Hydraulic fracture propagation in thick conglomerate formations: Insights from acid-induced weakening

Conglomerate formations are characterized by strong heterogeneity, high mechanical strength, and a high resistance to fracturing. To address the challenges associated with effectively controlling fracture propagation trajectories and fracture zones—stemming from the pronounced heterogeneity and strength variations within thick conglomerate layers—both experimental testing and the finite element method were employed to simulate the propagation behavior of hydraulic fractures during acid-composite fracturing. The study systematically investigated the influence of acidizing duration, in situ stress conditions, gravel physical properties, and fracturing process parameters on fracture initiation and propagation. The results indicate that acid treatment significantly reduces the mechanical strength of the conglomerate by weakening the cementation between particles. Acid fracturing promotes a higher incidence of deflected fractures, leading to increased fracture width and extension distance. The particle size and content of gravel exert a direct influence on fracture trajectories. When fractures encounter large gravel, they tend to deviate from the direction of the maximum horizontal principal stress. As the gravel diameter decreases, the extent of fracture deviation diminishes, and propagation aligns more closely with the principal stress direction. Furthermore, excessive fracturing fluid injection rates and high fluid viscosities can adversely affect fracture width and propagation extent. The optimization of fracturing parameters is essential for achieving effective stimulation and favorable engineering outcomes in conglomerate formations.