3D source-rock modelling in frontier basins: a case study from the Zambezi Delta Depression

Regional modelling is vital for the premliminary analysis of a basin's hydrocarbon potential, especially when working on incomplete datasets. The Zambezi Depression is a frontier basin that was selected to demonstrate how limited, publically available depth data can be used to evaluate source-rock maturity and hydrocarbon expulsion using three-dimensional (3D) basin modelling. A geological framework was built with multiple datasets correlated using a global sequence stratigraphic model. The identification of key events in the geological history of the region and the basin geometries allowed interpretation of intervals of organic enrichment within the basin during the Bajocian, Kimmeridgian and early Aptian. The reults from the pressure and temperature modelling show that thes potential source rock horizons are currently overmature to gas mature in the Zambezi Delta Depression. Using the most likely heat flow scenario, the timing of maturity and expulsion of the potential source rocks are strongly controlled by the geometry of the basin, with ages decreasing towards the SW. Expulsion modelling suggests that the late Cretaceous plays are most likely charged by the early Aptian source rock, with older potential plays charged by the Jurassic source rocks. As the heat-flow model was poorly contrained, warmer and cooler temperature scenarios were also applied to qualitatively compare the impact on maturity, expulsion and accumulation of hydrocarbons in the basin. The modelling results when compared with sparse published data favour the most-likely and warmer scenario.