关键词: 地下储气库, 储层应力, 交变荷载, 出砂, 临界生产压差

Abstract: Sandstone reservoirs are the principal type of underground hydrocarbon storage reservoirs. Cyclic injection and production in underground gas-storage facilities increase rock damage and sand production. Understanding the critical drawdown pressure for reservoir sand production supports safe and stable operation. The distribution and evolution of stress fields in reservoirs under cyclic injection-production form the foundation for studying sand production. Based on elastic mechanics, the evolution patterns of stress fields in both distant- and near-wellbore reservoirs were derived. Utilizing cyclic damage theory, a critical drawdown pressure model was developed. The study specifically analyzed the influence of parameters such as stress field mechanism, distance from the wellbore center, and annular angle on the evolution of stress fields in near-wellbore reservoirs. Taking the X23 gas storage reservoir project as an example, stepwise cyclic mechanical tests were designed and conducted, leveraging stress concentration in the near-wellbore region and gas-water interface characteristics. The trend of critical drawdown pressure with injection-production cycle frequency was analyzed, and a critical drawdown pressure chart was developed based on actual production curves. Results indicate that reservoirs with lower water saturation and finer grain size exhibit greater resistance to cyclic damage. Damage accumulates with increasing cycle count. The critical drawdown pressure at the upper operating pressure limit decreased monotonically from 22.4 MPa to 10.5 MPa, while at the lower operating pressure limit it decreased monotonically from 15.8 MPa to 3.9 MPa. This study provides a novel approach for designing cyclic damage experiments in gas storage reservoirs, refines the critical drawdown pressure formula for sand production, and guides drawdown pressure control during injection and production operations in gas storage facilities.

Key words: underground gas storage, reservoir stress, alternating load, sand production, critical drawdown pressure