Identification of kerogen type in source rocks and quantification of its transformation to hydrocarbon products upon thermal maturation are vital for petroleum exploration. These elements can be evaluated using the open pyrolysis of the Rock-Eval. Despite the importance of sulfur-rich marine kerogens (Type II-S) in petroleum systems, the maturation path of only Types I, II and III kerogens were characterized by the Rock-Eval parameters, and a comparison of the maturation path (defined as the HI-Tmax relation) for Type II and II-S is needed.

A comparison of the HI-Tmax relation between Type II and II-S kerogens is presented here by compiling literature data of laboratory thermal maturation for six well-known source rocks. The source rocks include the Toarcian Shale, Kimmeridge, Barnett and Woodford for Type II and the Ghareb and Monterey for Type II-S. When comparing the HI-Tmax relation among the different source rocks, the extent of kerogen transformation cannot be readily evaluated because of variations in the immature properties of kerogens. This variation is overcome by normalizing the HI and scaling the Tmax of mature samples to their immature values. These operations create a new thermal maturation scale defined here as HI_relative-ΔTmax. While the suggested scale minimizes the impact of the heterogeneity within each kerogen type, it generates two distinctive maturation paths for each of them. Although Type II-S kerogens have a lower Tmax at the onset of maturation, the maturation path needed for full transformation is longer than that for Type II kerogens. The two maturation paths are statistically analyzed to generate an empirical law for each of them. Thus, the extent of marine kerogen transformation can be estimated using the empirical law and the suggested HI_relative-ΔTmax thermal maturation scale. The longer maturation path of Type II-S is hypothesized to result from enhanced thermal stabilization of the residual kerogen, driven by the rearrangement of sulfur moieties.

识别烃源岩中的干酪根类型并量化其在热成熟过程中向烃类产品的转化对于石油勘探至关重要。这些元素可以使用 Rock-Eval 的开放热解进行评估。尽管富含硫的海相干酪根（II-S 型）在石油系统中很重要，但只有 I、II 和 III 型干酪根的成熟路径通过 Rock-Eval 参数以及成熟路径的比较（定义为II 型和 II-S 型的 HI-Tmax 关系）是必需的。

本文通过汇编六种著名烃源岩的实验室热成熟文献数据，比较了 II 型和 II-S 型干酪根之间的 HI-Tmax 关系。烃源岩包括属于 II 型的 Toarcian 页岩、Kimmeridge、Barnett 和 Woodford，以及属于 II-S 型的 Ghareb 和 Monterey。在比较不同烃源岩的 HI-Tmax 关系时，由于干酪根不成熟性质的变化，不能轻易评估干酪根转化的程度。通过对 HI 进行归一化并将成熟样本的 Tmax 缩放到其未成熟值，可以克服这种变化。这些操作创建了一个新的热成熟度等级，这里定义为 HI_相对-ΔTmax。虽然建议的尺度最大限度地减少了每种干酪根类型内异质性的影响，但它为每种类型生成了两条不同的成熟路径。尽管 II-S 型干酪根在成熟开始时具有较低的 Tmax，但完全转化所需的成熟路径比 II 型干酪根更长。对这两个成熟路径进行统计分析，为它们中的每一个生成一个经验法则。因此，可以使用经验法则和建议的 HI_相对-ΔTmax 热成熟尺度来估计海洋干酪根转化的程度。推测 II-S 型较长的成熟路径是由于硫部分的重排驱动的残余干酪根的热稳定性增强所致。