Paleocene exploration in the Faroe–Shetland Channel: disappointments and discoveries

Abstract

While the early drilling in the UK West of Shetlands area was concentrated on structural highs, the 1992 discovery of oil in the deep-water Paleocene sands of the Foinaven Field re-invigorated exploration interest in hydrocarbon traps with a stratigraphic element and encouraged a high level of participation in the UK 16th Licensing Round (1995) west of Britain. Many of the main exploration targets in these rounds were mapped as sand pinchouts onto either the basin margin or onto intra-basinal structural highs, for example, updip to the southeast of the 1989 well, 205/9-1. Few of the initial wells drilled to test this type of pinchout play were commercially successful but, as part of the exploration effort, a large area of the basin was blanketed with 3D seismic data on which more subtle features could be recognized. Seismic anomalies similar to those of the successful discoveries were sought on the new 3D data, as this type of play relied heavily on seismic attributes to help define risks and reserve size. The Foinaven and Schiehallion fields have a suite of attractive seismic characteristics and exploration effort was driven by the search for similar seismic anomaly features throughout the Atlantic Margin. As wells were drilled on 16th Round acreage, some of the targeted seismic reflection anomalies, originally seen as direct hydrocarbon indicators, turned out to have different causes. Representative examples are shown from the central part of Quadrant 205 in which tuning, seismic artefacts, porosity effects and unexpected igneous lithologies contributed to the drilling of unsuccessful exploration wells. The variation with depth of rock physics trends in the area are shown, the characteristics of some direct hydrocarbon seismic indicators are modelled and comments are made on the sensitivity of the modelled seismic response to shear velocity estimation. The former ‘White Zone’ or undesignated area, the previously unlicensed acreage between the UK and Faroe Islands, was opened through the Faroes 1st and the UK 19th Licensing Rounds in 2000 and 2001. By 2003 the first 8 of 15 commitment exploration wells were drilled in these licenses. Together with an assessment of the seismic anomalies and the risks of stratigraphical traps in the area, analysis of the petroleum system led to the siting of the 6004/16-1z well on the structural high of a Cenozoic inversion anticline. The resulting ‘Marjun’ discovery, the first in the Faroes, consisted of a gross 170 m hydrocarbon column in the T10 Early Paleocene interval, thus opening a new fairway in the area. The challenge has evolved in the last five years from finding an effective reservoir in the basinal areas to the search for a robust trap with an intact sealing lithology.