南京大学胡文瑄教授团队近日取得一项新成果。经过不懈努力，他们的研究揭示了富¹³C碳酸盐沉积反映了西北乌尔河组上段强产甲烷油的降解。相关论文于2024年8月13日发表于国际顶尖学术期刊《地质学》杂志上。

本研究首次提供了中国西北地区深层地下油藏中Fe(III)介导的产甲烷烃降解的岩石学证据。主要发现如下：(1)被归因于甲烷生成的次生方解石的δ¹³C正值较高(可达+16‰)；(2)高δ¹³C方解石与生物降解烃的共生关系；和(3)方解石中FeO含量高达8wt%，δ⁵⁶Fe比值高达+0.52‰，表明微生物对Fe(III)进行了还原。

研究结果表明，产甲烷烃的降解可以发生在Fe(III)还原环境中。这一过程将烃类转化为CO₂和CH₄，其中CO₂主要以富铁方解石的形式沉淀(碳汇)，而CH₄代表估计约1968Tg，可能在晚三叠世至早侏罗世期间从二叠纪储层逃逸到覆盖层和大气中，这可能是地质历史上全球气候变化中的一个重要的CH₄来源。

据介绍，原油中的微生物甲烷生成是气藏和大气温室气体中CH₄的重要来源。然而，其岩石学记录尚未在自然环境中发现，其可能发生的地质条件仍不清楚。

附：英文原文

Title: ¹³C-enriched carbonate precipitates reveal intense methanogenic oil degradation in the upper Wuerhe Formation, Northwest China

Author: Wendong Liu, Wenxuan Hu, Wenjie Zhang, Xiaolin Wang, Jian Cao, Xianglong Luo, Shichao An, Wenwen Li, Dongming Zhi, Weiqiang Li

Issue&Volume: 2024-08-13

Abstract: Microbial methanogenesis from crude oil is an important source of CH₄ for gas reservoirs and atmospheric greenhouse gases. However, its petrological records have not been found in natural environments, and the geological conditions under which it may occur remain unclear. Here, we provide the first petrological evidence of Fe(III)-mediated methanogenic hydrocarbon degradation in a deep subsurface oil reservoir in Northwest China. The major findings are as follows: (1) highly positive δ¹³C values (up to +16‰) of secondary calcite attributed to methanogenesis; (2) paragenetic relation of high-δ₁₃C calcite to biodegraded hydrocarbon; and (3) remarkably high FeO contents (up to 8 wt%) and heavy δ⁵⁶Fe ratios (up to +0.52‰) in calcite, indicative of microbial Fe(III) reduction. Our study shows that methanogenic hydrocarbon degradation can occur in Fe(III)-reducing environments. This process transformed hydrocarbons into CO₂ and CH₄, where the former mostly precipitated as Fe-rich calcite (the carbon sink), while the latter, representing an estimated 1968 Tg, might have escaped into the overburden and atmosphere from the Permian reservoir during the Late Triassic to Early Jurassic, which may have acted as an important CH₄ source in changing global climate in the geological past.

DOI: 10.1130/G52293.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G52293.1/646597/13C-enriched-carbonate-precipitates-reveal-intenseredirectedFrom=fulltext