Experimental studies on the effects of porosity on acoustic resonance spectroscopy for synthetic porous rock samples in a cylindrical resonant cavity

Based on our previous work on acoustic resonance spectroscopy (ARS) measurement, the ARSs in low frequency modes were measured for 10 synthetic oil-saturated rock samples with the porosities rang-ing from 22% to 30%, and the effects of porosity on ARS of the synthetic porous rock samples in a cylindrical resonant cavity were studied. The experimental results show that as the location of a syn-thetic rock sample changes from the top to the middle of the resonant cavity, the resonance frequency (RF) will gradually increase and the corresponding resonance amplitude (RA) will decrease. In the middle of the cavity, the RF reaches its maximum, while the RA reaches its minimum. When the syn-thetic rock porosity increases, the RF will decrease and the RA will decrease. Furthermore, the RF of a synthetic rock sample was numerically calculated with an average volume model in the resonant cavity. Our numerical results show that as the location of the sample changes from the top to the middle of the cavity, the RF gradually increases and the RF reaches its maximum value in the middle of the cavity. However, the RF decreases as the porosity of the sample increases in the middle of the cavity. The porosity effects on the ARS described above were confirmed by our experimental result as well as the theoretical analyses, which is important for porosity and fracture characterizations in a rock sample using the ARS in a low frequency mode.