Numerical simulation of near-wellbore zone under alternating loads in low-permeability sandstone UGS to improve formation sand production prediction accuracy

In depleted oil and gas reservoir UGS, sand production generally occurs during both gas injection and production phases, which poses significant challenges to the safe operation of the UGS facility. Integrating sand production erosion criteria and based on porous elastoplastic governing equation, a numerical simulation model of sand production is established under alternating loads to calculate the influence of such formation parameters as porosity, permeability, and elastic modulus on sand production in the near-wellbore zone of UGS, and analyze the sand production mechanism in the near-wellbore zone of UGS under alternating loads. The simulation results of UGS Y indicate that the sand erosion area in the wellbore gradually expands as the ratio of horizontal principal stress increases, resulting in higher cumulative sand production. The cumulative sand production exhibits positive correlation with reservoir permeability. In scenarios of high permeability (higher than 20.3×10⁻³ μm²), the sand production rate sharply increases after 50 days of production, exceeding 1×10⁻⁴ m³/m. Conversely, at lower elastic modulus (lower than 26.9 GPa), the sand production rate presents a stepped increase trend. However, as the elastic modulus increases, the growth rate of cumulative sand production significantly slows down. This sand production prediction method is of great significance for ensuring the safe and efficient operation of UGS.