Experimental study of artificial fracture conductivity during acid fracturing of radial wellbore

ABSTRACT: Acid fracturing is employed to enhance production from carbonate reservoirs. Fracture conductivity is a parameter governing the effectiveness of acid fracturing treatments. Conventionally, acid is injected through the wellbore into the artificial fracture to improve conductivity; however, this method is limited by the penetration distance of acid within the fracture. In this study, the effect of radial wellbores on fracture conductivity during acid fracturing was investigated. Rock slabs (17.78 cm x 3.81 cm x 1.9 cm) incorporating radial wellbores were prepared, and acidification experiments were performed. The etching patterns on the rock slab surfaces were analyzed using scanning electron microscopy (SEM). The conductivity of the treated slabs was then measured using a conductivity testing apparatus. The results indicate that radial wellbores alter the acid reaction mechanism. In rock slabs without radial wellbores, acid flow is lateral, with diffusion occurring from the wellbore towards the fracture tip; however, the acid penetration distance remains limited. The introduction of radial wellbores increases the acid penetration distance, suggesting coverage of the fracture network. Under radial wellbore conditions, the acid injection process transitions from a point-source to a line-source injection, wherein the vertical diffusion of acid plays a role in the treatment effectiveness. Analysis reveals that radial wellbore configurations achieve approximately a two-fold increase in acid penetration depth compared to conventional systems, with dissolution mass improvements ranging from 41.5% to 47.8% under identical reservoir conditions. The intersection of natural fractures with radial wellbores can compromise the fluid control exerted by the radial wellbores over the acid. Conductivity analysis reveals stress-dependent behavior in radial wellbore-enhanced systems. Radial wellbore architectures (L-3/L-4) demonstrate initial conductivity (>1000 µm2·cm below 50 MPa closure stress); however, they exhibit a decline in conductivity with increasing closure stress, characterized by reduction trends (R² > 0.95).