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Offshore Seismic Environmental Impact Assessment

A multi-national oil company operating extensively throughout North Africa commissioned BMT Cordah to prepare an Environmental Statement for a planned 2D seismic offshore survey.

BMT linked up with Tunisian in-country partners: "Environmental Assessment and Management" based in Tunis, to assist in the development of the Environmental Statement.

Proposed activities included the mobilisation of a 75-m length seismic vessel to tow a 6,000m array of streamers consisting of airguns and hydrophones behind the vessel.

As part of the EIA process, environmental and socio-economic sensitivities were described, potential impacts presented and mitigation measures adopted. 

In order to mitigate the potential impacts of underwater noise to marine mammals, the survey had been scheduled, in so far as possible, to reduce the likelihood of encounters with marine mammals, turtles and other sensitive species in the survey area.

The planned 2D seismic programme also has a potential for accidental spills of diesel and other chemicals to occur. 

All refuelling-at-sea operations were also stipulated to take place in calm sea conditions, and be completed in accordance with industry best practice.

Within the two offshore blocks, a Traffic Separation Scheme (TSS) area is present, where shipping traffic is directed between pre-identified geographical paths.

Planned mitigation to prevent vessel collision and loss or entanglement of streamer with third-party vessels within the TSS and elsewhere during the survey

Before mobilisation, all vessels were independently audited to ensure that a detailed list of spill prevention procedures stipulated was in place.

The environmental assessment undertaken for the Cap Serrat & Bechateur offshore blocks established that sufficient information had been obtained on both the environment and the proposed 2D seismic survey to evaluate the potential environmental consequences of the programme of operations.

In addition, the EA systematically evaluated the environmental risk-reduction measures to be taken by the oil company and concluded that sufficient safeguards to mitigate (and monitor) environmental risk were to be put into place.