1.Key Laboratory of Unconventional Oil Gas Development China University of Petroleum East China,Ministry of Education;2.P R China
nanoparticles have a good application prospect in enhancing oil recovery due to its unique nano-effects, but the ultra-low permeability reservoirs have small pore throats, and the adsorption of nanoparticles has a greater impact on the physical properties of the reservoir. In this paper, based on the displacement experiment of SiO2 nanofluid in the ultra-low permeability core, combined with the ultraviolet-visible spectrophotometer, a method for measuring the adsorption capacity of nanoparticles was proposed. The research results showed that with the increase of nanofluid concentration (0.01-0.50wt%), the core injection pressure and the retention rate of nanoparticles (7.60%-87.50%) increased, in addition the highest permeability loss rate can reach 96.46%. The subsequent displacement of NaCl solution took away a few unstably adsorbed free nanoparticles, but did not alleviate the adsorption obviously because of the formation of effective plugging in the rock core. The scanning images of core sections after displacement demonstrated that the nanoparticles were concentrated on the pore throat and matrix surface at the front end of the core, occupying the fluid seepage channel, which caused structural changes in the pore throat. As the concentration of nanofluid increased, the particle aggregation phenomenon became more obvious.