A geotechnical investigation was conducted to confirm the feasibility of using the Central Rock Limestone Mine, Lexington, Kentucky, U.S.A. for crude oil storage as part of the Strategic Petroleum Reserve. Evaluation of containment potential was based on the criteria that there should be a static head of water above the mine greater than the maximum allowable operating pressure in the vapor space in the storage cavern, and that there should be an hydraulic gradient toward the mine sufficient to prevent escape of vapors. In the investigation, emphasis was placed on evaluating the groundwater conditions around the mine by means of piezometers installed in boreholes drilled from the surface.

INTRODUCTION

As part of the United States Department of Energy Strategic Petroleum Reserve (SPR) program, a number of existing, conventional room and pillar mines have been evaluated to establish suitability as crude oil storage caverns. These include two salt mines, Weeks Island and Cote Blanche in Louisiana, and two limestone mines, Ironton in Ohio and Central Rock in Kentucky. This paper presents the results of the geotechnical certification program conducted for the Central Rock Limestone Mine which has a potential storage capacity of approximately 14.0 million barrels (2.2 million m3). Emphasis is given to the procedures used to demonstrate that the existing groundwater conditions around the mine are such as to prevent product leakage.

CERTIFICATION CRITERIA

Prior to the SPR program, there had been widespread experience in the United States with the storage of LPG's and natural gas in solution caverns in salt and in purpose-built mined caverns in a variety of rock types. Natural gas had been stored also in a converted coal mine, but there had been no experience with underground storage of crude oil either in solution caverns, purpose-built mined caverns or converted mines. This lack of experience meant that there were no established criteria for certifying a mine as suitable for storage. The solution caverns included in the SPR have been certified by means of hydrostatic testing, a straightforward technique for a cavern that is always full of a fluid. This technique could be considered for a converted mine using either water or a gas, but it would be expensive due to the extensive measures required to seal the mine, and possibly environmentally unacceptable due to problems with disposal of the test fluid. It was thus determined that the converted mines in the SPR should be certified by indirect means on the basis of thorough geotechnical investigations. The general criteria established were that the mine should be sufficiently stable as to allow safe and satisfactory operation for the projected life of the facilities, that there should be no significant leakage of stored product, and that there should be no adverse reaction between the stored product and the host rock. In the case of an existing mine, it is relatively straightforward to assess stability conditions on the basis of in-mine inspection, supplemented by appropriate quantitative analyses. The potential for reaction between the host rock and the stored product can be evaluated with appropriate laboratory tests and is also a relatively straightforward criterion to satisfy.

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