ALBERT

Description: Petrophysical properties of rocks and their applicability at larger scale are a challenging topic in Earth sciences. Petrophysical properties of rocks are severely affected by: boundary conditions, rock fabric/microstructure, and tectonics that require a multi-scale approach to be properly defined. Here we: (1) report laboratory measurements of density, porosity, permeability and P-wave velocities at increasing confining pressure conducted on Miocene foredeep sandstones (Frosinone Fm.); (2) compare the laboratory results with larger-scale geophysical investigations; (3) discuss the effect of thrusting on the properties of sandstones. At ambient pressure, laboratory porosity varied from 2.2% to 13.8% and P-wave velocities (Vp) from 1.5 km/s to 2.7 km/s. The P-wave velocity increased with confining pressure, reaching between 3.3 km/s to 4.7 km/s at 100 MPa. In situ Vp profiles, measured using sonic logs, matched the ultrasonic laboratory measurement well. The permeability varied between 1.4 × 10 -15  m 2 to 3.9 × 10 -15  m 2 and was positively correlated with porosity. The porosity and permeability of samples taken at various distances to the Olevano-Antrodoco fault plane progressively decreased with distance while P-wave velocity increased. At about 1 km from the fault plane, the relative variations reached 43%, 65% and 20% for porosity, permeability and P-wave velocity, respectively. This suggests that tectonic loading changed the petrophysical properties inherited from sedimentation and diagenesis. Using field constraints and assuming overburden-related inelastic compaction in the proximity of the fault plane, we conclude that the fault reached the mechanical condition for rupture in compression at differential stress of 64.8 MPa at a depth of 1500 m.