In the current economic downturn, operators direct more focus to cost optimization through process enhancement and innovative approach. Specifically in South East Kuwait field, where new well profiles are being employed to reach a deeper pay zone directionally. These new well profiles require the 16 inch hole section to be drilled deeper with inclination through interbedded abrasive sandstones and sticky shale; which were previously drilled in 12 ¼ inch hole size. Drilling becomes increasingly challenging using larger diameter bits where torque fluctuations, down-hole conditions and durability limit performance. The purpose of this paper is to demonstrate the engineering analysis for directional large diameter hole application and the selection of an optimized hybrid drill bit design, roller cone combined with Polycrystalline Diamond Compact (PDC), to maximize drilling performance where standard PDC or roller cone bits alone fail to provide an optimal solution.
The 16 inch directional section was typically drilled using a mud motor assembly with a roller cone bit or a PDC. Drilling parameters were reduced in the upper layers especially with PDC bits as they involve sticky shale which can induce bit balling. While in the lower layers the abrasive formations tend to wear down roller cone bits.
Selecting an appropriate hybrid design with an optimized drilling system for the application resulted in a breakthrough performance; tripling the Rate Of Penetration (ROP) of conventional technology. The time saving achieved was worth $250,000 for this section.
PDC bits generally provide faster rate of penetration than roller cone bits while generating higher torque fluctuations as they drill by shearing bottom hole formation. Due to their high torque demands, PDC bits require an additional mud motor to drive them efficiently in larger hole sizes. Roller cones crush and gouge the bottom hole formation and due to their mechanical rollers result in reduced reactive torque and a smoother hole profile. Hybrid drill bit technology proven the capability of achieving the benefits of both designs in specific selected applications.