Structural Characteristics and its Significances on Hydrocarbon Accumulation in the Yunkai Low Uplift,Pearl River Mouth Basin

The Yunkai low uplift with low exploration degree is close to the Baiyun sag,and has hydrocarbon exploration potential in the deepwater area of the Pearl River Mouth Basin.Based on seismic and drilling data,balanced profiles and growth strata,this paper mainly discusses geological structures and formation processes of the Yunkai low uplift,and also analyzes the characteristics of fault system and their influence on hydrocarbon migration and accumulation.The EWtrending basement faults divide the Yunkai low uplift into two parts,i.e.the southern sector and the northern sector.The northern sector is a relatively wide and gentle uplift,while the southern sector is composed of two secondary half-grabens with faulting in the south and overlapping in the north.The Yunkai low uplift experienced three major formation stages,including the rapid uplifting stage during the deposition period of the Eocene Wenchang Formation,the slow uplifting stage during the deposition period of the Late Eocene-Middle Miocene Enping-Hanjiang formations,and the whole burial stage from the Middle Miocene to present.The extensional faults in the Yunkai low uplift and its adjacent areas strike mainly along the NW,NWW and near-EW directions.Also,the strikes of faults present a clockwise rotation from the deep to the shallow strata.According to effects of faults on hydrocarbon accumulation the faults in the Yunkai low uplift and its adjacent areas can be divided into trap-controlled faults and source-controlled faults.The trap-controlled faults control trap development and can effectively seal oil and gas.The source-controlled faults connect directly source rocks and reservoirs,which are highly active during the rifting stage and weakly active since the Miocene.This activity features of the source-controlled faults is beneficial to migration of the early crude oil from the Baiyun sag to the high part of the Yunkai low uplift,but is not good for migration of the late natural gas.In the Yunkai low uplift and its adjacent areas,the traps in the deep Zhuhai and Enping formations that are close to source rocks in the Baiyun sag should be the favorable exploration objectives.