Effect of Salts on Interfacial Tension and CO2 Mass Transfer in Carbonated Water Injection

Carbonated water injection (CWI) is a promising enhanced oil recovery (EOR) and CO2 sequestration method, which overcomes the problems associated with CO2 EOR. CO2 mass transfer and interfacial tension (IFT) are important parameters that influence oil recovery efficiency. This study addresses the impact of MgCl2 and Na2SO4 in carbonated water (CW) on CW/hydrocarbon IFT and CO2 mass transfer. An axisymmetric drop shape analysis was used to estimate the IFT and the CO2 diffusion coefficient. It was found that CW+MgCl2 reduced both the CW/n-decane IFT (36.5%) and CO2 mass transfer, while CW+Na2SO4 increased both the IFT and CO2 mass transfer (57%). It is suggested that reduction in IFT for CW+MgCl2 brine is mainly due to the higher hydration energy of Mg2+. The Mg2+ ion forms a tight bond to the first hydration shell [Mg(H2O)6]2+, this increases the effective size at the interface, hence reduce IFT. Meanwhile, the SO42− outer hydration shell has free OH groups, which may locally promote CO2 mass transfer. The study illustrates the potential of combining salts and CW in enhancing CO2 mass transfer that can be the base for further investigations. Furthermore, the contribution and proposed mechanisms of the different ions (SO42− and Mg2+) to the physical process in carbonated water/hydrocarbon have been addressed, which forms one of primary bases of EOR.publishedVersio

Influence of Fracture Heterogeneity Using Linear Congruential Generator (LCG) on the Thermal Front Propagation in a Single Geothermal Fracture-Rock Matrix System

An implicit finite difference numerical model has been developed to investigate the influence of fracture heterogeneity on the propagation of thermal front in a single horizontal fracture-matrix system. Instead of depending on a complex and data-demanding geostatistical method for a precise representation of fracture aperture, a statistical linear congruential generator (LCG) method was applied in the present study to replicate the unpredictable nature of fracture aperture morphology. The results have been compared with the parallel plate model and simple sinusoidal model. Finally, sensitivity analysis of fracture aperture size and fluid flow rate has been carried out to identify the conditions at which fracture heterogeneity is critical. The results indicate that LCG-aperture enhances the heat transfer between fracture and hot rock matrix compared to the parallel and sinusoidal fractures. Further, the temperature profiles in hot rock indicate that there was a greater loss of heat for the case of LCG-aperture (25% loss) compared to sinusoidal (16%) and parallel plate (8%) apertures. It was found that heterogeneity does not play a major role at small fracture aperture size (≤50 μm) and at low flow rates. However, as fracture aperture size increases, the heterogeneity plays a vital part even at low flow rates.publishedVersio

Reliability analysis of 15MW horizontal axis wind turbine rotor blades using fluid-structure interaction simulation and adaptive kriging model

Over the course of the last four decades, the rotor diameter of Horizontal Axis Wind Turbines (HAWTs) has undergone a substantial increase, expanding from 15 m (30 kW) to an impressive 240 m (15MW), primarily aimed at enhancing their power generation capacity. This growth in blade swept area, however, gives rise to heightened loads, stresses and deflections, imposing more rigorous demands on the structural robustness of these components. To prevent sudden failure and to plan effective inspection, maintenance, and repair activities, it is vital to estimate the reliability of the rotor blades by considering all the forces (aerodynamic and structural dynamics) acting on them over the turbine’s lifespan. This research proposes a comprehensive methodology that seamlessly combines fluid-structure interaction (FSI) simulation, Kriging model/algorithm and Adaptive Kriging Monte Carlo Simulation (AKMCS) to assess the reliability of the HAWT rotor blades. Firstly, high-fidelity FSI simulations are performed to investigate the dynamic response of the rotor blade under varying wind conditions. Recognizing the computationally intensive nature and time-consuming aspects of FSI simulations, a judicious approach involves harnessing an economical Kriging model as a surrogate. This surrogate model adeptly predicts blade deflection along its length, utilizing training and testing data derived from FSI simulations. Impressively, the Kriging model predicts blade deflection 400 times faster than the FSI simulations, showcasing its enhanced efficiency. The optimized surrogate model is then used to estimate the flap wise blade tip deflection for one million wind speed samples generated using Weibull distribution. Thereafter, to evaluate the reliability of the blades, statistical modeling using methods such as Monte Carlo Simulation (MCS), AKMCS is performed. The results demonstrate the faster convergence of AKMCS requiring only 21 samples, as opposed to 1 million samples for MCS with minimal reduction in the precision of the estimated probability of failure (Pf) and reliability index (β). Demonstrated on the backdrop of an IEA-15MW offshore reference WT rotor blade, the proposed methodology underscores its potential to be seamlessly incorporated into the creation of WT digital twins, due to its near real-time predictive capabilities for Pf and β assessments.Reliability analysis of 15MW horizontal axis wind turbine rotor blades using fluid-structure interaction simulation and adaptive kriging modelacceptedVersio

CO2 mass transfer and interfacial studies for application of carbonated water injection: Axisymmetric pendant drop analysis for simultaneous calculation of CO2 diffusion coefficient and interfacial tension

Worldwide, enhanced oil recovery (EOR) projects have been on a gradual rise since early 2000, especially EOR by CO2 injection. Globally, at present, EOR by CO2 injection contributes approximately 67.5% of projects (83 of 123) among carbonate reservoirs, and approximately 23.5% of projects (50 of 213) among sandstone reservoirs and is expected to rise by 0.1 % per year. Additionally, the application of CO2-EOR is expected to increase, due to its contribution to mitigating anthropogenic CO2 (geological CO2 sequestration). However, problems associated with CO2-EOR, such as poor sweep efficiency, early breakthrough, high transportation cost, and trouble of CO2 availability, have reduced its value. Additionally, CO2-EOR may not be a safe option for geological storage of CO2, due to the upward movement of injected CO2. These problems have lead to the search for alternative injection strategies, which can increase EOR efficiency and, at the same time, promote increased CO2 geological storage capacity. In recent years, carbonated water injection (CWI) has shown to be a promising enhanced oil recovery (EOR) method and a suitable alternative to CO2-EOR. Laboratory and field studies have demonstrated that the injection of CO2 saturated water (carbonated water, CW) is a practical option for both EOR and CO2 sequestration. From an EOR point of view, carbonated water injection (CWI) enhances the sweep efficiency and mobility by reducing the gravity segregation that is frequently encountered by CO2-EOR, hence increasing the residual oil recovery. In addition to the EOR method, the CWI also promotes safe, increased, and long-term geological storage of CO2, as the carbonated water has a higher density, compared to native brine (formation water). At the pore scale CO2 mass transfer, fluid-fluid interfacial phenomena, mass transfer kinetics, and property alteration of hydrocarbon are critical in understanding and optimising CWI. CO2 mass transfer into the oil, coupled with CW-oil interfacial tension (IFT) alterations, is one of the first and primary processes which affect critical parameters like viscosity and density alterations, swelling and hence mobilisation of hydrocarbon. However, there is a lack of understanding of CO2 mass transfer and interfacial phenomena, and the factors influencing them for both CO2- EOR and CWI. Further, unlike other recovery methods, such as waterflooding and CO2-EOR, for CWI the effect of additives like salts and nanoparticles has not been fully understood.This thesis aims to address five main aspects that have been overlooked and are critical in understanding the mechanisms that form the principal part of oil recovery by CWI. The first is the estimation of CWhydrocarbon IFT and the development of a method to estimate the dynamic IFT. The second is to develop a mathematical and numerical model, which validates with experimental results, for calculating the effective CO2 diffusion coefficient. The model should be versatile so that it may be applied for both CO2-hydrocarbon and CW-hydrocarbon systems. The third is to analyse the interdependency of critical parameters such as diffusion coefficient, IFT, density, viscosity, mass/mole fraction, Gibbs free energy, temperature, pressure, and concentration gradient. The fourth aspect is to investigate the influence of combining additives such as nanoparticles/nanofluid and salts with CW on CO2 mass transfer and interfacial properties. Finally, the influence of three phases of CO2 (gas, liquid, and supercritical) on the IFT, CO2 mass transfer, and fluid properties of liquids in which CO2 is dissolved must be studied. [...

Colloid transport in a single fracture-matrix system: Gravity effects, influence of colloid size and density

A numerical model was developed to investigate the influence of gravitational force on the transport of colloids in a single horizontal fracture–matrix system. Along with major transport phenomena, prominence was given to study the mass flux at the fracture–matrix interface, and colloid penetration within the rock matrix. Results suggest that the gravitational force significantly alters and controls the velocity of colloids in the fracture. Further, it was shown that the colloid density and size play a vital part in determining the extent that gravity may influence the transport of colloids in both fracture and rock matrix. The mass flux transfer across the fracture–matrix interface is predominantly dependent on the colloidal size. As large as 80% reduction in penetration of colloids in the rock matrix was observed when the size of the colloid was increased from 50–600 nm. Similarly, the farther the density of colloid from that of the fluid in the fracture (water), then the higher the mitigation of colloids in the fracture and the rock matrix. Finally, a non-dimensional parameter “Rock Saturation Factor” has been presented in the present study, which can offer a straightforward approach for evaluating the extent of penetration of colloids within the rock matrix.publishedVersio

Dynamic interfacial tension measurement method using axisymmetric drop shape analysis

The current method describes a simple modification to the dynamic and equilibrium interfacial tension (IFT) measurement in a multiphase system (gas-liquid/liquid-liquid) by the Axisymmetric Drop Shape Analysis (ADSA) pendant drop technique. The primary difficulty associated with dynamic IFT measurement by ADSA is providing the appropriate phase densities, especially in a system consisting of gas (CO2, methane, and propane) and liquids (water and hydrocarbon). The density of the phases is calculated using a, considering the solubility og gases in liquids, as a function of time. The calculated densities of the phases are then used as inputs in the experiment to measure the IFT at high pressure and temperature PVT-cell. The method offers benefit such as: • Straightforward and cost effective as it does not require additional experimental setup (like density meter) or a complicated equation of state. • The composition of the binary mixtures (mole and mass) and the density changes of the binary mixture due to mass transfer may be obtained as a function of time at fixed pressure and temperature. • IFT as a function of time is measured by taking into consideration of correct phase density.publishedVersio

Combining Computational Fluid Dynamics and Gradient Boosting Regressor for Predicting Force Distribution on Horizontal Axis Wind Turbine

The blades of the horizontal axis wind turbine (HAWT) are generally subjected to significant forces resulting from the flow field around the blade. These forces are the main contributor of the flow-induced vibrations that pose structural integrity challenges to the blade. The study focuses on the application of the gradient boosting regressor (GBR) for predicting the wind turbine response to a combination of wind speed, angle of attack, and turbulence intensity when the air flows over the rotor blade. In the first step, computational fluid dynamics (CFD) simulations were carried out on a horizontal axis wind turbine to estimate the force distribution on the blade at various wind speeds and the blade’s attack angle. After that, data obtained for two different angles of attack (4◦ and 8◦) from CFD acts as an input dataset for the GBR algorithm, which is trained and tested to obtain the force distribution. An estimated variance score of 0.933 and 0.917 is achieved for 4◦ and 8◦, respectively, thus showing a good agreement with the force distribution obtained from CFD. High prediction accuracy and less time consumption make GBR a suitable alternative for CFD to predict force at various wind velocities for which CFD analysis has not been performed

Colloid transport in a single fracture-matrix system: Gravity effects, influence of colloid size and density

A numerical model was developed to investigate the influence of gravitational force on the transport of colloids in a single horizontal fracture–matrix system. Along with major transport phenomena, prominence was given to study the mass flux at the fracture–matrix interface, and colloid penetration within the rock matrix. Results suggest that the gravitational force significantly alters and controls the velocity of colloids in the fracture. Further, it was shown that the colloid density and size play a vital part in determining the extent that gravity may influence the transport of colloids in both fracture and rock matrix. The mass flux transfer across the fracture–matrix interface is predominantly dependent on the colloidal size. As large as 80% reduction in penetration of colloids in the rock matrix was observed when the size of the colloid was increased from 50–600 nm. Similarly, the farther the density of colloid from that of the fluid in the fracture (water), then the higher the mitigation of colloids in the fracture and the rock matrix. Finally, a non-dimensional parameter “Rock Saturation Factor” has been presented in the present study, which can offer a straightforward approach for evaluating the extent of penetration of colloids within the rock matrix

Interfacial tension and CO2 diffusion coefficients for a CO2 + water and n-decane system at pressures of 10 to 160 bar

The objective of this study is to address the influence of different CO2 phases and degrees of CO2 saturation on the interfacial tension and the diffusion of CO2 into a hydrocarbon drop. Axisymmetric drop shape analysis on a pendant drop was used to carry out experiments in a pressure range of 10 to 160 bar and temperatures of 25 °C, 35 °C, and 45 °C, thus covering the gaseous, liquid, and supercritical phases of CO2. A numerical model that estimates the diffusion coefficient of CO2 in the hydrocarbon was developed. The IFT between the carbonated water and the hydrocarbon increases with pressure in the gaseous phase of CO2 and decreases in the liquid and supercritical CO2 phases. Interestingly, when the pressure was increased above 120 bar, the IFT did not change (decrease); this indicates that above this pressure, complete miscibility may not be achieved for this system, as indicated by the stable IFT. From the results, it can be concluded that the maximum IFT, maximum density decrease, and minimum diffusion coefficient occurred at pressures near to and below the phase change pressure of CO2 (64 bar at 25 °C and 74 bar at 35 °C and 45 °C). Both CO2–water–hydrocarbon and CW–hydrocarbon systems show the same trends; however, there were significant differences in the CO2 mass transfer rate and the concentration gradient.publishedVersio

Combining Computational Fluid Dynamics and Gradient Boosting Regressor for Predicting Force Distribution on Horizontal Axis Wind Turbine

The blades of the horizontal axis wind turbine (HAWT) are generally subjected to significant forces resulting from the flow field around the blade. These forces are the main contributor of the flow-induced vibrations that pose structural integrity challenges to the blade. The study focuses on the application of the gradient boosting regressor (GBR) for predicting the wind turbine response to a combination of wind speed, angle of attack, and turbulence intensity when the air flows over the rotor blade. In the first step, computational fluid dynamics (CFD) simulations were carried out on a horizontal axis wind turbine to estimate the force distribution on the blade at various wind speeds and the blade’s attack angle. After that, data obtained for two different angles of attack (4° and 8°) from CFD acts as an input dataset for the GBR algorithm, which is trained and tested to obtain the force distribution. An estimated variance score of 0.933 and 0.917 is achieved for 4° and 8°, respectively, thus showing a good agreement with the force distribution obtained from CFD. High prediction accuracy and less time consumption make GBR a suitable alternative for CFD to predict force at various wind velocities for which CFD analysis has not been performed