Depth Migration
Our depth imaging capability is built around an integrated set of tools for developing models, and migration algorithms designed to get the most out of your imaging objectives. Our model building incorporates:
- Use of offset and angle gathers
- Global tomography
- Calibration of well velocity to seismic velocity
- anisotropy correction
- Kirchhoff ray based
- Common Azimuth Wave Equation Migration (WEM)
- Shot based WEM
- Beam Migration
- Reverse Time Migration
Common Azimuth 3-D Depth Migration
Common azimuth depth migration is an efficient and accurate “wave equation” migration for narrow-azimuth seismic data, such as conventional marine streamer data and Fairfield’s bottom-referenced receiver acquisition. Common azimuth migration offers accuracy approaching that of shot record migration, but at much cheaper cost. It can produce images superior to Kirchhoff migration in complicated geological areas such as regions of the Gulf of Mexico containing salt bodies. Fairfield designed its common azimuth depth migration to produce high quality steep dip images.
Common azimuth migration also naturally produces angle-domain common image gathers (ADCIGs). Common image gathers show the range of reflection angles, recorded by the acquisition and subsequently imaged, and whether the migration velocity was correct.
Azimuth Moveout
Common azimuth migration expects input data that are uniformly sampled in Iline, Xline and offset. It also expects the source-receiver azimuth for all input traces to be zero. Conventional narrow azimuth marine streamer data almost meet these criteria and are appropriate for common azimuth migration after data “regularization”. Azimuth moveout (AMO) is a data regularization technique that can take narrow azimuth field data, such as streamer data, and produce uniformly-sampled zero azimuth data suitable for common azimuth migration. Application of AMO before common azimuth migration can improve imaging of shallow steep dips, such as fault planes and salt flanks, when compared to simpler regularization schemes that ignore azimuth and use binning.
Beam Migration
For regions of simple velocity structure, such as above the top of salt, where there is only one ray path linking a surface point and a subsurface point, single-arrival Kirchhoff prestack depth migration imaging is adequate. For regions below the top of salt, when compared to the results of wave-equation migration methods, the single-arrival Kirchhoff algorithm can have degraded image quality in the subsalt. Therefore, Fairfield has developed a common-shot domain, multi-arrival, Kirchhoff beam prestack depth migration that can honor more than one ray path linking a surface point and a subsurface point, to provide higher fidelity imaging that retains steep dips. The accuracy and cost of this method lie between those of single-arrival Kirchhoff and wave-equation migration algorithms.
Reverse Time Migration
Fairfield Industries offers Reverse Time Migration (RTM) as a high-end tool for prestack depth imaging. RTM utilizes the full two-way wave equation, propagating both the source wavefield forward in time, and the receiver wavefield backward (or “reverse”) in time. This algorithm can properly image energy from all arrival paths, without dip limitation, in the presence of significant velocity variations, and in the presence of complex and overturned geologies. This allows RTM to provide extremely accurate image focusing without limitations. Although this method is computationally intensive, Fairfield’s RTM implementation can produce high fidelity images in a timely manner.