Deep Water Nigerian Field Challenge: Increasing ROP with Centrally Located Conical Diamond Element Saves Operator 26Hours Rig-Time, Agbami Field

摘要

Drilling a 12%-in hole section in the Agbami field offshore Nigeria presents a number of challenges.The section contains abrasive sandstone and shale that are interbedded with sandstone and siltstone, and all have unconfined compressive strengths (UCS) that vary across the field. The abrasive sandstone/shale section has UCS of 12,000 psi, and the interbedded sandstone/siltstone section has UCS of 15,000 psi or higher. The variation in lithology, formation strength, and abrasion/impact index make ensuring shoe to total depth (TD) runs with consistent ROP difficult because the conditions dull the polycrystalline diamond compact (PDC) bit's cutting structure, leading to a significant reduction in ROP before reaching section TD. An operator wanted to drill the 12 1/4-in section from shoe to TD in a single run with a 45% improvement in average ROP compared with the four-well offset median of 38.26 ft/h. To accomplish the objectives, the operator required a PDC bit with a differentiating drilling action designed to increase penetration rates and extend bit life in heterogeneous formations. A finite element analysis (FEA)-based modeling system was used to experiment with cutter types and their placement to improve drilling performance. Based on the modeling work, design engineers recommended a conical diamond element (CDE) with a thick synthetic diamond layer. The diamond layer on the CDE is approximately twice as thick as a conventional PDC cutter and exhibits 25% more wear resistance with almost double the impact strength. The element's unique geometry delivers high point loading for effective formation fracture. To fully exploit the CDE's advantages, the PDC bit body was redesigned by selectively abbreviating the blades at bit center and positioning a single CDE in the void space. The modeling system was also used to generate an operating parameter roadmap to maximize performance.