Oil-source correlation in Qingdong sag of Bohai Bay basin, China

Geochemical experiments on 11cores and 14 crude oil/oil sand samples from Qingdong sag have been performed. The oils range from immature to mature and some of the oils suffered biodegradation. The Es-3(l) member of the Shahejie Formation (group A) deposits under fresh water. The Es-4(u) member (group B) mainly deposits in brackish-saline evaporate environment, generating both immature and mature oils. Results show the nonbiodegraded oils in Es-3(l) reservoirs in the north of the sag (group I) come from mature Es-3(l) member (group A), while those in Es-4(u) reservoirs (group III) come from mature Es-3(l) (group A) and Es-4(u) (group B-1) members in the north; the less biodegraded oils (group II) in the western slope are the admixture of immature and mature oils of Es-4(u) member (group B-2) in the north; immature oils (group V) in the south are from the neighboring low mature Es-4(u) member (group B-3), and the most severely biodegraded oils (group IV) in the southern come from Dongying sag, except oils from well QD-8 that have a contribution from Es-4(u) member (group B-3) from Qingdong sag.