Watching the World Deep thoughts on drilling technology

With David Knott from London A Norwegian drilling contractor recently ordered what is claimed to be the world's first fifth generation semisubmersible (OGJ, Apr. 29, p. 29). Now Norway's Den norske stats oljeselskap AS has pressed the button that will lead to construction of an innovative twin hull vessel, offering an alternative to a semisubmersible rig for many well operations. Statoil issued a letter of intent to Smedvig AS, Stavanger, detailing a 1 billion kroner ($150 million)

June 10, 1996

3 min read

A Norwegian drilling contractor recently ordered what is claimed to be the world's first fifth generation semisubmersible (OGJ, Apr. 29, p. 29).

Now Norway's Den norske stats oljeselskap AS has pressed the button that will lead to construction of an innovative twin hull vessel, offering an alternative to a semisubmersible rig for many well operations.

Statoil issued a letter of intent to Smedvig AS, Stavanger, detailing a 1 billion kroner ($150 million) contract for well completion and intervention services for 5 years plus a 2 year option beginning Apr. 1, 1998.

The contract calls for construction of a small waterplane area twin hull (Swath) vessel Statoil helped design for use in development and operation of Aasgard field in the Norwegian Sea.

Smedvig will own and operate the Swath vessel, said to have stability, seakeeping, and loadhandling capability similar to a semisubmersible rig but to be more mobile (OGJ, Apr. 22, p. 20).

Subsea bonanza

Thor Viggo Aarrestad, Statoil's chief engineer for drilling and well technology, said the Swath concept is the result of company efforts to develop a cost effective technique for deepwater workovers and completions.

"Most of our coming developments are subsea," Aarrestad said. "For example, Aasgard will have 60 subsea wells. There are now about 800 subsea wells in production worldwide, and we have just put in orders for about 100."

Statoil's engineers reasoned that because subsea wells require a lot of rig work they could cut costs by using a relatively fast, dynamically positioned vessel specifically designed for workovers and completions.

Aarrestad said savings will flow from the shorter time required to move and position the rig between operations and the task-specific equipment on board the Swath vessel.

He estimates the Swath vessel will be able to perform well completions 36% cheaper than an anchored semisubmersible and well workovers 50% cheaper than an anchored semi.

"We reckon that in Aasgard development we will save $100 million in the first 5 years," Aarrestad said. "We also could save $45 million in development of Gullfaks field satellites."

Late last year Statoil announced a 6.5 billion kroner ($1 billion) development program for three satellites of Gullfaks field, using 23 wells tied back to the Gullfaks A platform through seven subsea templates (OGJ, Jan. 1, p. 31).

Drilling research

Statoil plans to push the limits of extended reach drilling and is developing other deepwater technology.

"Our goals include being able to drill wells with long horizontal producing sections that reach 10,000 m from a platform," Aarrestad said. "We want the option of platform drilling instead of subsea development at this distance."

Among technologies being tried for deepwater work is hammer drilling, a technique proven in the mining industry and being developed in conjunction with a mining company and other oil firms.

Hammer drilling could be used in hard rock, Aarrestad said. Tests show penetration rates have more than doubled compared with conventional drilling.