Nonionic Fast-Penetration System for Diffusion-Driven Degradation of Liquid Plugs

Degradable liquid gel plugs are increasingly required for zonal isolation in high-temperature reservoirs, yet their practical deployment is limited by slow internal degradation and insufficient structural failure under diffusive conditions. In this study, a diffusion-driven degradation strategy was developed based on γ-valerolactone and a nonionic fast-penetration agent (Tb), aiming to construct internal pathways and enhance decomposability of a model E51 epoxy–anhydride liquid plug. A multiscale characterization framework, including swelling index evaluation, SEM–EDS, FTIR mapping, CLSM imaging, μ-CT, AFM, and nanoindentation, was applied to investigate degradation behavior under varying temperatures (120–140 °C) and solvent-to-plug ratios (1:1–5:1). The plug exhibited a swelling index of 1.81 in GVL and formed tree-like degradation channels with widths of 20–30 μm. Functional group mapping revealed preferential cleavage of ester and ether bonds at the surface, and mechanical softening (modulus reduction > 57%) was confirmed by AFM and nanoindentation. Higher temperatures and solvent ratios synergistically reduced full degradation time from 84 h to 12 h. These findings validate a “penetration-induced softening–ester bond scission–diffusion channel construction” mechanism, offering an effective design pathway for intelligent degradation control in high-temperature downhole environments.