• Title, Summary, Keyword: 파형역산

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Time Domain Seismic Waveform Inversion based on Gauss Newton method (시간영역에서 가우스뉴튼법을 이용한 탄성파 파형역산)

  • Sheen, Dong-Hoon;Baag, Chang-Eob
    • 한국지구물리탐사학회:학술대회논문집
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    • pp.131-135
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    • 2006
  • A seismic waveform inversion for prestack seismic data based on the Gauss-Newton method is presented. The Gauss-Newton method for seismic waveform inversion was proposed in the 80s but has rarely been studied. Extensive computational and memory requirements have been principal difficulties. To overcome this, we used different sizes of grids in the inversion stage from those of grids in the wave propagation simulation, temporal windowing of the simulation and approximation of virtual sources for calculating partial derivatives, and implemented this algorithm on parallel supercomputers. We show that the Gauss-Newton method has high resolving power and convergence rate, and demonstrate potential applications to real seismic data.

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Acoustic Full-waveform Inversion using Adam Optimizer (Adam Optimizer를 이용한 음향매질 탄성파 완전파형역산)

  • Kim, Sooyoon;Chung, Wookeen;Shin, Sungryul
    • Geophysics and Geophysical Exploration
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    • v.22 no.4
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    • pp.202-209
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    • 2019
  • In this study, an acoustic full-waveform inversion using Adam optimizer was proposed. The steepest descent method, which is commonly used for the optimization of seismic waveform inversion, is fast and easy to apply, but the inverse problem does not converge correctly. Various optimization methods suggested as alternative solutions require large calculation time though they were much more accurate than the steepest descent method. The Adam optimizer is widely used in deep learning for the optimization of learning model. It is considered as one of the most effective optimization method for diverse models. Thus, we proposed seismic full-waveform inversion algorithm using the Adam optimizer for fast and accurate convergence. To prove the performance of the suggested inversion algorithm, we compared the updated P-wave velocity model obtained using the Adam optimizer with the inversion results from the steepest descent method. As a result, we confirmed that the proposed algorithm can provide fast error convergence and precise inversion results.

Frequency-domain Waveform Inversion using Residual-selection Strategy (잔여 파동장 분리 기법을 이용한 주파수영역 파형역산)

  • Son, Woo-Hyun;Pyun, Suk-Joon;Kwak, Sang-Min
    • Geophysics and Geophysical Exploration
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    • v.14 no.3
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    • pp.214-219
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    • 2011
  • We perform the frequency-domain waveform inversion based on the residual-selection strategy. In the residual-selection strategy, we classify time-domain residual wavefields into several groups according to the order of absolute amplitudes. Because the residual wavefields are normalized after regularization of the gradient directions within each group, the residual-selection strategy plays a role in enhancing the small-amplitude wavefields, which contributes to improving the deep parts of inverted subsurface images. After classifying residuals in the time domain, they are transformed to the frequency domain. Waveform inversion is performed in the frequency domain using the back-propagation technique which has been popularly used in reverse-time migration. The residual-selection strategy is applied to the SEG/EAGE salt and IFP Marmousi models. Numerical results show that the residual-selection strategy yields better results than the conventional frequency-domain waveform inversion.

Resolution Limits of Cross-Well Seismic Imaging Using Full Waveform Inversion (전파형 역산을 이용한 시추공 영상의 분해능)

  • Cho, Chang-Soo;Lee, Hee-Il;Suh, Jung-Hee
    • Geophysics and Geophysical Exploration
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    • v.5 no.1
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    • pp.33-45
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    • 2002
  • It was necessary to devise new techniques to overcome and enhance the resolution limits of traveltime tomography. Waveform inversion has been one of the methods for giving very high resolution result. High resolution image could be acquired because waveform inversion used not only phase but amplitude. But waveform inversion was much time consuming Job because forward and backward modeling was needed at each iteration step. Velocity-stress method was used for effective modeling. Resolution limits of imaging methods such as travel time inversion, acoustic and elastic waveform inversion were investigated with numerical models. it was investigated that Resolution limit of waveform inversion was similar tn resolution limit of migration derived by Schuster. Horizontal resolution limit could be improved with increased coverage by adding VSP data in cross hole that had insufficient coverage. Also, waveform inversion was applied to realistic models to evaluate applicability and using initial guess of travel time tomograms to reduce non-linearity of waveform inversion showed that the better reconstructed image could be acquired.

Time-domain Seismic Waveform Inversion for Anisotropic media (이방성을 고려한 탄성매질에서의 시간영역 파형역산)

  • Lee, Ho-Yong;Min, Dong-Joo;Kwon, Byung-Doo;Yoo, Hai-Soo
    • 한국지구물리탐사학회:학술대회논문집
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    • pp.51-56
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    • 2008
  • The waveform inversion for isotropic media has ever been studied since the 1980s, but there has been few studies for anisotropic media. We present a seismic waveform inversion algorithm for 2-D heterogeneous transversely isotropic structures. A cell-based finite difference algorithm for anisotropic media in time domain is adopted. The steepest descent during the non-linear iterative inversion approach is obtained by backpropagating residual errors using a reverse time migration technique. For scaling the gradient of a misfit function, we use the pseudo Hessian matrix which is assumed to neglect the zero-lag auto-correlation terms of impulse responses in the approximate Hessian matrix of the Gauss-Newton method. We demonstrate the use of these waveform inversion algorithm by applying them to a two layer model and the anisotropic Marmousi model data. With numerical examples, we show that it's difficult to converge to the true model when we assumed that anisotropic media are isotropic. Therefore, it is expected that our waveform inversion algorithm for anisotropic media is adequate to interpret real seismic exploration data.

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A Study of Waveform Inversion for Improvement of Sub-Salt Migration Image (암염돔 하부 구조의 구조보정 영상 개선을 위한 파형역산 기법 연구)

  • Ha, Wan-Soo;Pyun, Suk-Joon;Son, Woo-Hyun;Shin, Chang-Soo;Ko, Seung-Won;Seo, Young-Tak
    • Geophysics and Geophysical Exploration
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    • v.11 no.3
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    • pp.177-183
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    • 2008
  • The sub-salt imaging technique becomes more crucial to detect the hydro-carbonates in petroleum exploration as the target reservoirs get deeper. However, the weak reflections from the sub-salt structures prevent us from obtaining high fidelity sub-salt image. As an effort to overcome this difficulty, we applied the waveform inversion by implementing multi-grid technique to the sub-salt imaging. Through the comparison between the conventional waveform inversion using fixed grid and the multi-grid technique, we confirmed that the waveform inversion using multi-grid technique has advantages over the conventional fixed grid waveform inversion. We showed that the multi-grid technique can complement he velocity estimation result of the waveform inversion for imaging the sub-salt structures, of which velocity model cannot be obtained correctly by the conventional fixed grid waveform inversion.

Velocity Model Building using Waveform Inversion from Single Channel Engineering Seismic Survey (탄성파 파형역산을 이용한 엔지니어링 목적의 단일채널 탄성파 탐사자료에서의 속도모델 도출)

  • Choi, Yeon Jin;Shin, Sung Ryul;Ha, Ji Ho;Chung, Woo Keen;Kim, Won Sik
    • Geophysics and Geophysical Exploration
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    • v.17 no.4
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    • pp.231-241
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    • 2014
  • Recently, single channel seismic survey for engineering purpose have been used widely taking advantage of simple processing. However it is very difficult to obtain high fidelity subsurface image by single channel seismic due to insufficient fold coverage. Recently, seismic waveform inversion in multi channel seismic survey is utilized for accurate subsurface imaging even in complex terrains. In this paper, we propose the seismic waveform inversion algorithm for velocity model building using a single channel seismic data. We utilize the Gauss-Newton method and assume that subsurface model is 1-Dimensional. Seismic source estimation technique is used and offset effect is also corrected by removing delay time by offset. Proposed algorithm is verified by applying modified Marmousi2 model, and applied to field data set obtained in port of Busan.

Full Waveform Inversion using a Cyclic-shot Subsampling and a Reference-shot Subset (주기적 송신원 추출과 참조 송신원 부분집합을 이용한 완전 파형 역산)

  • Jo, Sang Hoon;Ha, Wansoo
    • Geophysics and Geophysical Exploration
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    • v.22 no.2
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    • pp.49-55
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    • 2019
  • In this study, we presented a reference-shot subset method for stable convergence of full waveform inversion using a cyclic-shot subsampling technique. Full waveform inversion needs repetitive modeling of wave propagation and thus its calculation time increases as the number of sources increases. In order to reduce the computation time, we can use a cyclic-shot subsampling method; however, it makes the cost function oscillate in the early stage of the inversion and causes a problem in applying the convergence criteria. We introduced a method in which the cost function is calculated using a fixed reference-shot subset while updating the model parameters using the cyclic-shot subsampling method. Through the examples of full waveform inversion using the Marmousi velocity model, we confirmed that the convergence of cost function becomes stable even under the cyclic-shot subsampling method if using a reference-shot subset.

Application of Displacement-Vector Objective Function for Frequency-domain Elastic Full Waveform Inversion (주파수 영역 탄성파 완전파형역산을 위한 변위벡터 목적함수의 적용)

  • Kwak, Sang-Min;Pyun, Suk-Joon;Min, Dong-Joo
    • Geophysics and Geophysical Exploration
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    • v.14 no.3
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    • pp.220-226
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    • 2011
  • In the elastic wave equations, both horizontal and vertical displacements are defined. Since we can measure both the horizontal and vertical displacements in field acquisition, these displacements compose a displacement vector. In this study, we propose a frequency-domain elastic waveform inversion technique taking advantage of the magnitudes of displacement vectors to define objective function. When we apply this displacement-vector objective function to the frequency-domain waveform inversion, the inversion process naturally incorporates the back-propagation algorithm. Through the inversion examples with the Marmousi model and the SEG/EAGE salt model, we could note that the RMS error of the solution obtained by our algorithm decreased more stably than that of the conventional method. Particularly, the density of the Marmousi model and the low-velocity sub-salt zone of the SEG/EAGE salt model were successfully recovered. Since the gradient direction obtained from the proposed objective function is numerically unstable, we need additional study to stabilize the gradient direction. In order to perform the waveform inversion using the displacementvector objective function, it is necessary to acquire multi-component data. Hence, more rigorous study should be continued for the multi-component land acquisition or OBC (Ocean Bottom Cable) multi-component survey.

Extraction of Flow Velocity Information using Direct Wave and Application of Waveform Inversion Considering Flow Velocity (직접파를 이용한 배경매질 유속정보 도출과 유속을 고려한 파형역산의 적용)

  • Lee, Dawoon;Chung, Wookeen;Shin, Sungryul;Bae, Ho Seuk
    • Geophysics and Geophysical Exploration
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    • v.20 no.4
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    • pp.199-206
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    • 2017
  • Field data obtained from marine exploration are influenced by various environmental factors such as wind, waves, tidal current and flow velocity of a background medium. Most environmental factors except for the flow velocity are properly corrected in the data processing stage. In this study, the wave equation modeling considering flow velocity is used to generate observation data, and numerical experiments using the observation data were conducted to analyze the effect of flow velocity on waveform inversion. The numerical examples include the results with unrealistic flow velocities. In addition, an algorithm is suggested to numerically extract flow velocity for waveform inversion. The proposed algorithm was applied to the modified Marmousi2 model to obtain the results depending on the flow velocity. The effect of flow velocity on updated physical properties was verified by comparing the inversion results without considering flow velocity and those obtained from the proposed algorithm.