Comparing the Aspects of the UBD Jobs in Iran

Underbalanced drilling (UBD) has opened its way in drilling practice as a technique to reduce problems associated with drilling fluid invasion. This increases the reservoir productivity especially if open hole completion is intended afterwards. UBD in Iran has been paid attention since 2003 as a way to escape drilling problems such as lost circulation, pipe sticking and also to mitigate formation damage surely not as the first priority.Although complementary reports of each UBD job have been prepared in NIOC, unfortunately not only is their access to the academic society restricted, but also each individual UBD job report is not compared with other ones, therefore the possible lessons could not be learned to enhance future UBD jobs. Different aspects of UBD final reports should be taken into consideration and also reasons for each negative event should be presented as is done here. In this paper, UBD jobs in Karanj and Parsi oil fields are compared in terms of UBD job objectives, magnitude of early production while drilling, real and predicted drilling time, actual and planned drilling progress charts, drilling operations time table, lost times, lost circulation times and volume, average rate of penetration and directional bottom hole assembly specifications and anassessment of their success or failure.