Abstract
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)反射震測與海底迴聲剖面調查研究:本年度將在前緣海脊探勘好景區收集一組3維震測資料以及在台灣南部海域普查區進行2維震測調查,沿測線並收集海底迴聲剖面資料。此外,亦將結合長支距反射震測與OBS資料來建立永安海脊與前緣海脊天然氣水合物儲集層的速度構造剖面,以及利用逆時深度成像及深度移位建立深度構造剖面。(2)海底地震儀對天然氣水合物研究的應用:本年度將分別在台灣西南海域被動大陸邊緣與增積岩體區選擇在規劃鑽井井位附近收集來的海底地震儀進行分析,將各測站理論合成震波與海底地震儀觀測波形進行比對,推求含天然氣水合物地層的P波與S波速度、地層深度與厚度、以及天然氣水合物飽和度。(3)天然氣水合物賦存區流體移棲模式研究:本年度將利用上年度所建立的3維流體移棲模型研究經驗,建立在下枋寮峽谷、澎湖峽谷以及前緣海脊這3組3維震測調查區塊的流體移棲模式。(4)天然氣水合物賦存區之地熱調查:本年度將在台灣南部震測普查區與前緣海脊3維震測精查區分別進行地熱量測,利用地溫梯度與地熱資料推估天然氣水合物穩定帶的深度,並探討天然氣水合物的分布情形。(5)天然氣水合物賦存區之地層構造與沉積特徵研究:本年度將分析解釋上年度在台灣南部海域震測普查區所收集來的反射震測資料,以及進行本年度地球化學團隊岩心採樣的沉積學分析。(6)台灣西南海域海水與沉積物之地球化學組成:本年度將於恆春海域震測普查區進行系統普查工作,採集活塞沈積物與底水樣品;接著對岩心樣品進行岩性描述及基本物理性質分析;另進行沈積物與海洋底水之甲烷氣體分析,以瞭解該地區海床淺處甲烷氣體滲漏情形、及其氣體來源;以及對沈積物岩心樣品中之孔隙水進行地球化學成分分析,以瞭解流體組成、來源、及可能移棲方式。(7)台灣西南海域沉積物之磁學性質及年代研究:本年度將量測岩心沉積物的磁學性質、鑑定磁性礦物,期能有助於瞭解沉積物岩心樣品是否已受到與甲烷活動有關的還原作用;另對完整岩心樣品進行碳-14定年,以瞭解當地可能的沈積速率,有助於瞭解天然氣水合物的生成機制。(8)台灣西南海域沉積物自生礦物之電子顯微分析:對於MD MD178-10-3290和MD178-10-3291岩心特定標本,進行自生礦物高解析度電子顯微分析,以瞭解藍鐵礦產狀、化學組成及其與硫化鐵礦物之生成關係和可能延伸之意義。預期年度計畫完成後,對台灣南部海域普查區天然氣水合物之分布與特性能有進一步之了解;而對台灣西南海域之3維震測精查區及可能鑽井之探勘好景區之精查作業結果亦能提供鑽井井位評估所需之重要資訊。
Abstract: This proposal requests the 2nd 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 11 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 both 2D and 3D seismic reflection data and underway chirp sonar data in the reconnaissance survey area offshore southern Taiwan and in the gas hydrate prospects off SW Taiwan. In addition, joint velocity analyses from both large-offset seismic data and from ocean bottom seismometer (OBS) data will be performed to establish good velocity model along seismic profiles across the Yung-An Ridge and the Frontal Ridge gas hydrate prospects, and to use seismic imaging techniques to build seismic depth profiles. 2. Ocean bottom seismometer investigation. This sub-project will analyze seismic data recorded by OBSs near the potential future gas hydrate drilling sites to derive both P- and S- wave velocity information of the substrata, and to extract other important geophysical properties of the substrata, such as the thickness and the amount of gas hydrate saturation of the hydrate-bearing substrata. 3. Fluid migration modeling of the gas hydrate provinces. This sub-project will build 3D fluid migration models for 3 gas hydrate prospects where 3D seismic data have been collected, using heat flow, seismic and bathymetry data. This modeling approach will help us to better understand the properties of possible gas hydrate reservoirs. 4. Heat flow investigation of the gas hydrate province. This sub-project will conduct heat flow measurements in both the 2D seismic reconnaissance survey area offshore southern Taiwan and in the Frontal Ridge gas hydrate prospect. Geothermal data will be analyzed and interpreted to provide information regarding the gas hydrate stability zone and factors affecting geothermal structures, such as fluid flows and gas hydrates. 5. Stratigraphic analyses and sediment deposition characters of the gas hydrate prospects. This sub-project will interpret the 2D seismic data collected last year in the reconnaissance survey area offshore southern Taiwan, and also to conduct sedimentary analyses on the core samples collected this year in the reconnaissance survey area offshore southern Taiwan. 6. Geochemical composition of sea water and sediments offshore SW Taiwan. This sub-project will collect and analyze the sea water and seafloor sediment samples to understand various geochemical characters of gases in the sub-strata, and to establish fluid migration models based on the observations and analysis results. 7. Magnetic properties, age and microfossils of the sediments offshore SW Taiwan. This sub-project will measure the magnetic susceptibility, hysteresis curve, identify magnetic minerals and forams, and determine the carbon-14 ages of cored sediments. 8. Electronic microscopic analyses of authigenic minerals in the sediments offshore SW Taiwan. This study will carry out a high-resolution electron microscope study for authigenic minerals, specifically vivianite found in selected specimens of long piston cores MD178-10-3290 and MD178-10-3291.
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.
Keyword(s)
天然氣水合物
台灣西南海域
大陸邊緣
反射震測
海底地震儀
合成震波
天然氣水合物飽和度
海底仿擬反射
流體移棲
3維熱流模擬
地溫梯度
地熱量測
地層構造
沉積環境
冷泉
硫酸鹽還原
化學自營性生物
Gas hydrate
Offshore Southwestern Taiwan
Continental Margin
Seismic exploration
Ocean Bottom Seismometer
Synthetic Seismogram
Gas hydrate saturation
Bottom simulation reflector
fluid migration
3-dimentional heat flow modeling
Geothermal gradient