Simulation of Nitrogen Foam Gravel Packing in Low-Pressure Unconsolidated Sandstone Horizontal Wells in Mature Oilfields

When gravel packing is performed for sand control in low-pressure unconsolidated sandstone horizontal wells in mature oilfields, severe loss of carrier fluid and premature sand fill are prone to occur, resulting in poor gravel packing quality. Therefore, based on a full-scale horizontal well gravel packing device, the dynamic evolution process of the sand bed was monitored, and the characteristics of the filling process using nitrogen foam under different gas-liquid ratios, foaming agent concentrations, sand ratios, and pumping rates were analyzed. A nitrogen foam packing numerical model was constructed by integrating pipe flow theory and particle mechanics. The experimental results indicate that nitrogen foam significantly reduces flow resistance and operational pressure and effectively delays sand bed lifting and plugging. The optimal foam stability and sand-carrying performance are achieved at a gas-liquid ratio of 2 and a foaming agent concentration of 1.0% to 1.5%. An excessively high sand ratio is found to impair the stability of the foam structure. When the sand ratio is increased from 5% to 15%, the packing efficiency decreases significantly. Increasing the pumping rate helps extend the packing distance but also increases frictional losses. The study validates the application potential of nitrogen foam in low-pressure and leaky well conditions, providing new insights for sand control completion techniques of horizontal wells.