WITHDRAWN: The impact of stylolitization on the elastic properties of carbonate reservoirs using laboratory measurements

Abstract

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