Deepwater drilling projects are inherently more challenging to execute due to the increased risks and complexity associated with narrow and unpredictable drilling formation pressure margins. With regards to well control, small gas influxes that are initially dissolved in the drilling mud can remain in solution and be circulated above the SS BOP undetected before finally breaking out in the riser; resulting an overboard diversion of oil based fluids, or worst case unloading the riser through the rotary table. In terms of drilling operations, the narrow and unpredictable nature of formation pressure margins experienced in offshore operations often require solutions that can dynamically control and adjust wellbore pressure to complete a hole section safely and efficiently. Finally, the lack of ability to respond quickly to an influx can result in kick sizes that cause significant safety concerns as well as Non Productive Time (NPT) and higher drilling costs.
Managed Pressure Operations (MPO) has designed a new Riser Safety System (RSS) to allow the effective implementation of contingency Riser Gas Handling (RGH) and Managed Pressure Drilling (MPD) operations. The RSS system is intended to reduce the environmental risks associated with diverting an uncontrolled flow of gas and drilling fluid overboard with a conventional rig diverter system. With regards to MPD, the RSS is able to support constant bottomhole pressure control and mud cap drilling to facilitate reaching total depth safely, and effectively and with minimized NPT. The RSS also offers the technology to rapidly respond to well control events by dynamically and rapidly adjusting wellbore pressure in MPD mode. The RSS consists of an API 16RCD rated Riser Drilling Device (RDD) for sealing the riser closing on the drill string during MPD, and an API 16A rapid closing riser gas handling annular. Beneath both sealing devices a flow spool is used to divert riser returns from subsea to a pressure control manifold and high flow rate MGS on the rig via 2 × 5.5” ID API 17K return hoses, with a third API 17K, 5.5” hose for over pressure relief.
The RSS subsea equipment is also designed to reduce the operational risk and deployment time associated with moon pool installation operations. As such, the RDD, RGH annular and flowspool are designed to drift through the rotary table like a joint of riser. Once suspended in the rotary table by the spider slips, the remainder of the deployment consists includes a control umbilical connection and return hose gooseneck connection of three 5.5” mud hoses. The hose gooseneck latch connection system consists of an adjustable padeye system, hydraulic latching mechanism, and clearance for a reasonable range of rotational offset during the connection process allowing for rig crews to quickly and safely rig up the RSS system.
This paper provides a detailed overview of the subsea equipment associated with the RSS system and how it is integrated with the rig's drilling riser. The RSS equipment conforms to the industry codes, i.e. API 6A, API 16A, API 16RCD, API 16R, API RP 17G, DNV OS E101 & ABS CDS, and it serves both RGH, MCD and MPD functions.