The importance of sill thickness and timing of sill emplacement on hydrocarbon maturation

Abstract

Magmatic sills in sedimentary basins can be relatively easy to interpret on seismic data because they stand out due to their high acoustic impedance in relation to the sediments. However, determining sill thickness is challenging unless the sills are drilled. This study explores the influence of magmatic sill thickness and timing of emplacement on temperature and hydrocarbon maturation in sedimentary basins. A 230 km long 2D transect through the Vøring Basin in the Norwegian Sea is modeled and sill thickness and timing of emplacement are the only parameters varied. The transect holds ∼40 sills that intruded at ∼55 Ma with a temperature of 1000 °C in a shale-dominated sequence. Several sill thickness scenarios were tested, but results for 0 m (no sills), 50 m and 100 m are presented here. Furthermore, the 50 m and 100 m thick sills were tested to intrude as upper and lower clusters separated by time intervals of 10 and 100 kyr. To study the effect of sills below seismic resolution, 1D modeling of well 7316/5-1 in the Barents Sea was performed. This well contains 9 sills distributed in an upper and a lower group. Vitrinite reflectance data from the well allow studying the effect of thin sills on temperature and maturation. The results show a clear connection between sill thickness and the temperature and maturation history of the basin. The largest impact of sill intrusions is at 3–5 km depth. For sills intruding as clusters, there are regionally marginal differences related to timing of emplacement but local differences especially in the close vicinity of the sills occur. This work indicates that the interpretation of sill thickness has a substantial influence on the prediction of the maturation and petroleum potential of sedimentary basins holding magmatic intrusions. Sills below seismic resolution contribute to increased maturation in its surroundings. Differences in the timing of sill emplacement within 10–100 kyr show local effects that may influence the petroleum potential of source rocks between two sill complexes.