P-wave Velocity in Sandstone under Controlled Temperature and Humidity

摘要

In this study, we measured P-wave velocities in Berea sandstone and Shirahama sandstone in airrnwith controlled temperature and relative humidity, and investigated their changes under differentrnhumidity conditions. To measure P-wave velocity, we used ultrasonic pulse method. Rock specimensrnwere placed in a chamber where the temperature and relative humidity can be controlled, while wernconducted measurements. P-wave velocity was measured in air at a constant temperature with thernrelative humidity of 50% or 90%. It was found that when the relative humidity increased from 50% torn90%, P-wave velocity decreased and the water content increased. By contrast, when we decreased thernrelative humidity to 50%, P-wave velocity increased and the water content decreased. It is consideredrnthat the observed changes of the velocity were caused by the changes of the amount for water in thernpores or cracks with tiny aperture by the capillary condensation. If the amount of the condensed waterrnincreases, the compressive stress around the tiny pores and cracks decreases. This decrease of therninternal compressive stress affected the decrease of P-wave velocity in rock. It is also considered thatrnthe observed increase of P-wave velocity was caused by the decrease of the amount of condensed waterrnand the increase of internal compressive stress by capillary condensation. It is concluded that thernphysical property of sandstone is affected by the change of the relative humidity.