Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou, Jiangsu 221008, China.
Department of Energy and Mineral Engineering, G3 Center and Energy Institute, The Pennsylvania State University, University Park, PA 16802, USA.
J Nanosci Nanotechnol. 2021 Jan 1;21(1):156-167. doi: 10.1166/jnn.2021.18463.
Shale gas has received widespread interest due to its successful commercial development in China. Pore structures in shale can directly control its gas storage and migration properties. In this study, field emission scanning electron microscopy (FE-SEM), low-pressure N₂/CO₂ adsorption and highpressure methane adsorption were used to investigate the nanoscale pore structures of the Lower Cambrian Niutitang Formation in the southeastern Upper Yangtze platform. The fractal parameters of the pore structures were also calculated using the Frenkel-Halsey-Hill (FHH) model. The relationships between the fractal dimensions and TOC content, mineral composition and pore structure parameters were also discussed. The results show that organic matter and clay minerals are primary factors affecting the nanoscale pore development. Slit-shaped pores and ink-bottle-shaped pores are the predominant pore types in the Niutitang shale. The Brunauer-Emmett-Teller (BET) surface areas vary from 4.91 m²/g to 34.33 m²/g, and the pore volumes range from 0.689 m³/100 g to 2.964 m³/100 g. Two fractal dimensions ( and ₂) of the Niutitang shale were obtained using the FHH model, with ranging from 2.605 to 2.684, and ₂ ranging from 2.681 to 2.865. adequately characterizes the surface roughness of the pore structures, while ₂ represents the complexity of the pore types. Inter-particle (InterP) pores commonly have greater shape complexities than OM pores and intra-particle (IntraP) pores, based on analyses using Image-Pro Plus software. In addition, the TOC content and clay minerals have great effects on the fractal dimension . Meanwhile, the fractal dimension increases with increasing BET surface area, but there is no definite relationship between the fractal dimensions and pore volumes. Both the fractal dimensions and ₂ are negatively correlated with pore sizes. Further investigation indicates that the fractal dimension exhibits a strong positive relationship with the methane adsorption capacity indicating that Niutitang shales with greater values of the fractal dimension have higher methane adsorption capacities.
由于在中国的商业开发取得了成功，页岩气受到了广泛关注。页岩中的孔隙结构可以直接控制其储气和运移特性。本研究采用场发射扫描电子显微镜（FE-SEM）、低压 N₂/CO₂吸附和高压甲烷吸附技术，对上扬子台地东南缘下寒武统牛蹄塘组的纳米级孔隙结构进行了研究。还使用 Frenkel-Halsey-Hill（FHH）模型计算了孔隙结构的分形参数。讨论了分形维数与 TOC 含量、矿物组成和孔隙结构参数之间的关系。结果表明，有机质和粘土矿物是影响纳米级孔隙发育的主要因素。板状孔和墨水瓶状孔是牛蹄塘页岩中的主要孔隙类型。BET 比表面积在 4.91 m²/g 到 34.33 m²/g 之间变化，孔体积在 0.689 m³/100 g 到 2.964 m³/100 g 之间变化。使用 FHH 模型得到了牛蹄塘页岩的两个分形维数（和 ₂），其中 范围在 2.605 到 2.684 之间， ₂范围在 2.681 到 2.865 之间。 充分描述了孔隙结构的表面粗糙度，而 ₂表示了孔隙类型的复杂性。基于 Image-Pro Plus 软件分析，可知粒间孔（InterP）比有机质孔（OM）和粒内孔（IntraP）具有更大的形状复杂性。此外，TOC 含量和粘土矿物对分形维数 有很大的影响。同时，分形维数 随着 BET 比表面积的增加而增加，但分形维数与孔体积之间没有明确的关系。分形维数 和 ₂都与孔径呈负相关。进一步的研究表明，分形维数 与甲烷吸附量呈强正相关，表明具有较大分形维数的牛蹄塘页岩具有更高的甲烷吸附能力。
