  Rapid gas depressurization leads to gas cooling that is followed by slow gas
warming when the cavern is kept idle. The decrease in the temperature of gas
depends upon the relative withdrawal rate (in %/day), and cavern size and
shape. Gas cooling may result in the onset of tensile stresses at cavern walls
and roofs that may generate fractures or cracks. However, in most cases, the
depth of penetration of these fractures is small, and they are perpendicular to
the cavern wall. The distance between two parallel fractures becomes larger
when fractures penetrate deeper into the rock mass, as some fractures stop
growing. Fractures form a polygonal pattern. Salt slabs are created, with
boundaries formed by the opened fractures. As long as the depth of penetration
of the fracture remains small, these slabs remain strongly bonded to the rock
mass, and it is believed that, in many cases, their weights are not large
enough to allow them to break off the cavern wall.
