Due to reservoir heterogeneities, oil recovery from fluid injection during secondary and/or tertiary recovery does not occur in an ideal piston-like displacement. Rather sweep efficiency can be much lower than 100% due to heterogeneities such as high permeability contrast between layers (aka thief zones) and fractures. These reservoir features require the use of a conformance control agent to improve sweep. Our proposed conformance control technique uses colloidal silica (aqueous silica nanoparticle dispersions) for a gelling system to address conformance control. Permeability reduction can be achieved through the in-situ gelation process even at low concentrations of nanoparticle. Under retarded gelation kinetics due to lower initial salinity, permeability reduction can be created deeper in the core. When the core salinity is initially lower, a weaker gel is formed, which allows for continued injection to break and mobilize some of the gel. Some nanoparticle will initially be retained due to suppressed energy barrier to absorption in the higher salinity environment. Most of the retained particles, though, will be released upon continued exposure to the low salinity nanoparticle solution.