岩石纳米孔隙中页岩气吸附和驱替的微力学机理研究

With the decrease of oil reserves and the severity of environmental problem, unconventional oil and gas resources have received more and more attention gradually. Due to its numerous advantages such as wide distribution, abundant resource and long production cycle, shale gas has become a hotspot of petroleum exploration and development. Shale gas has a variety of storage methods such as adsorbed gas, free gas and has multi-scale flow mechanisms such as gas desorption, gas diffusion, non-Darcy flow and Darcy flow. Hence, the exploitation of shale gas involves multi-scale and multidisciplinary science and engineering. Among them, the adsorption of gas in shale nano-pores and the micromechanics mechanism of gas displacement are still unclear. In this project, we establish a lot of molecular dynamics simulation models to study these problems, including the adsorption and desorption of shale gas, the competitive adsorption of multicomponent gases and the technology of gas displacement. The main purposes are to explore the micromechanics mechanism of gas adsorbed at the wall in shale nano-pores, to explain the hysteresis phenomenon between the adsorption and desorption isotherms and to study the micro mechanics mechanism of the competitive adsorption between multicomponent gases. Furthermore, we study the mechanical behavior of the displacing using gas injection and the influence of different parameters on the displacement effect. This research is not only the frontier of micro-nano-mechanics, but also of important significance for accurate prediction of production and efficient exploitation of shale gas.

随着石油储量的减少和环境问题的严重，非常规油气资源日益受到关注和重视，而页岩气以其分布范围广、资源量大、稳产周期长等特点，成为当前油气勘探开发的热点。页岩气具有多样的储集方式（如吸附、游离等）和多尺度的渗流方式（解吸附、扩散、非达西渗流、达西渗流等）。页岩气开采涉及到多尺度多学科交叉，其中岩石纳米孔隙中页岩气的吸附和驱替微力学机理尚不明确。本项目针对页岩气吸附、解吸附、多组分竞争吸附、注气驱替技术等问题，建立分子动力学模型并进行大规模并行数值模拟研究。主要目标是从分子尺度探究气体吸附于纳米孔隙固体表面的微力学机理，解释页岩气在纳米孔隙中的吸附/解吸附滞回现象，研究不同气体竞争吸附的微力学机理。本项目进一步研究驱替介质对吸附页岩气进行驱替的力学行为和参数影响规律。该项研究既是微纳米力学学科前沿，也对准确预测产能和高效开采页岩气具有重要的应用价值。

随着石油储量的减少和环境问题的严重，非常规油气资源日益受到关注和重视，而页岩气以其分布范围广、资源量大、稳产周期长等特点，成为当前油气勘探开发的热点，并逐渐成为重要的战略资源和能源需求的重要组成部分。页岩气主要以吸附和游离态贮存于页岩的纳米孔道中，开采过程中，吸附气体解吸附成为自由气体并从纳米孔流向多种尺度的裂缝孔道而最终汇聚在井筒。这一过程涉及到页岩气在多种尺度下的输运问题，因此正确的理解页岩气多尺度输运行为和机理对页岩气勘探开发具有十分重要的意义。采用自下而上的研究策略，我们首先探讨了页岩气在纳米孔道中的输运特性，详细研究了页岩气在纳米孔道中的吸附/解吸附、注气驱替、流动等一系列与输运相关的力学问题及其内在机理。为了进一步阐明页岩气在多尺度孔道中的输运行为，我们采用跨尺度的格子玻尔兹曼方法，并耦合分子动力学在纳尺度的模拟结果，给出了页岩气在多尺度下的输运机制，并且研究了变截面纳米通道对页岩气输运特性的影响。此外，基于扩展有限元方法，建立人工裂缝与粘结型和摩擦型天然裂缝交叉的数值计算模型，实现了对页岩气藏水力压裂缝网形态的模拟，并在数值模型中首次引入凝聚法，大大提高了模型的求解效率，有望为大规模工程应用奠定良好理论基础。本项目在执行过程中，进展顺利，超额完成计划任务书中所规定的研究内容并圆满达到预期目标，本项目共计发表致谢National Science Foundation of China (11472263)的SCI论文38篇。共培养硕士生2名，博士生9名。并且项目负责人获得2015年度国家杰出青年科学基金支持。