Comparative results obtained for coal bed methane from different types of sampling in the Sinifaná basin (Antioquia, Colombia)

Abstract

The objective of this work was to compare the coal bed methane obtained from different types of sampling: channel by ply, lateral, and vertical drilling cores at the San Fernando Mine in the Municipality of Amagá – Antioquia, Colombia. These samples were subjected to gas desorption, gas chromatography, porosity, permeability and high-pressure adsorption analyses. The studied coals are classified as subbituminous A coal and high-volatile C bituminous coal, according to the ASTM D388-19a standard classification of coal by rank. The average of total gas desorbed in the samples varied between 0.2 and 33.7 ft3/ton, which are low values compared to the other coal mining areas of Colombia and the world. Gas composition was primarily methane (C1) ranging from 92.2% to 98.98%, carbon dioxide (CO2) ranging from 0.30% and 4.27%, and amounts typically less than 1.0% other hydrocarbons. At a pressure of 1500 psi, the CH4 adsorption isotherms for the different types of samples varied between 45 and 340 ft3/ton. According to the results, it can be established that there is a lateral variability in depth of the methane gas contents and with a tendency to decrease in coal seam 2 and 3. Vertical variability was also found in the vertical drilling and in the samples taken from the channel per ply of the exploitation front faces. When comparing the results with those of previous studies, the gas contents were generally low (less than 60 ft3/ton). On the other hand, it can be determined in a simple way and at a low-cost manner in samples taken from the exploitation fronts faces.