Charging of Heavy Oil Fields Surrounding the Southern End of Liaoxi Uplift From Multiple Lacustrine Source Rock Intervals and Generative Kitchens, Bohai Bay Basin, China
The Liaoxi uplift is one of the most petroliferous uplifts in the Bohai Bay basin of China and accounts for more than 63% of the total oil reserves in the Liaodong Bay sub-basin. Almost all oils discovered on the southern end of this uplift are heavy oil (ρ≥0.934g/cm3, 20°C). The heavy oils have shallow burial depth ranging from 880m (2887ft) to 1619m (5312ft) with high density ranging from 0.949 to 1.011 g/cm3 (20°C) and high viscosity ranging from 305.3 to 74462 mPa s (50°C). The heavy oils on this uplift are characterized by sharp lateral oil-water contacts and oil-water inversion. The Liaoxi uplift is sandwiched by two generative kitchens (the Liaoxi sag to the west and the Liaozhong sag to the east) containing multiple mature source rock intervals. Biomarker associations of crude oil and source rock samples were analyzed to investigate the origin of oils on the uplift. Multiple parameter oil-source correlation and hierarchical cluster analysis using 11 selected biomarker parameters allowed the identification of two source-related oil groups. Group 1 oil mainly comes from the third member of Shahejie Formation (Es3), and group 2 oil is interpreted to be a mixture of the first and the third member of Shahejie Formation (Es1, Es3). The homogenization temperatures of fluid inclusions combined with burial-thermal history of individual well were taken to define the hydrocarbon charging time of reservoirs. The Dongying and Guantao reservoirs on this uplift have been charged during 26-22Ma and 5-0Ma, namely, the Late Oligocene and the Early Pliocene Quaternary respectively. The eastward decreases in gammacerane index and ETR[ETR=(C28+C29)/(C28+C29+Ts)], combined with the eastward increases in Ts/Tm and 4-methyl sterane indices, indicate decreasing proportions of Es1-sourced oil and increasing proportions of Es3-sourced oil from west to east. The compositional heterogeneity within fields and between oils from nearby wells in different fields was an effective means of determining the infilling histories of heavy oil fields in cases where multiple source rock intervals and multiple generative kitchens exist. The overall oil migration orientation on the southern end of Liaoxi uplift is generally from west to east. Therefore, the source kitchen for the southern end of Liaoxi uplift is predicted to be the Liaoxi sag. The western slope of the Liaoxi uplift, along the oil charging pathways, is identified as the most promising region for oil exploration.
AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017