Effects of the capillary-entrapped phase on fines migration in porous media

Abstract

A residual gas or oil present during fines migration in porous media can highly affect particle detachment, migration, and straining and thereby decrease rock permeability. Those effects are due to capillary forces and partial accessibility of the attached fines to the injected water under the presence of capillary-entrapped gaseous or oleic phase. We performed systematic study of fines migration in engineered sand-packs that contain different percentage of kaolinite and residual oil. Each coreflood consists of seven injections, the first with seawater ionic strength and the last with fresh water, and with piecewise-constant salinity decrease from step to step. Higher decline of permeability is found to occur during fresh water injection and to be accompanied by intensive fines production. Compared with fines migration under single-phase flow, having a residual phase significantly decreases the formation damage and the amount of produced kaolinite. For the first time, we determined dependencies of end-point saturations and end-point relative permeabilities versus kaolinite content. We established the phase permeability decrease with decrease in salinity for different kaolinite contents. The coreflood data are found to be in close agreement with the analytical model of 1D linear flow under the presence of residual phase. The laboratory-tuned model coefficients are used for well behaviour prediction using numerical 1D axisymmetric injection model.