Numerical investigation of the effect of fractures on acid dissolution patterns in naturally fractured carbonate reservoirs

Formation damage poses significant challenges in numerous carbonate oil and gas fields, often impeding hydrocarbon recovery. A widely adopted solution to mitigate these issues is the application of acid treatment, specifically matrix acidizing, which enhances permeability and repairs formation damage in carbonate reservoirs. Understanding the influence of fractures on fluid flow behaviour in naturally fractured carbonate reservoirs is both a critical and complex endeavour. Previous studies have inadequately characterized the mechanisms and effects of fractures on acidizing processes. This study introduces a novel model to quantitatively and qualitatively assess the impact of individual fractures under varying injection rates, as well as the influence of key fracture parameters on acidizing efficiency. The proposed model integrates a two-scale approach with a pseudo-fracture methodology to simulate acidizing in fractured carbonate media. Fluid transport equations were resolved at the Darcy scale and coupled with structural relationships at the pore scale. The findings demonstrate the distinct effects of horizontal and vertical fractures on dissolution patterns compared to fracture-free media. Specifically, the presence of a horizontal fracture reduces the pore volume to breakthrough (PV bt ) by 35% relative to homogeneous conditions, and also promotes the range of optimal injection rates rather than pinpointing a single rate. Conversely, a vertical fracture increases the PV bt by 18%, disperses acidic fluid and diminishes the dominant wormhole length. Adjustments to fracture parameters, such as reducing fracture permeability or increasing the distance from the wellbore, further influences the PV bt . Notably, extending the length and narrowing the aperture of horizontal fractures accelerates acidic fluid transfer, thereby reducing the dominant wormhole diameter. This study concludes that horizontal fractures generally facilitate the achievement of optimal acidizing conditions more rapidly. These findings provide the first comprehensive and quantitative analysis of the effects of critical fracture parameters on acidizing efficiency in fractured carbonate reservoirs, offering valuable insights for optimizing stimulation strategies in such complex formations.