Research On Micro-lactic Acid Flushing Fluid Suitable For Oil-based Drilling Fluids

With the development of oil and gas exploration,the application of oil-based drilling fluid is increasing.The mud cake and oil films produced by oil?based drilling fluid is difficult to be cleaned,which often results in low displacement efficiency and poor cementing strength between two interfaces,and threaten construction safety.Therefore,it is necessary to study a targeted flushing system to effectivelyflush the oil film and mud cake,so as to create conditions for subsequent cementing.Microemulsions have many advantages,including ultra tow oil-Water interfecial tension,strong dissolution ability and stable thermodynamic properties.The acid solution can react with the inorganic solid phase materials in the mud cake to etch and kiosen the mud cake.Based on the advantages of microemulsion and acid solution,a study on microemulsion acid flushing fluid was presented.In this paper,the influence of surfactant and oil types and proportions on phase behavior of microemulsion were investigated by pseudo-ternary phase diagram and orthogonal optimization experiment.Two kinds ofmicroemulsion formulations with large microemulsion regions were optimized and selected,their particle size,structure,teryperature resistance and salt resistance were analyzed.On the basis of microemulsion formulation,the type of acid solution suitable for preparing the microemulsion acid was determined by investigating the effection of acid on phase behavior of microemulsion.Furthermore,in order to achieve better washing efficiency,the optimal ratios of ingredients were found to be n-butanol:n-octanol=2:1,CTAC:NP-10=23,HF:CH3COOH=1:4,co-surfectant:main surfectant=1:1.5,surfactant:diesel oil=1:3.The properties and structures of microemulsion acid flushing fluid were analyzed.The results showed that the microemulsion acid formed by the optimized formula was O/W type.The particle size of microemulsion acid ranges from 20 to 30 nm.The microemulsion acid remained stable and non stratified urnder high speed centrifugation at 6000rpm.Its teirperature resistance was up to 80oC,and salt resistance(CaC12)was up to 60 g/L,rheological properties was good.Lastly,the flushing effects of flushing fluid were simulated and evaluated by six-speed rotating viscometer and dynamic flushing simulator.The flushing efficiency of the microemulsion acid flushing solution was 98.58%,the cementing strength of the first interface of cement sheath was 2.05 MPa,it was 8.9 times higher than before flushing;and the second interfece was 0.77 MPa,it was 6.4 times higher than before flushing.Tbe evaluation results showed that the microemulsion acid flushing fluid developed in this paper can improve the flushing efficiency,enhance the cementing strength of cement sheath.In this paper,a new research approach of flushing fluid for oil-based drilling fluid was put forward,and an effective formula was obtained through experimental study,which raises a new possibility for cementing pre-flushing fluid.