Saline Aquifers
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Recent papers in Saline Aquifers
Recently, the need to decrease CO2 concentration in the atmosphere has been recognized because of the role of CO2 as a greenhouse gas that contributes to global warming. Carbon Capture and Sequestration (CCS) is one of the most promising... more
Recently, the need to decrease CO2 concentration in the atmosphere has been recognized because of the role of CO2 as a greenhouse gas that contributes to global warming. Carbon Capture and Sequestration (CCS) is one of the most promising long term solutions for the reduction of CO2 in the atmosphere. To this end, injection of CO2 into saline aquifers has been proposed and investigated theoretically and experimentally in the last years. Modeling the storage of CO2 in saline aquifers on a reservoir scale is very demanding with respect to computational cost. Long-term subsurface storage of CO2 in saline aquifers may induce a range of chemical processes in response to disturbances in existing chemical equilibria that include, but are not limited to, dissolution of primary minerals and precipitation of secondary carbonates. CCS projects also can be done above the ground by injecting CO2 into designated fractures. The work presented in this thesis focuses on developing a fundamental understanding and modeling approach for 3 basic aspects of sequestration: 1) the effect of CO2 solubility on rates of geochemical reactions, 2) density of brine after dissolution of CO2, and 3) time dependent porosity variation of a single fracture due to precipitation of carbonates.
A new method is developed to determine the reaction rates of minerals, on the basis of transition state theory, in saline aquifers containing brine and a supercritical CO2 phase. A general Arrhenius-type equation that depends explicitly on the pH of brine is employed to determine the reaction rates. The dependence of pH on the amount of aqueous CO2 dissolved in brine is modeled in this study. An accurate pressure-volume-temperature-composition (PVTx) model is employed to determine the dissolution of supercritical CO2 in brine for the temperature range of 50-100°C and pressures up to 600 bar. Solubility of CO2 and dissolution rate of calcite predicted by the model are validated with experimental data available in the literature for specific thermodynamic and salinity conditions. The effects of CO2 activity on pH and reaction rates are evaluated by means of four different models for the activity coefficient of dissolved CO2. The results indicate that dissolution of CO2 decreases the pH of the system but an increase in the temperature and salinity values limits the pH reduction. The rates of reactions are found to increase with pressure and temperature. The results suggest that among the available mineral compositions in deep saline aquifers, the dissolution rate of anorthite is the rate limiting factor. The significance of the pre-exponential factor and the reaction order associated with the modified Arrhenius equation is evaluated to determine the sensitivity of the reaction rates as a function of the system pH. We find that the transition state theory can reasonably reproduce experimental data with new parameters that we are obtained in this study on the basis of sensitivity analysis. Finally, we develop a long-term geochemical modeling of CO2 storage on a designated fracture above the ground to investigate the impacts of temperature, pressure, and salinity on the reaction rates and, subsequently, the critical time of blockage due to precipitation of carbonates.
With regards to the second focus of this thesis, the effect of CO2 solubility on the density of binary H2O-CO2 and ternary H2O-CO2-NaCl solutions in saline aquifers is investigated. These solution densities as dispensable properties play pivotal roles in estimating the dynamic evolution of plume containing aqueous CO2 and brine and also affect fracture dynamics in geologic media. An improved model is proposed to predict the density of saturated binary and ternary solutions as a function of pressure, temperature, and salinity. The model is based on an extended form of the Redlich-Kwong Equation of State that yields more representative values of the molar volumes of liquid CO2. The extension involves finding new coefficients for the cubic Redlich-Kwong equation to match one of the solutions with the liquid molar volume deduced from experimentally measured density of binary solutions. The new coefficients are constrained to ensure that the solution branch corresponding to the molar volume in the gas phase remains unchanged. Due to variability in the experimentally measured density of binary solutions, an effective liquid molar volume is obtained with the help of a multi-parameter non-linear regression with respect to pressure and temperature. The proposed model is validated by comparing it with experimental data and is used to study the density-pressure-temperature-salinity relationship. It is found that the density of the saturated solution is proportional to the mole fraction of dissolved CO2. In general, solution density is found to increase with pressure but decreases with an increase in temperature within the range of 50-100_C. It is also found that the solution density decreases monotonically with an increase in salinity.
Finally, a new model is presented to simulate a reactive fluid within a fracture. Permeability of a fracture controls the path of aqueous CO2 migration, therefore aperture width of a fracture has a pivotal effect on solubility and mineral trapping of injected CO2. This study investigates the impact of the formation of precipitates within fractures on CO2 transport and storage capacity. The problem involves the flow of CO2 between finite walls that represents a single fracture. Fluid convection, diffusion, and chemical reactions inside a finite space are solved as a simplified representation of natural mineral trapping. The model is composed of direct numerical simulation of incompressible ow and transport combined with the kinetics of corresponding chemical reactions. For each time step, transport and reactions are solved by means of a finite difference method using a sequential non-iterative approach. The purpose of the current study is to show the time evolution of the aperture shrinkage caused by precipitation of calcite. The current model predicts the actual efficiency of the mineral trapping mechanism by considering the physical properties of the fluid such as its density, pH, and the characteristics of the mineral compositions. It is found that for low Peclet numbers (Pe < 100), the critical time for a fracture blockage is insensitive to the Reynolds number and increases with the Peclet number. At a high Peclet number Pe = 1000, however, the critical time generally decreases with increasing Reynolds number.
A new method is developed to determine the reaction rates of minerals, on the basis of transition state theory, in saline aquifers containing brine and a supercritical CO2 phase. A general Arrhenius-type equation that depends explicitly on the pH of brine is employed to determine the reaction rates. The dependence of pH on the amount of aqueous CO2 dissolved in brine is modeled in this study. An accurate pressure-volume-temperature-composition (PVTx) model is employed to determine the dissolution of supercritical CO2 in brine for the temperature range of 50-100°C and pressures up to 600 bar. Solubility of CO2 and dissolution rate of calcite predicted by the model are validated with experimental data available in the literature for specific thermodynamic and salinity conditions. The effects of CO2 activity on pH and reaction rates are evaluated by means of four different models for the activity coefficient of dissolved CO2. The results indicate that dissolution of CO2 decreases the pH of the system but an increase in the temperature and salinity values limits the pH reduction. The rates of reactions are found to increase with pressure and temperature. The results suggest that among the available mineral compositions in deep saline aquifers, the dissolution rate of anorthite is the rate limiting factor. The significance of the pre-exponential factor and the reaction order associated with the modified Arrhenius equation is evaluated to determine the sensitivity of the reaction rates as a function of the system pH. We find that the transition state theory can reasonably reproduce experimental data with new parameters that we are obtained in this study on the basis of sensitivity analysis. Finally, we develop a long-term geochemical modeling of CO2 storage on a designated fracture above the ground to investigate the impacts of temperature, pressure, and salinity on the reaction rates and, subsequently, the critical time of blockage due to precipitation of carbonates.
With regards to the second focus of this thesis, the effect of CO2 solubility on the density of binary H2O-CO2 and ternary H2O-CO2-NaCl solutions in saline aquifers is investigated. These solution densities as dispensable properties play pivotal roles in estimating the dynamic evolution of plume containing aqueous CO2 and brine and also affect fracture dynamics in geologic media. An improved model is proposed to predict the density of saturated binary and ternary solutions as a function of pressure, temperature, and salinity. The model is based on an extended form of the Redlich-Kwong Equation of State that yields more representative values of the molar volumes of liquid CO2. The extension involves finding new coefficients for the cubic Redlich-Kwong equation to match one of the solutions with the liquid molar volume deduced from experimentally measured density of binary solutions. The new coefficients are constrained to ensure that the solution branch corresponding to the molar volume in the gas phase remains unchanged. Due to variability in the experimentally measured density of binary solutions, an effective liquid molar volume is obtained with the help of a multi-parameter non-linear regression with respect to pressure and temperature. The proposed model is validated by comparing it with experimental data and is used to study the density-pressure-temperature-salinity relationship. It is found that the density of the saturated solution is proportional to the mole fraction of dissolved CO2. In general, solution density is found to increase with pressure but decreases with an increase in temperature within the range of 50-100_C. It is also found that the solution density decreases monotonically with an increase in salinity.
Finally, a new model is presented to simulate a reactive fluid within a fracture. Permeability of a fracture controls the path of aqueous CO2 migration, therefore aperture width of a fracture has a pivotal effect on solubility and mineral trapping of injected CO2. This study investigates the impact of the formation of precipitates within fractures on CO2 transport and storage capacity. The problem involves the flow of CO2 between finite walls that represents a single fracture. Fluid convection, diffusion, and chemical reactions inside a finite space are solved as a simplified representation of natural mineral trapping. The model is composed of direct numerical simulation of incompressible ow and transport combined with the kinetics of corresponding chemical reactions. For each time step, transport and reactions are solved by means of a finite difference method using a sequential non-iterative approach. The purpose of the current study is to show the time evolution of the aperture shrinkage caused by precipitation of calcite. The current model predicts the actual efficiency of the mineral trapping mechanism by considering the physical properties of the fluid such as its density, pH, and the characteristics of the mineral compositions. It is found that for low Peclet numbers (Pe < 100), the critical time for a fracture blockage is insensitive to the Reynolds number and increases with the Peclet number. At a high Peclet number Pe = 1000, however, the critical time generally decreases with increasing Reynolds number.
Motivated by geological carbon dioxide (CO2) storage, we present a vertical-equilibrium sharp-interface model for the migration of immiscible gravity currents with constant residual trapping in a two-dimensional confined aquifer. The... more
Motivated by geological carbon dioxide (CO2) storage, we present a vertical-equilibrium sharp-interface model for the migration of immiscible gravity currents with constant residual trapping in a two-dimensional confined aquifer. The residual acts as a loss term that reduces the current volume continuously. In the limit of a horizontal aquifer, the interface shape is self-similar at early and at late times. The spreading of the current and the decay of its volume are governed by power-laws. At early times the exponent of the scaling law is independent of the residual, but at late times it decreases with increasing loss. Owing to the self-similar nature of the current the volume does not become zero, and the current continues to spread. In the hyperbolic limit, the leading edge of the current is given by a rarefaction and the trailing edge by a shock. In the presence of residual trapping, the current volume is reduced to zero in finite time. Expressions for the up-dip migration distance and the final migration time are obtained. Comparison with numerical results shows that the hyperbolic limit is a good approximation for currents with large mobility ratios even far from the hyperbolic limit. In gently sloping aquifers, the current evolution is divided into an initial near-parabolic stage, with power-law decrease of volume, and a later near-hyperbolic stage, characterized by a rapid decay of the plume volume. Our results suggest that the efficient residual trapping in dipping aquifers may allow CO2 storage in aquifers lacking structural closure, if CO2 is injected far enough from the outcrop of the aquifer.
Many countries play an important role to carbon capture, utilization, and Storage (CCUS) to reduce emission. Geological storage is an important approach to cope with climate change. Live oil combined with saline aquifers and gas... more
Many countries play an important role to carbon capture, utilization, and Storage (CCUS) to reduce emission. Geological storage is an important approach to cope with climate change. Live oil combined with saline aquifers and gas reservoirs are among the candidates for carbon dioxide (CO2) sequestration, owing to their proven sealing capabilities and characterization. CO2 mainly from power industrial was captured to improve oil recovery in some oilfields in China, and solubility is a key factor to evaluate storage ability of reservoir and saline aquifer. In this paper, CO2 sequestration mechanisms in deplete reservoir and saline aquifer were explained. An experimental method to test solubility of CO2 in emulsion system of liver oil and brine was developed. The experimental results showed that with the salinity increased, the solubility of CO2 in reservoir oil increased slightly, and the solubility of CO2 in brine decreased. Salinity has little impact on solubility of CO2 in reservoir oil. With the pressure increased, the solubility of CO2 in reservoir oil and brine both increased. Molecular diameter of reservoir oil and white oil have inverse proportion relationship with the solubility Research on solubility of CO2 in brine and reservoir oil for depleted reservoir in China enabled us to better predict and deal with the challenges for rapid development of carbon storage.