Reservoir quality of the Stø Formation in the Hoop Fault Complex and Fingerdjupet Sub-basin, SW Barents Sea (The transition between the Stø and Fuglen Formations)

• Main Author: Farazani, Niloufar
• Format: Master Thesis
• Language: English
• Published: 2017
• Subjects: Barents Sea; Hanssen; Loppa; Nordmela; Stø; Tubåen
• Online Access: http://hdl.handle.net/10852/60878; http://urn.nb.no/URN:NBN:no-63500

The Early to Middle Jurassic Stø Formation is the most commercially important sandstones reservoir in the Barents Sea. Stø Formation was deposited in a relatively shallow epicontinental sea in northern Pangea. One of the main objectives of this thesis is to evaluate and compare the reservoir quality of Stø Formation in Hoop Fault complex (well 7324/7-2) and Fingerdjupet Sub-Basin (well 7321/9-1). Six distinct facies describe sedimentological features of Stø Formation in Hoop area and Fingerdjupet Sub-Basin. Stø Formation in Hoop area was deposited in a fluvial system (floodplain, channel base and channel fill), while the sedimentary characteristics of Stø Formation in Fingerdjupet Sub-Basin indicate deposition in upper delta plain environments (upper delta plain deposits and minor distributary channel). Coarse conglomerates in both wells mark the transition from Stø Formation to underlying Fuglen Formation, indicating a transgressive event. The condensed section at the top of Stø Formation comprises of matrix, phosphate nodules and exotic clasts indicating three different sources. Factors such as rapid transgression, minimum net of sedimentation and high productivity are responsible for development of phosphate minerals which later eroded due to the subsequent regression and formed phosphate nodules within the unit. Matrix of the condensed section most likely only represent reworked material derived from Realgrunnen Subgroup (Tubåen, Nordmela, Fruholmen and Stø formations). The coarse-grained pebbly size clasts are only observed within the well 7321/9-1 in Fingurejupet Sub-basin and is absent in the other wells in the basin and also in Hoop Fault area. Loppa High could not be considered as a possible source for these exotic clasts. From the geological study, it is evident that during Jurassic time Loppa High has not been eroded to that depth at which these clasts are present. Accordingly, this hypothesis is discredited. The exact source of these exotic clasts is still ambiguous and requires further work and more investigations in this area. Petrophysical results show that Stø Formation intervals in well 7324/7-2 have the best reservoir quality compared to well 7321/9-1. The best reservoir quality intervals have been found in the fluvial deposits (channel base and channel fill) which were responsible for the deposition of clean sands. Relatively shallow depth of Stø Formation reservoir in Hoop area, despite significant exhumation of the study area, indicates that the formation has not experienced such high degree for diagenesis reactions. Furthermore, despite the fact that Stø Formation is thinly developed (21 m) in Hanssen, the reservoir intervals are hydrocarbon saturated and can be expected to have a high potential for hydrocarbon discoveries in Hoop Fault area.