石油的次生变化对石油性质的改造有时会超过有机质来源和热成熟度作用的影响,而热蚀变是地史时期地质体中一种较为常见的次生变化。本文选取准噶尔盆地南缘原油样品系统模拟热蚀变过程,并进行数据分析,从中筛选出相关性良好的菲/甲基菲(P/MP)比值和(3-MP＋2-MP)/(9-MP＋1-MP)比值两项指标,它们能够很好地反映原油热变程度;根据筛选出的这两项指标,制作了判别原油热蚀变程度的图版。应用该图版分析准噶尔盆地南缘霍尔果斯和呼图壁油气田原油热蚀变程度,结果显示,霍尔果斯霍10井原油可能为原生油藏,热变程度较低,而霍浅1和霍002原油可能是由埋藏较深、热变程度高的原始油藏向上运移产生的次生油气藏;准噶尔南缘的安5井、石南31井及呼图壁气田中的呼2井原油处于正常成熟阶段,表明其所处油气藏基本上为原生油气藏。

The effects of secondary alterations on the characteristics of the crude oil are sometimes greater than those of the organic matter sources and the heat maturity. In the geological history, the thermal alteration is one type of common secondary alterations that occur in the subsurface. In this paper, by simulating in the laboratory the thermal alteration of the oil from the southern Junggar Basin and analyzing the obtained data, two indexes, P/MP and (3-MP＋2-MP)/(9-MP＋1-MP) are shown to have a good correlation with the thermal alteration. Moreover, a chart which can be used to identify the thermal alteration degree is proposed. With this chart, the relative thermal alterations of oils from Huoerguos and Hiutubu oil fields were identified based on the methyl phenanthrene composition. The crude oil from Well Huo 10 in the Huoerguos oil field with a slight thermal alteration indicates that the oil field is most likely a native reservoir. However, the crude oil from Well Huoqian 1 and Well Huo 002 with a severe thermal alteration shows that they are most likely secondary reservoirs migrated from deep buried reservoirs. The crude oil from Wells An 5, Shinan 31, and Hu 2 with a normal maturity shows that they are native reservoirs.