Global warming is one of the major threats of 21st century and the CO2 sequestration in unmineable coal seams can be a feasible solution to this problem. However, the effect of CO2 on the physical and mechanical properties of the host rock has a major control on the storage capacity of the coal seams. This paper presents the results of a laboratory based CO2 sequestration study on the Indian coal. The coal samples were treated for twenty-five and forty-five days in a "saturation chamber" under a low pressure and room temperature condition. The mechanical, physical and mineralogical properties of the pre- and post-saturation samples were analyzed to identify the potential changes. The comparative analyses show that CO2 adsorption in the coal matrix has a negative effect on the strength of coal. Moreover, the post-saturation particle size and pore size reduction are interpreted to be a direct effect of this adsorption.

1 Introduction

Carbon dioxide sequestration has emerged as one of the most potential way to curb the global carbon dioxide emission. In this regard, the high CO2 adsorption capacity of coal makes it an ideal candidate for sequestration. With the increasing global interest in the carbon dioxide sequestration and associated coal bed methane (CBM) recovery, a plethora of research have been undertaken throughout the world to investigate the mechanical, strength and reservoir properties of the coals (Khandelwal & Singh 2010, Busch & Gensterblum 2011 and Masoudian et al. 2013). Researchers have experimentally evaluated the effect of CO2 adsorption on the physical properties of different coals (Ettinger & Lamba 1957, Vishal et al. 2013 and Vishal et al. 2015). However, the relation between the adsorption nature and the poro-mechanical behavior of the coal varies widely and a generalized consensus is yet to be achieved. This is mainly because, the coal properties are controlled by the organic content, grade and rank of the coal, depth of the seam, presence of cleat, confining pressure and the surrounding temperature. So, it is required to develop basin and coal seam specific understanding of the strength properties of coal under normal and fluid-saturated conditions. This article discusses the results of an experimental investigation on the effect of carbon dioxide on the strength and micro-structure of Indian coal. By correlating the post-treatment strength of the coal with its micro-properties, a conceptual model of this interaction has been developed.

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