Exploration efforts in the Faroese area
|Location||International Geological Congress,oslo 2008|
|Author||Varming, Thomas; Ziska, Heri|
|Holding Date||03 September 2008|
The Faroese Continental Shelf, on the North Atlantic Margin, is severely dominated by volcanic activity that took place in Paleocene-Eocene time, with the most of the area covered by flood basalts. The first four wells drilled an area SE of the Faroe Islands, with no or limited basalt cover targeted stratigraphic or combined Paleocene play types, as this was seen to hold the most promising analogies to the fields of Schiehallion and Foinaven. However the volcanic related activity has been shown to also have a significant influence on the exploration efforts in this non-basalt covered area and adapting the approach from the UK side led to conspicuous results of the amplitude strategy. The Paleocene basin fill was very sandy and subsequent analysis of the encountered lithologies by e.g. heavy mineral analysis suggests an influx of volcanic derived material predating the eruption of the flood basalts on the Faroese platform.
The wells did confirm a working hydrocarbon system indicating a dual Jurassic source rock system and a dual charge history, with the first charge having been biodegraded. Reservoir properties were seen to be comparable with what is found in the UK side, except for the deeper, early Palaeocene sections (T10), where porosity-depth modelling suggest erosion of 1 km compared to time equivalent sections on the UK side, but also intrusive activity has been seen to decrease permeability due to flushing of hot water through the reservoir section.
Extensive mapping in the basalt covered areas show several large sub-basalt structures and the following two sub-basalt wells targeted structural plays. Though successful in terms of drilling performance, questions still remain; e.g. how was the structural development prior to and during volcanism? What kind of stratigraphy is present below the basalt? The basalt section itself does also pose questions like e.g. what is the influence of the potential rapid burial of the basalt on the reservoir parameters, hydrocarbon maturation and migration history? If the sub-aerial basalts, were colder than the surrounding material during the burial stage, then this cold basaltic material could have hindered the hydrocarbon maturation process. Rapid burial has also been known to result in overpressure induced porosity preservation. These issues make a better understanding of the structural evolution of the area and precise dating of the volcanic pile important, as this will constrain the deeper geology and burial history.
With the Rosebank discovery, intra-basalt sediments as potential targets have opened up. There is an increasing likelihood of the intra basalt sediments being volcaniclastic in origin closer to the Faroe Islands and higher in the volcanic section. This has prompted further research into the distribution and reservoir qualities of volcaniclastic rocks onshore Faroe Islands, and also in analogous areas.