中国科学院力学研究所机构知识库

进入21世纪以来，非常规油气获战略突破，页岩油气成为油气资源接替的重要新领域。页岩气藏储量大，分布广，具有非常大的开发潜能。然而，页岩中的多流动空间（有机/无机）、多流态（粘性/滑移/扩散）特征以及水力压裂使得气体运移成为复杂的多尺度系统。常规的流动模拟不再适用非常规的页岩气藏，建立一套适用于页岩气渗流的跨尺度模拟方法迫在眉睫。本文针对页岩气渗流，进行了从微观到宏观的多级跨尺度研究，并应用到页岩气勘探开发中。

首先，基于纳米分辨率的扫描图像建立了微尺度下页岩有机质和无机质的三维耦合模型，揭示了页岩微观孔隙空间的气体传输机制，探究了页岩气渗流中有机质和无机质的界面耦合效应，提出了针对于不同计算规模的并行方案并优化了模型精度，深入分析了微观参数对页岩气渗流的影响，明确了影响页岩渗透率的主导微观参数，为更大尺度的计算奠定了坚实的理论基础。

其次，引入了统计方法去掉对页岩渗透率影响微弱的参数，提出了准确快速地计算微尺度渗透率的等效模型，大幅提高了微尺度下的计算效率。基于多尺度扫描图像，建立了百微米尺度的统计耦合模型，形成了涵盖多尺度信息的有机质块体分布系统。针对页岩，提出了有机质表征单元体（oREV）的概念，搭建了页岩气渗流微观和宏观的桥梁。形成了页岩oREV确定及渗流计算方法，获取了页岩气渗流的表征单元体尺度特征参数。

最后，我们将跨尺度方法应用到页岩气勘探开发中。利用oREV联系微观信息和宏观模拟。一方面，针对产生于地化领域的甲烷碳同位素分馏问题，成功建立了oREV尺度双组分气体渗流-扩散-吸附模型，明确了甲烷碳同位素分馏的微观机理，并且基于同位素分馏这个全新的视角建立了一套跨尺度含气量计算方法，结合分馏数值模拟和同位素录井数据为“甜点”优选提供了新的参考依据。另一方面，考虑了页岩气产气过程中渗透率、吸附量等随压力变化，形成了基于oREV参数的页岩气藏多级压裂水平井数值模拟理论，建立了跨尺度产气量计算方法，分析了微观对宏观产气的影响。本文提出的含气量和产气量跨尺度计算方法，为页岩气藏的勘探和开发提供了全新的补充。随着近年来针对页岩的多尺度测量技术和数字岩心技术的兴起，跨尺度方法快速发展，将对以后的油气藏勘探开发产生重要影响。

Since the beginning of the 21st century, unconventional oil and gas has achieved strategic breakthroughs, and shale oil and gas has become an important new field for oil and gas resources. Shale gas has large reserves and wide distributions, with a very large development potential. However, the multiple flow spaces (organic matter/inorganic matter), multi-fluid (viscous/slip/diffusion) features, and hydraulic fracturing in shale make gas migration a complex multi-scale system. Conventional flow simulation is no longer applicable to unconventional shale gas reservoirs, and a set of trans-scale simulation methods for shale gas transport is imminent. In this paper, multi-level trans -scale research from microscale to macroscale is carried out for shale gas.

Firstly, a three-dimensional coupled model of organic matter and inorganic matter in micro-scale shale is established based on the nano-resolution scanned image. The gas transport mechanism of shale micro-pore space is revealed, and the interface coupling effect between organic matter and inorganic matter in shale is studied. And the parallel schemes for different computational sizes are proposed and the accuracy of the model is optimized. The influence of microscopic parameters on shale gas flow is analyzed in depth, and the dominant microscopic parameters affecting shale permeability are clarified, which provides a solid theoretical foundation for larger scale simulations.

Secondly, statistical methods are introduced to remove the parameters that have weak influence on shale permeability. An equivalent model for accurately and quickly calculating micro-scale permeability is proposed, which greatly improves the computational efficiency at micro-scale. Based on multi-scale scanning images, a statistical coupling model of ~100 micrometer scale is established, and an organic matter distribution system covering multi-scale information is formed. For the shale, the concept of organic matter representative element volume (oREV) was creatively proposed, and the microscopic and macroscopic bridges of shale gas flow were established. The determination and flow calculation method for oREV are formed, and the characterization parameters of oREV-scale shale are obtained.

Finally, we apply the trans-scale approach to shale gas exploration and development. Use oREV to connect micro information and macro simulations. On the one hand, for the carbon isotope fractionation problem of methane generated in the field of geochemistry, the oREV-scale two-component gas convection-diffusion-adsorption model was successfully established, and the microscopic mechanism of carbon isotope fractionation of methane was clarified. A perspective gas content calculation methods, based on fractionation numerical simulation and isotope logging data is proposed. And a new evaluation method for "sweet spot" is also formed. On the other hand, considering the variation of permeability and adsorption amount in shale gas production process, the numerical simulation theory of multi-stage fracturing horizontal well in shale gas reservoir based on oREV parameter is formed, which is based on unstructured PEBI grid. A multi-stage fracturing horizontal well finite volume simulator was used to analyze the effects of microscopic pore parameters and reservoir parameters on macro gas production. The trans-scale calculation method of gas production and gas content proposed in this paper provides a new supplement for the exploration and development of shale gas reservoirs. With the rise of multi-scale measurement technology and digital core technology for shale in recent years, the rapid development of trans-scale methods will have an important impact on the future exploration and development of oil and gas reservoirs.