Time-lapse seismic in Gannet A: One more lead firmly integrated

Abstract

The Gannet A field is a mature oil and gas field in the central North Sea. Its Upper Tay reservoir consists of generally high quality deepwater turbidite sandstones of Eocene age in a large, low-relief, mainly structural, partly stratigraphic trap. A 53-ft oil rim contains 190 million barrels of stocktank oil with 190 billion standard cubic feet (= Bscf) dissolved gas, overlain by a 325 Bscf gas cap. The reservoir sand has 30–33% porosity with 1/2-2 Darcy permeability. Reservoir quality deteriorates from 95–99% net-to-gross in the northwest to 40–50% in the south. The field has been developed with 11 evenly spaced horizontal oil producers, which have on average completions of about 3000 ft in the middle of the oil rim. By year-end 2002, 61 million barrels of oil had been recovered from the field. With a forecast ultimate oil recovery factor of 40%, the initial oil rim development could be considered successful and final, in particular if compared to recovery factors achieved for similar oil rims (Weber an...