CavBox is a console program written in C++. It reads the gas rates and calculates the cavern pressure. The cavern volume can be variable. For the de-brining process the cavern volume and the fluid level in the cavern were calculated according to sonar measurements giving a relation between depth and cumulative cavern volume. The gas temperature in the cavern is calculated regarding heat flow to the surrounding rock. The wellhead pressures are calculated considering the gas properties, flow rates, and the well tubing diameter.
When gas is injected into a cavern it is compressed and due to this compression the temperature of the gas increases. When the gas is produced from the cavern it is expanded and the temperature decreases. Further heat flows according to temperature differences to the surrounding salt and to the water which is left in the cavern.
The gas properties are considered in CavBox using the Hall-Yarborough correlation for the calculation of z-factors. The heating or cooling of the gas is calculated assuming adiabatic pressure change. The heat flow is accounted by a global function which calculates heat flow linear during a time step depending on the temperature difference between gas and rock/salt.
CavBox is using different files for input data and creates output files to be used for graphical display and post processing for storage in databases.
CavBox can be configured using a graphical user interface. Here the main properties can be edited and the CavBox console program can be started. The results can be shown in graphs. In the user interface adjustment to main parameters can be made performing a history match. The actual file configuration is store in a batch file that can be called from any other routine or th SCADA of a gas storage facility.
Parameters influencing pressure and temperature in a salt cavern
Match of well head pressure during a de-brining of a salt cavern