Abstract: Thick dolomitic/analcite mudstones and shales at the stage of lower maturity(R_o:0.3% -0.8%) are deve-loped in saline and restricted bay environment of the 4^th member of Shahejie Formation(Es⁴), Leijia area in West Depression, Liaohe Basin.Based on the analysis of casting thin sections and SEM images, it is found that structural fractures and constricted fissures are highly developed in shale reservoirs, intergranular pores in clastic minerals are also developed, and dissolved nanopores in dolomites and analcites are present without organic nanopores.What's more, the distribution of hydrocarbon source rocks with high abundance of organic matters(TOC>4%) is determined with the quantitative evaluation of well logging using TOC data(ΔlgR method).It reveals that quality hydrocarbon source rocks in Dujiatai and Gaosheng reservoirs are distributed mainly in Leijia and Chenjia sags.In addition, the experimental results of hydrocarbon expulsion efficiency show that at the current maturity stage, the expulsion efficiency of hydrocarbon source rocks ranges from 12% and 17%, with the hydrocarbon production totaling 10 to 35 mg/g.As for the high abundance and large cumulative thickness of hydrocarbon source rocks, it is estimated that the tight-shale oil reserves can reach 1.37×10⁸ t in Es⁴, Leijia area.According to the integrated analysis of source-reservoir assemblages, the Dujiatai reservoir in Es⁴, Leijia area is favorable for tight-shale oil exploration, while the Gaosheng reservoir is favorable for shale oil exploration.In a word, the studied area is favorable for integrated exploration of tight-shale oil since different types of hydrocarbon source rocks have certain hydrocarbon-generating and reserving potentials.

Key words: source-reservoir assemblage, medium-low mature source rock, hydrocarbon expulsion efficiency, tight-shale oil, Es⁴, Leijia area, West Depression of Liaohe Basin