Browsing by Subject "salt"
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Item Detection of Gas Hydrates in Garden Banks and Keathley Canyon from Seismic Data(2011-08-08) Murad, IdrisGas hydrate is a potential energy source that has recently been the subject of much academic and industrial research. The search for deep-water gas hydrate involves many challenges that are especially apparent in the northwestern Gulf of Mexico, where the sub-seafloor is a complex structure of shallow salt diapirs and sheets underlying heavily deformed shallow sediments and surrounding diverse minibasins. Here, we consider the effect these structural factors have on gas hydrate occurrence in Garden Banks and Keathley Canyon blocks of the Gulf of Mexico. This was accomplished by first mapping the salt and shallow deformation structures throughout the region using a 2D grid of seismic reflection data. In addition, major deep-rooted faults and shallow-rooted faults were mapped throughout the area. A shallow sediment deformation map was generated that defined areas of significant faulting. We then quantified the thermal impact of shallow salt to better estimate the gas hydrate stability zone (GHSZ) thickness. The predicted base of the GHSZ was compared to the seismic data, which showed evidence for bottom simulating reflectors and gas chimneys. These BSRs and gas chimneys were used to ground-truth the calculated depth of the base of GHSZ. Finally, the calculated GHSZ thickness was used to estimate the volume of the gas hydrate reservoir in the area after determining the most reasonable gas hydrate concentrations in sediments within the GHSZ. An estimate of 5.5 trillion cubic meters of pure hydrate methane in Garden Banks and Keathley Canyon was obtained.Item North Caspian Basin: 2D elastic modeling for seismic imaging of salt and subsalt(Texas A&M University, 2006-04-12) Bailey, Zhanar AlpysbaevnaThe North Caspian Basin (NCB) contains a significant number of major oil fields, some of which are yet to be put into production. The reason why some of these fields are not yet put into production is the exploration challenge that the NCB poses. In particular, the complex geological structure of this region makes it quite difficult to image its oil fields with conventional seismic techniques. This thesis sheds more light on difficulties associated with acquiring and processing seismic data in the NCB. The two central tools for investigation of these imaging challenges were the construction of a geological model of the NCB and the use of an accurate elastic wave-propagation technique to analyze the capability of seismic to illuminate the geological structures of the NCB. Using all available regional and local studies and my knowledge gained with oil companies, where I worked on subsalt and suprasalt 2D and 3D seismic data from the North Caspian Basin, I constructed a 2D elastic isotropic 10-by-6 km geological model of a typical oil field located on the shelf of the Caspian Sea in the southeastern part of the North Caspian Basin, which has the largest oil fields. We have propagated seismic waves through this model. The technique we used to compute wave propagation is known as the Finite-Difference Modeling (FDM) technique. Generating 314 shot gathers with stationary multicomponent OBS receivers that were spread over 10 km took two weeks of CPU time using two parallel computers (8 CPU V880 Sun Microsystems and 24 CPU Sun Enterprise). We have made the data available to the public. The dataset can be uploaded at http://casp.tamu.edu in the SEGY format. The key conclusions of the analysis of these data are as follows: - Combined usage of P- and S-waves allows us to illuminate subsalt reef, clastics and complex salt structures despite the 4-km overburden. - Free-surface multiples and guided waves are one of the key processing challenges in NCB, despite relatively shallow (less than 15 m) shelf water.Item Salt Tectonics and Its Effect on Sediment Structure and Gas Hydrate Occurrence in the Northwestern Gulf of Mexico from 2-D Multichannel Seismic Data(2012-10-04) Lewis, Dan'L 1986-This study was undertaken to investigate mobile salt and its effect on fault structures and gas hydrate occurrence in the northwestern Gulf of Mexico. Industry 2-D multichannel seismic data were used to investigate the effects of the salt within an area of 7,577 mi^2 (19,825 km^2) on the Texas continental slope in the northwestern Gulf of Mexico. The western half of the study area is characterized by a thick sedimentary wedge and isolated salt diapirs whereas the eastern half is characterized by a massive and nearly continuous salt sheet topped by a thin sedimentary section. This difference in salt characteristics marks the edge of the continuous salt sheets of the central Gulf of Mexico and is likely a result of westward decline of original salt volume. Beneath the sedimentary wedge in the western part of the survey, an anomalous sedimentary package was found, that is described here as the diapiric, gassy sediment package (DGSP). The DGSP is highly folded at the top and is marked by tall, diapiric features. It may be either deformed shale or the toe of a complex thrust zone detaching the sedimentary wedge from deeper layers. The dataset was searched for the occurrence of bottom simulating reflectors (BSRs), as they are widely accepted as a geophysical indicator of gas trapped beneath gas hydrate deposits, which are known to occur farther east in the Gulf. Although, many seismic signatures were found that suggest widespread occurrence of gas within the upper sediment column, few BSRs were found. Even considering non-traditional definitions of BSRs, only a few occurrences of patchy and isolated BSRs features were identified. The lack of traditional BSRs is likely the result of geologic conditions that make it difficult to recognize gas hydrate deposits. These factors include: (1) unfavorable layer geometries, (2) flow of warm brines from depth, (3) elevated geotherms due to the thermogenic properties of salt and its varying thickness, and (4) widespread low porosity and permeability sediments within the gas hydrate stability zone.Item Soil Salinity Abatement Following Hurricane Ike(2012-10-19) Mueller, RyanIn September 2008 Hurricane Ike hit the Texas Gulf Coast with a force stronger than the category 2 storm at which it was rated. With a 3.8 m (12.5 ft) storm surge, the agricultural industry in the area was devastated. The goal of this research was to determine the length of time required to reduce the salt levels brought by the storm surge to near pre-hurricane levels. To do this, four sets of samples were taken across two years and analyzed for salinity using the saturated paste extract method. The initial salt levels in November 2008 had an electrical conductivity (ECe) of the inundated soils as high as 26.7 dS/m. Fifty-four percent of the soils sampled in the 0-15 cm horizons and 9% in the 15-30 cm horizons of the edge area had an ECe >= 4 dS/m. In the surge area 79% of the soils sampled in the 0-15 cm horizons and 30% in the 15-30 cm horizons had an ECe >= 4 dS/m. In April 2009, 38% of the soils sampled in the 0-15 cm horizons and 13% in the 15-30 cm horizons of the edge area had an ECe >= 4 dS/m. In the surge area 71% of the soils sampled in the 0-15 cm horizons and 39% in the 15-30 cm horizons had an ECe >= 4 dS/m. By December 2009, none of the soils sampled in the edge area had an ECe >= 4 dS/m. In the surge area 21% of the soils sampled in the 0-15 cm horizons and 33% in the 15-30 cm horizons had an ECe >= 4 dS/m. By October 2010, all soils sampled had leached sufficient salts to be classified as non-saline to very slightly saline soils. Utilizing the November 2008 data set, 28 random samples were selected for exchangeable Na percent (ESP) in order to develop the ESP-SAR (Na adsorption ratio) predictive equation, ESP= 1.19(SAR)^0.82. The SAR-ESP relationship is statistically significant (95% confidence level), with a correlation coefficient of 0.964 (df=26).