Electro sequence analysis and sequence stratigraphy of wells EM1, E-M3 and E-AB1 within the central Bredasdorp Basin, South Africa
The study area for this thesis focuses on the central northern part of the Bredasdorp Basin of southern offshore South Africa, where the depositional environments of wells E-M1, E-M3 and E-AB1 were inferred through electro sequence analysis and sequence stratigraphy analysis of the corresponding seismic line (E82-005). For that, the Petroleum Agency of South Africa (PASA) allowed access to the digital data which were loaded onto softwares such as PETREL and Kingdom SMT for interpretational purposes. The lithologies and sedimentary environments were inferred based on the shape of the gamma ray logs and reported core descriptions. The sequence stratigraphy of the basin comprises three main tectonic phases: Synrift phase, Transitional phase and Drift phase. Syn-rift phase, which began in the Middle Jurassic during a period of regional tectonism, consists of interbedded red claystones and discrete pebbly sandstone beds deposited in a non-marine setting. The syn-rift 1 succession is truncated by the regional Horizon ‘C’ (1At1 unconformity). The transitional phase was influenced by tectonic events, eustatic sea-level changes and thermal subsidence and characterized by repeated episodes of progradation and aggradation between 121Ma to 103Ma, from the top of the Horizon ‘C’ (1At1 unconformity) to the base of the 14At1 unconformity. Finally the drift phase was driven by thermal subsidence and marked by the Middle Albian14At1 unconformity which is associated with deep water submarine fan sandstones. During the Turonian (15At1 unconformity), highstand led to the deposition of thin organic-rich shales. In the thesis, it is concluded that the depositional environment is shallow marine, ranging from prograding marine shelf, a transgressive marine shelf and a prograding shelf edge delta environment.