Basin Scale Sand Injection and Extrusion in the Mid/late Miocene of the Northern North Sea - A Result Silica Diagenesis

Until recently, all sand body occurrences in most sedimentary basins were thought to be depositional in origin. Improved seismic imaging and integration with well data have revealed peculiar characteristics that are inconsistent with conventional sand deposition. This paper presents one out of many sandstone occurrences that has been formerly interpreted as depositional but recently proven as a product of post-depositional remobilization and injection of sand. Our study area encompasses the Snorre field area in which the Utsira Fm has recently been interpreted as an extruded body of sand (Lseth et.al 2012). Our independent observations are in agreement with their study and extend the concept of large-scale sand extrusion to include overpressures due to silica diagenesis of Opal A/CT over large parts of the northern North Sea Basin. This is the largest scale remobilization/injection complex found within a single basin and similar complexes occur at deeper stratigraphic levels but at smaller scales. In many cases sand injectites constitute significant oilfields, but in the northernmost North Sea, sand injectites occur at such a density that they may have completely invalidated most intra-Tertiary seals, posing challenges to the next phase of exploration in the northern North Sea.