Summary
Antistall technology (AST) is a mechanical downhole solution that aims to
adjust the drilling torque automatically in real time. Originally, the tool was
developed by Tomax AS for coiled-tubing applications where it has proven its
ability to successfully reduce vibrations, motor stalls, equipment failures,
and general wear, in addition to increasing the penetration rate and run length
(Dagestad et al. 2006). The tool was then developed further based on the need
for a similar solution for rotary drilling. The goal was to eliminate
cutter-induced torque variations and string stalls in difficult formations and
resultant harmful effects. Prototype AST tools were made in sizes ranging from
6¾ to 8¼ in. The tools were then run in test wells and later in field
operations with a variety of tool configurations until the database, in
addition to two controlled trials, counted 25 regular jobs--mainly on the
Norwegian Continental Shelf. The paper describes in detail, both based on
theory and on field experience, how the bit-induced torque fluctuations are
significantly decreased to improve penetration, and how bottomhole-assembly
(BHA) damage is prevented to increase run lengths.
Introduction
Along with the introduction and development of fixed-cutter drill-bit
polycrystalline-diamond-compact (PDC) technology in the early 1980s, the
drilling industry has also seen continuous development of more sophisticated
drilling and formation-evaluation systems containing an increasing number of
electronic components in the instrumented part of the BHA. These advanced
downhole-drilling systems enable faster drilling, high-precision well bore
placement, and longer reach, but, because of their complexity and sophisticated
design, they are also more prone to premature failure caused by high energy
shocks and vibrations downhole. While being highly effective, the PDC bits have
a proven potential to produce dynamic forces and energy shocks at levels at
which they become destructive to the bit itself, the instrumented BHA, and the
drillstring connections (Fear et al. 1997). The industry's response to this
challenge has been to develop stronger downhole tools equipped with sensors for
measuring and monitoring the various downhole dynamic parameters. The drilling
process is then controlled on the basis of this information (Robnett et al.
1999). The principal idea behind the AST is to provide active downhole control
of the rock-cutting process by diverting energy from the drilling process and
using it to prevent dynamic forces from reaching destructive levels and thereby
preserving the drillstring components and optimizing rock-cutting efficiency.
To emphasize this point, one could draw a comparison with modern motor-racing
technology where it has proved highly beneficial to both performance and
durability to actively balance the amount of power transferred to the wheels
against the overall stability of the vehicle.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
14 December 2007
- Meeting paper published:
4 March 2008
- Revised manuscript received:
28 April 2008
- Manuscript approved:
29 April 2008
- Published online:
27 July 2009
- Version of record:
23 December 2009
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