McDermott plans to utilise Derrick Barge 30 for the subsea installation works at the Vashishta and S-1 gas fields. Credit: McDermott International, Inc.
Offshore drilling at the two fields will be completed in six to seven months. Credit: McDermott International, Inc.
McDermott International will employ its modular, portable spool base for the installation activities. Credit: McDermott International, Inc.

Vashishta and S1 gas fields located in the Krishna-Godavari (KG) Offshore Basin, off the east coast of India, are being developed under a greenfield deepwater development project by India’s biggest oil and gas exploration and production company Oil & Natural Gas Corporation (ONGC). The total investment for the integrated development is estimated to be $751.65m.

The project is expected to be completed by April 2016 with both the fields planned to be brought online that year. Offshore drilling is scheduled to be completed within a period of six to seven months.

The Vashishta field is estimated to produce 9.56 billion cubic metres (bcm) over a period of nine years with peak production reaching 3.55 million metric standard cubic metres a day (MMscmd) during the first five years. The S1 field is expected to deliver 6.22bcm over a period of eight years with a peak production of 2.2mmscmd for the first five years.

Vashishta and S1 field development details

The proposed development encompasses drilling, re-entry and completion of four wells, subsea tie-back of the wells to an onshore terminal at Odalarevu and expansion of the existing onshore terminal.

The four wells will be namely VA-DA and VA-DB at the Vashishta field and S1-A and S1-B at the S1 development. The wells will be drilled to a depth of 2,200m and tied back to the onshore facility in daisy chain architecture.

The daisy chain development will feature midline tees and crossovers situated at S1 wells, VA-DB and pipeline end terminations at VA-DA. A pipeline end manifold will be present at VA-DB to allow pigging for future expansions.

A 14in diameter and 45km-long dual pipeline will be used for the tieback that will follow the route of the existing G1 pipeline system to have minimal impact on the seabed and the surrounding area. The pipeline will be segmented into two sections, subsea and landfall, with varying wall thickness.

Location and reserves

The Vashishta field lies in water depths varying between 500m and 700m and approximately between 31km and 35km from the Amalapuram coast. The S1 field is located in water depths of between 250m and 600m, and approximately between 26km and 29km from the Amalapuram coast.

The Vashishta field is a free gas field with estimated reserves of 12.92bcm. The block occupies an area of 119m² and lies to the south of the G-1 field.

The S1 field lies to the east of G-1 field and is a free gas field with estimated reserves of 10.37bcm.

A proven petroliferous basin of the continental margin, the Krishna Godavari Basin consists of roughly 5km-thick sediments ranging from Late Carboniferous to Pleistocene age.

Onshore developments

The onshore processing terminal at Odalarevu will be expanded as part of the development to handle fluids from the Vashishta and S1 fields.

The newly constructed facility will be situated in close proximity to the existing onshore processing terminal, which receives hydrocarbons from the GS-15 field. The new terminal will be equipped to handle supply from the G-1 and GS-15 fields too along with the new fields.

The onshore section of the pipeline transporting the fluids will be roughly 4km-long and laid at a depth of approximately 2.5m. The terminal’s capacity upon expansion is proposed to be 7.25mmscmd of gas and 1,500m³/d of crude.

Key players

A contract for the engineering, procurement, construction and installation of major subsea field infrastructure was awarded to a consortium of McDermott and L&T Hydrocarbon Engineering (LTHE).

“The S1 field is expected to deliver 6.22bcm over a period of eight years with a peak production of 2.2mmscmd for the first five years.”

The scope of work includes supply and installation of a series of pipeline end terminations and in-line tee structures, a pipeline end manifold structure, rigid jumpers and approximately 30 miles of umbilical. McDermott will deploy its portable spoolbase, Derrick Barge 30 (DB30) and deepwater North Ocean 105 (NO105).

A contract was awarded to Technip for the construction of the onshore terminal as part of the integrated development. The €100m contract includes basic design, detailed engineering, procurement, fabrication, inspection and testing, installation, pre-commissioning and commissioning of the new onshore terminal facilities. The project will be managed and executed from Technip’s operating centre based in Delhi.

Consultancy services for the project were provided by Asian Consulting Engineers.