Experimental studies on resistance to fluid displacement in single pores
Kwelle, Stephen Okachukwu
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Understanding the resistance to displacement of one fluid by another in multiphase transport in a porous medium is very beneficial in hydrocarbon exploration and production as well as geological storage of carbon dioxide. Pore resistance behaviour of a porous medium controls the fluxes of fluids through the caprocks over the geological times and therefore directly determines the volume and localization of the hydrocarbons trapped (best locations for exploration) and also the overpressured formation (zone of drilling hazard). In the design for enhanced oil recovery and geological storage, it sets a limit on both the injection pressure and storage capacity of the reservoir to avoid an upward migration of the injected fluid into the overlaying formations. Many investigations have been carried out on the resistance to porous media flows for decades, yet the understanding of the individual factors affecting it is not complete, because most studies were carried out on core samples, whereas flow resistance depends on the flow details at the pore scale. For example, two core samples may have same porosity but different pore size. This research focused on advancing the understanding of resistance to multiphase displacement in a porous medium, using the pressure profile of interface flow through single pores, to measure the resistance to two-phase flow and then link the impact of pore geometry, surface tension, fluid properties, and wettability, on the pressure profile to the displacement process, in order to fill the noticed gap of knowledge. Experiments conducted in this research using tapered capillaries revealed that the resistance to two-phase flow is significantly higher than the single phase resistance and the pore throat of a porous medium is not just determined by a group of smallest pore sizes as understood using core samples, but by response of critical effective pore diameter to resistance to two-phase interface flow. The initiation of a pore throat is characterised by a drastic increase in the resistant pressure at the effective pore size. The effective pore diameter is generally less than 500 μm and increases with the pore tip diameter and the capillary gradient, interfacial tension, but decreased by surfactants. Viscosity does not have any significant effect on the effective pore diameter. The study also revealed a relationship between pore contact angle and pore throat; pore contact angle is maximum and remains fairly constant at the pore throat. The overall outcome of this research is a significant contribution to the influence of pore geometry on the resistance to porous media flows.