Top seal efficiency of the Lakes Entrance formation, Gippsland Basin: some constraints from seismic inversion and attributes

Abstract

The Gippsland Basin is a potential site for CO2 storage which is dependent on the regional top seal in providing a secure subsurface containment. We present here some geological parameters derived with the aid of seismic attributes and inversion from 2D and 3D reflection seismic surveys predominantly along the southern flank of the basin. These parameters are potentially influential on the top seal efficiency and CO2 containment security in the basin.An important factor in top seal efficiency is the spatial variation of its shale content (Vsh). The empirical relationship between acoustic impedance and shale content was used to estimate Vsh. Composite seismic amplitude and acoustic impedance traces were constructed to establish a tie with the well-derived reference Vsh. Using a multi-attribute regression analysis, a transformation was established from seismic attributes and impedance to Vsh and used to define Vsh pseudotraces. Eight vertical profiles were produced in the Southern flank of the basin and the Vsh data were interpolated to reveal the first order variation in shale content for the top seal.Equally important in the assessment of containment risk is the distribution and density of faults in top seal. Seismic spectral blueing and attributes were used to increase the resolution of the 2D seismic data and a meta- attribute that sharpens the faults and suppresses non-fault discontinuities was coupled with similarity attributes to ensure a better imaging of low-displacement faults (<20 m). Automated mapping of the faults provided fracture density maps which depict the intensely deformed areas with potentially decreased seal efficiency on the southern flank of the basin.