Pore-scale insights into transport and mixing in steady-state two-phase flow in porous media

Abstract

Hydrodynamic dispersion and mixing under two-phase flow can be found in many natural, industrial, and engineering processes such as the modified salinity water flooding (MSWF). In MSWF the injected water displaces the formation brine and will interact with the crude oil and rock to improve the oil recovery. We show throughout numerical simulations that access of the injection water to the available pore space is not homogeneous, even in homogeneous porous media, and it is controlled by the saturation topology and pore-scale velocity field.Under the steady-state two-phase flow in a homogeneous porous medium, the velocity field has a bimodal distribution. The bimodal distribution of pore-scale velocity dictates two different transport time scales spatially distributed over the stagnant and flowing regions at a given saturation topology. These distinctly different transport time scales lead to a non-Fickian transport, which cannot be captured using the conventional advection-dispersion equation.Using the volume-of-fluid method implemented in the OpenFOAM (ver. 4.0), we simulated pore-scale two-phase flow and the hydrodynamic transport at different saturations. We have investigated the impact of stagnant saturation and the tortuosity of flow pathways on the dispersion coefficient and the mass exchange rate -as the two major parameters controlling transport and mixing -under steady-state two-phase flow. At the Darcy scale, different theories such as the mobile-immobile (MIM) theory have been proposed to capture the non-Fickian transport and mixing in two-phase flow through porous media. Based on the simulation results, we assess the validity of the assumptions employed in MIM to define the stagnant saturation and mass exchange rate coefficient. The results of this research provide fresh insights into the potential impact of saturation topology on mixing between the modified salinity water and the formation brine under steady-state flow conditions, which has not been investigated and reported in the literature.Hydrodynamic dispersion and mixing in two-phase flow through porous 2 media are found in many natural, industrial, and engineering processes such 3 as contaminant transport in the vadose zone where the infiltrated water car-4 ries the contaminants and mixes with the resident water, while air has filled 5 some part of the pore space [37,4,23]. Another example is the modified-6 (or low-) salinity water flooding (MSWF) as one of the enhanced oil recovery 7 techniques, in which injection water with a tuned chemical composition is 8 injected into the reservoir filled originally with the formation brine and the 9 crude oil [31, 1,29,42]. The performance of MSWF depends on many pore-10 scale physio-chemical factors such as crude oil chemistry, formation brine and 11 injection water chemistry, temperature, and rock mineralogy, which have 12 been extensively studied [33, 2,25]. However, the larger-scale mechanical 13 factors such as transport and mixing of the modified-salinity water have not 14 been extensively studied. ...

Pore-network modelling of non-Darcy flow through heterogeneous porous media

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Novel insights into pore-scale dynamics of wettability alteration during low salinity waterflooding

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Pore-scale gas–water flow in rock: Visualization experiment and simulation

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