盆地尺度二氧化碳地質封存有效儲存量評估與 安全情境模型建置-以台西盆地為例

Abstract

對二氧化碳鹽水層地質封存發展計畫而言，一個具有足夠儲存容量之安全地質空間是至關重要的。有鑑於此，本論文認為有必要進行更深入的研究課題，包括：1.一個盆地尺度實體的三維地質模型建置方法，2.在地下深鹽水層內有效且實用的二氧化碳儲存量評估方法，3.在鹽水層內二氧化碳注入安全數值模型之模擬。此亦成為本論文研究之三個主要目標。 本文以台灣西部台西盆地為例，探究在盆地尺度下，二氧化碳地質儲存於盆地內鹽水層之安全所需規範。針對目標地質封存地層組設定4個安全門檻條件，包括：1.儲集層之安全頂部/底部深度介於900 m/3,000 m間，2.蓋層所需之安全厚度需大於40 m，3.排除距離陸上活動斷層小於5公里範圍，4.排除可能切過蓋層之下伏斷層。有關在台西盆地內可利用之區域範圍與儲存容量之總體積，針對兩個選定可確保安全與有效碳封存的地層組合（如錦水層/桂竹林層組合、打鹿層/北寮層組合），進行地質資料之全面蒐集。 利用體積估算法，分別對兩個選定的封存地層組，進行地下儲集層之有效的二氧化碳儲存量計算。更進一步，使用GIS繪圖技術配置蓋層之安全區域範圍，並劃定儲集層之安全厚度，進行深鹽水層之有效的體積計算。本研究通過可利用之區域設定範圍，蒐集區域周圍與地下所有相關目標層之等厚度(深度等高線)圖，建置完成可利用區域之三維地質模型。 在三維地質模型中，對每一選定封存地層組合給予體積估算法經驗公式需要之所有參數值，就可計算出概略之有效儲存量。在本研究中推估可利用之區域範圍有效的二氧化碳儲存量，錦水層/桂竹林層組大約是8.7×109噸（87億噸）；打鹿層/北寮層組大約是3.8×109噸（38億噸）。 利用在台中大坑地區從候選封存層由鑽孔岩心取樣，取得多孔隙砂岩試體，透過二相流試驗，求得相對滲透率與飽和度(K-S)曲線。K-S曲線為控制深部鹽水層地質封存可行性之關鍵輸入參數。在岩心滲流試驗過程中，採用沖排法以定流量注入超臨界二氧化碳，成功建立試驗流程及相對應之試驗分析方法。由成果顯示，直接從二相流排水循環測試結果獲得之K-S曲線，可提供數值模擬研究必要的輸入參數。為提高其可靠性與實際情況之適用性，更進一步利用電腦程式(如TOUGH2)進行歷史匹配過程以校正輸入參數。 本研究認為在一個定義完整之三維地質模型內，進行儲集層相關的二氧化碳注入，可作有效與實用之儲存量確認。透過數值模擬情境分析研究，安全儲存空間最佳化利用之關鍵問題得以評估，包括：1.可利用區域內注入井最佳數目之研究，2.在多口井配置情況下可注入總量之研究，3.在注入儲集層內壓力增量之研究。 對於台西盆地二氧化碳地質封存安全情境之數值模擬，係採用PetraSim/TOUGH2套裝軟體進行。該數值模型不僅可提供關於模擬二氧化碳團塊移棲路徑研判之重要資訊，並可對工程階段布井設計可行性，進行工程情境分析研究。模擬中大部分之關鍵輸入參數，係參考使用一些實際試驗與經驗數據，包括以往採樣岩心之研究數據，與在鄰近台西盆地地區台灣中油公司石油和天然氣勘探之井測結果。

A safe geological space with enough storage capacity is vital to the carbon geo-sequestration development program. Intensive studies for 1.building-up a realistic basin-scale 3-D geological model, 2.assessing the effective and practical carbon dioxide storage capacity in the underground saline aquifer, 3.the numerical modeling for simulating CO2 injecting safety within the aquifer are deemed necessary and become the three main objectives of this thesis study. Using Taihsi Basin in the western Taiwan as a example, the safety criterion for CO2 geological storage in saline aquifers is set for target geo-sequestration groups with four threshold condition including: 1.Safe top/bottom (900 m/3,000 m) depth of storage reservoirs, 2.Safe thickness (40 m) of cap rock, 3.Excluding area with unsafe distance (<5 km) from on-shore active faults, 4.Excluding underlying pre-existing faults cutting through cap rock. Within Taihsi Basin, the areal extent of the Area of Interest (AOI) and total volume of storage capacity had been further revised towards two selected sequestration groups (e.g. Chinshui Fm./Kueichulin Fm. Group and Talu Fm./Peiliao Fm. Group) in which the safe and effective carbon sequestration can be ensured. Effective carbon dioxide storage capacity in the underground aquifers is estimated by volumetric estimating method respectively for two selected Sequestration Groups. Moreover, Effective volume of the deep saline aquifers has been estimated using the GIS graphic skill to allocate the safe areal extent of the cap rock and delineate the safe thickness of storage (reservoir) rock stratum. Generation of 3-D geological Model has been made possible by collecting the isopatch (depth contour) maps for all relevant target Formations surrounding and underlying the study area. The CO2 storage capacity for each selected sequestration Group in the 3-D model can be calculated by giving all the parametric values required in the empirical formula involved in a volumetric estimating method. In this study, this effective storage capacity calculated for Chinshui Fm./Kueichulin Fm. Group is around 8.7×109 tons (8.7 Giga-tons), while the effective storage capacity for Talu Fm./Peiliao Fm. Group is around 3.8×109 tons (3.8 Giga-tons). Relevant permeability vs. saturation (K-S) curves for porous sandstone cores sampled from a candidate reservoir rocks had been obtained in the Takeng area of Taichung. The K-S curves are regarded as critical input parameters controlling the feasibility of geo-sequestration in a deep saline aquifer. A two-phase flow or core-flooding test process using the displacement method with constant flow injection has been successfully established with corresponding tests successfully carried out. It has been also shown that K-S curves obtained directly from the test results in the drainage cycle can provide essential inputs for numerical simulation study. To enhance their reliability and real-world applicability, the input parameters should be calibrated by history match processes using computer code, e.g. TOUGH2. It has been noted that effective and practical storage capacity can be recognized in a well defined 3-D geological model contained aquifers (reservoirs) with relevant CO2 injectivity. Key issues regarding the optimally utilization of safe reservoir space are investigated, including 1.Study of the optimal number of injection wells, 2.Study of total injectable amount under a multi-well configuration, and 3.Study of pressure build up within the injected aquifer. Numerical modeling regarding safety scenarios for carbon geo-sequestration within the Taihsi Basin had been conducted by PetraSim simulator. The modeling can provide not only crucial information regarding the simulated plume migration path, but also the scenarios analysis to design sophisticated plan for engineering feasibility study. Most of the key input parameters used in the simulation is borrowed from some empirical data including pre-existing rock core investigation data and well logging results from local oil and gas exploration by CPC Corporation, Taiwan adjacent to the Taihsi Basin.