Summary
This paper discusses the results of a global campaign to increase the length
of the gauge area of bits used on rotary-steerable systems (RSSs) to mitigate
bit whirl and its undesirable effects. The desired steerability was achieved
with lengths in excess of 4 in. with all RSS tools used. The modifications have
resulted in reduced vibrations, significant improvement in drill rate, improved
borehole quality, and reduced tool damage.
When the operator’s performance-management process was implemented,
real-time and post-drill analysis of mechanical specific energy (MSE) suggested
40% of footage drilled worldwide was affected by bit whirl or lateral
instability. One element in the programmatic response was an initiative
beginning in 2006 to extend bit-gauge lengths to constrain side cutting and
reduce the amplitude of whirl-induced patterns. The value of extended gauge
lengths has been demonstrated in numerous papers. However, field implementation
by the industry has not been uniform, and a significant issue has been concern
that steerability would be reduced. The purpose of the initiative was to
demonstrate that common build rates could be achieved with all RSS tools used
by the operator with bits having a minimum gauge length of 4 in. In the subject
wells over a 2-year period, normal build rates (2–4°/100 ft) were not affected
with 4-in. gauges if the profile and aggressiveness were designed properly. The
gauge profiles used to maintain steerability included full taper, full
undercut, and partial undercut. While the desired steerability was achieved
with both point-the-bit and push-the-bit RSS tools, specific modification
required in the gauge profile varied with the RSS used, desired build rate, and
drilling environment. Drill-rate performance and bit life also improved, but
this was attributed partly to implementation of the performance-management
process and specific rig-crew training. Extension of the gauge length is also
known to benefit bent-motor operations (Norris et al. 1998); however, the
effects of various gauge profiles are less certain, and motor operations are
not discussed in this paper.
The objective was not to determine the maximum build rates achievable but to
simply confirm that gauge lengths of 4 in. or greater could be used as standard
practice in normal operations. This paper discusses the rationale for the use
of extended gauges, the modified profiles used to maintain steerability with
various RSS tools, and the field performance achieved.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
11 December 2008
- Meeting paper published:
18 March 2009
- Revised manuscript received:
28 May 2009
- Manuscript approved:
28 October 2009
- Published online:
15 April 2010
- Version of record:
14 June 2010
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