應用三維反射震測技術調查台灣西南海域天然氣水合物系統

Applying 3D Seismic Technique for Gas Hydrate Investigation Offshore Southwestern Taiwan

廖士瑋(Shih-Wei Liao)

指導教授 ： 劉家瑄

國立臺灣大學/理學院/海洋研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.00285

摘要

天然氣水合物做為新型態的化石能源，擁有極大的潛力而廣為人注意。近年來，利用反射震測於台灣西南海域已發現大量的海底仿擬反射 (bottom simulating reflector, BSR)存在，此一訊號被認為是天然氣水合物存在的重要指標。但是過去的調查皆為大範圍的普查，並未有針對特定區域進行天然氣水合物的空間分析。本研究係針對此一課題，利用高解析度之二維及新整編之三維反射震測資料來進行探討。
研究區域位於台灣西南海域永安海脊。在這個區域，清楚且連續的BSR幾乎覆蓋整個研究範圍。本研究分別利用2004年及2008年所收集的三筆高解析度二維多頻道反射震測資料，將之重新整併成一筆三維反射震測資料。其中，東西方向測線可劃分為92條，測線間距為100公尺；南北方向可畫分為1,431條，測線間距為12.5公尺，資料含蓋範圍約180平方公里。本研究期望能利用三維震測資料在空間分析的優點，對永安海脊的天然氣水合物分布及流體移棲的模式有更深入的研究。
根據三維BSR的分布、反射訊號特徵與地形，我們將研究地區由西至東分為澎湖峽谷區、埋藏水道區、永安海脊、斜坡盆地西緣及盆地東緣等五個區段。天然氣水合物主要集中於埋藏水道區、永安海脊東翼、斜坡盆地西緣，其中又以永安海脊東翼與斜坡盆地西緣相鄰的地區BSR訊號最為連續且分布範圍最廣。而埋藏水道區以其良好的孔隙率和較為水平的地層而擁有最大範圍與最厚的游離氣層。此五個區段的水合物相關反射特徵各自受到不同的流體移棲機制影響，又可歸類構造活動、沉積作用兩種機制，兩種機制可能同時存在且互相影響。

關鍵字

三維反射震測 ； 天然氣水合物 ； 永安海脊

並列摘要

Gas hydrate as a potential new energy resource has been noticed worldwide in recent years. However, rapid dissociation of gas hydrate may cause serious environment problems such as submarine landslides and global warming. Offshore southwestern Taiwan, clear bottom simulating reflector (BSRs) and strong reflection amplitude anomalies have frequently been observed on 2D seismic profiles. In this study, we try to get detail in a small area by 3D seismic techniques.
The study area is located in the southern part of the Yung-An Ridge and adjacent slope basins offshore southwestern Taiwan. The 3D seismic data were collected using a single source and single streamer (thus, a 2D seismic system) shooting in E-W direction across the survey area with line spacing as close as 100 m. We built a 3D geometry from these closely spaced 2D seismic profiles. The 3D data volume contains 92 E-W trending in-lines with 100 m spacing, and 1431 N-S trending crosslines with 12.5 m spacing, the 3D volume covers an area about 180 km2.
From this 3D data volume, we can see that BSR appears almost throughout the entire study area. Base on the seismic characteristics typically associated with gas hydrate and structures and sedimentary features, we separate the study area into 5 small zones. They are from west to east, the Penghu canyon, the buried channel area, the Yung-An ridge, the western part of the intra-slope basin, and the eastern part of the intra-slope basin. Each zone has it own fluid migration mechanism, and all mechanisms are controlled by either structure associated or sedimentary processes.

並列關鍵字

3-D seismic ； Gas hydrate ； Yung-An ridge

參考文獻

林哲銓，2005，台灣西南海域含天然氣水合物地層之構造架構與沈積特徵。國立中央大學地球物理研究所碩士論文，145-146頁。

陳冠宇，2006，台灣西南外海之構造與地形特徵及澎湖海底峽谷演化。國立中央大學地球物理研究所碩士論文，99-102頁。

Chiang, C. S., and H. S. Yu, 2006, Morphotectonics and incision of the Kaoping submarine canyon, SW Taiwan orogenic wedge: Geomorphology, v. 80, p. 199-213.

Chuang, P., T. F. Yang, S. Lin, H. Lee, T. F. Lan, W. Hong, C. Liu, J. Chen, and Y. Wang, 2006, Extremely high methane concentration in bottom water and cored sediments from offshore southwestern Taiwan: Terrestrial, Atmospheric and Oceanic Sciences, v. 17, p. 903.

Ewing, J. I., and C. H. Hollister, 1972, Regional aspects of deep sea drilling in the western North Atlantic: Initial Reports of the Deep Sea Drilling Project, v. 11, p. 951-973.