Investigating the source of acoustic anisotropy in the Asmari Formation, a fractured carbonate reservoir, using a well in the Southwest Iran

Acoustic wave anisotropy in fractured carbonate reservoirs remains a key challenge for accurate reservoir evaluation and well placement. The Asmari Formation, one of Iran’s most productive reservoirs, is strongly affected by complex fracture networks and heterogeneity, significantly distorting its acoustic log responses. This study applies an integrated workflow combining facies analysis, borehole image interpretation, borehole geometry assessment, and advanced dipole sonic processing across five reservoir zones in a well in a Southwest Iranian oilfield. Geological controls were constrained through petrography and facies descriptions, while textural and structural features, fracture sets, and in-situ stresses were identified from borehole image logs. Dipole sonic data were processed to evaluate shear-wave splitting, azimuthal velocity variations, and Stoneley wave reflection coefficients, with fracture density used to assess connectivity and transmissivity. Results show that anisotropy is predominantly governed by fracture intensity and connectivity rather than facies variability. Zone 1 records the strongest anisotropy, while Zone 3 remains nearly isotropic. In contrast, Zone 4 demonstrates poor fracture connectivity reduces anisotropy despite higher fracture counts. Borehole effects in Zone 5 generate apparent anisotropy unrelated to the actual reservoir properties. Overall, anisotropy decreases systematically from Zone 1 to Zone 3, with connectivity and borehole artifacts as decisive modifiers. The above workflow highlights the necessity of integrating geological and geophysical datasets to separate genuine reservoir anisotropy from borehole-related effects, enabling more reliable prediction of fracture permeability and improved reservoir development strategies.