Preparation Of Surface Modified Nanosilica And Its Impact On Enhanced Oil Recovery Of Hpam Solution

Enhanced oil recovery（EOR）is a technique which utilizes chemical,physical and biological technologuies to improve the microscopic and mascroscopic sweep efficiency,thereby raising the oil production.At present,the majority of oil field in China using water flood is in the high water-cut period.Thus the development of EOR techniques to improve oil production is of paramount significance,especially from a standpoint of guaranteeing the national energy security.Polymer flooding has been large–scale application in many oil fields and achieves some effects.Partially hydrolyzed polyacrylamides（HPAM）,as the most widely used polyacrylamide in polymer flooding,is drawing more and more attention.Hydrophobically associating polymers containing a small proportion of hydrophobic groups in the form of pendent side chains or terminal groups has been of increasing interest in improved oil recovery.For instance,due to the hydrophobic association,hydrophobically associating polyacrylamides（HAPAM）showed a better in oil displacing capacity than the solution of HPAM.Recently,more attention has been paid to nanomaterials due to their due to their excellent properties,people have been paid more and more attention to nanomaterials.The combination of nanomaterials and polymers are becoming a promising research direction which may conquer the issues above-mentioned and facilitate the oil recovery.In this article,a series of hydrophobic nano-SiO₂（DNS）surface modified by different hydrophobic groups and various modified amount were prepared.HPAM/DNS suspension samples were prepared.The viscosity of HPAM/DNS suspension is investigated under different temperature and salinity conditions.Additionally,in order to examine the effect of DNS on the performance in EOR,a number of core flooding tests are conducted.The main contents and results of this paper are included below:1.The preparation and characterization of nano-SiO₂ surface modified by hydrophobic functional groupsIn this section,two series of DNS that surface modified by silane coupling agents Hexamethyldisilazane（denoted as DNS-HM）and Hexadecyltrimethoxysilane（denoted as DNS-HD）were prepared.Those obtained nano-SiO₂ nanoparticles were characterized by Transmission electron microscope（TEM）,Thermal Gravimetric Analyzer（TG）,Fourier Transform Infrared Spectrometer（FT-IR）,X-ray diffraction（XRD）.Results indicate that different silane coupling agents and various modification amounts have a great influence on wettability of nano-SiO₂.FT-IR and TG results indicated that hydrophobic groups deriving from silane coupling agents are chemically bonded onto the surface of nano-SiO₂ particles.2.Preparation and apparent viscosity characterization of HPAM/DNS suspension.The apparent viscosity of HPAM/DNS-HM and HPAM/DNS-HD suspensions were examined under different temperature（30⁸0 ^oC）and various salinity conditions（deionized water and simulated Shengli brine）.Under the same experiment conditions,the results show that HPAM/DNS-HM and HPAM/DNS-HD suspensions have higher viscosity to pure HPAM solution and HPAM/DNS-0 suspension.For samples DNS-HM8 and DNS-HD16,they exhibit increased viscosity results,by 49.1%and 28.4%,respectively,than that of pure HPAM solution.Flooding experiments directly demonstrate that the HPAM/DNS-HM8 are more effective at raising viscosity and improving sweep efficiency.0.6 PV HPAM/DNS-HM8 polymer flooding and subsequent water flooding can further increase the oil recovery to 36.85%,which is better than27.33%（HPAM）and 27.90%（HPAM/DNS-0）.3.Preparation of sulfonic group modified DNS-HM8（denoted as DNSS-HM8）and the oil displacement and salt-tolerance text of HPAM/DNSS-HM8 suspension.HPAM/DNS-HM8 suspension has no obvious salt tolerance capacity,though it has good thermal tolerance.In order to overcome such a drawback,DNSS-HM8 was synthesized by introducing the–SO₃H group onto the surface of DNS-HM8.Besides,basied on the former research work,DNSS-HM8 can become a kind of surfactant which can lower oil-water interfacial tension.Core displacement experiments show that pouring into 0.6 pore volume HPAM/DNSS-HM8 suspension improved 33.85%crude oil recovery.On the other hand,HPAM/DNSS-HM8 suspension also possesses oil emulsification,which indicate it is a kind of surfactant-functional polymer system for effective oil displacement.