Many countries have a regulatory requirement to conduct an Environmental Impact Assessment (EIA) prior to the initiation of any oil & gas exploration activities such as seismic surveying. The EIA assesses the risk of disturbance to primarily marine mammals, but also turtles and fish populations in the survey area in terms of possible effects on feeding, breeding and migration behaviour. Modern 3D multi-streamer seismic surveys deploy an array of high pressure airgun sources which put a considerable amount of sound energy into the water column. Cetaceans (whales, dolphins and porpoises) use sound to communicate and in some cases to echo-locate and therefore man-made or anthropogenic sound has the potential to adversely affect their normal activities. Environmental assessments form an integral part of the permitting process in many countries as regulated by authorities such as the DECC in the UK and the Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE) - formerly Minerals Management Service (MMS) - in the USA, that authorise approval of exploration activity. Historical data is used as a reference to aid in evaluating the likelihood and severity of any perceived risks and identification of mitigation measures appropriate for the survey location.
In the UK the Joint Nature Conservation Committee (JNCC) in conjunction with the Department for the Environment, Food and Rural Affairs (DEFRA) published the first guidelines in 1995 designed to minimise acoustic disturbance of marine mammals during the conduct of seismic surveys. Similar guidelines have been implemented by other national bodies in the USA, Canada, Australia, New Zealand, Ireland and Greenland amongst others, and this list is likely to increase with time. These guidelines vary in the detail but have a degree of commonality including the use of radial exclusion zones, procedures to be followed during 'soft starts', and standards for reporting.
Prior to the firing of the seismic sources most guidelines require a visual search for a specified period, usually 30 minutes, of an exclusion zone typically 500 to 1000m around the airguns. This is conducted by dedicated Marine Mammal Observers (MMOs) and should any animals be detected then the use of the guns must be delayed for a determined time period after the last sighting. After this a soft start procedure is initiated whereby the power of the seismic sources is gradually ramped up to full strength before the start of the seismic line. Standard reporting forms are used to record any mammal observations during the survey operation and particularly during line starts. Reports from each survey are collated by the appropriate national authority such as the JNCC and these datasets are gradually adding to our knowledge of the distribution and behaviour of different marine species. The number of experienced MMOs has increased over the years and these dedicated personnel are now recognised as key members of the acquisition team on many seismic surveys. A skilled MMO works closely with the seismic crew and can help minimise costly disruptions to production by ensuring compliance with regulations.
However, visual monitoring has a number of limitations, for example it is not effective at night-time, during poor weather conditions and when marine mammals are submerged. Modern seismic activity is a 24 hour operation that continues in poor visibility conditions and to address this issue Shell UK sponsored field trials from 1996 to 1999 of a Passive Acoustic Monitoring (PAM) system developed by Oxford and Birmingham Universities. That system consisted of a two element hydrophone array, a tow cable, a deck cable and dedicated hardware and software to capture, data process and display the recorded signals. The results of these trials were encouraging and development of the technology has continued over the subsequent decade. Refinements in the hardware and software have resulted in better range and bearing estimates and signal processing developments are refining the capabilities of automated species recognition. PAM originated in the UK and many of the equipment suppliers (e.g. Seiche Measurements, Vanishing Point, MSeis, AMS and OSC) are UK based. PAM software is available from a number of providers; the most commonly used are PAMGUARD, the IFAW suite of programs, and Ishmael. Skilled PAM operators are increasingly in demand and ideally have a background in marine biology, experience in marine species observation, technical skills with both hardware and software, and knowledge of multi-streamer seismic operations. PAM operators liaise closely with the back deck handling specialists to ensure safe deployment of the PAM hydrophone array to avoid entanglement with the seismic equipment, and as such it is a highly responsible role with significant QHSE implications.
A green future
Environmental disasters such as the Deepwater Horizon incident in the Gulf of Mexico in 2010 have focussed public attention on the activities of the E&P industry. Exploration companies will come under ever closer scrutiny to demonstrate that they are implementing socially responsible Environmental Management Plans as a core element in survey planning. Many companies now consider it Best Practice to employ MMOs and PAM on surveys even where there is no local mitigation legislation in place such as West Africa. Environmental observers are being deployed across the globe: from Seabird observers on seismic surveys off Greenland, to MMOs monitoring the sound impact of pile driving operations for wind turbines off the UK coast. Demand for skilled environmental personnel is destined to grow.
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JuliAnne Tidy, Luis Goncalves and Eulalia Pujol are with Geomotive Limited, Nicosia, Cyprus. www.geomotive.net