Submarine Fans in a Developing Extensional Regime--Their Significance in the North Sea Hydrocarbon Province: ABSTRACT

Abstract

The North Sea is a major hydrocarbon province with estimated proven recoverable reserves of approximately 23 billion bbl of oil and 50 tcf of gas. A significant proportion (22%) of these reserves occurs in reservoirs interpreted as submarine fan deposits. These include both oil and gas fields that are among the largest discovered in the province. The North Sea basin provides a classic example of long-term development of an extensional basin. Major tectono-sedimentary sequences can be broadly matched to pre-, syn- and post-rift phases of the Viking and Central grabens. Development of submarine fan systems within the basin can in turn be related to this framework. Submarine fans developed in the Viking graben within the syn-rift tectonic setting during the late Jurassic. The major controlling factor at this time is considered to be internal tectonics of the graben with subordinate influence from sea level changes. Small, coarse, scarp-fed fans formed a sediment apron along the fault-controlled graben margins. Finer-grained, rather better developed fan systems were also formed during this period, reflecting the relative importance of different controlling influences. The post-rift cycle in the North Sea basin is characterized by Late Cretaceous-Tertiary thermal subsidence of the graben as well as the former rift margins. The major influences on fan development in this phase were external tectonics in the source area, and, of equal importance, sea level changes which controlled sediment input to deeper parts of the basin. Late Paleocene and early Eocene fans developed in association with major prograding delta systems. The variability in space and time of submarine fan types in the North Sea highlights the importance of identifying the most appropriate fan model. This is critical to reservoir distribution in field development, as well as in future exploration where predictive models will be required to identify time periods and areas most likely for the development of submarine fans. End_of_Article - Last_Page 538------------