PowerLog
Wavelets
Normal Incidence and Angle Seismic Wavelet Estimation
Fugro-Jason has invested a great deal of resources in developing and implementing the most advanced wavelet estimation methods and a wide variety of QC capabilities to ensure that a high-quality wavelet is obtained.
Accurate wavelet estimation is absolutely critical to the success of any seismic inversion. The inferred shape of the seismic wavelet may strongly influence the seismic inversion results and therefore subsequent assessments of the reservoir quality.
Inversion is a two-step process. In step one, the seismic wavelet is estimated. In step two, that wavelet is used to estimate the seismic reflectivity. The final acoustic impedance is derived from that estimated seismic reflectivity. Therefore if the wavelet is incorrect, the seismic inversion results will be invalid.
Methodology
The Wavelets™ module encompasses several methods:
- Model-driven wavelet phase and amplitude spectrum estimation at well control.
- Wavelet amplitude spectrum estimation with and without well control.
- Wavelet constant-phase spectrum estimation with and without well control.
- AVA/AVO wavelet estimation for input partial stacks.
Key features common to these methods are:
- The methods may be applied to single wells, or multiple wells simultaneously.
- Dip and well deviations are handled by stratigraphic mapping to the selected traces.
- Seismic traces selected for the estimation are completely at the users control.
- Extensive QC displays are provided.
Model-Driven Wavelet Phase and Amplitude Spectrum Estimation
The wavelet amplitude and phase spectra can be estimated in a statistical manner from the seismic data only or with usage of well control. The availability of one or more wells with sonic and density logs opens an additional option for the process of estimating the wavelet. Statistical techniques are used to obtain an initial wavelet, which is then used to generate an initial well synthetic. When the estimated (constant) phase of the statistical wavelet is consistent with the final result from the model-driven method, the wavelet estimation converges more quickly than when you start with a zero phase assumption. Minor edits and stretch/squeeze can be applied to the well to better align the events, and then the wavelet phase and amplitude spectra are estimated.
Integrated Well Log Editor
Accurate wavelet estimation requires accurate tie of the impedance log to the seismic. Errors in well tie can result in phase or frequency artifacts in the wavelet estimation. Therefore, the Wavelets package is tightly integrated with the Well Log Editor of the EPlus™ module of the Workbench. If the wavelet is re-estimated or refined, the displays in the well log editor are automatically updated. Similarly, if the well is edited, an information message appears to prompt the user to re-estimate the wavelet with the new well tie.
