Browsing by Author "Dong, Xiaomeng"

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Open Access
Quantification of dissolution and exsolution dynamics of gaseous solvents in crude oil systems under reservoir conditions
(Faculty of Graduate Studies and Research, University of Regina, 2024-08) Dong, Xiaomeng; Yang, Daoyong (Tony); Gu, Yongan (Peter); Henni, Amr; Qing, Hairuo; Zeng, Hongbo
With a growing demand for fossil fuels, it is of a great importance to improve the oil recovery factor from both conventional and unconventional reservoirs. Among different enhanced oil recovery (EOR) methods, injecting gaseous solvents, including CO2, N2, flue gas, and alkane solvents, is considered as a more effective and efficient method in both light and heavy oil reservoirs, during which mass transfer is the key underlying recovery mechanism. In order to optimize the solvent injection method and achieve a higher oil recovery, it is of fundamental and practical importance to quantify both dissolution and exsolution dynamics of solvents in light and heavy oils under reservoir conditions. Firstly, a pragmatic method has been developed and applied to quantify the mutual mass transfer in different solvent(s)-light oil systems. Experimentally, diffusion experiments have been conducted for flue gas-light oil systems at constant pressures and temperatures. The dynamic liquid volume is monitored and recorded continuously during the experiments, while gas samples are collected at the beginning and end of each test to measure the gas fractions with gas chromatography (GC) analysis. Theoretically, by combining the Fick’s law and Peng-Robinson equation of state (PR EOS), the preferential and mutual diffusion between the flue gas and light oil can be quantified once the deviations between the measured and calculated parameters (i.e., dynamic swelling factor and gas composition) are minimized. Both individual diffusion coefficients for each gas component of a gas mixture in an oil phase and that of the extracted oil components in the gas phase are increased with pressure and temperature. Both the experimental and theoretical methods are modified and then extended to CO2/C3H8-heavy oil systems to quantify the mutual diffusivity between the gaseous solvents and heavy oil with the consideration of natural convection at high pressures and elevated temperatures or coupled with heat transfer process. Similarly, diffusion experiments are conducted with a PVT setup, during which the dynamic swelling factors of the heavy oil are measured continuously. Both oil and gas samples are collected at end of each test for oil compositional and GC analyses, respectively. The diffusivities of both solvents (i.e., CO2 and C3H8) in heavy oil and the extracted oil components in the gas phase are found to increase with pressure and temperature. Also, there exists an obvious extraction process from the oil to gas phases at elevated temperatures as light-medium components have been detected in the collected gas samples at end of the experiments. While coupling heat and mass transfer to determine the diffusivity of hot solvent in the heavy oil, thermal equilibrium is found to be achieved earlier than mass equilibrium. Combined heat and mass transfer will accelerate the oil swelling effect. Then, experimental and theoretical techniques have been developed to predict gas exsolution dynamics of CO2/CH4-heavy oil systems on the bubble level to reflect the physical behaviour of foamy oil. Experimentally, constant-composition-expansion (CCE) experiments have been performed in a sealed PVT system for a CO2-heavy oil system and a CH4-heavy oil system, respectively. Theoretically, the classical nucleation theory, population balance equations (PBEs), Fick’s law, and PR EOS has been integrated to predict the gas bubble number and size by reproducing the experimentally measured parameters (i.e., liquid volume and pseudo-bubblepoint pressure). It has been observed that both temperature and diffusivity of the gas component play an important role in the foamy oil behaviour. Compared with CO2, CH4 can induce a stronger and more stable foamy oil since more CH4 bubbles are dispersed in the oil phase.
Open Access
Quantification of Mutual Mass Transfer of Gas-Light Oil Systems at High Pressures and Elevated Temperatures
(Faculty of Graduate Studies and Research, University of Regina, 2019-05) Dong, Xiaomeng; Yang, Daoyong; Azadbakht, Saman; Aroonwilas, Adisorn
Numerous tight oil resources that are characterized by both low porosity and permeability have been found in North America during past decades. Due to the extremely low permeability, water injection has found its limitation with its relatively low injectivity. Alternatively, gas injection, such as CO2, N2, hydrocarbon gas, and flue gas, has been made physically possible for enhancing oil recovery under certain conditions, during which molecular diffusion is of great importance. Due to the affordability and sustainability of CO2, N2 and flue gas have been found to be costeffective for enhancing hydrocarbon recovery to a certain extent. Physically, there exists two-way mass transfer between the injected gas and light oil, though the light component extraction has been theoretically neglected. Therefore, it is essential to quantify the mutual mass transfer of gas-light oil systems under reservoir conditions. In this study, a novel and pragmatic technique has been developed to quantify mutual mass transfer between a gas and light oil by dynamic volume analysis. Experimentally, diffusion tests for a CO2-light oil system, a N2-light oil system, and two flue gas-light oil systems, have been conducted at a constant temperature and pressure with a pressure/volume/temperature (PVT) system, while the dynamic swelling factors of oil phase are measured and recorded continuously during the experiments. Gas samples have been collected at end of each diffusion experiment to measure gas compositions by performing gas chromatography (GC) analysis. Theoretically, by combining Fick’s second law and Peng-Robinson equation of state, the diffusion coefficients of both gas components and oil phase can be determined once the discrepancies between the measured and calculated dynamic swelling factors and gas compositions have been minimized simultaneously. At end of diffusion experiments, the swelling factor measured for the CO2-light oil system is 1.029, which is higher than that of N2-light oil system (i.e., 1.005). For the two flue gas-light oil systems, the enriched flue gas, which has a higher CO2 concentration, results in a higher swelling factor (i.e., 1.013) at end of diffusion experiment, comparing with that of flue gas-light oil system (i.e., 1.009). Besides, based on the GC analysis results, light components have been found in the gas phase, which proves that there exists two-way mass transfer between gas and oil phases. For the CO2-light oil system and N2-light oil system, at temperature of 336.15 K, the diffusion coefficients of CO2 and N2 are determined to be 12.87×10-9 m2/s at pressure of 2170 kPa and 1.35×10-9 m2/s at pressure of 5275 kPa, respectively. The diffusion coefficients of light oil in gas phase are determined to be 6.04×10-11 m2/s for the CO2- light oil system and 0.26×10-11 m2/s for the N2-light oil system under the corresponding conditions. Similarly, for the enriched flue gas-light oil system, the individual diffusion coefficients determined for CO2 and N2 are 8.35×10-9 m2/s and 1.52×10-9 m2/s at temperature of 336.15 K and pressure of 5275 kPa, respectively, while that of oil in gas phase is 0.07×10-11 m2/s. For the flue gas-light oil system, at the same condition, the individual diffusion coefficients calculated for CO2 and N2 are 6.42×10-9 m2/s and 2.19×10-9 m2/s, respectively, while that of oil in gas phase is 0.08×10-11 m2/s.