Simple kinetic models of petroleum formation. Part II: oil-gas cracking
Simple kinetic models of petroleum formation. Part II: oil-gas cracking
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DOI：
10.1016/0264-8172(95)98382-f
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发表时间：
1995
影响因子：
4.2
通讯作者：
A. Pepper;T. Dodd
中科院分区：
文献类型：
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作者：
A. Pepper;T. Dodd
描述油气裂解的动力学方案是预测烃源岩排出的石油的质量、组成和相的模型的必要组成部分；另一个应用是预测储层石油将被分解成天然气的温度范围。通过对16种不同烃源岩样品的封闭系统实验室热解校准，该简单的一级动力学模型描述了原油（C6+分子范围）向天然气（c1 - 5分子范围）的大量转化。不同样品的裂解率差别很大，这取决于生成的油的饱和与芳烃的比例。样品的初始氢指数（h0）作为其生成的油的饱和与芳香比的间接度量，与单个样品中油裂解的优化速率常数密切相关。因此，通过简单的常规地球化学筛选测量，就可以预测裂解速率。hl0高的烃源岩往往生成富饱和油，其平均活化能高，键能分布致密，在较高但较窄的温度范围内裂解速度相对较慢。低h0烃源岩生成富芳烃油，平均活化能低，键能分布广，在较低但较宽的温度范围内裂解较快。这是低h0烃源岩“III型”气相倾向观测的重要因素。预测的裂缝窗口（限定在初始原油降解的10-90%，参考升温速率2℃Ma - 1）在非常优质的烃源岩（h0 bb0 600 mg g C - 1）中为155 ~ 205℃，在非常劣质的烃源岩（h0 050 mg g C - 1）中为115 ~ 205℃。升温速率的一个数量级增加（减少）使这些温度窗升高（降低）约15°C。地质地下的外推受不优于7°C的置信度限制。对储层环境的推断需要谨慎，因为干酪根是一种重要的潜在催化剂和氢供体，可以使烃源岩的裂解效率达到100%。此外，排油过程中的分馏导致排油的饱和富集，最终形成储层。因此，储层内的裂缝至少应该与优质烃源岩中的裂缝一样缓慢，并且需要焦炭或焦沥青地层来保持氢平衡。基于英国北海中部深层油藏的历史案例证实了这些预测，表明在至少174°C甚至195°C的温度下，没有明显的储层开裂证据。以往的研究高估了储层内裂缝的重要性。未来旨在预测圈闭中石油成分的研究应集中于了解从厨房排出的电荷组成。
Kinetic schemes describing oil-gas cracking are a required component of models which predict the masses, compositions and phases of petroleum expelled from source rocks; an additional application is in predicting the temperature zone over which reservoired oil deposits will be degraded to gas. This simple first-order kinetic model, calibrated on closed-system laboratory pyrolysis of 16 different source rock samples, describes the bulk conversion of oil (C6+molecular range) to gas (C1–5molecular range). Cracking rates vary markedly between samples, depending on the saturate to aromatic ratio of the generated oil. The initial hydrogen index (Hl0) of the sample, taken as an indirect measure of the saturate to aromatic ratio of the oil it generates, correlates strongly with optimized rate constants for oil cracking in individual samples. Thus cracking rates are predictable using a simple, routinely performed geochemical screening measurement. Source rocks with high Hl0tend to generate saturate-rich oils with a high mean activation energy and a tight distribution of bond energies, which crack relatively slowly over a high but relatively narrow temperature range. Source rocks with low Hl0generate aromatic-rich oils with a low mean activation energy and a broad distribution of bond energies, which crack relatively rapidly over a lower, but relatively wide, temperature range. This is an important contributing factor in the observed gas-proneness of ‘type III’ source rocks with low Hl0. The projected cracking window (defined limits at 10–90% of initial oil degraded; reference heating rate 2°C Ma−1) varies from 155 to 205°C in very high quality source rocks (Hl0> 600 mg g C−1) to 115–205°C in very poor quality source rocks (Hl050 mg g C−1). An order of magnitude increase (decrease) in heating rate elevates (depresses) these temperature windows by ca. 15°C. The extrapolations to the geological subsurface are subject to a confidence limit no better than 7°C. Extrapolation to the reservoir environment requires caution because kerogen, an important potential catalyst and hydrogen donor allowing 100% cracking efficiency in the source rock, is absent. Furthermore, fractionation during expulsion causes saturate enrichment of expelled, ultimately reservoired oils. Thus in-reservoir cracking should be at least as slow as cracking in good quality source rocks, and coke or pyrobitumen formation is needed to conserve the hydrogen balance. A case history based on deep petroleum pools of the UK Central North Sea confirms these projections, demonstrating no positive evidence of significant in-reservoir cracking at temperatures as least as high as 174°C, and perhaps even 195°C. Previous studies have overestimated the importance of in-reservoir cracking. Future studies aiming to predict petroleum composition in traps should concentrate on understanding the charge composition expelled from the kitchen.