Reexamining the Necessity of Adding Water Curtain Borehole with Improved Understanding of Water Sealing Criterion

A water curtain system is widely adopted in the underground storage of gas/oil in unlined rock caverns to maintain a stable groundwater level and ensure a good water sealing condition for the storage facility. Hydrogeological tests were conventionally carried out in practice to assess the hydraulic conductivity of the surrounding rocks and evaluate the performance of the water curtain system. Among them, the hydraulic connectivity between adjacent boreholes is assessed using interconnectivity test, and it is commonly thought that, if the measured connectivity between two neighboring boreholes is low, a new borehole has to be added in the middle of them to improve the local efficiency of water curtain system. This paper reexamines the viewpoint of using interconnectivity test to determine the necessity of adding borehole. To this end, the conditions of water sealing were firstly discussed and the deficiency of existing water-sealing criterion was presented, with a new rigorous criterion proposed. The equivalent porous medium (EPM) flow model and fractured porous medium (FPM) flow model, two representative models for groundwater flow analysis, were then used to investigate the influences of borehole spacing and stored gas pressure on seepage field. These numerical results were employed to validate the proposed water-sealing criterion and suggested that, in terms of forming a stable water covering layer, the addition of borehole based on interconnectivity test is unnecessary and should be canceled for saving time and reducing cost.