The Molikpaq rig successfully mated to the spacer structure

Project Summary

In March through May of 1998, Argonautics Marine Engineering was part of a multi-national team of specialists, involved in the mating operation of the Molikpaq rig onto a purpose built spacer structure in Okpo, Korea.

The Molikpaq, a bottom founded, mobile arctic caisson type rig, has been refurbished by Daewoo Heavy Industries, Ltd. in Okpo, Korea for installation offshore Sakhalin. Since this new location is in deeper waters, a 16 m high steel structure was designed and built to increase the rig's hull depth. This "spacer" was built in sections at the Amur Shipbuilding Plant and assembled in Bolshoi Kamen. The octagonal, donut shaped 15,000 t spacer measured 110 x 110 m and was outfitted with 3 stability towers. A hydraulic operated valve system was installed for gravity ballasting. The Ballast Control Container was mounted on the center buoyancy tower. Upon completion in Russia, the spacer was towed to the Daewoo Heavy Industries, Ltd. shipyard for final preparations and testing before the mating operation. Computer simulations were used to optimize the spacer submersion procedure.

On May 23, the spacer was towed out to the carefully selected mating site and moored to a spread of pre-installed anchors and winch barges. A work barge, outfitted with generators and compressors (providing the compressed air needed for deballasting) was hooked up to the center tower. Following the procedure, the spacer was slowly submerged by free flooding the main ballast tanks while maintaining trim and heel control with the corner tanks.

On May 26, the Molikpaq was towed to the mating site and connected to the anchored winch barges. While monitoring the position relative to the submersed spacer with underwater cameras, the Molikpaq was slowly winched into position against 3 stoppers. Once in position, the spacer was deballasted, lifting the 43,000 t Molikpaq out of the water. Final position of the Molikpaq was confirmed to be within 5 mm, well within the 50 mm tolerance. The successfully mated units were unmoored and towed back to the yard for welding of the Molikpaq bottom to the spacer pedestal tops and completion of the refurbishing.  In August of 1998, the rig was towed to Sakhalin and successfully set down.

Scope of Work

The project scope included:

• Attending and working as a member of the Mating Task Force Team;

• Reviewing of all engineering output and procedures;

• Reducing the planned offshore time from 14 days to 5 days;

• Providing experience and operational input for the procedures;

• Design of safe and workable ballast procedures for the spacer submersion;

• On-site training of the Daewoo ballast team;

• Supervision of the actual spacer ballast and Molikpaq mating operations.

Project Paper

A project paper presented at the Northern California Section meeting of the SNAME, Berkeley, CA, on June 10, 1999, can be downloaded in PDF format.

  Mating of the Molikpaq Drilling Rig...  

Project Video

A short video shows the mating operation and welding of the drilling unit to the spacer structure, all filmed by Daewoo. Requires Windows Media Player.

Molikpaq Mating Operation...  

Project Photographs

The spacer structure arrived at the Daewoo yard after a long tow from Russia. The ballast system was tested and some modifications were made.	Slowly the spacer deck submerses as its tanks are flooded, in accordance with the ballast procedure. Positive stability was maintained at all times.	Using local tugboats, the Molikpaq is maneuvered over the submersed spacer. Final positioning was done using winches mounted on anchored barges.	After achieving firm contact and confirmation of correct positioning, the combined unit was deballasted with a small trim and list.