The seismic signature of heavy oil on carbonate reservoir through laboratory experiments and AVA modelling

The influence of unconventional oil on the petrophysical properties of carbonate rocks is of primary interest in petroleum science. In this work, we first provided a thorough petrophysical characterization in laboratory by measuring density, porosity, VP and VS of a bitumen carbonate reservoir rock outcropping in the Majella Mountain (Central Italy). The presence of bitumen stiffens the rock and causes an increases of the acoustic impedance (AI) and a strong decrease of the VP/VS ratio respect to brine saturation. On the contrary, lighter oil causes a decrease of the AI and a slight decrease of the VP/VS ratio in comparison with a saturation in brine. Then, we performed a Synthetic Amplitude vs Angles (AVA) modelling showing that through the AVA ana- lysis, it is possible to recognize the type of fluid that saturates the analyzed carbonate reservoir rocks. We also observed that the increasing porosity plays a key role in the AVA response, by decreasing the bulk density and seismic waves velocities and increasing the amount of fluids that saturate the rocks. By applying our laboratory and modelling results to a public stacked seismic line we show that our results may help in recognize heavy oil directly from seismic data.