For many years underbalanced drilling technology has been commercially exploited in North America whilst international Underbalanced Drilling (UBD) projects have been sporadic at best. Many technical papers have been written regarding these operations with the recurring theme that although the technical benefits of UB technology were seen, the overall cost was too prohibitive to justify further campaigns.

The many benefits of UBD are widely publicized; however, the highest impact that UBD can make is on the reservoir and its productivity. A recent focus in UB operations has been to quantify this benefit through productivity increase comparisons, or productivity improvement factors (PIFs) against field averages. The increased PIFs provide justification to offset the higher costs associated with the technology.

Petroleum Development Oman (PDO) has undertaken an extensive UBD campaign aimed at increasing production through the elimination of reservoir damage1 . To fully evaluate the technology, the PIFs of a one year campaign were analysed and measured against a pre-defined business case to determine if UBD were commercially viable. The UBD campaign was carried out in two fields in PDO. Although this paper focuses on the Saih Rawl campaign, the issues for the two fields were very similar.

Although early production results were very promising2 , the commerciality, in PDO's low cost, land operation environment, was marginal at best. Re-assessment of the approach to all aspects of the UBD operation by the Project Team, including scope of work, equipment design, equipment utilization and UBD operations resulted in improved operational efficiency and an innovative contracting strategy mutually beneficial to both Operator and Contractor. This new approach has shifted UBD from a trial to a commercially viable technology in PDO.

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