Geological Evolution and Hydrocarbon Plays of Madagascar (with Occasional Reference to Australia)

Jeans, Pete
PJ Exploration Ltd, Bourton on the Water, United Kingdom.

The stratigraphic succession and tectonic history of Madagascar are directly related to the progressive break-up of Gondwana, and the subsequent dismemberment of Eastern Gondwana, and three discrete phases of rifting can be discerned: Uppermost Carboniferous to Upper Permian (Karroo Supergroup); Lower Jurassic; and Turonian.

The hydrocarbon habitat of Madagascar is dominated by its two large heavy oil/tar accumulations known since the early 1900s: the Bemolanga Tar Sands, and the Tsimiroro Heavv Oil Field. Reported field data imply that migration of oil into these traps occurred prior to Turonian magmatism and uplift. Numerous other surface oil impregnations have been recorded, especially along the faulted southeastern margin of the Morondava Basin and over the plunge of the Cap St. Andre nose.

A total of over 70 exploration wells have been drilled since 1950 in Madagascar, most of which recorded some, albeit weak, indications of oil and gas throughout the stratigraphic column. However, only two wells recovered significant, though non-commercial, flows of hydrocarbons to surface: West Manambolo-1 (1988) flowed 17 mmscfgpd plus some condensate from thin Lower Cretaceous turbiditic sandstones, and Manandaza-l (1991) recovered 10 barrels of waxy 41 degree API oil from tight, fractured Lower Sakamena sandstones.

Source rocks are present at several stratigraphic levels though none have yet been demonstrated to be of regional extent, with the possible exception of the oil-prone source rocks proven in the Middle Sakamena of the Manandaza Basin - Karroo Corridor, and the early Jurassic syn-rift Beronono Shale of the southern Majunga Basin. Oil and source rock extract analysis suggests that the Tsimiroro/Bemolanga heavy oils, and the Manandaza light oil are derived from the Middle Sakamena shale. Though rich in outcrop, the Beronono shales have not yet been encountered in the subsurface, although imminent exploration drilling in the deep water Majunga Basin, and licensing of the deep water Manandaza Basin, are predicated upon the presence of these source rocks.

Where apparent to the author, parallels between the hydrocarbon geology of Madagascar and Australia will be drawn.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012