Underbalanced Drilling
Omani field tests compare UBD favorably to conventional drilling
In Oman’s Saih Rawl oil field, the underbalanced drilling technique was successfully field-tested, achieving the goal of minimizing formation damage while markedly improving the productivity index
Martin S. Culen, Precision Drilling Services UBD, and S. Al-Harthi and H. Hashimi, Petroleum Development Oman
Utilization of underbalanced drilling (UBD) at Petroleum Development Oman (PDO) stretches back to sporadic projects in the mid-1990s. However, not until recently were tangible gains realized using this technique. Although UBD’s benefits are widely accepted within North America, the technology has not been fully exploited internationally for several reasons, particularly justification of increased drilling costs against perceived “intangible” benefits. Such justification is particularly hard for asset managers and well planners to make in the absence of concrete industry data on production increases.
PDO embarked on a focused campaign to trial UBD and evaluate its applicability as an enabling technology.1 A “zero cost implementation” approach introduced the campaign, and drilling began in June 2002. Oil wells targeted in Saih Rawl field are underpressured, drilled as five-legged producer-injector pairs off a 7-in. backbone. The wells are normally completed with ESPs. Engineering for the Saih Rawl UBD project focused on the asset team’s mandate to eliminate reservoir damage. Equipment was chosen accordingly, and a program was developed to inject field gas via a concentric casing string to establish UBD conditions.
Because the technology was newly re-introduced to PDO and its local contractors, a step-by-step approach was adopted for the first well, and it ultimately demonstrated UBD’s benefits. Post-drilling flow tests proved invaluable for evaluating UBD’s applicability – results showed distinctly increased production from adjacent legs about 200 m (762 ft) apart in the same reservoir. Various design issues were solved, and results of drilling the SR 153 well were deemed successful.
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This article was adapted from a professional society paper for which World Oil was granted the right to print one time only. Therefore, to review the article, you should refer to the actual World Oil magazine in which it originally appeared.
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