The Riserless Mud Recovery (RMR) System is a new and emerging technology for top hole/open hole drilling. The technology is planned to beused in Russia in 2006. The RMR Technology is applied for the open hole sections (no BOP installed), enabling return of fluid and cuttings in a closed system. A subsea mud pump is returning mud and cuttings to the drilling rig for treatment/recirculation instead of dispersal on the seabed. Since weighted mud is used the risk of shallow gas influx is reduced compared to conventional top hole/open hole drilling. However, since the return is routed to the platform, shallow gas is a cause of concern.
A new transient coupled reservoir-well two phase well control simulator for modelling drilling and well control scenarios with a dual pump drilling system has been developed.
The paper describes the RMR System and its potential related to shallow gas detection and control compared to conventional top hole drilling.
Shallow gas scenarios during top hole drilling with the RMR System have been simulated and the results evaluated. The focus has been to detect a kick before gas reaches the return line. The evaluations have confirmed that the RMR System is a safe system, which can detect a shallow gas influx prior to gas reaching the return line, and also handle the influx in a safe manner. Modelling further shows that pit gain, sub sea power and RPM of subsea pump are the main parameters for kick indication. These results verify the feasibility of the RMR System related to safety and well control. In addition this System will reduce discharges to sea during top hole drilling, as well as significantly reduce the frequencies of shallow gas incidents.
AGR Subsea AS has developed a drilling concept named RMR - Riserless Mud Recovery - which is used for open hole/top hole drilling. The system is effectively a subsea pump drawing mud returns from a suction module mounted on the wellhead, via a hose line and pumping the fluid and cuttings back up to the rig. The RMR system enables the use of engineered drilling fluid. A sketch of the system is presented in Figure 1.
The qualification and demonstration of the system is documented in ref. 1.
Subsea Pump Module (SPM)
The pump module provides a support frame for;
Discflo™ Pumps in series
Electric pump motors
Junction boxes for power supply and instrumentation
Suction hose quick release on the pump suction side
Inlet and outlet diverter valves
Interface to the pressure transmitters
HPU for valve and quick release operations
See Figure 2.
Suction and Centralizing Module (SCM)
The SCM (Suction and Centralizing Module) is mounted on the wellhead and contains the mud-capand provides connection facilities for the RMR Suction Hose and power cable jumper line. A pressure relief valve and suction valve was developed and functions as a relief facility; against over/under pressurizing the well bore.
See Figure 3.
The Suction Module may be fully open to sea, utilising an Open Mud-Cap principle or may be closed with a Rotating Control Device with a seal. The Open Mud-Cap arrangement would normally be preferred if there is a risk of shallow gas. This would allow monitoring of the mud-cap with the subsea camera or ROV.
See Figure 4.