Determination of faults parameters controlling the Petroleum Systems Elements in the northern North Sea by using 3D basin Modelling

Abstract

3D basin modelling of the northern North Sea region covering 4886km2 is performed in order to understand the petroleum system elements within the area. The approach used to obtain the most likely model is to analyze and determine quantitatively the faults properties controlling the hydrocarbons accumulations in the Gullfaks, Visund, Kvitebjørn, and Huldra fields. This approach is made by varying the faults properties defined by shale gauge ratio until the reserves in place in the four fields are reached. Therefore, the oil accumulation in the Gullfaks field is controlled by three main faults. The first fault bounding the field is a non- sealing fault with SGR= 10%. The second located further south in field is a sealing fault and the third located in the North is a non-sealing fault. In the Visund field, the NE-SW trending fault is a non sealing fault. In the Kvitebjørn field, another NE-SW trending fault surrounding the field is defined by SGR= 30%. In the Huldra field, the gas in place is controlled by two N-S trending faults. The first fault is located in the west of the field and is defined by SGR= 40% and the other located in the east is a non-sealing fault. Throughout this study, it is observed that the faults properties vary from field to field and the gas accumulation is more sensitive to SGR than the oil accumulation. They have an important effect especially on the migration paths of the hydrocarbon but not on the other petroleum system elements.

After analyzing the fault properties, the petroleum system elements are analyzed from the obtained most likely model. Therefore, the burial history analysis shows that the uplift in late Jurassic-early Cretaceous is more pronounced in the footwall of the graben whereas in the axis of graben, this period is characterized by non-deposition of sediments. This uplift phase is also evident in the paleo-temperature distribution within the area. The source rocks, in the Draupne and Heather Fms, started to be mature at 135Ma and 155Ma and became more mature as the burial depth increased. The hydrocarbons generation occurred also very early, at the same time of the maturation with 120Mtons for Draupne Fm and 18Mtons for Heather Fm.

The properties of the reservoir rocks vary largely due to differences in compaction. For the Brent Group, the porosity varies from 5 to 34% and the permeability from 0.01mD to 10000mD. For the Statfjord Fm, the porosity varies from 3 to 25% and permeability from 0.01mD to 1000mD.