Those of you placing bets on The Next Big Thing in offshore drilling technology may want to check the current odds on riserless drilling. This technology continues to evolve and had a recent success in the North Sea, with the first North Sea oil well employing advanced Riserless Mud Recovery (RMR) technology successfully drilled by Total E&P UK PLC on the Jura West 3/15-10 prospect. Total E&P UK PLC acknowledged a significant time-saving over the previous technology used to drill similar 26-in. hole sections and regarded the implementation as very successful.


The return flow is intercepted at the seabed and activity pumped to the surface, giving the same effect as if the drilling had been moved to seabed level.

Riserless drilling has been under development for some time. According to the Offshore Technology Research Center (OTRC), “In 1996, three competing projects began aimed at mitigating many of the problems encountered in ultradeepwater drilling, including the narrow window between pore pressure and fracture gradient, high riser loads, high deck loads, and high costs of drilling fluids, etc. These three projects were conducted…in joint industry programs to develop the technology known as dual gradient drilling. All three projects achieved a dual gradient by placing a rotating diverter on top of the blowout preventer stack, which diverted the mud returns from the annulus to a set of seafloor pumps. These pumps then circulated the mud and cuttings back to the rig via an external return line. The marine riser was filled with seawater rather than mud as in the conventional case.”


OTRC points out that “Although these systems lowered the riser loads with a water-filled riser, the packages were still designed to be employed on fifth-generation drilling vessels using the existing riser system. Because these projects focused on deeper portions of the wells, massive, elaborate, and complex systems were developed.


“One dual gradient drilling application that has not been fully studied is the potential benefit of utilizing this technology in the top hole portion of the well.”


The riserless system uses a suction module and pump to collect drilling mud and cuttings at seabed level, and sends them to the surface via a flexible hose. (All images courtesy of Total E&P UK PLC)

RMR technology, developed by Norway-based AGR Subsea, is a move in that direction. It is intended for drilling tophole sections. As the company describes it, “On the seabed, AGR’s present riserless system has a one-meter diameter suction module mounted on the drilling template and connected to the top of the well’s upper conductor pipe, along with a subsea mud pump close by. This sends mud and cuttings back up to the surface-drilling rig via an 8-in. diameter flexible hose. Power and control systems are also carried on the rig.”


The company claims that “use of RMR technology is growing rapidly. More than 20 wells have been drilled in the Caspian Sea using RMR. It has been recently deployed off Sahkalin Island in Eastern Russia and in the Barents Sea where no drilling discharge is permitted. Other applications have been in areas of poor hole stability where an engineered fluid system is required. One of the main advantages of running the system is the ability to push planned casing setting depths deeper and simplify casing design. Using weighted, inhibitive fluid has also proven to give perfect topholes because the cementing is improved, which may extend the life of a well.”


RMR has been deployed in water depths of up to 1,312 ft (400 m). AGR Subsea says that it has commenced development work with two operators for water depths up to 4,920 ft (1,500 m), with field trials at these depths planned for 2007.

Comments