Interconnector with Greece successfully crosses Studen Kladenets Dam

The Greece-Bulgaria interconnector successfully passed under the bottom of the Studen Kladenets dam, overcoming the most critical and difficult stage of the construction of the gas connection. With a total length of 1,440 m and a 32-inch diameter, horizontal directional drilling (HDD) is already in the top five longest boreholes with this diameter in the EU. Currently, the longest such drilling is carried out under the bed of the Axios River in Greece, realized during the implementation of the Trans-Adriatic Pipeline (TAP).

The crossing under "Studen Kladenets" started shortly after the successful completion of the first drilling under the Maritsa riverbed (422 m). According to preliminary estimates, this complex activity was expected to take a total of 150 days, but thanks to the experienced field teams and the HDI subcontractor, as well as the excellent organization on site, the whole process was completed in less than 2 months. Compliance with the drilling deadline is extremely important not only for the timely completion of the IGB pipeline, but also for the strict environmental restrictions that prevent construction activities during the breeding season of protected species in the region.

The pilot drilling started in the first week of August after the necessary preparation on the construction site. A whole week of continuous operation of the equipment was needed to reach the southern part of the dam, and reaching the planned diameter in accordance with the approved project took another 4 weeks. The final withdrawal of the welded pipes through the drilling was completed after a 12-hour continuous operation in which more than 30 specialists were involved.

The method of horizontal directional drilling, although more difficult from a technical point of view, was chosen for the implementation of the IGB interconnector after an in-depth planning process and according to the EIA assessment. In this way, the pipeline passes deep below the bottom of the dam, limiting the impact on the environment as much as possible. The use of HDD as a crossing method also eliminates the need to apply more expensive alternatives such as extending the pipeline by tens of kilometers to bypass the dam, or construction by open excavation, which would have a significant impact on the environment.

The implementation of the crossing is accompanied by overcoming a number of challenges - the impressive total length of the pipeline and the diameter of the pipeline, the steep angles at the points of entry and exit of the pipes, the diverse geological profile of the region and strict time constraints.

 "This achievement is another proof that the interconnection Greece-Bulgaria brings a significant change in every respect - not only for the regional energy market, but also in terms of engineering and technical approach. This was the first successful horizontal directional drilling on a project of this scale in Bulgaria, "said ICGB Executive Directors Teodora Georgieva and Konstantinos Karayanakos. According to them, this is technically the most complex element in the project and with its successful implementation the risks in the process of building the linear infrastructure of the gas pipeline are far less.