Imbibition of Oil in Dry and Prewetted Calcite Nanopores

Fluid imbibition into porous media featuring nanopores is ubiquitous in applications such as oil recovery from unconventional reservoirs and material processing. While the imbibition of pure fluids has been extensively studied, the imbibition of fluid mixture is little explored. Here we report the molecular dynamics study of the imbibition of model crude oil into nanometer-wide mineral pores, both when pore walls are dry and prewetted by a residual water film. Results show the fastest imbibition and quickest propagation of molecularly thin precursor films ahead of the oil meniscus in the dry pore system. The presence of a thin water film on pore walls corresponding to an environmental relative humidity of 30% slows down but still allows the spontaneous imbibition of single-component oil. Introducing polar components into the oil slows down the imbibition into dry nanopores, due partly to the clogging of the pore entrance. Strong selectivity toward nonpolar oil is evident. The slowdown of imbibition by polar oil is less significant in the prewetted pores than in dry pores, but the selectivity toward nonpolar oil remains strong.