Stylolitization is one of the most important sedimentary features occurring during diagenetic 13 processes in carbonate rocks. This study experimentally explored how stylolitization and stylolite 14 types affect the elastic behavior of carbonate rocks using hydrostatic tests and ultrasonic 15 measurements. Moreover, petrophysical and well data, including logs (image logs, density, 16 porosity, compressional sonic wave, and shear sonic wave), and Computed Tomography (CT) 17 scans have been used for the selection of appropriate plugs and stylolite classification based on 18 their morphological properties. The observed stylolites were subdivided into four groups: 19 rectangular, seismogram, suture (sharp), and wave-like. To develop new insight into the 20 relationship between stylolites and elastic properties, hydrostatic laboratory tests were conducted 21 under two different saturation conditions: drained (zero pore pressure) and undrained (constant 22 pore pressure). Our results indicate that stylolite-free samples have higher porosity, which suggests 23 that they may have lower velocities. Furthermore, we observed that the stylolitified samples had a 24 higher gradient of VP changes compared with the VS changes, with a strong dependency on the 25 stress state variations (confining and effective pressures). These samples have more potential to 26 contain crack porosities than stylolite-free samples, and stylolites may act as weak surfaces. These 27 weak surfaces can cause different velocity behaviors in the stylolite-bearing samples at low and 28 high pressures (room and reservoir pressures). Our findings indicate that the opening or filling 29 material within the stylolites may have contributed to the increase or decrease in the sonic 30 velocities. If the stylolites are open, then their behaviors are similar to those of crack porosities and 31 can decrease the velocities. However, the filled stylolites showed a positive effect on the velocities 32 depending on the filling materials, which were dense. Finally, this study presents a mechanical 33 anisotropy analysis to identify the origin and type of stylolite.

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