Nonlinear Coupling of Solid–Liquid Invasion Damage in Tight Sandstone Reservoirs: A Multi-Scale Characterization and Suppression Modeling Approach

Formation damage in tight sandstone reservoirs is commonly evaluated by assuming that solid-phase plugging and liquid-phase filtrate invasion act independently and contribute linearly to permeability loss. In realistic drilling scenarios, however, these two phases invade the formation sequentially and interactively, rendering the linear superposition assumption physically questionable. This study develops a multi-scale experimental framework to investigate the nonlinear coupling between solid-phase and liquid-phase invasion damage in tight sandstone reservoirs. Progressive core flooding experiments were conducted under isolated and coupled invasion conditions, combined with NMR, micro-CT, and SEM/EDS analyses to characterize the evolution of permeability, pore structure, and particle retention. Results show that solid-phase plugging not only causes direct permeability reduction but also suppresses subsequent liquid-phase invasion by modifying pore–throat connectivity. To quantitatively describe this suppression effect, a coupling model based on a suppression factor ψ(θ) is proposed, in which the liquid-phase accessible damage fraction is expressed as a nonlinear function of solid-phase blocking intensity θ derived from CT-based bottleneck analysis. Among the tested functional forms, a sigmoid relationship best captures the observed threshold-dominated behavior (R2 = 0.956). Experimental results indicate that under strong solid-phase blockage, liquid-phase damage is reduced by up to approximately 37% compared with its uncoupled value, explaining why total coupled damage is significantly lower than the arithmetic sum of solid-only and liquid-only damage benchmarks. This work provides experimental evidence for nonlinear solid–liquid coupling in drilling fluid–induced formation damage.