A Comparative Analysis of Pore Attributes of Sub-Bituminous Gondwana Coal from the Damodar and Wardha Valleys: Implication for Enhanced Coalbed Methane Recovery

Abstract

With the increasing drive for geological CO2 sequestration, unconventional resources like shale gas and coalbed methane have gained massive popularity. With a vast resource of bituminous Gondwana coal, India has a good potential for enhanced coalbed methane recovery through CO2 sequestration. Pore attributes and their interconnectivity play a significant role in determining the gas storage capacity and ease of injection/production. In this study, samples from both opencast and underground measures were collected for a thorough comparison between coal samples of the Damodar and Wardha valleys belonging to the same Gondwana coal measure. Quantitative pore attributes determined using CO2 and N2 low-pressure gas adsorption suggests that the coal samples from Wardha are more adsorptive and thus have more gas storage capacity. The total mesopore volume in Wardha coals determined using the density functional theory model (low-pressure N2 adsorption branch) is higher with coals from opencast mines showing the highest pore volume. Two distinct Frenkel–Halsey–Hill fractal dimensions were observed in the mesopore range. Here, larger mesopores demonstrated higher fractal dimensions, indicating that surface roughness is higher for larger mesopores. The total micropore volume determined using CO2-density functional theory (DFT) (on low-pressure CO2 adsorption isotherm) is higher in the Wardha coals, showcasing a positive correlation with increasing depth and organic matter composition. The adsorption-derived pore attributes were validated using high-resolution microscopic imaging and subsequent image analysis. Elemental analysis of the isolated kerogen indicates an escalation of organic carbon with depth, whereas clay content (primarily kaolinite) shows an opposite trend. This study has elucidated the entire spectrum of micro- to mesopore attributes for these two significant coal basins, illustrating their distinguishing characteristics caused by different depositional settings and diagenesis, despite belonging to the same Gondwana measure.

Nanopore Characteristics of Barakar Formation Shales and Their Impact on the Gas Storage Potential of Korba and Raniganj Basins in India

“…Several researchers have provided the similar correlation and fitted the curve with the coefficient of determination ( R 2 ). ,− Wang et al showed a correlation between the fractal dimension and the TOC content, mineral matters, and pore structure parameters. It reveals a good correlation for the BET surface area and a negative correlation with the average pore diameter, while no correlation has been shown between the TOC content, mineral matter, and fractal dimension.…”

Systematic Pore Characterization of Sub-Bituminous Coal from Sohagpur Coalfield, Central India Using Gas Adsorption Coupled with X-ray Scattering and High-Resolution Imaging

“…For the selected experimental setup, the available Q-range was between 0.04 and 1.5 nm −1 . Raw data files obtained are processed using MATSAS Matlab module by Rezaeyan et al 62 Details of calculation are also mentioned in Chandra et al 17,23 Fractal dimension derived from the SAXS can be described with the following equation 17 (6) where D S is surface fractal dimension calculated from SAXS data and A is the slope of I(Q) versus Q plot. 2).…”

“…For the selected experimental setup, the available Q-range was between 0.04 and 1.5 nm −1 . Raw data files obtained are processed using MATSAS Matlab module by Rezaeyan et al 62 Details of calculation are also mentioned in Chandra et al 17,23 Fractal dimension derived from the SAXS can be described with the following equation 17…”

“…In recent times, advanced instrumentation facilities have provided detailed insights into the nanoscale pores. High-resolution imaging, i.e., scanning electron microscopy (SEM), plays a vital role in the both qualitative and quantitative characterizations of structural characteristics and pore morphology. − Intrusive methods like low-pressure gas adsorption (LPGA) provide the quantitative characterization of gas accessible pore systems including surface area, pore volume, and pore size distribution (PSD). − Also, indirect methods like small angle X-ray scattering (SAXS) can provide pore attributes for both accessible and inaccessible pores. − Numerous investigations revealed divergent capacities of different types of organic content to produce hydrocarbons. Based on hydrogen index (HI) and oxygen index (OI) produced from Rock-Eval pyrolysis, kerogens in hydrocarbon source rocks can be roughly divided into four basic categories, , which indicates the potential of the source rock.…”

A Review of Molecular Models for Gas Adsorption in Shale Nanopores and Experimental Characterization of Shale Properties

“…Low-pressure gas adsorption is a well-established method for characterizing pore structure, which has been applied to characterize the pore structure of shale samples in previous studies. − The pore size distribution is calculated using capillary condensation based on the Kelvin Equation in the pore through gas adsorption/desorption . Nitrogen adsorption at 77 K is the standard method for analyzing pore sizes, which is highly accurate for mesopores and macropores in shale samples .…”