Analysis of the correlation between fracture topology and mechanical properties of rocks in fractured carbonate reservoirs: In Dehram group, Fars arc Zone (Southwest Iran)

Abstract

Fractures play a critical role in fluid transport within brittle rocks, particularly in carbonate reservoirs. This study focuses on understanding the relationship between mechanical stratigraphy and natural fractures in the carbonate reservoirs of the Dehram Group in the Zagros region (Fars Arc), Southwest Iran. Using high-resolution borehole images and various well logs, the spatial distribution of fractures in this group are investigated. The study examines mechanical stratigraphy at two scales: large-scale mechanical stratigraphy, characterized by rock strength variations in units thicker than 1 m, primarily affecting overall fracture intensity; and small-scale mechanical stratigraphy, revealed through borehole images, which significantly influences fracture aperture and continuity. The connectivity of fractures was evaluated using the degree of fracture connectivity (D), with results showing "good" connectivity in terms of increased permeability (D = 2.6) in the Kangan formation and "excellent" connectivity (D = 3.5) in the Dalan formation. Block intensities (R₂₂) were measured at 0.4 in the Kangan and 0.2 in the Dalan, indicating varying degrees of rock fragmentation. Spatial variations in fracture connectivity across different zones are influenced by lithology, strain distribution, and the presence of weakness zones such as faults. These insights are essential for developing predictive models of reservoir performance in naturally fractured carbonate systems.