致密砂岩微纳米孔喉系统对储层含气性及气水运移的控制机理

Micro-nano scale pore-throat is the main space for occurrence and migration of gas and water of tight sandstone gas reservoir, on the basis of quantitative characterization of micro-nano pore throat of tight sandstone reservoir, revealing the mechanism of pore throat system which controlling gas bearing, gas and water migration in reservoir is very important for scientific and rational development of tight gas reservoirs. Aiming at the unclearly understanding on the problem of quantitative description and evaluation of pore throat system, and the mechanism of micro-nano pore throat system controlling gas bearing, gas and water migration, typical tight gas fields have been chosen as the research objects in this paper. In the research, a combined way of micro-nano scopic research is used, static description and dynamic simulation are comprehensive used, experimental and theoretical study are mixed; multidisciplinary theories such as reservoir physics, micro-nano scale porous flow mechanics, gas reservoir engineering, gas water two-phase seepage experiments are integrated, high and new experimental techniques, including mercury injection, nuclear magnetic resonance, X ray water saturation detection and dynamic simulation of reservoir formation and development are comprehensive applied. Based on the analysis of the dynamic mechanism of tight sandstone reservoir formation and development, simulation experiments, including reservoir filling, depletion development, two-phase flow are carried out to understand the occurrence and migration of gas and water, obtain the main factors of reservoir gas bearing and water production, revealing the mechanism of micro-nano pore throat system which controlling gas bearing, gas and water migration in reservoir. This research lays theoretical foundation for reasonable and scientific development of tight gas reservoir.

微纳米孔喉系统是致密砂岩储层气水赋存与运移的主要空间，在致密储层微纳米孔喉定量表征的基础上，揭示致密气储层微纳米孔喉系统对储层含气性及气水运移的控制机理对于科学合理开发致密气藏十分关键。本项目针对孔喉系统难以定量描述与评价，储层含气性及气水运移的控制机理认识不清的问题，选取典型致密气区储层为研究对象，采用微观和宏观相结合、静态描述与动态模拟相结合、实验研究和理论分析相结合的思路，综合应用油层物理学、微观渗流力学、气藏工程、气水两相渗流实验等多学科理论，采用恒速压汞、高压压汞、核磁共振、X射线含水饱和度测试、成藏与开发动态模拟等高新实验技术，在致密砂岩成藏与开发过程动力学机制分析基础上，开展充注成藏、衰竭开采及两相渗流等模拟实验，明确气水赋存状态与运移规律，获得储层含气性与产水主控因素，揭示微纳米孔喉系统对储层含气性及气水运移的控制机理。本研究可为科学合理开发致密气奠定关键科学理论基础。

我国致密砂岩气藏资源丰富，其规模开发是我国天然气实现战略接替及能源可持续发展的重要保障。微纳米孔喉系统是致密砂岩储层气水的主要运移空间，揭示致密气储层微纳米孔喉系统对储层含气性及气水运移的控制机理对于科学合理开发致密气藏十分关键。课题负责人及课题组成员长期从事低渗致密砂岩气藏储层孔喉结构评价及气水渗流机理研究。课题立项以来聚焦致密砂岩储层微纳米孔喉系统表征方法及分布特征，孔喉系统对含气性和对气水运移的控制机理三方面持续开展创新性研究工作。.首先，对比了当前使用较广泛且经济有效的储层孔喉结构测试方法，分析了不同方法的优缺点。针对不同区块典型致密砂岩储层采用铸体薄片、高压压汞以及基于CT图像的孔喉三维表征技术系统研究了致密气储层岩样孔喉全尺度分布及渗透率贡献率分布特征。建立了微观孔喉结构与宏观渗透率关系，实现了微纳米孔喉系统的表征与评价，为储层三维数字重构及数值模拟奠定了基础。.在孔喉系统对气水运移的控制机理研究中，针对气藏充注过程设计了半封闭充注模拟实验，充分考虑温度影响并最大限度模拟低速注气、缓慢充注过程，同时结合压汞测试和核磁共振分析，从微观孔喉结构出发，系统研究了储层物性、孔喉结构、充注动力、充注温度等关键因素对含气性影响，分析了充注过程中气、水移动机理，提出了含气性与储层物性、充注动力的对数函数关系。.在孔喉系统对气水运移的控制机理研究中，首先聚焦于低渗致密气藏气水运移规律，尤其是气水运移的启动压力变化规律；其次通过致密岩心不同压差驱替实验及核磁共振实验，研究了致密储层原始含水饱和度大小及在孔隙内的赋存状态，明确了孔隙水的可动性及产水机理；最后针对储层气水自发渗吸机理及理论开展了深入和创新性研究。利用分层核磁共振测试技术，刻画了储层内部湿相饱和度剖面动态变化过程，进一步揭示了渗吸前缘及渗吸液量变化规律。针对传统模型的局限性，建立了优化与修正方法并进行了实验验证。