McDermott wraps up offshore installation and startup job for ONGC

On ONGC's Vashishta project, the first end pipeline end termination is lifted from the supply boat by NO 105. This is the largest PLET that the vessel has ever installed, weighing 88 tons, including a 23-meter-long stress joint.

Houston-based McDermott has concluded the installation and startup on the Vashishta and S1 field, an engineering, procurement, construction and installation (EPCI) contract that it received from India’s ONGC in December 2015.

As recently reported by Offshore Energy Today, ONGC started commercial production at its Onshore Gas Terminal Plant in Odalarevu, Andhra Pradesh by processing gas from three offshore wells as part of ONGC’s integrated development of Vashishta (VA) & S1 fields. 

The fields are located 30-35 km off the Amalapuram coast in the KG Basin, off the East Coast of India, at water depths of 250 to 700 meters.

McDermott said on Wednesday that, together with consortium partner LTHE, a subsidiary of Larsen & Toubro (L&T), it was responsible for the engineering, supply and installation of a series of pipeline end terminations (PLETs) and in-line tee structures (ILTs), a pipeline end manifold structure (PLEM), rigid jumpers and approximately 50 kilometers (30 miles) of umbilicals.

The pipeline scope includes 93 kilometers (58 miles) of 14-inch dual rigid pipelines extending from the shallow water shore line to a maximum water depth of 700 meters (2,300 feet).

Ben Delves, McDermott’s Vashishta Project Director, said: “Engineering design for the Vashishta project was no easy feat due to the iterative nature of the design process which had to reconcile many factors such as soil conditions, jumper/spool loads, connector capacities, in-place environmental loads, pipeline expansion loads, installation weather limitations, vessel envelope constraints and mission equipment constraints.”

Typical weights for Vashishta PLETs and ILTs ranged from 35 to 85 metric tons (27 to 93 tons) and the PLEM weight was 200 metric tons (220 tons).

“A combination of soft soils and the significant weight of permanent equipment has contributed to some large structures which made the interfaces with the installation vessel challenging,” said Delves.

McDermott noted that the installation of the subsea infrastructure was particularly challenging because the comapny only had four months out of the year to work at the Krishna-Godavari basin before the monsoon season hit the field with bad weather and strong sea undercurrents.

McDermott deployed three of its specialty vessels to complete the installation phase, namely Derrick Barge 30, Lay Vessel North Ocean 105 and North Ocean 102. McDermott also deployed its trademarked portable spoolbase at the LTHE base in Kattupalli, India, to fast-track the production of pipeline stalk for loading onto the installation vessels.

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