One of the most useful geophysical tools for monitoring sub surface CO2 injection as well as monitoring possible fluids movement at depth is seismic imaging, particularly time-lapse characterization. Interpretation of seismic data for the quantitative measurement of the distribution and saturations of fluids in the subsurface requires knowledge of the petrophysical properties of involved rocks and fluids in particular for heterogenous rocks such as carbonates. The aim of this project is to unravel the fluid influence on the Vp/Vs ratio on carbonate rocks at depth through a complete characterization of the petrophysical properties of the carbonate rocks in presence of fluids. The project will focus on the most representative (thicker) carbonate formations of the Apennines: massive pure limestone (Calcare Massiccio, CM), layered pure limestone (Maiolica, MA), and layered marly limestone (Calcareous Scaglia, SC). We will then perform a complete petrophysical characterization of these different type of carbonates in laboratory to be compared with in situ measurements of the public ViDEPI project.
The comparison of the properties coming from borehole data and laboratory will help in understand how to upscale the data at crustal depth. Once the scaling relationship will be known we will proceed in particular to the upscaling of the Vp/Vs ratio that will be for the first time rigorously characterized. By comparing the Vp/Vs resulted from tomography studies and seismic surveys within the same lithologies, with laboratory data, we will be able to correctly reconstruct the boundary condition acting at depth inferring the actual values of pore pressure by using only indirect investigations. These pieces of information are crucial for example in the induced seismicity field CO2 storage where fluids pressure and lithology properties play a key role. The expect results will thus help in making the interpretation of subsurface images of the Northern Apennines definitely CLEARER.
