Leakage of stored bulk phase CO₂ is of particular risk to sequestration in deep saline aquifers due to the fact that when injected into typical saline aquifers, the CO₂ rich gas phase has lesser density than the aqueous phase resulting in buoyancy driven flow of the fluids. As the CO₂ migrates upward, the security of its storage depends upon the trapping mechanisms that counteract the migration. While there are a variety of trapping mechanisms the mechanism serving as motivation for this research is local capillary trapping. Local capillary trapping occurs during buoyancy-driven migration of bulk phase CO₂ within a saline aquifer (Saadatpoor, 2009). When the rising CO₂ plume encounters a region where capillary entry pressure is locally larger than average, CO₂ accumulates beneath the region. While research is continued by means of numerical simulation, research at the bench scale is needed to validate the conclusions made from simulation work. Presented is the development of a bench scale experiment whose objective is to assess local capillary trapping. The initial step in accomplishing this objective is to understand the fluid dynamics of CO₂ and brine in a saline aquifer which is categorized as two phase immiscible buoyancy driven displacement. Parameters influencing this displacement include density, viscosity, wettability and heterogeneity. A bench scale environment created to be analogous to CO₂ and brine in a saline aquifer is created in a quasi-two dimensional experimental apparatus, which allows for observation of plume migration at ambient conditions. A fluid pair analogous to supercritical CO₂ and brine is developed to mimic the density and viscosity relationship found at pressure and temperature typical of storage aquifers. The influences of viscosity ratio, density differences, porous medium wettability and heterogeneity are observed in series of experimental sequences. Three different fluid pairs with different viscosity ratios and density differences are used to assess density and viscosity influences. Porous media of varying grain size and wettability are used to assess the influence of heterogeneity and wettability. Results are qualitatively consistent with theoretical results and those from previous works. / text

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The purpose of this work was to investigate the evaporation rates of various brines and to compare them to the evaporation rates of pure water under the same environmental conditions in the laboratory. NaCl, MgCl 2 and KCl were the salts used in the experiments, at three densities. Mixtures of the salts were also used. One set of experiments was conducted under free convection while the other was conducted under forced convection, both over pans. Temperature was relatively constant for the experiments but relative humidity was not controlled. Wind profiles were measured during the forced convection experiments and an aerodynamic equation used to calculate evaporation for comparison with the observed evaporation rates. Surface temperatures were also measured. Water activities of all the brine and brine mixtures were also measured and compared to predictions by Raoult's law. In general, it was found the evaporation rate of brines was lower than that of pure water and that the water activities and evaporation rates were density-dependent to a certain extent. More precisely, they were dependent on the actual constituents in the brine due to the different molecular weights, and the number of ions dissolving from a given weight of salt or salt mixture. Evaporation rates can better be estimated on this basis than on the basis of density alone, as one would expect from Raoult's Law.

This study investigated the effect of water potential on soil microbial C and N pools. Two soil types were treated with additions of salt solution to establish osmotic water potentials, and by ceramic plate - pressure chamber apparatus to establish matric water potentials. Soils were then subjected to short-term incubations. Soil microbial C and N contents (BC and BN) were measured mainly by the fumigation-extraction and fumigation-incubation methods. Results showed that both Microbial C and N pools were markedly affected by soil water potential. The soil microbial C content always showed an increase with increasing water stress and then a decrease beyond a threshold value of water stress, compared to the microbial C content at a control water potential of -0.03 MPa (-0.3 Bar). This response pattern to water stress was true, not only for osmotic stress, but also for matric stress, and regardless of the osmotic agent employed. The response pattern of the microbial N pool to water stress generally contrasted with that of the C pool, and depended on the osmotic strength of the extraction solution (K₂SO₄) used in the determination. Non-isotonic extraction after fumigation resulted in a decrease in microbial N content with increasing water stress, while isotonic extraction resulted in an increase with increasing water stress, beyond a threshold value of water stress. Soil microbial C/N ratio always increased with increasing water stress. Matric water stress had a more marked effect on BC and BN than osmotic stress. The possible reasons for the response patterns of BC, BN and microbial C/N ratio have been discussed in this thesis. Some suggestions on the methodology of microbial biomass measurement for water stressed soil samples have been made, and mainly relate to the biomass fumigation techniques and possible changes in the Kc, Kce and Kn values under water stress, and to the substrate induced respiration (SIR) method and suppressed respiration under water stress.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Thesis (M.S. - Mechanical Engineering)--University of Arizona. / Includes bibliographical references.

Thesis (M. Env. Studies)--University of Adelaide, 1980. / Includes bibliographical references (leaves 118-127).

Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on Feb. 18, 2010). Includes bibliographical references.