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The Zhang 22 well was drilled in the Ordos Basin, penetrating the Chang 7 Member of the Yanchang Formation, which has more than 80 m cumulative black organic-rich shale of oil window maturity. Utilizing seventy-six samples collected every 1 meter from the well the effects of stratigraphic fractionation and petroleum expulsion within five intervals of the Chang 7 shale were qualitatively and quantitatively documented. The organic-rich intervals-1,-2 and-5, having an average TOC content of 6.79 wt% and pyrolyzable hydrocarbon potential S2 of 9.40 mg/g rock, are defined as "generative units" in the Chang 7 shale system, compared to the "in-source reservoirs" or "sweet spots"-the third and fourth intervals-which contain lower average TOC content of 4.19 wt% and an average S2 value of 7.17 mg/g rock, but the highest amount of free oil (av. total oil of 7.35 mg/g rock). Geochemical and molecular compositions display distinctive differences between samples from these source and reservoir groupings. For example, bitumens from the generative units proportionally possess lower saturated hydrocarbons (56% to 66%) than those from the in-source reservoirs (up to 81%). The proportions of aromatic and polar compounds in the generative units are accordingly higher than in their counterpart. The individual molecular weight distribution of sample extracts displays more light-end moieties being enriched in the generative units. By applying the compositional mass balance calculation, the overall and compound-specific expulsion efficiencies in the in-source reservoirs are abnormally negative compared to the positive values in the generative 2 intervals. This finding in conjunction with the effects of the preferential retention of aliphatic hydrocarbons and the differential expulsion of light molecular weight compounds in the in-source reservoirs together indicate a short-distance intrasource migration of generated petroleum into the sweet spot intervals (intervals-3 and-4) from the overlying units (intervals-1 and-2) and the underlying interval-5. Furthermore, when quantifying the total amount of retained petroleum in the shale system, an amended assessment has been introduced to overcome the systematic misestimations if only unextracted S1 values were considered. Thus, the oil crossover effect, Tmax shift phenomenon and the HI being shifted to higher values after extraction all account for identifying the intervals-3 and-4 as the in-source reservoirs. In this study, we have not only identified a set of promising in-source target for shale oil exploration and production, but we also presented the chemical and molecular composition for these shale oils. We have additionally speculated for the intrasource migration model, and further discussed the different expulsion efficiencies in the shale system upon the compositional mass balance calculation, and the stratigraphic fractionation on differentiating the chemical compositions during migration. The improved oil quality by fractionation, the extra storage potential derived from microfos...

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