--> Impact of Source Maturation and Migration Dynamics on the Accumulation and Leakage of Hydrocarbons in the Bredasdorp Basin (Offshore South Africa)

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Impact of Source Maturation and Migration Dynamics on the Accumulation and Leakage of Hydrocarbons in the Bredasdorp Basin (Offshore South Africa)

Abstract

This study investigates the contribution of Upper Jurassic-Cretaceous source rocks to the reservoired hydrocarbons and natural gas leakage using a 3D basin modelling technique. The established 3D model is based on an integration of subsurface datasets (2D seismics, well data and cores) and links the present-day configuration and related tectonic/geodynamic evolution of the basin at a crustal scale (Sonibare et al., 2014) with the local- to regional-scale thermal histories of the Southern African continental margin. The temporal and spatial distribution of critical moment for hyrocarbon generation, migration and accumulation reveals that three periods, coinciding with the main phases of hydrocarbon generation and expulsion, characterise the reservoir filling history of the basin. The first period corresponds to the Early Cretaceous syn-rift rapid subsidence and sedimentation rates. While the second period indicates the significance of post-rift thermal subsidence and the heating effect of the Late Cretaceous-Early Tertiary hotspot-related heat flow pulse, the third period corresponds to the Miocene margin uplift and thermal perturbation. According to our results, the largest amounts of hydrocarbon accumulations and possible seafloor gas leakages are respectively contributed by the syn-rift Late Hauterivian and Mid Hauterivian source rocks. By performing a series of sensitivity tests, we further gain better insights into the timing of migration pathways and dynamics. The coupling of faulting activity, seal bridging mechanisms and facies heterogeneity predicts the best location of discovered accumulations and observed leakage indicators and thus implies our best approximation of the probable controlling factors of migration, accumulation and leakage in the basin.