Abstract This contribution presents a new model for the Grampian-age tectonothermal development of the Buchan Block and Barrovian-type regions to its west, in the Grampian Terrane, Scotland. The model has drawn on evidence gathered from field mapping, microstructural analysis, metamorphic petrology and mafic magma geochemistry to propose that emplacement of the Grampian gabbros and regional metamorphic heating associated with production of Barrovian- and Buchan-type units occurred during syn-orogenic (Grampian-age), lithospheric-scale extension. Extension followed lithospheric thickening associated with the initiation of Grampian orogenesis and was followed by renewed lithospheric thickening and termination of the extensional heating. Mantle melting to produce the Grampian gabbros of the Grampian Terrane was achieved by extensional thinning of the lithosphere and decompression melting of the asthenosphere at depths of less than 70 km. Advection of heat from the mantle with emplacement of the Grampian gabbros augmented elevated heat budgets associated with attenuation of isotherms during extension. Deposition of the uppermost Dalradian (the Whitehills and Boyndie Bay Groups and the Macduff Slates) occurred during Grampian-age lithospheric extension. A gently-dipping, mid-crustal detachment focused metamorphic heat sources and accommodated significant lithospheric-scale strain, allowing independent thermal evolution of units in its hanging wall (the Buchan Block) and footwall (Barrovian-type units).

Abstract The NE–SW-trending Grampian Fold Belt has anomalous features that set it apart from other belts in the Caledonides. It consists mainly of polyphase-deformed (D1–D4) Neoproterozoic–early Ordovician rocks (Dalradian Supergroup), deposited in a basin that formed behind a microcontinent detached from Laurentia during Iapetus opening. Detailed cross-strike structural traverses through the D1/D2 Tay Nappe in the SW Highlands show that part of the Ligurian-type basin floor (Highland Border Complex) was obducted on to the Laurentian margin prior to orogenesis. On the top limb of the nappe, δ-porphyroclasts give a top-to-the-SE shear sense for the D1 stretching lineation, whereas D2 microlithons within a zone of non-coaxial strain on the lower limb indicate top-to-the-east. Subduction was initially orthogonal to the Belt but became oblique during D2. Synchroneity at c. 470 Ma of deformation, regional metamorphism, magmatism, termination of sedimentation and formation of the Buchan Block was probably linked to subduction of the spreading ridge. The driving force was NW-directed Andean-type subduction of part of the basin floor, and later of the microcontinental margin. These events caused progressive, diachronous non-coaxial D1–D3 deformation of the hanging wall (Dalradian). Crustal thickening on the SE margin was balanced by thrusting on to the foreland.

Abstract The Buchan Oilfield is a large mature field, now suspended, located in the Moray Firth. The field is situated 153 km NE of Aberdeen in water depths of c. 122 m. The reservoir comprises an overpressured and fractured Upper Devonian–Early Carboniferous fluvio-lacustrine sandstone. Production was via high permeability channel sandstones and permeable faults and fractures. The Buchan Field was brought onto production in May 1981 by BP Petroleum Development Ltd via the Buchan Alpha semi-submersible floating production vessel (FPV). The oil column is c. 2000 ft in height with a matrix stock tank oil initially in place (STOIIP) range of 322–471–668 MMbbl. Production from the ten vertical development wells was driven by pressure depletion (over 5000 psi since first oil) coupled with weak aquifer influx. Production from the Buchan Field ceased on 13 May 2017 after having produced 147.8 MMbbl. The Buchan FPV was subsequently taken off-station during August 2017. A new facility or tie-back redevelopment option will be required to access the remaining resources which are in the range of 20–90 MMbbl depending on the STOIIP, the production mechanism and the potential development plan.

Abstract The Alma Field (formerly Argyll and then Ardmore) is located within Blocks 30/24 and 30/25 on the western margin of the Central Graben. Hamilton drilled the first discovery well 30/24-1 in 1969 and the field, named ‘Argyll’, became the first UK offshore oilfield when production commenced in 1975. Oil was produced from the Devonian Buchan Formation, Permian Rotliegend and Zechstein groups, and Jurassic Fulmar Formation from 1976 until 1992, when the field was abandoned for economic reasons. In 2002, Tuscan Energy and Acorn Oil & Gas redeveloped the field and renamed it as ‘Ardmore’. A further 5 MMbbl were produced until 2005, when the field was again abandoned due to commercial considerations. In 2011, EnQuest was awarded the licence to redevelop the field and renamed it as ‘Alma’. The field came on stream in October 2015 and has produced oil at an average c. 6000 bopd since start-up. Total ultimate recovery was expected to be about 100 MMbbl. As of end 2005, the field had produced 72.6 MMbbl as Argyll and 5 MMbbl as Ardmore. A further 4.3 MMbbl has been produced from the Alma Field to September 2017 (which includes about 0.5 MMbbl from a long-reach well drilled into the Duncan/Galia Field immediately west of Alma). In January 2020 EnQuest announced that the Alma Field would cease production early. The total production from the three phases of field development will be about 85 MMbbl of oil.

Abstract As a result of substantial uplift and erosion during the Cenozoic, much of the Scottish landmass is devoid of Tertiary strata. In eastern Scotland, Tertiary deposits are limited to the Pliocene Buchan Gravels (Flett & Read 1921; Hall, A. M. 1985; McMillan & Merritt 1980) and an ice-rafted block of Miocene clay (Crampton & Carruthers 1914). The only substantial onshore deposits are the lavas and largely pyroclastic sediments of the Hebridean Igneous Province (see Chapter 14 ). These volcanic rocks constitute part of the North Atlantic Tertiary Igneous Province, which developed in response to the rise of the North Atlantic mantle plume beneath the continental crust of East Greenland during the Palaeocene. Regional plume-related uplift and associated rift tectonics in the North Atlantic region ( Fig. 13.1 ) led to the creation of a landmass that encompassed much of present-day Scotland and what is now the largely submerged Orkney-Shetland Platform. Uplift and erosion of this landmass, especially the Orkney-Shetland Platform, resulted in substantial sediment supply to the adjacent North Sea and Faeroe-Shetland basins, where the Tertiary successions attain maximum thicknesses of around 3 and 4km, respectively ( Fig. 13.2 ). The aim of this chapter is to give the reader a general account of the evolution of these sedimentary basins. Because of the long history of hydrocarbon exploration and production in these basins, a very substantial literature has developed, much of it of a highly technical nature. The following selection of references is intended to provide the reader with