Geological features, hydrocarbon accumulation and deep water potential of East Indian basins

Based on the tectonic evolution, sedimentary filling and hydrocarbon geological characteristics, this paper establishes a variety of deep water fan models and accumulation patterns and analyzes exploration potential of deep water area in East Indian basins. Due to the breakup of East Gondwana, the passive continental margins of East India are evolved. The basins in these margins experienced four evolution stages, which include intracratonic rift (P1-T), East Gondwana rift (J1-K1), post-rifted thermal subsidence (K2), and passive continental margin (K3-N). There are three obvious unconformities which were formed in the end stages of post-rift thermal subsidence and first and second phases of passive continental margin. Four sets of structural layers were formed, rift stage, and the first, second and third stages of passive continental marginal structural formation. The main deposition of these basins is the sediments evolved during the passive continental margin stage. Two prolific fan systems were developed: superposition fans are complicated in near shore and delta; low fans are located at fault slope-break while turbidity fans are located in front of delta. Four sets of proven source rocks were developed, the Lower Permian, Lower Cretaceous, Upper Cretaceous and Paleogene. There are many middle porosity reservoirs and lowstand permeability reservoirs, such as sandstone and local carbonate in rift period, sandstone of delta and deep water gravity flow in the rifted thermal subsidence and passive continental margin stages. Many seals were developed in the basins, regional seals in drifted stage and local seals in other stages, and the seals thickness change are enormous. There are eight plays in these basins which include Upper Cretaceous sandstone, Paleogene sandstone, Neogene sandstone, etc. The hydrocarbon exploration of deep water area during the passive continental margin stage should focus on Krishna and Cauvery river delta on the plane, and delta sandstone related to fault, lowstand fan located at fault slope-break and near shore fan complex in vicinity of 85°E ridge and south offshore of Cauvery basin vertically.