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Image based Q-compensation for 4D reservoir identification and interpretation – A case study at Gulf of Mexico

SEG - Society of Exploration Geophysicists, October, 2018
Robert Shank | Shane Carley | and George Rhoads | Chevron; Zhao Wang | Ji Qi | Yi Xuan and Min Yang | CGG
©2018 SEG

Imaged based Q-compensation coupled with FWI can solve for significant frequency and amplitude losses below shallow overburden absorptive geologic bodies. Applying Q-compensation to both the baseline and monitor 4D surveys improves the consistency of the 4D response, leading to more reliable placement of development wells. This should lead to enhanced production and improved reservoir management.

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Correcting for salt misinterpretation with full-waveform inversion

SEG - Society of Exploration Geophysicists, October, 2018
Zhigang Zhang | Jiawei Mei | Feng Lin | Rongxin Huang | and Ping Wang (CGG)
©2018 SEG

Using full-waveform inversion (FWI) to update velocity models that contain salt bodies with high velocity contrasts is challenging. It is even harder if erroneous salt geometry is part of the velocity model. Shen et al. (2017) showed a successful FWI application that corrected some misinterpretation of salt structures and resulted in improved subsalt images at the Atlantis field in the Gulf of Mexico. Their study stressed the importance of the low frequencies (usable down to 1.6 Hz), full azimuths, and wide offsets of OBN data. Encouraged by the success at Atlantis, we revisited some aspects of FWI algorithms to minimize cycle skipping and amplitude discrepancy issues that are common in the presence of salt and salt misinterpretation. Here we present the use of travel time misfit measured in frequency-dependent time windows as the FWI cost function. It is devised to minimize the negative impact from the amplitude discrepancy and cycle-skipping between the recorded data and modeled synthetic data. Furthermore, we use the crosscorrelation coefficient between the recorded data and shifted synthetic data as a weight function in gradient computation to promote travel time measurements of higher quality. We demonstrate the effect of our approach using a staggered full-azimuth streamer data set in an area of complex shallow salt bodies in the Gulf of Mexico.

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A demigration-based reflection full waveform inversion workflow

SEG - Society of Exploration Geophysicists, October, 2018
Ping Wang | Zhigang Zhang | Zhiyuan Wei | and Rongxin Huang (CGG)
©2018 SEG

Reflection FWI is effective at providing low-wavenumber velocity updates for deep areas beyond the penetration depth of diving waves and significantly improves seismic imaging. However, the tomographic term of the FWI gradient that is good for low-wavenumber velocity updates can be contaminated by the much stronger high-wavenumber migration term. We present a reflection FWI workflow that is based on Born modeling and thus is free from the contamination of the migration term. In addition, we propose to use a set of partial stacks as reflectivity models for Born modeling to reduce the risks of cycle-skipping and incorrect update sign and to use a traveltime cost function to mitigate the negative impact from amplitude mismatch between input data and modeled synthetic data. Finally, we demonstrate the benefit and effectiveness of our approach using one field data set in the Gulf of Mexico.

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Improving reflection FWI reflectivity using LSRTM in curvelet-domain

SEG - Society of Exploration Geophysicists, October, 2018
Adriano Gomes | Zhuocheng Yang | CGG
©2018 SEG

We investigate the benefits of considering the effects of the Hessian matrix in the reflection FWI (RFWI) reflectivity, i.e., using least-squares RTM (LSRTM) to estimate the short-wavelength component of the model. In addition, a more efficient approach using single-iteration LSRTM, more specifically, using curvelet-domain Hessian filters is proposed. Using synthetic and field data sets, we show how this approach can improve the reflectivity model and, therefore, the synthetic reflection data, which ultimately benefits RFWI. Finally, we discuss some of the limitations of this approach and some of the challenges that are still not addressed by it.

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3D VSP imaging under a complex salt finger at Atlantis, Gulf of Mexico

SEG - Society of Exploration Geophysicists, October, 2018
Chang-Chun Lee | Jing Yang | CGG; Robert Chrisman | Jean-Paul Van Gestel | Mark Benson | BP
©2018 SEG

To improve image resolution in the vicinity of the well, 3D VSP data was acquired at the Atlantis field in the Gulf of Mexico to complement the existing towed-streamer and OBN data. Two unique data challenges require special consideration and innovative techniques in order to unlock the full imaging potential at the Atlantis field: (1) illumination issues related to the receivers being placed in a well that goes through a complicated salt finger; (2) receiver reorientation issues related to the survey’s two-phase acquisition due to receivers being pulled out and placed back into well. We demonstrate how we mitigate the impact of these challenges through improved XYZ vector fidelity reorientation and least-squares RTM.

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