Sedimentary stylolites as key controls on elastic anisotropy and sonic velocities in heterogeneous carbonate reservoirs

• Morphologically identification of four groups of rectangular, seismogram, sutured, and wavy-like stylolites • The results indicated that stylolite-bearing samples generally show higher compressional wave velocity than the stylolite-free samples • It is clearly concluded that the effect of open stylolites on the elastic properties of studied samples is the same as soft porosities. • Higher velocities for sharp stylolite morphology (rectangular and seismogram) in a specific confining pressure are recorded in comparison to the low amplitude stylolites (wavy-like). • We detected the sedimentary stylolites origin for our selected samples based on mechanical anisotropy analysis. 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.