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Field structure and stratigraphy

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{{OR/19/034}}
The Hutton Field is located in the East Shetland Basin in Quadrant 211 to the west of the North Viking Graben in the UK Northern North Sea (Figure 1). It is approximately 480 km NE of Aberdeen and extends across blocks 211/28 and 211/27; it was discovered by Conoco well 211/28–1a in 1973 (Haig, 1991<ref name="Haig 1991">Haig, B. 1991. The Hutton Field, Blocks 211/28, 211/27, UK North Sea. In: Abbots, I.L. (editor). United Kingdom Oil and Gas Fields 25 Years Commemorative Volume. Geological Society London, Memoirs, 14, 135–143. https://doi.org/10.1144/GSL.MEM.1991.014.01.17 </ref>).

[[Image:OR19034fig1.jpg|thumb|center|500px| '''Figure 1'''    Location map of Hutton oil field. Contains public sector information licensed under the Open Government Licence v3.0. ]]
[[Image:OR19034fig2.jpg|thumb|center|500px| '''Figure 2'''    Simplified map of the Northern North Sea showing the main structures. From: Johnson et al. (1993)<ref name="Johnson 1993">Johnson, H, Richards, P C, Long, D, and Graham, C C. 1993. United Kingdom offshore regional report: the geology of the northern North Sea. London: HMSO for the British Geological Survey.</ref>, Figure 10. ]]

The field measures approximately 9 km north to south and 3 km east to west (Haig, 1991<ref name="Haig 1991"></ref>). A series of three tilted fault blocks (A, B, and C), downthrown to the northwest, make up the main structure (Figure 3).

[[Image:OR19034fig3.jpg|thumb|center|500px| '''Figure 3'''    Map showing the main fault blocks of the Hutton Field. From Haig (1991)<ref name="Haig 1991"></ref> Figure 3 copyright Geol. Soc. ]]

==Field structure and stratigraphy==
The East Shetland Basin formed as a result of Mesozoic rifting, although the precise structural evolution is still debated (Johnson et al., 1993<ref name="Johnson 1993"></ref>). The most likely model consists of two phases of rifting; initially in the late Permian/early Triassic, followed by another phase of rifting in the late Jurassic (Johnson et al., 1993<ref name="Johnson 1993"></ref>). However, sedimentation in the basin continued through the Mesozoic and Cenozoic with up to 11 km of syn and post-rift sediments present (Haig, 1991<ref name="Haig 1991"></ref>; Johnson et al., 1993<ref name="Johnson 1993"></ref>).

The East Shetland Basin comprises of a series of north north east to north-east trending tilted fault blocks that downthrow towards the Viking Graben in the east (Figure 2) (Johnson et al., 1993<ref name="Johnson 1993"></ref>; Zanella & Coward, 2003<ref name="Zanella 2003">Zanella, E, and Coward, M P. 2003. Structural framework. In: Evans, D, Graham, C, Armour, A, and Bathurst, P. (editors). The Millennium Atlas: petroleum geology of the central and northern North Sea. The Geological Society London. 45–59. </ref>). The Hutton field lies in the western of the two main north-trending blocks (Figure 2) (Johnson et al., 1993<ref name="Johnson 1993"></ref>). The faults with the largest offsets in the East Shetland basin have a northerly tend and are downthrown to the east (Johnson et al., 1993<ref name="Johnson 1993"></ref>). However, as shown in Figure 3, the faults in the Hutton field have a NE trend, which is a result of more variable fault block tilt direction (Johnson 1993<ref name="Johnson 1993"></ref>). The majority of the Hutton field sits in quad block 211/28 and a summarised stratigraphy from the Triassic to the present is shown in Figure 4.

The Jurassic age Brent Group is the main reservoir unit in the Hutton field and the Kimmeridge Clay Formation is the source rock (Haig 1991<ref name="Haig 1991"></ref>). The Brent Group conformably overlies the Toarcian to Aalenian age Drake Formation of the Dunlin Group in the East Shetland Basin, however, local unconformities have been observed (Johnson et al., 1993<ref name="Johnson 1993"></ref>; Richards et al., 1993<ref name="Richards 1993">Richards, P C, Lott, G K, Johnson, H, Knox, R W O’B, and Riding, J B. 1993. Jurassic of the Central and Northern North Sea. In: Knox, R W O’B, and Cordey, W G. (editors). Lithostratigraphic Nomenclature of the UK North Sea. British Geological Survey on behalf of the UK Offshore Operators Association. [https://www.bgs.ac.uk/downloads/browse.cfm?sec=1&cat=195/ www.bgs.ac.uk/downloads/browse.cfm?sec=1&cat=195/]</ref>). The Bathonian to Oxfordian Heather Formation of the Humber Group conformably overlies the Brent Group, however local unconformities have been observed (Richards, 1992<ref name="Richards 1992">Richards, P C. 1992. An introduction to the Brent Group: a literature review. In: Morton, A C, Haszeldine, R S, Giles, M R, Brown, S. (editors). Geology of the Brent Group. Geological Society London, Special Publications, 61, 15–26. https://doi.org/10.1144/GSL.SP.1992.061.01.03 </ref>; 1993<ref name="Richards 1993"></ref>).

The Brent Group is comprised of five Formations. These are, in order of oldest to youngest: the Broom Formation; Rannoch Formation, Etive Formation, Ness Formation and Tarbert Formation (Richards et al., 1993<ref name="Richards 1993"></ref>). The group consists of both coastal and marine sediments and was deposited in a regressive-transgressive deltaic system (Richards et al., 1993<ref name="Richards 1993"></ref>). As a result, the Brent Group can be laterally heterogeneous with Formation characteristics varying, particularly on wireline logs. The main stratigraphic units in the Quad Block 211/28 are referred to using a scheme after Bowen (1975)<ref name="Bowen 1975">Bowen, J M. 1975. The Brent Oil-Field. In: Woodland, A W. (editor). Petroleum and the continental shelf of north-west Europe. 353-360. Applied Science Publishers, London.</ref>. The relationship between Bowen (1975)<ref name="Bowen 1975"></ref> and the Brent Group Formations are shown in Table 1.

<center>
{| class="wikitable"

|+ Table 1    List of the main stratigraphic units in Quad Block 211/28 and how they correspond to the Formations of the Brent Group.
|- style="vertical-align:top;"

|
| '''Formation'''
| '''Unit Name (Bowen 1975)'''
|- style="vertical-align:top;"
| rowspan="6" | Brent Group
| The Tarbert Formation
| Upper sand unit

|- style="vertical-align:top;"

| The Ness Formation

| The Delta plain sediments of the Middle Shaly Unit
|- style="vertical-align:top;"
| The Etive Formation
| The Massive Sand Unit
|- style="vertical-align:top;"
| The Etive/Rannoch Formation
| The Massive/Mica Sand Unit
|- style="vertical-align:top;"
| The Rannoch Formation
| The Mica Sand Unit
|- style="vertical-align:top;"
| The Broom Formation

| The Basal Sand Unit

|}

</center>

[[Image:OR19034fig4.jpg|thumb|center|400px| '''Figure 4'''    Summarised Stratigraphy of quad block 211/28 Adapted from material provided to BGS by Oryx. ]]

==211/28 Main reservoir units==
This section contains a brief description of the main reservoir units in Quad Block 211/28 based on Haig (1991)<ref name="Haig 1991"></ref>, Johnson et al. (1993<ref name="Johnson 1993"></ref>; 2005<ref name="Johnson 2005">Johnson, H, Leslie, A B, Wilson, C K, Andrews, I J, and Cooper, R M. 2005. Middle Jurassic, Upper Jurassic and Lower Cretaceous of the UK Central and Northern North Sea. British Geological Survey Research Report, RR/03/001.</ref>) and Richards et al. (1993)<ref name="Richards 1993"></ref>.

===Broom formation===
The Broom Formation typically consists of well sorted medium to coarse-grained sandstone with large scale planar cross-beds and shallow marine burrows in the East Shetland Basin (Richards, 1992<ref name="Richards 1992"></ref>; Johnson et al., 1993<ref name="Johnson 1993"></ref>). The Aalenian age Broom Formation has been interpreted to have deposited in a range of depositional settings ranging from a transgressive tidal-flat to fan-delta setting (Richards et al., 1993<ref name="Richards 1993"></ref>; Johnson et al., 1993<ref name="Johnson 1993"></ref>). In the Hutton field, the formation is described as a laterally continuous series of medium-to coarse-grained sandstones with common mud clasts (Haig, 1991<ref name="Haig 1991"></ref>). The average thickness is 12.2 m (40 feet) (Haig, 1991<ref name="Haig 1991"></ref>).

===Rannoch formation===
The late Aalenian to early Bajocian Rannoch Formation typically consists of an upwards coarsening section of mudstones to fine grained sandstones (Johnson et al., 1993<ref name="Johnson 1993"></ref>; Richards et al., 1993<ref name="Richards 1993"></ref>). The Rannoch Formation is interpreted to have been deposited in a storm-influenced shoreface setting (Johnson et al., 1993<ref name="Johnson 1993"></ref>) and in progressively shallow water on the middle to lower shoreface of a delta front (Haig, 1991<ref name="Haig 1991"></ref>). In the Hutton field, the average thickness of the Rannoch Formation is 13.7 m (45 feet), comprised of fine grained micaceous siltstones and sandstones (Haig, 1991<ref name="Haig 1991"></ref>).

===Etive formation===
The late Aalenian to early Bajocian Etive Formation typically consists either of massive upward coarsening sandstones, or an upward fining sandstone unit (or units) with a sharp base (Johnson et al., 1993<ref name="Johnson 1993"></ref>; Richards et al., 1993<ref name="Richards 1993"></ref>). Deposition of the upward coarsening Etive succession has been interpreted as barrier-bar or beach deposits as a result of progradation (Haig, 1991<ref name="Haig 1991"></ref>; Johnson et al., 1993<ref name="Johnson 1993"></ref>). The upward fining succession has been interpreted to have been deposited in distributary channels (Haig, 1991<ref name="Haig 1991"></ref>; Johnson et al., 1993<ref name="Johnson 1993"></ref>). Sea level changes during deposition affected the thickness and distribution of this unit (Haig 1991<ref name="Haig 1991"></ref>). The average thickness of the Etive Formation in the Hutton field is 18.3 m (60 feet) and consists of medium to coarse grained sandstone in the south and east, with medium grained sandstone in the central and western parts of the field (Haig, 1991<ref name="Haig 1991"></ref>). Towards the north, the sands thin and become increasing micaceous (Haig, 1991<ref name="Haig 1991"></ref>).

===Ness formation===
The Bajocian age Ness Formation is comprised of a heterolithic series of interbedded sandstones, mudstones and coals deposited in a delta top setting (Johnson et al., 1993<ref name="Johnson 1993"></ref>; Richards et al., 1993<ref name="Richards 1993"></ref>; Johnson et al., 2005<ref name="Johnson 2005"></ref>). The Ness Formation represents deposition during progradation and regression of the Brent delta (Johnson et al., 1993<ref name="Johnson 1993">Johnson, H, Leslie, A B, Wilson, C K, Andrews, I J, and Cooper, R M. 2005. Middle Jurassic, Upper Jurassic and Lower Cretaceous of the UK Central and Northern North Sea. British Geological Survey Research Report, RR/03/001.</ref>) and fluvial channels are interpreted to cut through the deltaic sequence (Haig, 1991<ref name="Haig 1991"></ref>). The Formation is informally divided into three units: a lower interbedded unit; a middle mudstone unit; and an upper sandstone unit (Johnson et al., 1993<ref name="Johnson 1993"></ref>; Richards et al., 1993<ref name="Richards 1993"></ref>). The middle mudstone unit represents the temporary abandonment of the delta and flooding of the delta plain (Haig, 1991<ref name="Haig 1991"></ref>). The average thickness of the Ness Formation in the Hutton field is 50.3 m (165 feet) (Haig, 1991<ref name="Haig 1991"></ref>).

===Tarbert formation===
The late Bajocian to Bathonian age Tarbert Formation was deposited as the Brent delta retreated and consists mainly of shallow marine transgressive sandstones; it marks the final abandonment of the Brent delta (Haig, 1991<ref name="Haig 1991"></ref>; Johnson et al., 1993<ref name="Johnson 1993"></ref>; Richards et al., 1993<ref name="Richards 1993"></ref>). The succession is dominated by fine grained sandstones with coarse to very coarse grained sandstones at the base, which may represent a ravinement surface (Johnson et al., 1993<ref name="Johnson 1993"></ref>; Richards et al., 1993<ref name="Richards 1993"></ref>). The average thickness of the Tarbert Formation in the Hutton field is 3 m (10 feet) and consists of poorly sorted medium to coarse grained sandstones (Haig, 1991<ref name="Haig 1991"></ref>).

==References==
{{reflist}}
[[Category:OR/19/034 Oilfield in a box: The Hutton Field dataset | 05]]

OR/19/034 The Hutton Field - Revision history

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