Abstract: In order to penetrate the formation with high temperature and pressure successfully and protect the environment,it is nec-essary to study an invert oil-emulsion drilling fluid which can withstand high temperature and has high density and low toxic-ity. Optimum seeking and development of emulsifiers are very important in stabilizing the drilling fluids and enhancing its property of resisting elevated temperature. In this paper,the emulsification was tested by electrical stability and centrifugal method. Aging or measuring its electrical stability in high tem-perature and pressure evaluated the temperature stability. It was determined that the emulsifiers are composed of organic
acids,amides and alkyl benzene sulfonates(ABS). Results show that the emulsion and high-density emulsion drilling fluid have good stability in elevated temperature.

Key words: drilling fluid, emulsifier, invert emulsification, toxicity, high temperature, high density, optimum seeking