Preparation Of Nanoemulsions And Its Application In Water-based Drilling Fluid & Completion Fluid

With the exploration of unconventional gas,nanoemulsions had been used in the process of drilling of ultra-low permeability gas recently,but there are still few research on the preparation of nanoemulsions for oilfield chemistry.Therefore,how to prepare the nano emulsion with fine dispersity and long-term stability has become the bottleneck of the wide application of nanoemulsion in oil field.In addition,interaction nanoemulsion in water-based drilling fluids still keep unclear.According to water-based drilling fluid characteristics of shale gas and tight gas reservoirs,the preparation of nanoemulsions had been done,and the mechanism of nanoemulsions in water-based drilling fluids & completion fluids has been discussed.Nanoemulsion was prepared by two-step dilution method.The researcher investigated the influence of the phase inversion temperature,emulsification methods and the structure of microemulsion on the droplet size of nanoemulsion,and evaluated reservoir protection of nanoemulsion by water blocking damage evaluation,spontaneous imbibition experiment and core permeability recovery experiment.In addition,researcher prepared paraffin nanoemulsion optimization experiments of different composition and investigated performances of lubrication and wellbore stability of nanoemulsion by lubrication test,adhesion coefficient test and shale hot-rolling dispersion test.A new type of water-based drilling fluid for shale gas reservoir protection,SWP drilling fluid system,was developed.The results show that n-octane nanoemulsion made by bicontinuous or O/W microemulsion has smaller particle sizes,and the size of nanoemulsion was smallest when phase inversion temperature of n-octane microemulsion is close to the emulsion temperature.n-octane nanoemulsion with low surface tension can increase the contact angle between test solution and sand core,weaken pore throat shrinkage caused by hydrous swelling,and finally decrease the capillary pressure of pore throat caused by the incrusion of external fluid upon reservoirs.N-octane nanoemulsion has good performance of reservoir protection.Paraffin nanoemulsion with good lubrication can adsorb on the surface of metal,clay and drilling tool by electrostatic action.Paraffin nanoemulsion form a layer of hydrophobic membrane in the surface of the shale by adsorption,which can reduce the contact between the water molecules and the shale,weaken shale hydration swelling and contribute to the wellbore stability.A new type of water-based drilling fluid for shale gas reservoir protection,SWP drilling fluid system,was developed and its overall performance is good.