Hydrocarbon Accumulation Conditions Of Neogene Formations In Wensu Area,Tarim Basin

Surrounded by Wushi sag,Awati sag and Baicheng sag,Wensu uplift is located in the northwest of Tarim Basin.The Wensu uplift is located at high and the burial of Wensu is shallow.Although above factors are favorable for hydrocarbon to accumulate,few wells were drilled in the past and source rocks of hydrocarbon have been found.In general,the exploration degree of Wensu area is poor.In recent years,the prior understanding of hydrocarbon-free in Wensu uplift has been changed due to the latest exploration discoveries in the area.Based on the research of oil source correlation,seismic interpretation and field investigation,the following conclusions have been obtained:(1)The oils in Wensu area were derived from the Northern Kuqa petroleum system and has obvious terrestrial origin characteristics with low tricyclic terpene content,which is different from marine oil;(2)The Gumubiezi-Wushinan fault zone developed in the northern part of Wensu area.The Gumubiezi fault is the shallow faults,which breaks through the Neogene strata and connects the sand body.Therefore,the faults can be conducted as hydrocarbon migration pathway.(3)Because of the shallow burial depth,regional caprock are not discovered in Wensu area,and the breakthrough pressure of mudstones are low.Therefore,the sealing mechanism of caprock is the physical difference between mudstone and sandstone,and the thickness of the direct caprock above the reservoir.On the other hand,Wensu area has great reservoir contributes to the shallow burial.(4)The hydrocarbon accumulation model in Wensu area is “hydrocarbon accumulation from terrestrial source in other area” model.Oil and gas migrated into the sands of the Jidike Formation in Wensu uplift along the Gumubiezi fault and accumulated at the high point of structures.