Low-Permeability Shale Gas: Research on Sand-Carrying Flow Characteristics in Production Wellbore

To address the issue of reduced fracture conductivity caused by proppant particle backflow during the initial production phase of low-permeability shale gas wells, this study established a three-phase flow sand transport calculation model based on the Navier-Stokes equations, the renormalization group (RNG) k-ε model, and the theory of interphase momentum transfer in multiphase flow. The model accounts for the coupled effects of four primary factors: gas well production, water-gas ratio, sand content rate, and sand particle diameter. The accuracy of the model was validated by comparing it with actual production data. Through numerical simulation and orthogonal experiments, the quantitative analysis of the effects of gas well production, water-gas ratio, sand content rate, and sand particle diameter on sand-carrying capacity was conducted. The results indicate that the sand-carrying capacity of three-phase flow is directly proportional to gas well production and sand content rate, inversely proportional to sand particle diameter, and generally directly proportional to water-gas ratio (with a sharp decline in sand-carrying capacity at extremely low gas-water ratios). The weighting of each factor’s influence on sand-carrying efficiency (the ratio of the amount of sand carried out of the wellhead to the total amount of sand in the well) is as follows: sand particle diameter (dominant factor, 77.6% weighting), gas well production (17.2% weighting), sand content rate (2.8% weighting), and water-gas ratio (2.4% weighting). The dominance of particle diameter is attributed to its exponential influence on particle inertia and settling behavior, as characterized by the Stokes and Archimedes numbers. In contrast, the water-gas ratio and sand content primarily indirectly affect transport by altering continuous phase properties or interparticle interactions, resulting in relatively secondary effects. Based on regression analysis and sand production data under various operating conditions, a critical sand-carrying flow rate prediction model (R2=0.9415) was proposed, providing a theoretical basis and predictive tool for efficient sand control in shale gas wells, holding potential strategic value for the efficient development of unconventional natural gas and energy security.