Studies On Stability Of Water-in-White Oil Emulsions

The oil-based drilling fluids are essentially water-in-oil(W/O)emulsions.Studying the stability of W/O emulsions,especially their high-temperature stability,is of great significance for the development of high-temperature resistant oil-based drilling fluids.In this work,the surface/interfacial activities and emulsifying performances of a self-made carboxylic emulsifier SDR-10 were studied using 3#white oil as the base oil,in particular,the effect of aging temperature on the stability of its emulsions(simulating the circulation process in drilling engineering)was investigated,and the relevant mechanisms were discussed.It is expected to understand the application prospect of SDR-10.In addition,the emulsifying performances of a commercial emulsifier RHJ were determined using 3#white oil as the oil phase and 25 wt%CaCl2 aqueous solution as the water phase,and,especially,the properties of RHJ-formed high internal phase emulsions(HIPEs)were investigated.It is expected to provide useful information for the application of the HIPEs.The main research contents and conclusions of this thesis are as follows:(1)Interfacial activity of emulsifierThe surface/interfacial activities and dilational rheological properties of the self-made emulsifier SDR-10 as well as the effect of its concentration and temperature on the properties were investigated by surface tensiometer and interface rheometer.In particular,the interfacial activity and dilational rheology of SDR-10 after aging treated at high-temperatures(180232℃)were determined.The results show that the emulsifier SDR-10 is strongly lipophilic and has no surface activity for white oil,but it can significantly reduce the white oil/water interfacial tension,exhibiting obvious interfacial activity.SDR-10 has good temperature resistance.After hightemperature aging treatment for 8 h,its interfacial activity is slightly enhanced than before aging.SDR-10 can form elastic interfacial films at the white oil/water interface.In particular,after aging at 200℃ for SDR-10,the strength of the interfacial films is significantly improved,which is beneficial to the stability of emulsions.(2)Emulsifying performance and emulsion stabilityThe emulsifying performances of SDR-10 were investigated.The effects of various factors such as oil/water volume ratio(Ro/w)or water-phase volume fraction(φw),inorganic salts(CaCl2),Ca(OH)2,organoclay and,especially,the high-temperature aging treatment(180232℃,8 h)on the emulsion stability and rheology were determined,and the stability mechanism was discussed.The results show that SDR-10 can emulsify white oil-pure water mixtures to form emulsions(denoted as ’SDR-H2O’ for simplicity),which are W/O-type in the Ro/w range of 9/11/9.The high-temperature aging at 1 80℃ can not reverse the type of the emulsions.The hightemperature aging at 200 and 232℃ can reverse the type of the emulsions with φw≥ 0.9 andφw≥ 0.6 respectively.With an increase in the aging temperature(180-232℃),the stability of emulsions tends to decrease.In the presence of 25 wt%CaCl2 and 3.0 g/100 mL Ca(OH)2,the W/O-type emulsions can be formed in the Ro/w range of 9/1-1/9,called ’SDR-Ca’ for simplicity.The stability of the SDRCa is significantly enhanced compared with the SDR-H2O,indicating that CaCl2 and Ca(OH)2 have a synergistic stabilizing effect.After high-temperature aging treatment,no changes in the type and stability were observed for the SDR-Ca,indicating their good temperature resistance.At high temperatures,CaCl2 and Ca(OH)2 can react with carboxylic emulsifier SDR-10 to form carboxylic acid-calcium soap and ’organic Ca(OH)2’,which may be the main reasons for enhancing the temperature resistance of emulsions.By adding 2.0 g/100 mL organoclay to the SDR-Ca,a stable W/O-type emulsions can be formed in the range of Ro/w=9/1-6/4,denoted as ’SDR-Ca-OC’.The stability of SDR-Ca-OC systems is significantly improved in comparison with SDR-H2O and SDR-Ca,which may be caused by the increase of external-phase viscosity induced by organoclay.After hightemperature aging treatment,the emulsion type does not change,but its stability shows a decreasing trend.Before and after the aging treatment at 180℃,the SDR-H2O and SDR-Ca systems(Ro/w=8/2)are Newtonian fluids,with a dominant viscous behavior and without obvious thixotropy,but the SDR-Ca-OC system(Ro/w=8/2)is a non-Newtonian fluid,with a dominant elastic behavior and showing obvious positive thixotropy.With an increase in φw,the viscosity,elasticity,and positive thixotropy of SDR-Ca-OC emulsions all increase.The above results suggest that the self-made emulsifier SDR-1 0 has practical application prospects.(3)Stability and rheology of white oil-based high internal phase emulsionThe emulsifying properties of commercial compound emulsifier RHJ(including RHJ-1 and RHJ-2 components)were examined,and,in particular,the stability and rheological properties of RHJ-formed HIPEs were investigated.The effects of φw,emulsifier dosage(CRHJ),RHJ-1/RHJ-2 ratio(R1/2),and temperature on the HIPEs were investigated.The results show that,using 25 wt%CaCl2 aqueous solution as the water phase,RHJ can induce the formation of W/O emulsions,especially that of stable HIPEs with a maximum φw of～98.6%.After standing at room temperature for 30 days,no water and oil are obviously released from the HIPEs,but with an increase in the standing temperature,the stability of HIPEs decreases.With increasing CRHJ or with decreasing φw and R1/2,the stability of HIPEs is enhanced.The HIPEs formed by RHJ have good freeze-thaw stability.After three freeze-thaw(18℃/25℃)cycles,there are no significant changes in the appearance,droplet size,and rheological properties of the HIPEs systems.The HIPEs formed by RHJ are non-Newtonian fluids,with a dominant elastic behavior and showing positive thixotropy.With increasing φw and CRHJ,their viscosity,elasticity and thixotropy increase.The change in R1/2 do not affect their rheological and viscoelastic properties.With an increase in temperature,their viscosity,elasticity and thixotropy increase.