The industry acknowledges that well engineers in the Sultanate of Oman identified long ago a number of technical challenges when drilling through the Fiqa formation. The most daunting is wellbore instability which results in hundreds of unproductive rig-hours when drilling wells for both exploration/appraisal and development campaigns. But more recently, Casing while Drilling (CwD) was recognized as the most cost-effective mitigation system against the risk of stuck-pipe, continuous back- reaming and unplanned casing setting depths in such highly reactive, time-dependent shale. In consequence, current portfolio of deep and ultra-deep wells in Northern Oman (Figure 1) mandates CwD as the new conventional approach for drilling large- diameter surface sections, instead of the drill-pipe method.
During the trial-phase of CwD (2009–2010), the Drilling Efficiency Optimization (DEO) concept and a few related tools/techniques were rarely utilized. The reason responds to the fact that operator's major objective was to prove the CwD- concept in deep surface sections with minimum well-design integrity risk; in which the critical challenge was the delivery of a wide range of drilling performance optimization ideas. Nonetheless, a more systematic DEO approach during the phases of well planning, execution, and post-drill analysis was utilized in the subsequent ‘CwD Implementation Campaign’ to improve overall performance through the most-top formations in four different fields across the North.
The operator identified a few critical areas of opportunity that led to successful operations, such as specialized rig-crew training sessions, real-time management of drilling parameters, optimum mud properties and hydraulic energy, wellbore strengthening quality, bottom-hole-assembly (BHA) design, and mechanic energy surveillance. All enabling technologies and resources dedicated to these areas combined aided to accelerate well delivery time by up to 58% and reduce cost per meter drilled-and- cased by over 25%. A main conclusion is that CwD technology deployment with DEO approach is the best-in-class, value creative solution through troublesome, most top formations in Northern Oman.