Štramberk

Picturesque town of Štramberk in the foothills of Beskydy spreads over the slopes of Zámecký vrch and Bílá hora. It used to be protected by a castle from which only the watchtower has been preserved. It was rebuilt to a look-out tower (famous Štramberk Trůba) between 1902 and 1904. The central area of the underground gas storage is located two kilometers west from the town.

History

Natural gas accumulation in the area of Příbor-south surveying field located in the south-western part of Ostrava coal basin was located during coal surveying in 1960s. Several boreholes were made between 1961 and 1965 for the purpose of gas exploitation. Primary exploitation from Příbor-south took place between 1965 and 1975.

When considerations about suitable locations for underground gas storages construction came across in 1970s, it was decided to construct an underground gas storage, which would supply the North Moravian region, in partly exploited Příbor-south gas deposit. The deposit is located approximately 35 km southwest from Ostrava in Nový Jičín district, below cadastral areas of Štramberk, Kopřivnice, Ženklava, Závišice, Rybí, and Žilina over the area of 30 square kilometers, in the depth between 500 and 690 meters below the surface. Effective thickness varies between 1 and 10 meters.

Based on the knowledge collected during exploratory works, construction of Štramberk underground gas storage commenced between 1981 and 1983. Several new operating wells were made during the construction, some of the original wells were repaired, network of gas pipelines interconnecting individual wells was constructed, and an area of the facility (which also serves as the collection center) was built.

Second phase of underground gas storage construction took place between 1993 and 2000. The number of operating wells was increased, technology was reconstructed and extended, and a compressor and control system were installed.

Geology

Štramberk underground gas storage was created in Karpatian horizon H2 which belongs to Carpathian foredeep fill. Geological setting of the reservoir and its surroundings is determined by the nappes of the outer flysch belt of west Carpathians overthrusted sediments of Carpathian foredeep. Natural gas in Pribor – south deposit was accumulated in Karpatian layers overlapping the paleozoic sediments, in particular the Carboniferous rocks. The storage horizon is located in the depths of 500 – 690 meters below the surface. Prevalent lithologic types of reservoir rock comprise fine grained quartz-lime sandstone with clayey-silty matrix and coarse-grained to conglomeratic sandstone. The horizon forms flat dome structure. The overlying Silesian and Sub-Silesian units of the outer flysch belt, forms caprock for Karpatian H2 storage horizon.

Overground Part

Gas pressure in the supply DN 500 PN 63 Libhošť - Štramberk gas pipeline of the transmission system varies between 4.5 and 5.5 MPa. Natural gas is stored without use of a compressor. Technology within the underground gas storage area consists of filters (intended to remove mechanical and liquid impurities from the natural gas), regulating equipment for achieving necessary pressure level, and commercial metering which is used to determine the total injected natural gas quantity. Gas is subsequently transported by three pipeline systems to individual wells. The wells are connected by a collector pipeline which gradually branches to individual wells with simultaneous decrease of its inner diameter (from DN 500 to DN 100). In individual wells, the gas passes through regulating valve, metering orifice, and separator. During exploitation, the natural gas coming out through the well passes through separator, metering orifice, and regulating valve. Methanol is injected into the exploited gas in order to prevent formation of hydrates. In the underground gas storage area, the gas passes through filters, drying system, and after quantity measurement the gas is discharged into the distribution pipelines of Severomoravská plynárenská in the direction of Ostrava and Valašské Meziříčí. A compressor propelled by combustion turbine can be used for gas exploitation.

A control system ensures automatic underground gas storage operation control. The control system application enables individual or automatic operation of individual actuators, wells, technologies, and technological units and to control the process of natural gas storage and withdrawal.