Stylolitization is a key diagenetic feature in carbonate rocks that can influence their elastic behavior. This study investigates how different stylolite types affect wave velocities and mechanical anisotropy using hydrostatic and ultrasonic laboratory tests. Core plugs were selected based on petrophysical data, well logs, and CT scans, and stylolites were classified morphologically into rectangular, seismogram, suture, and wave-like types. The observed stylolites were subdivided into four groups: rectangular, seismogram, suture (sharp), and wave-like. Hydrostatic tests were conducted under drained and undrained conditions to evaluate the effect of pore pressure on elastic properties. Stylolite-bearing samples generally exhibited higher compressional wave velocities than stylolite-free samples, due to lower porosity and the stiffening effect of mineral or organic fillings. Shear wave velocities showed smaller variations. Open stylolites acted like crack porosity and reduced velocities, whereas filled stylolites increased velocities depending on the infill material. Our findings indicate that the opening or filling material within the stylolites may have contributed to the increase or decrease in the sonic velocities. Open stylolites behave similarly to crack porosity features and can decrease the velocities. However, the filled stylolites showed a positive effect on the velocities depending on the filling materials, which were dense. Morphology-controlled velocity variations and mechanical anisotropy analysis further confirmed the sedimentary origin of the stylolites. These findings provide quantitative insights into the elastic anisotropy induced by stylolites and their implications for engineering-scale reservoir characterization, subsurface geomechanics, and modeling of heterogeneous carbonate reservoirs.

Keywords