3D seismic analysis of salt tectonics and depositional systems in the Kwanza Basin (offshore Angola): from basin dynamics to geohazard analysis

Abstract

This thesis uses the combination of 2D and 3D seismic data and seismic attributes to investigate and understand the interaction between the salt tectonics and depositional systems in the Kwanza Basin (offshore Angola-block 21). In addition they are used to understand the mechanisms for sediment fairways, the geometries of the stratigraphic units, and slope failure in B21. Firstly, this thesis is focused on the understanding of the basin configuration, depositional systems and synsedimentary deformational processes since Aptian time (Lower Cretaceous). Secondly, to understand the sediments fairways and the facies distribution in space and time. Lastly, it undertakes an integrated analysis that spans from the basin dynamics to geohazard evaluation. A detailed analysis of 2D and 3D structural maps and seismic attributes have enabled an increased understanding of the impact of the salt tectonics on the depositional systems and the mechanism that triggered mass transport deposits. The studies made in B21 showed that the progressive subsidence of the depocenters and the rise of the salt diapirs due to the salt tectonic events, change the geometries of the stratigraphic units, by thinning the units close to the diapirs and thickening them further away from the diapirs. Moreover, the salt tectonics have a strong impact on the sediment fairways because the salt walls deviate the sediments transported through the channels and enforced them to pass through the mini basins created by salt walls. Importantly, the analysis made on variance attribute showed the existence of two large mass transport deposits in the north and in the south part of B21. Additionally, some traces of upward fluids migration called pockmarks were identified throughout. These events show that the B21 has overpressure zones. Hence, these events can pose implications for drilling operations, stability issues for offshore installations, and field development.