Assessing the impact of oil saturation on wormhole morphology in carbonate acidizing

Abstract

Carbonate acidizing is a well stimulation technique used to improve oil production by acid injection into the formation, creating conductive paths through rock dissolution. Most of the acidizing laboratory experiments are conducted on water-saturated rocks, assuming no oil is present after previous drilling and completion operations. However, different saturation conditions can occur in the rock formation, affecting the acidizing process. This study aims to assess the impact of oil saturation on carbonate acidizing. Reactive flow experiments were conducted on rocks saturated with water and oil using HCl 0.5 M and HCl 15%wt. at room temperature and 45 °C at flow rates of 1 and 20 mL/min. X-ray microtomography was used to visualize the wormhole morphology and compare the pore-volume-to-breakthrough (PVBT) values for each flow condition. Oil saturation resulted in efficient propagation of the wormhole with lower acid consumption and lower PVBT values. At 45 °C, PVBT values decreased by 54% for HCl 15%wt. at 20 mL/min. Wormhole morphology showed a smaller thickness in its propagation with oil saturation than with water saturation at the lower acid concentration, but not at the higher concentration. The presented results contribute to a deeper understanding of the significance of oil saturation in reactive flow during carbonate acidizing.