Appeal No. 2002-2203 Page 9
Application No. 09/584,526
APPENDIX
1. A method for controlling the pressure at the base of a gas-lifted riser during
drillling of an offshore well, said method comprising the steps of:
determining the rider base pressure (prb); and
using a throttling device located at or near the top of said riser to adjust the mass
flow rate out of the top of said riser (mo) and the riser surface pressure (prs)
to compensate for changes in the riser base pressure (prb).
12. A method for controlling the pressure at the base of a gas-lifted riser during
drilling of an offshore well, said method comprising the steps of:
determining a setpoint value for riser mix density (pmix);
determining the actual value of riser mix density (pmix);
adjusting one or both of the boost mud flow rate (qb) and the lift gas flow rate (qb)
to substantially minimize the difference between said setpoint value and said actual
value.
13. The method of claim 12, wherein said method further comprises the steps
of:
determining well return flow rate (qw) and drill string flow rate (qc); and
comparing the drill string flow rate (qc) to the well return flow rate (qw) to detect well
control problems such as kickers or lost circulation.
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