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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 scheduled for Q1 2007, within the two offshore blocks of Cap Serrat and Bechateur, northern Tunisia.

 

In accordance with BMT Cordah’s company strategy, the UK-based Project Team linked up with our Tunisian in-country partners: "Environmental Assessment and Management" based in Tunis, to assist in the development of the Environmental Statement.
 
Proposed activities include 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.  A total of 8 weeks was available to prepare the Environmental Statement in both English and French language for ultimate submission to the regulatory authorities.  As part of the EIA process, environmental and socio-economic sensitivities were described, potential impacts presented and mitigation measures adopted.  The EIA process followed an efficient approach was included the following steps:
 
Stage 1 – Initial kick-off meeting with client and contractor representatives.
Stage 2 – Data collection and analysis (desk-top) .
Stage 3 – Project Scoping to identify key potential impacts and associated data gaps including an in-country site visit.
Stage 4 – Preparation of a DRAFT Environmental Statement following modeling studies undertaken to evaluate key impacts (where possible) and outline the provisional form of an Environmental Management Plan.
Stage 5 – Internal review of the document by both the Client and selected seismic contractor.
Stage 6 – Preparation of a FINAL Environmental Statement and translation.

The following aspects of the proposed 2D seismic survey programme for Cap Serrat and Bechateur project were assessed as having “significant” risks:
 

  • Underwater noise generated during airgun start-up and operation and potential impacts to marine mammals
  • Entanglement of streamer on seagrass (Posidonia oceanica) within the survey area, plus physical interference with corals
  • Navigation of vessel, seismic array and chaser vessel within a designated shipping lane

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.  As marine mammals and turtles are mobile animals that could swim to avoid acoustic disturbance, the risks to these could mitigated by vigilance and employing ‘soft-start’ of the air gun array to enable animals in the vicinity to move away from the source of acoustic disturbance.  The JNCC (www.jncc.goc.uk) guidelines for minimising acoustic disturbance to marine mammals from seismic surveys were also followed during the survey to use Marine Mammal Observers, conforming to internationally accepted mitigation measures.  In addition, BMT Cordah's in-house noise modelling software was used to evaluate the risk associated with noise propogation within the marine environment and compared against audiograms of specific marine mammals so that the 'safe' distance of such sea life away from the seismic array, could be determined where behavioural changes are not expected.  An example of noise modelling results are illustrated below.

 

 

The planned 2D seismic programme also has a potential for accidental spills of diesel and other chemicals to occur.  Before mobilisation all vessels were independently audited to ensure that a detailed list of spill prevention procedures stipulated are in place.  All refuelling-at-sea operations were also stipulated to take place 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, included:

  •   A good watch shall be maintained to predict any situation arising well in advance of any emergency intervention being necessary and this shall be accompanied through the use of electronic onboard communication equipment.
  • Preparation of a line plan by the seismic contractor which is distribute to all relevant parties, including the Port Authority and Tunisian Coastguard. This plan shall state the expected time and position of the seismic vessel during the entire 2D survey so that they can warn other users of the sea.
  • A NAVAREA III warning will be given out to warn other users of the sea concerning the seismic operations, in addition to a “Notice to Mariners” to indicate the geographical position and time of the survey.
  • Use of two "chaser boats" to warn third-party vessels concerning the presence of the seismic survey vessel using communication equipment onboard.
  • The seismic vessels and chaser boats will display the correct warning signals as prescribed in Rule 27(b) of the International Regulations for the Prevention of Collisions at Sea.


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 oil company and concluded that sufficient safeguards to mitigate (and monitor) environmental risk were to be put into place.