Investigation on the Conductivity of Complex Acid-Etched Fractures Based on Large-Scale Mine Acid Fracturing experiments

Acid fracturing is a key technology in the development of fractured carbonate reservoirs, and the conductivity of acid-etched fractures is one of the critical indicators for evaluating the effectiveness of acid fracturing. However, current conductivity calculation models for acid-etched fractures primarily focus on single, regular fractures of small dimensions, which differ significantly from the morphology of real fractures. Moreover, calculation models for the conductivity of complex fractures are relatively scarce.

This study establishes a conductivity calculation model for complex acid-etched fractures based on large-scale acid fracturing physical model experiments, filling a research gap in the field of conductivity calculation models for complex fractures. The research first conducted large-scale physical model acid fracturing experiments (dimensions: 2m × 2m × 1m) and accurately obtained the etched morphology data of the generated complex fractures using three-dimensional laser scanning technology. Based on these data, the concept of contact ratio was introduced using linear elastic theory to calculate the deformation of acid-etched fracture surfaces under the influence of closure stress, determining the width distribution of the deformed fractures. Subsequently, a conductivity calculation model for complex fractures, accounting for natural fractures and multi-branch fractures, was constructed. Based on this model, the effects of various influencing factors on the conductivity of acid-etched fractures were systematically analyzed.

The study indicates that in complex fracture networks, fracture density, orientation, and length significantly influence conductivity. When the fracture density is high, the interconnectivity between fractures is greatly enhanced, forming an efficient flow network that substantially improves overall conductivity. Additionally, when the fracture orientation is parallel to the main fluid flow direction, the fractures provide the shortest and most unobstructed flow paths, achieving maximum conductivity. In contrast, when the fracture orientation is perpendicular to the flow direction, the contribution of the fractures to conductivity is significantly reduced, serving only a limited auxiliary role at fracture intersections or within the fracture diffusion range. Meanwhile, long fractures enhance overall reservoir conductivity by connecting more reservoir regions, whereas short fractures struggle to connect distant reservoir areas, resulting in poorer localized conductivity.

The complex fracture conductivity calculation model proposed in this study is more closely aligned with field conditions and holds significant value for the design and optimization of acid fracturing in reservoirs with well-developed natural fractures, addressing a critical gap in existing research.