Subsea engineering group Maris International gave a paper at the 2003 Offshore Technology Conference (OTC) on the SDR concept. Like so many good ideas, interest was expressed at the time, but there has been little money to move the idea forward so far.

It is a radical modular concept that could revolutionize riserless drilling and introduce a step change in offshore operations.

Recently there has been significant progress on concept development. Two separate studies have been carried out on the idea. One is a feasibility study under the UK Department of Trade and Industry's SMART initiative - a fast track research and development program for expediting innovative technology backed by oil companies. The second study was submitted to the international Deepstar committee looking specifically at the commercial benefits of the system compared with high rig costs. Together the studies have identified potential cost reductions, between 25% and 40%, on conventional drilling with large mobile offshore drilling units - either semisubmersibles or drillships.

Dubbed the Maris Seabed Located Drilling Rig (MSDR), the concept is claimed to be, "A significant step forward in stretching the deepwater drilling boundaries and significantly advances the premise that full rig automation is possible."

In addition, "The MSDR can also be used as a low cost exploration drilling tool for deepwater wells or on wells located in ice-prone regions," the contractor has argued.

Preliminary engineering work is underway and the contractor is actively seeking further oil industry participation.

Jim Jenner, one of the authors of the 2003 OTC paper, recently said, "We have had a lot of response and we have talked to potential backers."

Informal discussions have taken place between Maris and a South American operator that has shown interest in the concept for deepwater drilling. Talks have also been held with potential backers in Russia about the applicability of the concept for arctic exploration.

"It needs millions, but people need to know what they are getting first," Jim Neffgen, JIP co-coordinator at Maris, said.

One of the problems of moving the concept forward is selling its potential benefits to prospective users.

Concept

Essentially the concept involves placing main drilling system components on the seabed, using modularized components and avoiding the requirement for a rigid riser. Consequently imposed and variable loads on surface support vessels can be reduced. This then offers the scope for a reduction in vessel size and complexity and, ultimately, to lower capital and operating costs.

At the heart of the design is a mechanical device called a continuous circulation coupler (CCC) - designed by Maris - that enables drilling fluid circulation to be maintained while making and breaking drillstring connections.

Maris International's concept was funded by the UK-based Industry Technology Facilitator (ITF) to launch new oil and gas technology and it follows on from a 1999 joint study by Shell and Saipem into seabed drilling.

Maris said its concept eliminates a large mobile drilling unit, and requires only a smaller, lower cost rig support vessel (RSV) to deploy and recover drilling equipment, wellhead and consumables in modules, and to provide power and drilling fluid circulation to the seabed.

After concept feasibility work completed April 2003, a final report on the project was issued October that year.

That ITF report indicated components of the SDR had been identified, and preliminary specifications had been developed. "An animation of the SDR in operation has been completed from a 3-D CAD (computer aided-design) model. The work is concentrating on determining the equipment needed for the drilling and tubular handling systems and on identifying solutions to address drilling problems associated with deepwater drilling. In this phase the primary focus was on the determination of technical feasibility of the drilling system and for construction and operation of the seabed rig," the ITF report noted.

Currently Maris is performing preliminary engineering studies on the SDR and is inviting industry participation in further work. To take it further forward, the contractor plans to develop the SDR over several work phases through a joint industry project scheduled to start by April 2005. Also preliminary work has been completed on identifying specifications for the RSV.

Economic

Principal advantages of the concept are its insensitivity to surface weather conditions, and the economic potential to provide a 25% to 40% reduction in drilling costs compared with floating drilling platforms, and the ability to leapfrog riser-less drilling technology.

Maris has argued the concept's drilling costs would compare favorably with a floating drilling facility in as little as 1,000-ft (305-m) water depth, and "do not increase significantly with water depth."

Reductions in well construction costs of up to 30% have been suggested by using the SDR in a water depth of 7,500 ft (2,287 m), and, when compared with a floating drilling platform operating in 10,000 ft (3,050 m), the SDR could provide a less technical and economic solution. Also, the concept is said to be extendable to much greater depth - 20,000 ft (6,100 m).

There is no rigid riser between the SDR and a surface vessel. Instead, all connections are made by flexible risers. The system is modular and deployable through an RSV moonpool. It uses standard drilling procedures, jointed tubulars and features mud circulation control at the seabed.

An abstract of the OTC paper pointed out, "In the medium term of some 4 or 5 years, the opportunities to reduce well construction cost by up to 30% in 3,609 ft (1,100 m) water depth to 7,500 ft (2,287 m) water depth will become compelling."

Technical challenges faced by the SDR include the need to be self-supporting in sloping or unstable seabed sand or mud, and the need to launch and recover components from an RSV in adverse weather. Transportation and remote handling of tubulars and assemblies is another issue, while a key environmental challenge is isolating drilling fluid from surrounding seawater. Control of mud flow in and out of the well at seabed is a further challenge. However, none of these technical challenges are thought to be insurmountable. Instead, Maris believes solutions can be found for all of them, eventually.

Overcome

Installation on unstable seabeds is overcome with a 42-in. conductor casing, upon which all other subsequent assemblies would be supported, approximately 10 ft (3 m) above the seabed. Once the conductor is installed, all other equipment in International Standards Organization (ISO) standard containers would be lowered from the RSV via cable and installed on the seabed. This would include a central drilling module, through which well components would be conveyed, plus other units for power, drilling, mud, and a rig mast, and tubular modules, all arrayed on the seabed in a matrix configuration.
The central drilling module contains well control equipment, drilling facilities, a blowout preventer (BOP) stack, a rotating BOP, and the CCC - which allows drilling fluid circulation while making up and breaking drillstring connections and ensures drilling fluid remains isolated from the surrounding environment.
A surface-mounted CCC was previously tried out successfully in December 2002, using a Houston land rig, Maris reported, with Varco as a development partner. That test entailed making 70 connections using 41/2-in. drillpipe on a BP well.

On the SDR, it is intended that tubulars would be in standard casing sizes, 13 and 5/8-in. and 11-in., or larger, to allow for low pressure drilling.

Tubulars are designed to be deployed in ISO containers, cut with slots to ease the ingress and egress of water as they are lowered and recovered via the RSV's moonpool to and from the seabed.
The mast module comprises a top drive assembly with 45 ft (12.8 m) of vertical movement. Up to 18 ft (6 m) of lateral movement is required for the drill mast to access all containerized tubulars with automated pipe-handling equipment.

Integrated with the mast module is the stinger - a Maris automated tubular handling system (MaTHS) - which accesses and grips all tubulars from inside. The stinger is sized for the internal diameter (ID) of drill pipe tubulars, and penetrates up to 16.4 ft (5 m) inside the length of pipe, avoiding the need for different clamps for varying tubular diameters, and allows for automated drilling.

With the introduction of monobore wells and expandable tubular liners, this handling process could be simplified further.

Once the top drive has sealed to the stinger, drill fluids can pass to the stinger via a short flexible hose, through the bore of the stinger and on into drill pipe.

Mud is injected at the seabed from the mud module, which consists of a high pressure (HP) flexible riser to surface for drilling fluids to be conveyed into the drillstring. It returns via a second HP connection below a rotary BOP back up to the RSV where mud and cuttings can be treated before re-injection.
Chokes are used to control the flow of mud and circulating pressure, allowing the SDR to be used for conventional single gradient drilling, or, for dual gradient drilling, where pore pressure and fracture gradients are critical to the success of the operation.

All power is provided via the power module through the floor of the foundation conductor base so that every other module can connect to the power supply as required.

This involves both electrical power up to 2 MW supplied by the RSV and hydraulic power generation.
If Russian and Latin American operators are prepared to take the concept forward, then a new generation of subsea drilling rig may not be too far away.

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