History-dependent erosion mechanics and reverse-shear instability in alternating flows

Under the alternating injection and production stress acting on the storage reservoir pipe column, it will continuously be impacted by solid sand–grain particles carried by the high-speed fluid at specific angles and speeds, resulting in material damage and detachment, which affects its injection and production performance. To explore the erosion characteristics of the pipe column, this study developed a jet-type gas–solid–liquid three-phase erosion experimental system, using the typical plastic pipe material steel L80 as the research object, systematically studying the influence of particle impact angle, speed, and particle size on the erosion rate, and analyzing the microscopic wear mechanism of the material through scanning electron microscopy. Based on the experimental data, an erosion model applicable to the injection and production conditions of the storage reservoir was established using the least squares method, and its performance was assessed through computational fluid dynamics-based comparisons with the available experimental data. It was also compared with classic models such as the Generic model. The study shows that the L80 steel exhibits typical plastic material erosion behavior. The erosion rate reaches its peak at a 30° impact angle during the gas production stage and increases exponentially with the increase in particle speed and size. During the gas injection stage, the erosion is relatively mild but still follows a similar pattern. The established model is in good agreement with the experimental results and outperforms the commonly used classic models in terms of prediction accuracy. This study reveals the core mechanism of cyclic erosion, namely, after forming directional micro “lip-shaped structures” during the gas production stage, the reverse fluid impact during the gas injection stage will cause accelerated damage to its weak root points, which is the key physical mechanism for the exacerbation of material loss under alternating conditions. The research results deepen the understanding of the erosion mechanism of the pipe column in the storage reservoir and provide a theoretical basis and engineering references for predicting pipeline lifespan and ensuring safe operation.