Coalbed Methane Enrichment Law And Favorable Zone Prediction In Chongqing Libi Gorge Anticline

Coalbed methane, a kind of unconventional gas associated with coal, exists in coal seam and surrounding rocks of coal seam. CH4, main ingredient of coalbed methane, is a new kind of clean gas resource. Exploitation and utilization of coalbed methane is beneficial to not only prevent the mine methane disaster, but also reduce greenhouse effect generated by methane, meanwhile, exploitation of huge reserves coalbed methane has important strategic meaning for China to optimize energy structure dominated by coal and reduce energy shortage.There are huge coalbed methane reserves and attractive development future in China. But up to now, China has not moved into commercialization phase of coalbed methane exploiting. The main reason was that the coal seam has characteristics of high stress, high rank and low permeability in China, which makes coalbed methane enrichment regular complicated. According to five key scientific problems: the enrichment zone of coalbed methane has not been predicted quantitatively; high permeability zone of that is hard to predict exactly and quantitatively; calculation precision of gas storage capacity is not enough; appraisal indexes of favorable zone selecting are incompatible; coalbed methane enrichment law and mechanisms is lack of systematic study. The main achievements of the thesis are followings:Pressure and content prediction equations of coalbed methane are established in geothermal and geo-stress field. The quantitative prediction theory and method of coalbed methane enrichment zone is put forward. Ground stress testing by Kaiser Method, experiment of adsorption at different temperature and coal quality analysis is carried out. The coalbed methane content and pressure distribution of main coal seam of Yanjing mine area in Chongqing Libi gorge is predicted quantitatively, meanwhile, gas enrichment zone is determined. The problem of coalbed methane enrichment zone quantitative prediction is solved.Base on the above achievements, two new calculation methods of gas reserves are provided. Geological reserves and technical recoverable reserves of coalbed methane are estimated in liibi gorge Yanjing first mine area. The heterogeneity problem of gas reserves calculation is solved.The quantitative prediction theory and method of coalbed methane high permeability zone is established in geothermal and geo-stress field. Corrector method of permeability is put forward between experiment and actual measurement. The permeability distribution of seven coal seams is calculated, at the seam time, the high permeability zone of main coal seam is divided. CH4 and He seepage experiment in coal at different stress and temperature is carried out. The relationship between permeability and temperature at different stress is found. The pore model of internal expansion and out expansion is provided during gas flowing with temperature increasing. The permeability increases with the temperature increasing at low effective stress, but decreases with the temperature increasing at high effective stress. The seepage equation is put forward in geothermal and geo-stress field. The flowing process is simulated.Coalbed methane enrichment regular was studied. SEM and pore distribution experiments of coal are carried out. Coalbed methane enrichment law at Libi gorge high-steep anticline is systematically studied on four aspects, such as creation, reservoir, preservation and flow of coalbed methane. Compared content and the factors, main controlling factors and their controlling mechanism were studied. Main influencing factors of gas enrichment were found. The main influencing factors are coal seam thickness, depth, faults and FCd( coal rank), the main controlling factors is tectonic. The tectonic rebuilding generates changing of coal seam thickness, depth, permeability, coal mass structure, pore structure and stress and so on. Meanwhile, degree of coalification is promoted because of tectonic rebuilding in some locations..Mechanical property of rock is tested. Stress field is simulated in Libi gorge anticline. According to stress distribution, the cause and deformation of anticline, faults, and coal seam thickness is studied, the factors controlling mechanism is studied too.Fuzzy element method, a new evaluation method, is provided. Based on former research results, evaluation index system is established. The favorable exploration zone is predicted, and exploration condition of four zones are comprehensive assessmented.According to above results, suggestion of developing coalbed methane in Chongqing is put forward. There are close relations between coalbed methane enrichment and tectonic stress. Combined qualitative tectonic dynamics with quantitative rock mechanics, is a main research direction about coalbed methane in Chongqing. Drawing after reducing stress is favorable development method in the research area.