High hopes for offshore Mayo oil field

By Andrew Bushe

DUBLIN — The British exploration company Enterprise Oil has begun drilling an appraisal well 34 miles off County Mayo and are hopeful it will establish the commercial viability of what could be the country’s biggest offshore gas field.

The SEDCO 711 rig has spudded in on the Corrib field and is expected to finish the well by late June or early July, according to Enterprise Oil’s Irish general manager, John McGoldrick.

The rig will then move 5 miles south to carry out the first exploratory well on a new prospect, called Shannon, which they hope is related to the Corrib geological structure.

"We are treating it as a sort of satellite, but it doesn’t look as if it is connected," McGoldrick said. "It is at a similar depth and has similar geology."

A well on Corrib last year flowed 63 million standard cubic feet of gas a day.

McGoldrick said that if the test had used larger production tubing the flow would have been 80 to 100 million SCF a day or about a third of the total Irish gas consumption.

"Corrib looks very promising and if we have another well this year with such high flow rates then we will be in very good shape," he said.

McGoldrick said they were drilling the back-to-back well on the two prospects in the hope of linking extraction equipment together.

"Planning for success and with good results this year, we are aiming for production into the market by 2002-3," he said.

Industry estimates have suggested that Corrib could contain 1.2 trillion cubic feet of gas and Shannon 0.8 trillion cubic feet.

Kinsale Head, Ireland’s only producing gas field — discovered in the early 1970s off the south coast by the American Marathon oil company — had reserves of about 1.4 trillion cubic feet.

Kinsale is due to run out in the next five to 10 years just as Corrib production would be coming on stream if it proves commercial.

McGoldrick said the company is looking at a number of possible landfall sites for a production pipeline in Mayo.

"We are examining the economics and the environmental aspects," McGoldrick said. "Most of this gas will end up on the east coast where there is the biggest energy usage. We are also looking at regional development aspects like a spur pipeline to Galway.

"Our working assumption is that we will build the line ourselves. I know Bord Gais would like to do it but we have done this sort of thing before."

Enterprise has spent about £50 million so far — the current well is the fifth off Ireland. They have also drilled on the Kish Bank off Dublin and in another prospect called Avonmore off the west coast.

So far, 130 exploration wells have been drilled off Ireland, most of them in the Celtic Sea off the south coast.