Paper Summary

This study addresses the regional interpretation of 2D seismic surveys across the offshore regions of Western Madagascar (Morondava Basin). It describes the geology, structure and hydrocarbon potential of the offshore area of Morondava basin between west coast of Madagascar to the Davie Ridge. In 2003, TGS acquired, processed and interpreted 2158 line Km of good quality seismic data from offshore Morondava Basin. Once the presence of deep water basin had been confirmed, 10300 line Km of new regional 2D seismic data was acquired in 2005-2006 to further define basin detail. Satellite gravity data interpretation suggests that western coastal basins of Madagascar can be split into two tectonic provinces i.e a western passive margin and an eastern failed rift. The structural, depositional environments and burial histories of these two provinces are quite distinct. Hence, the potential petroleum systems that occur in each province are also different. Morondava Basin is filled with 10 km thick sediments from Mesozoic to recent age with minor volcanics and no evidence of salt. The offshore part of the basin is under-explored but found to be highly prospective. Direct hydrocarbon indicators have also been identified. The burial and hydrocarbon expulsion histories for source rocks of Permo-Triassic and Mid-Jurassic ages were modelled and encouraging results have been seen. The structuration happened before the oil expulsion from these potential source rocks which maximize the chances of finding hydrocarbons in place. Potential good quality reservoirs including predominantly sandstones and limestones have been found present covered by interbedded seals. Hence, all elements of an effective petroleum system were identified during this study.