Abstract:

Tainan Sag underwent Jratak and Bogda foreland two depression stages.The sag has been a secondary sag on the north dip slop of Turpan-Harmi Basin since Late Permian.The study area underwent three big transformation:(1)the northward transformation from Jratak foreland basin to Bogda foreland basin in Early Permian;(2)uplifting and denudation in the end of Taodonggou Group sedimentation;(3)tectonic inversion,denudation,fault-block dip and disintegration in Late Indosinian-Early Yenshan Period.The above mentioned transformations determined the characteristics of the source rocks in Tainan Sag such as restricted distribution,lower thermal evolution degree,small source potential and predominant with lower maturity of thick crude oil.Therefore,the oil of huge thick oil pools of Lukqin structure belt should be mainly drived from Taibei Sag.Lukqin trap was formed in late Indosinian epoch and the oil pools were formed in the end of Indosinian-Early Yenshan Period.Then the oil was further thickenen,remigrated and destoried,thus causing Lukqin structural belt to be separated into many fault-blook thick oil pools and asphalt-plugged reservoirs.

Key words: Turpan Depression, Tainan Sag, thick oil, reformed basin, low mature crude oil