Abstract

In June 2010 Sakhalin Energy Investment Company Ltd. (Sakhalin Energy) successfully acquired a 4D seismic survey offshore Sakhalin covering the Astokh oil field development. This survey is the first 4D seismic survey carried out in Russia. The aim of this survey is to aid further field development optimization and infill drilling in the Astokh field, onstream since 1999. Rock property and 4D-seismic modeling studies indicated that hydrocarbon saturation and pressure effects can over time potentially be identified with 4D repeat seismic surveys. Feasibility studies were followed by the acquisition of a seismic test line in autumn 2009. This test showed amplitude and time differences at reservoir level in the seismic section when comparing the 2009 test line with the 1997 pre-production seismic survey. These differences can be correlated with the production history. Disturbances of seismic events were minimized by accounting for azimuthal velocity anisotropy during seismic data processing.

The proximity of the Astokh field development to the feeding grounds of the Western Gray Whales (WGW) offshore Sakhalin was fully taken into account for the planning and execution of this seismic survey. To this extent, Sakhalin Energy has benefited from collaborative efforts with independent scientific bodies and the Russian Government. This collaboration with recognized Russian and International scientific experts has yielded an exemplary set of monitoring and mitigation measures to protect the whales, whilst allowing responsible surveying activities to proceed without unnecessary delay. This includes:

  • Execution of the survey as early as possible in the summer season, when the sea is ice-free and before the whale-feeding season

  • Real-time measurement of acoustic sound generated at the edge of the feeding area to steer operations

  • Strict operating and shut-down criteria when WGWs are observed in the near-survey feeding area

  • Continued monitoring of distribution and behavior of the WGWs during and after the survey

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