Recently, a lot of achievements has been made in Member 1-L of Shahejie Formation (Es1L) tight oil exploration in Raoyang Sag, showing great exploration potential. However, due to the lack of research on the organic geochemistry, hydrocarbon generation and expulsion characteristics of source rocks, the evaluation and development of tight oil are restricted. Based on more than 130 mudstone samples from the Es1L in the Raoyang Sag and the data of organic carbon (TOC), vitrinite reflectance (Ro), saturated hydrocarbon gas chromatography, pyrolysis and kerogen organic isotope, the study systemically evaluate the geological and geochemistry characteristics of the Es1L mudstone and its hydrocarbon generation and expulsion characteristics to evaluate the resource potential of tight oil. The results show that there are two sedimentary centers in the middle and east of the Raoyang Sag, and the sedimentary environment is reductive continental salt lake. Source rocks are widely distributed and the maximum thickness of source rocks is over 100m. The thickness of source rocks decreases from troughs to the western slope. The abundance of organic matter is high and most of the source rocks belong to good source rocks (Fig.2). The measured TOC values of the Es1L source rocks ranged from 0.3% to 6.02% with an average value of 1.40 %. Organic matter types are mainly type Ⅱ kerogen(Fig.3), indicating the organic matter is in the early mature and mature stage. The measured Ro values of Es1L source rocks ranged from 0.44% to 1.20%, and the peak was between 0.5%-0.9%(Fig.4), showing that it has great hydrocarbon generation potential. The threshold and peak of hydrocarbon expulsion for mudstone source rocks are at 0.56% Ro and 0.70% Ro, respectively (Fig.5). The greatest intensity of hydrocarbon expulsion for mudstone source rocks is greater than 100× 104 t/km2. The quantities of hydrocarbon generation and expulsion from mudstone source rocks are 12.83 × 108 t and 4.89 × 108 t, respectively, and the comprehensive hydrocarbon expulsion efficiency is 38.11%. The tight oil is developed in sandstone tight reservoirs. The total tight oil resource is 1.27 × 108t, which has great exploration potential.

Raoyang Sag, Bohai Bay Basin