Charging of JZ20-A Oil Field on the Northern End of Liaoxi Uplift From Multiple Lacustrine Source Rock Intervals and Generative Kitchens, Bohai Bay Basin, China

Abstract

The Liaoxi uplift is one of the most petroliferous uplifts in the Bohai Bay basin of China. Almost all oils discovered on the northern end of this uplift are light oil (ρ≤0.855g/cm³, 20°C). The production of A1 well in JZ20-A oil field can reach up to 114.2 m³/day(oil) and 290617 m³/day(gas) demonstrated by drill stem test.

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 northern end of this uplift. Multiple parameter oil-source correlation and hierarchical cluster analysis using 8 selected biomarker parameters allowed the identification of three source-related oil groups. Group 1 oil mainly comes from the third member of Shahejie Formation (Es³). Group 2 and group 3 oils are both interpreted to be a mixture of the first and the third member of Shahejie Formation (Es¹, Es³). However, group 2 oil displays higher gammacerane index, low Ts/Tm and low-medium 4-methyl sterane indices(4-MSI), which is most similar with the Es¹ and Es³ source rocks in Liaoxi sag. Group 3 oil displays medium gammacerane index, high Ts/Tm and medium-high 4-MSI, which correlates reasonably with rock extracts from Es³ and Es¹ source rocks in Liaozhong sag.

The thermal maturity of crude oil was evaluated based on analysis of the saturate biomarkers. The analyzed group 3 oil samples display C₂₉ ββ/(ββ + αα) sterane ratios between 0.55 and 0.60. The thermal maturity of group 3 oil is higher than group 1 and group 2 oils, which is consistent with the thermal evolution of Shahejie source rocks in the Liaozhong sag. 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 western and eastern Shahejie reservoirs of JZ20-A oil field has been charged during 4-0Ma and 2-0Ma, namely, the Early Pliocene Neogene and the Early Pleistocene Quaternary respectively.

As most traps on Liaoxi uplift have been drilled, petroleum exploration is moving to the basin slopes. The western slope of the Liaozhong sag, along the preferential petroleum migration pathways, is identified as the most promising region for commercial petroleum accumulations.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018