Ultrasonic P-wave to determine pore parameters of Spergen limestone.

Ultrasonic waves are capable of helping characterize pores of rocks. A model of viscous squirt is used to simulate phase velocity and the quality factor of ultrasonic P-wave measured in water-saturated Spergen limestone, thus determining pore parameters of the limestone. The measured P-wave had a centroid frequency of ∼0.75 MHz, and two simulations are conducted in this paper. The first simulation yields a dispersion curve with a dipping spike followed by a rising spike. However, it cannot yield the measured quality factor. Another drawback is that one of the pore parameters violates rock physics. The second simulation yields a dispersion curve with a small velocity depression followed by an upward velocity concave; the measured phase velocity and quality factor are simultaneously predicted. The resulting dimensions of the rock unit are 0.3 by 0.333 mm, which is consistent with the mean grain diameter of 0.3 mm. The relative first and second porosities are ascertained to be 0.97 and 0.03, respectively. The aperture distance at contact of grains is inverted as 1.8 µm. Remarkably, the minimum phase velocity of the water-saturated limestone is lower than the Gassmann velocity. [ABSTRACT FROM AUTHOR]