The threat of riser gas in deepwater drilling operations is real. Studies show that gas kicks unintentionally entrained in oil-based mud in deepwater are unlikely to break out of solution until they are above the subsea blowout preventers (BOPs). The rig diverter is conventionally used to vent riser gas with minimal control and considerable risk and environmental impact involved.
Reactive riser gas systems provide a riser gas handling (RGH) joint that is composed of a retrofitted annular BOP and a flow spool with hoses installed on top of the rig marine riser. A proactive, alternative approach to riser gas handling, called riser gas risk mitigation, is proposed by using managed pressure drilling (MPD) equipment. MPD involves the use of a rotating control device (RCD) to create a closed and pressurisable drilling system where flow out of the well is diverted to an automated MPD choke manifold with a high-resolution mass flow meter that increases the sensitivity and reaction time of the system to kicks, losses and other unwanted drilling events.
Experiments and field deployments have shown that the deepwater MPD system can detect a gas influx before it dissolves in oil-based mud, allowing for management of the same using conventional well control methods. Since the MPD system has already closed the well in, automatic diversion and control of gas in the riser is also possible, if required. This paper presents experience gained from deepwater MPD operations in the Asia-Pacific to illustrate this, and possible deployment options in Australia are discussed.