High-tech help enlisted to extract gas from new field

The extraction of gas from the newly-discovered Corrib gas field will generate few jobs because of advances in mining technology.

As Enterprise Oil's feasibility study of the area 70 kilometres from Achill Island gets under way, sub-sea robots - similar to unmanned submarines - will be deployed to perform tasks on the sea bed.

According to Dr Graham Ross, Enterprise Oil's drilling manager, there is a continuous effort in the energy industry to get as many people onshore as possible, for both safety and cost benefit reasons.

"Divers are only safe to a maximum of 200 metres, while ROV's (remotely operated vehicles) go to 300 metres and can be worked for unlimited hours. Divers would have to go down in a diving bell with decompression chambers. There has been a whole history of North Sea diver deaths, you avoid it whenever you can."

The gas in the Corrib field is located 350 metres below sea level. The logistics involved in extracting the energy make for a long and costly process as Enterprise Oil plans to put a total of six wells in place by 2002.

All of Corrib's wells need to be drilled from a floating rig, as the water is too deep to accommodate a fixed standing rig similar to that located off Kinsale.

"Floating rigs are ideally suited to deep sea drilling. If we were to put a fixed rig out on the Corrib sea bed, it would be the tallest standing steel structure known to man," says Dr Ross.

Instead the floating rig positions the wellheads, with the assistance of sub-sea cameras attached to ROVs, and guided by an ROV controller aboard the rig.

The wellheads, which are huge steel casings shaped like an inverted telescope, are embedded in the seabed, and it is through these the gas will be piped when Enterprise hopes to start producing gas in November 2000.

The ROV's primary job is to remotely guide "Christmas trees" onto the wellheads prior to drilling. Christmas trees are 30-foot high metal structures comprised of a series of valves and connections which hook on to the wellhead.

According to Dr Ross, the ROVs are capable of doing anything a diver could do. With the aid of mechanical arms, the operator affixes a series of umbilical pipes to the Christmas trees which feed the gas through to a central manifold.

The ROV operators need to be highly skilled to manipulate the mechanical arms for intricate functions like screwing nuts and bolts. Each ROV costs several million dollars, with the mechanical arms alone costing around $1 million (€950,000) each to replace.

As part of the feasibility study, Enterprise is also conducting a sub-sea survey along the seabed to assess the optimum route for the gas to be piped from the central manifold to the shoreline.

With the use of sonar technology, technicians above water can reconstruct images of the seabed detailing the exact contours of the terrain. The path needs to be as even as possible to maintain the gas pressure in the pipe all the way from the manifold to the land.

Enterprise Oil plans to have its feasibility study concluded by the end of September, after which it hopes to receive a Government sanction to produce.