Summary
This paper discusses a successful initiative begun 6 years ago to eliminate
differential sticking across global operations. In the 5-year period from 2004
through 2008, there were only three differential-sticking events in 3,476 wells
drilled with the recommended practices. There were an additional 17 sticking
events with designs that did not conform to recommended practices, and 14 of
these were freed. The drilling environment was diverse. Overbalances in excess
of 1,000 to 2,000 psi were common in multidarcy rock and at high angle, and
depleted reservoirs have been drilled with overbalance as high as 7,800 psi in
vertical wells.
The early focus of the stuck-pipe-avoidance practices was the elimination of
differential sticking. However, some level of sticking occurs routinely in
drilling operations, and these events become problematic only if the force
required to initiate pipe movement exceeds what can be delivered to the stuck
point. It is now accepted that sticking cannot be prevented and that
elimination of sticking is not a proper design objective. The philosophical
objective has now shifted from elimination of sticking to "maintaining
conditions that allow the pipe to be pulled free," assuming that it will become
differentially stuck. The desire to maintain this ability to move the pipe has
required the implementation of a range of practices, some of which were not
common in the industry.
Changes were made in bottomhole assembly (BHA) design, fluid design,
real-time cake-shear-strength recognition, and real-time cake-remediation
practices. A finite-element (FE) model was also applied to redesign new systems
or applications that lie outside the operator's previous experience. The
stochastic model predicts cake growth and sticking force and the probability
that it will be possible to deliver a force that can free the pipe for any
given still-pipe time. The model inputs were calibrated through pullout tests
with a variety of fluids to determine mechanical cake-strength properties, the
rate at which those properties develop, changes in the pressure transient
through the cake as it matures, and the cake contact areas and geometry at any
point in time.
Engineering and operations training also contributed greatly and allowed
relatively uniform implementation to be achieved across a large, globally
diverse operation in less than 1 year. A small number of noncompliant designs
continued to be used, and these contributed greatly to the incidence of stuck
pipe in the first 3 years. Last year, there was only one incident of stuck pipe
with a noncompliant design.
The paper describes the underlying sticking concepts, the engineering design
and field practices used, the modeling capability, and the field results.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
31 January 2010
- Meeting paper published:
2 February 2010
- Revised manuscript received:
4 June 2010
- Manuscript approved:
8 June 2010
- Published online:
1 March 2011
- Version of record:
11 March 2011
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