Preparation And Oil Displacement Performance Study Of Janus-SiO₂ Nanofluid

With the continuous exploitation of energy resources,most oil fields have entered the later stage of high water cut production.At present,most low-permeability and dense heavy oil reservoirs face the major issues of rock densification,fine pore throat,low permeability and poor flow of crude oil;and the primary oil recovery is less than 10%.Enhance oil recovery?EOR?technology is a new oil displacement technology which combines physical,chemical and biological technologies to enhance oil recovery.Particularly,nano-chemical flooding as a new and efficient oil flooding technology can greatly enhance oil recovery and improve reservoir environment.With a view to our previous researches on the preparation of Janus-SiO₂ nanofluid via surface-modification and chemical breaking technology,this paper uses surface-modified nano-silicas obtained with different dosages of surface modifiers as the precursors to prepare Janus-SiO₂.It systematically investigates the effects of various surfactants and surface-capped nano-silicas on the dispersion stability of Janus-SiO₂ nanofluids.Thus laser particle size analyzer,visible spectrophotometer and transmission electron microscope were performed to analyze the dispersion stability of Janus-SiO₂nanofluids;and spinning drop interfacial tensiometer,multi-functional core displacement device and contact angle meter were performed to evaluate the oil displacement performance of Janus-SiO₂ nanofluids.Furthermore,the influence of the concentration and salinity of chemical breaking agent on the dispersion stability and oil displacement performance of Janus-SiO₂ nanofluids was also studied.The main contents and conclusions are as follows:1.Matching of nano-silica with surfactant and their effect on Janus-SiO₂nanofluids: Nano-silica NPS-Z,CG1631,DNS-1,and DNS-1N modified by different dosages of organic modifier?mass fraction: 20%?were adopted to prepare Janus-SiO₂ nanofluids.Nano-silica DNS-1 with good dispersion stability in aqueous solution was screened as the desired precursor for preparing Janus-SiO₂ nanofluid;and the resultant Janus-SiO₂ nanofluids exhibits the optimal dispersion stability as well as a light transmittance of 98% and a particle size of less than 10 nm.The influence of cationic surfactant CTMAB,anionic surfactant SDS,nonionic surfactant OP-10 and composite surfactant F12 as dispersion agents on the dispersion stability of DNS-1 in aqueous solution and oil displacement performance of the as-obtained Janus-SiO₂ nanofluid was investigated.Results show that DNS-1 has the best dispersion stability under the regulation of composite surfactant F12 as well as an average particle size of less than 10 nm;and it can quickly reduce the oil-water interfacial tension to 0.30 m N/m,strip the crude oil from the glass surface completely,and provide a total oil recovery rate of 49.92%,showing excellent oil displacement performance.2.Effect of surfactant on dispersion stability and oil displacement of Janus-SiO₂ nanofluids prepared at different dosages of organic modifier: The dispersion stability of Janus-SiO₂ nanofluids prepared from DNS-1 series nano-silicas with different dosages of organic modifier?coded as HB100,HB105,HB110,HB115,HB120 and HB125 according to different dosages of the modifiers?was evaluated in the presence of composite surfactant F12 as the dispersion agent.The effect of Janus-SiO₂ nanofluids on oil displacement performance was also investigated.Results show that the optimal concentration of chemical breaking agent for preparing Janus-SiO₂ nanofluid with good dispersion stability is 1.0 wt%;and the resultant Janus-SiO₂ nanofluid prepared with HB120 has the best ability to reduce the oil-water interfacial tension and can completely remove the crude oil from the surface of glass slide,exhibiting the highest oil washing efficiency and enhancing oil recovery by 21.81% in association with primary water flooding.Further,the effect of surfactant SDS on the dispersion stability and oil displacement efficiency of DNS-1 series?HB100-HB120?nano-silicas was investigated.Results show thatunder the regulation of surfactant SDS,Janus-SiO₂ nanofluids have increased dispersion stability;and the oil-water interfacial tension and oil displacement efficiency increase initially and then decrease with the increase of the organic modifier dosage.Particularly,the Janus-SiO₂ nanofluid prepared from HB115 can reduce the oil-water interfacial tension to the lowest level of 1.80 m N/m,and it also exhibits the best oil displacement efficiency and can enhance oil recovery by 17.27% in association with primary water flooding.3.The salt tolerance and emulsification behavior of Janus-SiO₂ nanofluids: The salt HB120 Janus-SiO₂ nanofluid with excellent dispersion stability and oil displacement performance under the regulation of F12,the dispersion stability and oil displacement performance of HB120/F12 Janus-SiO₂ nanofluid in the presence of single salinity sodium chloride and multiple salinity was investigated.Results show that both single salinity and multiple salinity sodium chloride have significant effects on the dispersion stability and oil displacement efficiency of Janus-SiO₂ nanofluids.The dispersion stability and particle size of Janus-SiO₂ nanofluids decrease with the increase of salinity.And in low salinity environment,Janus-SiO₂ nanofluids show good salt tolerance and can effectively enhance oil recovery.Moreover,and the method of preparing Pickering emulsion and the oil-water ratio affording stable Pickering emulsion were examined.Results show that the Pickering emulsion prepared by homogeneous shearing approach,a stable O/W Pickering emulsion,has better emulsifying effect than the one prepared by ultrasonic route.The optimum oil-water ratio affording Pickering emulsion with diesel oil and paraffin wax as the oil phases is 1 : 50,and the resultant Pickering emulsions have stable storage time of 72 h and 100 h,respectively.Particularly,the Pickering emulsion obtained with diesel oil as the oil phase has better emulsifying efficiency.