Abstract: The pore structure, pore types, and specific mineral composition of coral reef limestone endow it with distinct acoustic characteristics compared to conventional limestone and other rocks. Previously, limited research has been conducted on the microscopic pore structure characteristics of reef limestone and their impact on P-wave velocity. In this study, borehole core samples from the Nansha Islands reefs were selected to measure and calculate the horizontal P-wave velocity, porosity, and pore structure. Combined with 3D digital core pore models, the influence of microscopic pore structure on the horizontal P-wave velocity of coral reef limestone was systematically investigated. The results indicate that the high-resolution horizontal P-wave velocity ranges from 4,441 m·s⁻¹ to 6,525 m·s⁻¹, and the porosity ranges from 0.40% to 31.46%, the density ranges from 2.07 g·cm^-3 to 2.72g·cm^-3. The pore shape is dominated by an-equant pore structures, and the main pore type is inter-crystalline dissolution pores. Furthermore, the P-wave velocity exhibits a negative correlation with porosity. This study demonstrates that the Nansha coral reef cores possess a compact structure and exhibit good geological stability.

Key words: coral reef limestone, microscopic pore structure, porosity, P-wave velocity, South China Sea