Kerogen transformation with thermal maturation is often assessed using open system Rock-Eval pyrolysis. The decrease in hydrogen index (HI, mg HC/g TOC) with increase in Tmax of kerogen can be viewed as a maturation path that describes kerogen transformation. However, natural heterogeneity causes the initial properties (i.e., HI_initial and Tmax_initial) of immature kerogens to vary. This heterogeneity, as well as instrument variability, can lead to distinct maturation paths on the classical HI-Tmax plot, especially when comparing sulfur-lean (Type II) and sulfur-rich (Type II-S) marine kerogens. For these reasons, a scaled maturation path (HI_relative-ΔTmax) was previously formulated based on laboratory maturation data. The HI_relative-ΔTmax maturation path considers the HI_initial and Tmax_initial of each kerogen, shows their relative change with thermal maturation, and reveals two distinct maturation paths for Type II and II-S kerogens.

In this contribution, natural maturation data for Type II and II-S kerogens were compiled and used to test the applicability of the HI_relative-ΔTmax maturation path. The compilation is based on literature data for 16 datasets of natural thermal maturation, comprising eight different source rocks, including the Barnett, New Albany, Monterey, Ghareb (Ein Zeitim), Nordegg, Upper and Lower Eagle Ford, Bakken and Posidonia formations. As long as the immature HI_initial and Tmax_initial can be adequately estimated, the data for most of these source rocks fall within the expected kerogen type on the HI_relative-ΔTmax plot, supporting the usefulness of the scaled maturation paths. Moreover, the scaled HI_relative-ΔTmax maturation paths minimize the impact of the heterogeneity of different kerogens and instrumental variability that can affect the measured Rock-Eval parameters. Hence, the HI_relative-ΔTmax scale is a tool to evaluate the transformation ratio of marine kerogens better.

通常使用开放系统 Rock-Eval 热解来评估热成熟干酪根转化。氢指数（HI，mg HC/g TOC）随着干酪根 Tmax 的增加而降低，可以看作是描述干酪根转化的成熟路径。然而，天然的非均质性导致未成熟干酪根的初始特性（即 HI _initial和 Tmax _initial）发生变化。这种非均质性以及仪器的可变性会导致经典 HI-Tmax 图中不同的成熟路径，尤其是在比较贫硫（II 型）和富硫（II-S 型）海洋干酪根时。由于这些原因，先前基于实验室成熟数据制定了缩放成熟路径（HI_相对-ΔTmax）。HI_亲戚-ΔTmax 成熟路径考虑了每种干酪根的 HI_初始值和 Tmax_初始值，显示了它们随热成熟的相对变化，并揭示了 II 型和 II-S 型干酪根的两种不同的成熟路径。

在此贡献中，编译了 II 型和 II-S 型干酪根的自然成熟数据，并用于测试 HI_相对-ΔTmax 成熟路径的适用性。该汇编基于 16 个自然热成熟数据集的文献数据，包括 8 个不同的烃源岩，包括 Barnett、New Albany、Monterey、Ghareb (Ein Zeitim)、Nordegg、上和下 Eagle Ford、Bakken 和 Posidonia 地层。只要可以充分估计未成熟的 HI_初始值和 Tmax_初始值，大多数这些烃源岩的数据都属于 HI_相对-ΔTmax 图上的预期干酪根类型，支持缩放成熟路径的有用性。此外，缩放的 HI_相对-ΔTmax 成熟路径最大限度地减少了不同干酪根的异质性和仪器可变性的影响，这些影响可能影响测得的 Rock-Eval 参数。因此，HI_相对-ΔTmax 尺度是更好地评价海相干酪根转化率的工具。