Investigation Of Physical Properties Of Nano-cellulose Based Nano-fluids And Oil Displacement Mechanisms

Combined with the confliction between production and environment,the development of"stable,efficient,and green" displacement agents has become one of the topics in the enhanced oil recovery for oilfield exploitation.Based on the current increasing demand for the chemical systems in the enhanced oil recovery technologies and the difficulty about the development of "high-efficiency,green-injection" systems,this work have used the "plentiful,rich resource,degradable,green" biomass polymer material—nanocellulose(NC,NC-KY,NC-KYSS)in the EOR due to the unique properties such as viscoelastic through the chemical modification.Through these fundamental investigations,the properties of nano-cellulose based nano-fluids;the interfacial tension between oil/water/solid phases;the influence of different factors on oil displacement efficiency;the observation of the percolation law and displacement efficiency through a microscopic visualization model have been studied.Therefore,it was found that the amphiphilic nano-cellulose(NC-KYSS)has been selected due to the improved performance.Meanwhile,the result shows the influence of different factors on the flow characteristics of nano-cellulose and the efficiency of oil-displacement efficiency,as well as the phenomena of the micro-displacement efficiency of nano-cellulose.Furthermore,it was also hoped to explore the relationship among chemical structure,physical properties,flow behavior and the enhanced oil recovery.The relationship is very useful for us to understand the mechanisms of nano-fluids in EOR.These mechanisms of nano-cellulose in EOR can provide us a theoretical and experimental basis for the development of this "green"nano-fluid flooding system and its application in oilfields.In this work,the physical properties such as thermal stability,salt resistance,morphology,rheological properties and dispersity were investigated.It was found that the nano-cellulose fluids show the non-Newtonian feature and viscoelasticity.After grafting,the morphological features of the nano-cellulose fluids were not altered.The nano-cellulose maintained the fibrous structure with the exception of slight roughness surface of NC-KY and NC-KYSS.And the thermal stability of NC-KY and NC-KYSS was slightly higher than NC.The dispersion and salt tolerance were also improved due to the enlarged electrostatic repulsive force and molecule space after chemical modification.In summary,the physical properties of the amphiphilic nano-cellulose fluids(NC-KYSS)grafted by AMPS and ASA groups were improved.To comprehensively investigate the static and dynamic properties of these nano-cellulose fluids,the oil/nano-fluids/solid interfacial behaviors,IFT and emulsifiability were carried out.The results showed that the proposed nano-cellulose can "wedge spread" on the rock surf-aces and reverse the strongly oil-wet to intermediate or water-wet states relying on surface adsorption.The IFT(interfacial tension)between oleic and aqueous phases was reduced to 0.4 mN/m.Moreover,the prepared O/W emulsions were fairly stable upon storage due to the interface stabilizing effect of the nano-fluids.Through macroscopic displacement experiments,the effects of injected nano-fluids,core penneability,crude oil viscosity,and core heterogeneity on the oil displacement efficiency were studied.The results showed that with the increase of the injected nano-cellulose and the permeability of the core,the enhanced oil recovery will increase continuously and then reach stable.There was a good potential in enhanced oil recovery when the crude oil viscosity is high.The injected nano-cellulose will regulate the high permeability zones and start the middle or lower permeability zones,indicating the profile control effect.Finally,the dynamic displacement and flow behaviors of the nano-fluid were investigated with a five-spot visualization micromodel and microscopic visual displacement model.The flow behaviors and production dynamics of the nano-fluids flooding were elucidated based on the observations.It was found that the residual oil was emulsified and entrained in the aqueous phase due to the unique properties of nano-cellulose;the oil film on the core surface can be separated;nano-cellulose can drag the oil droplets into "silk" because of the viscoelasticity properties,forming the new flow channel.In summary,amphiphilic nano-cellulose by chemical modification can be used in enhanced oil recovery technologies because of their unique properties,indicating the potential in enhanced oil recovery technology and significance of research.