Reservoir quality of the Upper Triassic to Lower Jurassic sediments, NW Barents Shelf: understanding porosity evolution through diagenesis and sedimentology

Abstract

This work presents a study on the interrelationship of burial diagenesis, depositional facies, the origin and distribution of diagenetic clay minerals, and diagenesis in sediment–sill sequences, as well as the thermal history evolution and their effect on reservoir quality distribution of the Upper Triassic to Lower Jurassic sequences on Svalbard. The study unequivocally demonstrates that there is systematic variability of diagenetic signatures as a function of depositional facies. Chlorite coating that inhibits porosity-occluding quartz cement is facies controlled. Sorting, grain size distribution and the clay fraction percentage exert a stronger control on the modes of occurrence of chlorite than on its abundance. This suggests that the best reservoir quality in a deltaic setting can be predicted with knowledge on the distribution of diagenetic signatures, specific depositional facies and sediment composition. Sedimentary basins containing igneous intrusions within sedimentary reservoir units represent an important degree of uncertainty in petroleum exploration. The intrusions obscure the normal burial diagenesis and thermal history of the basin. A new approach is employed in this study, coupling organic with inorganic paleotemperature proxies. The thermal history of a basin can then be accurately constrained. The method works well also in the important task of discriminating between sill-induced diagenesis and burial diagenesis. The findings of this study can be applicable for understanding and predicting reservoir quality distribution of the exploration target potential petroleum reservoir rocks in the subsurface.