進階搜尋


   電子論文尚未授權公開,紙本請查館藏目錄
(※如查詢不到或館藏狀況顯示「閉架不公開」,表示該本論文不在書庫,無法取用。)
系統識別號 U0026-1207201111201500
論文名稱(中文) 震幅還原轉換S波移位
論文名稱(英文) Prestack True Amplitude Migration of Converted Waves
校院名稱 成功大學
系所名稱(中) 地球科學系碩博士班
系所名稱(英) Department of Earth Sciences
學年度 99
學期 2
出版年 100
研究生(中文) 吳啟銘
研究生(英文) Chi-Ming Wu
學號 l4697114
學位類別 碩士
語文別 中文
論文頁數 41頁
口試委員 指導教授-孫鎮球
口試委員-張永孚
口試委員-陳光榮
中文關鍵字 振幅  還原  轉換S波  移位 
英文關鍵字 True Amplitude Migration  Converted Waves 
學科別分類
中文摘要 本研究是發展P波震波經轉換產生的S波(即PS波)做疊前逆時移位,並使移位影像振幅還原,即振幅不隨入射角的變化,真實反映反射面的P波與S波速度對比的振幅還原移位演算法。
由於近年電腦計算速度大幅進步,使得疊前逆時移位可以商業應用。另外,PS波逆時移位可以得到PP波影像得不到的部分地質資訊,因此PS波移位的應用逐漸增加。但PS波移位的振幅隨著入射角的不同而有變化,因此移位影像的振幅不能真實反映反射面兩側的P波與S波速度對比。因此,本研究希望發展可以真實反映P、S波速度對比的移位演算法。
本研究的輸入資料是反射二維彈性波資料中的S波(即PS波)。首先須將彈性波中的PP波和PS波分離。這裡使用的分離法程序是:(a)將彈性波在彈性速度模型中使逆時外插;(b)在某一淺部深度計算散量(divergence)和旋量(curl);(c)將散量在P波速度模型中做順時外插得到分離反射P波(即PP波);(d)將旋量在S波速度模型中做順時外插得到分離S波(即PS波)。
下一步是PS波疊前移位。移位需做兩輪。第一輪是一般的PS波疊前移位及疊加。對個別震源產生的PS波在S波速度模型中做逆時外插得到接收器波場 (receiver wavefield);同時計算P波由震源順時傳播得到震源波場 (source wavefield);震源波場與接收器波場的交叉對比便是單一震源的PS波移位影像。將所有震源的PS波移位影像疊加,便得到疊後移位影像,但這個影像尚未經振幅還原。第二輪是得到振幅還原影像。利用第一輪疊後PS波移位影像,利用slant stack 找到反射面的傾角及位置。然後,對每一個震源利用射線追踪找到在所有反射點的P波入射角及PS波反射角,再加入P波和S波速度,可以計算PS波的反射係數。由於移位影像的振幅應與PS波反射係數成正比,因此,將單一震源的PS波影像除以反射係數,即得到還原振幅的單一震源影像。將所有單一震源的PS波振幅還原影像疊加,即得到疊後還原振幅影像。
本研究完成單一傾斜反射面彈性模型的人工合成資料測試。
英文摘要 This study is to develop a prestack (P-wave source emitted) converted S-wave (PS-wave) reverse-time depth migration algorithm with true amplitude in the migrated image, that is, the amplitude of the migrated image is independent of the incident angle of the converted wave, but truly responds the velocity contrast of the reflector.
Thanks to the rapid recent advancement of computing technology, reverse-time migration can be commercially applied because its included mass computation can be implemented with tolerable computing time, say, a few hours. Besides, for some special geological condition, PS-wave migration images can provide underground information that is not available in PP-wave (P-wave emitted reflected P-wave) migration images. For this reason, PS-wave migration is increasingly applied. Yet the PS-wave image depends on the incident angle (with 0 amplitude at normal incidence), thus does not respond the velocity contrast of the reflector. Therefore this study intends to develop an algorithm to respond the velocity contrast.
The input data for this algorithm is the P-source emitted elastic seismic data (that contains PP- and PS-waves) received at the earth’s surface. First we need to separate the PP- and PS-waves from the elastic data.
Next we proceed the prestack PS-wave migration that includes two passes. Pass 1 is regular prestack PS-wave reverse-time migration for each individual source. The separated PS-waves for each individual source is reverse-time extrapolated into an S-velocity acoustic model to obtain the receiver wavefield. In parallel, we compute the forward-time wave propagation from the source location into a P-velocity model to obtain the source wavefield. The 0-lag cross-correlation between the source wavefield and receiver wavefield marks the migrated image at each point. Stacking the prestack images over all sources gives the stacked PS-wave image.
Pass 2 is to adjust the amplitude of the migration image. We apply local slant stack on the reflectors of the pass 1 stacked image to obtain the dip angle of the reflectors. We perform ray tracing from each source to determine the incident angles at the reflectors. We determine the reflection angle and reflection coefficient of PS-wave at the reflector. Then PS-wave prestack reverse-time depth migration is perform again and the migration image amplitude is divided by reflection coefficient such that the amplitude of the image is unified, and therefore true amplitude prestack migration image is obtained. We then stack the prestack images over all source to obtain the stacked true amplitude migration image.
Testing is implemented on synthetic data from a single dipping reflector elastic model.
論文目次 目錄
摘要(ABSTRACT)……………………………………………………………Ⅰ
ABSTRACT(摘要)……………………………………………………………Ⅲ
致謝…………………………………………………………………………Ⅴ
目錄…………………………………………………………………………Ⅶ
圖目錄………………………………………………………………………Ⅷ
第一章 緒論 ………………………………………………………………1
第二章 研究方法 …………………………………………………………3
2.1 有限差分法 ………………………………………………………3
2.2 分離彈性波中的PP波和PS波 …………………………………6
2.3 第一輪:PS波疊前逆時移位……………………………………12
2.4 第二輪: PS波移位影像的振幅還原 …………………………18
第三章 結果 ………………………………………………………………28
第四章 討論與結論 ………………………………………………………38
4.1 討論 …………………………………………………………………38
4.2 結論 …………………………………………………………………39
參考文獻 …………………………………………………………………40
參考文獻 Aki, K., and P. G. Richards, 1980, Quantitative seismology: Freeman Co.
Deng, F., and McMechan, G. A., 2007, Prestack True-Amplitude Depth Migration. Geophysics, 72, S155-S166.
Grant, F. S. & West, G. F., 1965. Interpretation theory in applied geophysics, McGraw-Hill, New York.
Kelly, K. R., Ward, R. W., Treitel, S., and Alford, R. M., 1976, Synthetic seismograms: A finite difference approach: Geophysics, 41, 2-27.
Sun, R., 1999, Separating P- and S-waves in a prestack 2-dimensional elastic seismogram: 61th Annual Meeting, European Association of Geoscientists and Engineers, Extended Abstracts, Paper 6-23.
Sun, R., and G. A. McMechan, 2001, Scalar reverse-time depth migration of prestack elastic seismic data: Geophysics, 66, 1519-1527.
Sun, R., G. A. McMechan, C. S. Lee, J. Chow, and C. H. Chen, 2006, Prestack scalar reverse-time depth migration of three-dimensional elastic seismic data: Geophysics, 71, no. 5, S199-S207.
梁均合,2007,三維複雜地形彈性波資料的P波與S波分離及逆時移位地層影像,碩士論文,國立成功大學地球科學研究所。
論文全文使用權限
  • 同意授權校內瀏覽/列印電子全文服務,於2014-08-03起公開。


  • 如您有疑問,請聯絡圖書館
    聯絡電話:(06)2757575#65773
    聯絡E-mail:etds@email.ncku.edu.tw