Interfacial Behaviour Of Kaolinite-based Amphiphilic Janus Nanosheet At Oil-water Interface:Implications For Enhanced Oil Recovery

To meet the increasing global energy demand,it is a matter of significance to extract residual oil after primary and secondary recovery with an economical and environmentally friendly enhanced oil recovery(EOR)method which remains challenging.EOR methods such as surfactant flooding have limited applications,require high volume,expensive,and pose environmental risks.Nanofluid flooding can be implemented on conditions where other EOR methods such as surfactant flooding cannot be implemented(i.e.,high temperature and high salinity conditions),does not require high volume,cheap,and is eco-friendly.Particularly,nanofluids containing amphiphilic Janus nanoparticles(AJNPs)have been recently demonstrated to be highly efficient for EOR by generating Pickering emulsions or macroscopically observable interfacial films at oil-water interface.However,the current AJNPs for EOR require complex and costly synthesis methods,and its mechanisms for EOR especially its interfacial behavior at oil-water interface remain unclear.In this thesis,an economic,environmentally friendly,and reliably effective EOR method based on a nanofluid containing kaolinite-based amphiphilic Janus nanosheets(AJNS),which is a cheap and abundant material,has been presented.Firstly,kaolinite-based AJNS(Kaol KH)was developed via a facile and scalable method by exfoliating pristine kaolinite(Kaol)into nanosheets(Kaol NS)aided by dimethyl sulfoxide(DMSO)intercalation then grafting 3-methacryloxypropyltriemethoxysilane(KH-570)onto the Alumina Octahedral Sheet(AOS)side of Kaol NS.The grafting amount of KH-570 which affects the amphiphilic feature of the Kaol KH Janus nanosheets was found to be dependent on reaction temperature,with more KH-570 grafted at 70°C(Kaol KH@70)than at 40°C(Kaol KH@40)resulting to a more hydrophobic surface obtained on the AOS side of Kaol KH@70 than that of Kaol KH@40 which favors the formation of an interfacial film.Secondly,the unmodified Kaol NS can stabilize Pickering emulsions in both hydrophilic glass tube and hydrophobic plastic tube as a typical colloidal particle with a surface-active property.The interfacial behavior of Kaol KH at oil-water interface was investigated and found to be fascinating as it either produces stable Pickering emulsions or forms an eye-observable planar interfacial film or both,depending on surface chemistry of the Janus nanosheets,its concentration,and container surface wettability.Specifically,Kaol KH@40 was able to stabilize Pickering emulsions in hydrophilic glass tube while forming interfacial films in hydrophobic plastic tube whilst Kaol KH@70 formed interfacial films in both hydrophilic and hydrophobic tubes while having emulsions co-existing at high particle concentrations(c.a.(?) 0.015wt%).Moreover,the interfacial film was demonstrated to be strongly elastic.Thirdly,to address the detriments of emulsion to the oil recovery equipment and oil quality,a temperature-responsive Pickering emulsion that can be created and destroyed at will has been developed based on a poly(N-Isopropylacrylamide)(PNIPAAm)grafted kaolinitebased Janus nanosheets(Kaol NP).Kaol NP exhibited a “smart” feature as at room temperature,Kaol NP formed and stabilized Pickering emulsions whereas above ?30°C,the emulsions collapsed and then formed an interfacial film.Such controllable behavior has been well demonstrated by rheological measurement.Finally,EOR efficiency of Kaol,Kaol NS,and Kaol KH nanofluids has been evaluated based on core-flooding experiments using a hydrophilic rock saturated with crude oil.Results indicated that the kaolinite-based AJNS nanofluids enable a great enhancement in oil recovery even at a particle concentration as low as 0.010 wt%,particularly Kaol KH@40,which formed stable Pickering emulsions,showed a superior EOR efficiency of 22.37%,comparable to chemical methods or even better.The reason could be that that Pickering emulsions have higher performance as they reduce the mobility ratio or increase the capillary number which results to an improvement of the macroscopic oil displacement efficiency or an increase in the microscopic displacement efficiency,respectively.