Summary
Riserless drilling with weighted-drilling-fluid systems, commonly referred
to as a "pump-and-dump" drilling strategy, is an established drilling technique
used on deepwater wells with shallow hazards. Large holes and high flow rates
result in very large volumes of fluid being required to drill to total depth
(TD), circulate the well clean, and cement the conductor-casing string. Fluids
management becomes a major issue in the riserless hole section. In the Gulf of
Mexico, mud is often densified in excess of well requirements and then blended
with seawater in a "cut-back" operation to reach the desired density to pump
downhole.
When performing riserless drilling into salt, a pump-and-dump strategy is
often used. Dilution with seawater, however, results in an undersaturated
fluid. This fluid leaches the salt, resulting in substantial hole enlargement.
The hole enlargement can result in poor cementing jobs that require remediation
or even an additional string of casing. A unique operation has been employed in
the Santos basin of Brazil where a supersaturated-brine fluid was used to
conduct a pump-and-dump operation with the goal of drilling with a
saturated-brine fluid and minimizing hole enlargement. This paper details the
planning of the operation, fluid design, and pilot testing. Fluids management,
equipment rig up, and results are discussed in detail. The operation has been
executed successfully twice, with both operations achieving the set objectives
for the wells. Unforeseen complications that were encountered are discussed
along with lessons learned that have been applied to subsequent operations.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
4 February 2010
- Meeting paper published:
2 February 2010
- Revised manuscript received:
23 July 2010
- Manuscript approved:
28 July 2010
- Published online:
7 February 2011
- Version of record:
11 March 2011
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