Fault reactivation and its effects on the petroleum systems of continental margins

This research project uses high-quality seismic data from the Ottar Basin offshore Norway, Espírito Santo Basin offshore Brazil and Taranaki Basin offshore New Zealand. It investigates the geometry of multiple families of extensional faults and the effect(s) of fault growth on their seal competence. The main aims of this thesis are to investigate: a) the relationship between fault growth and deposition, b) the influence of fault reactivation in the compartmentalisation of strata around salt structures, and c) three distinct study areas as potential zones for enhanced fluid migration and seafloor seepage. Structural controls on three distinct petroleum systems were analysed based on the interpretation of the 3D geometry of seismic horizons, the mapping of fault displacements and throw distributions, and by modelling distinct faults taking into account present and past tectonic stresses. The geometry and kinematics of the Samson Dome, offshore Norway, were investigated to propose a new evolutionary model for this salt structure, and to assess the timing(s) of salt uplift, salt collapse, and reactivation of adjacent faults. Faults were investigated using detailed displacement analyses and 3D models. Fault modelling took into consideration present-day in situ stresses, and also relative paleostresses. The results demonstrate an evolution occurring in three distinct stages, which were thoroughly discussed in this thesis. The Samson Dome is a structure where structural compartmentalisation is more important at depth, with dip-linked reactivated faults being preferential paths for fluid migration at shallow depths. However, their seal competence is enhanced 1100 ms below the sea floor, below which fluids can be trapped. iv The geometry of fault families adjacent to distinct salt structures was assessed in the Espírito Santo Basin, offshore Brazil. Halokinesis is recorded from the Late Aptian to the Early Eocene, for four distinct salt structures, and controlled fault geometry and fluid flow patterns. The results in this thesis indicate a decrease in the seal competence of faults generated close to the studied salt diapirs. A conceptual model proposes that salt structures are linked by corridors of reactivated faults, which comprise preferential fluid-flow pathways from the South to the North-Northwest. The Parihaka 3D survey of the Taranaki Basin was used to investigate the geometry of submarine channel systems formed in association with the reactivation of fault segments during the opening of the Northern Graben, a structure with regional expression offshore New Zealand. Three main drainage types were described around the Parihaka Fault. The results in this thesis suggest that the larger displacements observed led to the formation of two depocentres to the NE of the study area, which were progressively filled by submarine-channel and prograding deltaic units. New results from this thesis include the assessment of the evolution of the Samson Dome, SW Barents Sea, and any controls of fault reactivation on the generation of structural compartments above this structure. This approach resulted in the recognition of the Samson Dome as a smaller seepage structure than previously considered in the literature. In the Espírito Santo Basin, faults reactivated by dip-linkage adjacently to salt diapirs and salt walls are the structures most favourable to record fluid leakage. In the Taranaki Basin, submarine channels may not use relay ramps between reactivated fault segments to reach hanging-wall depocentres. The results in this thesis can also be extrapolated to petroleum systems developed on continental margins worldwide