Problems with the application of heptane and isoheptane values as light hydrocarbon parameters

Abstract

The light hydrocarbon data from 772 oil samples in 25 oilfields, together with GC/MS data from 338 saturated hydrocarbon samples were used to discuss the relationship between kerogen types, using the heptane value, isoheptane value and C29 sterane 20S/(S+R) ratio. Although the heptane and isoheptane values are related to kerogen type, the correlation is different from that in Thompson's interpretation, so the correlation cannot be directly used in research on land facies oils in China. Consideration should be taken when using the heptane and isoheptane values, as secondary alteration and mixed oil sources are the main factors leading to the abnormal change in heptane and isoheptane values. The heptane and isoheptane values have a larger maturity range than that of C29 sterane 20S/(S+R). There are three types of oil samples (original immature oil, altered oil and mixed source oil with different maturity) that may fall into the “Biodegradation” area of the Thompson interpretation. For the biodegraded oil in Thompson's interpretation, the reservoir may have undergone a secondary charge. 摘要: 用采自中国国内25个油区的772个原油轻烃分析数据, 结合其中338个样品的饱和烃GC/MS分析数据, 就原油正、异庚烷值与烃源岩干酪根类型的关系以及与C29甾20S/ (20S+20R)成熟度参数的相关性, 对影响参数值发生异常变化的因素等作了研讨。研究认为, 正、异庚烷值确实与母源干酪根类型有关, 但相关关系与Thompson的图版有所差别, 研究中国陆相原油时不宜直接引用; 原油次生蚀变和混源是使原油正、异庚烷值发生异常变化的重要因素, 在用正、异庚烷值作研究时必须备加注意; 正、异庚烷值标示原油成熟度的范围大于C29甾20S/(20S+20R)所能标示的; 落入Thompson图版“Biodegraded”区域的油样可能有3类: 原生的未熟油, 已遭蚀变的原油和成熟度不同的混源油, 对于未落入该区域内的生物降解油, 认为油藏存在二次注入的可能性。图6表2参26 Key words: light hydrocarbon, heptane value, isoheptane value, maturity parameter, secondary alteration, mixed source oil