Abstract: Geological Aspects of the Construction of Gas Caverns in Salt

FOLLE, STEFAN

After the initial exploration phase to determine the presence of structures for the construction of gas storage caverns, the first step is to establish the depth of the base and the top of the salt structure. The position and dimensions of the cavern within these geological boundaries is related to its planned pressure range and volume. In addition to the standard-exploration procedure, a number of special methods are implemented to determine the location and size of any anomalies.

Solution mining anomalies caused for example by carnallite can affect the development of a cavern ranging from an irregular cavern shape to leaching unacceptably close to adjacent caverns. Determining solubility is undertaken by correlating special dissolution tests with well logs and the associated definition of mineral paragenesis. The amount of insolubles, often comprising clay, silt, carbonates and sulphates, is a factor which can greatly influence the economic assessment of a project. In extreme cases the cavity created can be completely filled with loose insoluble bulk material, effectively prohibiting any use for storage purposes.

Geomechanics is applied to specify the pillar thickness between caverns, to minimize any interaction due to different pressure regimes during operation. In addition, other requirements can include minimum thicknesses for the underlying and overlying beds, safety distances to anomalies (anhydrite) and to the margins of the salt structure. The determination of the density profile of the cover rock has a major influence on the permissible pressure range and consequently the economic viability of gas caverns.

AAPG Search and Discovery Article #90942©1997 AAPG International Conference and Exhibition, Vienna, Austria