Acid-driven self-thickening VES foamed acid: Tailoring foam stability and acid retardation via micellar evolution

Conventional foam acids suffer from rapid foam collapse and poor retardation under high‑temperature and high‑salinity conditions, limiting their efficiency in deep carbonate reservoir acidizing. By systematically screening suitable foaming agents, VES stabilizers, corrosion inhibitors, and auxiliary stabilizers, an optimized high-performance VES foamed acid formula was obtained for reservoir acidizing treatment. The VES foam acid exhibits excellent foam stability: at 90 °C, the acid‑rock reaction rate is 0.00308 g·cm−2·min−1, which is 45.6% lower than that without VES. Even at a salinity of 50,000 mg/L (CaCl2 or NaCl), the initial foam volume remains above 550 mL, and the drainage half‑life is 10 minutes. Dynamic light scattering (DLS) and polarized light microscopy reveal a clear morphological transition of micelles as the acid reacts with Ca2+ released from the carbonate: from spherical micelles (13.5 nm) to rod‑like micelles (84.8 nm) to wormlike micelles (WLMs; 222.8 nm). The WLMs significantly increase the apparent viscosity and foam film thickness, providing an in‑situ self‑thickening effect. This work offers a practical foam‑acid system for high‑temperature, high‑salinity carbonate reservoirs and elucidates the Ca2+-induced WLM formation mechanism in strong acidic media.