Evaluation of Methane Potential of Coal Seams Using Thermal Analysis

Gupta, Anuj and Siddarth Nahar
University of Missouri-Rolla, Rolla, MO

Coalbed methane has gradually established as an economically viable energy resource. In order to effectively exploit this resource, an urgent need exists to develop analytical techniques that provide a quick and reliable method to determine gas content of various coals. Although variations of USBM method are generally used with varying degrees of precision to determine gas yields, the lack of an industry standard for this application leads to inconsistent and inconclusive results. The analytical tools available today include experimental methods that involve monitoring of desorbed gases from coal samples over a period of time. Empirical gas content relationships are also used to determine the volume of gas contained in coalbeds. The problem with these methods is that they are either too slow (desorption experiments) or unreliable (empirical methods).

This paper explores a novel approach for estimating the methane content of coal formations by using thermal analysis. Thermogravimetric analysis (TGA) shows some promise in overcoming the limitations of current techniques. This technique involves heating a coal sample and recording the evolution of gas as a function of temperature; a mass spectrometer (MS) coupled to the TGA apparatus can be used to determine compositions of the gases released at different temperatures, thus providing a potentially more reliable method of determining gas volumetrics in a fraction of the time used by desorption experiments. Advantages and shortcomings of the above method are discussed along with recommendations for further refining the technique.