Combination of a Unique Stabilized Bi-Center Bit and Vibration Dampening Tool Improve Hole Opening Performances Through Interbedded Formations in Saudi Arabia

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 midreamer 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. Introduction Lukoil Saudi Arabia drills some challenging exploration wells in southern Saudi Arabia. These wells have encountered several difficulties involving severe borehole stability problems. On the well "D", the 13–3/8 casing was planned to be set on top of Sulaiy Formation at around 9,258 ft. However, the 16" phase was unable to reach this depth, having to be stopped at a much shallower depth of 7,625 ft because of lost circulation problems Additionally, the 13–3/8" casing could not be run to 16" hole total depth due to restriction in the hole. The 13–3/8" casing was set at 6,865ft and the rest of the 16" open hole was finally covered by 11–3/4" expandable casing that was set at 7,617ft to ensure that the 9–5/8" casing setting depth could be reached as per the drilling program Fig.1. Since the 11–3/4" expandable casing has 11.286" drift ID after expansion, a hole opening tool was required to open the hole from the casing pass through size to 12–1/4" hole size, to allow the 9–5/8" casing to be set properly.

A Review of the Evaluation, Control, and Application Technologies for Drill String Vibrations and Shocks in Oil and Gas Well

“…The downhole tool drop can be prevented by integrated design of the stabilizer. A new expandable stabilizer was proposed by Al-Thuwaini [37,38]. The detailed structure of the expandable stabilizer is shown in Figure 13(a).…”