The marine shale of the Upper Ordovician Wufeng Formation–Lower Silurian Longmaxi Formation is the main source rock and the target of shale gas exploration in the southern Sichuan Basin. The maturity of organic matter (OM) is a vital indicator for source rock evaluation. Due to the lack of vitrinite, the organic matter maturity of the Wufeng–Longmaxi Formations in the southern Sichuan Basin is difficult to accurately evaluate. In total, 33 core samples of the Wufeng–Longmaxi Formations in the southern Sichuan Basin were selected to observe the optical characteristics of solid bitumen and graptolites and measure their random reflectance. Simultaneously, Raman spectroscopic parameters of kerogen were also used to quantitatively analyze the change in maturity. By using Raman spectroscopic parameters as mediators, conversion equations between graptolite random reflectance (GR_or) and equivalent vitrinite reflectance (EqVR_o) were established. Taking the calculation results of EqVR_o as constraints, the tectono-thermal evolution history of Wufeng–Longmaxi Shale in the southern Sichuan Basin is constructed through basin modelling. The results show that the maturity of Wufeng–Longmaxi Shale in the western Changning, Luzhou-western Chongqing, eastern Changning and Weiyuan areas decreases successively. The EqVR_o falls in the ranges of 3.61%~3.91%, 2.92%~3.57%, 3.08%~3.25%, 2.41%~3.12%, and the average EqVR_o is 3.73%, 3.30%, 3.18% and 2.80%, respectively. Thermal evolution in western Changning was controlled by the thermal effect of the Emeishan mantle plume and paleo-burial depth, while the thermal evolution of other areas was mainly controlled by paleo-burial depth. This study provides a reliable parameter for the evaluation of thermal maturity and makes a more accurate calibration of the maturity of the Wufeng–Longmaxi Formations in the southern Sichuan Basin; it also expounds the factors for the differences in thermal evolution in different parts of the area.

Accurately characterizing the utilization state of shale oil reservoirs is important for understanding post-development hydrocarbon occurrence and remaining oil potential. This study investigated mudstone–shale reservoirs from the Chang 6₃ to Chang 7₃ intervals of Well Y1 in the Ordos Basin, with Chang 7₂ representing the principal fractured target. A total of 27 samples were analyzed by Rock-Eval pyrolysis, 24 by saturated-hydrocarbon GC–MS, and 22 by pore-structure characterization. These data were integrated with logging-interpreted hydrocarbon saturation and statistical analyses to evaluate development-associated geochemical responses. Relative to Chang 7₃, Chang 7₂ exhibits a distinct molecular-compositional pattern, characterized by an increase in the mean Pr/nC₁₇ ratio from 0.190 to 0.320 and a decrease in the mean ΣC₂₀₋/ΣC₂₁₊ ratio from 2.477 to 1.416, together with corresponding variations in terpane and sterane assemblages. These characteristics are consistent with selective mobilization and redistribution of hydrocarbon components during development. Pyrolysis parameters, logging-interpreted saturation, and sealed-core comparisons are further consistent with a preferential development response in Chang 7₂ while indicating that a substantial residual oil-bearing basis was retained. Its relatively large macropore and total pore volumes and low D2 value provide favorable pore-scale conditions for the potential mobility of movable oil, whereas the more complex smaller-pore system favors retention of less-mobile hydrocarbons. The results clarify the geochemical response characteristics and pore-scale controls of shale-oil utilization in the Chang 7 Member, providing geochemical constraints on the post-development utilization state and remaining-oil potential. Overall, the combined evidence supports a qualitative interpretation that Chang 7₂ underwent preferential and selective utilization while retaining a substantial residual oil-bearing basis.