Tecto-sedimentary evolution of deep-water pre-salt and its effect on hydrocarbon accumulation in Gabon basin
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Abstract:
Based on comprehensive analysis of the present exploration research,the tecto-sedimentary evolution features of the deep-water pre-salt in Gabon basin and its effect on hydrocarbon accumulation were studied to reveal the hydrocarbon accumulation conditions and key factors and to guide the hydrocarbon exploration in the area effectively. The results show that the pre-salt in Gabon basin experienced three tecto-sedimentary evolution stages:the faulting stage(early Cretaceous Neocomian-early Barremian),the faulting-downwarping stage(late Barremian-early Aptian)and early basin transition stage(middle Aptian). Pre-salt lacustrine source rocks developed during the faulting stage. Influenced by the strong basin rifting in the south and the weak basin rifting in the north,the pre-salt lacustrine source rocks in the sub-basin of north Gabon developed only within the rifting belt,while those in the sub-basin of south Gabon distributed widely. The different distribution of source rocks is the main reason that the deep-water pre-salt hydrocarbon discoveries success in the sub-basin of south Gabon but failed in the sub basin of north Gabon. The main pre-salt reservoirs developed during the faultingdownwarping and the early basin transition stage. Due to the inherited effects of outward migration of subsidence center from the rift belt and strong subsidence in the south and weak subsidence in the north,the fluvial deposits widely developed in the inner rift belt and the central uplift belt in the Dentale Formation during the faulting-downwarping stage,while the deltaic front-shallow lacustrine deposits developed in the outer rift belt(deep-water sub-basin in south Gabon).In the ear? ly basin transition stage,the Gamba Formation deposited under a peneplain setting;the fluvial-deltaic plain deposits developed in the inner rift belt and central uplift belt,and the deltaic front-shallow lacustrine deposits developed in the outer rift belt(present deep-water area),both of which are at risk of reservoir properties deteriorated toward deep-water area. The long-distance provenance migration along the N’Komi Fracture Zone might play a positive role in the development of Gam? ba and Dentale reservoirs in the deep-water outer rift belt.
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Huang Xingwen, Yang Huaizhong, Liu Xinying, Sun Pengchao. Tecto-sedimentary evolution of deep-water pre-salt and its effect on hydrocarbon accumulation in Gabon basin[J]. Petroleum Geology and Recovery Efficiency,2015,22(4):14~19