The underground gas storage is located 6 km to the north from Mikulov at eastern bottom of Pavlovské vrchy in cadastral areas of Dolní Dunajovice, Horní Věstonice, and Březí. This is the largest underground gas storage in the Czech Republic.
A promising structure for hydrocarbons accumulation has been discovered along Věstonice fault near Dolní Dunajovice during a regional seismic survey of Carpathian foredeep. Already the first borehole led to discovery of high quantities of natural gas accumulation in basal Eggenburg clastics back in 1973. A decision about underground gas storage establishment was made already during the primary exploitation. It was decided that the underground gas storage would be formed after withdrawal of approximately 50% of the natural gas.
Reservoir rocks of the gas deposit located in the depth of 1,050 meters below the surface consists of glauconitic sandstones and siltstones developed in seven hydro-dynamic interconnected layers partly separated by irregular interbedded claystones thus forming a single hydrodynamic unit. The top of the structure consists of Věstonice fault with the height of approximately 150 meters at the level of mezozoic limestones which are covered by onlap of Eggenburgian clastics. The overburden of the gas bearing horizon consists of calcareous claystones with the Eggenburgian – Carpathian boundary passing through their top part. A small gas accumulation was discovered also in Karpatian sediments in the depth of 660 meters.
The underground gas storage is equipped for both injection and exploitation of the natural gas. A part of the technology is common for both injection and exploitation. The underground gas storage comprises four collection points. The underground gas storage is connected to DN 700/500 PN 63 pipelines between Uherčice and Dolní Dunajovice.
The injection technology consists of the elementary parts listed below
Inlet filters for gas purification, gas quantity metering before injection into the underground gas storage, four boxer compressors ČKD type 4 JBK 240 with electric drives, gas coolers, oil separators for oil elimination from the gas, collection centers with metering and regulating runs of wells, operating wells, gas pipelines, and interconnection collectors.
The withdrawal technology consists of the elementary parts listed below
Operating wells and equipment for methanol injection, collection centers with metering and regulating runs of wells, equipment for separation (formation water removal) and gas heating (increase of gas temperature before decrease of its pressure), gas drying (by elimination of water vapors from the gas) amendment glycol regeneration, outlet filters for gas purification, measurement of gas quantity before its delivery into the transmission system, gas pipelines with interconnection collectors.
Monitoring and control of the entire underground gas storage technology is performed with a control system. The following functions are available for the operator: transparent view of the technological process control status, possibility of manual intervention into the operation, and archiving of the control data including alerts and failure reports.