09 January 2017
The Central North Sea and the Moray Firth belong to the core areas of hydrocarbon exploration and production on the UK Continental Shelf (UKCS). With a total number of 11800 wells drilled on the UKCS, about 4800 of those are located in these areas alone. One factor explaining such a high number of wells is the wide variety of successful petroleum plays; economic quantities of oil and gas have been proven and are currently produced from reservoirs ranging from Devonian to Pleistocene age.
With so many wells drilled it may sometimes look as if there is nothing left to explore for. This view, however, can also be turned around - with so many wells available a next stage of exploration has been entered where established plays can be revisited using all the new data generated. Let’s look at the Upper Cretaceous Play in the Central North Sea as an example (see map).
The Upper Cretaceous Play has proven successful since the start of exploration in the North Sea- the Ekofisk Field was the first oil discovery in 1969. In UK waters, the play has been pursued mainly in Quadrants 29 and 30. Further north and west, Palaeocene sands overlie the most prolific Ekofisk and Tor Chalks which prevented effective sealing of hydrocarbons except in a few cases where salt diapirs (e.g. Banff, Kyle) provide effective trapping mechanisms. Therefore, the Chalk play has proven more successful in the Norwegian and Danish sectors.
One may argue that exploring the Chalk further north is not worth the effort because there is a valid geological explanation as to why there is limited potential. However, plotting all Drill Stem Tests obtained in Upper Cretaceous rocks on a map shows that there are examples of hydrocarbon finds in the interval north of the supposed play fairway and in the area where Palaeocene sands are found (see map). For instance, wells 22/27a-1 and 22/08a-2 are marked as a small Chalk oil accumulation in a recent analysis published by the Oil and Gas Authority to further stimulate development of small pools.
Maps like these, where information from various sources is combined, should trigger new questions as to why the Chalk is prospective in an area it is believed to be risky. Maps and datasets produced for the Regional Mapping project we are currently working on with the OGA, will enable a new generation of explorationists to use the legacy of the past to build on a more complete subsurface understanding of the North Sea. This will hopefully lead to new discoveries or appraisal of older ones and as such extending the life of this very intriguing petroleum province.
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Lloyd's Register secured two major UKCS projects with the Oil and Gas Authority (OGA) for the UK Continental Shelf (UKCS), for the provision of Regional Exploration Maps and Regional and Field Support Engineering Services to help the OGA independently assess remaining undiscovered resources and improve geotechnical understanding. Read more details of the project win.
This is article three in a series of posts dedicated to our project for the OGA. Read the previous article.
Senior Geologist, LR