Enhanced Heat and Mass Transfer for Alkane Solvent(s)-CO2-Heavy Oil Systems at High Pressures and Elevated Temperatures

Date
2016-09
Authors
Zheng, Sixu
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Publisher
Faculty of Graduate Studies and Research, University of Regina
Abstract

The tremendous heavy oil reserves have recently attracted considerable attention for sustaining the increasing global oil consumption. Heavy oil reservoirs are characterized by high oil viscosity and drastic drop of reservoir pressure in a short period during production, imposing great challenges to recover such heavy oil resources. In practice, conventional steam-based thermal recovery techniques are generally ineffective or uneconomical in thin heavy oil reservoirs due to operational and environmental constraints. Since CO2 is a highly soluble, low cost, and environment-friendly injectant, hot CO2 injection is alternatively considered to be a promising technique for enhancing heavy oil recovery from these thin reservoirs. Not only does it take advantages of both thermal energy and dissolution of solvents to recover heavy oil resources, but also it contributes to the alleviation of carbon footprint. Compared with the CO2-alone processes, addition of alkane solvents to the CO2 stream leads to enhanced viscosity reduction and swelling effect of heavy oil. Thus, it is of fundamental and practical importance to study the underlying mechanisms of hot alkane solvent(s)-CO2 processes for enhancing heavy oil recovery at high pressures and elevated temperatures. In order to more accurately determine the equilibrium phase properties for alkane solvent(s)-CO2-heavy oil systems with the Peng-Robinson equation of state (PR EOS), heavy oil is characterized as multiple pseudocomponents, while a volume translation strategy is employed to improve its prediction performance. The binary interaction parameter (BIP) correlations are tuned with the experimentally measured saturation pressures for the same heavy oil. Such volume-translated PR EOS with a modified alpha function incorporating the tuned BIP correlations is capable of accurately predicting the saturation pressures and swelling factors of the aforementioned systems. The alkane solvent-CO2-heavy oil pressure decay systems under a constant temperature have been theoretically modelled to not only examine the effect of adding alkane solvents into CO2 stream, but also determine both apparent diffusion coefficient of a gas mixture and individual diffusion coefficient of each component in heavy oil. It is found that alkane solvents (i.e., C3H8 and n-C4H10) diffuse much faster than CO2 in heavy oil at reservoir temperature. Compared to pure CO2, addition of C3H8 into the CO2 stream tends to accelerate the swelling of heavy oil under similar conditions. Experimental and theoretical techniques have also been developed to couple heat and mass transfer for hot CO2-heavy oil systems with and without addition of alkane solvents. Both molecular diffusion coefficient of each component and apparent diffusion coefficients of alkane solvent(s)-CO2 mixtures are determined once the discrepancy between the measured and calculated dynamic swelling factors has been minimized. The thermal equilibrium is found to achieve in a much shorter time than mass equilibrium. CO2 diffusion coefficient in heavy oil increases with temperature at a given pressure. Compared with hot CO2 injection, addition of C3H8 into hot CO2 stream contributes to an enhanced swelling effect of heavy oil. A higher concentration of C3H8 in the CO2-C3H8 mixture tends to accelerate gas diffusion and thus induce a stronger oil swelling. Among the n-C4H10-heavy oil system, n-C4H10-CO2-heavy oil system, and C3H8-n-C4H10-CO2- heavy oil system, smaller dynamic swelling factors are obtained for the n-C4H10-heavy oil system, while the largest dynamic swelling factor of 1.118 at the end of diffusion test is achieved for the C3H8-n-C4H10-CO2-heavy oil system.

Description
A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fulfillment of the Requirements For the Degree of Doctor of Philosophy in Petroleum Systems Engineering University of Regina. xxi, 225 p.
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