孔隙率及滲透率為評估儲集層油氣儲存量及二氧化碳封存重要的參數，因此，在CO2封存前必須對儲集層進行評估，為使評估更準確，對儲集層岩石特性的了解是相當重要的課題。砂岩孔隙率主要受控於岩石的組織 (粒度、淘選度)或是膠結作用而有所差異，而砂岩滲透率的大小則受到孔隙的連通性、孔隙幾何、孔隙型態、孔喉大小等因素所控制，為了瞭解儲集層砂岩孔隙率及滲透率異向性和砂岩特性之間的關係，本研究選用苗栗地區出磺坑背斜中新世至更新世的砂岩，以氦氣作為孔隙流體，利用高圍壓滲透/孔隙儀 (YOKO2)，量測圍壓3至60MPa下垂直與平行層面之氣體滲透率，探討砂岩滲透率異向性之差異，並利用偏光顯微鏡對樣本進行礦物成份及組織分析，另外也配合電子顯微鏡對砂岩進行微觀構造分析，辨別樣本中較微小的礦物、膠結作用和孔隙型態，最後進一步探討不同砂岩氣體滲流異向性、孔隙率、孔隙型態和砂岩特性之間的關聯性，以作為未來評估CCS於儲集層之參考。實驗結果顯示大部份樣本平行層面的滲透率大於垂直層面的滲透率，且滲透率異向性隨圍壓增加而增加。苗栗地區砂岩樣本孔隙型態主要是以巨孔中的原生孔隙為主，另外黏土礦物中也包含了微孔隙，次生孔隙含量較少，礦物組成主要以石英和岩屑為主，長石含量不高。利用偏光顯微鏡定量的巨孔孔隙率和滲透率的R2為0.78， 顯示滲透率值受到了砂岩中巨孔的影響。 Porosity and permeability are important assessment factors for CO2 sequestration in reservoir rocks. In order to improve the assessment, properties of reservoir rock are important and need to be evaluated in advance. Porosity of sandstone is controlled by texture and degree of cementation, whereas permeability is controlled by pore-throat size, pore type and connectivity of pore throat. Sandstones aged Miocene to Pliocene in Miaoli area, NW Taiwan, were collected in this study. YOKO2 porosity/permeability detector is used to measure their permeability perpendicular and parallel to bedding planes under 3 to 60MPa confining pressure with Helium as media. Optical microscope and scanning electron microscope (SEM) were then used to observe the mineral composition, lithology, texture and pore type of sandstones, so as to explore the influence of rock properties on porosity and anisotropy of permeability, as well as the storage potential for CO2 sequestration in the future. The experimental results show that most of the horizontal permeability exceeds the vertical permeability and the anisotropy increases with increasing confining pressure. Mineral composition of sandstones studied were mainly quartz and lithic with little feldspar content. The pore types were mainly primary megapores and micropores in this study. The correlation between macropores and permeability were stronger than that of total porosity and permeability, mainly due to total porosity contains micropores which contribute little to permeability.
