In 4D dynamic warping, PGS estimates deformation caused by very small time-lapse displacements that could be caused by either reservoir production (saturation and pressure changes) or environmental and acquisition misfits such as water velocity changes or acquisition positioning errors.
PGS uses broadband 4D NRMS criteria to detect and compensate for small time misalignments as small as 1/20 of a sample, thereby optimizing 4D repeatability. Best results are achieved on broadband multisensor datasets processed to recover the ghost-free up-going wavefield.
- Uses broadband-specific NRMS criteria
- Time deformations can be constrained by the dominant frequency of each wavelet
- Allows the detection of very small 4D time misalignments (about 1/20 of a sample)
- Can be applied as global or semi-global corrections
- Optimizes 4D repeatability
Customized to Broadband 4D Data Characteristics
The traditional least-squares minimization criteria used by warping corrections are replaced by a Normalized RMS (NRMS) formulation customized for broadband 4D data. Parameters such as signal-to-noise ratio (SNR), RMS amplitude ratio, time-shift and dominant frequency are each decomposed from the data. By minimizing this broadband NRMS estimation, the resulting time-deformation can be constrained by the dominant frequency of the wavelet and the associated noise level.
4D dynamic warping corrections are used in processing as a final global or semi-global matching to improve the 4D repeatability. Careful QC is applied to ensure the preservation of genuine 4D signal.
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