Abstract
When control drilling interbedded formations due to lost circulation challenges, Bi-Center bits often fail to open the hole to the expected drill size. Possible causes include inconsistent downhole weight on bit due to formation changes, lateral and torsional vibration. Each leads to the pilot of the Bi-Center bit drilling an oversized hole which results in the bit drilling off-center, giving an undersized hole.
To combat this, a patented double profile Bi-Center bit was developed. Its elongated pilot section includes a unique mid-reamer section which improves lateral stability due to more balanced cutter forces. Also, the mid-reamer provides an additional gauge section immediately below the reamer which in conjunction with the pilot gauge has proven to reduce tilt and keep the pilot bit centralized, providing more consistent full gauge hole.
Additionally, vibrations generated by the drillstring are common during the hole-opening process. These affect not only the drilling performance but also the quality of the wellbore. A unique eccentric stabilizer, ideally located in tension in the BHA, provides vibration dampening in the drill-string. The V-Stab interrupts harmonic modes vibration as well as reducing the magnitude of shocks due to its unique geometry.
Caliper logs from field trials of a 10-5/8 × 12-/14" CSDX6413S-B1 Bi-Center bit with a 10-5/8 × 12" vibration dampening tool demonstrate excellent hole opening performance and improved borehole quality.
In contrast, logs for conventional Bi-Center bits run with the vibration dampening tool showed inconsistent hole opening and poor borehole quality in the same application.
This paper describes the benefits of the unique combination of these new technologies, presenting detailed drilling performance data showing how they resulted in significant performance improvement and cost savings in southern Saudi Arabia.
