台灣西南外海多頻道震測之甲烷水合物與海洋精細構造成像研究; Multi-channel Seismic Study For Imaging Gas Hydrate and Ocean Fine Structures Offshore Southwest Taiwan

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题名:	台灣西南外海多頻道震測之甲烷水合物與海洋精細構造成像研究;Multi-channel Seismic Study For Imaging Gas Hydrate and Ocean Fine Structures Offshore Southwest Taiwan
作者:	羅薇雅
贡献者:	地球科學學系
关键词:	多頻道震測;海底仿擬反射;甲烷水合物;海洋精細構造;成像;MCS;BSR;Gas Hydrate;Ocean Fine Structure;Imaging
日期:	2013-07-30
上传时间:	2013-08-22 11:43:10 (UTC+8)
出版者:	國立中央大學
摘要:	自從2004年起，中央地質調查所持續針對台灣西南外海進行甲烷水合物的勘探與調查。本研究針對其多頻道震測資料同時進行海床下沉積與海水柱的構造成像，以探討西南外海處甲烷水合物的空間分布與其所富含甲烷水合物的潛能以及大尺度的海水的精細構造特徵，並建立甲烷水合物之沉積系統。甲烷水合物調查中，本研究主要著重於確定與標定海床下海底仿擬反射之空間分布為主，並同時偵測沿著震測測線之海水柱中可能存在的海流聲學構造之形貌。沿著多頻道反射震測測線MGL0905-01與01R資料為TAIGER計劃於2009年四月2-3日期間進行探勘所蒐集。聲波能量經由40個體積為6600立方英吋的空氣槍組成的陣列以每隔50公尺擊發所產生。空氣槍陣列拖行於研究船Langseth後方，水下深度為8公尺。拖纜全長6公里，含468個水聽器群，各接收器的間距為12.5公尺，拖行於研究船後方，海水表面下的水平取樣空間為6.25公尺。每隔2毫秒取樣一次反射訊號。探勘測線範圍覆蓋約215公里，沿著水深小於100公尺的高屏下部斜坡，往南至水深達2600公尺的深海環境。多頻道反射震測以傳統震測資料處理程序之順序進行資料處理，產生最後的震測剖面。處理程序包括描線編修、帶通濾波、雜訊壓制、預測解迴旋、速度分析、重合及克希何夫重合後時間移位。甲烷水合物的存在關聯著震波空白、低頻率內涵、極性相反且連續的海底仿擬反射清楚可見，而海底仿擬反射於海床下的分布變化在雙程走時0.2~0.5秒之間。數個逆斷層可解釋為扮演著流體移棲的通道與封閉，而脆性區、多孔隙傾翻岩床、滑脫面推測可能是潛在的油氣苗移棲路俓。水柱中反射訊號的出現顯示出水柱間有阻抗的差異存在，於雙程走時1200毫秒處相對地強反射訊號的出現表示其可辨識出海水中溫鹽所產生的精細構造。反射訊號的主要形貌在中間層處較深層含更多連續性且清楚地振幅，而在靠近陸坡則變相當不連續。精糙海底地形可歸屬於動態海洋學過程中所產生。本研究方法未來可納入標準震測資料處理的流程之一。 Multi-channel seismic data has been implemented for simultaneous imaging the sub-seafloor sedimentary structure features and characterizing the spatial distribution of gas hydrate and the large-scale ocean current structure in the water column. The imaging sub-seabed features in exploration of gas hydrate potential in SW Taiwan have been investigated and supported under Central Geology Survey since 2004. This study was primarily focusing on the gas hydrate investigation to determine the distribution of BSRs in the subsurface and additional purpose to detect the possible presence of the oceanic current acoustic structure features in the water column along the survey line. Multi-channel seismic reflection data along MGL0905-01 and 01R were acquired by the TAiwan Integrated GEodynamics Research (TAIGER) project. The surveys were performed during April 2-3, 2009. Acoustic energy produced from 40 of air-gun array with combined volume of 6600 cubic inches was fired every 50 m. The airgun array was towed behind Langseth at depth of 8 m. An six-km-long streamer containing 468 hydrophone groups with receiver space of 12.5 m was towed behind the ship resulting in a horizontal subsurface sampling spacing of 6.25 m. Reflected signal was sampled every 2 ms. The survey line covered about 215 km and along lower slope of Kaoping shelf with water depth of less than 100 m then further south towards the deep marine environment where water depth reaches 2600 m. The MCS data was sequentially processed with conventional seismic processing strategy including trace editing, bandpass filtering, noise suppression, predictive deconvolution, velocity analysis, stacking and Kirchhoff post-stack time migration to create the final seismic profile. The presence of gas hydrates are associated with blanking, low frequency contents and clear reverse polarity of continuous BSRs. The distribution of the BSR varied from 0.2 to 0.5 s in two-way travel-time (TWTT) below seafloor. Several thrust faults had been interpreted which act role as fluid conduits. The brittle zone and porous tilted beds can be speculated as the other potential migration pathways for gas-seepages. At the same time, the appearance of reflectors revealed the existence of distinct impedance contrast inside the water column affected by complex physical processes. The reflectors were identified as thermohaline fine structures that appear relatively strong in approximately above 1200 ms TWTT. The major reflectors patterns in the middle layer are more continuous with clear amplitude changes in deeper water region and fairly discontinuous when it is near the continental slope. Rough morphologic seafloor could be attributed to the dynamics oceanographic processes that occur.
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