Abstract Exploration drilling activity, discovery history and creaming curves in the offshore UK are analysed for each UK Continental Shelf (UKCS) basin and each play in the North Sea from the earliest wells drilled in 1965 until the end of 2017. Around 52 Bboe of commercially recoverable oil and gas has been discovered, with around half of this volume found in the first 10 years of exploration. UKCS exploration plays are generally at a mature or super-mature stage and the exploration challenges reflect this. Although technical success rates have steadily increased since the 1990s, pool sizes are becoming smaller. In the last 10 years the average commercial discovery size has been 27 MMboe recoverable, and since 2010 only 10% of discoveries have been bigger than 43 MMboe recoverable. The UK Oil and Gas Authority's 6 Bboe mid-case yet-to-find estimate, as published in 2018, would take 40 years to unlock at the current rate of discovery. Future exploration in the mature UKCS is intertwined with prolonging the life of production infrastructure and is increasingly dependent on the development of new low-cost development concepts. Increased focus on the search for subtle traps, and more reliable pre-drill risk and volume estimation through improved benchmarking and calibration will be key to future exploration success.

Abstract The Buzzard Field remains the largest UK Continental Shelf oil discovery in the last 25 years. The field is located in the Outer Moray Firth of the North Sea and comprises stacked Upper Jurassic turbidite reservoirs of Late Kimmeridgian–Mid Volgian age, encased within Kimmeridge Clay Formation mudstones. The stratigraphic trap is produced by pinchout of the reservoir layers to the north, west and south. Production commenced in January 2007 and the field has subsequently produced 52% over the estimated reserves at commencement of development, surpassing initial performance expectations. Phase I drilling was completed in 2014 with 38 wells drilled from 36 platform slots. Platform drilling recommenced in 2018, followed in 2019 by Phase II drilling from a new northern manifold location. The evolution of the depositional model has been a key aspect of field development. Integration of production surveillance and dynamic data identified shortcomings in the appraisal depositional model. A sedimentological study based on core reinterpretation created an updated depositional model, which was then integrated with seismic and production data. The new depositional model is better able to explain non-uniform water sweep in the field resulting from a more complex sandbody architecture of stacked channels prograding over underlying lobes.

Abstract The Huntington discoveries are an unusual exploration success in that two oil accumulations were tested in separate syn- and post-rift reservoirs with a single well. The discoveries are located 205 km east of Aberdeen in the East Central Graben some 35 km east of Forties Field in 300 ft of water. The 22/14-5 discovery well, drilled in May 2007, encountered a 122 ft oil column in the Paleocene Forties Sandstone and also a 136 ft oil column in the Upper Jurassic Fulmar Sandstone. Both the Forties and the Fulmar contain high-quality oil, 41 and 39° api gravity, respectively. Aggregate flow rates from the two zones exceeded 11 000 boepd on test. Appraisal drilling of the Forties was completed in late 2007 with first oil targeted for 2011. The Fulmar appraisal programme is currently in progress. The Forties reservoir is a high net to gross sandstone containing stacked channel sequences deposited in a submarine fan system. The Fulmar reservoir also contains a thick sand package deposited in a shallow marine shelf setting. Pre-drill mapping based on reprocessed 3D seismic indicated a structural closure on both horizons at the location tested by the well. At both the Forties and Fulmar targets, however, the oil column height exceeded the pre-drill prognosis. This overview will focus on pre-drill perceptions of the prospect relative to actual drilling results.