Depth and Least-Squares Imaging

DUG has extensive experience with complex depth imaging projects from all major oil and gas precincts.

This combined experience, along with our advanced toolkit, means that we are ready and able to tackle any project, large or small. Our migration and least-squares imaging solutions cater for 2D, 3D and time-lapse projects using towed-streamer, ocean-bottom and onshore seismic datasets.

Model building

DUG’s model building workflow incorporates both full waveform inversion and high-resolution reflection tomography. The entire workflow, including all interactive parts, is performed in DUG Insight, our 2D/3D/pre-stack interpretation system — allowing the geophysicist to immerse themselves in the data.

LAND IMAGING – ANISOTROPIC KIRCHHOFF PreSDM. Anisotropic (TTI) pre-stack Kirchhoff depth-migrated section from onshore Texas. Final velocity model and corresponding migrated stack after six iterations of anisotropic reflection tomography. Note the excellent match to the well markers over a range of depths. Multi-client data presented with permission from Geophysical Pursuit, Inc.

MARINE IMAGING – ANISOTROPIC KIRCHHOFF PreSDM Anisotropic (TTI) pre-stack Kirchhoff depth-migrated section from offshore Gabon. The final stack and interval velocity model after five iterations of anisotropic reflection tomography are shown. Image is courtesy of Harvest Natural Resources Inc.

Kirchhoff migration

Kirchhoff migration uses the integral form of the wave equation (Kirchhoff integral) to back-propagate the seismic wavefield. We offer time and depth and pre- and post-stack solutions including least-squares Kirchhoff pre-stack depth imaging for better illumination, improved resolution and amplitude fidelity.

DUG MigQ and DUG TomoQ

Geological complexities in the overburden (for example structure, gas hydrates, shallow gas and carbonate reefs) result in spatially varying and frequency dependent attenuation of the recorded seismic wavefield. DUG MigQ is a pre-stack depth migration-based workflow that compensates for laterally and vertically varying attenuation (or quality factor Q). In order to compensate for attenuation a Q model must first be estimated. DUG TomoQ is a robust frequency-dependent Q tomography process.

Before DUG MigQ and DUG TomoQ Model. The impact of spatially varying and frequency dependent attenuation of the seismic wavefield is clearly visible on the full stack section after Kirchhoff depth migration. A 1/Q model, derived using DUG TomoQ, show high 1/Q layers (in blue/purple) corresponding to shallow gas, which are conformable to a four-way dip closure. This model was used to produce DUG MigQ results shown in the second comparison.

Before and after DUG MigQ. Before (left) is the full stack section after Kirchhoff depth migration. After (right) is the full stack section after DUG Mig Q.

20 Hz RTM with legacy interval velocity model overlay (left) and final anisotropic (TTI) 30 Hz RTM, overlain with the final interval velocity model (right). A comprehensive salt model building workflow was an integral part of this project (South Campeche 3D Ultracube).

DUG Wave RTM

DUG Wave reverse-time migration is a two-way, wave-equation depth migration. It is capable of handling extremely complicated structure and abrupt lateral velocity changes.

Features of DUG Wave RTM include:
> Deconvolution imaging condition
> VTI or TTI anisotropy
> Surface-offset gathers (SOG)
> Vector offset output (VOO) for higher SNR images to aid interpretation
> State-of-the-art post-processing toolkit
> Scenario RTM (sRTM) for rapid scenario testing
> Least-squares imaging solutions: LS-RTM and LS-Q-RTM for better illumination, improved resolution and amplitude fidelity and compensation for laterally and vertically varying Q.

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