Riser Gas Risk Mitigation with Advanced Flow Detection and Managed Pressure Drilling Technologies in Deepwater Operations

Abstract

Studies have revealed that gas kicks unintentionally entrained in oil or synthetic based mud in deepwater drilling operations at water depths greater than 3000 ft are unlikely to break out of solution until they are above the subsea BOPs. The rig diverter is conventionally used to vent riser gas with minimal control and with considerable risk and environmental impact through the uncontrolled discharge of drilling fluids. Riser gas handling (RGH) systems currently being offered provide a reactive solution to the problem by supplying a riser joint equipped with additional components for this specific purpose. This joint is normally composed of a retrofitted annular BOP and a flow spool with hoses that is installed on top of the rig marine riser. An alternative and proactive approach to riser gas handling, which we prefer to call riser gas risk mitigation, is proposed by utilizing managed pressure drilling (MPD) equipment. MPD involves the use of a rotating control device (RCD) to create a closed and pressurizable 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, thereby further minimizing the likelihood of an environmental discharge should a riser gas event occur. Experience gained from deepwater MPD operations in Asia Pacific will be presented to illustrate this.