The Cranfield field, located in southwest Mississippi, is an enhanced oil recovery and carbon sequestration project that has been under a continuous supercritical CO₂ injection by Denbury Onshore LLC since 2008. Two 3D seismic surveys were collected in 2007, pre-CO₂ injection, and in 2010 after > 2 million tons of CO₂ was injected into the subsurface. The goal of this study is to characterize a time-lapse response between two seismic surveys to understand where injected CO₂ is migrating and to map the injected CO₂ plume edge. In order to characterize a time-lapse response, the seismic surveys were cross equalized using a trace-by-trace time shift. A normalized root-mean-square (NRMS) difference value was then calculated to determine the repeatability of the data. The data were considered to have “good repeatability,” so a difference volume was calculated and showed a coherent seismic amplitude anomaly located through the area of interest. A coherent seismic amplitude anomaly was also present below the area of interest, so a time delay analysis was performed and calculated a significant added velocity change. A Gassmann-Wood fluid substitution workflow was then performed at two well locations to predict a saturation profile and observe post-injection expected changes in compressional velocity values at variable CO₂ saturations. Finally, acoustic impedance inversions were performed on the two seismic surveys and an acoustic impedance difference volume was calculated to compare with the fluid substitution results. The Gassmann-Wood fluid substitution results predicted smaller changes in acoustic impedance than those observed from acoustic impedance inversions. At the Cranfield field, time-lapse seismic analysis was successful in mapping and quantifying the acoustic impedance change for some seismic amplitude anomalies associated with injected CO₂. Additional well log data and refinement of the fluid substitution workflow and the model-based inversion performed is necessary to obtain more accurate impedance changes throughout the field instead of at a single well location. / text

During carbon dioxide (CO₂) sequestration, CO₂ injection suffers from viscous fingering and low sweep efficiency. In addition, the lower density of CO₂ compared to in-situ brine leads to the possibility of sequestered CO₂ rising up through the relatively permeable path in the cap rock and being emitted back out to the atmosphere. This research proposes a mechanism of CO₂-in-brine emulsion stabilization by surface-coated nanoparticles as a potential cure for these problems. This mechanism is studied in detail by conducting a series of core floods to investigate the interactions between nanoparticles and the surroundings such as fluids and rock surfaces during nanoparticle transport in sedimentary rocks. The experiments presented here use n-octane as a low-pressure analog fluid to supercritical CO₂ as they share several key characteristics. Comparisons of pressure drop and CT images from drainage displacement experiments with and without nanoparticles show that nanoparticle-stabilized emulsions were generated in-situ in highly permeable and homogeneous Boise sandstones tested in this study. Roof snap-off is proposed as the key mechanism for generating the emulsions. The imbibition experiment presents a case where Roof snap-off does not occur. The pressure drop for the control experiment and the nanoparticle experiments confirmed that without Roof snap-off nanoparticles do not affect the dynamics of the displacement except for the viscosity increase of the aqueous phase. However, it was inferred from the saturation profiles and effluent concentration history that nanoparticles were traveling faster than the aqueous phase in which they were dispersed and accumulating at the main displacement front. Inaccessible pore volume is proposed as a mechanism responsible for the accelerated transport of nanoparticles. The single-phase flow experiments demonstrate the accelerated transport of nanoparticles in porous media that was invoked to explain observations during imbibition displacement. During these experiments, tracer and nanoparticles were simultaneously injected into a porous medium and their effluent concentrations were monitored using a UV-Vis detector. The results show that nanoparticles traveled faster than the tracer in Boise and Berea sandstones studied in this research. Two-site model developed by Zhang (2012) was used to fit the data. Simulations suggested that the two-site model could replicate the overall shape of the experimental data when a slug of nanoparticle dispersion was injected, but it was not able to accurately predict the leading edge and the trailing edge of the effluent concentration history, where nanoparticles appeared before tracer due to accelerated transport. To account for the enhanced transport of nanoparticles, a modified two-site model with an acceleration factor, E, is proposed. The resulting fit matched the experimental data better than the original two-site model. / text

Leakage of CO₂ saturated fluid along wellbores has critical implications for the feasibility of geologic CO₂ storage. Wells, which are ubiquitous in locations ideal for CO₂ storage, develop leaks (e.g. fractures) for many reasons and at different points in their age. Small leaks pose the most significant risk to geological CO₂ sequestration because they are difficult to detect and provide a direct pathway through which fluid can escape the storage formation. This dissertation shows that due to complex coupling between reaction and flow, leaking wells will tend to self-seal via secondary precipitation of calcium carbonate in the open pathway. Residence time, fluid reactivity, and initial fracture aperture all play a key role in determining the time required to seal the leakage pathway. To test the self-sealing hypothesis, laboratory experiments were conducted to inject reactive fluids into naturally fractured cement. Restriction of the leakage pathway, i.e., the fracture, was inferred from the relationship between flow rate and pressure differential. Precipitation was observed in both constant flow rate and constant pressure differential experiments. In the former precipitation resulted in an increasing pressure differential, while precipitation caused a decrease in flow rate in the latter. Analysis by electron microprobe and x-ray diffraction, and corroborated with effluent chemical analysis, showed that the reacted channel was depleted in calcium and enriched in silicon relative to the original material. The remaining silicon rich material prevents widening of the reacted channel and development a self-enhancing (e.g. wormhole) behavior. Self-limiting behavior is caused by calcium mixing with carbonate ions in high pH slow flow regions where local residence time is large and calcium carbonate is insoluble. Secondary precipitation initially develops next to the reacted channel and then across the fracture surface and is the source of pathway restriction and the self-sealing behavior. Results from the experiments are used to develop a simple analytical model to forecast well scale leakage. Future work is needed to test a broader range of experimental conditions (e.g. brine salinity, cement formulations, cement-earth interface, effect of CO₂ saturation, pressure, and temperature), to improve our understanding of both the fundamental behavior and the leakage model. / text

Geologic sequestration of CO₂ in deep saline aquifers has been studied extensively over the past two decades as a viable method of reducing anthropological carbon emissions. The monitoring and prediction of the movement of injected CO₂ is important for assessing containment of the gas within the storage volume, and taking corrective measures if required. Given the uncertainty in geologic architecture of the storage aquifers, it is reasonable to depict our prior knowledge of the project area using a vast suite of aquifer models. Simulating such a large number of models using traditional numerical flow simulators to evaluate uncertainty is computationally expensive. A novel stochastic workflow for characterizing the plume migration, based on a model selection algorithm developed by Mantilla in 2011, has been implemented. The approach includes four main steps: (1) assessing the connectivity/dynamic characteristics of a large prior ensemble of models using proxies; (2) model clustering using the principle component analysis or multidimensional scaling coupled with the k-mean clustering approach; (3) model selection using the Bayes' rule on the reduced model space, and (4) model expansion using an ensemble pattern-based matching scheme. In this dissertation, two proxies have been developed based on particle tracking in order to assess the flow connectivity of models in the initial set. The proxies serve as fast approximations of finite-difference flow simulation models, and are meant to provide rapid estimations of connectivity of the aquifer models. Modifications have also been implemented within the model selection workflow to accommodate the particular problem of application to a carbon sequestration project. The applicability of the proxies is tested both on synthetic models and real field case studies. It is demonstrated that the first proxy captures areal migration to a reasonable extent, while failing to adequately capture vertical buoyancy-driven flow of CO₂. This limitation of the proxy is addressed in the second proxy, and its applicability is demonstrated not only in capturing horizontal migration but also in buoyancy-driven flow. Both proxies are tested both as standalone approximations of numerical simulation and within the larger model selection framework. / text

This dissertation focuses on quantitatively interpreting the elastic properties of the Cranfield reservoir for CO₂ saturation. In this work, quantitative interpretation starts by examining the relationship between CO₂ saturation and the elastic properties of the reservoir. This relationship comes from a rock-physics model calibrated to measured well data. Seismic data can then be inverted using a model for CO₂ saturation and rock-property estimates. The location and saturation of injected CO₂ are important metrics for monitoring the long-term effectiveness of carbon capture utilization and storage. Non-uniform CO₂ saturation is a contributing factor to both lateral and time-lapse changes in the elastic properties of the Cranfield reservoir. In the Cranfield reservoir, CO₂ saturation and porosity can be estimated from the ratio of P-wave velocity (Vp) to S-wave velocity (Vs) and P-impedance (Ip), respectively. Lower values of Ip for a given rock matrix often correlate to higher porosity. Similarly, for a given area of the reservoir, lower Vp/Vs frequently can be associated with higher CO₂ saturation. If a constant porosity from the baseline to the time-lapse survey is assumed, changes in Ip over time can be attributed to changes in CO₂ saturation in lieu of using Vp/Vs. Decreases in Ip between the baseline and time-lapse survey can be attributed to increases in CO₂ saturation. With a rock-physics model calibrated to the reservoir, Ip and Is from a vertical seismic profile were correlated to statistical ranges of porosity and CO₂ saturations. To expand the lateral interpretation of reservoir porosity and CO₂ saturation, the time-variant changes in Ip between baseline and time-lapse surface seismic datasets were compared to changes in CO₂ saturation calculated from the rock-physics model. Characterizing the CO₂ saturation of the Tuscaloosa sandstones helped to establish a workflow for estimating reservoir properties and fluid saturation from multiple types of geophysical data. Additionally, this work helped establish an understanding for how CO₂ injected into a reservoir alters and changes the elastic properties of the reservoir and the degree to which those changes can be detected using geophysical methods. / text

Geological carbon dioxide (CO₂) capture and storage in geological formations has the potential to reduce anthropogenic emissions. The viability of technology depends on the long-term security of the geological CO₂ storage. Dissolution of CO₂ into the brine, resulting in stable stratification, has been identified as the key to long-term storage security. The dissolution rate determined by convection in the brine is driven by the increase of brine density with CO₂ saturation. Here we present a new analog laboratory experiment system to characterize convective dissolution in homogeneous porous medium. By understanding the relationship between dissolution and the Rayleigh number in homogeneous porous media, we can evaluate if convective dissolution occurs in the field and, in turn, to estimate the security of geological CO₂ storage fields. The large experimental assembly will allow us to quantify the relationship between convective dynamics and the Rayleigh number of the system, which could be essential to trapping process at Bravo Dome. A series of pictures with high resolution are taken to show the existence and movement of fingers of analog fluid. Also, these pictures are processed, clearly showed the concentration of analog fluid, which is essential to analyze the convective dissolution in detail. We measured the reduction in the convective flux due to hydraulic dispersion effect compared to that in homogeneous media, to determine if convective dissolution is an important trapping process at Bravo Dome. / text

When CO₂ is injected in deep saline aquifers on the scale of gigatonnes, pressure buildup in the aquifer during injection will be a critical issue. Because fracturing, fault activation and leakage of brine along pathways such as abandoned wells all require a threshold pressure (Nicot et al., 2009); operators and regulators will be concerned with the spatial extent of the pressure buildup. Thus a critical contour of overpressure is a convenient proxy for risk. The location of this contour varies depending on the target aquifer properties (porosity, permeability etc.), the geology (presence of faults, abandoned wells etc.), and boundary conditions. Importantly, the extent also depends on relative permeability (Burton et al., 2008). First we describe ways of quantifying the risk due to pressure buildup in an aquifer with a constant pressure boundary, using the three-region injection model to derive analytical expressions for a specific contour of overpressure at any given time. All else being the same, the two-phase-region mobilities (and hence relative permeability characteristics) provide a basis for the ranking of storage formations based on risk associated with pressure elevation during injection. The pressure buildup during CO₂ injection will depend strongly upon the boundary conditions at the boundary of the storage formation. An analytical model for pressure profile in the infinite-acting aquifer is developed by combining existing water influx models in traditional reservoir engineering (Van-Everdingen and Hurst model, Carter-Tracy model) to the current problem for describing brine efflux from the storage aquifer when CO₂ injection creates a "three-region" saturation distribution. We determine evolution of overpressure with time for constant pressure, no-flow and infinite-acting boundary conditions, and conclude that constant pressure and no-flow boundary conditions give the most optimistic and pessimistic estimates of risk respectively. Compositional reservoir simulation results, using CMG-GEM simulator are presented, to show the effect of an isolated no-flow boundary on pressure buildup and injectivity in saline aquifers. We investigate the effect of multiple injection wells on single-phase fluid flow on aquifer pressure buildup, and demonstrate the use of an equivalent injection well concept to approximate the aquifer pressure profile. We show a relatively inexpensive method of predicting the presence of unanticipated heterogeneities in the formation, by employing routine measurements such as injection rate and injection pressure to track deviation in the plume path. This idea is implemented by combining Pro-HMS (probabilistic history matching software, that carries out geologically consistent parameter estimation), and a CMG-GEM model which has been tuned to the physics of the CO₂-brine system. / text

In this study, the co-optimization of carbon dioxide sequestration and enhanced oil recovery and the co-optimization of carbon dioxide sequestration and methane recovery studies were discussed. Carbon dioxide emissions in the atmosphere are one of the reasons of global warming and can be decreased by capturing and storing carbon dioxide. Our aim in this study is to maximize the amount of carbon dioxide sequestered to decrease carbon dioxide emissions in the atmosphere and maximize the oil or methane recovery to increase profit or to make a project profitable. Experimental design and response surface methodology are used to co-optimize the carbon dioxide sequestration and enhanced oil recovery and carbon dioxide sequestration and methane recovery. At the end of this study, under which circumstances these projects are profitable and under which circumstances carbon dioxide sequestration can be maximized, are given. / text

To address the environmental changes associated with increasing levels of atmospheric CO?, a possibility of mineralizing CO? with the species such as Ca°? and M°? ions that are already present in sea water was studied. A series of experiments conducted at temperatures in the range of 20 to 40°C showed that the activation energy for the formation of nesquehonite (MgCO?°3H?O) is 64.6 kJ/mol. It was found that the activation energy barrier can be readily overcome by simple agitation and heating at slightly elevated temperatures, e.g., 40°C. The kinetics of mineralization and the %M°? ion utilization varies depending on energy dissipation rate, temperature, pH, and NaCl concentration. The maximum M°? ion utilization achieved was 86%. Thermodynamic calculations were carried out to construct the species distribution diagrams, predict the pH of CO? mineralization, and to predict %Mg ion utilization (or extraction) from sea water. To address the issues concerning the acidification of sea water during CO? mineralization, spent solutions were treated with basic minerals such as limestone and olivine. It was found that in the presence of these minerals the pH rises to the pH of minimum solubility of the buffering mineral. The pH of minimum solubility of limestone is 8.3 and that of olivine is 8.6. Other means of pH neutralization were also discussed. / Master of Science

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.