A discussion on drilling technologies of Cheng 2 well in piedmont basement thrust nappe

Basement of 2039. 40m thick was encountered in 180. 00-2 219. 40 m interval in Cheng 2 well positioned on a typical piedmont structure. The drilling tools broke or split for 40 times in the whole drilling process. Both the thickness of basement penetrated and the number of times and frequency of the drilling tool breaking or splitting are rare in China. Drilling operation in this well was faced with many big challenges, mainly including low ROP, thread gluing of drill collar, drilling tool breaking, large formation dip, enlargement of well deviation, as well as difficult well trajectory control. The occurrence rate of drilling tool breaking accidents is largely lowered through optimizing drill bits and the make - up of string as well as strengthening drilling operation. Some experiences are accumulated for drilling in piedmont thrust nappe.