South Viking Graben Basin

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The South Viking Graben Basin [1]

Introduction

The South Viking Graben basin is located in the northern part of the North Sea. The petroleum basin extends from the United Kingdom to Norway. The South Viking Graben hosts many large oil and gas condensate reservoirs, some within Middle Jurassic and Cenozoic rocks, but most within thick submarine fan sandstone and conglomerate sequences of the Upper Jurassic Brae Formation, also called the Brae Play.[1]

Viking Graben Structure [1]

Geologic History

The South Viking graben is a Middle to Upper Jurassic rift basin. Thermal doming during the Toarcian–Aalenian period, resulted in the deposition of thick Middle Jurassic sequences along a north-trending basin that is now the South Viking Graben.[1]. Deflation of the dome was followed by significant rifting in the SVG, which began in the Callovian period. However, the most active phases of rifting occurred during the Oxfordian to early Volgian when very thick synrift sequences were deposited in the graben.[1] The graben is bounded on the west by the Fladen Ground Spur and on the east by the Utsira High.


Brae Formation; source rock [2]

Source Rock

The Brae Formation is overlapped by the Kimmeridge Clay Formation which is also called the Draupne Formation in Norway. The KCF-Draupne Formation is the major source rock and is the most significant seal for trapped Brae Play hydrocarbons.[1] A large proportion of the hydrocarbon reserves are found in synrift to early postrift, deep-marine clastic sediments of the Brae Formation. These are Thick sequences of Upper Jurassic conglomerates and sandstones meaning they are mainly type 2 oil and gas prone petroleum within the Kimmeridge Clay Formation that were deposited as submarine fans within the graben. Most sediment was derived from the west (i.e. the Fladen Ground Spur) but some important fan systems were fed from the east(i.e. the Utsira High).[3]

Seismic Section Across Brae Play [4]

Seal/Trap

The uppermost Kimmeridge Clay Formation (Draupne Formation), which is the top seal and dominant source rock for Brae Play fields, over laps this eroded slope and limits the western extent of the syn-rift section.[5] At depth, the top of the pre-rift Bathonian Sleipner Formation can be mapped along this fault margin abutting the un-eroded footwall fault; this boundary defines the edge of the thickest Upper Jurassic syn-rift section within the graben.[6] The syn-rift/post-rift transition represents a gradual change from extensive fault activity through localized faulting and passive infill to sporadic faulting during post-rift The top of the pre-rift section becomes progressively shallower to the east, where an approximate minimum limit of the graben can be defined along much of its length by the eastern limit of the KCF/Draupne Formation.[7]

Drilling in North Sea [8]

Production

Production of the North Sea oil peaked in 1999, it was producing 128 million tonnes per year, (6 million barrels) per day[9]. This soon changed drastically as of 2010 this had halved to under 60million tonnes/year, and continued declining further, and between 2015 and 2020 has produced between 40 and 50 million tonnes/year, at around 35% of the 1999 peak[9]. Natural gas production in the North Sea followed a similar trend as oil with its peak at nearly 10 trillion cubic feet in 2001[9]. Norwegian crude oil production as of 2013 is 1.4 million barrels per day[9]. This is a more than 50% decline since the peak in 2001 of 3.2mbpd[9].

Potential Drilling Locations in The South Viking Graben Basin [10]

Future Production

As reported in the World Petroleum Assessment 2000 report , undiscovered oil resources in the North Sea Graben Province as a whole were estimated to range from 4.3 to 25.6 billion barrels of oil (BBO), with a mean estimate of about 13 BBO[10]. Of this province-level total, the Viking Graben was believed to contain 2.3 to 14.8 BBO, with a mean estimate of 7.4 BBO[10]. It was also estimated that the province contains 11.8 to 75.0 trillion cubic feet (TCF) of undiscovered associated and non associated natural gas in fields larger than 12 billion cubic feet (BCF), with a mean estimate of 37.7 TCF[10]. The Viking Graben was estimated to contain the most undiscovered natural gas, with a range of 6.8 to 44.5 TCF undiscovered and a mean value of 22.2 TCF[10].

Uncertainties

In 2016 all nations across the globe were brought together by The Paris Agreement. This agreement was a response to global climate change and holds every nation responsible. Every nation pledged to help keep global temperatures from rising above 2 degrees celsius with a target goal of 1.5 degrees celsius[11]. There was also an agreement among fossil fuel companies to reduce pollution. These major oil companies pledged to reduce emissions by 40% by 2040 compared to 2019 levels[11]. In short this mean there is very little room for new offshore oil rig projects. Companies that continue to sanction these new projects risk creating stranded assets or assets that are no longer able to earn an economic return.


References