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AAPG Bulletin, V.
Reservoir quality of intrabasalt volcaniclastic units onshore Faroe Islands, North Atlantic Igneous Province, northeast Atlantic
1Jarðfeingi (Faroese Earth and Energy Directorate), Brekkutún 1, Postbox 3059, FO-110 Tórshavn, Faroe Islands; [email protected]
2GEUS Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1210 København K, Denmark; Institute of Science and Technology, University of the Faroe Islands, Nóatún 3, FO-100 Tórshavn, Faroe Islands; [email protected]
3Department of Geosciences and Natural Resources Management, University of Copenhagen, Øster Voldgade 10, DK-1210 København K, Denmark; [email protected]
The Paleocene and Eocene strata in the western part of the Faroe-Shetland Basin contain abundant volcanic and volcaniclastic rocks. Recently, hydrocarbon discoveries have been made in reservoirs of siliciclastic origin in intra- and post-volcanic strata in the central Faroe-Shetland Basin that show an active petroleum system is present in the volcanic affected area. The siliciclastic reservoirs are present in the same stratigraphic levels as the volcanic and volcaniclastic rocks, and in places, the siliciclastics and the volcanics interfinger. The assumption from published studies so far, based on limited data, is that the volcanic and volcaniclastic rocks are nonreservoir facies. In this study, based on studies of 140 core samples representing more than 70 different volcaniclastic interbeds from onshore Faroe Islands, it is demonstrated that 18 samples are in the helium (He) porosity range of 20% to 43% and a gas permeability range of 1.0 to 110 md, and among these samples, 7 are of epiclastic and 11 of pyroclastic origins. These 18 samples have been investigated further. Among the seven samples of epiclastic origin, five stem from Glyvursnes-1 well Argir Beds that is a fluvial deposit located close to a fault. These samples are correlated and compared with the wireline logs from Glyvursnes-1. Based on this comparison, it is found that the porosity of the Argir Beds is best estimated from wireline logs using (P-wave seismic velocity), (S-wave seismic velocity), or resistivity logs.
Onshore samples are used as Faroese offshore volcaniclastic intervals are represented by a few confidential samples where the stratigraphic level is uncertain. The onshore samples have been taken from 29 geotechnical (made related to tunnel building, etc.) and 2 scientific (made related to research of the geology) boreholes and represent almost the entire stratigraphic volcaniclastic interval onshore Faroe Islands. In addition, they also cover most of the Faroe Island area geographically. The intervals where the samples are taken represent both in situ and transported material. Three units are ascribed to fluvial, mass flow, and swamp deposit environments, whereas the remaining beds are most likely pyroclastic deposits. The He porosity, gas permeability, and grain density were measured, and in addition, thin sections of all the samples have been produced.
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