Method and application for identifying TOC threshold of hydrocarbon-expelling source rocks

Considering the fact that hydrocarbon-expelling source rocks are difficult to identify in oil and gas geology, a method to distinguish hydrocarbon-expelling source rocks was proposed using the conventional TOC and pyrolysis analysis parameters (Rock-Eval). This method is used to identify the TOC threshold, based on hydrocarbon-generation amount parameters I_HC=S₁/w(TOC) and w(A)/w(TOC). Only when TOC content is higher than the threshold, can the source rock be regarded as hydrocarbon-expelling source rock. This method was applied to the source rocks in the Permian Lucaogou Formation in the Junggar and Santanghu basins, the Cretaceous Xiagou Formation in the Ying'er and Qingxi sags in the Jiuquan Basin, and the Upper Triassic Yanchang Formation Chang-7 member in the Ordos Basin. The discriminant results are useful, but it requires source rocks with similar organic matter type and maturity. The parameters represent liquid hydrocarbon amount. Gaseous hydrocarbons are lost easily, and as a result, the method is more effective for oil source rock.