Quantitative Analysis Of Free Gas Occurrence Types In Coal Seams In The Permo-Carboniferous In Qinshui Basin

Coal Measure Strata in Qinshui Basin are rich in natural gas resources which provide material foundation for forming medium-large gas pools. Coal-formed gas in this region has experienced complex geological process such as generation, transportation, aggregation and losing which lead to the diversity of occurrence and the complexity of conditions of loss, accumulation, dissolution and diffusion. This project can not only enrich gas accumulation theory, but also establish the direct relationship between evaluation and selection of exploration target of natural gas, which are of great significance to the study of natural gas accumulation in Qinshui Basin. Besides, this project found theoretical principle for the achievement of reasonable co-mining of coalbed methane and free gas.This paper summarizes the occurrence states of coal-formed natural gas in Qinshui basin such as absorption state, free state and dissolved state and the law of mutual transformation between those states owing to pressure, temperature and tectonic movements; and the quantitative methods for natural gas migration and accumulation have got further improvement and development together with the guide of the theory of the dynamic balance of natural gas migration and accumulation, the quantitative research of accumulation of natural gas has been promoted, what is more, this paper also describes the trade-off relationship and dynamic evolution characteristics between "Gas Supply" and "Dissipation" in the process of gas accumulation. Through analyzing and summarizing the principle of natural gas migration together with the proper application of many geomathematical geology models such as Burial History model, Thermal History model, Hydrocarbon-Generating model, Hydrocarbon-Expulsion model, Adsorption model, Water-Dissolved gas model, Accumulation model, Fault-Lost model and Trap-Aggregation model, furthermore, we took on more elaborate numerical simulation which leads to strong pointed and practical achievement such as adsorption quantity, dissolved gas, gas diffusing amount, gas available for accumulation and history of trap resource quantity, which provide foundation for dynamic accumulation condition assessment.