No abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractAfter most operators quit using Pin connector, Riser and Diverter for safety reasons, when drilling the tophole section of subsea wells, the use of seawater and sacrificial mud with return to seafloor has to date been the only available practical method.The RMR spread was run through the moon pool on a single derrick rig, and guided and stabilized by a heave compensated guide wire extending to a subsea anchor. Ref. System Schematic, Fig 1. The equipment was engineered and manufactured within an 8month period, and the field trial took place in December 2004.The paper also discusses the fluid system used, the operational benefits and limitations by applying the RMR technology.At the same time as the RMR Demo 2000 project was initiated, AGR was requested to design and build a Riserless Mud Recovery System for BP to be tested on the West Azeri field in The Caspian Sea. During 2004 the AGR Dual Gradient RMR system has been used to successfully drill the unstable 26" tophole using weighted inhibited silicate-based mud at approximate 120 -160 meter water depth (reference 1 and 2). This is a somewhat lighter version, which is suspended over the rig side by a winch and using a hose for the returns. Equipment Specification and EngineeringThe design basis and scope of work was based on the results from the Pre-Engineering phase. Further design detailing was developed with input from Hydro and Statoil, and was verified by the Project Steering Committee. The main design and operating requirements were:• The RMR System to be designed for 450 m water depth. • Offshore test to be performed in 330 m water depth.

A riserless mud recovery system enables dual gradient subsea drilling operations to take place with the well open at the seabed. There are no pressure containment devices at the wellhead, but as with earlier systems developed for deep water drilling [1], mud and cuttings are returned to the rig by means of a subsea pumping system, fluid recovery hose and umbilical. The system was field tested as part of the Norwegian DEMO2000 project [2]. Subsequently, it has seen operational service in a multi-well drilling campaign in the Caspian Sea. This paper describes how the system was implemented in a remote area exploration drilling operation off Sakhalin Island. Following experience in 2004 and 2005 [3] a clear business case emerged with the underlying drivers of limited weather window, shallow gas and stringent discharge regulations. Accordingly a formal project was established and a number of critical risk reduction studies were carried out in relation to shallow gas and integrity of the return hose under high current conditions. Correct interfacing onboard the rig required careful choice of location, power supply, wellhead and remotely operated subsea vehicle. There changes were verified by means of a formal hazard and operability review. A significant part of the effort involved gaining certification of the equipment for use in the Russian Federation in parallel with the fabrication, acceptance testing, mobilisation, offshore installation and commissioning of the system. The paper concludes with a review of the operational experience from the 2006 drilling season along with the associated lessons learned and forward plan. Introduction Elvary Neftegaz, a joint venture between Rosneft and BP, drilled wells on the northeast Sakhalin shelf during the summers of 2004, 2005, and 2006. The operation encountered numerous challenges in regard to logistics, schedule, location, harsh environment, limited weather window, environmental sensitivities, and stringent regulations [3]. Discharges of drilling waste, even water-based fluids and cuttings are prohibited in the waters offshore Sakhalin once the 30″ conductor is set. In the surface hole, before the blowout preventers are run, mud and cuttings have to be returned to the rig by attaching a marine riser directly to the 30″ wellhead with a hydraulic latch connector. With this arrangement, the only protection against shallow gas blowouts is the rig's diverter system. This practice was the cause of a number of serious incidents during the 1980s [4]. As a result, the industry has moved away from using a riser when drilling surface-hole and present practice is to drill with returns to seabed whenever possible. So, in accordance with Company Policy, having to run the riser system to satisfy the discharge regulations, a risk assessment was carried out. It determined that a pilot hole should be drilled to surface casing depth to prove absence of shallow gas before the riser system was installed. Clearly, this is a time-consuming and still potentially hazardous way of operating and an alternative and safer means had to be investigated. There is a clearly defined weather window within which operations can be conducted. Although satellite images suggest that locations first become clear of ice in early May, the area is affected by drifting pack ice until late June. Severe storms and rapidly decreasing air temperatures in the autumn result in a very clear cut-off date in mid-October for an un-winterised drilling unit. Effectively, the weather window lasts for four months, from about 21st June until 21st October. Clearly, elimination of activities from the "critical path" would enable more to be achieved within a strictly limited period. The combination of being compelled to recover cuttings from the surface hole, to eliminate discharges associated with the pilot hole, to mitigate the risks posed by shallow gas and maximise productive activity within the rigidly constrained weather window drove an urgent search for a different approach. A riserless mud recovery system developed by AGR Subsea AS of Bergen, Norway [2] and actively used in the Caspian was identified as a possible candidate to achieve all the desired objectives. Accordingly, a phased project was initiated to review the feasibility of the technology and, if viable, proceed with implementation.

This paper introduces a method to enable continuous automatic online updates of the density and frictional effects of the drilling fluid during drilling operations. The placement of differentialpressure sensors along the circulation path from the rig pump to the connection to the drillstring enables the fluid properties to be examined more thoroughly at various flow rates, pressures, and temperatures. The paper presents results from a full-scale test in which different fluids were examined. The results show that the method may give reliable data on the main drilling-fluid properties, which are important in all drilling operations, and especially in automatic modes.

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. RMR Technology 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. Hardware Overview 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.