典型致密砂岩天然气运移机理及成藏机制研究

The dynamic research of hydrocarbon migration and accumulation has always been a frontier direction of Petroleum Geosciences, and it is of essential importance to the hydrocarbon exploration. In recent years, exploration and exploitation of tight sandstone gas is developing greatly which put forward great challenge and requirement to this research. Since the reservoir is characterized as extremely low permeability and porosity, high irreducible water and high capillary pressure, the dynamic mechanism is much more complicated than conventional reservoirs. However, understanding dynamic mechanism of gas migration and accumulation in low permeability reservoir is still weak. Therefore, This project will focus on the basic scientific problem of hydrocarbon exploration-the migration and accumulation mechanisms of tight sandstone gas, and the object of this research is tight sandstone gas accumulation of Tiassic unit in Chuanxi depression. On the basement of detailed analysis of characteristical tight sandstone gas accumulation, the heterogeneity experiment model and gas migration experimental condition will be expected to be built. In this project, a series of gas-water displacment experiments under high temperature and high pressure will be conducted using the observational method of NMR imaging and measuring techniques. The objectives are to study the characteristics, process and influencing factors of natural gas migration through the low permeability porous media and its dymanic mechanism. Based on the acknowledgements aquired from these experiments, this project will analysis the migration process and mechanisms, and suggests accumultaion model of tight sandstone gas. Finally, the theoretical knowledges will be applied in the tight sand gas migration and accumulation process in Chuanxi depression. The results will provide effective theoretical and methodological support for tight sandstone gas exploration and exploitation.

油气运聚动力学研究一直是石油地质学的前沿领域，对指导油气勘探有重要意义。近年来致密砂岩气勘探和开发的大发展，对该研究提出了新挑战和要求，致密砂岩气藏具有低孔渗、高束缚水和高毛管力等特点，其运聚机理较常规储层更为复杂，但目前人们对低渗储层天然气运聚过程和动力学机制的认识薄弱。本项目立足于勘探急需解决的基础科学问题"致密砂岩天然气运移机理及成藏机制"展开研究，以川西坳陷上三叠统致密砂岩气藏为研究对象，基于典型致密砂岩气藏特征的细致解剖，建立非均质实验模型和运移实验条件；通过低渗岩心高温高压下气驱水运移的系统模拟实验，采用核磁共振成像和测量技术作为观测手段，研究天然气在致密储层内运移的特征、过程和影响因素，认识致密砂岩气的运聚动力学条件和机制；根据实验获得的认识，分析典型实际气藏致密砂岩气的运移过程和机理，建立致密砂岩气成藏模式，并推广到全区的富气区预测，获得成果将为致密砂岩气勘探开发提供科学的依据。

天然气如何进入致密砂岩并形成工业性聚集的过程和机理是长期困扰学界的基础科学问题，项目针对致密砂岩气运移机理与成藏机制问题开展研究，选择川西坳陷须家河组和临清坳陷东部石炭-二叠系为重点研究对象，细致解剖典型致密砂岩气藏的地质特征，研究致密砂岩非均质储层的成岩作用-烃类充注过程，重建了关键成藏期油气运聚的动力学环境，在地质模型指导下完成一系列气体运移模拟实验，研究了天然气侵入致密砂岩的动力学条件、运移路径特征、演变过程和影响因素，探索了致密砂岩气运聚机理与模式，并应用于实际盆地的有利区预测。项目取得以下重要成果：1)提出以烃类充注作为划分成岩演化的时间节点，发现致密砂岩经历了差异性成岩致密化-烃类充注，指出早期致密砂岩无油气注入，早期未致密且充注石油的砂岩在晚期致密条件下发生了规模性天然气成藏；2)将先进的核磁共振T2谱测量技术引入致密砂岩气运移实验，研发了超低渗砂岩孔径分布和含气饱和度的核磁T2测试方法，实现了真实致密砂岩内气体运移路径演变的高精度、在线观测；3)模拟发现致密砂岩气运移分为路径不稳定扩展和准稳定运移阶段，主要存在“优势式”和 “弥漫式”路径2种模式，致密砂岩气注入速率高于流出速率造成了充注增压，增压幅度受控于岩石渗透率和供气速率；4)致密砂岩气没有绝对的运移下限，但孔隙度4%、渗透率0.04mD可能是有效充注的临界物性，混合润湿性降低了油气运移的毛细管阻力，指出运移路径分布和规模是物性、供气速率、压差和负荷应力等多因素耦合的结果，初步构建了判识运聚效率的动力学模型；5)提出早期常规油充注改善运聚动力学条件和天然气充注自增压是促使致密砂岩气运聚的重要机制，建立了早期充油晚期致密聚气、多级致密-压差耦合驱动、近源优质相带高效运聚的成藏模式，探索提出了适用实际盆地的致密砂岩气甜点预测方法。研究成果显著提升了致密砂岩气运聚过程与机制的理论认识，形成的思路和方法可以为实际勘探发现做出贡献。