Expansion of the capacity of the Chiren underground gas storage facility

Contracting Authority
Bulgartransgaz EAD

Chiren, Vratsa municipality

Period of implementation
July 2023 – March 2025 (Above ground facilities), April 2023 – November 2024 (Drilling operations), May 2023 – October 2024 (Gas pipeline)
Glavbolgarstroy’s role in the project
Prime contractor
Nature of works

The construction works on the expansion of the capacity of the Chiren underground gas storage facility are carried out in three separate projects:


  • Above Ground Facilities: Construction and commissioning of new above-ground facilities to meet the demands for increased daily production and injection capacities, as well as to enhance the maximum working pressure at the Chiren underground gas storage facility. The project encompasses the establishment of a compressor station alongside all requisite technological infrastructures, such as individual separators, a gas filtration and drying system, and a gas measuring station. It also includes connections to the Vratsa 1 and Vratsa 2 gas pipelines, along with pipelines leading to existing wells.


  • Drilling Operations: Design, construction, and commissioning of 10 new operational wells for the extraction and injection of natural gas, 3 new observation wells to monitor storage capacity, 10 connecting underground pipelines to link with the above-ground facilities at the Chiren underground gas storage. Key project activities include the creation of a 3D geological model, identification of the most suitable locations for the 13 new wells, development of a Detailed Development Plan complete with all necessary administrative procedures for approval and coordination, ecological assessments, and evaluations of environmental impacts on affected areas. The physical execution of the project involves procurement of essential materials and cutting-edge technology, including equipment and services from the American company Halliburton. The scope of work also includes drilling, conducting pressure tests at 150 bar, and commissioning a total of 13 wells, each with an approximate depth of 2000 meters, and 10 connecting loops, incl. a parallel optical cable line extending roughly 15 kilometers.


  • Gas Pipeline: Investment design, procurement of necessary materials and equipment, construction, and commissioning of a connecting gas pipeline between the Chiren underground gas storage facility and the existing gas transmission network operated by "Bulgartransgaz" in Butan village. The pipeline spans approximately 41.432 kilometers, designed to withstand a pressure of 75 bar, equipped with a pipe diameter of 711 mm.