Enhanced 3D prestack depth imaging of broadband data from the South China Sea: a case study*
Hao Zhang 1 3 Jincheng Xu 1 Jinbo Li 21 Chinese Academy of Sciences, Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, PO Box 9825, Beijing 100029, China.
2 China National Offshore Oil Corporation Research Institute, 6 Dongzhimen Waixiaojie, Beijing 100010, China.
3 Corresponding author. Email: zhanghao@mail.iggcas.ac.cn
Exploration Geophysics 47(3) 219-227 https://doi.org/10.1071/EG16009
Submitted: 28 January 2016 Accepted: 19 July 2016 Published: 5 August 2016
Abstract
We present a case study of prestack depth imaging for data from the South China Sea using an enhanced work flow with cutting edge technologies. In the survey area, the presence of complex geologies such as carbonate pinnacles and gas pockets creates challenges for processing and imaging: the complex geometry of carbonates exhibits 3D effect for wave propagation; deriving velocity inside carbonates and gas pockets is difficult and laborious; and localised strong attenuation effect from gas pockets may lead to absorption and dispersion problems. In the course of developing the enhanced work flow to tackle these issues, the following processing steps have the most significant impact on improving the imaging quality: (1) 3D ghost wavefield attenuation, in particular to remove the ghost energy associated with complex structures; (2) 3D surface-related multiple elimination (SRME) to remove multiples, in particular multiples related to complex carbonate structures; (3) full waveform inversion (FWI) and tomography-based velocity model building, to derive a geologically plausible velocity model for imaging; (4) Q-tomography to estimate the Q model which describes the intrinsic attenuation of the subsurface media; (5) de-absorption prestack depth migration (Q-PSDM) to compensate the earth absorption and dispersion effect during imaging especially for the area below gas pockets. The case study with the data from the South China Sea shows that the enhanced work flow consisting of cutting edge technologies is effective when the complex geologies are present.
Key words: broadband, model building, prestack depth imaging, Q-tomography.
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