Estimation of the physical, petrophysical and mineralogical properties of Messinian salt rocks, Sicily: Implications for multidisciplinary applications

摘要

The Messinian Salinity Crisis (MSC) was a short-term (5.96-5.33Ma) and dramatic paleoenvironmental event, which led to the deposition of a thick evaporitic layer throughout Mediterranean area. However, several studies have demonstrated that Messinian evaporites have different characteristics and properties from East to West in the Mediterranean area, and the Caltanissetta Basin (Sicily, West Mediterranean) provides an excellent Messinian onshore record for investigating evaporitic succession. Given the scarcity of representative halite samples and, at the same time, widespread research and scientific drilling in the Mediterranean area, new physical, mechanical, petrophysical, mineralogical, and thermal characterization of Messinian halite could provide useful information for several disciplines and applications. Hence, 50 samples of Messinian halite were obtained from a Sicilian mine (Italkali), analyzed and tested using different instruments. Ultrasound velocities measured under hydrostatic confining pressure up to 120 MPa, ranged from 4210 to 4780 m/s and 2510-2650 m/s, respectively, for P- and S-waves. The results further showed that the halite samples had low porosity (2.5-8.5%) and negligible permeability, demonstrating the weak presence of pores and the total lack of interconnection among them, which is typical of rock salt units. Densities of the halite, determined with the hydrostatic weighing method and gas-porosimeter, were low and ranged from 2.14 to 2.23 g/cm(3), while high values were obtained for thermal conductivity (17.0 and 32.0 degrees C). It is significant that the mineralogical heterogeneity of the halite was due to the presence of clay-bearing veins. Although this work was performed mainly using onshore data and observations, the results have wider applications for offshore studies of the MSC and its deposits. Furthermore, the study provides important insights for future Mediterranean drilling projects, geological modelling, hydrocarbon exploration and/or fluids storage, and the understanding of salt rheology under different conditions of pressure and temperature.