摘要:本計畫為執行中央地質調查所推動之4年期「天然氣水合物資源潛能調查:震測、地熱及地球化學調查」工作,以震測、地熱以及地球化學等探測技術及分析方法在台灣南部與西南海域進行天然氣水合物之調查與探勘研究,一以了解台灣南部過去未曾進行過天然氣水合物調查的海域中是否亦有天然氣水合物的資源潛能,二則以過去在台灣西南海域天然氣水合物調查的成果為基礎,在擇定的探勘好景區內進行天然氣水合物儲集層之資源特性調查。為達成計畫目標,本計畫結合了過去執行中央地質調查所天然氣水合物調查計畫中地球物理與地質、地球化學團隊成員,組成一堅強的調查分析團隊來執行此計畫。除了總計畫負責整個計畫之規劃、協調工作以及維護與擴充天然氣水合物資料庫外,另有8 個分項計畫:
(1)反射震測與海底回聲剖面調查研究:本年度將針對101與102年度2維震測調查區域中海底仿擬反射較明顯的區域,進行2維震測調查加密測線分布,並沿測線收集海底回聲剖面資料,期能於臺灣南部海域開發新的探勘好景區。此外,亦將重點放在整合分析過去幾期以來收集的2維、3維反射震測、底質剖面及海底仿擬反射等資料,配合各分項計畫成果,針對各探勘好景區進行評估,嘗試建立天然氣水合物可能的流體移棲系統。(2)海底地震儀對天然氣水合物研究的應用:子計畫於103年度研究成果中發現在活動大陸邊緣永安海脊,及被動大陸邊緣福爾摩沙海脊二區域具有較淺的BSR分布,可做為未來進行淺層鑽探的目標井位之一。因此本子計畫規劃於104年度以上述二海脊為研究區域,整合過去幾期各子計畫在研究區域得到的水深、海床水溫、壓力、地熱梯度、孔隙水鹽度、氣體供應與組成等資料,結合海底地震儀(OBS)過去得到的速度構造與多頻道震測(MCS)成果,探討天然氣水合物穩定帶(GHSZ)厚度與深度的空間分布特性。(3)天然氣水合物賦存區流體移棲模式研究:本年度預計將指標海脊之3維溫度場模擬解釋完成外,並運用震測取得的速度資訊將海底仿擬反射觀測溫度場成果進行更新,以期得到溫度場差異解釋更佳貼近真實化。並且,本年度會將歷年來流體移棲研究(1維、2維、3維)成果,配合區域地質及其他研究,進行整合性的分析討論。(4)天然氣水合物賦存區之地熱調查:將整編臺灣西南海域所有地熱測量資料,完成BGHS深度、地溫梯度、熱導係數等資料分析,並比較地熱實測與震測BSR導出之地溫梯度差異性,以探討BGHS與BSR深度之關係,了解未來預計鑽井區之地熱特徵。(5)天然氣水合物賦存區之地層構造與沈積特徵研究:本年度將彙整過去2012~2015年所收集的震測資料,彙編研究區域的構造與BSR的分布,以了解恆春南部海域地體構造與沉積環境的演化,同時整合地質與地物資料,提出恆春南部海域天然氣水合物成藏系統,並評估天然氣資源量。(6)台灣西南海域海水與沈積物之地球化學組成:本年度計畫主要工作擬包括:(i)於102及103年的調查區域再進行調查並予以地質地化分析。(ii)對101年度至104年度所有航次岩心的結果有所整理與討論。期能更深入瞭解與探討台灣西南海域不同大地構造區域深部沉積物地質地化特徵之區域與垂直(時序)變化,及其與甲烷移棲和天然氣水合物賦存之關係。本計畫主要將102及103年的調查研究成果總報告,結合今年的各項地質地化分析資料,並與地物及底拖團隊共同評估台灣西南海域天然氣水合物最佳賦存區域及甲烷移棲模式。(7)臺灣西南海域沉積物之磁學性質及年代研究(綜論):本年度將彙整2015年及2015年之前所有台灣西南海域所收集岩心之磁學性質與年代資料,包括磁感率、磁滯曲線磁性參數、磁性礦物、碳-14定年,藉以彰顯在各不同天然氣水合物探勘區域內沉積物受到甲烷活動而還原的程度。(8)臺灣西南海域沈積物自生礦物之電子顯微分析:本計畫擬針對臺灣西南海域岩心含有酸可萃取硫化物或相關硫化鐵礦物之特定標本進行高解析度電子顯微分析,以瞭解酸可萃取硫化物相關礦物之產狀特徵及其與其他硫化鐵礦物之生成關係和可能延伸之意義,著重與天然氣水合物賦存及解離之可能關聯性。另並總結論述本期四年計畫自生礦物電子顯微分析研究成果,探討西南海域相關自生礦物之生成模式及其與天然氣水合物賦存或解離延伸冷泉作用之可能關聯性。
Abstract: This proposal requests the 4rd year support of the 4-year gas hydrate project entitled“Investigation of Gas Hydrate Resource Potential: Seismic, Heat Flow and Geochemical Studies”. Seismic, heat flow and geochemical investigations will be carried out in the area offshore south and southwestern Taiwan with 2 purposes in mind: 1. To explore the areas where no gas hydrate investigation has been conducted before to see if there are gas hydrate energy potentials existed in those areas; 2. To investigate potential gas hydrate reservoir characteristics in the gas hydrate prospects delineated in the previous gas hydrate investigation projects of the Central Geological Survey (CGS). To achieve these goals, a team which consists of 10 scientists/researchers has been formed to carry out this project. The team members are experts in gas hydrate research and all have been involved in the previous gas hydrate investigation projects of CGS. Based on the needs of applying various investigation techniques and approaches, this project will be carried out by one master project and 8 sub-projects. The master project is responsible for the project planning and coordination among different sub-projects, also to maintain and continuous developments of the gas hydrate database. The 8 sub-projects and their respective roles in this project are described below: 1. Seismic reflection and chirp sonar investigations. This sub-project will collect 2D seismic reflection data and underway chirp sonar data in the previous survey area during 2012~2013 offshore southern Taiwan, especially in the area of clear bottom simulating reflectors (BSRs), and try to find new gas-hydrate prospects. In addition, this sub-project will focus on evaluating each gas-hydrate prospect by integrating previous data such as 2D and 3D seismic data, chirp sonar data, BSR etc., and comparing with the analysis results by another sub-projects. The integration will be performed to establish possible fluid migration system of gas hydrate in each prospect. 2. Ocean bottom seismometer investigation. The results of this sub-project in last year showed shallow BSR sub-bottom depths both in the area of Yung-An Ridge in active continental margin and Formosa Ridge in passive continental margin. The shallow BSR sub-bottom depth may suggest as targets for gas hydrate drilling sites in the shallow area. In this year, based on the two ridges mentioned above as study area, this sub-project will try to discuss the spatial distribution of the depths and thickness of gas hydrate stability zone by integrating the result of OBS and MCS data with water depths, water temperatures above seafloor, pressure, thermo-gradient, salinity of pore water, gas composition and supply which collected by several sub-projects in the past years. 3. Fluid migration modeling of the gas hydrate provinces. This sub-project plans to update our BSR-based temperature field from seismic velocity, and study the thermal structures and fluid migration patterns of the Pointer Ridge site using the 3D method we have developed in the last two years. For each gas hydrate proposed drill site, we will integrate our previous results from 1D, 2D, and 3D modeling, then propose a general model to discuss the different fluid migration patterns between the active and passive margin. 4. The goals of heat flow investment sub-project will integrate all heat flow measurements off SW Taiwan. It included the accomplishment of the data analysis, such as BGHS, thermal gradients and thermal conductivity. The heat flow characters on the proposed drilling sites could also be obtained by the comparisons of the BGHS, BSR and the related thermal gradients. 5. Stratigraphic analyses and sedimentary characteristics of the gas hydrate prospects. This sub-project will try to understand the evolution of tectonic architectures and sedimentary environments from interpretation of structure features and BSR distribution in the study area by integrating seismic data collected during the cruises of year 2012~2015. This sub-project will also suggest possible gas-hydrate petroluem system and resource assessment by summerizing geological and geophysical data. 6. Geochemical composition of sea water and sediments offshore SW Taiwan. Major works of this project in 2015 include: (1) continue the geological and geochemical survey in the area of year 2013 & 2014; (2) integrate the results of year 2012 to 2014 with those results obtained in this year. Analyzing cores retrieved in 2015 will be our target of this year. Major objectives of this project is to understand the source and spatial and temporal variation of methane and migration and, subsequently, to constrain the major geochemical processes which controll the geochemical characteristics in this area. 7. Magnetic properties and carbon-14 ages of sediments offshore SW Taiwan (a synthesis): this sub-project will integrate all data of magnetic susceptibility, hysteresis property, magnetic mineralogy and carbon-14 age of cores offshore SW Taiwan collected in 2015 and prior to 2015 to characterize their reducing extents related to methane activities in different gas hydrate prospected areas. 8. Electronic microscopic analyses of authigenic minerals in the sediments offshore SW Taiwan.This study plans to carry out a high-resolution electron microscope study for acid volatile sulfide (AVS) materials and/or related iron-sulfide minerals in selected samples cored from sediments off southwestern Taiwan. The results obtained in the past three years and 2015 will be summarized and discussed, especially in the context of gas-hydrate dissociation and/or cold-seep processes.
Overall, this project will continue to investigate and to better define the gas hydrate prospects in the area offshore SW Taiwan for energy resource potential evaluation, and to prepare for future drilling investigation. Also, this project will survey other areas offshore southern Taiwan to find new gas hydrate prospects.