Since 1998 Rosneft SMNG (Sakhalinmorneftegas) has been developing the northern part of the Odoptu structure, near-shore to eastern Sakhalin Island, using ERD (extended reach drilling). Discovered in 1977, North Odoptu is alone among Sakhalin ERD projects in that it is entirely Russian operated and utilizes a unique hybrid of both Russian and international capabilities to address the considerable challenges of ERD well construction. To date 21 wells, with horizontal displacement/TVD aspect ratios up to 4.1, have been drilled and completed from two land-based drilling locations.

The use of rotary steerable (RSS) technology has more than doubled net drilling performance compared with early wells drilled using positive displacement motors (PDM's). A hole-cleaning challenge remains however, due to a practical necessity for back-reaming while tripping out of the hole. This has led to serious delays as localized unstable sections of the well-bore collapse due to mechanical disturbance, forming cavities that complicate hole-cleaning operations with pack-offs and stuck-pipe.

Low-resolution 2-D seismic has been a limitation on understanding the detailed nature of the over-burden stratigraphy and thus the ability to characterize the cavities. Geo-mechanical models, while clarifying the impact of the regional stress regime, have indicated that the origin of this instability phenomenon may not be due to compressive shear-failure.

The primary focus has therefore been on the development of cost-effective and innovative drilling optimization techniques to predict and identify cavity zones early in the drilling operation, and application of a fit-for-purpose, rig-based, risk-management approach to well-bore instability events. The progressive application of these techniques and the adopted risk-mitigation strategies is documented. This approach, in conjunction with the use of a regularly updated geo-mechanical model, has resulted in a successful outcome for well construction in a previously severely problematic region of the field.

The ability to recover well from instability-related setbacks has helped to foster a co-operative, continuous-improvement culture among the extended drilling team - Russian operator and international contractors alike. Recommendations are made for follow-on technologies and strategies that will have the greatest impact on the next phase of field development.

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