Quantitative Classification of Shallow Gas Blowout during OffshoreDrilling Process

Shallow gas is in form of natural gas accumulation at abnormal pressure, which may exist in shallow sediments below the seabed. Gas can blowout unexpectedly during well drilling that can pose a great hazard to drilling safety. In this paper, the occurrence and geological feature of shallow gas in offshore sediments are described and a quantitative classification of shallow gas hazards is given based on gas blowout rate, which can provide guidelines for the assessment and control of the shallow gas hazards. Several measures for prevention of shallow gas blowout in offshore drilling are described, including dynamic well killing technology.