Summary
A computer-based method expedites interpretation of pressure data during
subsea blowout-preventer (BOP) tests. This can reduce the time and cost of
current subsea-BOP testing practices in a safe and objective manner.
Currently, individual tests can require more than 1 hour of shut-in time,
and a complete series of subsea-BOP tests may comprise at least 12 individual
tests.
The digital method employs computer software to produce an accurate model of
the pressure-decline behavior relatively early in each test. The model can thus
predict if future pressures will stabilize at an acceptable level. With
regulatory approval and a reliable method to forecast pressure, the duration of
subsea-BOP tests can be reduced significantly.
Comparison of the digital method to conventional subsea-BOP testing on
numerous field trials shows excellent agreement. If implemented, the digital
method could save hours of valuable critical-path rig time during every series
of subsea-BOP tests.
Working in concert with regulatory authorities to gain endorsement of this
method is integral to the project. Functionality of the software, example
results, and implementation status are reported.
Introduction
Industry trends toward deeper water, use of synthetic oil-based fluids, and
subsurface conditions that require higher test pressures contribute to lengthy
delays while waiting for pressures to stabilize during subsea-BOP testing.
Also, subsea-BOP stacks with redundancy of components and use of multidiameter
drillstrings lead to greater numbers of tests that must be conducted.
Franklin et al. (2005) investigated the phenomenon of lengthy subsea-BOP
testing times. They conclusively attributed the prolonged decay of pressure
with time to the heating of the test fluids during pressurization, followed by
the cooling of the fluids during shut-in test periods. They proposed that
real-time digital analysis of the pressure decay could yield large time and
cost savings, with safety benefits gained through reduced exposure time of
personnel to pressurized lines.
The current authors continued the aforementioned work. A digital algorithm
for real-time interpretation of subsea-BOP tests was implemented in software
and was tested successfully in Gulf of Mexico trials. This paper explains the
algorithm and presents field-trial results.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
11 November 2006
- Meeting paper published:
20 February 2007
- Revised manuscript received:
5 February 2008
- Manuscript approved:
5 February 2008
- Version of record:
10 December 2008
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