Casing drilling is a new method for drilling wells that is aimed at reducing both drilling time and the incidence of unscheduled drilling events.With casing drilling,the well is not drilled with drill pipe;instead,it is drilled with standard oilfield casing that remains in the hole.Drill bits and other downhole tools are lowered on wireline inside the casing and latched to the bottom joint of casing.Since the casing remains in the well and circulation is maintained at all times,wellbore integrity is preserved,reducing the likelihood of certain problems associated with unscheduled events such as sloughing formations and washouts.Since drill pipe is not being tripped,the risk of swabbing oil or gas into a well causing a kick or blowout is reduced.