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Modelling Gas-Oil Interactions for Enhanced Oil Recovery: A Numerical and Analytical Study
- Author / Creator
- Doranehgard, Mohammad Hossein
In the first part of this study, we use an analytical approach and the interpolation-supplemented lattice Boltzmann method (ISLBM) to quantify convective and diffusive transport during CO2 dissolution in the oil bulk phase. In the first step, we use a turbulence analogy and the ISLBM to determine the relationship between the Rayleigh number (Ra) and the ratio of the pseudo-diffusion coefficient to the molecular diffusion coefficient (D^/D ). We then use experimental data from two oil samples, condensate and crude oils, to validate the obtained relationship between D^/D and Ra. We also use the Sherwood number (Sh), total mixing and diffusive transport curves to analyze different periods during CO2 dissolution for condensate and crude oils. We focus in particular on how Ra affects the characteristics of density-driven fingers and the convection field. Our results show that there is a logarithmic trend between D^*/D and Ra. Analysis of the total mixing and diffusive curves indicates that the CO2 dissolution process can be divided into three distinct periods, namely diffusive transport, early convection, and late convection. We find that more than 50% of the ultimate CO2 dissolution occurs in the early convection period. We also show that the analytical results obtained for the critical time and critical depth at the onset of convection is in good agreement with those of ISLBM. After the onset of convection, the formation of initial fingers leads to enhanced convective transport, with marked implications for the concentration variance and mixing rate.
In the second part of this study, we propose a novel analytical solution to predict the diffusion coefficient and depth of gas (C1 and a mixture of C1/C2 with the molar ratio of 70/30) penetration during the soaking period of the cyclic gas injection process.
Our analytical solution is derived from the modeling of gas-phase pressure declines by use of mass-balance and continuity equations. We model mass transport during the soaking period as a counter-diffusion process, and found that diffusion coefficient and velocity are controlled by the pressure gradient at the early soaking times and the concentration gradient when the soaking progresses. The estimated diffusion coefficients through our solution for a mixture of gas/oil under tight porous media conditions are in agreement with published literature. We calculate the depth of gas penetration in the plug, and show that the gas front reaches the other end of the plug at the end of the soaking period in the gas-mixture case. Also, the model is capable of predicting swelled oil volume by gas dissolution. A thermodynamic consistency check was performed by comparing the amount of leaked-off gas in the experiment and that of the model. The results show that these values are in the same range.
- Graduation date
- Fall 2021
- Type of Item
- Master of Science
- This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.