Fabrication and characteristics of self-aggregation nanoparticles used for conformance control treatment

In order to alleviate the contradiction between injectability of the profile control agent and its profile control performance, a novel core-shell heterogeneous structure colloidal particles (CSA) were synthesized, and the mechanism of self-aggregation plugging was proposed. Cross-linking inside the nanoparticles and chain-growth polymerization via capturing acrylamide in the aqueous phase result in the formation of core-shell heterogeneous structures as proved by TEM observation and XPS analysis. Moreover, CSA nanoparticles exhibit good hydrophilic properties, outstanding thermal stability and limited expansion capacity. Effects of different metal cations and surface group on the self-aggregation time of CSA nanoparticles were systematically studied. Results showed that divalent cations contributed to more significant aggregation of CSA nanoparticles in comparison to monovalent cations. The increasing cations concentration and valency decreased the thickness of electric double layer, which lead to a decrease in the zeta potential. Core flooding test shows that the injection of nanoparticles which diameter is much smaller that of pore-throats into the target reservoir can not only successfully enter the depth of porous media, but also effectively block the high permeability areas by the formation of self-aggregation particle clusters. This study provides a new method for the equilibrium between nanoparticles injectivity and in-depth profile control of nanoparticles.