Enhancing Gravel Packing Efficiency in High-Fluid-Loss Horizontal Wells with Nitrogen Foam: Experiments, Mechanisms, and Optimization

Summary Gravel packing is a widely used sand control technique in oil wells, but its application in deviated and horizontal wells remains challenging. Unconsolidated sandstone reservoirs exhibit weak cementation, low diagenesis, high hydration susceptibility, and poor borehole stability, often leading to wellbore collapse and severe fluid losses. In such reservoirs, conventional gravel packing using Newtonian fluids is prone to premature sand plugging, significantly reducing operational success. To address these challenges, we investigate the feasibility and effectiveness of nitrogen foam–based fluids as an alternative transport medium for gravel packing in horizontal wells. A full-scale horizontal well gravel packing simulation device was used to conduct nitrogen foam gravel packing experiments. Experimental results showed that nitrogen foam improved the final packing rate by 38.23% and increased the comprehensive packing performance index by 59.48% compared with conventional oilfield waste water. The results demonstrated that nitrogen foam, as a non-Newtonian fluid, possesses elasticity and lubrication properties that reduce pipe flow resistance. Compared with oilfield waste water and viscosified water, nitrogen foam reduced the average injection pressure in β-wave gravel packing by a factor of 1.26 to 4.43. Additionally, two main flow patterns were observed—gas/liquid stratified flow at low sandbed heights and slug flow at higher sandbed heights. These flow characteristics effectively mitigated premature plugging, significantly enhancing packing length and efficiency. Optimization experiments revealed that a gas/liquid ratio of 2 (foam quality of 66.7%) achieved the best results, yielding a packing rate of 75.59% and a comprehensive performance index of 0.8123. Increasing the foaming agent concentration from 0.5% to 1.5% improved the packing rate by 17.63%, with optimal concentrations between 1% and 1.5%. However, an increase in the sand-carrying ratio from 5% to 15% reduced the packing rate by 22.84%, highlighting its negative impact on foam stability. A pump rate increase from 6 m³/h to 12 m³/h enhanced the packing rate by 27.44% but also resulted in higher pressure losses, limiting its practicality. In addition, we conducted field construction verification, and the application yielded good results. This study confirms that nitrogen foam–based gravel packing significantly enhances packing performance, offering higher packing rates, lower injection pressures, and improved packing density. The findings provide a theoretical and practical basis for optimizing foam-based gravel packing parameters in horizontal wells, contributing to more effective sand control strategies in unconsolidated sandstone reservoirs.