Characteristic features of salt-cavern behavior
Résumé
The behavior of an idealized spherical cavern leached out from a salt formation can be described by a first-order integro-differential equation when the Poisson’s ratio is 0.5. Three constitutive laws are considered: Norton-Hoff (N-H), Munson-Dawson (M-D) and Marketos-Spiers (M-S). The parameters of the M-D law can be fitted against both short- and long-term field data. It is shown that, following a pressure change, a “geometrical” transient evolution of the cavern volume is observed even when the constitutive law includes no “rheological” transient behavior (N-H, M-S). Following a large pressure increase, geometrical reverse creep and onset of tensile effective stresses at the cavern wall are observed. In a cavern subject to cyclic pressure, volume loss rate is faster than in a cavern where the average cycle pressure is applied. The loss rate is not extremely sensitive to cycle period; it is much faster when the M-D law (rather than the N-H law) is adopted. The M-S law, which accounts for the effect of pressure solution creep at low deviatoric stresses (in addition to dislocation creep), predicts a higher volume-loss rate (than the N-H law) when caverns are more shallow. A simple solution of the leaching problem (in which cavern radius is a function of time) can be found.
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