Frictional loss and permeability estimation of sediment in salt cavern: A combined approach of mathematical model, experimental validation, and numerical simulations

Abstract

Harnessing gas storage in sediment voids presents a promising trajectory for the future construction of large-scale underground gas reservoirs in low-grade salt mines. This approach not only augments the effective gas volume but also enhances the stability of the cavern. In contrast to traditional gas injection and brine discharge process, where brine is expelled from the upper pure brine space without involving brine seepage in sediment voids, gas storage in sediment voids entails expelling brine from these spaces, thus necessitating an understanding of the brine seepage characteristics in the sediment, which remains unclear. This study presents a comprehensive approach for estimating sediment frictional loss and permeability in interconnected wells, integrating mathematical modeling, experimental validation, and numerical simulation. The mathematical principles governing sediment behavior during in-situ gas/brine injection and brine discharge tests are theoretically elucidated, accompanied by derived formulas. Experimental verification is conducted in the horizontal interconnected wells (Ha4-5) of the Huaian salt mine in Jiangsu, yielding the sediment frictional loss (0.53 MPa) and permeability (6.9 × 10⁻¹¹ m²). Subsequently, a 2D cross-sectional numerical model is established using the COMSOL software, considering the measured and predicted well morphologies. The model provides insights into the relationship between sediment frictional losses and permeability, yielding an inverse calculation of the average permeability (1.016 × 10⁻¹⁰ m²). Simulation results depict laminar brine flow characteristics in the cavern during gas/brine injection and brine discharge processes, with frictional loss occurring as brine passes through sediment. Examination of the brine seepage and pressure fields in the sediment reveals consistent brine flow velocity after passing through the sediment. This combined approach focuses on investigating the seepage characteristics of sediment at the bottom of salt caverns, offering valuable insights for estimating frictional losses and permeability in similar salt mines.