Well log petrophysics and re-interpretation of the exploration target intervals in the southern Walvis basin

A thesis submitted in partial fulfillment of the requirements for the Degree of Master of Science in Petroleum Geology

The Walvis Basin is situated in the eastern Atlantic margin south of the Walvis Ridge offshore Namibia. The Basin is underexplored with only 8 exploration wells drilled in the basin to date. The basin and the entire offshore Namibia at large are extensively covered by 2D and 3D surveys, and despite these comprehensive activities, no commercial discovery of hydrocarbons has been made to date. Some of the reasons the wells failed discovering economic quantities of recoverable hydrocarbons include lack of one or two petroleum system elements and/or processes; with the absence of reservoir or charge being the more common reasons of failure. This project included the analysis of three well log data (Wingat-1, Murombe-1 and 2213/06-1 well) with focus on reservoir unit’s prognoses from seismic profile and comparing them to those of volcanics. Characterization and differentiation of turbidite reservoir units from volcanic intervals involved observing actual petrophysical characteristics and relating those characteristic to seismic reflection amplitudes. Interpretation and preconditioning of well data was performed in Interactive Petrophysics (IP) using standard petrophysical property equations. These properties include neutron-density, resistivity, γ-ray and sonic logs. Thereafter, acoustic impedances were calculated of those volcanic and sandstone unit that have been penetrated by the respective wells at the predicted reservoir depths. The results indicate that volcanic units of the Murombe-1 prospect depicted petrophysical properties similar to those of turbidites sandstones (e.g. the Murombe-1 Baobab sandstones and the Wingat-1 Cenomanian sandstones). In addition, integration of well log with seismic profiles revealed that the volcanics are lava flows with intercalated sediments. The lava flows deposited as a stratified sequence onlappping against an eastern high and herewith their seismic expression is similar to that of a sedimentary succession. Despite the challenges, the basin at large is deemed to be prospective for hydrocarbons with both, mature source rocks and good reservoirs being present.