The new drillship concept introduced by IHC Merwede and Huisman Special Lifting Equipment B.V. is capable of drilling in ultra-deep water. (Image courtesy of IHC Merwede Offshore & Marine)

Buoyed by ongoing, long-term deepwater drilling programs, drillship utilization numbers have been hovering near 95% globally. With demand this high, it is no surprise that there are more than 20 drillships under construction and additional vessels on the drawing board.

One of the more interesting designs in the works is a compact vessel developed by IHC Merwede. Early last year, the Dutch company announced it would work with Huisman Special Lifting Equipment B.V. to develop and construct a compact drillship.

Thinking outside the box

The concept vessel is an IHC Merwede mono-hull that is suitable for ultra-deepwater drilling operations in most areas of the world.

According to the developers, the compact size of this vessel does not diminish its capabilities but delivers a number benefits. For starters, the steel weight is reduced, the vessel uses less power, and dynamic positioning (DP) performance is enhanced.

An interesting element of the design is that the drilling equipment has been integrated into the ship’s hull to a great extent. The result is that drillpipe and casing pipe storage, along with riser storage, dry bulk storage, and the mud tanks, are all below the main working deck.

Another feature that differentiates this design from traditional drilling vessels is the absence of an elevated substructure, which results in a lower drill floor and consequently a lower center of gravity.

The 30,000 dwt drillship is 620 ft (189 m) long, 105.6 ft (32.2 m) wide, has a beam of 105 ft (32 m), and is capable of drilling in 10,000 ft (3,000 m) water depth. The hook load is 1,090 metric tons or 2,400 kips for each of the two working positions. The vessel has 15,000 bbl (2,400 cu m) of liquid mud storage capacity onboard and 39,550 cu ft (1,120 cu m) of dry bulk storage.

This innovative design calls for a dual multipurpose tower with two workstations, one forward and one aft. Drilling operations will be carried out at the forward main drilling position while construction activities will be carried out at the aft station. The main drilling position, has a double-drum drawworks, and the construction side has a single-drum drawworks, both of which have passive heave compensation. The main drawworks has active heave compensation as well.

The setback carousels on the vessel can accommodate approximately 475 metric tons of drillpipe and casing pipe, or a total of 2,000 kips. Tubulars can be stored in containers or baskets in the hold and on deck. A special transporter moves the tubular baskets forward when needed.

The drilling tower is shaped as a square box girder and contains, among others components, the drawworks, drill string compensators, transformers, frequency converters, and hydraulic power packs for all of the equipment in and around the two drill floors. The top drive also can be parked inside the tower when not in use. Four 2,400-hp electrically driven mud pumps along with six shale shakers are built into the vessel, which also features an enclosed space for a cementing unit.

A plus for this design is that the installation of the equipment inside the tower makes adoption to cold climate and winterization a fairly simple task because most of the equipment is already enclosed.

Another advantage of the smaller design is that it can relocate more easily than a bigger drillship because it can pass through the Panama Canal, the Bosporus Straits, and the Suez Canal.

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