Seismic Characteristics of Large-Scale Sandstone Intrusions in the Paleogene of the South Viking Graben, UK and Norwegian North Sea

Abstract

Post-depositional remobilization and injection of sand can significantly change the geometry of deepwater clastic reservoirs. Features associated with these processes are particularly well developed in the lower Paleogene of the South Viking Graben of the UK and Norwegian North Sea. Seismic scale sandstone intrusions can be grouped in two classes. Class 1 comprises low-angle (20-40 degrees) tabular sandstone intrusions emanating from steep-sided in situ sand bodies within the Balder Formation. The intrusions may be 5-30+m thick and crosscut 120-250+m of compacted stratigraphic section. They terminate at an unconformity at the top of the Frigg interval where they may have extruded onto the palaeo-seafloor. Class 2 comprises conical sandstone intrusions that emanate some 50-300+m upward from distinct apexes located 400-700+m above the nearest depositional sand body. The conical intrusions may have been sourced from underlying sand bodies by clastic blow out pipes. Both types of intrusions seem to adopt their particular geometry independently of (but occasionally exploiting) polygonal faults within the encasing mudstones. Sandstone intrusions may be highly porous and permeable and are thus important both as reservoirs and as plumbing within thick mudstone sequences.

Eocene sandstone intrusions in the Tampen Spur area (Norwegian North Sea Quad 34) imaged by 3D seismic data

“…A particular type of discordant anomalies is seen as V-shaped high amplitude events in vertical seismic sections with subcircular outlines in 3D seismic time slices. They have recently been documented from the Outer Moray Firth (Lonergan, Lee, Johnson, Cartwright, & Jolly 2000;Gras & Cartwright, 2002;Molyneux, Cartwright, & Lonergan, 2002), the South Viking Graben (Løseth, Wensaas, Arntsen, & Hovland 2003;Huuse et al, 2004), the North Viking Graben, and the southern part of the Tampen Spur (Løseth et al, 2003). The V-shaped anomalies are circular to elongate or angular in plan view, forming conical structures in three dimensions (Lonergan et al, 2000;Molyneux et al, 2002;Huuse et al, 2004).…”

“…They have recently been documented from the Outer Moray Firth (Lonergan, Lee, Johnson, Cartwright, & Jolly 2000;Gras & Cartwright, 2002;Molyneux, Cartwright, & Lonergan, 2002), the South Viking Graben (Løseth, Wensaas, Arntsen, & Hovland 2003;Huuse et al, 2004), the North Viking Graben, and the southern part of the Tampen Spur (Løseth et al, 2003). The V-shaped anomalies are circular to elongate or angular in plan view, forming conical structures in three dimensions (Lonergan et al, 2000;Molyneux et al, 2002;Huuse et al, 2004). Borehole calibration of the anomalies in the Outer Moray Firth and in the South Viking Graben have linked the anomalies to tens of metres thick sandstones formed by sand injection from underlying aquifers (Molyneux, 2001;Gras & Cartwright, 2002;Molyneux et al, 2002;Løseth et al, 2003;Huuse et al, 2004).…”

“…The V-shaped anomalies are circular to elongate or angular in plan view, forming conical structures in three dimensions (Lonergan et al, 2000;Molyneux et al, 2002;Huuse et al, 2004). Borehole calibration of the anomalies in the Outer Moray Firth and in the South Viking Graben have linked the anomalies to tens of metres thick sandstones formed by sand injection from underlying aquifers (Molyneux, 2001;Gras & Cartwright, 2002;Molyneux et al, 2002;Løseth et al, 2003;Huuse et al, 2004). Whilst similar features are abundant in the North Viking Graben and Tampen Spur areas, they have so far not been associated with the occurrence of sandstones, and instead interpreted as seismic artefacts (over-migrated point-source diffractions), tuffs injected from the Balder Formation and/or cemented fault planes (Løseth et al, 2003).…”

“…V-shaped tuff intrusions, cemented fault planes and/or seismic artefacts in the Eocene of the North Viking Graben (NVG)/Tampen Spur area (Løseth et al, 2003); 4. Conical sandstone intrusions in the Lower-Middle Eocene of the South Viking Graben (Huuse et al, 2004); 5. V-shaped amplitude anomalies in the Paleogene of the Faeroe-Shetland Basin (FSB: Huuse et al, 2001).…”

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

“…Large-scale injection features have been identified in a number of fields (Dixon et al 1995;Huuse et al 2004;Schwab et al 2014) and outcrop descriptions enable some prediction of what subseismic architectures might be anticipated (Hurst et al 2003;Surlyk et al 2007;Vigorito et al 2008;Scott et al 2009). However, as mentioned above, the anomalous connectivity of some reservoirs that were expected to be stratigraphically compartmentalized could be the result of smaller-scale injection processes able to breach thin shale drapes and connect discrete sandbodies (Hurst & Cartwright 2007).…”