Formation Imaging from Three-Component Borehole-Seismic Data Using both Space-time Relations and Wave-Field Polarization

Geophysical Prospecting

Jahren

2021

Self Cite

By applying a ray‐based three‐dimensional vector migration process to fully elastic three‐component synthetic Vertical Seismic Profiling data, we are able to demonstrate that the process gives an accurate compressional reflection image of the complex formation without much visible artefacts from spatial aliasing, or from ‘migration smiles’ caused by the limited aperture of the receiver array. We demonstrate that the process reconstructs images of both steeply dipping salt flanks, and the sediments that tend to be dragged along by the moving salt and truncated against the sides of the salt body. The process uses raw unseparated data as input, and the wavefield separation of compressional and shear waves are done by projection operators inside the kernel of the migration process. The compressional reflection image appear to have no visible artefacts from the abundance of converted shear.

Section: Imaging With Vector Datamentioning

confidence: 99%

Section: Imaging With Vector Datamentioning

confidence: 99%

Section: Applicationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Imaging complex three‐dimensional structures, applying three‐component vector migration to synthetic vertical seismic profiling data

Geophysical Prospecting

Jahren

2021

Self Cite

Imaging below a complex overburden with borehole-seismic data

Jahren²

2020

GEOPHYSICS

We have determined how the measured polarization and traveltime for P- and S-waves can be used directly with vertical seismic profile data for estimating the salt exit points in a salt-proximity survey. As with interferometry, the processes described use only local velocities. For the data analyzed in this paper, our procedures have confirmed the location, inferred from surface-seismic data, of the flank of a steeply dipping salt body near the well. This has provided us more confidence in the estimated reservoir extent moving toward the salt face, which in turn has added critical information for the economic evaluation of a possible new well into the reservoir. We also have found that ray-based vector migration, based on the assumptions of locally plane wavefronts and locally plane formation interfaces, can be used to create 3D reflection images of steeply dipping sediments near the well, again using only local velocities. Our local reflection images have helped confirm the dips of the sediments between the well and the salt flank. Because all parameters used in these processes are local and can be extracted from the data themselves, the processes can be considered to be self-sufficient.

Spatial aliasing and 3C seismic sensors

2021

GEOPHYSICS

Temporal aliasing occurs when a waveform is sampled with less than two points per time period for a signal at a given frequency. This insufficiently sampled frequency will incorrectly be mapped into a lower (aliased) frequency. Analogous to this, spatial aliasing is said to occur when a propagating waveform is measured at spatial intervals larger than half the wavelength of any given signal in that waveform. Temporally aliased frequencies cannot be recovered with standard methods. On the other hand, we argue that "spatial aliasing" can be viewed as an expression of a non-uniqueness for estimating the direction of the propagation for signal at a given frequency, and that spatial aliasing may be overcome when three-component seismic sensors are used. Realizing this allows for using higher frequencies, and therefore enables the generation of higher resolution images from the data. This is particularly useful for borehole-seismic data which tend to contain higher frequencies than surface-seismic data, but does require that an array of three-component sensors is used, or that an array of less expensive single-component sensors is supplement by three-component sensors.