Well-Driven Seismic
Integrating well data throughout the seismic workflow for superior imaging and inversion
Well-Driven Seismic (WDS) is the integration of borehole information throughout the surface-seismic workflow to provide better seismic images, more reliable stratigraphic interpretation, and greater confidence in seismic reservoir characterization.
Wireline logs (compressional, shear, and density), VSPs, and surface-seismic data represent the elastic response of the earth at various resolution scales. A principle of the Well-Driven Seismic concept is that these data should be processed with respect to their mutual consistency, i.e., that the seismic data must tie with logs and VSPs in time and depth. The aim of the Well-Driven Seismic method is to involve all the available borehole information to optimize the entire seismic workflow to deliver seismic images of superior resolution (in time or depth) and calibrated prestack seismic amplitudes that are suitable for inversion and detailed seismic reservoir description.
Earth properties from logs, VSPs, and surface-seismic data
The Well-Driven Seismic workflow invokes new proprietary software and analysis techniques from WesternGeco and Schlumberger to derive an earth property model from the integrated analysis of wireline logs, VSPs, and surface-seismic data. The property model includes compressional and shear velocities, attenuation (Q) factors, VTI anisotropy parameters, and interbed multiple mechanisms, and is derived at the well location (or locations) and extended across the survey area in 3D. The 3D model is applied in the seismic processing sequence for true amplitude and phase recovery, deconvolution, multiple attenuation, anisotropic prestack time and depth imaging (including of converted-wave data), AVO analysis, and 4D processing.
Well data for high-resolution seismic imaging
Well information can improve many key stages of the conventional seismic processing sequence. VSP data provide excellent discrimination of primary and multiple events, and are used to guide surface-seismic multiple attenuation processes. Furthermore, interbed multiple mechanisms identified in separated VSP wavefields are used as input to data-driven multiple attenuation processes, such as the WesternGeco Interbed Multiple Prediction (IMP). Inverse-Q operators derived from VSP data (and new methods for walkaway VSP data) can significantly improve seismic resolution. WesternGeco employs a proprietary deconvolution process that is constrained by the signal-to-noise level in the seismic data and by the well reflectivity to enhance further the seismic resolution. The calibrated anisotropic velocity model is vital for prestack time and depth migration (including of converted waves) to improve steep-dip imaging, lateral positioning of reflectors, signal-to-noise ratios, and seismic resolution.
Optimized well ties
The Well-Driven Seismic method optimizes the processing sequence and the processing parameters within that sequence to tie the seismic data to the wells. Attributes based on the well tie and on the quality of the extracted wavelets are used for deterministic seismic processing decisions. Space-adaptive wavelet processing corrects 3D seismic data to true zero phase between well locations, and stabilizes residual spatial wavelet variations.
Borehole-calibrated seismic inversion
The Well-Driven Seismic approach provides greater sensitivity to seismically derived reservoir attributes through calibrated AVO or acoustic impedance inversion. The well data are particularly important for successful processing of seismic data for inversion. Compensation for the offset-dependent effects of Q, geometric spreading, transmission losses, and anisotropy are essential for processing data over very long offsets (where the strongest AVO expression of the reservoir may be visible). The method calibrates the AVO signatures in the prestack seismic data with the offset-dependent amplitude response synthesized from well logs and/or the response expressed in the walkaway VSP to provide assurance of the seismic processing sequence.
With the seismic processing sequence optimized for resolution and consistency with the well data, Well-Driven Seismic processing is a vital prerequisite for acoustic impedance or AVO inversion and subsequent reservoir characterization.
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