Modified salinity waterflooding (MSW) is an effective technique to increase oil recovery. The impact of MSW has been studied for a wide range of scales and rock types, most of which have shown a potential improvement in oil recovery. The improvement has been attributed to several chemical and physical interactions that led to a change in surface charge, consequently, wettability to become more water-wet [1]. However, the efficiency of MSW in naturally fractured porous media has been less investigated.
Recovery efficiency in fractured reservoirs can be dramatically lower in comparison to conventional reservoirs because injected water will flow into the highly permeable network of fractures and the matrix, containing most of the oil remains unswept. Spontaneous imbibition is considered one of the most important displacement mechanisms in fractured porous media, which can drive oil into the fracture by capillary forces. The potential increase of matrix-fracture mass transfer due to imbibition can be strongly impacted by wettability [2]. In MSW, the wettability alters toward a more water-wet state by the inter-relation between flow, transport, and chemical reactions at the pore-scale. In this work, a numerical model that includes multi-component reactive transport two-phase flow capable of capturing wettability alteration is implemented based on the Direct Numerical Simulation of the Navier-Stokes equations and surface complexation modeling. The developed model is used to study the pore-level effect of wettability change on the co-current and counter-current imbibition for simple 2D micromodels and evaluate the impact of several parameters such as water composition and injection velocity on the phase recovery rates. The simulation outcomes reveal the interplay among mixing, reactions and flow contributing to the better understanding of MSW effects in fractured reservoirs.

[1] H. Mahani, A. Levy Keya, S. Berg, W. Bartels, R. Nasralla, W.R. Rossen, “Insights into the mechanism of wettability alteration by Low-Salinity Flooding (LSF) in carbonates”, Energy Fuels, 29 (2015)
[2] C.A. Hatiboglu, T. Babadagli, “Experimental and visual analysis of co- and counter-current spontaneous imbibition for different viscosity ratios, interfacial tensions and wettabilities”, J. Petrol. Sci. Eng., 70 (2010)