Summary
Oil deposition in the area surrounding a blowout is one of the most visible
consequences of the loss of control over well flow. Less visible, but equally
serious, are the short- to medium-term effects of oil coverage on the
environment. Apart from the direct damage, studies indicate effects (e.g.,
reduced tree growth) that persist many years following the incident.
Hence, oil fallout, in the case of loss of well control, is a factor to be
taken into account in decisions on well locations, emergency procedures,
contingency planning, etc. This requires an estimate of the area around the
well likely to be affected by oil fallout, given the geomorphology of the
terrain, prevailing winds, and expected outflow conditions. Models to obtain
such an estimate have been proposed, but application of these models (e.g., for
environmental impact assessment) has been limited. In part, this limitation can
be attributed to a lack of validation of the models because this requires a
combination of well-effluent data, outflow conditions, meteorological data, a
detailed terrain description, and fallout maps.
For the field case discussed in this paper, all the data necessary for
validation were assembled from various sources ranging from the well operator
and environmental agencies to meteorological and cartographic institutes. The
relation between the observed pattern of oil deposition around the well and
factors such as outflow conditions and wind speed and direction is analyzed
with a simple model. This relationship demonstrates that the main factors
determining the area affected by deposition of oil are the outflow conditions
and the wind direction.
To verify this result, a comparison with historical observations on oil
fallout around gushers has been made. Although more sketchy, the same patterns
emerge from this comparison, which strongly suggests that the methods developed
to explain the fallout pattern of the field case discussed can be used over a
wide range of conditions to predict the area affected by a blowout. This
prediction can serve several purposes, such as site selection, definition of
emergency procedures, environmental impact assessment, and contingency
planning. Finally, it is noted that this method also applies in less dramatic
situations (e.g., predicting droplet deposition around vent stacks).
Introduction
When control over an oil well is lost, oil fallout in the vicinity of the
well is often one of the main factors contributing to the eventual cost of the
incident. Apart from the direct damage to capital goods, crops, and water
basins and the cost of subsequent cleanup operations, there are medium- to
long-term effects, such as reduced tree growth over a period of many years
following the incident (Baker 1991). Furthermore, there can be penalties and
considerable indirect costs resulting from the loss of reputation.
© 2006. Society of Petroleum Engineers
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History
- Original manuscript received:
1 May 2006
- Revised manuscript received:
30 August 2006
- Manuscript approved:
19 September 2006
- Version of record:
20 December 2006
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