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Nanomaterials 2019, 9(3), 390; https://doi.org/10.3390/nano9030390

Nanopore Structure and Fractal Characteristics of Lacustrine Shale: Implications for Shale Gas Storage and Production Potential

1,2,3
,
1,2,*
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3,4,*
,
5
,
1,2,*
,
6
and
1,2
1
State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China
2
Unconventional Oil & Gas Cooperative Innovation Center, China University of Petroleum, Beijing 102249, China
3
Energy & Geoscience Institute, University of Utah, Salt Lake City, UT 84108, USA
4
Key Laboratory of Tectonics and Petroleum Resources, Ministry of Education, China University of Geosciences, Wuhan 430074, China
5
School of Geosciences, China University of Petroleum, Qingdao 266580, Shandong, China
6
School of Geosciences and Info-physics, Central South University, Changsha 410012, China
*
Authors to whom correspondence should be addressed.
Received: 13 February 2019 / Accepted: 26 February 2019 / Published: 7 March 2019
(This article belongs to the Special Issue Nanotechnology for Clean Energy and Environmental Applications)
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Abstract

In order to better understand nanopore structure and fractal characteristics of lacustrine shale, nine shale samples from the Da’anzhai Member of Lower Jurassic Ziliujing Formation in the Sichuan Basin, southwestern (SW) China were investigated by total organic carbon (TOC) analysis, X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FE-SEM), and low-pressure N2 adsorption. Two fractal dimensions D1 and D2 (at the relative pressure of 0–0.5 and 0.5–1, respectively) were calculated from N2 adsorption isotherms using the Frenkel–Halsey–Hill (FHH) equation. The pore structure of the Lower Jurassic lacustrine shale was characterized, and the fractal characteristics and their controlling factors were investigated. Then the effect of fractal dimensions on shale gas storage and production potential was discussed. The results indicate that: (1) Pore types in shale are mainly organic-matter (OM) and interparticle (interP) pores, along with a small amount of intraparticle (intraP) pores, and that not all grains of OM have the same porosity. The Brunauer–Emmett–Teller (BET) surface areas of shale samples range from 4.10 to 8.38 m2/g, the density-functional-theory (DFT) pore volumes range from 0.0076 to 0.0128 cm3/g, and average pore diameters range from 5.56 to 10.48 nm. (2) The BET surface area shows a positive correlation with clay minerals content and quartz content, but no obvious relationship with TOC content. The DFT pore volume shows a positive correlation with TOC content and clay minerals content, but a negative relationship with quartz content. In addition, the average pore diameter shows a positive correlation with TOC content and a negative relationship with quartz content, but no obvious relationship with clay minerals content. (3) Fractal dimension D1 is mainly closely associated with the specific surface area of shale, suggesting that D1 may represent the pore surface fractal dimension. Whereas fractal dimension D2 is sensitive to multiple parameters including the specific surface area, pore volume, and average pore diameter, suggesting that D2 may represent the pore structure fractal dimension. (4) Shale with a large fractal dimension D1 and a moderate fractal dimension D2 has a strong capacity to store both adsorbed gas and free gas, and it also facilitates the exploitation and production of shale gas. View Full-Text
Keywords: shale gas; pore structure; fractal characteristics; lacustrine shale; Sichuan Basin shale gas; pore structure; fractal characteristics; lacustrine shale; Sichuan Basin
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Chen, L.; Jiang, Z.; Jiang, S.; Liu, K.; Yang, W.; Tan, J.; Gao, F. Nanopore Structure and Fractal Characteristics of Lacustrine Shale: Implications for Shale Gas Storage and Production Potential. Nanomaterials 2019, 9, 390.

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