The Blue Stream subsea gas pipeline system will transport up to 16 bcm/y of Russian gas to Turkey. The twin 24-in. pipelines will run about 380 km across the floor of the Black Sea between Djumba in Russia and Samsun, Turkey at a depth of over 2,000 meters.
In addition to overcoming the challenges of running a pipeline at this depth, the engineers will have to face a fairly hostile seafloor environment along the route. Hazards include: severe inclines and ridges off continental slopes, seafloor instability, possible seismic activity, high inner and outer pressure, and high corrosiveness of water environment. To ensure safe operating conditions, the project called for continuous monitoring of the technical state of the pipeline and its sea environment.
The following procedures were used to monitor the technical state of the deepwater section of the Blue Stream pipeline:
- Feasibility study, routing, and development of a geo-information database made up of results from these activities
- Pipeline laying process, specifically the quality of the main installation operations
- Regular surveying of the technical state of the gas pipeline during its operation
- Analysis of pipeline data to schedule maintenance operations and estimate availability for meeting the planned gas transportation rate.
Spatial database
Supervisors from OAO Gazprom were onboard vessels that carried out the feasibility study and gas pipeline routing survey. OAO Gazprom contracted with ZAO Intari to study the pipeline corridor and analyze of impact of different environment factors on the proposed gas pipeline. To do this, Intari developed an applied spatial database containing almost 6 gigabytes of primary and processed results from the surveys performed.
The database structure consists of two interacting modules: the Caris geo-information system and the Microsoft SQL Server 6.0 database management system. The Caris geo-information system provides storage, processing, and presentation of spatial data distributed into layers. The data consist of a bathymetric map of the seafloor along the corridor; a map of geological structures; side-scan sonar images of the seafloor and seismic profiles; locations of soil sampling sites and hydrological stations; coastline features with the elements of a navigation map including cables, anchorage, navigation marks; potential geological hazard zones that might indicate landslides, turbidity currents, or natural gas vents; additional information that duplicates data of exact depths and offers alternative interpretations of the soil structure.
Tools of geo-information data make it possible to carry out processing, numerical analysis, and engineering analyses using survey results. The database can translate this data into needed information in the form of maps, graphs, and tables that reconstruct exterior appearance of the corridor including the gas pipeline elements. Any section of these maps can be viewed from different angles and in any scale.
The survey vessel "Akademik Golitsyn" was used for ROV support on the surveys conducted for the Blue Stream pipeline project.
Environmental conditions
The large pressure differential, due to the varying depths and diverse seafloor topology along the pipeline route imposes a number of threats to the integrity and stability of the line. At various stages, the pipeline will face unstable soil conditions; depressions and obstacles in seafloor relief, due to the natural geography of the seafloor; washout and erosion below the pipe; creeps, currents, and turbidity; and corrosive processes.
For preliminary study of these factors, a geomorphologic analysis was carried out on the Russian near-shore seafloor along the gas pipeline corridor. From this analysis, it was learned that on the Russian continental slope, lithodynamic processes are the most intensive in the so-called transit zones - areas of change of seafloor geological structure. The study estimated the power of accumulative streams, characteristics of the heterogeneity of the route's relief-like depressions and obstacles, and the distribution of incline slopes for different sections of the corridor.
From the results it was concluded that different sections of the pipeline will face significantly different environmental conditions that must be taken into account when developing procedures and schedules for monitoring the pipeline's technical state. These help to establish which parameters should be monitored, the intervals of this monitoring, and the level of detailed information needed.
Monitoring technical state
A remotely operated vehicle (ROV) will be used to monitor the exterior of the pipeline's deepwater section. The ROV will move along the pipeline corridor a short distance from the pipeline, carrying out various surveys and measuring the parameters needed to estimate its technical state.
In addition, the ROV will be fitted with a wide range of equipment to monitor conditions along the pipeline corridor. A set of video cameras will be used for inspection of exposed gas pipeline sections to locate zones of soil erosion and wash-out, soil drifts and bulks, pipe submerging into the soil, pipe sags, stresses and deformations of the pipe coating, damage and loss of supports, weight insulation, or elements of electrochemical protection.
A multi-beam echosounder will be used for surveying route relief and measuring the position of exposed pipeline sections to determine length of spans, bending and sag values, as well as displacements in the horizontal plane. This information is used to analyze the stress-deformed state at the areas of gas pipeline bed disturbances. A pipeline tracking and profiling system will be used to measure the position of the pipeline sections located under the seafloor soil, laid in trenches, or submerged into silts. During the exterior survey, the level of vibration of free spans of gas pipeline sections, level of protection potential, temperature of outer surface of the pipe walls, and other parameters are to be measured.
Comparison of the results of the exterior pipeline survey with the data obtained using innerpipe diagnostics will be the foundation for recommendations on maximum and optimal gas transportation rate.
The OAO Gazprom research vessel Akademic Golitsyn will support the ROV activities. The vessel is currently undergoing modification, including mounting a dynamic positioning (DP) system, satellite and submarine navigation systems, a shipborne computer complex, and space communications facilities. Initially a company-operator will supply and operate the ROV. As the Gazprom operators become familiar with ROV operations, the responsibility for the ROV will gradually transfer over to Gazprom.
Integrated geo-information
The Integrated geo-information system (GIS) for Blue Stream will be the core of the gas pipeline monitoring system. This GIS will provide a fast loading information model of the pipeline's subsea section - an integrated, efficiently controlled, easy-access base of all existing data on the pipeline, its environment, and history of operation.
In this GIS, all primary data obtained during gas pipeline operation will be stored, processed, and analyzed. During processing, background and historical information of the gas pipeline obtained at the preceding project stages will be considered.
The result of this analysis will be up-to-date estimates and forecasts of the technical state of the gas pipeline, recommendations needed to determine optimal and maximum gas transportation rates, and plans and schedules for pipeline maintenance and its repeated diagnostics.
The main users of Blue Stream will be companies carrying out operation and maintenance of the gas pipeline, research and project organizations from Gazprom, Gazprom authorities, and consulting and insurance companies.
Prospective operations
Before construction begins, Gazprom plans to create a full-scale geo-information system with input of all available and recently obtained data on the gas pipeline. Gazprom also plans to develop a detailed design, procedure, and schedule for equipping an ROV with the complex survey equipment needed to inspect the pipeline. Gazprom will purchase survey equipment, carry out its system integration and installation on the Akademic Golitsyn. The company also has plans to train maintenance personnel, create a testing area near the construction site, and carry out integrated training on the monitoring technology in advance.
This training and database development will provide independent control over installation operations from the start, using the Akademic Golitsyn survey vessel. Such advanced preparation will initially increase the quality of installation, and later aid in the efficient and safe operation of the subsea section of the pipeline, including timely scheduling and carrying out preventive maintenance.
