International Journal of Heat and Mass Transfer 154 (2020) 119688 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/hmt Numerical modeling of viscous fingering during miscible displacement of oil by a paraffinic solvent in the presence of asphaltene precipitation and deposition Nasser Sabet, Mohammadjavad Mohammadi, Ali Zirahi, Mohsen Zirrahi, Hassan Hassanzadeh ∗ , Jalal Abedi Department of Chemical and Petroleum Engineering, Schulich School of Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada a r t i c l e i n f o Article history: Received 26 November 2019 Revised 12 February 2020 Accepted 22 March 2020 Keywords: Viscous fingering Miscible displacement Deposition Asphaltene precipitation High-order compact finite difference Pseudo-spectral Large viscosity contrast Porosity and permeability alteration a b s t r a c t We study the mixing dynamics of a paraffinic solvent with oil in the context of miscible displacement in porous media for enhanced oil recovery. Typically, injected solvents are less viscous compared to the resi- dent oil, leading to the rise of interfacial instabilities known as viscous fingering. This, in turn, accelerates precipitation of initially dissolved asphaltene particles in the oil. The formed precipitates are carried with the flow and may deposit in the porous media, altering porosity and permeability fields. Although asphal- tene precipitation and deposition are inevitable in most of the solvent-based recovery techniques, they have been neglected in the previous works of miscible displacement due to their added complexity. In this work, we present a rigorous formulation of the physics of the problem and conduct high-resolution nonlinear numerical simulations to investigate the effects of asphaltene precipitation and deposition and the resulting formation damage. For this purpose, the related governing equations are derived based on the velocity-vorticity formulation, and a high-order hybrid scheme is applied to solve them. This type of handling enables us to simulate viscous fingering at large viscosity ratios and Peclet numbers, beyond what has been previously reported in the literature. Furthermore, experimental measurements are con- ducted for viscosity and asphaltene content of the oil at various solvent concentrations and are used in the simulations. The results of our numerical simulations reveal that despite having a great impact on the permeability field, asphaltene precipitation and deposition do not influence the growth of viscous fingers, noticeably, which is due to the substantial viscosity ratio of the studied system. However, de- position of the formed precipitates leads to in-situ upgrading of the oil and thus enhances the quality of the produced liquid. Finally, regarding the effect of the choice of viscosity mixing rule, we compare two commonly used viscosity mixing rules in the previous works (exponential and quarter-power) and elaborate on their main differences in terms of the observed dynamics. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction Miscible displacement of a more viscous fluid by a less viscous one leads to complex mixing dynamics known as viscous fingering [1,2]. Such dynamics could be encountered in many areas of sci- ence and engineering such as subsurface hydrology [3,4], polymer processing [5], micromixers [6], and enhanced oil recovery [7–9]. Fig. 1 depicts an example of the miscible viscous fingering in a sys- tem of fluids with a viscosity ratio (VR) of ~20. As is seen, intricate viscous fingering evolves during the displacement process, which is due to the adverse viscosity gradient between the two fluids (i.e., ∗ Corresponding author. E-mail address: hhassanz@ucalgary.ca (H. Hassanzadeh). lower viscosity of the displacing fluid compared to the displaced one). Various aspects of miscible viscous fingering have been in- vestigated in the past including the effects of chemical reactions [10], hydrodynamic dispersion [11], non-monotonic viscosity pro- file [12], nanoparticles [13], permeability heterogeneity [14], non- Newtonian viscosity behavior [15], and double diffusion [16]. For more details, the interested reader is referred to the above-cited works and the references therein. Mixing of two miscible fluids in porous media is occasionally associated with precipitation of initially dissolved species that may deposit in the porous media, obstruct and modify the flow path- ways, and subsequently change permeability and porosity [17]. A fascinating example of such a phenomenon is the precipitation and deposition of asphaltene or the so-called cholesterol of petroleum https://doi.org/10.1016/j.ijheatmasstransfer.2020.119688 0017-9310/© 2020 Elsevier Ltd. All rights reserved.