Abstract:

Based on seismic, logging and geochemical data, the Easy-R o model was adopted to invert the paleogeothermal
history of the Qingdong sag, and to calculate the paleogeothermal gradient. Based on data of artificial wells and thickness
of the hydrocarbon source rocks, the maturity and distribution of the upper 4th member and the lower 3th member of the
Shahejie Formation were discussed and the potential hydrocarbon generation zone was predicted. The results showed that the
paleogeothermal gradient of the Qingdong Sag was 3.8℃/100m; the maturity of source rocks in the upper 4th member of the
Shahejie Formation was higher than that of the lower 3th member of the Shahejie Formation which are in the stages of matureover
mature and mature-low mature, respectively. In a vertical plane, the hydrocarbon generation domain and maturity of source
rocks of the upper 4th member of the Shahejie Formation was larger than those of the lower 3th member of the Shahejie Formation,
while in a plane, the main hydrocarbon zone are located on the main part of the Qingdong Sag (North fault-step, north sub-sag,
middle sub-sag and south sub-sag) and the Qingnan subsag. The western slope of the Qingdong Sag did not reach the hydrocarbon generating threshold.

Key words: Qingdong sag, source rocks, vitrinite reflectance, geothermal gradient, thermal history