The geotechnical performance of a pilot unlined crude oil storage caverns in granite is assessed using finite element method. Laboratory and field tests were performed to determine the geotechnical properties of the granite. Numerical simulations were carried out to assess the groundwater dropdown and stability of the caverns according to the test results. 5 numerical cases with different permeability coefficients were performed to investigate the influence of permeability coefficient. The simulation results indicated that the operation period of the storage caverns will be less than the designed period if there is no groundwater supply system. It was also found that there is an approximately linear relation between groundwater inflow flux and permeability in the double logarithm space. On the stability of the caverns, it is shown that the stability of pillars between different caverns is different as a result of the different stress paths experienced of the pillars.

1 Introduction

The demand for natural carbonate resources is increasing all over the world. Safe and stable natural carbonate resource supply is of critical importance for many countries to fuel the economic and social developments. Storage of these resources often provides an economic way to secure the supply. Underground storage takes advantages over ground surface storage in terms of safety, environment and economy. The carbonate resources could be underground stored in the state of liquefied petroleum gas (Goodall et al. 1988), gas (Liang & Lindblom 1994, Lu 1998,Yang & Guan 2001, Kim et al. 2007), or crude oil (Yang et al. 2004).

The basic principle of crude oil storage in unlined caverns is that the groundwater pressure around the caverns should be higher than the pressure of the stored gas, liquefied petroleum gas, or crude oil to prevent leakage toward the surrounding rock mass (Goodal et al. 1988, Liang & Lindblom 1994). For example, in Chinese code for underground unlined caverns design, the minimum allowable difference between groundwater head and storage pressure head is 15 m. The unlined caverns should maintain a stable state all through its life. In the case of crude oil storage, the bedrock is usually dominated by crystalline hard rocks. In this case, the performance of the storage caverns depends greatly on the geotechnical, i.e., permeable and geomechanical properties of rock mass.

In China, an unlined storage cavern facility, which is one of the first unlined crude oil storage caverns in crystalline hard rocks, is being constructed in granite to meet the fluctuant need for carbonate fuels. Prior to the construction, it is of importance to assess the geotechnical performance of the pilot unlined caverns, including the groundwater drawdown and stability of rock mass around caverns.

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