National Strategic Crude Oil Storage in the Weeks Island Dome Salt Mine—Part II: Rock Mechanics Evaluation

Abstract

This paper, the second in a series of two, presents the results of a rock mechanics evaluation of the Weeks Island dome salt mine. The purpose of the evaluation was to assess the structural stability of the old mine workings in conjunction with a proposed new deeper mine level during the use of the facility for the long-term storage of crude oil under the Federal Energy Administration’s Strategic Petroleum Reserve Program. The scope of the work involved laboratory testing of the strength and deformational characteristics of the rock salt; determination of a minimum web (or sill) thickness between the old workings (within which crude oil would be stored) and a proposed new mine level development below; and assessment of the effects of crude oil emplacement and withdrawal on the mine stability, as related to both the old workings and the proposed new mine level development. The finite element results, wherein use was made of the strength and deformation properties of the salt from the laboratory tests, indicated that a minimum sill thickness of 90 m (300 ft) should be maintained between the old mine workings and the new level development. Furthermore, the emplacement and withdrawl of crude oil from the old workings will have little influence on pillar and sill stabilities for the entire mine, including the proposed lower level development. The only noticeable effect could, perhaps, be obtained in the creep rate due to changing stress conditions.