Browsing by Subject "Salt domes -- Texas"

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Hydrocarbon accumulation patterns in the East Texas salt dome province
(University of Texas at Austin. Bureau of Economic Geology, 1982) Wood, Debra H.; Giles, Alice Burns
Mobilization of the Louann Salt created the present structural configuration in the central part of the East Texas Basin and was the major control on hydrocarbon accumulation in the area. Salt-cored anticlines, turtle-structure anticlines, and salt diapirs were produced by flow of salt. Of these, the most prolific oil- and gas-producing structures have been anticlines with deep salt cores. These deep-seated salt domes uplifted thick stratigraphic sections; thus, their crestal anticlines are multiple-zoned productive structures. Turtle-structure anticlines are less important as hydrocarbon traps. Low productivity of turtle-structure anticlines compared with salt-cored anticlines may result from later development of turtle structures and from uplift of a relatively thinner stratigraphic section. Production associated with shallow salt domes has been relatively minor. If a large amount of oil or gas accumulated over the early pillow forms of these diapirs, then much of it may have leaked along faults associated with dome growth or been caused by erosional breaching of reservoirs over the dome crest after uplift. Deeper exploration of each type of structure (salt-cored anticlines, turtle-structure anticlines, and shallow salt domes) may be productive to the oil and gas companies. Shallow salt domes in East Texas have been evaluated as repositories for isolation of nuclear waste. A suitable site must not harbor natural resources that might attract interest and lead to future breaching of the repository. Substantial hydrocarbon accumulations have not been discovered at most of the shallow domes in East Texas. However, these domes have attracted much drilling activity primarily because of highly successful exploration of shallow salt domes in the Gulf Coast Basin.
Lithology, microstructures, fluid inclusions, and geochemistry of rock salt and of the cap-rock contact in Oakwood dome, East Texas : significance for nuclear waste storage
(University of Texas at Austin. Bureau of Economic Geology, 1982) Dix, Owen R.
Oakwood salt dome in Leon and Freestone Counties, Texas, has a core composed of a diapiric salt stock at a depth of 355 m. A vertical borehole in the center of the salt stock yielded 57.3 m of continuous rock-salt core overlain by 137 m of anhydrite-calcite cap rock. The lower 55.3 m of rock salt exhibits a strong, penetrative schistosity and parallel cleavage dipping at 30 to 40 and more than 60 variably dipping layers of disseminated anhydrite. Anhydrite constitutes 1.3 0.7 percent of the rock-salt core. The upper 2 m of rock salt is unfoliated, comprising a lower 1.4-m interval of medium-grained granoblastic rock salt and an upper 0.6-m interval of coarse-grained granoblastic rock salt. An abrupt, cavity-free contact separates rock salt from laminated cap rock consisting of granoblastic-polygonal anhydrite virtually devoid of halite or pore space. Microstructures and concentration gradients of fluid inclusions suggest that the unfoliated rock salt at the crest of the salt stock was once strongly foliated, but that this fabric was destroyed by solid-state recrystallization. Downward movement of brine from the rock-salt - cap-rock contact was apparently accompanied by two recrystallization fronts. Dissolution of halite at the contact released disseminated anhydrite that presumably accumulated as sand on the floor of the dissolution cavity. Renewed rise of the salt stock closed the cavity, and the anhydrite sand was accreted against the base of the cap rock. Much, if not all, of the lamination in the 80 m of anhydrite cap rock may result from cycles of dissolution, recrystallization, and upward movement in the salt stock, followed by accretion of base of the cap rock. These processes, which are strongly influenced by fluids, act both to breach waste repositories and to geologically isolate them. Despite repeated attrition and uplift of the salt stock, the geologic system has the ability to offset, at least partially, these negative processes by self-sealing and recovery.
Sedimentary record of Cretaceous and Tertiary salt movement, East Texas basin : Times, rates, and volumes of salt flow and their implications for nuclear waste isolation and petroleum exploration
(University of Texas at Austin. Bureau of Economic Geology, 1984) Seni, Steven J.
Post-Aptian strata (younger than 112 ma) in the East Texas Basin were strongly influenced by halokinesis and recorded the evolution associated sate structures. Comparisons with model diapirs and dome-induced changes in patterns of sandstone distribution, depositional facies, and reef growth indicate that thickness variations in strata surrounding domes were caused by syndepositional processes rather than by tectonic distortion. Salt domes in the East Texas Basin exhibit three stages of growth: pillow, diaper, and postdiapir. Each stage affected surrounding strata differently. Pillow growth caused broad uplifting of strata over the crest of the pillows. The resulting topographic swells influenced depositional trends and were susceptible to erosion. Fluvial-channel systems bypassed pillow crests and stacked vertically in primary peripheral sinks on the updip flanks of the pillows. Diapir growth was characterized by expanded sections of shelf and deltaic strata in secondary peripheral sinks around the diapirs. Lower Cretaceous (Aptian stage) reefs on topographic saddles between secondary peripheral sinks now host major oil production at Fairway Field. Postdiapir crestal uplifting and peripheral subsidence affected smaller areas than did equivalent processes that occurred during pillow or diaper stages. Long-term and recent rates of dome growth in East Texas indicate a low probability that future dome uplift will breach an intradomal waste repository. During deposition of the Eocene Wilcox Group, fine-grained floodplain sediments accumulated over and around active diapirs in the East Texas Basin, including Oakwood salt dome. These fine-grained sediments now sheathing diapirs are aquitards favorable for waste isolation. However, sand-rich channel facies in rim synclines commonly surround the fine-grained sheath and constitute interconnected aquifers around diapirs. A potential pathway for radionuclides leaking from a dome could occur if interconnected aquifers intercept the dome. Dome-specific facies variability is difficult to detect because the variability commonly exceeds available well spacing. Site characterization of a potential waste repository must therefore be based on dense well control and on an understanding of dome growth history and diapiric processes in order to better predict facies distributions around domes. Facies variations over and around domes at different stages of growth enable prediction of the location of subtle, facies-controlled hydrocarbon traps. These facies traps are likely to be the only undiscovered traps remaining in mature petroliferous basins such as the East Texas Basin.
Studies of the suitability of salt domes in east Texas basin for geologic isolation of nuclear wastes
(University of Texas at Austin. Bureau of Economic Geology, 1980) Kreitler, Charles W.
The suitability of salt domes in the east Texas basin (Tyler basin), Texas, for long-term isolation of nuclear wastes is being evaluated. The major issues concern hydrogeologic and tectonic stability of the domes and potential natural resources in the basin. These issues are being approached by integration of dome-specific and regional hydrogeologic, geologic, geomorphic, and remote-sensing investigations. Hydrogeologic studies are evaluating basinal hydrogeology and ground-water flow around the domes in order to determine the degree to which salt domes may be dissolving, their rates of solution, and the orientation of saline plumes in the fresh-water aquifers. Subsurface geologic studies are being conducted: 1) to determine the size and shape of specific salt domes, the geology of the strata immediately surrounding the domes, and the regional geology of the east Texas basin; 2) to understand the geologic history of dome growth and basin infilling; and 3) to evaluate potential natural resources. Geomorphic and surficial geology studies are determining whether there has been any dome growth or tectonic movement in the basin during the Quaternary. Remote-sensing studies are being conducted to determine: 1) if dome uplift has altered regional lineation patterns in Quaternary sediments: and 2) whether drainage density indicates Quaternaq structural movement. On the basis of the screening criteria of Brunton et al. (1978), Oakwood and Keechi domes have been chosen as possible candidate domes. Twenty-three domes have been eliminated because of insufficient size, too great a depth to salt, major hydrocarbon production, or previous use (such as liquid propane storage or salt mining or brining). Detailed geologic, hydrogeologic, and geomorphic investigations are now being conducted around Oakwood and Keechi salt domes.