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.
There are several application of the proposed project as it will provide a flexible tool to assess uncertainty and define a sensible use of seismic data in Exploration and Production activities linked to the scientific community, the Oil & Gas Industry, as well to CO2 sequestration projects, but also for ¿induced seismicity¿ feasibility and monitoring projects.
The results of the project will have significant implications for research in many fields. In fact, the study of the petrophysical and seismic properties of the involved lithologies is extremely useful for the characterization of reservoir and sealing horizons in oil and gas exploration, for fault-hosted mineralization and for the identification of good geological site for a safe geological sequestration of CO2 and storage of radioactive waste.
Moreover, although Vp/Vs ratio is widely recognized as one of the best parameters to assess the presence or monitoring the movement of fluids at depth, a rigorous characterization of the boundary conditions that determine an increase or a decrease of such factor in particular on carbonate rocks has never been performed yet. This is due to several factors. Firstly, a complete characterization of the variation of the Vp/Vs start from a good knowledge of the involved lithologies. The easily accessible carbonate rocks outcropping in the Northern Apennines that represent the same buried formation due the Apennines orogeny is a non-common characteristic elsewhere. The large number of drilled wells in the area and the presence of an extensive public dataset of borehole data is once again rare elsewhere. The consequent well known structures that characterize the subsurface of the Northern Apennines and the contemporaneous presence of many earthquakes in the area make the NA a perfect natural laboratory to perform such kind of research. Moreover, Laboratory machines able to reach pore pressure close to the confining pressure are not so diffuse, whilst we will have the possibility of working at very high pore pressure on both proposed laboratory (INGV-Rome and Durham). The proposed research will bring to the scientific community a unique dataset writing a new page in the experimental field with several applications for both academic and industrial field. Carbonates are widespread all around the world and a large number of seismic sequences in Italy and all around the world, nucleate or propagate through carbonate sequences, moreover in fold-thrust belts, involving sedimentary rocks, fractured carbonates commonly occur at the core of the anticlines, surrounded by low-permeability, ductile horizons, representing good reservoirs. However, mechanisms of fluid circulation and petrophysical properties of these systems are still poorly understood mainly due to difficulties in characterizing the influence of complicated litholologies such as carbonates. This project will also offer new and precious data for the oil and geothermal applications where fluid flow on carbonate rocks is always a challenging and not well constrained issue to be addressed.
Moreover, the aim of this integrated project is to provide additional tools to geoscientists in interpreting seismic data of the subsurface, to increase the geological value and predictivity of their interpretation and reduce uncertainty: this will result in a direct economical benefit as will allow to better plan and carry on expensive standard activities linked to the both Exploration, Development and Production.
Other possible economical benefits are linked to development phases of a carbonate related project, where the learning from applying a similar integrated approach could produce benefits in planning key decision with important economic impact for such as a decision on a well location.