Application of Rotary Steerable System(RSS) drilling in one of the biggest Indian offshore field, Mumbai High was driven by the increasing difficulties associated with directional drilling by mud motor technology, especially in Extended Reach wells. ONGC has focused largely on finding economic and competitive ways of exploiting the mature and depleted field. Rotary Steerable System provides the opportunity to reach farthest unexploited subsurface targets without adding new platforms with significant improvement in drilling performance and challenging subsurface objectives.

Since first application in the year 2004, RSS has successfully overcome the drilling challenges & problems, especially in 12¼"section, deliver improvement in drilling time. The paper will discuss in detail, each step of continuous improvement in RSS applications & operations, field specific bit design, drill string, fluid system modifications and real time drilling optimization during the last seven years. The actual result on overall directional drilling efficiency enhancement after implementation of each optimization methodology is also discussed.

The discussion covers some unique RSS applications in Mumbai High Fields such as:, drilling top hole 17-1/2" section to complete the well in required hole size, drilling 8-1/2" multilateral section including open hole sidetrack, drilling 6" with RSS & pro-active geo-steering technologies keeping the well in good reservoir with high penetration rate and long horizontal drift. Based on the field results and performance analysis it is concluded that continuous up gradation of mud system, bit design, string design and real time monitoring with proven technology of RSS lead to successful completion of high drift wells.

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