Bi-Center Innovations Impact Deepwater Drilling

Abstract In 1994, bi-center bits were introduced which contained new technology. For the first time, a single tool could reliably be used to simultaneously drill and underream, even in highly directional applications, all with no moving parts. The results were fewer trips, fewer rotating hours, and less "problem" time. The only major draw back to using bi-center bits has been that they could not be used to drill out cement, float equipment, and casing guide shoes. It was required that a conventional drill bit be used first to drill out into new formation, then a trip was needed to pick up the bi-center bit. In 1999, advancements in bi-center technology have resulted in a bi-center bit that can be used to drill out and then continue to drill ahead. At the same time ROP, directional control, and hole quality have also improved. On the first field test of this new technology, bi-centers were used to drill out and drill ahead on three consecutive intervals of a deepwater Gulf of Mexico well. The intervals included a vertical section, a build section, and a tangent section. In all three cases, the drill out was performed with results similar to offset PDC bits, directional targets were all hit with no steering difficulties encountered, and in all three sections, the casing or liner was run to bottom with no problems. The cost savings in trip time alone amounted to over $560,000 (5 trips eliminated). This paper describes the new technology and gives details on the performance (drilling out and in the formation) which lead to the cost savings.