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Global Distribution of Original Petroleum Reserves in Deep Reservoirs

Abstract

Exploration for deep petroleum accumulations, which refer to those at burial depths of no less than 15,000 ft (about 4,572 m), deserves more specialized attention. Excluding US onshore Lower 48 States, 87 major sedimentary basins are identified to host deep petroleum accumulations throughout the world. North America contains the largest quantities of the discovered deep petroleum with original proved plus probable (2P) reserves of 28,060 MMBOE. The three most prolific basins for deep petroleum are the Gulf of Mexico, Arabian and East Venezuela Basins, and they contain 48.6% of the total deep original 2P petroleum reserves in the world. 63.3% of the total are reservoired in clastic rocks, 35.0% in carbonates and 1.7% in crystalline rocks. In terms of trap type, 95.7% of the total are entrapped in structural and combination traps. Passive margin and foreland basins contain the bulk of the deep original 2P petroleum reserves in the world, with the former accounting for 47.7% of the total and the latter 46.4%. Salt-bearing deep sedimentary basins are significantly more prospective for deep petroleum than basins without salt, which is attributed to the relative cooling effect for the subsalt sediments induced by salt and associated salt structures. The effect is responsible for retardation of source rock maturation in the deep parts of petroliferous basins. The petroliferous basins in the Tethyan realm contain 85.0% of the world total deep original 2P petroleum reserves, which is similar to the distribution of petroleum in shallow-intermediate reservoirs. 92.3% of the total occur in reservoirs with burial depths of 15,000 ft (about 4,572 m) to 20,000 ft (about 6,096 m). Stratigraphically, the deep petroleum reserves are largely confined to five reservoir intervals: Neogene (hosting 22.3% of the total), Upper Paleozoic (22.2%), Cretaceous (18.4%), Paleogene (12.8%) and Jurassic (12.8%). The concentration of deep petroleum reserves in the Jurassic-Tertiary reservoir rocks may be a direct result of widespread availability of more effective source rocks in these stratigraphic intervals. There exists an objective similarity in the stratigraphic distribution of generated and trapped original reserves for both deep and shallow-intermediate petroleum. Therefore, we suggest that the deep petroleum exploration should target the play fairways where substantial shallow-intermediate petroleum reserves have already been discovered.