ENI Petroleum commissioned Conam Construction to install approximately 18,550 ft of 10-in. pipe inside of an existing 14-in. subsea pipeline routed between ENI’s Spy Island Drill site and the Oliktok Production Plant in northern Alaska near the Beaufort Sea.


The flowline was being used to transport the crude oil from an island to the mainland. Because of the declining conditions of the 14-in. line, the client was looking at the option of installing a 10-in. pipeline inside the 14-in. flowline.


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Mears was invited to provide a unique solution to the challenging problem. It was required that the 10-in. line be installed using push force as far as practicable because of concerns of putting uplift forces on the 14-in. line if high pull forces were applied. Mears scope methodology involved inserting 6-5/8-in. drill pipe using a 500-Ton HDD drill rig and then simultaneously using a HK750PT pipe thruster to install the 10-in. NPS product pipe while pull force being provided by the HDD rig.


One of the significant challenges was caused by the availability of workspace to set up equipment. The length of 18,550 ft represents the length between the flange connections at both mainland and the island side. There was no space behind the flange on either side to setup any equipment. The pipe loops on to the facilities and their support, especially on the island side would not be allowed to move.


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Additionally, exit angles on both sides were approximately 16 degrees, which would require high over-bend for installation pipeline or any ramp to be built. There was only less than 500 ft of pipe string area available on the mainland side following the alignment of the pipeline. This would increase the schedule significantly.




Project Owner: ENI US Operating

Prime Contractor: Conam Construction Co.

Primary Subcontractors: Price Gregory, Mears, Flowline Alaska Inc., Applus/TRTD; and Acuren

Value of Trenchless Project (US$): > $25 million



Sharon M. Bueno is managing editor of Trenchless Technology.



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