Pre-Drill Overpressure Prediction in the South Caspian Basin Using Seismic Data

Abstract

Results are presented of the first pre-drill overpressure prediction in the South Caspian basin (SCB) on the basis of seismic data. The method is based on the REZAYR software package, which operates in Microsoft Windows. The analyzed seismic time-section fragment in the SCB was initially converted to an impedance section and then to a formation velocity section. Three overpressure zones of different thicknesses and extents are established. The shallowest overpressure zone extends to depths of less than 1 km. The nature of this relatively thin zone can be associated with biochemical gas generation. The second overpressure zone covers the depth interval 1.5–3 km and is most likely the result of non-equilibrium compaction (under compaction) because of high sedimentation rates. The third overpressure zone, the longest and thickest, is observed in the 6–9 km depth interval and is most likely attributed to hydrocarbons generation. This deepest zone poses the greatest risk for drilling. The seismic method of direct overpressure prediction in the SCB is in agreement with theoretical and experimental estimates and so is recommended for use in the SCB.