Summary
A well-testing operation was performed to confirm productivity potential in
an ultradeepwater area where a 5,660-ft exploratory well had been drilled. This
was a gas well drilled from a semisubmersible drilling rig. Because well
testing from semisubmersible rigs is a critical and sensitive operation, all
planning had been carefully reviewed by the operator to ensure a safe,
environmentally friendly operation.
The formation of hydrate plugs during ultradeepwater well testing is a
critical concern because water can be trapped and form a solid crystalline
structure around gas when there are low temperatures near the mudline. This
hydrate formation is a common occurrence in deepwater drilling operations,
particularly while using water-based mud. Thermodynamic inhibition may not be
effective in these cases because several limitations in achieving the required
injection rate exist.
Oilwell testing operations in deep and ultradeep water have become common
practice around the world, and vast experience with these types of operations
has been acquired; experience with gas wells, however, has not been as
comprehensive, and only a few gas wells have been tested under the conditions
presented in this type of scenario. Because of the low number of gas wells
tested in these deepwater conditions, best-practice information is limited.
The intention of this paper is to present a case history and the lessons
learned during a well-testing operation in which water production in the gas
well was greater than anticipated during the cleanup period. A massive hydrate
plug was formed while coiled tubing was being pulled out of hole, and the
coiled tubing became stuck. The steps taken to free the coiled tubing will be
discussed, and the discussion will include the following:
- Conditions that must be present to form hydrates
- How the problem in this case was resolved
- How to help prevent hydrate formation
- Best practices for well testing in deepwater gas wells to maintain safety
and economic viability
This case history discusses a gas well being drilled with a semisubmersible
drilling rig in ultradeep water, offshore Mexico.
© 2011. Society of Petroleum Engineers
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History
- Original manuscript received:
3 May 2011
- Meeting paper published:
3 February 2011
- Revised manuscript received:
22 June 2011
- Manuscript approved:
28 June 2011
- Published online:
17 October 2011
- Version of record:
22 November 2011
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