Effect Of Wax Precipitation During The Cooling Process On The Stability And Rheology Of Water-in-Oil Emulsions

With the development of oilfields,oil-water mixed transportation has gradually become the main transportation method in gathering and transportation systems.Therefore,in most cases,water-in-oil crude oil emulsions exist in oilfield gathering and transportation systems.When the pipelines are under low temperature conditions,wax crystals will be precipitated in the waxy crude oil emulsions,which greatly improves the stability of the emulsions and also makes the rheology of the emulsions more complicated.It increases the cost of pipeline transportation and also increases the risk of pipeline blocking.So this paper studied the effect of wax crystallization on the stability and rheology of waxy model oil emulsions,which is of great significance for the safe operation of oil-water mixed pipelines in oilfield gathering and transportation systems.In this paper,glycerol monooleate(GMO),polyoctadecyl acrylate(POA)and asphaltenes were selected as emulsifiers to prepare model oils and their W/O emulsions.The interaction between the three emulsifiers and the wax molecules was explored through the crystallization exothermic characteristic experiments,the gelation point measurement experiments and the microscopic observation experiments.The results showed that GMO did not co-crystallize with wax molecules,and the wax crystal morphology in the model oil doped with GMO was slender and needlelike.Both POA and asphaltenes could co-crystallize with the wax molecules,and the wax crystals in the model oils were all spherical aggregates.The precipitation of wax crystals at the oil-water interface was jointly studied by microscopic observation experiments and interface rheological experiments.The results showed that GMO,POA and asphaltenes could greatly reduce the interfacial tension.This is because the wax molecules could co-crystallize with POA and asphaltenes adsorbed at the interface,wax crystals were precipitated at the oil-water interface to form an elastic interface film.When GMO was used as an emulsifier,wax crystals could not be precipitated at the interface.The effect of the network structure of wax crystals on the stability and rheology of the emulsifier-doped model oil emulsions was studied through macroscopic stability experiments and rheological experiments.The results showed that both wax crystals and water droplets contributed to the formation of the emulsion gel structure.Under the same conditions,with the precipitation of wax crystals,the wax crystals overlapped each other to form a network structure.The macroscopic stability of the emulsions was improved,and the viscoelastic parameters and the yield stress were both increased.The effect of water cut on the stability and rheology of emulsions was studied through crystallization exothermic characteristic experiments,macroscopic stability experiments and rheological experiments.The results showed that when there was a co-crystallization effect between the emulsifier and the wax molecules,the addition of water phase could increase the wax appearance temperature(WAT)of the emulsions,and the WAT was increased with the increase of the water cut.When there was no co-crystallization effect between the emulsifier and the wax molecules,the water phase could not affect the WAT.During the formation of the emulsion gel system,wax crystals and water droplets formed a network structure together.When there was a co-crystallization effect between the emulsifier and the wax molecules,water droplets played a dominant role in the formation of the network structure,and the structural strength of the gelling system increased as the water cut increased.Otherwise,wax crystals played a dominant role in the formation of the network structure,and the structural strength of the gelling system decreased as the water cut increased.The effects of the cooling rate and the dynamic cooling process on the stability and rheology of emulsions were studied through macroscopic stability experiments and rheological experiments.The results showed that with the increase of the cooling rate,the stability of the emulsions increased,and the viscoelastic parameters and the yield stress increased.In the low shear rate range,as the shear rate increased,the macroscopic stability of the emulsions decreased,and the viscoelastic parameters and the yield stress decreased.In the high shear rate range,with the increase of shear rate,the demulsification of high-speed shear in the emulsions doped with GMO dominated,the macroscopic stability of the emulsions decreased,and the viscoelastic parameters and the yield stress decreased.In the high shear rate range,with the increase of shear rate,the emulsification of high-speed shear in the emulsions doped with POA or asphaltenes dominated,the macroscopic stability of the emulsions increased,and the viscoelastic parameters and the yield stress increased.