The Application of a High Temperature Low Density Oil-in-Water Drilling Fluid in Well Lishen-1

The target zones of Well Lishen-1,Yingcheng Formation and Shahezi Formation,both have low formation pressure gradient(0.94～0.98).A low density(0.89～0.91 g/cm3) oil-in-water drilling fluid was chosen to drill the reservoir in underbalanced mode.This paper discusses the formulation optimization and maintenance of the high temperature low density oil-in-water drilling fluid.Using this fluid,the bottom hole pressure was not fluctuating in a wide range.At high temperature of 160 ℃,and oil/water ratio of 70∶30,the oil was still well emulsified in water.The shale formation in this well had been rinsed for 69 d,and no borehole sloughing and caving were observed.Hole diameter enlargement was only 9.3%.The well was successfully fired at well depth of 3,799.33 m and completed at well depth of 4,368.5 m.The well was drilled while blowout.Thirteen gas zones(totally 26 m in thickness) were found,with the highest production rate of 3,326 m3/h.