Abstract

The Mesozoic reservoirs below basalt (Sub-basalt province) are prolific producers in many exploratory basins namely, Kutch and Saurashtra offshore of Western offshore basin, the Faeroes-Shetland Basin in North Sea and many others. The seismic imaging has major stake holding in identification of entrapment conditions within Mesozoic, below basalt. The regular PP imaging (using streamer data) may not be amenable for accurate subsurface mapping. The poor signal penetration through basalt section, masking of signals with multiples and presence of converted waves namely PSP, PSPP and PSSP are some of the serious impediments. The mode converted PSSP (symmetric waves) waves are found to be generated from basalt top (existing up to an offset distance of 8 Km +) duly validated by elastic modelling with synthetic responses. The PSSP waves were segregated in slowness domain and reflected PSSP signal was enhanced. Proper velocity estimation (RMS and Interval) could be achieved to perform time and depth imaging of PSSP waves. Mixed mode depth imaging was evolved summing PP and PSSP depth gathers which provides productive viable option for more precise structural interpretation for mapping of sub-basalt reflectors. The partial wide-angle imaging was also carried out to retrieve signal from higher offsets (12 Km as available in data) using a simple processing technique without applying front-end mute. The deeper events below basalt (imaged using the offset range 4-12 Km) were prominently brought out. Both the methodologies (Mixed Mode Imaging and partial Wide-Angle Imaging) will aid the structural interpretation appreciably.