Acid-Oxygen Synergistic Technology for Targeted Dissolution of Hybrid Organic–Inorganic Blockages in Low-Permeability Reservoirs

Low-permeability reservoirs are plagued by persistent hybrid organic-inorganic blockages in associated water injection wells (or pipelines), particularly under harsh environmental conditions. In northern Shaanxi, China, water injection wells exhibit chronic high-pressure under-injection (>10 MPa), a critical issue linked to unresolved scaling and organic residue accumulation. Conventional chemical treatments fail in subzero winters due to reagent freezing and inefficient dual-phase targeting. Here, we developed a staged acid-oxygen synergistic system (LTDS) integrating sulfamic acid (inorganic scale dissolution), ammonium persulfate (radical-driven polymer oxidation), and alkyl polyglycoside surfactants, augmented by an antifreeze additive (YangtzeU-TRA). Multimodal characterizationelemental analyzer (EA), X-ray diffractometer (XRD), Fourier transform infrared spectrometer (FTIR), and inductively coupled plasma optical emission spectrometer (ICP-OES)confirmed the formation of hybrid blockages. Specifically, the blockages consist of inorganic phases dominated by calcium carbonate (CaCO₃, 40.8 wt %) and iron-(III) hydroxide (Fe-(OH)₃, 1.3 wt %), alongside organic components (20 wt %) that are identified as oxygen-rich polymers (characterized by the presence of carboxyl [-COOH] and amide [-CONH₂] functional groups via FTIR analysis). The LTDS system achieved ≥85% dissolution within 1 h and ≥90% within 12 h at 40 °C. Crucially, LTDS retained fluidity after 48 h at -20 °C (no coagulation), addressing winter operational failures. The field test results of 3 typical wells all showed a sustained pressure reduction effect: post-treatment injection pressure stabilized at 2 MPa (vs pretreatment >10 MPa), with 100% single-operation success and 6 month stability. This study provides a solution for the dual-target dissolution of complex blockages in low-permeability reservoirs, which has direct implications for energy security and sustainable hydrocarbon recovery.