Hydro-geochemical analysis of the interplay between the groundwater, host rock and water curtain system for an underground oil storage facility

Hydro-geochemical analysis was performed to investigate the interplay between the groundwater, host rock and water curtain system for the start-up of a pilot underground oil storage facility in China. 54 groundwater samples were collected and analyzed to obtain the characteristics of the hydro-geochemical environment evolution for the start-up period. The groundwater-rock mass interaction was studied with comparing the changes in the ion concentrations, pH values and total dissolved solid concentrations in the groundwater and a mineralogical analysis of the host rock. The groundwater-water curtain system interaction was identified using statistical analysis of the similarity in chemical contents in the groundwater samples. A mixing calculation was performed to evaluate the mixing ratios of the water curtain system, background water and oil/vapor in the seepage water into the storage caverns. It was concluded that calcium carbonate equilibrium is the predominant chemical reaction. The 54 groundwater samples could be classified into 5 clusters. Among the 5 clusters, there is one cluster showing that the tap water injected to the water curtain system is similar in chemical contents to those in the monitoring boreholes around the facility, which confirms the efficiency of the water curtain system for the start-up of the facility. It was found that the two dominant factors influencing the evolution of groundwater chemical content were host rock dissolution and groundwater seepage. Most of seepage water was originated from oil/vapor and water curtain system while the percentage from the background water was almost zero in the start-up period of the facility.