Unveiling the Diverse Effects of Water Cuts in a Supercritical CO2 Environment on the Corrosion Behavior of P110 Steel

The corrosion behavior of P110 tubing in a supercritical CO2/oil/water environment (20 MPa, 90 °C) was investigated over a test duration of 168 h by means of weight loss testing and corrosion scale analysis. The results reveal a significant transition at 50% water cut, where the uniform corrosion rate surged by approximately two orders of magnitude, while the localized corrosion rate exhibited a distinct convex trend, peaking at this threshold due to inhomogeneous wetting dynamics. The corrosion scales were identified as Calcium-substituted Iron Carbonate solid solutions (FexCa1−xCO3). Based on the competitive crystallization between corrosion-derived Fe2+ and bulk Ca2+, a mechanism for scale morphological evolution is proposed. This model explains the structural transition of the scale from a heterogeneous multi-layered film at a low water cut (30%) to a kinetic-controlled single layer at the critical water cut (50%), and finally, to a diffusion-controlled tri-layer gradient structure under fully water-wetted conditions (100%).