Controls on the Distribution of Intra and Post-Volcanic Sediments, West of Shetland

Abstract

Hydrocarbon exploration and production has been ongoing in the Faroe-Shetland Basin for the past 40 years. Despite initial optimism, the basin has not achieved the same success as the North Sea, being both technically and geologically challenging in terms of hydrocarbon exploration. In 2002 and 2004, major oil and gas discoveries were made within the Palaeocene and Eocene intra to post-volcanic succession of the Faroe-Shetland Basin. Consisting of terrestrial to marginal marine reservoir sequences, the Rosebank Field consists of siliciclastic sediments, in places separated by basaltic lava flows and volcaniclastics. These sequences contain interbedded sediments sourced from within and out-with the lava field. The interplay between volcanics and siliciclastics sediments, and the resultant effect on reservoir quality and connectivity is key to unlocking intra-volcanic prospectivity. Despite the identification of a major intra-volcanic incised drainage system running parallel to the Rosebank Field, the controls on the emplacement of volcanics and intra-volcanic sediments remains poorly understood. Whilst the volcanic succession on the Corona Ridge has been shown to contain significant accumulations of petroliferous siliciclastic intra-basaltic sediments, other intra-basaltic prospects drilled throughout the Faroe-Shetland Basin have so far proven to be less successful. Regional seismic datasets, petrophysical well logs and biostratigraphical data facilitate a re-examination of the Faroe-Shetland Basin volcanic sequence. This work has found that the distribution of intra-basaltic sediments is primarily controlled by the underlying basement structure. Through examination of the Rosebank Field and nearby exploration wells, the prospectivity and extent of the intra-basaltic play within the Faroe-Shetland Basin is re-evaluated and the fundamental controls on the distribution of volcanic and intra-volcanic sediments within basins detailed. Following eruption of the volcanic succession the Faroe-Shetland Basin subsided non-uniformly exerting a primary control on the distribution of the reservoir quality sandstones in the basin, however, key differences are thought to exist between the rate of subsidence in a volcanic dominated rift basin and a non-volcanic rift basin. Thus we examine the long lasting effects that emplacement of a volcanic succession may have on a basin.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017