Petroleum Development Oman LLC is one of the leading oil companies in the Middle East with a long history of early utilization of new technology. The cumulative production from its fields to date runs into millions of barrels of oil, with production starting back in 1967.
Drilling in PDO's mature fields using conventional drilling methods has become a challenge these days as severe reservoir impairment has been seen in Nimr and Saih Rawl fields. Much of this impairment is due to high overbalances resulting on the low reservoir pressures. Other problems were high water cut above that predicted from logging while drilling (LWD) evaluation. Underbalanced drilling (UBD) was identified as a method of overcoming this problem.
UBD trail wells have been drilled using 2 different UBD techniques (Concentric casing and Drill pipe gas injection). To date 18 UBD horizontal wells have been put onstream: 14 horizontal single lateral wells in the Nimr Field (12 new wells and 2 re-entries); and 4 horizontal multi lateral (total of 9 legs) UBD wells in the Saih Rawl Field.
Significant productivity improvements have been observed, and valuable reservoir data has been gathered during the drilling of these wells. Drilling performance has also shown marked improvements. This paper is written to highlight the key learning points which have been captured and applied in the UBD campaigns.