Corrib Gas Field, Republic of Ireland

The Corrib field is a Triassic gas development in the Atlantic Ocean, situated off the coast of Ireland. It is approximately 50 miles west of the Mullet peninsula in County Mayo and lies in the Slyne Trough in Blocks 18/20 and 18/25. The Corrib gas field was discovered in 1996 and represents the first commercial find offshore Ireland, since Kinsale Head in 1973.

Equity

The Corrib co-venturers are:

• Shell E&P Ireland (operator) - 45%
• Statoil Exploration (Ireland) Limited - 36.5%
• Marathon International Petroleum Hibernia Limited - 18.5%

The water depth in the area is 355m and the gas reservoir is located 11,500ft to 13,000ft below the seabed. Development costs are estimated at around £500 million. The hydrocarbons will be produced over a period of between 15 and 20 years. The Corrib gas is H2S-free and exhibits an expected condensate yield of less than 0.5bbls/mmscf, 0.3% CO2.

Drilling

Enterprise anticipates that five wells will be on-line at the start-up, with the system being designed for up to eight wells. Enterprise has used the Sedco 711 drilling rig for appraisal and production drilling. Tests have confirmed a flow rate of 60 million ft³/day. Reserves in the field are around 1 trillion ft³, or about 70% the volume of the Kinsale field.

Development

The development concept for Corrib comprises subsea wells, tied back to a central gathering manifold, connected to an offshore pipeline. This will carry gas back to a landfall point and then a short distance onshore to a processing terminal, also in Co Mayo. ABB won a $30 million order to deliver the subsea production system. Under the terms of the contract, ABB is responsible for the engineering, procurement, fabrication and testing of the subsea and associated shore-based equipment. ABB's involvement will include project management, engineering and the supply of the manifold and protection structures, control system, subsea trees, diverless tie-in equipment, intervention equipment, integration testing and installation support. The Co Galway port of Rossaveal is to be examined as an oil and gas exploration service base. In May 2008, Shell E&P Ireland Limited (SEPIL) confirmed that applications for consent to modify the Corrib onshore pipeline route were submitted to the Department of Communications, Energy and Natural Resources under the Gas Act.

Pipeline landfall

For the pipeline landfall, a trench has been excavated in the seabed from the high water level to approximately 10m below the lowest tide. Following this, either the pipeline will be strung onshore and pulled offshore through the trench or the lengths of pipeline will be welded together offshore and pulled onshore. After this, the landfall section will be welded to the offshore pipeline on the lay barge. The control and chemical injection umbilical will be installed alongside, but not necessarily at the same time as the export pipeline.

Processing

The gas will pass through the slug catcher in order to remove the bulk of the liquid. Following that, the gas will then be compressed and metered. Condensate produced in the gas, as well as that separated from the feed gas in the slug catcher / inlet separator, will be routed to the condensate stabilisation system. This is essentially a two-stage flash system with intermediate heating. The stabilised condensate is cooled in an air cooler and sent to storage.

Methanol recovered from the slug catcher will be fed through a particulate filter into the flash drum and onto the raw methanol storage tanks. It will be then pumped to the methanol still via the still feed / bottoms exchanger. The column overhead vapour product is condensed in forced draught air coolers and flows to the product methanol storage tanks.

Water produced from the Corrib field will contain small amounts of naturally occurring dissolved salts and trace elements and small volumes of liquid hydrocarbons. The water will be comprehensively treated in the terminal to ensure that the levels of trace elements discharged into Broadhaven Bay will be so low as to have no discernible impact on background levels in the Bay.