天然气运移地质色层效应机理和指标探讨

Migrational Geochromatograph of Natural Gas and Discussion on the Mechanism and Indices

笔者采集了四川盆地威远和中坝气田沿水平方向剖面分布的气井中天然气、凝析油样品,进行了色谱和色谱-质谱分析表明,大部分组分参数向构造圈闭顶部递增,少数呈现递减趋势。认为这种组分分布是天然气(凝析油)渗流运移过程中地质色层效应的结果。笔者着重从分子极性、分子量和分子直径(体积)的角度探讨了参数递增或递减的机理。经过对化和筛选,认为凝析油ABI_1,参数和天然气△R_3参数是较理想的渗流运移专属性指标.

During the process of petroleum migration, it would develop compositional fractionation by mutual effect of stationary-mobile phase, called 'Geochromatograph' In this paper, samples of natural gas and condensate oil have been collected from two typical gas fields in Sichuan Basin-Weiyuan and Zhongba Gas Fields, which are different in age of source beds, reservior strata、precursor and maturity.Results of GC and GC-MS analysis reveal a regular compositional variation of the hydrocarbons within the well- locality sections, which is different from that caused by either gravitational fractionation or diffusive homogenization, suggesting the geochromatographic effusive. Along the direction from wing to top of anticlinal gas traps, parameters such as C1 / (C2+C3) 、 iC4/ nC4、 CH4% 、 N2、 △R1 and △R3 show increasing trend, while iC4/ C3 and CH4/ N2 show decreasing tendency; among condensate oil parameters, cyclohexane/ normalheptane、 ethylcyclohexane / (D+P) dimethylbenzene、 Pr/Ph、 ACL1 and ACI2 increase, while ABI1 and ABI2 show decreasing trend. During the percolative migration process, besides the molecular weight、 molecular volumn and so on, polarity difference is the dominant factor for controlling the relative migration velocity of different composition. Polarity different derives from both variances of molecular length and molecular structure, but structure factor plays a much more important role than the former. Among parameters illustrating the geochromatography, △R3 and ABI1 are the best ones with two remarkable features in common: 1. highest resolution in responding to the fractionation, 2. mono-explanatory for migration. While ABI1 value has been least influenced by the evaperative depletion of condensate oil samples during the transportation, showing its stable geochemical property.