Gas Drilling Technology for Carboniferous Nappe in Northern Huoshaoshan

The carboniferous nappe in northern Huoshaoshan is over 1 000 m in thickness,which poses low penetration rate problem in drilling.In order to speed up well drilling,test of gas drilling was conducted in Well Huobei 021 and Huobei 022.To ensure the successful implementation of gas drilling,drilling and logging data of offset wells were used to predict pore pressure,fracturing pressure and borehole collapse pressureset up the three formation pressure of the carboniferous nappe interval,borehole stability was evaluated based on these pressure profiles;formations with potential stability problems were sealed through optimizing casing program;optimum gas injection rate was calculated by using annular drilling cutting transport ratio.The test showed that gas drilling technique is suitable for carboniferous nappe in Northern Huoshaoshan,where average penetration rate of gas drilling reached 5.37 m/h,about 4 times higher than conventional drilling at the same interval,resulting in significant reduction in drilling cycled.This showed that gas drilling in Huobei Area could increase drilling speed,which not only provides technical guarantee for rapid exploration of tight oil,but also accumulates valuable experience for expediting drilling speed in volcanic strata of Junggar Basin.