富长石砂岩油气藏中长石蚀变作用及其与烃类裂解的相关性研究

Feldspar-rich sandstone reservoirs, which are significan exploration targets in deep formations, develop commonly in rifted basins of East China. These reservoirs are characterized by multiple and early hydrocarbon emplacement. After the hydrocarbon charge, with incrasing temperature and pressure during deep burial, the equilibrium of rock-water-hydrocarbon system will be maintained through diagenetic reactions of minerals (eg. feldspars) and hydrocarbon degradation, and these chemical processes have important impact on quality evolution of sandstones and hydrocarbons. Deeply buried Eocene sandstone reservoirs in Jiyang Depression are taken as research objects, and the research idea of ‘characterizing phenomena, exploring essence, summarizing rules’ is employed in this project. Through analyzing various features of the sandstones and hydrocarbons, feldspar diagenesis and hydrocarbon evolution in reservoirs after hydrocarbon emplacement will be studied. Numerial simulation and physical simulation experiments on organic-inorganic interactions in ‘rock-water-hydrocarbon’ system with constraints of reservoir mediums will be conducted. With test of features of solid-liquid-gas before and after the experiments, the products of feldspar-hydrocarbon interactions will be investgated. With combination of thermochemical processes, the organic-inorganic interaction mechanism will be deciphered. Based on characteristics of diagenesis and hydrocarbons in buried natural reservoirs, with combination of results from ‘rock-water-hydrocarbon’ thermal simulations, co-evolution models of feldspar diagenesis and hydrocarbon degradation in feldspar-rich sandstone reservoirs will be proposed. The research achievements will enrich the theories of organic-inorganic interactions in hydrocarbon reservoirs, and will provide guidance for exploration of these feldspar-rich reservoirs.

我国东部断陷盆地富长石砂岩油气藏发育，是深层油气勘探的重要目标。多(早)期成藏是该类油气藏的重要特征，烃类充注后油气藏中“岩-水-烃”体系通过长石等矿物的成岩蚀变和烃类的裂解演化在后续增热增压过程中实现再平衡，对储层和油气质量演化有重要影响。本项目以济阳坳陷古近系深层油气藏为对象，遵循“现象表征-本质探索-规律总结”的思路，利用储层微观特征和烃类特征分析，明确烃类充注后油气藏中长石成岩作用和油气演化作用；开展储层介质环境约束的“岩-水-烃”无机-有机反应数值模拟实验和物理模拟实验，分析体系中固-液-气的变化特征，明确长石和烃类相互作用产物，结合热化学过程，阐明无机-有机相互作用机理；在实际油气藏成岩特征和油气特征解剖基础上，结合“岩-水-烃”热模拟实验成果，建立富长石砂岩油气藏中长石蚀变-烃类裂解的演化模式。研究成果可以丰富油气储层有机-无机作用理论，并对富长石油气藏的勘探具有指导意义。

我国东部断陷盆地富长石砂岩油气藏发育，是深层油气勘探的重要目标。油气充注后，油气藏中有机-无机相互作用持续进行，并控制着油气和储层质量演化。本项目以济阳坳陷沙四段深层富长石砂岩油气藏为对象，遵循“现象表征-本质探索-规律总结”的思路，对富长石砂岩油气藏中烃类演化和长石成岩蚀变作用特征、烃-水-长石相互作用过程和机理、以及油气藏中长石蚀变与烃类裂解演化模式等开展了系统研究。. 研究结果表明：孔隙水对烃类和矿物之间的有机-无机相互作用具有重要纽带意义，在孔隙水存在的条件下，油气藏中有机-无机相互作用在油气充注后仍持续进行；同时水和长石矿物等无机成分的存在可改变烃类热降解演化路径，对油气藏质量演化具有重要控制作用。具体来说，同一油气藏不同位置有机-无机相互作用过程及其对油气和储层质量演化具有明显差异：在高含油饱和度的油层，烃类降解主要通过自由基裂解作用和自由基铰链作用发生，以生成低分子天然气和沥青为主，生成的CO2和有机酸较少，沥青的发育一方面使得油气质量变差，另一方面会堵塞孔隙，造成储层质量变差。在油水过渡带和含油水层，水的存在使得烃类的降解以自由基热裂解、自由基水氧化路径为主，自由基铰链作用被抑制，烃类降解以生成低分子天然气为主，高分子沥青质生成较少；同时烃类降解生成大量CO2等酸性流体，能够溶解长石等矿物并形成更多的次生孔隙，整体过程使得油气质量和储层质量得到改善。高温条件下烃类热降解生成的酸性流体在纵向上有效接力烃源岩排出的有机酸，溶蚀矿物并使得次生孔隙在深层-超深层储层中仍大量发育；由于特定地质背景下无机成分能够加速原油热降解生气过程，使得在160-170℃门限温度即可发育规模性天然气藏。. 研究成果为含油气盆地深层油气藏中有机-无机协同演化的研究探索了新思路，同时为深层富长石砂岩储层的油气勘探提供了科学参考。发表SCI论文8篇，其中SCI一区3篇，二区3篇，授权专利2项，获省部级科技奖励2项。