The execution of survey operations is a recurrent task during both the design and operation phases of a field development. As such, developments in survey techniques and optimization of costs vs. results are a key factor when considering the constant moving of the industry towards deeper water developments.
Between October 1999 and August 2000, Sonsub Ltd developed a leading capability in this field by planning and executing one of the most challenging pre-engineering surveys of this type, involving the detailed investigation of the two pipeline routes for the Blue Stream Project.
This project, led by Saipem as Main Contractor, involves the installation of two 24" pipelines across the Black Sea joining the coasts of Russia and Turkey. The route is characterized by long and steep slopes at both shore approaches, and by an Abyssal Plain section of 240 kilometres in a water depth of 2,150m.
Sonsub Ltd addressed the challenging survey requirements by combining their new generation "Innovator" ROV technology with state of the art survey sensors and systems to provide a reliable but highly flexible solution for high specification data acquisition and seabed intervention.
The Sonsub remote intervention vessel "Polar Prince" provided a sophisticated operating platform, which guaranteed maximum productivity and reliability throughout the project.
This paper will describe preparatory works, operating equipment spread, difficulties and problems encountered, together with the solutions and results, which contributed to the successful completion of the Blue Stream Pre-Engineering and Abyssal Plain Survey.
The Blue Stream project includes the installation of two 24" gas transportation pipelines supplying gas from Southern Russia across the Black Sea to Turkey (see figs. 1 and 2).
Prior to the construction and installation phase, Saipem have commissioned a detailed engineering survey to fully consider the options available for final route selection and engineering of the proposed pipelines. This will include design of the optimum routes to minimise the need for seabed preparation, pipeline stabilisation and intervention works, all having high cost implications on such a project.
Route survey investigations had taken place during the previous four years period; these including conventional surveys using hull mounted sensors, geotechnical investigation and some ROV geophysical survey in selected areas.
These surveys indicated that it was possible to install the pipelines however, the route was subject to potential hazards including instability or movement of the seabed; boulders strewn across sections of the pipeline route; low bearing capacity and fluidity of surficial sediment on the Abyssal Plain and even the possibility of large scale seabed instability caused by seismic activity.
Fig. 1: Blue Stream Route (available in full paper) This new detailed pre-engineering survey would investigate further the feasibility of the proposed routes and also explore hazards, obstructions and potential re-routes.
This task was placed with Sonsub Ltd. the underwater contracting and ROV operating subsidiary of Saipem. Fig. 2: Blue Stream Longitudinal Profile (available in full paper)