| Summary: | 碩士 === 國立成功大學 === 資源工程學系碩博士班 === 101 === The coalbed methane reservoirs (CBM) are adsorbed with a lage amount of natural gas and characterized by dual porosity system, and the production mechanisms are dominated by desorption, diffusion and natural fracture flow. Therefore, the CBM transient pressure behaviors will be affected by dual porosity system and production mechanisms. The purposes of this research are to study transient pressure behaviors affected by desorption and diffusion mechanisms in CBM. To analyze the transient pressure data, the methods used include A-E analytical method, Gerami type curve, A-G type curve, traditional well test method and nature fracture well test method.
The results show that A-E analytical method is most appropriate to analyze CBM transient pressure data, and the nature fracture permeability, nature fracture porosity, Langmuir volume constant and sorption time constant can be obtained. In order to estimate sorption time constant, the sorption time criteria ( )is developed in this study.
If only want to estimate the nature fracture permeability simply without considering dual porosity system and desorption and diffusion mechanisms in CBM reservoir, the traditional well test method would be an effective method.
In the study of production and pressure behavior of CBM two-phase reservoir, in initial condition, the pores of fracture are always filled with water. As the reservoir pressure decreases, water in pores of fracture is drained out to the wellbore. As the result, adsorbed gas is released and diffuses to nature fracture, and there will be an inclined trend of gas production rate. As the CBM reservoir depleted gradually, there will be a declined trend of gas production rate.
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