Oil and gas accumulation periods and charging path of continental lake basin: A case study of the Chang 9-Chang 10 oil reservoir in the Yanchang formation in the Ordos Basin.

The Chang 9-Chang 10 Formation in the Ordos Basin has been explored intensively in recent years. However, the accumulation timing and migration paths of the oil in the formation reservoir are still unclear. This study uses reservoir geochemistry and software basin modeling to study the hydrocarbon accumulation periods of the oil-bearing sandstones in four wells in different areas of the basin. The results show that the principal oil charging period of the Chang 9-Chang10 formation was from 100 Ma – 130 Ma. The Chang 10 oil reservoirs in the Shanbei area and the Chang 9 oil reservoirs in the Jiyuan and Longdong areas experienced a single oil charging period. However, the Chang 9 oil reservoirs in the central lake area experienced two oil charging periods, from 190 Ma – 210 Ma and from 100 Ma – 130 Ma. The relative abundances of 1,8-/2,7-Dimethylcarbazole and PSNs/Ens carbazole indicate that there are hydrocarbon charging points in the source rocks of the Chang 7 formation in the Jiyuan area, and charging points of Chang 9 source rocks in the Shanbei area. Chang 9 crude oil in the Longdong area shows the characteristics of long distance migration. This study improves understanding of the hydrocarbon accumulation process in the Chang 9-Chang 10 oil reservoirs, which will inform and support future oil and gas exploration in the area. • Oil charging period of the Chang 9 and Chang10 oil formation were determinate by geochemical methods. • The path of petroleum accumulation is traced by two geochemical parameters of crude oil. • There are differences in the time and times of accumulation in different areas in Ordos Basin. • The hydrocarbon accumulation process of the Chang 9-Chang 10 oil formation was established. [ABSTRACT FROM AUTHOR]