Diffractions caused by, e.g., faults, fractures, and small-scale heterogeneity localized near the surface are often used in ground-penetrating radar (GPR) reflection studies to constrain the subsurface velocity distribution using simple hyperbola fitting. Interference with reflected energy makes the identification of diffractions difficult. We have tailored and applied a diffraction imaging method to improve imaging for surface reflection GPR data. Based on a plane-wave destruction algorithm, the method can separate reflections from diffractions. Thereby, a better identification of diffractions facilitates an improved determination of GPR wave velocities and an optimized migration result. We determined the potential of this approach using synthetic and field data, and, for the field study, we also compare the estimated velocity structure with crosshole GPR results. For the field data example, we find that the velocity structure estimated using the diffraction-based process correlates well with results from crosshole GPR velocity estimation. Such improved velocity estimation may have important implications for using surface reflection GPR to map, e.g., porosity for fully saturated media or soil moisture changes in partially saturated media because these physical properties depend on the dielectric permittivity and thereby also the GPR wave velocity.

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.

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