Petroleum Accumulation in Passive Margin Basins

Zhang, Guangya; Liang, Yingbo

Passive margin basin is the main type of petroliferous basins, the present-day passive margin basins are mainly distributed in the peripheries of Atlantic, India, Arctic Oceans and Southeast periphery of Mediterranean Sea. In recent years, most of giant oil and gas discoveries and reserves are originated from several leading basins including greater Campos Basin in Brazil offshore, Rovuma Basin in East Africa offshore, Cote d'Ivoire Basin in West Africa offshore, Levantine Basin in Mediterranean Sea etc. These giant discoveries are mainly located in deepwater and ultra-deepwater, oil fields of which are mostly distributed in Atlantic margin, and gas fields in the India margin. In addition, over 54 percent of hydrocarbon reserves of which is in the presalt play.

Hydrocarbon accumulations of passive margin basins are affected by basin evolution and sedimentary filling. The following will mainly focus on South Atlantic margin basins According to stress differences, the passive continental margin basins of south Atlantic peripheries can be divided into two categories of extensional basin and extensional basin with strong shear stress. According to the characteristics of sedimentary filling, the former can be subdivided into salt basin, no salt basin and delta-type basin, which divided South Atlantic margins into three segments from south to north, which are the southern, the middle and northern sections. The south is mainly consisted of the extensional basins without salt, the middle section is salt basin, the north is basins with little salts and strong shear stress.

Hydrocarbon accumulation patterns present obvious distinction among these basins. The middle salt basins generally form two giant post-salt and pre-salt plays consisted of turbidite and carbonate reservoirs respectively, whose accumulation pattern is controlled obviously by salt deformation. The south usually forms gas field due to the lack of salt. In the north, passive basins usually have thick drift sequence and thin rift sequence, both source rock and reservoir are originated from drift sequence, oil and gas are mainly accumulated in deepwater and ultra-deepwater turbidite lithologic trap. Among these basin types, the middle salt basins and delta-type basin have proved abound hydrocarbon reserves. The southern and northern basins have also drilled to meet several giant discoveries in recent years, which have become the important exploration region in the world.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013