Emissions from surrounding strata in coalbeds: Guaduas formation (Colombia)

Abstract

During underground coal mining operations, greenhouse gas emissions are produced, mainly methane. These emissions originated not only from coal, but also from the subsidence of the surrounding rocks. Until now, emissions from surrounding rocks have been calculated from international tables, but it is proposed that they be calculated from gas measurements on coal-adjacent rocks in coalbed methane exploration in which drillings and canisters desorption systems were used in the provinces of Boyacá and Cundinamarca. The gas contents of the surrounding rocks, and thus the emissions, are less than those found in the coal at the same depth. The areas with the highest gas content values in the surrounding rocks are Samacá and Chinavita with contents between 40 and 50 feet3/ton. These values equate to one-third or a quarter of those obtained from the coalbeds close to such samples. The highest gas content did not correspond to the highest coal rank (Socotá) which would be explained by the intense folding and faulting in that area. The gas contents found in the shales (clays) of the Guaduas formation can also be used as a proxy indicator for older and deeper formations that could have good shale gas potential.