【摘要】：勘探地震學(xué)中,背景速度是決定地震波傳播的關(guān)鍵因素,是進一步反演速度場更高成分的基礎(chǔ)。對于透射波和折射波,其具有較大的入射角孔徑,可以用來恢復(fù)速度模型中的長波長分量;但是對于反射波,由于較小的反射角孔徑,通常用于恢復(fù)速度場短波長分量。本文針對上述問題圍繞反射波路徑的推導(dǎo)方法,反射波層析目標(biāo)泛函的構(gòu)建及其反射波層析對全波形反演效果的改善進行了研究。從而實現(xiàn)了利用反射波信息來反演速度場長波長分量的過程�！安窂健蹦芨鼫�(zhǔn)確地描述地震波在地球介質(zhì)中的傳播過程,相對傳統(tǒng)射線路徑,波路徑能夠避免高頻射線路徑在高速區(qū)域聚焦、在低速區(qū)域發(fā)散的問題。波動方程層析成像正是在波路徑的基礎(chǔ)上提出的。本文提出的反射波路徑由兩部分構(gòu)成,一部分是背景入射場入射到地下一個散射點,產(chǎn)生二次場,二次場對地下所有其它點激勵后產(chǎn)生的場的變化;另一部分代表從源點出發(fā)的Green函數(shù)激勵地下一個散射點,產(chǎn)生二次場,二次場對地下所有其它點激勵后產(chǎn)生的場的變化。這兩部分的疊加產(chǎn)生完整的梯度量,即反射波路徑。我們將數(shù)據(jù)殘差沿著該反射波路徑進行反投影,便可實現(xiàn)反射波層析反演。反演過程中根據(jù)不同的初始速度場選擇不同的目標(biāo)函數(shù)。由于模擬地震數(shù)據(jù)中地震波振幅的不確定性,建立在傳統(tǒng)最小二乘誤差泛函基礎(chǔ)上的波形反演嚴(yán)重受到了制約。但是,各種形式的波動方程基本遵循共同的程函方程,其旅行時信息基本不會受到影響。故在波形反演中應(yīng)當(dāng)更注重旅行時信息。當(dāng)初始速度場與真實速度場相差較大時,我們選擇旅行時反演,降低其對波動方程的依賴程度。只有在初始速度場較為準(zhǔn)確時我們方可采取波形反演。本文利用偏移與反偏移算子從背景速度場中獲取反射波信息,構(gòu)建了反射波路徑,進而建立波動方程反射層析的梯度公式。在反演過程中,本文對比了不同的目標(biāo)函數(shù)的反演效果。在波動方程反射旅行時反演中,結(jié)合Ma Y和Luo Y的思想改進了反射層析中其伴隨源的形式。同時運用動態(tài)圖像校正方法來計算反射波旅行時差,實現(xiàn)了利用反射波旅行時信息來反演速度場中低波數(shù)成分的過程。在波動方程反射波形反演中,實現(xiàn)了較為復(fù)雜的模型試算,并改善了FWI的效果。模型試算結(jié)果表明,該方法能夠提高反演的穩(wěn)定性,具有更高應(yīng)用潛力。
[Abstract]:In exploration seismology background velocity is the key factor to determine the propagation of seismic wave and the basis for further inversion of the higher component of velocity field. For transmission wave and refraction wave, it has large incident angle aperture, which can be used to recover the long wavelength component in velocity model, but for reflection wave, it is usually used to restore the short wavelength component of velocity field because of small reflection angle aperture. This paper focuses on the derivation of the reflected wave path, the construction of the target functional of the reflection wave tomography and the improvement of the full waveform inversion effect by the reflection wave tomography. Thus, the long wavelength component of velocity field can be retrieved by using reflected wave information. The "wave path" can more accurately describe the process of seismic wave propagation in the earth's medium. Compared with the traditional ray path, the wave path can avoid the problem of high frequency ray path focusing in the high speed region and divergence in the low speed region. Wave equation tomography is based on the wave path. The reflected wave path proposed in this paper is composed of two parts. One is the background incident field incident to a scattering point under the ground, which produces the secondary field and the change of the field after the secondary field excites all the other underground points. The other part represents the Green function from the source point which excites a scattering point in the ground and produces the quadratic field and the change of the field after the quadratic field excites all the other points in the ground. The superposition of these two parts produces a complete gradient, that is, the reflected wave path. The reflection wave tomography inversion can be realized by back-projecting the data residuals along the reflected wave path. In the inversion process, different objective functions are selected according to different initial velocity fields. Because of the uncertainty of the amplitude of seismic wave in simulated seismic data, the waveform inversion based on the traditional least square error functional is seriously restricted. However, all kinds of wave equations follow the common equation, and the travel information will not be affected. Therefore, more attention should be paid to travel time information in waveform inversion. When the difference between the initial velocity field and the real velocity field is large, we choose travel time inversion to reduce its dependence on the wave equation. Only when the initial velocity field is more accurate can we take waveform inversion. In this paper, the reflected wave path is constructed by using migration and inverse migration operators to obtain the reflected wave information from the background velocity field, and then the gradient formula of reflection tomography for wave equation is established. In the process of inversion, the inversion effects of different objective functions are compared. In the reflection travel time inversion of wave equation, the form of accompanying source in reflection tomography is improved by combining the ideas of Ma Y and Luo Y. At the same time, the dynamic image correction method is used to calculate the travel time difference of the reflected wave, and the process of retrieving the low wavenumber component of the velocity field by using the travel time information of the reflected wave is realized. In the reflection waveform inversion of wave equation, a more complicated model trial calculation is realized, and the effect of FWI is improved. The model results show that this method can improve the stability of inversion and has higher application potential.
【學(xué)位授予單位】：中國石油大學(xué)(華東)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：P631.4

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