Dissolution and Exsolution Kinetics of Ethane/Bitumen and Vapor-Liquid Equilibrium of Ethane/Bitumen/Water System for Applications to Solvent-Aided Recovery Processes
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2024-09-17
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Abstract
This thesis presents an experimental study on the dissolution and exsolution kinetics and vapor-liquid equilibrium of ethane/bitumen system applicable to solvent aided recovery processes. In heavy oil and bitumen recovery, dissolution occurs across the gas-liquid interface when gaseous solvents are injected to enhance oil recovery. On the other hand, when gas-saturated oil undergoes a pressure drop, exsolution (degassing) of gaseous solvents happens from the heavy oil phase, whereby the supersaturation aiding the oil recovery. The phase behavior and thermophysical properties of solvent/bitumen system are also of crucial importance for heavy oil and bitumen in-situ recovery techniques. This thesis experimentally examines the dissolution and exsolution kinetics of ethane/bitumen system, phase equilibria of ternary ethane/water/bitumen mixtures, and related thermophysical properties to address an evident knowledge gap in the literature. First, a PVT setup was used to measure the exsolution/dissolution kinetics of ethane and bitumen systems across the test temperature range of 80–140 ℃, and a pressure difference of 0.69 and 0.35 MPa. An analytical model was adopted to analyze the experimental data for the estimation of the exsolution and dissolution coefficients. The diffusivity values for the exsolution and dissolution processes were estimated to be in the range of (2.65-10.48) × 10-8 m2/s and (0.73-6.18) × 10-9 m2/s, respectively, at a pressure difference of 0.69 MPa, and (1.61-8.33) × 10-8 m2/s and (0.89-10.78) × 10-9 m2/s, respectively, at a pressure difference of 0.35 MPa. The results indicated that the exsolution process was faster than dissolution at both pressure differences. Additionally, the liquid phase shrinkage (exsolution) and liquid phase swelling (dissolution) increased with increasing temperature, indicating that the dominant factor is the transport property (diffusion coefficient). Next, the experimental studies vapor-liquid equilibria (VLE) of a ternary system of ethane/water/bitumen were performed. The phase behavior and thermophysical properties (density and viscosity) were measured by varying the feed fractions of ethane and water while keeping bitumen composition constant at temperatures ranging from 190-210 °C and at 2.5 MPa pressure. The cubic-plus-association equation of state (CPA EoS) was used to model the phase equilibria and feed composition was chosen based on the model to study the VLE region. The model accurately predicted the existing phase equilibria, and experimental results confirmed vapor-liquid equilibrium (VLE). The vapor phase comprises ethane and water, while liquid phase (hydrocarbon-rich) primarily consists of bitumen (up to 75% mole fraction), along with ethane and water. The CPA model and stability analysis was used to construct ternary diagrams at three different temperatures 190, 200, and 210 °C and pressure at 2.5 MPa. The phase boundaries between different regions were determined using stability analysis.
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Turkman, S. (2024). Dissolution and exsolution kinetics of ethane/bitumen and vapor-liquid equilibrium of ethane/bitumen/water system for applications to solvent-aided recovery processes (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca.