Modeling Tracer Flow Characteristics in Different Types of Pores: Visualization and Mathematical Modeling

Abstract

Structure of porous media and fluid distribution in rocks can significantly affect the transport characteristics during the process of microscale tracer flow. To clarify the effect of micro heterogeneity on aqueous tracer transport, this paper demonstrates microscopic experiments at pore level and proposes an improved mathematical model for tracer transport. The visualization results show a faster tracer movement into movable water than it into bound water, and quicker occupancy in flowing pores than in storage pores caused by the difference of tracer velocity. Moreover, the proposed mathematical model includes the effects of bound water and flowing porosity by applying interstitial flow velocity expression. The new model also distinguishes flowing and storage pores, accounting for different tracer transport mechanisms (dispersion, diffusion and adsorption) in different types of pores. The resulting analytical solution better matches with tracer production data than the standard model. The residual sum of squares (RSS) from the new model is 0.0005, which is 100 times smaller than the RSS from the standard model. The sensitivity analysis indicates that the dispersion coefficient and flowing porosity shows a negative correlation with the tracer breakthrough time and the increasing slope, whereas the superficial velocity and bound water saturation show a positive correlation.