A dynamic biodegradation model suggested by petroleum compositional gradients within reservoir columns from the Liaohe basin, NE China
A dynamic biodegradation model suggested by petroleum compositional gradients within reservoir columns from the Liaohe basin, NE China
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DOI：
10.1016/j.orggeochem.2003.11.003
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发表时间：
2004-01-01
影响因子：
3
通讯作者：
Oldenburg, TBP
中科院分区：
文献类型：
--
作者：
Huang, HP;Larter, SR;Oldenburg, TBP
通过对辽河盆地一套油藏抽提物的分析，研究了生物降解对石油组成的影响和控制作用。在两个生物降解油柱中观察到了系统性变化，表现为石油本体组成、组分浓度和分子指标的明显梯度。在Es3柱（1700 - 1850米）中，生物降解已经去除了大量的正构烷烃和类异戊二烯烷烃。更严重的生物降解发生在较浅的Es1柱（1500 - 1650米），甾烷和藿烷被部分去除。温度对两个柱中的生物降解具有总体控制作用，较低的储层温度导致较高的生物降解程度。然而，在不同地点的Es3柱中观察到的生物降解程度的变化是由水相大小控制的，更高水平的降解与更厚的水相关联。据认为，来自水体的营养物供应对生物降解的程度有重大影响。除了水腿的大小/养分供应，组成梯度也由新鲜油进料的相对混合速率控制。只有当扩散混合速率类似于或低于碳氢化合物去除速率时，生物降解石油柱中的梯度才能保持不变。提出了一个耦合地球化学和地质因素的生物降解模型，为评估降解对石油的影响提供了一个连贯的方法。我们的地球化学研究表明，生物降解主要发生在一个狭窄的区域内或附近的石油柱的底部。稳定的组成梯度后产生的初始诱导期涉及扩散运输的烷烃的油-水接触（OWC）和扩散的生物降解产物，如25-降藿烷和其他代谢物远离反应位点。连续加载的石油与"住宅"生物降解石油通过扩散的混合可以被认为是控制生物降解过程的最重要因素之一。概念模型说明了所有这些过程，并打开了模型驱动的石油性质和“甜点”在油藏中的位置预测的可能性。(C)2003 Elsevier Ltd.保留所有权利。
A suite of petroleum reservoir extracts from the Liaohe basin, NE China, was analyzed to investigate the effects and controls of biodegradation on petroleum composition. Systematic changes, seen as marked gradients in petroleum bulk composition, component concentrations and molecular indicators, have been observed in two biodegraded oil columns. In the Es3 column (1700-1850 m), biodegradation has removed substantial amounts of normal and isoprenoid alkanes. More severe biodegradation occurs in the shallower Es1 column (1500-1650 m), with both steranes and hopanes being partially removed. Temperature has an overall control on biodegradation in the two columns, a lower reservoir temperature leading to a higher degree of biodegradation. However, observed variation in the degree of biodegradation in the Es3 column at different sites is controlled by water leg size, with a higher level of degradation being associated with a thicker water leg. The supply of nutrients from the water leg is thought to have a significant impact upon the degree of biodegradation. In addition to water leg size/nutrient supply, the compositional gradients also are controlled by the relative rate of mixing of fresh oil charge. Gradients can only be conserved in biodegraded petroleum columns if the rate of diffusive mixing is similar to or lower than the rate at which the hydrocarbons are removed. A biodegradation model is proposed that couples geochemical and geological factors to provide a coherent approach for assessing the impact of degradation on petroleum. Our geochemical study indicates that biodegradation occurs mainly within a narrow region at or near the base of the oil column. The stable compositional gradients are produced after an initial induction period involving diffusive transport of alkanes to the oil-water contact (OWC) and diffusion of biodegradation products such as 25-norhopanes and other metabolites away from the reaction site. The mixing of continuously-charged oil with `residential' biodegraded oil by diffusion may be considered as one of the most important factors controlling the biodegradation process. The conceptual model illustrates all of these processes and opens the possibility of model-driven prediction of oil properties and 'sweetspot' location in reservoirs. (C) 2003 Elsevier Ltd. All rights reserved.