The Rosebank Field, NE Atlantic: Volcanic characterisation of an inter‐lava hydrocarbon discovery

Abstract

The Rosebank Field is located in the Faroe-Shetland Basin and hosts hydrocarbons within siliciclastic sediments interlayered with volcanic packages of the Late Paleocene to Early Eocene aged Flett Formation. Within this study the volcanic sequences are investigated based on an integrated appraisal of available drill cuttings, sidewall cores, core and wireline logs including image log and geochemical logs from eight wells supported by 3D seismic data. The Rosebank lower (RLV), middle (RMV) and upper (RUV) volcanic sequences are inter-layered with Colsay Member (C1-C4) fluvial to shallow marine siliciclastic intervals. A comprehensive cross-field borehole based lithofacies interpretation is presented characterising simple, compound and ponded effusive lava flow facies along with pillow lavas, invasive lava flows, volcaniclastic sediments and complex lava-sediment interactions.Geochemical analyses of core, sidewall core, and hand-picked cuttings spanning the field reveal separate high-titanium (RHT) and relatively lower-titanium (RLT) basaltic magma suites. These compositions can be identified and correlated across much of the field utilising geochemical logging data which, in combination with the geochemical analyses, reveals a two-part stratigraphic sub-division of each of the RLV, RMV and RUV. Geochemical logging data is also used to define a volcanic proxy (Fe/10+Ti) which utilises the elevated iron (Fe) and titanium (Ti) within all effusive and volcaniclastic basaltic lithologies to differentiate siliciclastic from volcaniclastic sediments where other logging parameters overlap. By comparing the borehole analyses with seismic data, a localised eruptive vent is interpreted within the north of the field. Finally, a cross-field volcanic model is presented and compared with relevant global field analogues, providing a constrained spatial framework for sub-surface modelling of inter-volcanic sequences.

Volcanic facies architecture of early bimodal volcanism of the NW Deccan Traps: Volcanic reservoirs of the Raageshwari Deep Gas Field, Barmer Basin, India

“…Detailed logging of the volcanic facies was undertaken by compiling graphic facies logs for each core followed by the development of a volcanic facies and intra‐facies scheme (e.g. Jerram, 2002; Millett et al., 2021; Single & Jerram, 2004; Watton et al., 2013) which encompassed all the encountered facies. Industry standard petrophysical RCA (routine core analysis) data was available for this study including Klinkenberg corrected gas permeability, helium porosity and grain density which were screened to ensure only analyses made on robust cores were included.…”

“…Jerram et al, 2019;Millett et al, 2015;Planke, 1994). The lithofacies scheme presented in Figure 14 incorporates the main facies and intra-facies elements identified based on the core-log integration, modified after Millett et al (2021) to incorporate the more evolved and pyroclastic lithofacies of the RDG.…”

The interactions of volcanism and clastic sedimentation in rift basins: Insights from the Palaeogene‐Neogene Shaleitian uplift and surrounding sub‐basins, Bohai Bay Basin, China

“…The rapid fall of erupted volcanic breccia and tuff results in a highly heterogeneous deposit that shows in seismic data as chaotic reflections with poor‐continuity (e.g. Millett et al, 2021; Planke et al, 2017; Table 4c). The stratigraphic occurrence of pyroclastic facies underlying lava‐flow facies suggests they mark the initiation of a volcanic eruption and may potentially be altered by subsequent lava flows (Table 4c).…”

“…Flowing lava will naturally seek out existing topographical lows, which in these settings are often the hanging walls of rift bounding normal faults (e.g. Millett et al, 2021; Schofield & Jolley, 2013; Zanchetta et al, 2004). D’Elia and Martí (2013), working in the Lower and Upper members of the Sañicó Formation of the Jurassic Neuquén basin, Argentina, suggested that thick lava units deposited in the immediate hanging wall of the basin's boundary faults reduced topography within rift depocentres.…”

“…Volcanic processes supply a large volume of volcanic‐denued sediment, ranging from gravel to clay grade, into syn‐ and post‐eruptive clastic depositional systems (e.g. D’Elia & Martí, 2013; Millett et al, 2021; Planke et al, 2000; Schofield & Jolley, 2013). In this study petrographic analysis indicates that igneous rock debris comprises between 46% and 97% (average of 68%) of all the rock fragments in preserved sediments of the main syn‐rift (Eocene) and late syn‐rift (Oligocene) stages (Figure 6).…”