P-wave velocity estimation of unconsolidated sediments containing CO2

Carbon dioxide (CO2) can be geologically stored in unconsolidated sediments that have overlain impermeable layers that act as a cap rock. The migration of injected CO2 can be monitored by analyzing the P-wave velocities of the hosting sediments. This study suggests a new empirical bulk modulus model for the CO2 that considers the temperature and pressure effects (in the ranges of 5-35 °C and 4-22 MPa) of the storage site. Moreover, a P-wave velocity model of unconsolidated sediments containing CO2 is developed and verified by experimental tests. Because of the model's simple formula, the suggested model can be readily applied to general numerical analyses and seismic exploration. The effects of temperature, pressure, CO2 saturation, and effective stress on the P-wave velocities are also discussed on the basis of the proposed P-wave velocity model. The effects of temperature and pressure are more significant at shallow depths. Therefore, CO2 saturation may be incorrectly estimated at shallow depths if the temperature and pressure of the storage site are not carefully considered.