Complexity of Sandstone Bodies in the Northern North Sea and Their Implications on Hydrocarbon Prospectivity

Abstract

Millions of barrels of hydrocarbon are produced daily from sandstone reservoir intervals in deep-water settings from petroliferous basins such as the North Sea, Niger Delta etc. These sandstones are commonly believed to have been deposited by gravity-flow processes inform of large, deep-water channel-lobe systems and low-stand fans; however, detailed investigation reveals unusual geometries that are difficult to unravel by normal depositional processes. It is believed that, the sandstones have been subject to sub-surface remobilization and injection that significantly modified their geometries. Early Tertiary sandstones in the South Viking Graben, Outer Moray Firth and East Shetland Platform in the North Sea (Alba, Balder, Chestnut, Kraken, Mariner, Volund etc) show evidence of such modifications from seismic, wireline logs and core data (Lonergan et al. 2000). Products of these post-depositional processes are recognized from the Cretaceous to Pliocene intervals in the study area. They include remobilized sands, sand injectites and sand extrudites embedded in mud-rich successions. Evidences show the Cenozoic Northern North Sea underwent basin-scale remobilization and injection in a scale that has not been previous documented in the North Sea or any other basin in the world. We observe an exclusive stratigraphic overlay of these unconventional sandstones and if the sands are connected; could have impacted hydrocarbon prospectivity in the basin. Therefore, there is need to incorporate them into the current Cenozoic stratigraphic framework and geologic models at the early stages of exploration; to ascertain to what degree they may have influenced fluid flow in the basin. We propose a multiple phase emplacement through the interval.