B Sadeghlou - B.Sc, Petroleum University of Technology, Faculty of Petroleum Engineerning At Ahwaz
M Azami - B.Sc, Petroleum University of Technology- Faculty of Petroleum Engineering At Ahwaz

In the petroleum industry there is a great need for time saving and recovering the original oil as much as possible ,at the recent years a lot of works have been done to lessen the time of drilling a well, such as top drive drilling, down hole machine drilling etc, but one of the best ways to drill a well that is being worldwide is Under balanced Drilling (UBD) .This is the most popular technology between new brands, this technology even increases penetration rate by 2 to 5 folds in south Iranian oil fields[6], here we are going to show some of advantages and challenges about this kind of drilling which is also called flow drilling. Note that using this method in Iranian fields is restricted because of lack of technology and its initial cost.

Under Balanced, Drilling (UBD), Penetration, rate (ROP), Formation Damage, Bottom hole, Pressure (BHP), aniline point