Seepage Behavior and Grouting Effects for Large Rock Caverns

The analysis of seepage behavior through a rock mass is vital to the design of any underground oil storage project. A sufficient amount of water pressure is necessary for the hydraulic confinement of the stored product in unlined caverns in order to prevent any leakage to the outside environment. This water is supplied through a network of water curtain tunnels and boreholes located above the caverns some distance away. However, excessive leakage inside caverns is controlled by carrying out grouting of rock fissures such that seepage is brought under acceptable limits. Most flow studies of fractured rock mass are carried out using continuous models, taking into account the effect of the essential rock mass features in order to develop a firsthand idea of the prevailing seepage conditions around the excavated boundary. This paper presents the results of simplified numerical studies that were carried out to analyze seepage variations around the storage cavern under changing hydraulic conditions. A case study through a hydrogeologically sensitive zone was also analyzed during this study, where actual seepage measurements inside large caverns were compared with the model values. It was observed from the analyses that the hydraulic conductivity and thickness of the grouted rock mass zone, along with the excavation sequence, have a significant impact on seepage assessment inside caverns. It was shown from the analysis that the cavern invert contributes to most of the seepage measured inside caverns. The predictions of the simplified numerical model compares well with the field measurements.