Thesis (Ph.D.)--University of Wyoming, 2008. / Title from PDF title page (viewed on June 24, 2009). Includes bibliographical references (p. 120-127).

Holding approximately 89,000 Tg of organic carbon, tropical peatlands are one of the largest pedological sinks of carbon (Page et al., 2011). Waterlogged conditions in undisturbed peatlands reduce heterotrophic respiration and provide environments in which organic matter accumulates (Moore et al., 2013). However, from 1990 to 2010, the forest cover in the peatlands of South East Asia fell from 77% to 36%; at this rate of decline, all of the undisturbed peatlands are likely to have disappeared by 2030 (Li et al., 2007; Koh et al., 2011; Miettinen et al., 2011). Land-use changes in these ecosystems can have important consequences for carbon (C) budgets (Page et al., 2002; Hooijer et al., 2010). Recently a number of studies have been carried out on tropical peatlands (e.g. Couwenberg et al., 2010; Hergoualc'h and Verchot, 2011; Hirano et al., 2012; Jauhiainen et al., 2005, 2012; Li et al., 2007; Melling et al., 2005; Page et al., 2009), but some parts of the C budget are yet to be quantified. In order to fill these gaps in our knowledge, the goal of this work was to assess heterotrophic and total soil respiration, litterfall, litter decomposition and evaluate peat properties in an intact peat swamp forest, a transitional logged drained forest and an oil palm plantation located on the same alluvial peat plain. This in-situ research lasted two years, and heterotrophic and total soil respiration were separated using the trenching method. Our results from the carbon dioxide flux monitoring in the three land uses showed that the trenched plots provided a good proxy for heterotrophic respiration. The annual integrated total soil respiration was lower in the intact and drained forest than in the oil palm plantation, at 20.2 ±3.4, 18.7 ±1.1 and 26.4 ±1.7 Mg C ha-1 y-1, respectively. A similar pattern was seen in the heterotrophic respiration for the same land uses, 9.6 ±7.7, 15.7 ±1.0 and 22.9 ±2.0 Mg C ha-1 y-1, respectively. When extrapolated to the landscape, the percentage of heterotrophic 4 respiration appeared to have significantly increased following drainage, even before the conversion to oil palm, with percentages of 47.6 ±10.1, 83.9 ±7.3, 86.6 ±1.9 for intact forest, drained forest and oil palm plantation, respectively. The average litterfall in the three land uses was not significantly different, at 26.3 ±4.1, 23.2 ±4.2 and 18.6 ±3.5 kg dry litter ha-1 d-1 respectively. Overall, the C fluxes results produced in this thesis point towards a negative C balance (i.e. net ecosystem loss of C) for the drained forest, a pronounced negative C balance for the oil palm plantation and a near neutral balance for the intact forest. Other relevant findings in the study were: (1) the impacts of N fertilizer application in the oil palm plantation lasted only a few days and were unlikely to have significant consequences on the annual C budget; (2) concerns over the diurnal variability of carbon dioxide fluxes are not particularly pertinent in these tropical peatlands; and (3) the principal soil property affected by drainage and land-use change was the abundance of logs in the soil. In summary, the results produced in this thesis represent noteworthy data about the C budget and C dynamics in tropical peatlands and will help decision making by policy makers and land managers for sustainable use of these ecosystems.

Rising concentration of CO2 in the atmosphere is attributed to increasing consumption of fossil fuels. One of the most effective mechanisms to store CO2 captured from power plants is via geological injection of CO2 into formations that contain calcium and magnesium silicate and alumino-silicate minerals and rocks. The mechanism that ensures permanent storage of CO2 within rocks is mineral carbonation. When CO2 is injected into mineral or rock formations rich in calcium or magnesium silicates, they react with CO2 to form calcium or magnesium carbonates, which is also known as carbon mineralization. Calcium and magnesium carbonates are stable and insoluble in water. However, the kinetics of in-situ mineral carbonation involve CO2 hydration, mineral dissolution and formation of carbonates, and the relative rates of these phenomena when coupled, are not very well understood. In this study, the coupled interactions of CO2-reaction fluid-minerals were investigated to determine the optimal conditions for carbon mineralization, and to identify the chemical and morphological changes in the minerals as they react to form carbonates. Carbon mineralization in various minerals and rocks such as olivine ((Mg,Fe)2SiO4)), labradorite ((Ca, Na)(Al, Si)4O8), anorthosite (mixture of anorthite (CaAl2Si2O8), and basalt (rock comprising various minerals) were studied at high temperatures (Tmax = 185 oC) and high partial pressures of CO2 (PCO2, max = 164 atm) which are relevant for in-situ conditions. These minerals and rocks differ considerably in their chemical compositions and reactivity with CO2. A systematic comparison of the effects of reaction time, temperature, partial pressure of CO2, and fluid composition on the conversion of these magnesium and calcium bearing minerals and rocks showed that olivine was the most reactive mineral followed by labradorite, anorthosite, and basalt, respectively. Previous studies at Albany Research Center (Gerdemann et al., 2007; O'Connor et al., 2004) reported that a solution of 1.0 M NaCl + 0.64 M NaHCO3 was effective in achieving high extents of carbonation in olivine, heat-treated serpentine, and wollastonite. However, the independent effects of NaCl and NaHCO3 and their role in mineral carbonation were not sufficiently explained. In this study, the role of varying concentrations of NaCl and NaHCO3 on carbon mineralization of various minerals was elucidated. NaHCO3 buffered the pH and served as a carbon carrier, resulting in higher carbonate conversions. Except in the case of olivine, NaCl had a negligible effect on enhancing mineral carbonation. Unlike NaHCO3, NaCl does not buffer the pH or serve as a carbon carrier, but Cl- may serve as a weak chelating agent can complex with Mg or Ca in the mineral matrix to enhance dissolution. The competing effects of ionic strength and pH swings as the mineral dissolves and carbonation further complicate the role of NaCl on mineral carbonation. Based on the experimental methodologies developed to study carbon mineralization in minerals and rocks at high temperatures and pressures, alternative applications such as the remediation of hazardous alkaline wastes such as asbestos containing materials were identified. Asbestos is composed of chrysotile, a fibrous hydrated magnesium silicate mineral and a form of serpentine known to cause respiratory illnesses. By treating asbestos containing materials with CO2 in the presence of 0.1 M Na-oxalate, dissolution of chrysotile and precipitation of newer phases such as glushinkite (Mg(C2O4)* 2H2O) and magnesite (MgCO3) occurred, which reduced the chrysotile content in asbestos. Based on the methodologies for studying mineral dissolution and carbonation kinetics, and coupled mineral dissolution and carbonation behavior, a scheme for connecting laboratory scale experiments with simulations to estimate the uncertainties associated with carbon mineralization was developed. The effects of temperature, different dissolution rates, and varying levels of surface area changes due to passivation or reactive cracking on the rates of carbon mineralization were simulated using PhreeqC, a computer program developed for geochemical speciation calculations (Parkhurst & Appelo, 1999). Various studies proposed that microfractures and cracks may occur in geologic formations due to the extensive growth of carbonate crystals (Kelemen & Hirth, 2012; Kelemen & Matter, 2008; Matter & Kelemen, 2009; Rudge et al., 2010). Other studies have suggested that the formation of carbonates may plug the pore spaces and limit further reactivity (Hövelmann et al., 2012; King et al., 2010; Xu et al., 2004). The effects of changes in surface area due to the formation of microfractures or passivation due to carbonate growth on the rates of carbon mineralization were also simulated. Overall the results of these studies demonstrate the effect of various parameters on carbon mineralization and how these parameters can be connected to predict CO2 storage in mineral formations. The frameworks to connect laboratory scale experiments with simulations to determine carbon mineralization rates and to assess the risks associated with CO2 injection in reactive formations, can be used to direct future research efforts to predict the fate of injected CO2 with greater accuracy for sensor placement and optimization of CO2 monitoring technologies.

In the wake of concerns about the long-term integrity and containment of sub-surface CO₂ sequestration reservoirs, many efforts have been made to improve the monitoring, verification, and accounting methods for geo-sequestered CO₂. This Ph.D. project has been part of a larger U.S. Department of Energy (DOE) sponsored research project to demonstrate the feasibility of a system designed to tag CO₂ with radiocarbon at a concentration of one part per trillion, which is the ambient concentration of ¹⁴C in the modern atmosphere. Because carbon found at depth is naturally free of ¹⁴C, this tag would easily differentiate pre-existing carbon in the underground from anthropogenic, injected carbon and provide an excellent handle for monitoring its whereabouts in the subsurface. It also creates an excellent handle for adding up anthropogenic carbon inventories. Future inventories in effect count ¹⁴C atoms. Accordingly, we developed a ¹⁴C tagging system suitable for use at the part-per-trillion level. This tagging system uses small containers of tracer fluid of ¹⁴C enriched CO₂. The content of these containers is transferred into a CO₂ stream readied for underground injection in a controlled manner so as to tag it at the part-per-trillion level. These containers because of their shape are referred to in this document as tracer loops. The demonstration of the tracer injection involved three steps. First, a tracer loop filling station was designed and constructed featuring a novel membrane based gas exchanger, which degassed the fluid in the first step and then equilibrated the fluid with CO₂ at fixed pressure and fixed temperature. It was demonstrated that this approach could achieve uniform solutions and prevent the formation of bubbles and degassing downstream. The difference between measured and expected results of the CO₂ content in the tracer loop was below 1%. Second, a high-pressure flow loop was built for injecting, mixing, and sampling of the fast flowing stream of pressurized CO₂ tagged with our tracer. The laboratory scale evaluation demonstrated the accuracy and effectiveness of our tracer loops and injection system. The ¹⁴C/¹²C ratio we achieved in the high pressure flow loop was at the part per trillion level, and deviation between the experimental result and theoretical expectation was 6.1%. Third, a field test in Iceland successfully demonstrated a similar performance whereby ¹⁴CO₂ tracer could be injected in a controlled manner into a CO₂ stream at the part per trillion level over extended periods of time. The deviation between the experimental result and theoretical expectation was 7.1%. In addition the project considered a laser-based ¹⁴C detection system. However, the laser-based ¹⁴C detection system was shown to possess inadequate sensitivity for detecting ambient levels of ¹⁴CO₂. Alternative methods for detecting ¹⁴C, such as saturated cavity absorption ring down spectroscopy and scintillation counting may still be suitable. In summary, the project has defined the foundation of carbon-14 tagging for the monitoring, verification, and accounting of geological carbon sequestration.

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

Mineralization has the potential to capture CO₂. In nature, mineralization is the chemical weathering of alkaline-earth minerals in which stable carbonate minerals are formed, which leads to the removal of CO₂ from the atmosphere. The adsorptive carbonation reaction of olivine ((Mg,Fe)₂SiO₄)), consisting mainly of pure magnesium silicate (Mg₂SiO₄), a main constituent of the Earth’s crust, was carried out to estimate its potential application to the separation of CO₂ in the presence of water vapor in combustion plumes. Based on the thermodynamics for a basis of the reaction mechanism, the olivine carbonation reaction is thermodynamically favorable. Water vapor was found to play an important role in improving the carbonation rate, and experimental results revealed that carbon dioxide carbon dioxide can bind into olivine minerals to form highly stable surface carbonates. The reaction activity of olivine and pure Mg₂SiO₄ in the presence/absence of water vapor was carried out by varying the temperature, reactant concentrations, and space time. Based on changes in CO₂ concentration with time, the reaction kinetic model of pure Mg₂SiO₄carbonation was developed. The reaction order was found to be approximately 1 for CO₂. The activation energy derived for the Arrhenius equation of Mg₂SiO₄-based carbonation is 76.2 ± 4.8 kJ/mol based on the changes in the reaction rates with temperature in the range of 150-200°C. To investigate the molecular reaction mechanism of CO₂ adsorption on the metal oxide surface, forming carbonates, we performed the quantum mechanical calculation of CO₂ adsorption on a CaO (100) surface. It shows that CO₂ molecules strongly react with the CaO surface due to its high reactivity and high basicity. Consequently, this study will basically lay the groundwork for the chemical mechanism of mineral carbonation of olivine with carbon dioxide in the presence of water vapor and as provide relevant information for the practical application of CO₂ sequestration by stable adsorption on mineral silicates.

Compositional reservoir simulation studies were performed to investigate the effect of uncertain reservoir parameters, flood design variables, and economic factors on coupled CO₂ sequestration and EOR projects. Typical sandstone and carbonate reservoir properties were used to build generic reservoir models. A large number of simulations were needed to quantify the impact of all these factors and their corresponding uncertainties taking into account various combinations of the factors. The design of experiment method along with response surface methodology and Monte-Carlo simulations were utilized to maximize the information gained from each uncertainty analysis. The two objective functions were project profit in the form of $/bbl of oil produced and sequestered amount of CO₂ in the reservoir. The optimized values for all objective functions predicted by design of experiment and the response surface method were found to be close to the values obtained by the simulation study, but with only a small fraction of the computational time. After the statistical analysis of the simulation results, the most to least influential factors for maximizing both profit and amount of stored CO₂ are the produced gas oil ratio constraint, production and injection well types, and well spacing. For WAG injection scenarios, the Dykstra-Parsons coefficient and combinations of WAG ratio and slug size are important parameters. Also for a CO₂ flood, no significant reduction of profit occurred when only the storage of CO₂ was maximized. In terms of the economic parameters, it was demonstrated that the oil price dominates the CO₂ EOR and storage. This study showed that sandstone reservoirs have higher probability of need for CO₂i ncentives. In addition, higher CO₂ credit is needed for WAG injection scenarios than continuous CO₂ injection. As the second part of this study, scaling groups for miscible CO₂ flooding in a three-dimensional oil reservoir were derived using inspectional analysis with special emphasis on the equations related to phase behavior. Some of these scaling groups were used to develop a new MMP correlation. This correlation was compared with published correlations using a wide range of reservoir fluids and found to give more accurate predictions of the MMP. / text

The Gulf Coast Carbon Center (GCCC), a branch of the Bureau of Economic Geology of the University of Texas at Austin, conducted a pilot CO2 sequestration experiment in the Oligocene, Frio Formation at the South Liberty Oil Field, Dayton, Texas. Petrographic examination of core samples from the Frio “C” sandstone, ranging in depth from 1500m-1657m, classifies the sandstone as a poorly cemented, subangular to subrounded, subarkose with mean composition of Q70F24L6. Detrital grains are dominated by quartz, plagioclase, K-feldspar, and volcanic rock fragments. Matrix increases with depth. Measured core plug mean porosity is 32% (±3) and mean permeability is 1513md (±872). Point count porosity, dominated by primary intergranular porosity, is 24% (±10). Formation waters, sampled during the sequestration experiment, exhibited a rapid decrease in pH and increases in alkalinity and dissolved metals (Ca, Fe, Mn, Zn, Pb, & Mo). In an effort to identify the source of ions in solution, XRD and SEM analyses were completed. XRD and SEM analyses identify illite/smectite clay coats with rare amounts of kaolinite. SEM with EDAX analyses identified authigenic pyrite, occurring as framboids and euhedral crystals, and lesser amounts of quartz and feldspar overgrowths, and barite. Secondary porosity, through the dissolution of feldspar, is also observed (1% ±1). EDAX analysis of clay grain coats identifies Fe, Si, O, Al, K, Na, and Mg and BSE identifies pyrites (≤ 1μm) intergrown with the clays. Electron microprobe analyses of euhedral and framboidal pyrite were conducted to quantify trace element concentrations. Microprobe analyses identified Mn as the dominant trace element associated with these upper Frio Formation pyrites, indicating that pyrite serves as the source for Fe and Mn ions identified in the formation waters. Alteration mechanisms of the pyrite, allowing the release of Fe and Mn into solution, are still unknown though may result from surface complexes created when the pyrite is exposed to increasing HCO3- concentrations- a by-product of CO2 injection. These data are essential in understanding the chemical changes occurring in the formation and assisting in a model simulation of the Frio sandstone’s chemical reactive properties, all in response to increased CO2 concentrations. This research supports the GCCC’s CO2 sequestration efforts, assessing the Frio Formation as a repository for anthropogenic CO2, and ultimately, atmospheric CO2 reduction / Department of Geology

Global energy consumption will increase in the next decades and it is expected to largely rely on fossil fuels. The use of fossil fuels is intimately related to CO₂ emissions and the potential for global warming. Geological CO₂ storage aims to mitigate the global warming problem by sequestering CO₂ underground. Coupled hydro-chemo-mechanical phenomena determine the successful operation and long term stability of CO₂ geological storage. This research explores various coupled phenomena, identifies different zones in the storage reservoir, and investigates their implications in CO₂ geological storage. Spatial patterns in mineral dissolution and precipitation are examined based on a comprehensive mass balance formulation. CO₂-dissolved fluid flow is modeled using a novel technique that couples laminar flow, advective and diffusive mass transport of species, mineral dissolution, and consequent pore changes to study the reactive fluid transport at the scale of a single rock fracture. The methodology is extended to the scale of a porous medium using pore network simulations to study both CO₂ reservoirs and caprocks. The two-phase flow problem between immiscible CO₂ and the formation fluid (water or brine) is investigated experimentally. Plug tests on shale and cement specimens are used to investigate CO₂ breakthrough pressure. Sealing strategies are explored to plug existing cracks and increase the CO₂ breakthrough pressure. Finally, CO₂-water-surfactant mixtures are evaluated to reduce the CO₂-water interfacial tension in view of enhanced sweep efficiency. Results can be used to identify optimal CO₂ injection and remediation strategies to maximize the efficiency of CO₂ injection and to attain long-term storage.

Thesis (Ph.D.)--University of Alberta, 2009. / Title from PDF file main screen (viewed on Apr. 1, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Geotechnical Engineering, [Department of] Civil and Environmental Engineering, University of Alberta. Includes bibliographical references.