Studies On Stability Of White Oil-Based Emulsions

Oil-based drilling fluids are water-in-oil(W/O)emulsions.Studying the stability of W/O emulsions,especially their high-temperature stability,can deepen the understanding of the hightemperature resistance of oil-based drilling fluids.In this work,the surface/interface activities and emulsifying performances of a commercial ternary compound emulsifier(CRJ)and a self-made emulsifier(SDR-8)were investigated using 3#white oil as the oil phase and pure water or CaCl2 aqueous solution as the water phase.Especially,the effect of high-temperature aging treatment(simulating the circulation process in drilling engineering)on the stability of emulsions was determined.The relevant mechanisms were 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)Interfacial activity of emulsifiersThe surface/interface activities of the commercial emulsifier CRJ and its components(CRJ-1,CRJ-2 and CRJ-3)and the self-made emulsifier SDR-8 were determined.The effect of concentration,temperature,and electrolyte(CaCl2)as well as the temperature resistance of SDR-8 were examined,and the related mechanisms were discussed.The results show that the lipophilic CRJ-1 doesn’t reduce the surface tension of white oil,and the hydrophilic CRJ-2 and CRJ-3 can significantly reduce the surface tension of water.All of the three emulsifiers can significantly reduce the white oil/water interfacial tension,exhibiting obvious interfacial activity.The order of interfacial activity is CRJ-1>CRJ-3>CRJ2.The combination of the three emulsifiers can significantly enhance the interfacial activity,showing obvious synergistic effect.SDR-8 can significantly reduce the white oil/water interfacial tension and form elastic films at the interfaces.After high-temperature(180℃)treatment for 8 h,its interfacial activity and film elasticity was somewhat enhanced,indicating its potential as a high-temperature emulsifier.(2)Emulsifying performance of emulsifiers and stability of emulsions at room temperatureThe emulsifying performances of CRJ and SDR-8 as well as the stabilities of emulsions were investigated at room temperature.The effects of various factors such as the oil/water volume ratio(Ro/w,9/1-5/5),CaCl2,Ca(OH)2,and organoclay were determined,and the related mechanisms were discussed.The results show that Both CRJ and SDR-8 can emulsify white oil-pure water system to form emulsions,called CRJ-H2O and SDR-H2O systems,respectively,for simplicity.The CRJH2O system is O/W emulsion in the Ro/w range of 8/2-6/4,while SDR-H2O system is W/O emulsion in the Ro/w range of=9/1-7/3 but O/W emulsion at Ro/w=6/4 and 5/5.The CRJ-H2O and SDR-H2O emulsions both have good stability,and the latter is better than the former.Adding 25 wt%CaC12(aqueous phase)and 30 g/L Ca(OH)2 into CRJ-H2O and SDR-H2O systems can also form W/O emulsions,called CRJ-Ca(OH)2 and SDR-Ca(OH)2 systems,respectively,for simplicity.The former exhibits high standing stability,but the latter is extremely unstable(demulsification within 5 min).Addition of 20 g/L organoclay in the CRJCa(OH)2 and SDR-Ca(OH)2 systems can remain their W/O emulsion states,called CRJCa(OH)2-OC and SDR-Ca(OH)2-OC systems,respectively,for simplicity.Organoclays can enhance the stability of the emulsions at room temperature.(3)Effect of high-temperature aging on the stability of emulsionsThe effect of high-temperature(150,180 and 232℃)aging treatment for 8 h on the type and standing stability of the emulsions was determined,and the relevant mechanism was discussed.The results show that the high-temperature aging doesn’t change the type of CRJ-Ca(OH)2,SDR-Ca(OH)2,CRJ-Ca(OH)2-OC,and SDR-Ca(OH)2-OC emulsions.With an increase in the aging temperature,the stability of CRJ-Ca(OH)2 and SDR-Ca(OH)2 emulsions increases,probably arising from the formation of "organic Ca(OH)2" nanoparticles,while that of CRJCa(OH)2-OC and SDR-Ca(OH)2-OC decreases,probably arising from the aggregation of organoclay particles.With a decrease in Ro/w(or an increase in the volume fraction of aqueous phase),the stability of each emulsion after high-temperature aging tends to increase.This is because the increase in dispersed droplets may inhibit their settlement.Notably,After high-temperature(232℃)aging treatment,the stability of SDR-Ca(OH)2-OC system is obviously higher than that of CRJ-Ca(OH)2-OC,indicating that the emulsifying ability of SDR-8 at high temperature is better than that of the compound emulsifier CRJ.(4)Performance evaluation of oil-based drilling fluidsThe performance of oil-based drilling fluid(mud)prepared using SDR-8 was evaluated.The results show that,after aging at 232℃ for 16 h,the heavy mud(with Ro/w=9/1,emulsifier dosage of 40 g/L,and mud density p of 2.4 g/cm3)exhibits good performances,such as the yield stress of～5.5 Pa,the demulsification voltage of～740 V,and the high-temperature/highpressure(176 ℃/500 psi)filtration loss of～4.2 ml,which may meet the requirements of drilling engineering.In addition,SDR-8 can be used to prepare the oil-based mud with high aqueous phase(Ro/w=5/5)and low density(ρ=1.2 g/cm3),which is of great significance for the reduction of the mud costs.