Patent ID: 7578350

Claim:
A system for controlling gas in a subsea drilling operation, the system comprising: a wellbore extending below the sea bed; a subsea blow-out preventer coupled to the wellbore; a riser coupled to the subsea blow-out preventer, said riser, wellbore and blow-out preventer enclosing a pathway through and below the sea bed; a drillstring extending through said pathway, surrounded therein by an annular space, the blow-out preventer being configured to seal the annular space at a point of closure below the riser; a gas sensor located at a position within said pathway below said point of closure and exteriorly of said drillstring, such that the sensor is positioned and configured to contact wellbore fluids which have ascended within said annular space during normal drilling operation but have not yet passed the point of closure, said gas sensor being effective to detect the presence of gas in the wellbore fluid which it contacts; a controller configured to automatically cause manipulation of the subsea blow-out preventer based upon information from the gas sensor, and a signal pathway which couples the gas sensor with the controller.