期刊
JOURNAL OF NATURAL GAS SCIENCE AND ENGINEERING
卷 35, 期 -, 页码 860-872出版社
ELSEVIER SCI LTD
DOI: 10.1016/j.jngse.2016.09.030
关键词
Fractal dimensions; Pore structure; Shale; Nitrogen adsorption; NMR
资金
- China Geological Survey [12120115007301-01]
- National Natural Science Foundation of China [41272132]
The fractal dimensions of the Lower Cambrian Niutitang Formation shales in the Middle Yangtze Platform, Southwest China were investigated for pore structure and fractal characteristics using low-field nuclear magnetic resonance (NMR) and N-2 adsorption. The field emission scanning electron microscopy (FE-SEM), N-2 and CO2 adsorption, NMR, porosity and permeability analysis were performed on six shale samples collected from outcrops. The NMR T-2 distributions are consistent with the combination of pore size distributions from N-2 and CO2 adsorption. The discrepancy of fractal dimensions between NMR and N-2 adsorption resulting from the pore size distribution indicates that NMR fractal dimensions provide more accurate insight into the fractal characteristics of pore structure in shales than N-2 adsorption fractal dimensions. The results show that the min(D-NmR), with respect to the shorter relaxation times, reflects the roughness of the micropore surface area and the max(D-NmR), with respect to the longer relaxation times, reflects pore volume for larger pores. The surface fractal dimension min(D-NMR) has a positive correlation with TOC contents and thermal maturity, attributable to the conversion of kerogen and occurrence of organic matter pores. Min(D-NmR) increases with increasing quartz content, while max(D-NmR) increases with increasing clay content. The porosity from helium gas injection ranges from 2.8% to 6.7%, and permeability is between 3.55 and 6.62 x 10(-2) mD. The min(D-NmR) has a positive correlation with permeability, and the max(D-NmR) exhibits a positive correlation with porosity, indicating that the volume fractal dimension max(D-NmR) and surface fractal dimension min(D-NmR) provide new indicators to measure porosity and permeability, respectively. (C) 2016 Elsevier B.V. All rights reserved.
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