Influence of Boundary Layer on Oil Migration into Tight Reservoirs

The boundary layer thickness and influence in the single-phase flow in the tight reservoirs have been widely measured. The influence of boundary layer on the oil migration into originally water-saturated tight reservoirs has been theoretically deduced but has not been experimentally validated. In this work, the existence of boundary layer in tight reservoir oil migration is investigated by comparing the oil migration with the influence of boundary layer (measured by tight sandstone oil accumulation experimental simulation) and theoretical oil migration without the influence of boundary layer (derived from rate-controlled mercury injection). The distribution of boundary layer in the tight reservoir is detected by nuclear magnetic resonance centrifugation. The influence of boundary layer on oil migration is discussed by modeling tight reservoir oil migration and analyzing the relationships between oil migration characteristics and tight reservoir pore-throat structures. The results turn out that the boundary layer distributes in all sizes of pores in the tight reservoirs and becomes thinner with the pressure gradient increment. The oil migration into the tight reservoirs is a coupled effect of the increasing driving force and the decreasing capillary pressure caused by boundary layer thinning. The pore-throats in the tight reservoirs are heavily blocked by boundary layer, while the pore-bodies are almost unaffected by boundary layer.