The Conductivity of Combined Acid and Hydraulic Fracturing in the Fractured Tight Sandstone Reservoir: An Experimental Study

In fractured tight sandstone reservoirs characterized by high calcium content, the composite stimulation technique that combines acid fracturing and hydraulic fracturing could show great production-enhancing capabilities. Nevertheless, the mechanisms of this composite technique remain unclear, and the field applications exhibit variability. Therefore, this study carried out fracture conductivity experiments, simulating different stimulation technologies to explore the influence of these techniques on the conductivity of artificial fractures, natural fractures, and reservoir fracture systems. The results indicate that composite stimulation enhances the conductivity of artificial fractures, natural fractures, and fracture networks. For artificial fractures, composite stimulation increases the conductivity to 2.5 times as much as that of sand-supported fractures at a sand concentration of 2 kg/m2. For natural fractures, after acid dissolution, the maximum sand concentration of 70/140 mesh proppants reaches 2 kg/m2, maintaining a conductivity of 4.2 D·cm under 40 MPa closure stress, while the conductivity of acid-etched fractures without proppant nearly vanishes. For fracture networks, when the sand concentration increases to 4 kg/m2, the conductivity reaches 3.5 times that at 2 kg/m2 and 2.8 times that of sand fracturing followed by acidizing. This study can provide guidance for the composite technique design in fractured tight sandstone reservoirs with high calcium content.