Modeling of Chemical Tracers to Estimate Oil Volume Contacted and Sweep Efficiency in Porous Media Under Countercurrent Spontaneous Imbibition

Abstract

Abstract Modeling of chemical tracers is an important technique to estimate oil saturation in porous media. Although numerous models exist to analyze the flow of tracers in systems under dynamic conditions, modeling in capillarity-dominated systems has not been sufficiently examined. In tight porous media and the matrix of fractured reservoirs, spontaneous imbibition (SI) represents a key driving mechanism for fluid infiltration because the low permeability in these systems results in a negligible transport by advection. We present a new semi-analytical solution for the flow of tracers under countercurrent SI valid during the infinite-acting and boundary-dominated flow regimes. The model presented is derived from the analysis of fluid imbibition driven by capillarity and numerically solved as a function of water distribution and initial tracer concentration. We model ideal and partitioning tracers to investigate the average oil saturation in the contacted region by tracer and sweep efficiency of countercurrent SI as a recovery mechanism in porous media. To verify the applicability of our solution, we compared it against numerical simulation cases under flow conditions with diverse solute and phase properties. The concentration profiles exhibit a significant delay in displacement behind the imbibition front when hydrodynamic dispersion is ignored and for high partitioning coefficients, demonstrating the importance of determining these properties before conducting a field test. The solution presented is the first to examine countercurrent SI for the modeling of oil volume contacted by tracers in porous media. We consider the model can be extended for the analysis of the flow of tracers in systems such as fractured reservoirs to estimate oil saturation in the matrix medium, and those using chemical solutions that promote SI by altering wettability and capillary pressure.