Impact of Wetting Film Flow in Pore Scale Displacement

ABSTRACT In flow through porous media, the wetting films may contribute many phenomena which directly affect the oil recovery. While some of these phenomena might limit the overall recovery process tremendously by trapping the non-wetting phase, the others may provide means for certain molecular processes to occur. The latter has gained importance over the last few decades and led some of the enhanced oil recovery processes (EOR) to develop. Whether limiting or enhancing the recovery these films have an important impact in scales larger than their own. Due to their very thin structure (a few micrometers the most) experiments often get limited, and direct observation is not possible, especially in a three-dimensional porous medium. The numerical simulations also struggle with such small scales as it requires a very high resolution to capture the film flow physics and a significant computational power is necessary to simulate flow on a sample with a representative size within a reasonable time. We present a summary on the wetting film flow and try to put them in perspective regarding in which scale they occur and in what scale(s) their impacts are visible and unavoidable. First a few experiments outline when/how the films form and provide visual proof on their behavior during multi-phase flow. The findings of these experiments clearly show the impact of, for example, snap-off events which provide an important basis for the numerical methods. We then present a dynamic pore network model (PNM) which accommodates the wetting film flow, coupled into the flow in network elements without any sub-gridding. For both wetting and non-wetting phase, the flow equation is solved and the wetting phase pressures calculated in the wetting films as well as each network element. This way of coupling helps to upscale a nano/micro scale event to the Darcy scale. But, regardless of the physics a PNM has, its prediction capacity is always dependent on the quality of the network extraction process. Direct methods, free from the extraction ambiguities, can provide a much more detailed physical representation of the processes, but at a higher computational cost. Here, these two numerical approaches are also compared in terms of their capability and way of handling the thin film flow, their potential to simulate EOR processes and the computational efficiency