Environmental Impact Assessment of Marine Electromagnetic Survey Techniques

Abstract

AbstractAn environmental impact assessment (EIA) of electromagnetic (EM) survey techniques used for oil and gas exploration in the marine environment was completed and published in November 2011. The EIA was funded by the member companies of the International Association of Geophysical Contractors (IAGC) EM Subcommittee and prepared by an independent environmental consulting company.EM survey technologies currently utilized offshore use either the Earth's natural electromagnetic field or an induced low-frequency electromagnetic field transmitted by an antenna towed behind a vessel. The electric and magnetic fields are measured and recorded by an array of receivers. To date, these receivers have usually been deployed on the seafloor and then retrieved to process the measurements. Tests are currently being conducted to commercialize a system that tows the receivers underwater behind the vessel, similar to the method used in most marine seismic surveys. The data from EM surveys can help identify differences in the resistivity of subsurface rocks that may be related to the presence of hydrocarbons.The goal of the EIA was to provide a comprehensive resource summarizing available literature and potential effects of EM technologies on marine life. Designed for a broad audience, the document provides a basic description of EM survey technologies, naturally-occurring EM fields, and the potential use of these fields by diverse animal groups. The assessment focuses on survey activities considered to have at least some potential to affect marine animals, such as EM, noise, light emissions, and accidental events.The EIA concluded that EM sources as presently used have no potential for significant effects on animal groups such as fish, seabirds, sea turtles, and marine mammals. In addition, cumulative effects from EM surveys are negligible compared to natural EM anomalies, induced fields from natural water currents, and other anthropogenic EM sources such as those originating from permanently installed undersea equipment.