11 avril 2000 – Vibrations and oscillations in deep cavities
by Benoît BROUARD, Pierre BÉREST
In this presentation we considered deep caverns (from 300 m to 2000 m and more) that are connected to ground level through a cased and cemented well, which allows injection or withdrawal of fluids into or from the cavern. These caverns are, in general, leached out from salt formations. The purpose of these caverns is to provide chemical plants with brine or, more commonly, to provide storage of large quantities of hydrocarbons. The volumes of such caverns range from 5,000 m3 to 1,000,000 m3.
Compressibility of these deep fluids-filled cavern was discussed. Compressibility is measured both through statical and dynamical tests. Statical compressibility is influenced by cavern shape and cavern fluids nature. This parameter plays an important role for such applications as the determination of stored hydrocarbons volume, of volume lost during a blow-out, and of pressure build-up rate in a closed cavern. Dynamical compressibility is measured through the periods of waves triggered by pressure changes. Both tube waves and longer period waves associated to the existence of an interface between a liquid and a gas can be observed. They allow to check the results of the statical tests and can provide additional information, for instance the existence of trapped gas in the well-head.