Pre-drill Overpressures Prediction in the South Caspian Basin using Seismic Data

The results of the first attempt of pre-drill overpressures prediction in the South Caspian basin (SCB) on the basis of seismic data are presented in this paper. The used 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 into an impedance section and then into formation velocities. The three overpressure zones of different thicknesses and extents are established. The first uppermost overpressure zone extends to depths of less than 1 km. The nature of this relatively thin zone can be associated with the biochemical gas generation. The second overpressure zone is covered the depths 1.5-3 km and is most likely the result of non-equilibrium compaction (undercompaction) of the rocks 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 the hydrocarbons generation. This zone poses the greatest risk for drilling. The seismic method of the direct overpressure prediction in the SCB is quite agreed with theoretical and experimental estimations and recommended for use in SCB.