Catalysis Of Minerals And Elements During Coal Bed Methane Generation

The gas formation mechanism catalyzed by mineral/metal elements were discussed and studied based on the coal from late Permian in Eastern Yunnan and Western Guizhou, using gas geochemistry, coal petrology, mineralogy, catalytic chemistry etc., and combining with the thermal simulation experiment of coal alone and the coal in present of pyrite or Mo,. Innovative understanding is as followings:(1) The output characteristics of minerals and metal elements which have potential catalysis during gas generation in coal of late Permian from Eastern Yunnan and Western Guizhou were identified. The coals contain the minerals that are catalytic in theory. Pyrite and kaolinite are the main minerals. The content of Ti, Cr, Mn V, Co, Ni, Y, and Zr and elements are higher than the average level of China coal. Solo or manifold transition metal elements contents in most coal seams are over 3 times higher than national average. The occurrences of Mn, Ni and Co in coal are various.(2) Mineral/elements made the coal organic have greater potential during hydrocarbon generation. Pyrite mainly had a positive and significant catalytic role to the methane. Adding the pyrite and Mo at the same time made the coal samples generate heavier hydrocarbon gases, and pyrite and Mo were helpful to the olefins output. Transition metal Mo had remarkable catalytic effect on the C_7～14 forming, but if there were also pyrite exist at same time, it would make C_7～14 reduce. Pyrite and Mo influenced aromatics hydrocarbon and asphalt qualitative yield peak. High content of transition metal elementals can inhibit the H₂S forming from the sulfur of coal itself. Catalysts had catalysis of hydrocarbon generation in middle to high temperature range. Heating rate affected the pyrite catalysis for saturated hydrocarbons, aromatic hydrocarbon and asphalt, reflecting geological geothermal conditions was an important influence factors for mineral/elements catalysis in the generation of hydrocarbons. Pr/nC17,Ph/nC18 and Pr/Ph were decreased along with the increase of temperature.(3) Some new understanding on evolution law of carbon isotopes during the catalytic hydrocarbon-generating process was obtained. Results show that theδ¹³C₁ changed in theδ¹³C₁ change range of south China coal. Pyrite and Mo made theδ¹³C₁ value heavier.δ¹³C₁ had the same change way which was decreases at first, and then increases along with the increase of temperature. The gas carbon isotope have the same characteristics which isδ¹³C₁<δ¹³C₂<δ¹³C₃. (4) The dynamic process of the hydrocarbon generation by minerals/metal elements catalysis was analyzed and identified mode of coal bed methane generation by minerals/ metal elements catalysis which was composed by minerals/metal elements geochemical characteristics and geochemical index of oil and gas was established. The dynamic parameters of methane and the total gaseous hydrocarbon generation were calculated. The results show that activation energy significantly reduced in presence of mineral/metals, which proved that minerals/metal elements have catalysis during methane formation. Combining with buried evaluation process of Permian coal in studied area, original gas yield from different historical periods were estimated. On this basis, combining with the minerals variety, transition metal elements contents and the evolution stages of coal, coal bed methane favorable exploration areas were forecasted primarily.