Structural and sedimentary evolution of passive continental margin basins around the Indian Ocean and its effects on hydrocarbon accumulation

The passive continental margin basins around the Indian Ocean have huge exploration potential for oil and gas resources, and they are becoming hotspots for current global oil and gas exploration. With IHS commercial data and previous research results, this study defined the tectonic evolution history of passive continental margin basins around the Indian Ocean, analyzed the influence of tectonic evolution on filling structure and hydrocarbon accumulation in the basins, evaluated the resource potential by Monte Carlo statistical methodology and predicted favorable exploration zones. The results show that the passive continental margin basins around the Indian Ocean have experienced three stages of tectonic evolution, which are pre-rift, syn-rift, and passive continental margin stages. According to the dominant stage of evolution, the passive continental margin basins can be divided into four types: extensional marginal pre-rift, extensional marginal fault depression superimposition, extensional marginal depression and transform marginal fault depression superimposition. The source rocks in the passive continental margin basins are mainly developed from the pre-rift to the early passive continental margin stages, and the main source rocks vary by region. Reservoirs are mainly developed between the pre-rift and late passive continental margin stages; regional seals were mainly developed in the passive continental margin stage. The resource evaluation indicates that the undiscovered oil and gas resources (mean value) in the main passive continental margin basins around the Indian Ocean are 4.49×10⁸ t of oil, 15.86×10¹² m³ of natural gas, and 5.23×10⁸ t of condensate, amounting to 137.69×10⁸ t. The pre-rift Middle-Upper Triassic zone in North Carnarvon Basin, Northwest Shelf of Australia, the Middle Cretaceous-Neogene delta-deep water fan zone in northern Ruvuma Basin and southern Tanzania Basin, East Africa, are the most promising exploration zones.