Abstract The generation and primary migration of hydrocarbons in organic-rich shale leaves void space in organic matter, which is the porosity associated with organic matter commonly observed under scanning electron microscope (SEM). In this study, Middle Devonian black shale core samples were collected from three wells penetrating the organic-rich Marcellus Shale and the organic-lean Mahantango Formation in Pennsylvania and West Virginia. Pyrolysis, ion milled SEM and low-pressure nitrogen adsorption analysis were conducted to investigate the organic richness and the properties of the pore system. Vitrinite reflectance (Ro) values in the range of 1.36%–2.89% represent a maturity spectrum covering the wet-gas to post-mature zones. In general, the pore system is composed of organic matter-hosted pores and mineral-hosted pores. However, the dominant pore types and pore sizes vary stratigraphically across lithology and abundance of organic matter. All the organic matter observed in this study shows an amorphous occurrence. Pore space between mineral grains (both silt-size and clay-size) can be filled by organic matter, which contains secondary porosity generated by thermal cracking of kerogen. Mineral-hosted pores are concentrated in organic-lean samples in which secondary organic matter could not fill most of the primary pore space. The destruction of primary mineral-hosted pores and the generation of secondary organic matter-hosted pores were observed. TOC values show positive correlations with the porosity, specific surface area, and the abundance of micropores. Increasing thermal maturity correlates with a significant decrease of pore volume and surface area, primarily through diminishing or vanishing of micropores. The richness and thermal maturity of organic matter in organic-rich Devonian shale can be effective parameters for evaluation of reservoir quality and upscaling the appraisal.

中文翻译：

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阿巴拉契亚盆地 Marcellus 页岩和 Mahantango 页岩孔隙结构演化

摘要 富含有机质页岩中烃类的生成和初级运移在有机质中留下空隙，这是在扫描电子显微镜（SEM）下常见的与有机质相关的孔隙。在这项研究中，中泥盆统黑色页岩岩心样品是从三个井中收集的，这些井穿过宾夕法尼亚州和西弗吉尼亚州富含有机质的 Marcellus 页岩和贫有机质的 Mahantango 地层。进行热解、离子研磨扫描电镜和低压氮吸附分析以研究有机质丰富度和孔隙系统的性质。镜质体反射率 (Ro) 值在 1.36%–2.89% 范围内代表了涵盖湿气到后成熟区的成熟度光谱。一般而言，孔隙系统由有机质为主的孔隙和矿物为主的孔隙组成。然而，主要的孔隙类型和孔隙大小在岩性和有机质丰度的地层学上有所不同。在这项研究中观察到的所有有机物质都显示出无定形的发生。矿物颗粒之间的孔隙空间（粉砂级和粘土级）可以被有机质填充，其中包含由干酪根热裂解产生的次生孔隙。含矿物孔隙集中在贫有机质样品中，其中次生有机质无法填充大部分原生孔隙空间。观察到原生矿物赋存孔隙的破坏和次生有机质赋存孔隙的生成。TOC 值与孔隙率、比表面积和微孔丰度呈正相关。热成熟度的增加与孔隙体积和表面积的显着减少相关，主要是通过微孔的减少或消失。富含有机质泥盆纪页岩中有机质的丰富度和热成熟度是评价储层质量和扩大评价的有效参数。