Carbonate Reservoirs: Recent Large to Giant Carbonate Discoveries Around the World and How They Are Shaping the Carbonate Reservoir Landscape

Carbonates are very heterogeneous when compared to clastic reservoirs in terms of reservoir properties. Yet, some of the biggest discoveries in recent times have come from carbonates alone. In 10 years, between 2006 and 2015, there have been four major discoveries and some of them have the potential of being called giants and supergiant. First, it was Tupi discovery renamed as Lula in the pre-salt which opened a new play in the deep-waters of Santos basin. A few more discoveries followed in the same play but then the next big discovery, even bigger than Lula, came in the year 2011 with the discovery of another Oil pool Libra in the same basin. Till 2006, Santos basin was underexplored as it was considered a frontier basin and all the focus was in the neighbouring Campos basin where there were many pre-salt and post-salt discoveries. Post-2006, with a couple of discoveries, the Lower Cretaceous carbonate reservoirs have come up as a new play in the upper Synrift and post-rift sequences. Looking at the tectonic reconstruction of the plate, 140 million years ago (Early Cretaceous) the conjugate margins of Brazil and Angola were juxtaposed before the opening of south Atlantic. This also tells us that Santos and Campos basin of Brazil was located adjacent to Benguela and Kwanza basin of Angola. It is common wisdom that two basins with similar geological history should have similar hydrocarbon prospects. So, the question was whether the pre-salt success of Brazil would recur in Angola where pre-salt drilling was nearly absent before 2011. The answer came with the discovery of Azul by Maersk, which proved a working petroleum system and later Cameia discovery by Cobalt in 2012. With reserves to the tune of 30 TCF (5.5 billion BOE) housed in a 100 km(2) of carbonate mound, it has a potential to become one of the largest gas discoveries of the world. It is already the biggest in Egypt and the Mediterranean. These discoveries and many more are changing the carbonate reservoir landscape. Once upon a time when talking about Carbonates, the reservoir of Middle East basins used to come to mind, not any more. In the age of globalization, it appears that carbonates and large to giant carbonate discoveries have also globalized.