Seismic forward modelling for shale gas characterisation in the Laurel Formation, north Canning Basin

Abstract

The Carboniferous Laurel Formation is a thick, regionally extensive package of sand, shale, and limestone with significant liquids content. This study aims to investigate the relationship between total organic carbon (TOC) content and seismic attributes by forward modelling of seismic response to variations in TOC content and calibrating the models using available well and seismic data. A regional relationship between acoustic impedance and TOC content has been established based on the TOC measurements of core samples taken from wells penetrating the Laurel Formation. This regional function has then been calibrated to the Sundown–1 well, which is located in the Bunda 3D seismic survey in the northern Canning Basin. The calibrated function has been used to estimate the acoustic impedance of the shale interval for a range of TOC values. Based on these acoustic impedance estimates, the reflectivities have been calculated and the synthetic seismograms for corresponding TOC values have been generated. A direct transformation of seismic amplitudes to TOC content has been achieved by plotting the AI against TOC and fitting the appropriate trend function to the data. The seismic tuning effect has been modelled as an important cause of variations in amplitudes to be considered and compensated for in TOC estimates. A map of scale factors has been generated based on results of a wedge model to remove the seismic tuning effect from TOC estimates. The resulting TOC content map includes some interesting features that can be considered as shale gas sweet spots.