Survey Operations for the Blue Stream Project

Abstract

Abstract The aim of this paper is to provide an insight into the deepwater multibeam echosounder and geophysical ROV survey operations based on the technical experience gained on the Blue Stream Project in the Black Sea. Introduction At the request of PeterGaz, NeSA performed a detailed geophysical survey with an Remotely Operated Vehicle (ROV) along a 380-km long proposed pipeline(s) route crossing the Black Sea from Djubga (Russia) to Samsun (Turkey) in water depths up to 2,150-m. This survey was known as Step 2 of Gazprom's Blue Stream Project Phase II. The survey was conducted in co-operation with the ROV company Canyon Offshore and vessel owner Diamar. The Italian DP-vessel Mare Oceano was used for the data acquisition during the period 15th May to 19th September 1998. Fig. 1 - Overview map of the Eastern Black Sea, showing the Blue Stream Pipeline Route from Djubga (Russia) to Samsun (Turkey) (Available in full paper) Phase I of the Blue Stream Project, a reconnaissance survey, revealed that pipelines could be installed insofar as pipeline stress criteria would not be exceeded. The review of the Phase I survey results indicated in general the following potential geohazards:Slope failure and movement mechanisms on the heavily canyoned Russian Continental Slope.Potential instability and unpredictable bearing capacity of the surficial sediments on the Abyssal Plain.Sliding, slumping and mass gravity flows on the Turkish Continental Slope. The possibility of tectonically induced slope collapse.Instability of the seabed due to gas seepages and faulting activity principally on the Turkish Continental Shelf. The potential for geohazards along the route required further investigation by means of a detailed geophysical survey. The main objectives of the detailed geophysical survey were:to finalise the preferred routing for two pipelines within the corridor,to gather high resolution bathymetric and geophysical data required for detailed pipeline design,to quantify and delineate potential geohazards andto provide site specific information required for seismic risk analysis. In order to achieve these objectives, a high-resolution multibeam echosounder, side scan sonar and Chirp sub-bottom profiler was mounted on an ROV to reduce the water column height between the sensors and the seabed. This resulted in increased data accuracy and density, as well as provision of visual inspection capabilities. The proposed route alignment was defined within a nominal 1000-m wide corridor, reduced to 'individual' route options of a minimum 400-m width at the approach of the Russian Continental Shelf. During the Phase II Step 1 survey, detailed bathymetry and geophysical surveys were performed on the Russian and Turkish Continental Shelf areas, using vessel mounted multibeam echosounder and towed side scan sonar and sub-bottom profiler. During the Phase II Step 2 survey, detailed ROV surveys were performed in the critical sections across the Russian and Turkish Continental Slopes and at discrete locations over the Abyssal Plain. The navigation, bathymetry and geophysical data were processed and interpreted immediately onboard the Mare Oceano to allow adjustments in the survey lineation in case inaccessible or hazardous terrain was detected for pipelines.