選擇適當的二氧化碳封存場址，為執行二氧化碳地下封存重要步驟。挑選適合場址時需考慮合宜的地質條件與二氧化碳灌注後的傳輸特性。本研究為探討上述兩項問題，利用地下地質與地物資料以及二氧化碳三維傳輸模擬，評估二氧化碳封存場址之地質條件合適性。 由震測與鑽井資料顯示，桃園台地，有厚約450公尺的高孔隙率砂岩(南莊層及桂竹林層)，其頂部約位於1000公尺深，可成為良好的二氧化碳儲集層。儲集層上覆約100公尺厚的低滲透率泥質蓋層(錦水頁岩)。岩層由西北往東南方向加深，地層傾角約1度。此區域內斷層皆未切穿地表與海床，有良好的儲集層與蓋岩配對，且儲集層深度適中，是一適宜的鹽水層二氧化碳封存場址。本研究並利用蒙地卡羅模擬法，計算出桃園台地及其相鄰海域二氧化碳封存量最可能為49億噸。 本研究建立三維地質模型，配合適當參數，利用三維有限元素法，進行二氧化碳灌注後的傳輸模擬。模擬結果顯示二氧化碳灌注初期，因浮力作用，而使二氧化碳向上移棲，但被蓋層所封阻，不易逸散至地表。又因地層往東南方傾斜的關係，二氧化碳往西北方向移棲。灌注後期，大量二氧化碳與地下鹽水反應並溶入鹽水中，使地層水密度增加，向下流動，增加二氧化碳的封存率。研究結果顯示桃園台地濱海區下方南莊層與桂竹林層為良好的二氧化碳封存場址，灌注後的二氧化碳將往台灣海峽(西北方向)移棲。Geological features and transport characteristics for CO2-rich fluids in porous media are two major factors that must be carefully evaluated when selecting sites for CO2 geosequestration. We use well logs, reflection seismic data and simulation on CO2-rich fluid to assess and suitable sites for CO2 geologic storage in NW Taiwan. In Taoyuan Tableland and its adjacent offshore, Nanchuang Formation and Kueichulin Formation are good CO2 reservoirs as they contain multiple layers of high-porosity sandstones with their formation top lying slightly deeper than 1000 m. Those porous sandstones are capped by thick Chinshui Shale (around 100-150 m thick) of low permeability rocks that inhibit CO2 from leaking to surface. This area is characterized by a gently sloping (~1°) and SE-dipping surface with little faulting and seismicity. The most likely CO2 storage capacity in this region is around 4,900 megatons as estimated by Monte Carlo simulation. We use finite element method to simulate the transport characteristics for CO2-bearing fluid or plume in 3D after CO2 is injected in geologic media. Simulation results show that in the early stage, CO2 plume migrate upward due to buoyancy until it reaches the base of thick and the low-permeability shale (i.e. the Chinshui shale). The CO2 plume then migrates in a northwest direction opposite to its stratal dip direction and along the top of CO2 reservoirs (i.e. the Kueichulin Formation). The amount of dissolved carbon dioxide increases with increasing time, leading to a density increase for the formation brine with dissolved CO2. The heavier CO2-bearing brine will following sink to a deeper level, preventing CO2 from leaking to shallow subsurface or to the atmosphere. Our results indicate that the coastal zone along the Taoyuan Tableland is suitable for CO2 geologic storage in terms of geological criteria. The injected CO2 will migrate toward the Taiwan Strait in the west and along the deeper CO2 reservoir but not toward the onshore urban area in the east.
