Experimental study on composite technology of pulse discharge and acidization for reservoir pollution removal and permeability enhancement

Sandstone acidizing effectively removes mud and particulate blockages, dissolves acid-soluble minerals, and enhances porosity and permeability, thus increasing reservoir productivity. However, traditional acidizing methods face challenges such as poor adaptability, uneven effectiveness, increased costs, and risks in complex reservoir environments. Underwater high-voltage electric pulse discharge technology can instantaneously release high-energy shockwaves, improving rock porosity and permeability conditions. Combining electric pulse and acidizing technologies reduces acid usage, mitigates reservoir damage, and enhances overall treatment effectiveness. In this study, a high-voltage pulse discharge platform was used to investigate fracture propagation, permeability evolution, and microstructural changes in sandstone cores under different discharge conditions. Results indicate that shockwaves preferentially damage weak rock zones, with fracture propagation influenced by pre-existing fissures. Damage to structurally intact rock primarily manifests as mechanical erosion and fatigue fracturing. Microscopically, pores enlarge and interconnect into fractures, significantly improving permeability. Acid dissolution experiments revealed that a mixed acid solution of 12% hydrochloric acid and 3% hydrofluoric acid achieves optimal dissolution. Composite technology experiments demonstrated that for permeability enhancement, the optimal procedure involves electric pulse application followed by acidizing. Conversely, for deep acid-soluble blockages, acidizing before electric pulses is most effective; for shallow, acid-insoluble blockages, electric pulses followed by acidizing yield better results. This study confirms the efficacy of the combined electric pulse-acidizing technique, proposing a novel, complementary method for reservoir stimulation and blockage removal.