Numerical modelling of seismic reflection in basalt terrains

Abstract

We have used numerical modelling to improve understanding of seismic reflection in basalt covered regions. Our models are based on hydrocarbon prospects in the Denison Trough (Queensland, Australia). Reflectivity modelling has been used to assess the influence of a range of model and source parameters. Models that include a single near-surface basalt layer generally result in relatively noise-free reflection signals, provided the basalt is reasonably attenuative. Reflection quality is poorest for models with buried high-velocity basalts, or for multi-layered basalts interspersed with lower-velocity material. Such models result in strong reverberatory noise, apparently propagating between the surface and basalt, or within the multi-layered basalts. In these situations, reflection strength is significantly improved if the source can be positioned below the basalt. Finite-difference modelling permits analysis of models incorporating lateral variations in basalt geometry. Shot records generated with this approach exhibit basalt-related features seen routinely in real field data. Simple stacking of the finite-difference records indicates that reasonable sections can be obtained in areas of near-surface, or thin, basalts. Poorer stack quality is associated with thicker, buried basalts although deeper reflectors may be imaged by undershooting the basalt.