Detection of low-efficiency zones of water curtain system for underground LPG storage by a discrete fracture network model

Water curtain system is the key architecture to maintain the hydrodynamic containment of underground storage for liquefied petroleum gas in unlined rock caverns. Additional water curtain boreholes have to be drilled and tested to eliminate any low-efficiency zone. The drilling and testing is, however, a time-consuming and costing job. In this paper, statistical characteristics of fractures (joints, bedding planes, or even faults) obtained at different phases of the project (e.g., site investigation phase and underground excavation phase) are input to a discrete fracture network model to generate realizations representing the fracture network of the considered domain (500 m × 250 m × 200 m). A grid system is created for the domain with the cell size of 50 m × 50 m × 50 m. Based on the Cubic Law, a 3D equivalent hydraulic conductivity field is obtained. With the parameter of the Low-Efficiency Index (LEInd), criteria are created to help identify the low-efficiency areas based on the hydraulic conductivity field. The predictions of the low-efficiency zones are then cross checked with the actual water curtain efficiency test results. Four out of five predicted low-efficiency cells were proved to be fully or partly matched with the results identified from the water curtain efficiency test. This work can help to determine the reasonable water curtain borehole layout spacing during the design phase, thus effectively reduce the water curtain boreholes drilling workload after the test, shorten the construction period, and reduce the engineering cost.