Gao Qichao, Dong Pingchuan, Liu Chang
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing), Beijing 102249, China.
College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, China.
ACS Omega. 2021 May 16;6(20):12931-12951. doi: 10.1021/acsomega.0c04606. eCollection 2021 May 25.
Shale gas is an important unconventional natural gas resource. Studying the microstructure of shale and the gas transport law is of great significance for the development of shale gas. This paper uses the field emission scanning electron microscope to observe shale samples of the BC shale gas reservoirs in southern China. It is found that there are three types of storage spaces on the micro-nano-scale of shale samples. The storage space can be distributed either in pure organic matter or pure inorganic matter or in both organic matter and inorganic matter. They are called organic storage space, inorganic storage space, and mixed storage space of organic matter and inorganic matter, respectively. According to these types of storage spaces, an ideal conceptual model that reflects various types of storage spaces has been researched and established on the micro-nano-scale. At the same time, the transport mechanisms of slip, diffusion, adsorption, and coupling have been considered, and shale mixed storage space has also been considered in particular. On this basis, a comprehensive equation that can simulate the transport of shale gas in various types of storage spaces is derived. The equation also introduces the proportional parameters of the organic part, fractal characteristics, and water film of the inorganic part in the mixed storage space. Researchers can adjust this parameter to simulate shale gas transportation in different types of storage spaces and then use the finite element method to solve it numerically. This paper analyzes the influence of shale reservoir space types on shale gas transport. The larger the proportion of organic components in the mixed pores, the better the gas transport. The rough fractal dimension of the pores also affects the gas transport. However, when the pore diameter is less than 300 nm, the rough fractal dimension of the pores has a negligible influence on gas transport. For the water film on the inorganic wall surface of mixed pores, the gas transport of the macropore is more sensitive to the change in water film thickness.
页岩气是一种重要的非常规天然气资源。研究页岩微观结构及气体运移规律对页岩气开发具有重要意义。本文利用场发射扫描电子显微镜对中国南方BC页岩气藏的页岩样品进行观察。发现页岩样品在微纳米尺度上存在三种类型的储集空间。储集空间可分布于纯有机质、纯无机质或有机质与无机质两者之中。它们分别被称为有机储集空间、无机储集空间以及有机质与无机质混合储集空间。根据这些储集空间类型，在微纳米尺度上研究并建立了一个反映各类储集空间的理想概念模型。同时，考虑了滑脱、扩散、吸附及耦合等运移机制，并特别考虑了页岩混合储集空间。在此基础上，推导了一个能够模拟页岩气在各类储集空间中运移的综合方程。该方程还引入了混合储集空间中有机部分的比例参数、无机部分的分形特征以及水膜。研究人员可调整此参数来模拟页岩气在不同类型储集空间中的运移，然后用有限元法进行数值求解。本文分析了页岩储层空间类型对页岩气运移的影响。混合孔隙中有机组分比例越大，气体运移越好。孔隙的粗糙分形维数也影响气体运移。然而，当孔径小于300 nm时，孔隙的粗糙分形维数对气体运移的影响可忽略不计。对于混合孔隙无机壁面上的水膜，大孔隙的气体运移对水膜厚度变化更为敏感。
