Study and application on drilling fluid in Shahejie formation of Chengdao Oilfield

In order to prevent the collapse of Shahejie formation in Chengdao Oilfield during drilling,a new seawater drilling fluid with strong inhibition was developed.According to analysis for instability mechanism,main reasons that result in well bore instability in Shahejie formation were found.Experimental results and field applications showed that new inhibitive drilling fluid is characterized by good rheology,low filtrate loss,superior collapse-preventing effectiveness,strong seawater and clay resistance.Satisfactory anti-collapse effectiveness has been achieved from the tested wells in Shahejie formation.