play, the Houston Embayment salt domes, accounts for nearly all the oil and more than two-thirds of the total production from deposits of the episode. Four offshore plays offer the greatest area for discovery of substantial new reserves, primarily of gas. To date, however, the yield per volume of reservoir sandstone for Miocene plays remains low relative to more prolific units, such as the Frio Formation.Item Regional Tertiary cross sections, Texas Gulf Coast(University of Texas at Austin. Bureau of Economic Geology, 1976) Bebout, Don G.; Luttrell, P. E.; Seo, J. H.The Bureau of Economic Geology has been conducting regional studies of the Frio Formation along the Texas Gulf Coast to evaluate potential geothermal energy from deep, geopressured sandstone reservoirs (Bebout, Dorfman, and Agagu, 1975; Bebout, Agagu, and Dorfman, 1975). The procedures used in this evaluation were reviewed at the Second Geopressured Geothermal Energy Conference held at The University of Texas at Austin and sponsored by the United States Energy Research and Development Administration. The index map (fig. 1) and cross sections (figs. 2-7) included in this circular were prepared for that meeting and were included in the Proceedings (Bebout, 1976). Published regional cross sections (Corpus Christi Geological Society Study Group, 1954-55, 1964; Deussen and Owen, 1939; Houston Geological Society Study Group, 1954, 1972; and South Texas Geological Society, 1951), unpublished cross sections provided by several major oil companies, and extensive micropaleontological and electrical-log files at the Bureau of Economic Geology served as basic data. These sections are meant to show gross regional distribution of sand and shale facies both laterally and vertically throughout the entire Tertiary section along the Texas Gulf Coast. Closely spaced wells were used for detailed correlation, but for clarity many have been omitted for these cross sections (fig. 1 and table 1). Growth faults tend to obscure regional trends and have been omitted. The top of the geopressure zone is indicated by an arrow. At least eight sand-shale wedges are easily recognized on regional electrical-log cross sections (figs. 2-7). Hardin (1961) illustrated the major wedges as the Midway/Wilcox, Reklaw/Queen City, Weches/Sparta, Cook Mountain/Yegua, Jackson, Vicksburg, Frio, and Anahuac/Fleming. The Pliocene and Pleistocene comprise additional cycles but are undifferentiated in this study. These cycles reflect changes in the ancient shoreline resulting from variations in sediment supply, rate of subsidence, and position of sea level. In general, in the updip end of the wedge the main sand depocenter is in the lower part of the section and downdip it is progressively higher in the section; this is a progradational cycle. In order to emphasize these wedges, the boundary between the facies-related sand-shale couplet is defined by a dashed line on the cross sections. Time lines within the couplet are expected to cross the dashed line as the deltaic or barrier sands prograde basinward over the prodelta or shelf shales.