Abstract Oil generation (C14+ hydrocarbons) of three Type II kerogen samples isolated from brackish-lacustrine mudstones from Palaeogene strata (Ed3, Es1, Es3) in the southern Bohai Sea was simulated by closed-system gold tube experiments. In addition, a series of complementary analyses (Rock-Eval pyrolysis, total organic carbon, vitrinite reflectance, trace element, X-ray diffraction and flash pyrolysis-gas chromatography–mass spectrometry) were also performed to identify the bulk geochemistry, palaeo-environment and chemical composition of the kerogen. The aim of this study was to achieve a better understanding of the kinetics of oil generation from lacustrine source rocks in the southern Bohai Sea. The results show that the three samples are Type II source rocks deposited in similar palaeo-environments (hot and arid climates, anoxic conditions, and brackish water in shallow to semi-deep lakes) with consequent similarity in the chemical compositions of their kerogens. The organic matter inputs are predominantly composed of lacustrine microalgae, with a relatively small contribution from land plants. The activation energies of oil generation from these samples show a range of 44–52 kcal/mol, with a frequency factor varying from 1.116 × 1014 to 1.274 × 1014 s−1. Due to the similar palaeo-environments and chemical composition, samples in this study exhibit strong consistencies in kinetic parameters. Transformation ratio (TR) evolution curves of oil generation from the three samples, calculated under a linear heating rate (3 K/Ma), exhibit a slight difference, which varies within 4 °C at a given TR. Due to the great similarities of the three kinetic models, an average kinetic model for the Type II brackish-lacustrine source rocks in the southern Bohai Sea was established. This model integrates the characteristics of the three kinetic models and is still dominated by activation energy of 52 kcal/mol. The geological temperature of the oil generation phase for the average model in the southern Bohai Sea is from 92 to 137 °C.

中文翻译：

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渤海南部咸水湖相烃源岩生油动力学

摘要 采用封闭系统金管实验模拟了渤海南部古近系地层（Ed3、Es1、Es3）微咸湖相泥岩中分离出的3个II型干酪根样品的生油（C14+烃）。此外，还进行了一系列补充分析（Rock-Eval 热解、总有机碳、镜质体反射率、微量元素、X 射线衍射和闪蒸热解-气相色谱-质谱）以识别大块地球化学、古环境和干酪根的化学成分。本研究的目的是更好地了解渤海南部湖相烃源岩的生油动力学。结果表明，3个样品为Ⅱ类烃源岩，沉积于相似的古环境（炎热干旱气候、缺氧条件、和半深湖中的咸水），其干酪根的化学成分相似。有机质输入主要由湖相微藻组成，陆生植物的贡献相对较小。这些样品的生油活化能范围为 44-52 kcal/mol，频率因子从 1.116 × 1014 到 1.274 × 1014 s-1。由于相似的古环境和化学成分，本研究中的样品在动力学参数上表现出很强的一致性。在线性加热速率 (3 K/Ma) 下计算的三个样品生油的转化率 (TR) 演化曲线表现出轻微差异，在给定的 TR 下，在 4 °C 内变化。由于三个动力学模型的巨大相似性，建立了渤海南部Ⅱ型微咸湖烃源岩平均动力学模型。该模型综合了三种动力学模型的特点，仍以52 kcal/mol的活化能为主。渤海南部平均模型生油期地质温度为92～137℃。