孔隙率與滲透率為評估煤層內流體流動性之重要參數，尤其滲透率異向性對於煤層氣開採扮演了重要的角色。本研究以室內試驗方法探討承受應力狀態下之滲透率異向性，並綜合煤層特性及微觀構造解釋孔隙率與滲透率之控制因素，據以提供未來針對煤層進行二氧化碳－強化採收煤層甲烷之評估。試體選用煤層甲烷蘊藏量相當高的澳洲Bowen與Sydney盆地之成熟度相近的煙煤，探討於承受不同圍壓（5~40MPa）下平行與垂直煤層層面之滲透率以及煤層特性與微觀構造對孔隙率與滲透率之影響。研究結果顯示，平行層面之煤樣滲透率約介於10-16~10-22m2，垂直煤樣層面滲透率約介於10-18~10-22m2，且承受不同圍壓下煤樣之滲透率異向比有明顯變化。以平行層面之煤樣為例，具有亮煤之煤樣滲透率約介於10-16~10-19m2，至於以暗煤為主者，其滲透率約介於10-19~10-22m2；此外，冪次律適用於表示有效圍壓與滲透率之關係，平行與垂直層面之初始滲透率分別介於1×10-12~6×10-19m2與5×10-16~1×10-21m2；初始孔隙率主要介於3.2~13.7%之間，且與滲透率呈現正相關，但趨勢較不明顯，推測受到煤岩成熟度、煤素質、煤岩類型、裂隙與割理之影響。以電子顯微鏡觀測發現富含惰煤素之暗煤結構不均勻導致滲透性差，而富含鏡煤素之亮煤具有均勻結構且利於割理發育，可提昇滲透性，利於煤層甲烷氣體回收，顯示煤岩類型之微觀構造為影響滲透率並導致滲透率異向性之主因。 Porosity and permeability of coal are important parameters for considering fluid flow properties through coal seams. Both porosity and permeability are affected by tectonic stress and coal characteristics, anisotropy of permeability also plays an important role on coal bed methane (CBM) recovery. This study tried to establish the relation among coal characteristics, porosity and permeability under confining pressure (5~40MPa). Eight bituminous coal samples with high CBM potential from Bowen and Sydney basin, Australia were examined in this study. The results indicate that permeabilities parallel to bedding varied from 10-16 to 10-22m2 whereas permeabilities perpendicular to bedding varied from 10-18 to 10-22m2. The lithotype of the samples is the most important factor in affecting their anisotropy of permeability. In addition, power law for describing the pressure-dependent permeability can be used to fit the experiment results. The initial permeability is ranging from 1×10-12~6×10-19m2 for parallel to bedding, and 5×10-16~1×10-21m2 for perpendicular to bedding. Porosity varied from 3.2~13.7%, positively correlated with permeability. Both porosity and permeability were affected by maturity, maceral and lithotype of coal, as well as cleat and/or microfractures. SEM showed that the high permeability coals were mostly bright-banded coals (rich in vitrinite) with well-developed cleats. These results indicate that bright coal possesses the best potential for gas transmission, in considering CO2-ECBM.
