Lightweight and ultra-lightweight solid materials are being used in gravel packing for horizontal wells instead of traditional quartz and ceramsite to decrease the risk of premature plugging and improve packing efficiency. Physical and numerical simulation experiments of gravel packing were conducted to assess the effectiveness of reducing solid material density and investigate its impact on packing and sand control. Packed gravel destabilization experiments highlighted the importance of high-compaction degree packing for effective sand control. Further gravel packing experiments examined the packing performance of different solid materials, revealing that lightweight solids have minimal gravitational deposition effect because their density is similar to the gravel slurry, relying primarily on fluid flow for compaction. The numerical simulation indicated that lightweight ceramsite is unsuitable for horizontal and highly-deviated wells because of its poor compaction degree and sand control, especially with high-viscosity slurry. High-density particles enhance gravitational deposition, improving packing compaction and sand control. Lightweight materials are recommended only when advanced plugging of α wave packing cannot be avoided. In highly-deviated wells, high-density materials significantly improve packing stability and sand control. This study provides clear technical guidelines for selecting solid materials for gravel packing in horizontal and highly-deviated wells.

Sand production poses a significant problem for marine natural gas hydrate efficient production. However, the bottom hole gas–water–sand inflow pattern remains unclear, hindering the design of standalone screen and gravel packing sand control completions. Therefore, gas–water–sand inflow patterns were studied in horizontal and vertical wells with the two completions. The experimental results showed that gas–water stratification occurred in horizontal and vertical standalone screen wells. The gas–water interface changed dynamically, leading to an uneven screen plugging, with severe plugging at the bottom and high permeability at the top. The high sand production rate and low well deviation angle exacerbated screen plugging, resulting in a faster rising rate of the gas–water interface. The screen plugging degree initially decreased and then increased as the gas–water ratio increased, resulting in the corresponding variation in the gas–water interface rising rate. Conversely, gas–water stratification did not occur in the gravel packing well because of the pore throat formed between the packing gravels. However, the impact of gas and water led to gravel rearrangement and the formation of erosion holes, causing sand control failure. A higher gas–water ratio and lower packing degree could result in more severe destabilization. Therefore, for the standalone screen completion, sand control accuracy should be designed at different levels according to the uneven plugging degree of the screen. For the gravel packing completion, increase the gravel density without destabilizing the hydrate reservoir, and use the coated gravel with a cementing effect to improve the gravel layer stability. In addition, the screen sand control accuracy inside the gravel packing layer should be designed according to the sand size to keep long-term stable hydrate production.

Unconsolidated sandstone reservoirs, particularly in offshore and marine environments, are highly susceptible to sand production, which leads to flow-capacity degradation, plugging evolution, sand-retention instability, and erosion–corrosion damage in gravel-pack completion systems. To address the lack of system-level and quantitative integrity evaluation methods, a unified assessment framework is developed by coupling flow behavior, sand-retention mechanisms, and erosion–corrosion damage processes. The gravel-pack completion system is idealized as a concentric multilayer porous-medium structure under steady-state radial Darcy flow, and an equivalent radial permeability model is established to characterize flow capacity and anti-plugging performance, which enables consistent comparison of different completion schemes under identical plugging conditions. Based on sand-retention mechanisms, a sand-retention capacity index is proposed by integrating formation particle size distribution, screen aperture, gravel size, and sand-leakage risk. An erosion–corrosion coupled damage model is further developed to predict screen damage rates in CO₂-containing environments, and an integrity index is formulated to link damage evolution with long-term service performance. By integrating flow capacity, anti-plugging performance, sand-retention capacity, and structural integrity using a weighted geometric mean, a comprehensive evaluation index is established for overall system integrity assessment. Using the proposed framework, a representative formation sand with d₁₀ = 30 μm, d₅₀ = 180 μm, and d₉₀ = 500 μm is evaluated. The optimal sand control design corresponds to a gravel median size of 971.53 μm (equivalent to a standard 16/20 mesh gravel) and an optimal screen aperture of 523.11 μm, with a screen porosity of 0.56. Under these conditions, the selected screen aperture and gravel size are well matched with the formation sand size, falling within recommended engineering ranges and achieving a favorable balance among sand retention, flow capacity, anti-plugging performance, and structural integrity. The proposed framework provides a quantitative and engineering-applicable basis for the optimization and integrity classification of offshore gravel-pack sand control completions under multi-constraint operating conditions.

Summary: Gravel packing is a widely used sand control technique for horizontal wells in unconsolidated sandstone reservoirs. Traditional optimization methods for gravel packing parameters aim to maximize the gravel-packing rate. However, some horizontal wells with high packing rates still experience production decline after being put into operation. Improving the optimization method for gravel-packing parameters is crucial to ensuring the production capacity of horizontal wells. In this paper, we investigate the dune migration patterns during gravel-packing operations, identify key parameters affecting gravel-packing performance, and propose a new gravel-packing parameter-optimization method through gravel-packing operation and production simulation experiments. First, gravel-packing operation simulations reveal that the density difference between the sand-carrying fluid and packing gravel is a crucial factor influencing dune migration and gravel-packing density. A downward-deposited dune forms in the α-wave packing process of conventional ceramsites because of a large density difference, thereby forming premature bridges during migration and reducing the gravel-packing ratio. When reducing the density difference, α-wave packing with ultralight ceramsites forms an upward-deposited dune. This migrates from the upper side of the well toe to the lower side of the well heel, avoiding premature bridges but weakening the gravel particles’ compaction, resulting in lower packing density and reduced stability of the gravel layer and affecting the productivity of horizontal wells. Second, further production simulation experiments explored the impact of gravel-packing density on the performance of gravel-packed horizontal wells. Results show that even when the gravel-packing ratio reaches 100%, lower packing density in certain zones can lead to instability in the gravel layer, forming erosion holes due to uneven inflow, which may cause sand control failure. This instability indicates that gravel-packing density should be a key consideration in optimizing packing parameters to ensure stable and efficient horizontal well production. Finally, a new optimization approach is proposed to recognize the limitations of current gravel-packing parameter optimization methods, and its feasibility was verified using actual field data from two wells in the Sinopec Shengli Oilfield. The approach integrates three factors, wich are gravel-packing ratio, packing density, and operational safety window. A new set of indexes for gravel-packing ratio, density, and safety is introduced. Simulation experiments on horizontal well gravel packing have analyzed the effects of gravel concentration, sand-carrying fluid viscosity, pump rate, and gravel density on packing performance. The results show that significant antagonistic effects were observed among key parameters. High-viscosity fluids cannot tolerate high pump rates but can accommodate a slight increase in gravel concentration. Importantly, the use of low-density gravel is a critical factor for achieving overall optimization in horizontal gravel-packing operations. A reasonable gravel concentration (4–6%), sand-carrying fluid viscosity (3–7 mPa·s), and gravel density (1.28–1.84 g/cm3) can effectively enhance gravel-packing ratio and stability while maintaining high packing density and safety. This study provides new theoretical foundations and comprehensive guidance for optimizing gravel-packing parameters in horizontal wells and helping to improve the long-term stability and production capability of gravel-packed horizontal wells.