Improved seismic interpretation of a salt diapir by utilization of diffractions, exemplified by 2D reflection seismics, Danish sector of the North Sea

Abstract

Development of salt diapirs affects the hydrocarbon trapping systems in the Danish sector of the North Sea, where the reservoirs mainly consist of chalk. Seismic imaging and interpretation of the salt structures are challenging, primarily due to the complex geometry of the salt bodies and typically strong velocity contrast with the neighboring sediment layers. The quality of seismic imaging in the North Sea is highly dependent on the quality of the estimated velocity model. We have studied diffracted arrivals originating from the salt flanks and adjacent sedimentary structures using a diffraction imaging technique. The diffracted waves carry valuable information regarding seismic velocity and the location of geologic discontinuities, such as faults, fractures, and salt delimitations. We apply a plane-wave destruction method to separate diffractions from our stacked data. We optimize imaging based on diffraction analysis by using a velocity continuation migration technique, which leads to an estimation of the optimum focusing velocity model. We determine that the diffraction-based approach significantly improves the seismic imaging adjacent to the salt diapirs and the neighboring layers when compared with a standard approach in which we mostly ignore the diffractions. The new poststack time-migrated results provide detailed information that optimizes our interpretation of the salt diapir itself (e.g., the width of the salt neck) as well as the sediment layers related to the rim synclines. Processing schemes such as prestack depth migration and full-waveform inversion may potentially provide high-resolution images of the salt structures. We only account for diffractions in nonmigrated stacked data to better constrain seismic velocity and improve imaging around the salt diapir. The obtained results are critical for reservoir characterization.