Seismic attributes for characterizing gas hydrates: a study from the Mahanadi offshore, India

Abstract

Seismic attributes have become successful in illuminating subsurface features and are widely used for identifying hydrocarbon reservoirs. The present work delivers case study carried out in the Mahanadi offshore basin lying in the eastern margin of India to delineate gas hydrates bearing zones using high resolution 2D seismic data. The presence of gas hydrates is identified by a bottom simulating reflector (BSR) on seismic section based on its characteristic features. Seismic attributes are computed to ascertain whether the BSR is related to gas hydrates. The data is conditioned using several post-stack processing steps such as detailed and background steering. The conditioning begins by steering of seismic data, which stores dip and azimuth information at every sample location. The Original seismic data is then filtered using a statistical filter to generate the dip-steered median filter data for extracting the instantaneous amplitude, instantaneous phase, instantaneous frequency, RMS amplitude and sweetness attributes. These are then used in demarcating the zones of gas hydrates or free gas occurrences. The low amplitude, high frequency and low sweetness attributes characterize the presence of gas hydrates. Whereas, free gas zones are characterized by bright amplitudes associated with low frequency and high sweetness below the BSR.