Application of an integrated workflow for shallow-hazard characterization using a 3D high-resolution survey offshore Azerbaijan

Abstract

A methodology has been developed for quantitative prediction of shallow-hazard zones based on 3D high-resolution (3DHR) seismic and shallow-log data. The main goal of the integrated workflow is to produce an optimal structural image, conduct an AVO feasibility study and, if applicable, identify AVO trends within the depositional sequences of the shallow overburden at the Azeri field offshore Azerbaijan. Shallow, near-surface geologic-engineering hazards and features are not always visible on seismic volumes typically processed for reservoir targets. The 3D high-resolution seismic data provide good definition of shallow stratigraphy, indication of buried mudflows and landslides, and good fault delineation. AVO feasibility from rock-property analysis was affected by uncertainties arising from lack of or poor log data quality. With limited amounts of log data increasing the uncertainties, the use of trends based on data provided offered some initial understanding of shallow-seismic sensitivity. In depths < 300 m below mud line (BML), there is greater uncertainty because rock-physics models are not well understood in a generally unconsolidated section. However, where log data are available, there is an opportunity to use the integrated workflow in combination with geohazard interpretation to reduce uncertainty in subsurface description.

3D geometry of a shale-cored anticline in the western South Caspian Basin (offshore Azerbaijan)

“…They occurred in a close basin formed by terrigenous input provided by turbidity currents and deltas (e.g., Abdullayev, 2000). Complex diapiric structures occur in the fold core of the KAD anticline and are fed by overpressured muds, which produce a characteristic low-velocity zone and a shallow seismic attenuation (Lee et al, 1998;Gherasim et al, 2015;Hill et al, 2015). Most of the mud-diapir bodies are developed within the PS units, with a diapir head situated just below the PS-top, although the more mature structures occurring in the KAD fold culmination achieve exceptionally the Akchagyl Unit.…”