Effects of Rock Sample Size on Critical Proppant Flowback Velocity and Implications for Production Optimization

Sand production in tight gas wells can cause severe erosion of downhole and surface facilities and pose a significant risk to safe and stable production. Proppant flowback is recognized as a key mechanism governing this process, and laboratory determination of the critical sand-production velocity provides an effective means for quantitative evaluation. Most existing studies are based on modified American Petroleum Institute (API) conductivity tests, which require large sample volumes and involve long experimental cycles and high costs. Building on previous work, critical sand-production behavior was investigated under consistent experimental conditions by comparing plunger core samples with conventional API cells, focusing on the influence of closure pressure and sample scale. The results show that, under identical closure pressure, the critical sand-production velocity measured using plunger cores is lower than that obtained from API cells. At a closure pressure of 10 MPa, the critical velocity is approximately 30.8% lower, while the difference decreases to 0.67% at 30 MPa. Based on the experimental data, critical sand-production velocity models corresponding to the two sample scales were established and show good agreement with experimental observations. The model was further applied to the production history of Well W-1 in the Wenxing gas field to evaluate sand production risk and support production optimization. The field results demonstrate that the model can identify high-risk sand-production stages and provide quantitative guidance for stabilizing production and reducing sand production in tight gas wells.