Combined Proppant and Acid Stimulation Method in Ultra-Low-Permeability Dolomite Reservoirs: Laboratory Investigation

This study explores the viability and efficiency of employing a dual approach, combining proppant fracturing with acid fracturing, in ultra-low-permeability dolomite reservoirs. The damage of guar gum fracturing fluid and slick water fracturing fluid on rock permeability was assessed through high-pressure pulse permeability testing. The mechanical properties of rocks post-acid treatment were evaluated using gelled acid, and fracture conductivity under various stimulation methods was measured. The results reveal that both guar gum and slick water fracturing fluids induce minimal damage to reservoir permeability. Following 10 and 30 min of acid treatment, the Young's modulus of the rocks is decreased by 10.65% and 17.63%, respectively, enhancing the effectiveness of hydraulic fracturing. As closure pressure increases, the conductivity of acid-etched self-propped fractures decreases rapidly due to the highly non-uniform etching caused by the acid. The addition of proppants markedly enhances the conductivity retention of fractures. The particle size of proppants exerts a significant influence on fracture conductivity, with larger proppant sizes leading to enhanced conductivity. However, as closure stress escalates, the disparity in conductivity between fractures with varying proppant sizes diminishes. Fracture conductivity tests conducted under various stimulation methods reveal that introducing proppants before acid treatment yields the highest fracture conductivity. Delayed addition of acid prevents proppants from occupying the acid-etched channels, thus enhancing reservoir treatment effectiveness. This study holds significant importance for designing effective stimulation techniques tailored to ultra-low-permeability dolomite reservoirs.