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Calculation Method Of Maximum Allowable Gas Invasion Overflow In Deepwater Drilling
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| 2017-06-27 |
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| Deepwater drilling requires more rigorous well control.
Accordingly, proactive gas invasion detection is a hot
topic in research of deepwater well control. The warning
overflow value is an empiric value, so the existing put-
gain method is less applicable and reliable for the wells
with a high initial reservoir pressure in deep water. The
well-killing risks under different overflow conditions
were calculated with consideration to maximum allowable
shut-in casing pressure and the annulus gas-ascending
position. Then, a back calculation method was developed on
the basis of the warning overflow value of gas invasion so
as to monitor gas invasion overflow more accurately and
reliably with the existing well control equipment,
construction parameters and formation parameters.
Furthermore, this method was improved by integrating the
credibility formation pressure prediction method to
minimize the gas invasion monitoring errors caused by
inaccurate formation pressure prediction. Practical
calculation shows that this method takes the annulus gas-
ascending positions and well-killing risks into full
account, so the accuracy and reliability of proactive gas
invasion detection in deepwater drilling are improved
greatly. This method plays a practical role in designing
well-specific warning overflow value and reducing gas
invasion monitoring costs. Finally, it was recommended to
monitor the pit gain by using the import and export flow
meters of higher accuracy and stability so as to satisfy
the measurement accuracy of semi-submersible drilling
platforms.
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