Appeal No. 2002-2203 Page 5
Application No. 09/584,526
density of the mud in the riser at a point just above the blowout preventer, locally
measuring the density of the mud and comparing the predicted and measured density
values. If gas is present in the mud, thereby indicating a “gas kick,” the measured
density will be lower than the predicted value. Note the paragraph bridging columns 3
and 4. While Calcar focuses primarily on “kick” detection, Calcar also points out
(column 4, lines 8-10) that, in addition to gas kicks, “lost circulation conditions can be
determined using this invention.”
It is our opinion that the combined teachings of Bruce and Calcar are sufficient to
have suggested the subject matter of claim 12. Specifically, the combined teachings of
Bruce of adjusting lift gas flow rate to control the riser base pressure and of Calcar of
comparing measured riser mud density to a predicted density as an early indicator of a
kick or lost circulation situation would have suggested to one of ordinary skill in the art
at the time of appellants’ invention a method including predicting riser fluid density,
measuring the actual riser fluid density, comparing the predicted and measured values
to determine if either a kick or lost circulation situation exists, as taught by Calcar, and
increasing the lift gas flow rate, as taught by Bruce, if a lost circulation situation is
detected.
Appellants argue that the examiner’s combination of Bruce and Calcar is
improper because neither reference indicates a recognition that decreasing the rate of
injection of lift gas cannot provide sufficient control with regard to preventing the influx
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