44 research outputs found
Damped wave-equation-based first-arrival traveltime tomography using the embedded boundary method
No full textFirst-arrival traveltime tomography (FATT) is used to delineate shallow velocity structures to identify static effects in oil exploration as well as to characterize the near surface for geotechnical purposes. Because FATT is generally used for land seismic data processing, it becomes necessary to consider irregular topography especially when performing wave-based tomography. However, the standard Cartesian finite-difference method cannot properly handle irregular topography. Hence, the embedded boundary method (EBM) is incorporated into the frequency-domain damped-wave equation in order to correctly describe irregular topography. The developed modeling algorithm is used to calculate first-arrival traveltimes and to perform FATT. The EBM-based modeling algorithm accurately describes the irregular surfaces of numerical velocity models on a regular mesh by exploiting the mirror image principle. The accuracy of the EBM-based traveltime calculation is validated by using two homogeneous velocity models with dipping and complex surfaces. The validation results demonstrate that the proposed algorithm is unaffected by the staircase approximation. The FATT is then applied to synthetic and real data to demonstrate the applicability of the developed algorithm to velocity models with complex topography. For the real data example, the inverted velocity model is used to apply static corrections. The processing results demonstrate an improvement in the continuity of seismic events, thus confirming the accuracy of the developed FATT method.11Nsciescopu
First-arrival traveltime inversion with embedded boundary method for irregular topography
No full textEquivalent source distribution for efficient 3‐D acoustic wave equation modeling in the Laplace domain
No full text
Refraction traveltime tomography based on damped wave equation for irregular topographic model
No full textFirst-arrival traveltime tomography using limited-acquisition geometry in an irregular topography
No full textAdaptive preconditioning of full-waveform inversion based on structure-oriented smoothing filter
No full textPractical considerations in the implementation of time-domain acoustic full waveform inversion
No full textFull waveform inversion (FWI) plays a major role in the oil and gas industry as a state-of-the-art technique that produces quantitative subsurface structures with high-fidelity images. Various FWI studies have been conducted, and these suggest that FWI is a promising inversion method. Recently, many attempts have been made toward three-dimensional (3D) and four-dimensional FWI applications (which were difficult to perform in the past) because of the progress made in computer science and the growth of computer resources. To manage the very large data requirement of 3D problems, a time-domain FWI that is relatively efficient in terms of memory demands must be implemented. However, it could encounter practical issues, leading to failure in its convergence. In this paper, we introduce these practical issues and several alternative methods for mitigating them. The first issue is the bandpass filtering of the observed seismograms. We suggest that the frequency-domain filter based on a reference wavelet would be optimal in terms of both bandpass filtering and source wavelet estimation. The second issue is related to acoustic approximation. We show that a simple density model comprising only water and solid layers is a reasonable option to address seafloor reflectivity properly. The last issue is the accumulation of round-off errors due to the massive computation of the objective function. We demonstrate that a simple modification of the error calculation can resolve this round-off error problem. © 2021 Australian Society of Exploration Geophysicists.11Nsciescopu
Evaluation of Kirchhoff hyperbola in terms of partial derivative wavefield and virtual source
No full textThe Kirchhoff migration is computationally the most economic choice of migration currently available. From its beginning, the Kirchhoff migration has been developed and improved separately from wave-equation based migrations although they are founded on the same principle. In this paper, we reveal a link between the Kirchhoff depth migration and the wave-equation based migration such as reverse-time migration and least squares migration in terms of the partial derivative wavefield and the virtual source. The Kirchhoff prestack depth migration uses the partial derivative wavefield approximated by the Dirac delta function to migrate the seismic signals. Accordingly, the Kirchhoff hyperbola is defined as kinematic approximation of the partial derivative wavefield.This work was financially supported by the Korea Science and Engineering Foundation (KOSEF) grant funded by Korea government (MOST) (No.R0A-2006-000-10291-0) and the Brain Korea 21 project of the Ministry of Education
A Study of Waveform Inversion for Improvement of Sub-Salt Migration Image
No full textThe 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
the 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. ; 석유탐사 분야에서 탐사대상이 되는 저류층이 갈수록 심부화되고 복잡한 지층 구조로 옮겨감에 따라 암염층 하부 구조를 영상화하는 기술은 석유 및 가스층의 탐지를 위해 매우 중요하게 부각되고 있다. 그러나 암염돔 구조의 특성상 암염돔 하부로부터의 반사 에너지가 미약하기 때문에 하부구조의 정확한 영상을 얻기는 힘들다. 이러한 어려움을 극복하고자 본 연구에서는 암염돔 하부 구조 영상화를 위해 다중격자(multi-grid) 기법을 사용하여 파형역산을 수행하였다. 고정격자를 이용한 통상적인 주파수 영역 파형역산 기법으로 얻은 결과와의 비교를 통해 암염돔 구조 및 하부 구조의 영상화에서 다중격자를 적용한 파형역산 기법의 장점을 확인하였다. 본 연구 결과를 통해 고정격자를 이용한 파형역산 기법으로는 정확한 영상을 얻기 어려웠던 암염돔 구조에서도 다중격자를 적용하여 향상된 영상을 얻을 수 있음을 보여 주었다.이 논문은 2006년도 한국석유공사의 지원에 의하여 연구되었습니다(Sub-salt 구조에 대한 구조보정 연구)
