Teleco Oilfield Services Inc.

Arthur Hay

Donald S Grosso

Thomas M Bryant

In accordance with the present invention, several methods are presented for the detection of gas into an offshore marine riser (e.g., riser gas). In a first embodiment of this invention, an acoustic transmitter is positioned on or nearby the subsea blowout preventor stack and imparts continuous low frequency waves into the annular fluid in the marine riser. These imparted waves define pressure perturbations which are received by a pressure transducer positioned on the riser at a location above the acoustic transmitter. Gas detection in the riser is then indicated by determining the rate of change of certain characteristics of the output. The output characteristics are preferably the moduli and phase angles of the acoustic fundamentals and their harmonics. In a second embodiment of this invention, continuous or pulsed pressure waves are imparted into the marine riser using a transducer ring surrounding the riser comprised of piezoelectric or magnetostrictive elements which change shape when electrically stimulated. When such electrical stimulation occurs, preferably by a pulse containing multiple harmonics, the transducer rings impacts the riser pipe causing compressional waves to be set up in the annular fluid. The compressional waves are then sensed at or near the surface and changes in amplitude or phase shift are detected for determining the presence of influx gas.

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Cheshire, CT, United States of America

Arthur Hay