Causes of well deviation during gas drilling and its control

The well deviation law of gas drilling is induced and analyzed,the effects of formation anisotropy,formation dip,borehole geometry,and drilling parameters on well deviation during both gas drilling and mud drilling are compared and studied. The conclusion demonstrates that sharp increase in formation anisotropy is the root cause of the well deviation. And the borehole diameter enlargement is significant cause of well deviation during gas drilling under medium or high WOB. Formation dip,WOB,bit cutting anisotropy and BHA produce effects on gas drilled well deviation is in a similar way to mud drilling. It is recommended to adopt air hammer,pendulum assembly and air motor to minimize or eliminate the well deviation during gas drilling.