Managing the pressure

OE Staff

May 1, 2017

AFGlobal sheds light on its launch of a key RGH component for deepwater MPD operations.

For deepwater, subsea applications, the Active Control Device offers a significant departure from conventional RCDs with a purpose-built, non-rotating, hydraulically controlled sealing sleeve around the drill pipe. Photo from AFGlobal.

The venerable rotating control device (RCD) that has long been the enabling component of managed pressure drilling (MPD) operations has a purpose-built replacement with an innovative new design that eliminates wear and maintenance prone rotating components. AFGlobal’s Active Control Device (ACD) provides the prerequisite seal and diversion of annular wellbore returns using a novel, non-rotating device enabled by an actively pressurized, co-molded element.

The new device eliminates the bearings and rotating components that are a regular source of maintenance and failure in standard RCDs. Instead, its active pressure sealing system hydraulically applies closing pressure to maintain consistent wellbore sealing integrity over time as the sealing sleeve is worn.

RCD elimination

While the basic design for RCDs has evolved from early diversion devices used in air drilling, the ACD is designed specifically for MPD. It is API 16RCD-qualified to isolate and seal off the top of the riser to divert mudflow during MPD operations. The ACD is installed subsea in the marine drilling riser below the rig riser tension ring and slip joint. Configured as part of a riser gas handling system (RGH), the device enables MPD operations on floating drilling rigs equipped with any generation of riser.

The ACD’s non-rotating, hydraulically controlled sealing sleeve that surrounds the drill pipe features a unique co-molded element manufactured with an enhanced urethane matrix reinforced with a durable polytetrafluoroethylene (PTFE) inner shell. As the sealing sleeve wears, pressure is actively applied to force the element against the drill pipe to maintain a consistent seal. With standard RCDs, the passive rotating elastomer seal is degraded with use, resulting in a performance decline requiring regular replacement. The rotating system also includes a bearing assembly that must also be maintained.

Active sealing

Active pressure sealing is a significant advance over RCD operations that degrade the performance of a passive rotating elastomer seal, says AFGlobal. The device varies hydraulic pressure on the seal to compensate for wear and accommodate passage of wear inducing tool joints. In addition, active pressure is a positive wear indicator to inform maintenance and assure MPD operations. Service life and performance is further enhanced by the greater durability of the co-molded element and lubrication of the seal with clean drilling mud.

MPD integration

The ACD is a component of AFGlobal’s RGH system, which is an integral part of the drilling riser. The RGH is used to address safety issues that occur when formation gas breaks out of solution in the riser. It is also the basis for establishing an MPD-ready rig configured for the addition of manifolds, instrumentation, control systems, and other MPD equipment. The component-based RGH system easily accommodates MPD service company equipment in addition to AFGlobal MPD systems owned by the drilling contractor or operator.