Zugl.: Halle (Saale), Univ., Diss., 2009

No description available.

Monetizing gas has now become a high priority issue for many countries. Natural gas is a much cleaner fuel than oil and coal especially for electricity generation. Approximately 40 percent of the world's natural gas reserves remain unusable because of lack of economic technology. Gas produced with oil poses a challenge of being transported and is typically flared or re-injected into the reservoir. These are gas transportation issues we now face. Gas hydrate may be a viable means of capturing, storing and transporting stranded and associated gas. For example, stranded gas in Trinidad could be converted to gas hydrates and transported to the islands of the Caribbean. This study will seek to address some of the limitations from previous studies on transporting natural gas as a hydrate while focusing on small scale transportation of natural gas to the Caribbean Islands. This work proposes a workflow for capturing, storing and transporting gas in the hydrate form, particularly for Caribbean situations where there are infrastructural constraints such as lack of pipelines. The study shows the gas hydrate value chain for transportation of 5 MMscf/d of natural gas from Trinidad to Jamaica. The analysis evaluated the water required for hydrate formation, effect of composition on hydrate formation, the energy balance of the process, the time required for formation, transportation and dissociation and preliminary economics. The overall energy requirement of the process which involves heating, cooling and expansion is about 15-20 percent of the energy of the gas transported in hydrate form. The time estimated for the overall process is 20–30 hrs. The estimated capital cost to capture and transport 5 MMscf/d from Trinidad to Jamaica is about US$ 30 million. The composition of the gas sample can affect the conditions of formation, heating value and the expansion process. In summary, there is great potential for transporting natural gas by gas hydrate on a small scale based on the proposed hydrate work flow. This study did not prove commerciality at this time, however, some of the limitations require further evaluations and these include detailed modeling of the formation time, dissociation time and heat transfer capabilities.

The amount of carbon trapped in hydrates is estimated to be larger than in conventional oil and gas reservoirs, thus methane hydrate is a promising energy resource. The high water pressure and the relatively low temperature needed for hydrate stability restrict the distribution of methane hydrates to continental shelves and permafrost regions. Stability conditions add inherent complexity to coring, sampling, handling, testing and data interpretation, and have profound implications on potential production strategies. New guidelines are identified for sampling equipment and protocols. Then a novel technology is developed for handling, transfering, and testing of natural hydrate bearing sediments without depressurization in order to preserve the sediment structure. Natural samples from the Nankai Trough, Japan, are tested as part of this study. In-situ testing prevents dissociation and the consequences of sampling and handling disturbance. A new multi-sensor in-situ characterization tool is designed and prototyped as part of this research. The tool includes advanced electronics and allows for automated stand-alone operation. Finally, a robust analytical model is developed to estimate the amount of gas that can be recovered from hydrate bearing sediments using depressurization driven dissociation. Results highlight the complexity of gas extraction from deep sediments, and inherent limitations.

Siegen, Univ., Diss., 2001. / Computerdatei im Fernzugriff.

Siegen, Univ., Diss., 2001. / Computerdatei im Fernzugriff.

Siegen, Universiẗat, Diss., 2001.

Sediments collected from various cores in Mississippi Canyon 118 were tested to evaluate the abilities to promote natural gas hydrate formation. Memory effects for hydrate formation of sediments with in-situ seawater were of a major concern. The possible mechanisms of memory effects were combined to give an overall hypothesis on the bioproducts-mineral-microorganism system. Unique permanent memory effects in the sediment were found. Temperatures from 50 to 65°C dissipated all memory effects by disrupting microbial cell wall material. Bacillus subtilis is known to produce several types of biosurfactants, including surfactin. The catalytic effect of purified surfactin from B. subtilis on hydrate formation was studied in the presence of smectite clays. The interlayer spacings of clay minerals measured by X-ray powder diffraction indicated that hydrate formation and surfactin adsorption on the smectite clays have impacts on their structures. Laboratory gas mixture sequestering was also conducted by hydrate formation to study the various factors that may affect the separation of its hydrateorming gases. The effects of agitation, temperature, initial pressure and thermal conductors were explored.

This study presents a two-step desalination process, in which produced water is cleaned by forming gas hydrate in it and subsequently dewatering the hydrate to remove the residual produced water trapped in between the hydrate crystals. All experiments were performed with pressure in the range of 450 to 800psi and temperature in the range of -1 to 1°C using CO? as guest molecule for the hydrate crystals. The experiments were conducted using artificial produced waters containing different amounts of NaCl, CaCl₂ and MgCl₂ at varying temperature (T) and pressure (P). The results are presented as functions of %Reduction of difference chemical elements, CO? requirements and applied T and P conditions. The impact of dewatering techniques, including centrifuge and filtration process, on gas hydrate solid product is studied. The results showed that over 99% of dissolved NaCl and MgCl2 can be removed from artificial saline water in laboratory experiments. This was achieved in a process involving a single-stage hydrate formation step, followed by a single-step solid-liquid separation (or dewatering). The results also show that the %Reduction (percentage of the concentration decrease) of artificial produced water increases with centrifugation time and rotational speed (rpm). The %Reduction was increased considerably after hydrate crystals were crushed and filtered, indicating that the artificial process water was entrapped in between the hydrate crystals. It was found also that the finer the particle size, the higher the extent of salt removal. In general, filtration was a better than centrifugation for the removal of TDS (Total Dissolved Solids). / Master of Science

No description available.