In the 12 ¼-in. section of an Abu Dhabi offshore company's wells, complex directional well profiles and varied formation characteristics create a challenging drilling environment. Outcomes of the drilling efforts in this environment include non-productive time (NPT) as a result of tripping, as well as lower rates of penetration (ROP) as a result of vibration. Conventional positive displacement motors (PDM) were typically used in this offshore application. Polycrystalline diamond compact (PDC) bits were run with the PDMs because of their longer life and increased ROP through the varied formations; the particular designs used had provided good steerability in previous applications. The conventional PDM-PDC system, however, often creates high vibrations that reduce overall performance. In addition, the section has always required two runs so that the bent housing could be changed in the second run, which resulted in lost time for tripping.
To address these issues, a new system was designed that provides significant advantages over conventional steerable assemblies. This system includes a specially designed long-gauge PDC bit run on a point-the-bit rotary steerable tool, both of which were designed and modeled together. The advantages observed using this system in the field includes improved hole quality and increased ROP, as well as reduced hole spiraling and tortuosity, reduced vibration, better steerability and hole cleaning, increased bit life, and reduced tripping time.
This paper provides three case studies of the use of this system in which one of Abu Dhabi offshore operators achieved the objective of drilling the 12 ¼-in. interval, which averaged more than 2,500 ft, in a single run, and optimized the ROP without compromising hole quality or cleaning efficiency. A summary of results indicates the effectiveness of design improvements, with the new bits achieving the highest single run ROP in history for this particular operator and longest footage achieved in a single run.
These benefits are expected to have considerable implications on future drilling operations.