The origin of North Sea injectites is still under debate. John Wild, ex ExxonMobil, advocates pre-Tertiary beds as "source rocks".
Large-scale sandstone remobilization is commonly interpreted to occur through the rapid liquefaction or fluidisation of a large body of sediment causing the upward and lateral injection of sand into hydraulic fractures.
Hence, in the North Sea and adjacent regions the search for a source bed tends to stop at the deepest high quality sand in the Tertiary.
Wild & Briedis (2010), however, showed the relationship between mounded, stratigraphically isolated sands and the presence of rafts of chalk above corresponding ‘pock marks’ in the underlying chalk surface, separated by stratigraphically anomalous sand. To create this geometry requires a process to elevate the chalk rafts and fill the intervening space with sand, but the underlying geology is not favourable to invoking the established model.
An alternative model that some injectite systems are a consequence of basin dewatering processes will be proposed. The failure of an over-pressured Mesozoic trap fluidizes and entrains Jurassic or older sand to be redeposited in the overburden. The transport process from initial entrainment through vertical piping and emplacement within a sill progressively winnows or flow-strips finer material from the remobilized sediment forming the massive clean sands associated with injectite complexes.
The applicability of this model more broadly to some other documented complexes will be discussed at the forthcoming Hydrocarbon Habitats seminar on injectites in February. The pre-conditions to formation will be explored, controls on timing and implications for the search for other areas where similar systems may await discovery.
Oslo – February 16 / Stavanger – February 17
Study the program
Register for the seminar here