Sedimentological control of fluid flow in deep marine turbidite reservoirs: Pierce Field, UK Central North Sea

Abstract

The Pierce Field in the Central UK North Sea is a twin diapir structure that produces from the Paleocene Forties Sandstone Member (Forties Sandstone). Different hydrocarbon–water contacts encountered in the wells around both diapirs have been variously ascribed to a hydrodynamically tilted oil–water contact or else some form of stepped (compartmentalized) contact. Recent reinterpretation of the structure, sedimentology and fluid geochemistry has indicated that the stratigraphic architecture of the reservoir is the prime control on fluid flow over both geological and production time-scales. These depositional architectures deflect the hydrodynamic flow of aquifer water around the field, resulting in a modified-tilted-contact. The same depositional architectures control the flow of fluids under production. The Forties Sandstone was emplaced by turbidity flows influenced by pre-existing seafloor topography that funneled the flows into discrete sediment corridors and into the Pierce area. The rising twin diapirs further influenced the flows by forming: (a) a small salt withdrawal basin between the diapirs that captured sediment; and (b) enough seafloor topography to prevent the bulk of the flows from depositing significant amounts of sand over the crest of the diapirs. Because the bulk of the high permeability sands were deposited in a rim around the diapirs, the aquifer and injected water does not always flow to structurally higher elevations, but follows the geometry of the channelized sands. While faults are present on both South and North Pierce, they are not extensive and do not appear to play a major role in the compartmentalization of the field. From production data, pressure communication can be inferred around North Pierce and around the majority of South Pierce, the main exception being a block bound by large throw faults in the SE of the southern diapir. Geochemical fingerprinting of the hydrocarbons in Pierce shows families of oils that suggest that the northern and southern parts of the reservoir are separate oil compartments, which is a result of the interaction of the filling history and the stratigraphic and structural architecture of the reservoir.

Sedimentological evolution of Sele Formation deep-marine depositional systems of the Central North Sea

“…12). The diapirs protrude through the Sele Formation in this location, and seismic data highlight 'channelized fairways' wrapping around these (Scott et al 2010). Wells logs and core indicate that the channel fairways are characterized by thick, amalgamated sandstone facies (Fig.…”

“…Towards Pierce, T70 channels were funnelled through remnant Lista (T60) palaeotopography and active salt diapirs, resulting in the rechannelization of parts of the T70 lobe system (cf. Scott et al 2010). Later cannibalization of the lobe complex is noticeable towards Quadrant 30, with additional feeder channels identified.…”

“…Fram and Puffin). The east axial fairway (through the eastern Central Graben) consists of both channel and lobe deposits from Everest through to Pierce (Scott et al 2010), which eventually pinch out in Quadrant 30. These sands also extend further south and east into the Norwegian sector.…”

The geological risks of exploring for a CO2 storage reservoir

“…Some Paleogene oilfields in UK water have a complex architecture, formed by turbidite channels, sheet turbidite sandstones and sealing faults . Examples include the Schiehallion Field and Pierce Field (Gainski et al, 2010;Scott et al, 2010). In the Southern North Sea, it has been reported that the Triassic Bunter Sandstone aquifer is more suitable for CO2 storage reservoir than the Permian Rotliegend Sandstone because it has less compartmentalization problems (Holloway et al, 2006).…”

Tertiary deep-marine reservoirs of the North Sea region: an introduction

“…Ongoing movement subsequently deformed these deposits, inducing steep dips, overturned stratigraphy, injection and faulting (e.g. Stewart 2007;Scott et al 2010). In these situations, it is critical to understand the impact on reservoir sand deposition of the deforming seafloor and the subsequent structural deformation (Charles & Ryzhikov 2015).…”