@article{LIU2026, 
author = {Xingzhou LIU and Yongcheng CHEN and Chang CHEN and Yang LI and Xiaolong ZHOU and Zijing LI and Gaofei WANG and Wenwen LEI},
title = {Geological characteristics, enrichment model, and exploration practices of shale oil in the fourth member of the Shahejie Formation, Western Sag of the Liaohe Depression, Bohai Bay Basin},
year = {2026},
journal = {Oil & Gas Geology},
volume = {47},
number = {3},
pages = {875-891},
keywords = {hydrocarbon generation characteristics, reservoir development characteristics, enrichment model, sweet spot evaluation, shale oil, Western Sag, Bohai Bay Basin},
url = {https://www.sciopen.com/article/10.11743/ogg20260311},
doi = {10.11743/ogg20260311},
abstract = {The fourth member of the Shahejie Formation (Es4) in the Western Sag of the Liaohe Depression, Bohai Bay Basin, hosts multiple types of shale oil. With favorable geological conditions and promising exploration prospects, it represents the primary target for shale oil exploration in the Liaohe oil and gas province. To clarify the enrichment characteristics and exploration potential of shale oil in this province, systematic studies were conducted on the hydrocarbon generation and storage processes and the oil-bearing properties of the Es4 member based on drilling, well logging, seismic surveys, and various analytical test datasets. A shale oil enrichment model was established; sweet spots were identified and evaluated; and exploration practices in this area were systematically analyzed. As indicated by the research results, the total organic carbon content (TOC) ranges from 0.20% to 11.86%, the hydrocarbon generation potential (S1+S2) has a peak value of 100 mg/g and an average value of 40 mg/g, organic matter is dominated by Type Ⅰ-Ⅱ1, vitrinite reflectance (Ro) ranges from 0.38% to 0.79%, and maximum pyrolysis temperature (Tmax) is mainly at 440 ~ 450 ℃. Overall, the organic matter is characterized by favorable types, high abundance, and is in the medium-to-high maturity stage. The Es4 is mainly composed of clay minerals, quartz, K-feldspar, plagioclase, ammonium feldspar, calcite, dolomite group minerals and pyrite, with well-developed laminae displaying diverse stacking patterns. The main lithofacies include laminated calcareous-dolomitic shale, laminated felsic shale, and laminated mixed shale. Dissolution pores, intercrystalline pores, organic pores, dissolution fractures, and bedding fractures are well developed throughout the member. The overall porosity is relatively low, and the pore system is primarily composed of micro- to nano-scale pores; mesopores (pore diameter of 10 ~ 100 nm) are dominant, accompanied by a small proportion of macropores. Oil and gas are mainly stored in bedding fractures, intercrystalline pores, microfractures, organic pores, intergranular pores, and calcite cleavage fractures. Sedimentation provides the essential material basis for shale oil enrichment. Moderate total organic carbon content (TOC of 2% ~ 4%) and medium-to-high thermal maturity are prerequisites for enrichment, resulting in a shale oil enrichment model for this area. Based on a multi-parameter integrated reservoir evaluation method, Type Ⅰ reservoirs in sublayers c11 and c12 are dominated by calcareous mud shale, while those in sublayers c8-c10 are dominated by dolomitic (calcareous) mud shale and argillaceous dolomite, with brittleness increasing proportionately with dolomite content. Combined with pre-stack seismic inversion, the planar distribution of sweet spots was predicted. This study systematically summarizes the geological characteristics and enrichment model of shale oil in the Es4 member of the Western Sag and effectively identifies sweet spots, providing a reliable geological basis for shale oil exploration program design in this province.}
}