Cao Zhanyuan, Liang Mingliang, Zhang Xilong, Su Long
Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences, Lanzhou, 730000, China.
Key Laboratory of Petroleum Resources Exploration and Evaluation, Lanzhou, 730000, Gansu Province, China.
Sci Rep. 2024 Sep 27;14(1):22360. doi: 10.1038/s41598-024-73382-z.
This study investigates the hydrocarbon generation potential of Jurassic source rocks under ultradeep conditions by utilizing semiclosed system hydrous pyrolysis experiments to simulate the geological processes at play. This study examines four distinct lithologies (shale, mudstone, carbonaceous mudstone, and coal) and three kerogen types (I, II, and III) across a temperature range of 250-650 °C and fluid pressures ranging from 34 to 100 MPa. The results indicate a bimodal distribution in total oil yields, with peak generation observed at approximately 350 °C and 600 °C. This pattern suggests a complex relationship between temperature, pressure, kerogen type, and hydrocarbon output. Notably, while I-Shale and II-Mudstone display higher hydrocarbon efficiency, III-type rocks exhibit superior oil and gas production rates because of their higher total organic carbon content. Research revealed that the oil expulsion rate exceeds 99% at temperatures above 500 °C, with the expelled oil predominantly comprising nonhydrocarbons and asphaltenes. Our findings suggest that Jurassic hydrocarbon source rocks maintain oil and gas potential under ultradeep conditions (high-over maturity stages at depths exceeding 6000 m). Under sustained fluid overpressure exceeding 70 MPa, the hydrocarbon generation peaks of various kerogen types in source rocks are markedly delayed. This phenomenon enables the source rocks to retain the potential for liquid hydrocarbon generation even during the stages of overmaturity. The results significantly enhance the theoretical framework of hydrocarbon generation under ultradeep conditions, thereby providing a crucial extension to the existing thermal boundary theory of hydrocarbon formation. These insights are crucial for the oil and gas industry, directing future exploration efforts towards ultradeep reservoirs and informing the development of new technologies to exploit these resources. This research not only enhances the understanding of subsurface hydrocarbon systems but also has implications for strategies aimed at maximizing resource recovery and managing the environmental impact of deep Earth exploration.
本研究通过利用半封闭系统含水热解实验模拟实际地质过程，来研究超深层条件下侏罗系烃源岩的生烃潜力。本研究考察了四种不同岩性（页岩、泥岩、碳质泥岩和煤）以及三种干酪根类型（I型、II型和III型），温度范围为250 - 650℃，流体压力范围为34至100MPa。结果表明，总产油量呈双峰分布，在约350℃和600℃时出现生烃高峰。这种模式表明温度、压力、干酪根类型和烃产量之间存在复杂关系。值得注意的是，虽然I型页岩和II型泥岩显示出较高的烃生成效率，但III型岩石因其较高的总有机碳含量而具有更高的油气产率。研究发现，温度高于500℃时，排油率超过99%，排出的油主要由非烃类和沥青质组成。我们的研究结果表明，侏罗系烃源岩在超深层条件下（深度超过6000米的高过成熟阶段）仍保持油气潜力。在持续流体超压超过70MPa的情况下，源岩中各种干酪根类型的生烃高峰明显延迟。这种现象使源岩即使在过成熟阶段仍保留液态烃生成的潜力。这些结果显著增强了超深层条件下的生烃理论框架，从而为现有的烃形成热边界理论提供了重要扩展。这些见解对油气行业至关重要，指导未来对超深层油藏的勘探工作，并为开发利用这些资源的新技术提供依据。这项研究不仅增进了对地下烃系统的理解，还对旨在最大限度提高资源采收率和管理深部地球勘探环境影响的策略具有重要意义。
