Pressure dependence of elastic wave velocities of unconsolidated cemented sands

We have developed lower and upper bounds for the pressure-dependent elastic wave velocities of unconsolidated cemented sands, which are due to variations in cement layer thickness and direct grain contact area with effective pressure, respectively. Investigating the factors influencing these bounds, we have found that the elastic wave (P- and S-wave) velocities increase with the effective pressure, whereas their ratio (V-P/V-S) decreases. The elastic wave velocities and their ratio have an almost linear relationship with the effective pressure for the lower bound, whereas that for the upper bound is nonlinear. For both lower and upper bounds, the sensitivities of the elastic wave velocities and their ratio to the effective pressure increase with decreasing precompacted pressure, cement elastic moduli, and cement volume content. By comparing the theoretical predictions with ultrasonic measurements on heavy-oil sands and cemented glass beads, we have validated that the experimental data fall within the proposed lower and upper bounds. The experimental data shift from the lower bound to the upper bound as the effective pressure increases, revealing that the grain compaction pattern changes with increasing effective pressure.