In unlined underground rock caverns, liquid petroleum and petroleum gas can be stored by making use of natural or artificial ground water pressure. In case of applying the unlined underground storage caverns to the cracky rock mass, it seems to be most important that the behaviour of the ground water through the rock mass surrounding the caverns is studied in advance. This study, therefore, discusses the following subjects concerning unlined underground oil storage caverns.
The numerical study on the effects of natural ground water pressure on the storage caverns.
The numerical study on the effects of artificial ground water pressure on the storage caverns.
Model experiment about gas leakage into the crack of rock mass.
Unlined underground storage system of petroleum has been proven to be efficient in the effective exploitation, environmental preservation, safety and economy. The system has already many past references in Europe and America. However, in case when the said system is adopted to the cracky rock mass, it is necessary to study and examine the nature of the rocks, the structure of fuel storage tank and the influence over the environment. This report is intended to describe the results of the analysis and experiments on the seepage flow made in relation to the matters most important for the construction of the unlined underground storage tank for petroleum, that is to say, the water pressure required for preventing leakage of oil and gas, the lowered level of ground water liable to give influence over the environment, and the water leakage volume indispensable for determining the capacity and the economy of the equipments and apparatuses to be involved.
The petroleum like heavy oil and light oil having low vapor pressure can be stored under the atmospheric pressure when the underground caverns are not found in the state completely covered with ground water. This is to say, there happens no gas leakage and no oil leakage even if the ground water level reaches the cavern. On the other hand, when the underground caverns are excavated in the rock mass beneath the natural ground water level, the seepage flow into the caverns through the surrounding rock mass will be happened. Consequently, it is worried that the ground water level on the upper part of the caverns will fall down after the excavation of the cavern. Therefore, it is necessary to understand the behaviour of natural ground water around the cavern in case when heavy oil, light oil, etc. are to be stored under natural ground water only. In this chapter the behaviour of ground water around the cavern will be analyzed through two dimensional analysis of seepage flow in saturated-unsaturated porous media (Komada, 1978) and the possibility of unlined underground storage under natural ground water only will be examined.