Discovery of a new Proterozoic paleo-reservoir and its oil source in the Jianchang Sag, Yanliao Faulted-Depression Zone, North China

Abstract

The discovery of many Proterozoic primary oil and gas reservoirs around the world testifies that the Meso-Neoproterozoic petroleum is an energy resources realm worthy of attention. This paper firstly reports the occurrence of hydrocarbon accumulations in the Neoproterozoic Luotuoling Formation in the Jianchang Sag, the Yanliao Faulted-Depression Zone. Petrography observation shows that the lower sandstone member of the Luotuoling Formation contains yellow fluorescent liquid hydrocarbons, while the upper sandstone member is rich in solid bitumen. Further analysis of the biomarkers and isotopic compositions reveals that the upper and lower reservoirs have different oil sources. The bitumen in the lower reservoir is rich in C 19 –C 20 tricyclic terpanes (TTs), 13 α (n-alkyl)-tricyclic terpanes and rearranged hopanes, but lacks gammacerane and steranes and depletes 13 C isotope (−33.4‰ to −30.6‰). This is consistent with the properties of the Hongshuizhuang Formation source rocks. The upper reservoir bitumen has C 23 TT as the major peak among C 19 –C 23 TTs, lacks 13 α (n-alkyl)-tricyclic terpanes, has a low abundance of rearranged hopanes, obvious distribution of gammacerane and steranes, and depletion of the 13 C isotope; essentially the same as the Gaoyuzhuang Formation source rocks. The discovery of oil seepage in the Luotuoling Formation of the Han-1 well is a promising indicator of the Precambrian oil and gas exploration potential of the Jianchang Sag.