High-temperature Stability Of Water-in-oil Emulsions

The oil-based drilling fluids are the water-in-oil(W/O)type emulsions,supplemented with various treatment agents such as filtration reducers,flow pattern adjusting agents,and weighting agents to regulate the performance of drilling fluids to meet the requirements of drilling engineering.Emulsions are thermodynamically unstable,and phase separation or demulsification easily occurs at high temperature,which limits their application in drilling engineering under high temperature conditions.The development of high-temperature resistant oil-based drilling fluids has become one of the hot topics in the field of oilfield chemical engineering.Studying the high-temperature stability of W/O emulsions can deepen the understanding of the high temperature stability of oil-based drilling fluids.In this thesis,gas-to-liquids and white oils were chosen as base oil,and the high-temperature stability of W/O emulsions was investigated,involving the surface/interfacial tensions of oil and water phases,the interfacial activity of the emulsifiers used in oil-based drilling fluids,and the high-temperature stability of W/O emulsions,as well as the effect of various factors such as temperature,salts,aging treatment,and compositions on the properties or performance.The relative mechanisms are discussed.It is expected to provide useful information for the development and application of high-temperature resistant oil-based drilling fluids.The main research contents and conclusions of this thesis are as follows:(1)Effect of temperature and salts on surface/interfacial tensions of oil and water phasesTwo base oils(gas-to-oil and 3#white oil)were chosen as models,and the influence of temperature and salts on the interface tensions of oil and water phases(?o and ?w)as well as their interfacial tension(?o-w)was determined.The salts studied include inorganic NaCl,KCl and CaCl2 and organic CH3COONa,CH3COOK,HCOONa,HCOOK and Ca(HCOO)2.The results show that with an increase in temperature in 25-66?,the ?o and ?w all decrease,but the ?o-w increases,and salts have no influence on the increase tendency.The type and concentration(Csalt)of salts exhibit obviously impact on the ?w??o-w.With an increase in the Csalt of NaCl,KCl,CaCl2,HCOONa,and HCOOK,the ?w almost linearly increases.Relatively speaking,the increasing magnitudes of NaCl,KCl and CaCl2 for ?w are higher than those of HCOONa and HCOOK.The organic salts CH3COONa,CH3COOK and Ca(HCOO)2 have on obvious influence on ?w under the studied conditions.The inorganic salts NaCl and KCl have no obvious impact on the ?o-w.However,CaC12 and the organic salts studied lead to a decrease in ?o-w.The ability of reducing ?o-w varies with the type of salts.For the gas-to-oil/water interface,the order of reducing ?o-w capability is:CaCl2?CH3COONa?HCOOK>HCOONa?Ca(HCOO)2?CH3COOK>NaCl?KCl.For the 3#white oil/water interface,it is:HCOOK?CH3COONa?Ca(HCOO)2>HCOONa?CH3COOK?CaCl2>NaCl?KCl.CH3COONa and HCOOK have the strongest ability to reduce the ?o-w.In particular,CaCl2 can significantly reduce ?o-w,which is one of the reasons why CaCl2 solutions are often used as the internal phase in oil-based drilling fluids.(2)Interfacial activity of emulsifiers used in oil-base drilling fluidsThe surface/interfacial activities and the interfacial dilatational rheology of the emulsifiers RHJ-? and RHJ-? used in oil-base drilling fluids were determined,and the effect of temperature and aging treatment on the properties was examined.The result show that the RHJ-? and RHJ-? cannot change the surface tensions of synthetic oil(a gas-to-oil)and 3#white oil,but all can significantly reduce the ?o-w(by-40 mN/m),showing obvious interfacial activity.In addition,the interfacial activity of RHJ-? is stronger than that of RHJ-?.The change in temperature in 25?66? almost does not affect the interfacial activity of the two emulsifiers.After treated at high-temperature(180 and 232?)for 16 h,the colors of RHJ-?and RHJ-? turned black,but their surface/interface activities had no obvious change,indicating that they have good temperature resistance.The aging treatment at high-temperatures,especially at 180?,can enhance the dilatational modulus of interfacial films.RHJ-? and RHJ-? form viscoelastic films at oil/water interfaces,and the interfacial film strength(dilatational modulus)of RHJ-? is stronger than that of RHJ-?.The combination of RHJ-? and RHJ-? can form a mixed interfacial film,which strength is between those of RHJ-? and RHJ-?.With an increase in the concentrations of emulsifiers,the dilatational modulus of interfacial films initially increases and then decreases,showing a maximum.(3)High-temperature stability of W/O emulsionsUsing synthetic oil and 25%CaCl2 aqueous solution as oil and water phases,respectively,water-in-oil(W/O)emulsions were prepared in the presence of Ca(OH)2.The effect of various factors such as system composition,aging temperature,and standing temperature on the stability of the emulsions was determined,and the stability mechanism was discussed.The results show the resultant emulsions have good dispersion stability,and the combination of RHJ-? and RHJ-? exhibits a synergistic stabilizing effect.The aging treatment at high temperature(180 and 232?)for the emulsions can obviously enhanced their stability,mainly arising from the reaction between the emulsifiers and Ca(OH)2 to form "organic Ca(OH)2",thus enhancing the high-temperature stability of the emulsions.With an increase in the volume ratio of water to oil phase(from 1:9 to 5:5),the stability of the emulsions is obviously enhanced.These results provide an important basis for the development of high temperature-resistant oil-based drilling fluids.