Study On The Preparation And Phase Inversion Mechanism Of Acid/base Responsive Reversible Invert Emulsion

The requirments for the fine development and the environmental protection is higher and higher with the development of the oilfield,so the working fluids with a single property can not meet the requirments of the field and the reversible invert emulsion which can performs different properties?wettability,viscoelasticity,stability,compatibility,et al?in different stages has a high research value.Such as reversible invert emulsion drilling fluid can reverse between O/W emulsion drilling fluid and W/O emulsion drilling fluid by changing environmental conditions which can focus the advantages of different liquid form on the reversible invert emulsion drilling fluid.In this paper,the preparation and phase inversion mechanism of reversible invert emulsion are studied which can provide guidance for the wider application of reversible invert emulsion in oilfield.The preparation scheme of a newly developed reversible invert emulsifier N,N-dimethyl-N'-oleoyl-1,4-butanediamine?reversible invert emulsifier DMOB?was studied by organic synthesis experiments and optimization experiments,and the reaction conditions were optimized.The acid/base responsive reversible invert emulsion which can achieve multiple reversible phase inversion was prepared by reversible invert emulsifier DMOB.The effects of the oil-water ratio;acid/base type;acid/base concentration on the reversible phase inversion process was studied through the study of the changes of the macro-properties?emulsion-breaking voltage;conductivity;pH;standing stability?and micro-properties?disperse droplet morphology?of the reversible invert emulsion during the reversible phase inversion process.The increase of the oil-warer ratio lead to the more difficulty of acid-induced phase inversion and the easier of base-induced phase inversion.The effect of the acid/base on the phase inversion due to they can provide effective amuonts of H⁺and OH^-differently.The reversible invert emulsion drilling fluid is studied base on the research results about the reversible invert emulsion.High-temperature-assistance and high density reversible invert emulsion drilling fluid which can achieve multiple reversible phase inversion?SKLAN 5^#oil+25.00 wt.%CaCl₂ solution?oil-water ratio is 50:50?+1.25g/100mL reversible invert emulsifier DMOB+2.49g/100mL wetting agent LKD+2.00g/100mL Organic soil NTC+0.50g/100mL CaO+1.00g/100mL Filtrate reduce agent DLG+83.00g/100mL barite?.The reversible invert emulsion drilling fluid prepared by laboratory?180?,1.50g/cm³?has obvious advantages over the reversible invert emulsion drilling fluid which is used by Shengli oilfield?120?,1.20g/cm³?,but also perform well in the aspects of sedimentation stability,oil cuttings disposal,filter cake removal.The change of the reversible invert emulsifier?HLB?during the reversible phase inversion process was studied;the change of the distribution of the reversible invert emulsifier at the oil-water interface during the reversible phase inversion process was studied using Zeta potentiometer;the change of the micro-properties of the reversible invert emulsion during the reversible phase inversion process was studied using microscope,Cryo-TEM,laser particle sizer.;the change of the macro-properties of the reversible invert emulsion during the reversible phase inversion process was studied using Electrical stability tester,Conductivity meter,pH meter,Viscometer,Rheometer The reversible phase inversion process?acid-induced phase inversion:W/O emulsion?W/O/W emulsion?O/W emulsion;base-induced phase inversion:O/W emulsion?Double continuous structure?O/W/O emulsion?W/O emulsion?and the reversible phase inversion mechanism of the reversible invert emulsion is revealed:the decrease/increase of pH value of the emulsion system can due to the increasing/decreasing of the proportion of ionic surfactant in the oil-water interface film,thereby the HLB value of the oil-water interfacial composite emulsifier increase/decrease,causing the change of the microstructure of the emulsion,eventually leading to the reversible phase inversion of the reversible invert emulsion.The mechanism of the effect of organic soil on reversible invert emulsion was revealed from the perspective of the microstructure of the emulsion and the oil-water composite interface membrane:the organic soil not only distributes in the oil-water interface with the surfactant forms the composite emulsifier but also can affect the microstructure of the emulsion which affect the reversible phase inversion of the reversible invert emulsion,due to the more difficulty of acid-induced phase inversion,the easier of base-induced phase inversion and the increase of the emulsion-stability.The mechanism of the effect of CaCl₂ on reversible invert emulsion was revealed from the perspective of the Zeta potential of the emulsion and the density of the water-phase:the adding of the CaCl₂ not only can change the oil-water composite interface through compressing diffusion electric double layer,but also can change the density difference between oil-phase and water-phase which can due to the change of the emulsion-stability,due to the easier of acid-induced phase inversion,the more difficulty of base-induced phase inversion and the decrease of the emulsion-stability.