A novel and efficient engine for P-/S-wave-mode vector decomposition for vertical transverse isotropic elastic reverse time migration

Author:

Zhang Lele1ORCID,Liu Lu2,Niu Fenglin3ORCID,Zuo Jiahui1ORCID,Shuai Da1,Jia Wanli4,Zhao Yang5ORCID

Affiliation:

1. China University of Petroleum, State Key Laboratory of Petroleum Resource and Prospecting, Unconventional Petroleum Research Institute, Beijing, China.

2. Aramco Research Center - Beijing, Aramco Asia, Beijing, China.

3. Rice University, Department of Earth, Environmental and Planetary Sciences, Houston, Texas, USA.

4. CNOOC Research Institute, Beijing, China. .

5. China University of Petroleum, State Key Laboratory of Petroleum Resource and Prospecting, Unconventional Petroleum Research Institute, Beijing, China. (corresponding author)

Abstract

Wave-mode decomposition plays a very important role in elastic reverse time migration (ERTM). Improved imaging quality can be achieved due to reduced wave-mode crosstalk artifacts. The current state-of-the-art methods for anisotropic wavefield separation are based on either splitting model strategy, low-rank approximation, or lower-upper (LU) factorization. Most of these involve expensive matrix computation and Fourier transforms with strong model assumptions. Based on the anisotropic-Helmholtz (ani-Helmholtz) decomposition operator and decoupled formulations, we develop a novel and efficient P-/S-wave-mode vector decomposition method in vertical transverse isotropic (VTI) media with application in ERTM. We first review the basics of classical Helmholtz decomposition and isotropic decoupled formulations. In addition, the ani-Helmholtz decomposition operator is built from the P- and S-wave polarizations of the Christoffel equation in VTI media. We then derive novel decoupled formulations of anisotropic P-/S-waves based on the obtained ani-Helmholtz operator. Moreover, we use the first-order Taylor expansion to approximate the normalization term from the derived decoupled formulations and obtain an efficient ani-Helmholtz decomposition approach, which produces vector P- and S-wavefields with correct units, phases, and amplitudes. Compared with the previous studies, our approach mitigates model assumptions, avoids intricate calculations, such as LU factorization or low-rank approximation, and only needs three fast Fourier transforms at each time step. In addition, the graphic processing unit technique is used to dramatically accelerate various functions of ERTM, such as wavefields extrapolation, decomposition, and imaging. Three synthetic examples demonstrate the effectiveness and feasibility of our proposed approach.

Funder

National Key RD Program of China

National Natural Science Foundation of China

Science Foundation of China University of Petroleum, Beijing

China Postdoctoral Science Foundation

Strategic Cooperation Technology Projects of CNPC and CUPB

Publisher

Society of Exploration Geophysicists

Subject

Geochemistry and Petrology,Geophysics

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