Static Reservoir Modeling of the Valanginian Depositional Sequence of Gamtoos Basin, Offshore South Africa
Gamtoos Basin is an echelon sub-basin under the Outeniqua offshore Basin, South coast of South Africa. Gamtoos Basin is a complex rift type basin comprises of onshore and offshore components, consists of relatively simple half grabens bounded by major fault to the northeast. The basin fill comprises of organic-rich shale of considerable thickness and are considered to be responsible for generation of hydrocarbon in this area. The present study is mainly focused on formation evaluation of the reservoir heterogeneity of the Valanginian depositional sequence. The prime objective of this work is to generate a 3D static reservoir model for better understanding of the spatial distribution of discrete and continuous reservoir properties (porosity, permeability and water saturation) of the depositional sequence. The methodology adopted in this work includes an integration of 2D-volume seismic data and well log data from six selected wells. These data were used to construct 3D-model of lithofacies, porosity, permeability and water saturation through petrophysical calculation, upscaling, Sequential Indicator Simulation (SIS) and Sequential Gaussian Simulation (SGS) algorithms respectively. The statistical analysis model revealed the effective porosity, permeability and water saturation concentration ranges between 8% to 19%, 0.1mD (< 1.0 mD) to 1.0 mD and 30% to 45% respectively across the study area from the north to the south in the basin. The result shows that the Valanginian depositional sequence is a potential hydrocarbon bearing reservoir revealed by the water saturation cut-off value, with good to poor porosity and poor permeability from the north to the southern part of the basin. Keywords: 3D-Reservoir Modeling; Reservoir Heterogeneity; Porosity; Permeability; Water- saturation; Hydrocarbon; Petrophysics; Valanginian.