Study On Invert Emulsion Drilling Fluids

The global growing demand for oil and the industry’s progress has made the amount ofcomplex wells, including high temperature deep wells, horizontal wells and offshore wells,gradually increase. As a necessary condition of drilling, drilling fluid has achievedconsiderable development. Because of its excellent anti salt and anti high temperatureperformance, outstanding lubricating properties and reservoir protection performance,oil-based drilling fluid has become the first choice for drilling complex wells.Compared with water-based drilling fluid, oil-based drilling fluid has experienced ashorter-time development, and there are far less basic theoretical studies and treatment agentfor oil-based drilling fluid than for water-based drilling fluid. Foreign oil-based drilling fluidsystems and technology are relatively mature, and oil-based drilling fluid treatment agents arealso variable. The chance of using oil-based drilling fluid in China is relatively less, and thevariety of treatment agent for oil-based drilling fluid is single. In order to avoid the adverseimpact on environment and penetration rate while using asphalt products as oil-based fluidloss additive, organic amine is used to modify humic acid. Then through orthogonalexperiments, the optimal conditions of the synthesis reaction are found out, and a kind ofoil-based fluid loss additive, CYFL-2, is synthesized. Experiments show that CYFL-2canhelp reduce the fluid loss of oil-in-water emulsion drilling fluid, and have little impact on therheological properties of the drilling fluid system, and can handle the temperature of180°C.Through experiments for optimizing the type and amount of the treatment agents, theformulation of invert emulsion drilling fluid system is determined as follows:5#white oil+3%primary emulsifier DCMul+1%primary emulsifier DSY-1+0.5%secondary emulsifierFB-MOCOAT+CaCl2solution (20wt%)+3%organic soil HFGEL-130+1%CaO+3%fluid loss additive CYFL-2。The oil/water ratio is8:2. Barite is used to increase the weight ofdrilling fluid and the wetting agent is DCWET, with the optimal dosage1g/100g barite. The system has good rheological performance and electrical stability before and after180℃/16h’saging, and the high temperature and high pressure filtration at180°C/3.5Mpa is small whichshows better fluid loss performance. Evaluation experiments show that the system has goodresistance to water pollution, which it is still able to maintain good rheology, fluid loss andelectrical stability when the percentage of water pollution reaches15%. It has goodlubricating property with friction coefficient only0.065. It has excellent inhibitionperformance with shale recovery96.5%, and the coefficient of linear expansion of shale coreis almost zero. It has good reservoir protection performance with permeability recoverypercentage more than90%. It has great sealing performance with small Invasion depth ofsand bed.