oa Modern CSEM and Impact on African Exploration-from Girassol to Fieldwide Estimates of Saturation

Shell entered the Orange Basin block PEL 0039 early 2014 based on the identification of the large Barremian Cullinan carbonate prospect, located on top of an SDR outboard high, which was initially mapped on a wide 2D seismic grid. The prospect was interpreted to be overlain by the Aptian source rock (Kudu shale) and a thick sequence of deepwater shales. The Cullinan structure is a 4-way closure formed by both the underlying volcanic SDR sequence, and post-depositional erosion. Initial interpretation of the prospect on 2D showed distinctive carbonate features, which were comparable to some known global analogues.

The Cullinan evaluation journey spans over 10 years. In late 2014 Shell acquired a 2520 km2 3D seismic over the prospect. Subsequent detailed 3D evaluation invalidated some of the initial 2D observations, and it was concluded that the prospect was a high-risk, high reward opportunity, with presence of effective reservoir as the main risk. In 2017, Shell started focusing on Cretaceous clastic plays and the JV decided to acquire new 3D surveys over these plays in 2018 and 2019 and matured several clastic prospects for drilling. The Cullinan prospect stayed in the background, with some detailed reprocessing, geological studies and analogue studies being carried out. This work failed to further reduce the risk on the prospect, and it was concluded that only an exploration well could de-risk it further. The drilling success of the clastic plays in PEL 0039, and the start of an extended drilling campaign late 2022, offered the opportunity to test the Cullinan prospect efficiently and it was finally drilled in June/July 2023. The well failed to find commercial HC volumes, however provided encouraging results indicating a working petroleum system in the previously untested northern area of the license. Further evaluation of the Cullinan-1X results is currently ongoing.