Abstract：In drilling engineering, 75% of the drilled formation is a shale formation, wellbore instability problems caused by it are more than 90%. Summary the research status of the wellbore stability ,and shale expansion mechanism,from the perspective of drilling fluids of different pH values and different degree of mineralization analysis the shale inhibition.Wellbore stability problems is a complex worldwide problem,it involves a multidisciplinary field and influenced by a variety of main objective factors,so this paper without considering mechanics and temperature and pressure effect ,only considering chemical ,take a simple discussion about the wellbore stability from the Angle of northern jiangsu province. Due to shale contains water-sensitive clay minerals and when it contacts with drilling fluids, shale and drilling fluids interact and lead to hydration expansion. Through the shale inflation experiment, it indicates that the effect of different salinities and different pH value on the shale inhibitory. The experimental results obtained hydroxide was the promotion of hydration of shale clay dispersion. The higher the concentration of sodium chloride and potassium chloride,the stronger inhibition of shale. Concentration of 2% -10% calcium chloride solution of shale expansion is not very different, but as the concentration further increased, suppression will be significantly improved.
Key words: wellbore stability; Shale expansion; fluid property; pH value; mineralization degree...