Underbalanced drilling techniques in deep buried hill reservoirs in Huabei Oilfield

Aiming at improving the drilling velocity in deep buried hill reservoirs,preventing hole section leaking,detecting and protecting pay zones,the underbalanced drilling techniques were successfully applied to over ten wells in Jizhong exploration areas by integrating the underbalanced drill technical feature and formation characteristics there.The proposed methods of optimizing the underbalanced formation,well structure,bit correlation and drill fluid system,exactly calculating the drill fluid density and the well head control pressure have gained evident effects.ROP on underbalanced section of buried hill was 2-2.5 times faster than that of the adjacent well with no leak off happening.The shows of gas and oil given by DST results were active while drilling.Daily oil production of well Chang 6 was 108 m~3 and gas production was 2376m~3.At the same time, well Wengu 3 was producing 302.6m~3 of oil and 9.8×10~4 m~3 of gas every day.The successful implement of deep well underbalanced drilling technique in Huabei Oilfield pointed out a new way of improving the comprehensive exploitation benefit,as well as accumulated rich experience for application and dissemination in the future.