Ireland's Corrib North gas discovery by Enterprise Oil plc, London, could become the first field development off the country's west coast.
Wood Mackenzie Consultants Ltd., Edinburgh, said Block 18/20 Corrib North is commercial despite its remote location, and could be developed as a subsea field to supply Ireland's growing gas market.
The 18/20-1 discovery well was drilled by Enterprise in 1996, said the analyst. The company intended to test the well, but its casing partially collapsed due to pressure from the overlying salt layer, and the test string could not be run.
Enterprise acquired 420 sq km of 3D seismic data over the Corrib North structure in 1997 in preparation for drilling an appraisal well, 18/20-2, the results of which the company disclosed recently (OGJ, Oct. 5, 1998, p. 42).
"The latest well," said Wood Mackenzie, "was spudded a couple of kilometers to the northeast of the discovery well and was intended to prove up the extent of the reservoir and to better define the reserves base. The well successfully tested gas at a relatively high stabilized rate of 63 MMcfd through a 2-in. choke and a flowing wellhead pressure of 1,306 (psi), the rate being limited by the test equipment."
Corrib potential
The overlying salt layer was said to be deeper than anticipated from the discovery well, reducing the potential upside for reserves, which had been estimated to be at 2-4 tcf range."Although the discovery has yet to be fully appraised," said Wood Mac- kenzie, "and, therefore, reserves estimates are tentative, we estimate that the structure could hold around 1.2 tcf of recoverable gas."
The analyst reckons the Slyne/Erris Trough gas play in which Corrib was found could have total reserves amounting to 5 tcf of gas. Enterprise reportedly identified several similar prospects in the vicinity, and Statoil (U.K.) Ltd., operator of an adjacent license, is interpreting seismic data from Block 5/94.
"The Corrib North reservoir," said Wood Mackenzie, "is not believed to be geologically complex, and, if the recent appraisal well is representative, (it is expected to be) very productive. "This could allow the field to be drained with perhaps as few as three to six subsea wells, as the area of the field is not particularly large.
"These could be tied back to a wellhead tension leg platform or, if the properties of the gas allow, tied back directly to shore.
"Despite lying in fairly deep water (350 m), Corrib North lies only 70 km from Achill Island. We estimate that a subsea development tied back to an onshore plant could cost in the region of $750 million, including the building of a pipeline link to the main grid on the east coast."
Copyright 1998 Oil & Gas Journal. All Rights Reserved.
