SPIC, WOB, ONGC, Mumbai Email: lavendra@gmail.com 10 th Biennial International Conference & Exposition P 387 2D Acoustic Modeling Studies in Strong Velocity Contrast Area of Mumbai Offshore Basin Lavendra Kumar*, D.K. Vishnoi, D. Chatterjee Summary Areas having high velocity gradient and strong velocity contrast exist in Mumbai Offshore Basin of India due to presence of carbonates layers. Refracted, critically refracted, diving rays and converted modes seismic events are present in such areas in addition to surface related multiples and other form of multiples. Artifacts are also generated in high velocity contrast area on application of NMO or Kirchhoff depth migration. Identification of type of noises, their behavior on migration and proper techniques for their attenuation is very important. Modeling studies were carried out for identifying these non-reflecting events and their behavior on application of NMO and migration. The acoustic modeling was performed taking the interval velocity model in depth representing an area of Mumbai Offshore Basin India. The studies were, first, carried out on a grossly simplified model but representative of the area. Modeling studies were also carried with more complex 2D velocity model extracted from the final interval velocity volume obtained during PSDM project carried out recently in this area. Only acoustic (P-wave) modeling was undertaken. Elastic modeling could not be carried out but mode converted energy is expected in the area. The bifurcation of events was observed on modeled data with the application of NMO or migration and compared with real CRP gathers. The spurious events observed in migrated gathers during the processing of PSDM project were well understood with the modeling studies. Keywords: Carbonates, Forward Modeling, PSDM, Mumbai Offshore Basin Fig. 1: Study area Introduction Mumbai offshore area (Fig.1) is prolific producers of hydrocarbon mainly from carbonates reservoir. Deccan trap of Upper Cretaceous age unconformably rests on granitic basement of Achaean age in the area. The Panna formation of Paleocene to Lower Eocene age overlies unconformably on Deccan trap. It consists of mainly basal clastics and become the limestone towards the top part. The Bassien formation, which is limestone, overlies unconformably and overlaid by Mukta, Heera, & Bombay Formations. The Bassien limestone deposited during middle to late Eocene times is porous and forms the reservoir in the area. Overlying formations of late Tertiary age are dominantly consists of Shale interspersed with limestone bands and exhibits strong velocity gradient. Fig.2 shows the P-wave sonic log from a well in the area. The velocity gradient of roughly 1 s -1 (1 m/s increase of velocity per meter) is present above a high velocity layer at a depth range of 2200 mts to 2500 mts. Anisotropic depth migration had been carried out recently in this area. The interval velocity volume from this project was used for modeling studies. The data pre-conditioning, initial velocity model building and tomographic iterations issues encountered during the progress of the project had