Groundwater response to oil storage in large-scale rock caverns with a water curtain system: Site monitoring and statistical analysis

Site monitoring provides not only critical information for the safe operation of underground facilities but also important data for characterizing the groundwater flow within heterogeneous rock masses. Site monitoring and statistical analysis were performed to ascertain the groundwater response to oil storage in the Huangdao pilot large-scale underground oil storage facility. An all-sided monitoring scheme was designed and implemented for the assessment of the performance of the facility. The groundwater level and pressure along with rainfall, storage pressure, water curtain level were obtained with the monitoring system. The containment property was assessed according to the monitoring results, showing that the containment property of the facility can be maintained under operational conditions. Autocorrelation and cross-correlation analyses of the monitored data were performed to investigate the quantitative relations of the groundwater response to the rainfall amount, water curtain level and storage pressure. The correlation coefficients and time delays of the groundwater responses to the rainfall amount, water curtain level and storage pressure were obtained through statistical analysis. Evidently, the influence of rainfall on both the groundwater level and the groundwater pressure is insignificant. The groundwater pressures in the upper cavern pillars are influenced mainly by the water curtain system, while the groundwater pressures in the lower cavern pillars are influenced by the storage pressure. The hydro geological conditions determine the time delays of the groundwater level and groundwater pressure responses to the water curtain level and storage pressure. Eventually, it was concluded that the groundwater response to oil storage in rock caverns with a water curtain system is related to both the geometrical layout and the hydro geological conditions of the facility.