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

Abstract

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. [...]