An assessment of gas content and composition of Eskişehir - Alpu and Tekirdağ - Çerkezköy coal basins

Coal seam gases, particularly methane, have significance in energy industry. One aspect of this is the health and safety concerns of mining operations performed in order to produce coal. Gas content of the seams may cause methane explosions that is generally resulted numbers of fatalities in an only one accident if not investigated and necessary precautions are taken properly. Furthermore, gas and dust outbursts during mining activities is directly related to gas content of the strata, its origin and generation process. Also, fire ratios utilized to monitor gob area of longwall mining is produced by several calculations performed on various gas composition values. On the other hand, if it is technically and economically feasible, this gas content can be utilized to produce natural gas that can be used to assist mining activities as energy supply or it can be sold to the energy market. Today, both coal and natural gas dominate energy industry in Turkey and in the World. And, it is hard to change these energy sources in the following decades. Another affect of coalbed methane is environmental results that even if this methane isn't produced or doesn't cause any mining accident, allowing it to escape atmosphere means increasing effect of greenhouse gases that methane is far more effective in causing global warming than carbon dioxide. These issues are covered in this thesis and basically, gas content and composition of coal seams and adjacent rock formations are studied. Gas content of coal seam is generated through coalification process that takes up to hundereds of million years to be completed. Deposited organic material mostly coming from plants are become peat due to activities of microorganisms. Methane generation is started during this process with several other gas compounds. After this stage, the organic material becomes lignite. As coalification process continues gas content of the material increases. Also, carbon content as it is more and more locked in cyclic compounds and calorific value of coal increses. On the other hand, volatile compounds, moisture and content of other elements decreases. Then, lignite turns into bituminous ranked coals and finally, anthracite is formed. Methane generation is occured in all of these stages. Formation of other gases is occured depending on biologic activity, geologic factors, temperature and stress conditions. Some of formed gas content can be deposited in coal seam and rest of the content migrates to other formations and atmosphere. Because of this process, gas content with variety of compounds and coal features possess clues concerning coalification of the very basin. Gas composition of coal gas content is dominated by methane. Carbon dioxide and nitrogen gases can also be found as dominating compounds. Beside of these, complex hydrocarbons, hydrogen, helium, carbon monoxide and hydrogen sulfide can be found in coal seams in trace amounts. Each of these gas compounds is formed in different conditions. Such as at specific temperature intervals, different gas compounds are generated. Stress may promote other chemical reactions to occur. And, available element and compounds in burried organic material determines what sort of gas molecules can be formed in strata. Gas composition and amount are crucial parts of this thesis. The gas content of coal is formed as a result of physical and chemical factors present during the carbonization process and it is also stored and transported by this way. In order to investigate gas content and compositions and also relationship between these gases, two coal basins are selected. These coal basins are located in Alpu/Eskişehir and Çerkezköy/Tekirdağ in Turkey. The coal seams in both basins show property of lignite rank with high moisture and volatile content. In this study, the properties of coal bed methane in terms of geological, occupational safety and gas production are evaluated. First of all, the process of coal and coal content formation are explained due to the studies which have been carried out on the world. In experimental studies, the coal samples are taken from the surface drillings and they are placed into the desorption canisters as soon as they reached the surface. The obtained samples are analysed by different methods. Gas emission, residual gas measurement, gas composition analysis and proximate analysis are realized to investigate the properties of them. The methods used during these works are firstly gas content measurement by direct desorption measurement as gas content is determined in three parts. These parts are desorbed gas, residual gas and lost gas before specimen is put into desorption canisters. In this method, lost gas is estimated. Gas concentration determination is applied on samples taken from desorbed gas. Then, the samples are introduced to a gas chromatograph which is capable of measure almost whole compounds. Since desorbed gas samples taken are contaminated with athmospheric air, normalization calculations are utilized. Proximate analysis experiments are done in order to understand the most basic properties of the coal basins. According to the results, Çerkezköy basin is not gassy and Alpu basin coals gas content is relatively higher. Many gas compunds are found in both fields that methane, nitrogen, carbon dioxide, ethane and other hydrocarbons, hydrogen, helium and carbon monoxide in Alpu Basin. Methane and nitrogen are the first and the second dominating gases in both fields. Although Çerkezköy basins' gas composition is generally similar and in order, results of Alpu samples are highly scattered with high standard deviation caused by fracture and hydrogeologic mechanisms. Gas content is firstly formed in coal seams and transported to close rock formations. Secondary transport from host back to home might occur via these fractures and groundwater. A secondary transport provides decreasing effect of gas content of coal and this interactions' footprints can be found in gas composition of coal and adjacent rock layers. Due to this, nitrogen ratio has a negative relation with gas content. On the other hand, ethane is positively correlated with gas content of both basins. Origin of formation of almost each gas compound, which can be found in coal, is explained with examples in literature. Formation of less mentioned gas compounds such as nitrogen and carbon monoxide are explained. Nitrogen gas and ethane are found in basins showing biogenically generated gas signals. Carbon monoxide represents strong relation with ethane which can occur starting around hundered celcius degree with thermogenic gas formation process. Since many gas compounds are present in the fields, there will be extra criteria for each gases in order to determine air quantity that should be sent to underground. Also, concentration of some of the gas compounds present in gas content of coal are used in calculations of fire ratios which used to monitor oxidation reactions on coal surfaces. Because of this, fire ratios can be highly misleading that this case is explained and shown with curves of fire ratios with respect to methane readings. One step further is improvements on fire ratio equations that based on eliminating coal gas content sourced gases from readings and recalculating fire ratios.