煤層氣地層為煤層中吸附著大量的天然氣。因為煤層氣地層特性為雙孔隙地層，且其生產機制包含有吸脫附、擴散及自然裂縫的達西流動。所以，煤層氣地層的暫態壓力行為與其地層特性及生產機制（吸脫附及擴散機制）相關。本研究目的是分析煤層氣地層在生產時的暫態壓力行為，以及研究暫態壓力資料而估算地層參數。所使用的暫態壓力分析方法，包含A-E解析法、Gerami典型曲線分析法、A-G典型曲線分析法、傳統均質地層暫態壓力分析法以及自然裂縫地層暫態壓力分析法。所估算的地層參數包含自然裂縫滲透率、自然裂縫孔隙率、Langmuir體積常數、擴散時間常數以及膚表因子。
由分析結果顯示，若使用各種暫態壓力分析方法分析煤層氣地層暫態壓力，A-E解析法，最適合分析煤層氣地層暫態壓力資料。若推求煤層氣地層參數，可估算出自然裂縫滲透率、自然裂縫孔隙率、Langmuir體積常數以及擴散時間常數。其中，本研究對Anbarci and Ertekin（1991）在A-E解析法中推求擴散時間常數的概念進行量化，而建立新的擴散時間準則（ΔpD≤ 0.12），可準確估算擴散時間常數。
若僅要簡單的推求煤層氣地層的自然裂縫滲透率，而不考慮地層中複雜的雙孔隙地層以及生產機制，使用傳統均質地層暫態壓力分析法進行煤層氣地層暫態壓力分析，即可得到良好的結果。
由於煤層氣地層的自然裂縫在初始狀況，一般皆充滿著水。因此，煤層氣地層在生產前期，首先會進行抽水降壓。當地層壓力逐漸下降，煤層氣會從煤基中脫附出來，並擴散到自然裂縫之中，最後再流到生產井進行生產，因此煤層氣產率會有逐漸增加的趨勢，此時可稱之為煤層氣的上升階段。當煤層氣產率逐漸上升到生產曲線的頂峰，而後隨著煤層氣的不斷生產，地層逐漸耗竭，而使地層壓力逐漸下降。此時，煤層氣產率也會逐漸下降，此階段則為煤層氣的下降階段。

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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