| 摘要: | 二氧化碳地質封存是將二氧化碳灌注至地下岩層，藉由物理和化學的機制將其封存在地層中。灌注之二氧化碳可能與岩石中之礦物產生溶蝕或礦化反應，因此了解地層的礦物組成，有助於釐清二氧化碳在岩石中可能的化學反應機制。本研究樣本採集自台灣中部的苗栗明德水庫剖面、台中大甲溪與草湖溪剖面，採樣地層由老至新分別為東坑層、上福基砂岩、桂竹林層 (關刀山砂岩段、十六份頁岩段、魚藤坪砂岩段)、錦水頁岩及卓蘭層。利用岩象分析及X光繞射分析檢測潛在二氧化碳封存層及蓋層之礦物組成。 砂岩岩象分析結果顯示地層中主要礦物皆為石英，其中又以上福基砂岩的石英含量最高；其次為長石，以東坑層與上福基砂岩最多；岩屑含量以錦水頁岩與卓蘭層較多。次要礦物包括雲母、綠泥石、碳酸鹽類礦物與含鐵不透光礦物。東坑層、上福基砂岩、關刀山砂岩段底部與魚藤坪砂岩中段之樣本的孔隙填充物以基質為主，且含有較多孔隙；而關刀山砂岩含有相當多的膠結物，孔隙比例很低。全岩X光粉末繞射分析結果顯示主要礦物相為石英、正長石、微斜長石、斜長石、方解石、白雲石、伊萊石、高嶺石與綠泥石。黏土礦物則以伊萊石為主，唯上福基砂岩含量相對較低；其次為綠泥石，幾乎所有地層皆含有綠泥石，唯上福基砂岩含量較低；高嶺石以東坑層、上福基砂岩與魚藤坪砂岩段含量較高；膨脹性黏土礦物含量一般相當低，其中東坑層與上福基砂岩幾乎不含膨脹性黏土礦物。 地層中與二氧化碳封存之礦化機制相關的主要礦物包括長石、碳酸鹽類礦物與綠泥石，由於這些礦物普遍分布於所有地層當中，所以合併孔隙率與封存穩定性來討論。東坑層、上福基砂岩與魚藤坪砂岩中段具有較多的孔隙，可做為主要灌注目標層，而錦水頁岩可以做為主要的蓋層。封存層中東坑層、上福基砂岩與魚藤坪砂岩中段具有較少的碳酸鹽類礦物，可以提供較穩定的封存環境。而關刀山砂岩段含有大量的碳酸鹽類礦物，在灌注二氧化碳初期可能造成碳酸鹽類礦物大量溶蝕影響封存層的穩定性。桂竹林層含有大量的層間頁岩具有短期阻擋二氧化碳往上移棲之效益，延長移棲時間並增加與周圍礦物反應的機會。另外，由於封存深度較淺，主要次生的礦物可能會以碳酸鹽類礦物為主，而矽鋁黏土礦物則需要較長的時間才有機會生長。 另一方面，礦物組成變化是受到地體構造與來源區的影響。砂岩岩象結果顯示以石英與長石為主、岩屑含量低的東坑層與上福基砂岩來源區是屬於來自大陸華南地區 (穩定大陸地塊)；相反的含有大量岩屑的卓蘭層則是以造山帶為沉積物主要來源區。根據古水流方向顯示桂竹林層時期的沉積物來自西方，表示主要來源區為大陸華南地區。地層中的砂岩與泥岩岩屑可能來自於受到造山帶荷重影響而抬升的前陸前凸起，使得關刀山砂岩段與魚藤坪砂岩段之母岩區地體構造分類偏向於造山帶沉積物。黏土礦物含量顯示，錦水頁岩以後伊萊石含量逐漸增加，表示來源區有造山帶變質岩出露。綠泥石則是不論來自大陸華南地區或是台灣造山帶皆有穩定的供給量，因此維持著穩定的含量。高嶺石主要來源是大陸華南地區花崗岩受風化後的產物，因此以大陸地區為主要來源區的東坑層與上福基砂岩含有大量的高嶺石，相反以造山帶為主要來源區的錦水頁岩與卓蘭層含量偏低。此外，高嶺石亦具有越靠近陸源含量越高的現象，可能影響魚藤坪砂岩段的高嶺石含量相對高於十六份頁岩與關刀山砂岩段。膨脹性黏土礦物含量變化與地層深埋深度無關聯，表示研究地層尚未受到明顯成岩作用的影響。 The geological storage of CO2 is a means that stores CO2 in deep porous rocks with CO2 trapped by physical and chemical processes. Injected CO2 may react with minerals in the host rocks, resulting in mineral dissolution or mineralization. In order to understand possible chemical reactions between CO2 and rocks, one needs to characterize the mineral contents of CO2 reservoirs and caprocks. Mineralogy of reservoir and seal rocks are characterized by petrographic studies and X-ray diffraction (XRD) analyses. Studied samples are collected from three stratigraphic sections of Ming-Der Dam, Tachiachi and Tsaohuchi, in central Taiwan. Those samples are from six stratigraphic units of Tungkeng Formation, Sangfuchi Sandstone, Kuantaoshan Sandstone, Shihliufen Shale, Yutenping Sandstone, Chinshui Shale and Cholan Formation, in a stratigraphically ascending order. Predominant minerals in sandstone are quartz, feldspar and rock fragments. According to petrographic analysis, Many pores in sandstones are filled with cements for Kuantaoshan Sandstone, Yutenping Sandstone and lower part of Cholan Formation, but more open pores are found in the Tungkeng Formation, Sangfuchi Sandstone, lower part of the Kuantaoshan Sandstone and middle part of the Yutenping Sandstone. The results of whole rock XRD analyses show that main minerals in samples are quartz, orthoclase, microcline, plagioclase, calcite, dolomite, illite, kaolinite and chlorite. Dominant clay mineral is illite except for the Sangfuchi Sandstone. Chlorite is also common found in studied samples. Kaolinite is the most abundant clay mineral in Tungkeng Formation and Sangfuchi Sandstone. Smectite and mixed layered minerals are rarely found in whole studied samples. Results of this study shows that there are high porosity for the Tungkeng Formation, Sangfuchi Sandstone, lower part of th Kuantaoshan Sandstone and middle part of the Yutenping Sandstone. They may serve as good CO2 reservoirs. Chinshui Shale may serves as main caprocks. Sandstones of the Tungkeng Formation, Sangfuchi Sandstone and middle part of the Yutenping Sandstone consist of minor amount of carbonate minerals, serving as stable reservoirs for CO2 geosequestration. Predominant minerals in sandstones of the Tungkeng Formation and Sangfuchi Sandstone are quartz and feldspar with rare rock fragments, indicating that tectonic setting of source terranes are of South China continental block affinity. Abundant rock fragments in the Cholan Formation indicate that sediments were derived from Taiwan mountain belt. |
