Underbalanced drilling in its various forms has been used in the oil and gas industry for more than 20 years. A growing body of technical publications documents the mechanics and advantages of underbalanced drilling (UBD) technology, including details related to casing sizes, circulation rates, depths, rate of penetration, etc. There are also many mentions in the literature of resultant well productivity improvements. In contrast, there is little written in the literature about what contribution UBD makes to reserves and ultimate recovery.
This paper provides a basis for considering the reserve contributions of UBD technology. The six reservoir case histories presented here document tangible reserves attributable to the three key reservoir-related benefits of UBD: improved reservoir access, reduced skin damage, and better ability to evaluate the reservoir while drilling.