Exploration play statistics in the central–northern North Sea region of UK–Norway–Denmark

Abstract

The central–northern North Sea region represents one of the richest and most diverse petroleum basins in the world. This paper presents an analysis of the historical results of exploration in the Central Graben, Outer Moray Firth and Viking Graben, plus surrounding regions, including West of Shetlands. The richness and maturity of the main late Jurassic source rock accounts for almost 100 billion barrels of oil equivalent (boe) recoverable resource in the three North Sea rift arms in reservoirs as old as Devonian and as young as Quaternary. Within a contiguous area of 100 000 km2, 29 different proven part plays (area-confined, deposition-specific stratigraphic intervals or play segments) have been analysed in detail. These range in age from Triassic to Eocene, representing 717 discoveries with a total of 78.1 billion boe recoverable resource present in primary reservoirs. The most prolific plays in terms of total resource found are Mid Jurassic paralic sandstones (in the Viking Graben), Upper Cretaceous chalk (in the Central Graben) and Paleocene turbidite sandstones (in all three rift arms). The average discovery rate (historical chance of geological success) across all the plays is 44% with a relatively low variance. No significant improvement is seen in success rate over the last 50 years, despite increased well density, knowledge and huge advances in geophysical data. Of the discoveries, 404 are commercial fields representing 57% of all discoveries but the rate has decreased to 33% over the last 10 years, as average discovery sizes have decreased significantly. Discovery size is highly variable (10 to more than 600 MMboe) but the historical average is 114 MMboe, a world-class value. Dividing discovery recoverable resource size by footprint area produces a useful measure of reservoir yield, MMboe/km2, and the median value for the different part plays varies from 1.3 MMboe/km2 for an Eocene turbidite to 5.3 MMboe/km2 for a Jurassic turbidite.From a global perspective, the North Sea is not only unusual in the volume of petroleum, diversity of reservoirs and size of discoveries but also for its number of overlapping part plays and for the fact that the largest volume of total resource is found in reservoirs older than the source rock, syn-rift sandstones having been charged from an end-of-rift marine shale.