The characteristics of coalbed water and coal in a coal seam situated in the Red River Basin, Vietnam.

Abstract An in-depth understanding of the hydrogeochemical characteristics of coal mines is helpful in establishing an effective and successful exploration program of coalbed methane (CBM). This study provides a comprehensive analysis of hydrogeological characteristics, characteristics of coalbed water, and characteristics of the coal sample from a coal seam located in the Red River Basin (RRB). These physicochemical characteristics along with the microbial composition of coalbed water were critically analyzed. A high concentration of chloride and sodium was found in the coalbed water, presumably due to the coal mine's stratigraphic association with marine or marine-transitional beds. A correlation between the occurrence of microbes and the chemical components in the coalbed water was established. The characteristics of the coal were systematically analyzed, including proximate, ultimate, and petrographic analyses. Based on the coal macerals, coal rank is classified as low-rank (sub-bituminous) with a vitrinite reflectance (Ro, max) of 0.36%, suggesting that this type of low-rank coal is favorable for biogenic methane generation. Pore structures and pore types were characterized using different methods, including low-temperature nitrogen adsorption/desorption (LTNA), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM). Coal from the study area has microporous and macroporous features. Pore types of the coal were also characterized using SEM. The primary genetic pore types of the Red River coal include plant tissue holes and blowholes.