This work examines the impact of a viscosity force parameter, fluid velocity, and a capillary force parameter, interfacial tension, on the saturation, morphology, and topology of NW fluid in Bentheimer sandstone after primary imbibition, drainage, and secondary imbibition. Brine and air (used as a proxy for supercritical CO₂) flow experiments were performed on 6 mm diameter Bentheimer cores and were quantified via imaging with x-ray computed microtomography (x-ray CMT), which allows for three dimensional, non-destructive, pore-scale analysis of the amount and distribution of NW phase fluid within the sandstone cores. It was found that trapped NW phase saturation decreases with increases in capillary number, average blob size decreases with increases in capillary number, and the number of NW blobs increases with increases in capillary number. In addition, it was found that NW phase trapping is dependent on initial NW phase connectivity within the porous medium; with more negative values of initial NW phase Euler number resulting in less trapping. We suggest that the Euler number-saturation and the capillary number-saturation relationships for a given medium should be taken into consideration when designing a CO₂ sequestration scenario. / Graduation date: 2013

The Gulf Coast of Texas has been proposed as a high capacity storage region for geologic sequestration of anthropogenic CO₂. The Miocene section within the Texas State Waters is an attractive offshore alternative to onshore sequestration. However, the stratigraphic targets of interest highlight a need to utilize fault-bounded structural traps. Regional capacity estimates in this area have previously focused on simple volumetric estimations or more sophisticated fill-to-spill scenarios with faults acting as no-flow boundaries. Capacity estimations that ignore the static and dynamic sealing capacities of faults may therefore be inaccurate. A comprehensive fault seal analysis workflow for CO₂-brine membrane fault seal potential has been developed for geologic site selection in the Miocene section of the Texas State Waters. To reduce uncertainty of fault performance, a fault seal calibration has been performed on 6 Miocene natural gas traps in the Texas State Waters in order to constrain the capillary entry pressures of the modeled fault gouge. Results indicate that modeled membrane fault seal capacity for the Lower Miocene section agrees with published global fault seal databases. Faults can therefore serve as effective seals, as suggested by natural hydrocarbon accumulations. However, fault seal capacity is generally an order of magnitude lower than top seal capacity in the same stratigraphic setting, with implications for storage projects. For a specific non-hydrocarbon producing site studied for sequestration (San Luis Pass salt dome setting) with moderately dipping (16°) traps (i.e. high potential column height), membrane fault seal modeling is shown to decrease fault-bound trap area, and therefore storage capacity volume, compared with fill-to-spill modeling. However, using the developed fault seal workflow at other potential storage sites will predict the degree to which storage capacity may approach fill-to-spill capacity, depending primarily on the geology of the fault (shale gouge ratio – SGR) and the structural relief of the trap. / text

Woodlot and natural woodland systems in the semi-arid regions in Tanzania are believed to have a high potential to sequester carbon (C) in their biomass and the soil which may qualify for C credits under the current voluntary C market schemes like, the REDD program. However, our understanding of the processes influencing storage and dynamics of C in soils under semi-arid agroforestry systems such as these woodlot systems is limited. This study evaluated C pools in soil and tree biomass in woodlot species of Albizia lebbeck, Leucaena leucocephala, Melia azedarach, and Gmelina arborea; and in farmland and ngitili systems. Synchrotron-based C K-edge x-ray absorption near-edge structure (XANES) spectroscopy was also used to study the influence of these land use systems on the soil organic matter (SOM) chemistry to understand the mechanisms of soil C changes. Soil samples were collected to 1 m depth and subsamples for each land use system to 0.4 m depth were fractionated into macroaggregates (2000-250 μm), microaggregates (250-53 μm), and silt and clay-sized aggregates (<53 μm) to provide information of C dynamics and stabilization in various land uses. SOC was analyzed in whole and soil aggregates and biomass C was estimated using developed biomass models from the literatures. Aboveground biomass carbon in the woodlots from the Kahama district ranged from 11.76 Mg C ha-1 to 24.40 Mg C ha-1. Based on the age of woodlots and the rate of carbon sequestration potential (CSP), Gmelina arborea had the highest rate of aboveground C sequestration (3.59 Mg C ha-1 year-1). The SOC stocks in whole soil for the land use systems from the two districts ranged from 43-67 Mg C ha-1. The degraded ngitili did not show a reduction in SOC stocks despite reducing aboveground biomass C stocks by 15.11 Mg C ha-1. SOC in the woodlots were found to be associated more with the micro and silt-and clay-sized aggregates than the macroaggregates, reflecting high stability of SOC in the woodlot systems. The XANES C K-edge spectra revealed the stabilization of recalcitrant aromatic C compounds in the silt and clay-sized aggregates. This study demonstrates the significant contributions of woodlots in biomass C accumulation as well as long-term SOC stabilization in soil fractions. Thus, these agroforestry practices hold promise to meet household energy needs while contributing to climate change mitigation and adaption.

Started as an EOR technique to produce oil, injection of carbon dioxide which is essentially a greenhouse gas is becoming more and more important. Although there are a number of mathematical modeling studies, experimental studies are limited and most studies focus on injection into sandstone reservoirs as opposed to carbonate ones. This study presents the results of computerized tomography (CT) monitored laboratory experiments to characterize relevant chemical reactions associated with injection and storage of CO2 in carbonate formations. Porosity changes along the core plugs and the corresponding permeability changes are reported for varying CO2 injection rates, temperature and salt concentrations. CT monitored experiments are designed to model fast near well bore flow and slow reservoir flows. It was observed that either a permeability improvement or a permeability reduction can be obtained. The trend of change in rock properties is very case dependent because it is related to distribution of pores, brine composition and as well the thermodynamic conditions. As the salt concentration decreased the porosity and thus the permeability decrease was less pronounced. Calcite scaling is mainly influenced by orientation and horizontal flow resulted in larger calcite deposition compared to vertical flow. The duration of CO2 &ndash / rock contact and the amount of area contacted by CO2 seems to have a more pronounced effect compared to rate effect. The experiments were modeled using a multi-phase, non-isothermal commercial simulator where solution and deposition of calcite were considered by the means of chemical reactions. The calibrated model was then used to analyze field scale injections and to model the potential CO2 sequestration capacity of a hypothetical carbonate aquifer formation. It was observed that solubility and hydrodynamic storage of CO2 is larger compared to mineral trapping.

M. Tech (Department of Chemistry, Faculty of Applied and Computer Sciences) Vaal University of Technology. / Macadamia activated carbon (MAC) was impregnated with different concentrations of nitric acid and heated under reflux to improve the structural characteristics of the adsorbent for both considerable reduction and enhanced removal of Cr(VI). The chemical oxidation of ACs increased the surface oxygenated functional groups. Adsorption of Cr(VI) was carried out by varying parameters such as contact time, pH, concentration, and adsorbent dosage. The optimum operating conditions for the adsorption of Cr(VI) were pH 1, contact time 240 min, adsorbent dosage 10.67 g/L and Cr(VI) concentration 100 mg/L. The results showed that the Macadamia–based AC could be used efficiently for the treatment of chromium-containing solutions as a low-cost alternative compared to commercial AC and other adsorbent reported. The results showed that treated MAC performed better than untreated MAC, signifying the effect of secondary treatment on the enhanced removal of pollutants. Comparable to the application of ACs is the development of imprinting technologies for selective metal ion remediation in environmental samples. The combination of ion imprinting effects and functionalized carbon adsorbents produce materials which effectively remove and selectively recognize the target analyte. Macadamia activated carbon (MAC) was chemically pre-treated with nitric acid to generate carboxyl groups on the surface. The carboxylated MAC was then reacted with triethylenetetramine, N,N’-diisopropylcarbodiimide and CrCl3.6H2O to produce MACN20-imprinted sorbents (MACN20-IIP). MACN20-non imprinted (MACN20-NIP) counterparts were prepared, but Cr3+ was excluded in the synthesis. Alteration of surface structural characteristics and characterization of prepared adsorbents as confirmed by Fourier transform infrared spectroscopy, thermogravimetric analysis, elemental analysis, Brunauer–Emmett–Teller and scanning electron microscopy. MACN20-IIP and MACN20-NIP adsorbents were evaluated for their Cr3+ uptake from aqueous solution in batch format. Maximum conditions were achieved at pH 5, 50 mg/L Cr(III) initial concentration and 33.33 g/L of adsorbent dosage. Presence of co-ions slightly diminished the removal of Cr(III) by MAC-IIP adsorbents. Application of the MACN20-IIP and MACN20-NIP on spiked acid mine drainage artificial sample led to collapse in the removal efficiency of MACN20-NIP while MACN20-IIP still showed good removal efficiencies. These results demonstrated that surface imprinting led to better adsorption rates and capacity. The data was better described by the Freundlich multilayer adsorption and pseudo-second order kinetic rate model. The combination of both the carbon sorbent and the surface-mediated IIPs effectively improved total chromium remediation in aqueous systems.

Carbon capture, utilization and storage (CCUS) in confined saline aquifers in sedimentary formations has the potential to reduce the impact of fossil fuel combustion on climate change by storing CO2 in geologic formations in perpetuity. At PT conditions relevant to CCUS, CO2 is less dense than the pre-existing brine in the formation, and the more buoyant CO2 will migrate to the top of the formation where it will be in contact with cap rock. A typical cap rock is clay-rich shale, and interactions between shales and CO2 are poorly understood at PT conditions appropriate for CCUS in saline formations. In this study, the interaction of CO2 with clay minerals in the cap rock overlying a saline formation has been examined, using Na-rich montmorillonite as an analog for clay-rich shale. Attenuated Total Reflectance -- Fourier Transform Infrared Spectroscopy (ATR -FTIR) was used to identify potential crystallographic sites (AlAlOH, AlMgOH and interlayer space) where CO2 could interact with montmorillonite at 35"C and 50"C and from 0-1200 psi.  Analysis of the data indicates that CO2 that is preferentially incorporated into the interlayer space, with dehydrated montmorillonite capable of incorporating more CO2 than hydrated montmorillonite. No evidence of chemical interactions between CO2 and montmorillonite were identified, and no spectroscopic evidence for carbonate mineral formation was observed.  Further work is needed to determine if reservoir seal quality is more likely to be degraded or enhanced by CO2 - montmorillonite interactions. / Master of Science

In order to reduce the rate of climate change, particularly global warming, it is imperative that industries reduce their carbon dioxide (CO2) emissions. A promising solution of CO2 emission reduction is Carbon dioxide Capture and Storage (CCS) by sequestration, which involves isolating and extracting CO2 from the flue gases of various industrial processes, and thereafter burying the CO2 underground. The capture of CO2 proved to be the most challenging aspect of CCS. Thus, the objective of this research was to identify the most promising solution to capture CO2 from industrial processes. The study focussed on capturing CO2 emitted by coal power plants, coal-to-liquids (CTL) and gas-to-liquids (GTL) industries, which are common CO2 emitters in South Africa. This thesis consists firstly of an extensive literature review detailing the above mentioned processes, the modes of CO2 capture, and the various CO2 capture methods that are currently being investigated around the world, together with their benefits and drawbacks in terms of energy penalty, CO2 loading, absorption rate, capture efficiency, investment costs, and operating costs. Modelling, simulation, and pilot plant efforts are also described. The study reviewed many CO2 capture techniques including solvent absorption, sorbent capture, membrane usage, hydrate formation, and newly emerging capture techniques such as enzyme based systems, ionic liquids, low temperature cryogenics, CO2 anti-sublimation, artificial photosynthesis, integrated gasification steam cycle (IGSC), and chemical looping combustion The technique of solvent absorption was found to be the most promising for South African industries. Vapour-liquid-equilibrium (VLE) measurements of solvent absorption using amine blends were undertaken, using blends of methyl-diethanol amine (MDEA), diethanol amine (DEA) and water (H2O) with composition ratios of 25: 25: 50 wt% and 30: 20: 50 wt% respectively, and with CO2 and N2 gases at CO2 partial pressures of 0.5 to 10.5 bar. Experiments were conducted under system pressures of 5 to 15 bar and temperatures of 363.15 and 413.15 K, using a static analytic apparatus. CO2 liquid loading results were analysed and discussed. The experimental data were regressed in Matlab (R2009b) using the Posey-Tapperson-Rochelle model and the Deshmukh-Mather model. The Matlab programmes are presented along with the regressed binary interaction and model parameters. The accuracy of model predictions are discussed. Thereafter an Electrolyte-NRTL model regression and simulation of the absorption process was conducted using Aspen Plus V 7.1. for flue gas compositions, solvent compositions, temperature, and pressure conditions similar to that of process operating conditions. CO2 loading, design factors, CO2 recovery, and CO2 purity results were analysed and compared where appropriate, with experimental results. Finally a general preliminary energy efficiency and cost analysis was conducted based on the simulation results. The main conclusions reached are that the amine solvent blend containing 25:25:50 wt% of MDEA:DEA:H2O, produced higher CO2 loadings for its respective system conditions than other solvents studied and those found in literature. However, absorption of CO2 was found to be highly dependent on system temperature and pressure. The Deshmukh-Mather model provided higher accuracy than the Posey-Tapperson-Rochelle model, producing CO2 loading predictions with a relative error not exceeding 0.04%, in 1.5 to 3 minutes using a dual core processor. Aspen absorption simulations provided significantly lower CO2 loading results than those experimentally obtained, due to the low contact time achieved and higher temperature dependence in the proposed absorption process. Process improvements were highlighted and implemented to increase CO2 recovery and purity. Energy penalty values were found to be higher than those found in literature, but room for process and design improvement was identified and recommendations were given. Investment cost estimates were found to be justifiable and within reason. Limitations of the simulation were also identified and discussed. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

Water management that alters riverine ecosystem processes has strongly influenced deltas and the people who depend on them, but a full accounting of the trade-offs is still emerging. Using palaeoecological data, we document a surprising biogeochemical consequence of water management in the Colorado River basin. Complete allocation and consumptive use of the river's flow has altered the downstream estuarine ecosystem, including the abundance and composition of the mollusc community, an important component in estuarine carbon cycling. In particular, population declines in the endemic Colorado delta clam, Mulinia coloradoensis, from 50-125 individuals m(-2) in the pre-dam era to three individualsm-2 today, have likely resulted in a reduction, on the order of 5900-15 000 tCyr(-1) (4.1-10.6 mol Cm-2 yr(-1)), in the net carbon emissions associated with molluscs. Although this reduction is large within the estuarine system, it is small in comparison with annual global carbon emissions. Nonetheless, this finding highlights the need for further research into the effects of dams, diversions and reservoirs on the biogeochemistry of deltas and estuaries worldwide, underscoring a present need for integrated water and carbon planning.

Doctor of Philosophy / Department of Agronomy / Ganga M. Hettiarachchi / Soil carbon (C) sequestration has been recognized as one of the most effective potential mitigation options for climate change. Underlying mechanisms of soil C sequestration/preservation is poorly understood, even after decades of soil C research. The main research objectives of this dissertation were three-fold: (1) enhancing our understanding in mineralogical and physicochemical mechanisms of soil C sequestration in microaggregates, (2) understanding the chemistry of organic C sequestered in soil aggregates, and (3) to determine the resilience of C to different temperature-moisture regimes and physical disturbance in a six-month incubation. An integrated approach was used in obtaining a better picture on mechanisms of C preservation. Two long-term agroecosystems located at the North Agronomy Farm, Manhattan, KS (Mollisols) and the Center of Experimentation and Research Fundacep in Cruz Alta-RS, Brazil (Oxisols) were used. Main plots of both systems were till and no-till. Mollisols consisted of three fertilizer treatments; control, manure/compost and urea. Oxisols had three different crop rotations; simple, intermediate, and complex. Submicron level information gathered by spectromicroscopy approaches, identified the direct preservation of OC structures with the original morphology; suggesting that the preservation of OC is a primary mechanism of C sequestration in these soils. Physical protection and organo-mineral associations seemed to also be involved in OC preservation. Manure/compost addition and no-till favored labile C preservation in aggregates of Mollisols. Significant associations observed between reactive minerals and C pools in Mollisols indicated the significance of organo-mineral associations in OC preservation. Large microaggregates exerted strong C preservation through physical protection and organo-mineral associations. Unlike in Mollisols, Oxisols showed a poor correlation between reactive mineral fraction and organic C which indicated the significance of physical protection over organo-mineral associations. Resilience of sequestred C was significantly affected by temperature across both temperate and tropical soil ecosystems, directly and indirectly. High temperature influenced soil acidity and reactive minerals, ultimately affecting organo-mineral associations. Macromolecular propeties of humic acid fraction showed changes after six months. Overall, direct and indirect evidence from this study suggested that the preservation of SOC is an ecosystem property supporting the newly proposed theories in soil C dynamics.

Soil organic carbon (SOC) is important not only for improving soil quality but also for contributing to climate change mitigation in agriculture. However, net greenhouse gas (GHG) balances, including methane (CH4) and nitrous oxide (N2O), need to be considered, as practices that increase SOC might increase GHG emissions. Sustainable use of soil resources needs to be assessed over long time periods and across spatial scales; biogeochemical models are useful tools to estimate GHG emissions and corresponding mitigation potentials. A process-based, ecosystem model DayCent that simulates soil carbon and nitrogen dynamics from diverse agroecosystems, has been applied to observe SOC sequestration, GHG emissions and yield in a contrasting climatic region UK and Bangladesh agriculture. The study mainly focus on determination of GHG mitigation potentials under improved management practices in rice based cropland Bangladesh. We hypothesized that alternative management would increase SOC and reduce net GHG emissions. As crop yield is the most important variable for Bangladesh, it was includes in the simulations. Since site test simulations under different management using the DayCent model were satisfactory, the model was used to simulate GHG covering 64 districts of Bangladesh, considering climate, soil and SOC content for the period 1996-2015. An integrated management scenario consisting of irrigation, tillage with residue management, reduced mineral nitrogen fertilizer and manure application increased annual SOC stocks, and offset net GHG emissions while maintaining yield. The model outcome suggests that the “4 per mille” target is feasible for Bangladesh. It is also possible to contribute to the GHG reduction target by 2030 set by policy makers.