Wettability effects on mobilization of ganglia during displacement

Abstract

Mobilization of trapped ganglia is of fundamental importance in two-phase displacement. Wettability alteration could be an effective approach to mobilizing ganglia, yet its feasibility as well as the impact of wettability in general lacks study. We investigate the wettability effects on trapped ganglia by theoretical analysis and numerical simulations for both fixed and altering wettability. For fixed wettability, it is found out that the critical pressure to mobilize trapped ganglia is symmetric about and usually peaks at the neutrally wet conditions (for simplicity, the invading and defending fluid are referred to as water and oil), but mobilized ganglia favor more water-wet conditions to be further displaced. This is due to the difference in the evolvement of ganglia after initial mobilization under different wetting conditions: water-wetness contributes to the cooperative advancing of multiple interfaces, making ganglia continue moving as a whole, while oil-wetness leads to Haines jump in a single throat, which easily breaks up ganglia into smaller ones and leaves them trapped again. For altering wettability from oil-wet to water-wet through the transport of certain solute, we for the first time identify two crucial factors for the mobilization of ganglia. First, only the heterogeneous wetting state during the dynamic altering process enables the initial mobilization, whereas a step-wise alteration has little effect. Second, ganglia have to be able to merge with one another during the time window of the altering process for further displacement. Otherwise, an isolated trapped ganglion can only have limited mobilization at first by wettability alteration, and gets trapped again when the alteration is complete.