Achievements and Lessons Learned from a 4-Year Experience of Extended Reach Drilling in offshore Dagang Oilfield, Bohai Basin, China

Abstract

The long-term continuous exploitation makes it increasingly difficult to maintain sustainable hydrocarbon production onshore in Dagang Oilfield. The shelf sea area of Bohai Basin with an average water depth of about 2.5m is identified as the main take-over battlefield, which needs to be developed by extended reach drilling (ERD) due to the lower loading capability of subsea thick silt and the inaccessibility of drilling rigs onshore or offshore. This is one of the major ERD campaigns implemented independently onshore in China.Favorable achievements have been obtained during the 4-year ERD play. Four extended-reach horizontal wells with the horizontal displacements larger than 4000m have been successfully completed by integrated application of pseudo-catenary trajectory design, casing floating running technology, compound drilling method, real-time ECD monitoring, highly inhibitive drilling fluid, optimized hole cleaning operation and enhanced drag/torque reduction technology. The maximum horizontal displacement to vertical depth ratio reaches 3.92. Many other ERD records have also been made in China onshore, building basic foundations for much larger-scale of application of ERD in Bohai Basin. Meanwhile, many new challenges have also emerged, such as the wellbore instability in highly deviated intervals, inappropriate design and optimization of PDC bit, instable bottom hole assembly (BHA), difficult control on well trajectory for the long angle-holding section, etc. This calls for technical innovations to address problems associated with previous ERD activities.This paper focuses on the technical achievements as well as the lessons learned from the ERD play in recent years, with its purpose to explain where we are and what to do next for further research and development of ERD technology in China. Helpful case histories and recommendations will also be presented.