Microgravity Observations to Investigate an Installed Crude Oil Tank Instability

Large metal oil tank, with a diameter of 60 m, has been constructed for crude oil reservation at a coastal terminal. Preliminary filling tests of the tank show abnormal subsidence of the tank and inhomogeneous variable subsidence of the tank. This indicates the existence of some weakness zones on the layer sequences beneath the tank. On the other hand, some drilling wells around the tank showed voids and weakness zones on depths from 20 to 40 m. Microgravity observations have been carried out in and outside the tank to locate possible existence of voids responsible for the tank instability. After the adjustment of the gravity data, Bouguer gravity anomaly map can be drawn which reflect the existence of weakness zones or mass discontinuity. Important weakness zones have been detected and evaluated for the geotechnical applications for the tank stability.