Synthesis of HEDP/PMMA Submicron Capsules for Long-Term Scale Inhibition in Oil Reservoirs

To address the short effective duration of conventional scale inhibitors in mature oilfields, hydroxyethyl diphosphonic acid (HEDP) / Methyl methacrylate (PMMA) submicron capsule were engineered via reverse microemulsion evaporation for sustained release. Optimized synthesis (core-wall ratio 1:6, Span80/W ratio 1:2, 3.5 h curing) achieved 95.3% encapsulation efficiency. The submicron capsule maintained 70–90% scale inhibition efficiency against CaCO₃ over 8 h. Flow tests demonstrated exceptional retention: submicron capsule withstood > 860 pore volumes (PV) before breakthrough, outperforming liquid inhibitors (160 PV) by 5.4-fold. Pretreatment with Cetyltrimethylammonium(CTAB) bromide further enhanced adsorption. Crucially, mechanistic studies revealed surface charge (zeta potential) as the dominant retention controller, while particle size showed negligible influence. This study proposes a surface-charge-dominated retention strategy for long-term scale inhibition in oilfields, which may contribute to more sustained scale control.