Jones D M, Head I M, Gray N D, Adams J J, Rowan A K, Aitken C M, Bennett B, Huang H, Brown A, Bowler B F J, Oldenburg T, Erdmann M, Larter S R
School of Civil Engineering and Geosciences, University of Newcastle, Newcastle upon Tyne, NE1 7RU, UK.
Nature. 2008 Jan 10;451(7175):176-80. doi: 10.1038/nature06484. Epub 2007 Dec 12.
Biodegradation of crude oil in subsurface petroleum reservoirs has adversely affected the majority of the world's oil, making recovery and refining of that oil more costly. The prevalent occurrence of biodegradation in shallow subsurface petroleum reservoirs has been attributed to aerobic bacterial hydrocarbon degradation stimulated by surface recharge of oxygen-bearing meteoric waters. This hypothesis is empirically supported by the likelihood of encountering biodegraded oils at higher levels of degradation in reservoirs near the surface. More recent findings, however, suggest that anaerobic degradation processes dominate subsurface sedimentary environments, despite slow reaction kinetics and uncertainty as to the actual degradation pathways occurring in oil reservoirs. Here we use laboratory experiments in microcosms monitoring the hydrocarbon composition of degraded oils and generated gases, together with the carbon isotopic compositions of gas and oil samples taken at wellheads and a Rayleigh isotope fractionation box model, to elucidate the probable mechanisms of hydrocarbon degradation in reservoirs. We find that crude-oil hydrocarbon degradation under methanogenic conditions in the laboratory mimics the characteristic sequential removal of compound classes seen in reservoir-degraded petroleum. The initial preferential removal of n-alkanes generates close to stoichiometric amounts of methane, principally by hydrogenotrophic methanogenesis. Our data imply a common methanogenic biodegradation mechanism in subsurface degraded oil reservoirs, resulting in consistent patterns of hydrocarbon alteration, and the common association of dry gas with severely degraded oils observed worldwide. Energy recovery from oilfields in the form of methane, based on accelerating natural methanogenic biodegradation, may offer a route to economic production of difficult-to-recover energy from oilfields.
地下石油储层中石油的生物降解对世界上大部分石油产生了不利影响，使得这些石油的开采和提炼成本更高。浅层地下石油储层中生物降解现象普遍存在，这归因于含氧大气降水的地表补给刺激了需氧细菌对烃类的降解。在地表附近储层中更容易遇到降解程度更高的生物降解油，这一现象从经验上支持了这一假设。然而，最近的研究结果表明，尽管反应动力学缓慢且油藏中实际发生的降解途径尚不确定，但厌氧降解过程在地下沉积环境中占主导地位。在这里，我们通过在微观世界中进行实验室实验，监测降解油和生成气体的烃类组成，以及井口采集的气体和油样的碳同位素组成，并结合瑞利同位素分馏箱模型，来阐明油藏中烃类降解的可能机制。我们发现，实验室中产甲烷条件下原油的烃类降解模拟了储层降解石油中观察到的化合物类别的特征性顺序去除。正构烷烃最初的优先去除主要通过氢营养型产甲烷作用产生接近化学计量的甲烷。我们的数据表明，地下降解油藏中存在一种常见的产甲烷生物降解机制，导致烃类变化模式一致，以及在全球范围内观察到的干气与严重降解油的常见关联。基于加速自然产甲烷生物降解，以甲烷形式从油田回收能量，可能为从油田经济生产难以开采的能源提供一条途径。
