Characterization of shale matrix pore structure via experiment and model
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ORIGINAL PAPER
Characterization of shale matrix pore structure via experiment and model Hao Zhang 1,2 & Ying Zhong 2 & Jiping She 1,2 & Guanfang Li 3 Received: 29 March 2017 / Accepted: 18 June 2018 # Saudi Society for Geosciences 2018
Abstract Shale gas reservoirs develop multi-scale pores ranging in size from nanometer to micrometer, the characteristics of gas transport involve the multi-scale pore space which divided into organic and inorganic matrix pores. This paper reveals the shale pore structure with large amounts of organic mesoporous based on the techniques of focused ion beam scanning electron microscopes (FIB-SEM), high-pressure mercury intrusion (MICP), and low-pressure adsorption (LPA), which also shows the size and distribution of these pores. Then the research characterizes effective pore scale via circular tube bundle model with due regard for gas adsorption layer thickness on the walls of organic pores and water film thickness on the walls of inorganic pores, and the investigation of shale pore geometry is significant for designing and developing shale gas reservoirs. This work shows that the widely existing shale mesoporous volume with diameter of 2~50 nm accounts for 81% based on experimental testing, then it reduces to about 76% via effective diameter model calculation. Keywords Shale gas . Multi-scale pore . Adsorption layer . Water film . Circular tube bundle
Introduction Shale gas is the third one of unconventional gas resource after coal bed methane and tight sandstone gas, and the shale gas reservoirs have broad prospects for exploration and development (Zhao et al. 2008; Pan and Huang 2009; Liu and Yan 2012). Nano-micro pores have been discovered in the shale matrix with the characteristics of complex pore structure, large BET surface area, and poor connectivity; gas in the pores is enriched in free state and adsorbed state (Cui et al. 2012; Yang et al. 2013a; Wang 2014). Gas transport in porous media, which can be done both convective and diffusive, is determined by the dimensionless Knudsen number (Kn): defined as the ratio of the molecular mean free path length to a * Ying Zhong [email protected] 1
State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Chengdu University of Technology, Chengdu 610059, Sichuan Province, China
2
College of Energy, Chengdu University of Technology, Chengdu 610059, Sichuan Province, China
3
Institute of Geology And Geophysics, Chinese academy of sciences, Beijing 100029, China
representative physical length scale (Chen et al. 2013; Li et al. 2013, 2014; Shi et al. 2013). The knowledge of pore structure and properties is critical for efficient development of shale gas reservoirs. The investigation of gas transport mechanism in shale gas reservoirs should consider the pore structure and properties. Using micro-CT to get the number of pores and throats as well as analyze the distribution of coordination number, the distribution of coordination number accords with exponential law (Zhao et al. 2017). Besides, the geo-mechanical effec
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