压力对深部油藏原油热裂解影响的实验研究

There is a serious debate on the "how high pressure affects the thermal stablity of crude oil in deep-buried reservoirs?" in the field of petroleum geochemistry in last three decades. In this project, an excess of highly pure water pressure pyrolysis system is employed to investigate the pressure effects on the thermal cracking of crude oil with consideration of reservoir physico-chemical conditions. The research focuses on the measurements of components and stable carbon isotopic compositions of individual gasoline hydrocarbon produced by water pressure experiments, and conducts a comprehensively comparative study between normal pressure system and high pressure system. We hope that molecular isotopic parameters can be extracted to identify the pressure effects on the thermal cracking of crude oil, and further provide robust evidence for pressure retardation on the hydrocarbon maturation and destruction in high pressure environment. The results will be helpful to the development of theory in terms of deep oil and gas accumulation and implications for the deep exploration.

围绕“深部高压-超压环境究竟如何影响油藏石油的热稳定性？”这一国际油气勘探界长期争议问题，本项目拟在前人研究基础上，利用过量水增压系统，综合考虑深部油藏物理化学条件，开展高压条件下原油热裂解实验，并以裂解产物气态烃(gasoline HCs, C1-C9)分子碳同位素地球化学特征为基础，基于正常压力和高压条件下原油裂解体系化学反应发生的理论分析与实验对比研究，试图提出“高压-超压条件下石油热裂解过程与正常压力环境石油热裂解过程”的分子碳同位素地球化学识别指标，为 “压力对有机质演化与成藏影响”研究提供新的证据。研究成果不仅对于发展深部油气成藏理论具有重要意义，而且对指导深部油气勘探具有现实意义。

以缺失轻烃馏分高蜡原油作为研究对象，利用水压热裂解装置开展不同演化阶段高压与低压环境原油裂解实验(温度区间350oC到425oC，压力最高至900 bar)。结果表明，高压显著抑制高分子量烃类裂解转化，储层矿物对于原油裂解以蒙脱石的催化效应最为显著，其它矿物的加入与纯原油体系相比并没有发生显著差异。深部高压环境对原油裂解生成甲烷反应起主控作用，产生异常甲烷碳同位素分馏效应，而重烃气分子碳同位素具有不变性。同时，轻烃中链烷烃、环烷烃、芳香烃的分布显著受压力控制，中-高压条件导致Mango K1值和甲苯/正庚烷比值升高，以及正庚烷/环己烷比值下降。反映中-高压环境下的热裂解优先异构化和芳构化，可能为双分子反应途径。优先的异构化和芳构化反应使得链烷烃和芳香烃在热裂解过程产生显著碳同位素分馏效应，分别达到2‰和4‰，而环烷烃不发显著碳同位素的分馏效应。据此提出气体分子碳同位素对比曲线和轻烃中分子碳同位素组成可识别深部油藏的压力蚀变效应及其程度。研究成果不仅对于深部地层油气勘探评价具有重要现实指导意义，而且对于石油的高压炼制也具有一定参考价值