| dc.description.abstract | Although the Triassic-Jurassic sandstones of the Realgrunnen Subgroup form the primary reservoir units in the Barents Sea, there are relatively few published studies targeting these formations in the central and northern parts of the southwestern Barents Sea. This thesis documents reservoir properties in the sandstones of the Wisting Central III (7324/8-3) drill core, thereby aiming to academically contribute to the understanding of the geological development in this area. Additionally, lateral variations in the vicinity of the Wisting field are studied, particularly with respect to the Gemini North (7325/4-1) wellbore. Wisting Central III is the 6th and most recent appraisal well of the Wisting discovery, located in the Hoop Fault Complex in the southwestern Barents Sea. In Wisting Central III, the Realgrunnen Subgroup comprises Triassic-Jurassic deposits of the Fruholmen, Nordmela and Stø formations. The aim of this thesis is to describe reservoir properties and gain insights on factors influencing the reservoir quality of these formations, such as climate, provenance, depositional environment and diagenesis. This is achieved by employing sedimentological, petrographical, and petrophysical methods with use of the Wisting Central III drill core. Based on observations from the drill core, facies associations of the Realgrunnen Subgroup are described and interpreted to record a range of shallow marine to coastal depositional environments. The Fruholmen Formation is interpreted to represent the overall progradation of a delta system, with a low-order transgression at the top. The Nordmela Formation is interpreted to record the migration of a tidal dune complex, while the Stø Formation is interpreted to comprise upper shoreface deposits. Petrographic results show that there are stark changes across the Triassic-Jurassic transition. This is strongly reflected in XRD results, which show that the Triassic Fruholmen Formation has a high mineralogical diversity as opposed to the mineralogically mature Jurassic Nordmela and Stø formations. Point counting yields similar results. The Fruholmen Formation is significantly more immature than the Jurassic Stø and Nordmela Formations, with moderate proportions of lithic rock fragments and feldspars. These constituents are virtually absent in the Jurassic formations. Textural maturity is also found to increase across the boundary. Differences across the T-J boundary are concluded to relate to a change in provenance, from the primarily Uralian-sourced Fruholmen Formation to the primarily Caledonian/Fennoscandian-sourced Nordmela and Stø formations. A change in provenance area is likely accompanied by forebulge uplift in the area, creating a regime of reduced accommodation, promoting extensive reworking. These events changed the initial sandstone composition towards higher maturity. The first-generation Uralian sourced Fruholmen Formation deposits are heavily affected by diagenetic reactions such as kaolinitization and chloritization. Sandstones of the highly reworked Caledonian/Fennoscandian sourced Stø and Nordmela Formations are almost entirely absent of such diagenetic reactions, having exclusively evidence of quartz cementation. Results from this study demonstrate the fundamental importance of sediment provenance, accommodation, depositional environment, and burial diagenesis in determining reservoir quality seen today. | eng |