Earth Science Frontiers ›› 2019, Vol. 26 ›› Issue (3): 220-235.DOI: 10.13745/j.esf.sf.2018.10.1

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Analyses of the characteristics and main controlling factors for the micro/nanopores in Niutitang shale from China's southeastern Chongqing and northern Guizhou regions

ZENG Weite,DING Wenlong,ZHANG Jinchuan,LI Yuxi,WANG Ruyue, JIU Kai   

  1. 1. Hainan Bureau of Geology, Haikou 570206, China
    2. College of Marine Geosciences, Ocean University of China, Qingdao 266100, China
    3. Hainan Geological Survey, Haikou 570206, China
    4. Hainan Key Laboratory of Marine Geology Resources and Environment, Haikou 570203, China
    5. School of Energy Resources, China University of Geosciences(Beijing), Beijing 100083, China
    6. Ministry of Education Key Laboratory for Marine Reservoir Evolution and Hydrocarbon Abundance Mechanism, China University of Geosciences(Beijing), Beijing 100083, China
    7. Ministry of Natural Resources Key Laboratory for Shale Gas Exploration and Assessment, China University of Geosciences(Beijing), Beijing 100083, China
    8. Mineral Resources and Reserves Center, Ministry of Natural Resources, Beijing 100035, China
    9. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China
    10. Beijing Jingneng Petroleum & Gas Resources Co., Ltd，Beijing 100022, China
  • Received:2018-07-11 Revised:2018-09-19 Online:2019-05-25 Published:2019-05-25
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Abstract: We performed nitrogen adsorption isotherm and scanning electron microscopy (SEM) analyses on core and fresh outcrop samples of Niutitang shale from the southeastern Chongqingnorthern Guizhou region, which allow us to classify the micro/nano scale pore types and quantify the pores developmental stages and morphological structures. In addition, we carried out qualitative or semi-quantitative geochemical analysis on the controlling factors for the micro/nanopore development. The results show that the micro/nano scale pores in Niutitang shale can be divided into 3 types (including 7 subtypes): organic and inorganic pores and micro fracture. Structurally, the organic pore features spherical fine neck and ink bottle, the inorganic pore has bead, sphere and wedge features, and the micro fractures develops parallel plates with four-side opening and splint structures. The organic and intergranular pores and micro fracture are the main pore types, which could serve as storage space and seepage channels for shale gas with good connectivity. Shale pores are dominated by mesopores, followed by macropores, with pore diameters ranging from 1 to 50 nm. The specific surface area (SSA) is mainly provided by nanopores with diameters less than 5 nm, so that smaller pores make greater contribution to SSA and are more favorable for shale gas adsorption and accumulation, while SSA increases with increasing total pore volume. Our study further show that organic carbon content is the most important internal factor for controlling micro/nanopore development and SSA, particularly in controlling micro and mesopores. Moreover, increasing clay mineral content could enhance shale adsorption capacity, however, its controlling effect on pore volume and SSA is not obvious. The brittle mineral content mainly controls macropore development with negligible contribution to shale adsorption. For high and post mature shale, the order of organic pore development and specific surface area is type Ⅰ>type Ⅱ>type Ⅲ for different kerogen types.

 

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