Summary
Detailed measurements of downhole pressures and temperatures have been
performed during simulated drilling operations at ultradeepwater offshore
Brazil. Sensors were placed at six different positions along the drillstring,
which made high-frequency recordings of pressure and temperature during
• Surges and swabs at different depths.
• Gel-breaking tests.
• Circulation sweeps.
• Migration of gas in the riser.
It was expected that the special conditions in ultradeep wells with low
temperature along most of the very long riser would cause some significant
deviations from corresponding measurements in more-normal wells. The
measurements aimed at identifying, understanding, and quantifying such effects.
This is considered very important because a narrow window between pore and
fracture pressure is common in very deep waters.
Advanced transient models were used to identify the most interesting
effects. Effects that are reliably reproduced by advanced transient models are
also important, but operators are able to do calculations to prepare for
them.
A remote-operated vehicle (ROV) recorded temperature outside the riser
during experiments to give input to a detailed study of heat transfer from
drilling fluid inside the riser to the seawater outside.
The purpose of the tests was to obtain detailed measurements of physical
effects that may be important in ultradeepwater wells.
This paper presents a detailed analysis of the recorded data, including
comparing them to advanced computer models for transient pressure and
temperature during drilling, circulation, and surge/swab. In addition, the gas
migration is simulated with an advanced kick simulator.
Introduction
Safe and economic drilling in ultradeepwater poses a number of technical
challenges. Some assumptions made for moderately deep water depths (<1500
m) cannot be extrapolated to ultradeepwater drilling conditions.
A joint-industry research program has focused on several challenges
associated with well control, hydraulics, and drilling-fluid performance inside
the riser and well in cold, ultradeepwater environments.
The program has addressed the following issues: ultradeep-riser hydraulics
and temperature, critical pressure effects for ultradeepwater drilling, and gas
rise and migration in ultradeep risers.
In summary, the following benefits have been anticipated on the basis of
this project:
• Improved drilling practices and economics on the basis of increased
understanding and knowledge of ultradeep drilling-fluid hydraulics and
temperatures in the riser.
• Increased control of downhole pressures and formation fractures on the
basis of drilling-fluid hydraulics in the riser section of ultradeepwater; this
will reduce occurrence of costly problems downhole.
• Fewer well and formation problems result in unanticipated downhole
pressures that are a direct result of mud-gelling properties in the
seawater-cooled riser.
• Safer prediction and handling of gas in ultradeep risers.
© 2005. Society of Petroleum Engineers
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History
- Original manuscript received:
21 January 2004
- Revised manuscript received:
22 August 2005
- Manuscript approved:
4 September 2005
- Version of record:
15 December 2005
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