A high temperature resistance and hyper-dispersed nanoparticle grafted by multi-monomer via in-situ polymerization: Preparation, characterization, and its imbibition performance

In recent years, the excellent cleaning-oil capacity of nanofluid has attracted extensive attention and it has been widely used in oilfields as an imbibition agent. To solve the poor dispersion stability of nanoparticles in high-temperature and high-salt reservoir, this paper has prepared a hyper-dispersed nanoparticle, polymer grafted nanosilica (PNS) that is anti-salt monomer and anti-temperature monomer simultaneously grafting on the surface of nanosilica via in-situ polymerization reaction. Its imbibition performance has been discussed. Results show that (1) The two monomers are all successfully grafted on the surface of nanosilica via optimization of in-situ polymerization reaction conditions. This hyper-dispersed nanoparticle has 14.5% final grafting rate, approximately 18 nm in particle size, and -41.2 mV of zeta potential; (2) PNS fluid has excellent dispersion stability and its grain size has no obvious change in 20 wt.% of NaCl or 4 wt.% of CaCl2 fluids at room temperature (25 degrees C), as well as in 18 wt.% of NaCl or 4 wt.% of CaCl2 fluids at 130 degrees C after 1 week; (3) Crude oil-water interface tension can be decreased and the hydrophilicity is significantly boosted by this PNS fluid. Meanwhile, the 10-3 mN/m of interface tension can be obtained and the contact angle of water phase is decreased to 12.8 degrees by surfactant erucamide propyl hydroxysulfobetaine (EHSB) synergizing with PNS fluid; (4) Oil recovery efficiency replaced by PNS in surfactant fluid has reached 39.3%. That is mainly because the hyper-dispersed nanoparticle provides a stronger spreading force to enhance the efficiency of cleaning oil.