Summary
Calculating the blowout rate of oil and gas wells is commonly one of the
first steps in environmental-impact assessment, contingency planning, and
emergency response. The blowout rate is a direct measure for the economic and
environmental damage caused by a blowout and an indicator for the effort
required to regain control over the well. Hence, a simulator was developed to
estimate blowout rates.
This simulator was validated for field cases by comparing calculated blowout
rates with estimates based on observable phenomena such as flame length and
heat release rates. This limited validation to onshore- and platform-well
blowouts, which are usually governed by critical outflow conditions at surface,
because ambient pressure is usually considerably less than the wellbore
pressure just upstream of the outflow. For subsea wells, blowing out against
the substantially higher pressures at seabed, this does not apply. The blowout
rate is determined by the total system performance from inflow at sandface to
outflow at seabed.
To validate the blowout-rate calculations under these conditions, data were
collected on high-rate well flow through an annulus against elevated surface
pressures, resembling subsea blowout conditions. A comparison of the measured
rates with the calculated rates demonstrated that the rates could be predicted
with a high accuracy, provided that the mechanical condition of the tubulars is
taken into account properly. Default assumptions for the hydraulic roughness of
the tubulars lead to overestimates of the blowout rates and consequently to
worst-case estimates for the environmental and economic damage caused by a
blowout.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
26 April 2008
- Meeting paper published:
26 August 2008
- Revised manuscript received:
12 January 2010
- Manuscript approved:
19 January 2010
- Published online:
7 June 2010
- Version of record:
13 September 2010
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