Although few people think of sound as a part of offshore exploration, sound waves are integral to the search for oil and gas. The industry uses seismic technology to help determine where to drill. A seismic imaging tool sends sound waves from an exploration vessel to geologic formations below the ocean floor. The vessel then records the returning waves to create 3-D images of sedimentary formations that may hold oil and gas. This is a bit like taking a picture of underground rocks using sound waves instead of light waves—just as an ultrasound “sees” tissue inside the body with sound.
Prior to offshore operations, environmental studies are conducted to understand the distribution of species, especially marine mammals such as whales and dolphins. “This enables industry to protect areas with higher marine mammal concentrations, such as migration corridors, as well as breeding and feeding areas,” says Dr. Gary Isaksen, manager of ExxonMobil’s Sound and Marine Life Programs. “Computer models to identify remaining potential risk scenarios are constructed—taking into account the hearing ranges of marine mammals—and a suite of mitigation measures are then used during operations to minimize the level of sound that whales and dolphins could detect.”
Although there is no scientific evidence that mitigated seismic exploration causes any harm to marine wildlife, a point that top officials have made emphatically in recent years, companies involved in offshore projects still take extra precautions to ensure the sounds they produce have minimal interference with the communication between marine mammals.
Marine mammal observers
“We employ trained observers on vessels whose sole purpose is to look for wildlife,” says Isaksen. Crews are not just looking out for marine mammals; they are listening for them as well. If you have ever been on a whale-watching tour, you have actually come much closer to a marine mammal than these vessels will ever be when the sound source is active. Industry vessels cannot get closer than a permitted distance from protected marine mammals, usually at least 500 meters, which is more than a quarter mile away. If marine mammals are observed after the survey begins—either visually or acoustically—swimming toward the exclusion area around the vessel, then the seismic acquisition is shut down until after the whales pass through and swim away.
With all the time and technology oil and gas companies dedicate to keeping an eye and ear on marine life, the companies often find themselves providing essential support—such as marine mammal observational data—to marine conservation and monitoring efforts.
New science and technologies
Ultimately, though, companies are interested in deploying even more advanced methods for mitigating any effects seismic activities can have on the marine environment. ExxonMobil is part of a consortium to develop new seismic acquisition technology called “marine vibroseis.” Still in testing, the method may be an alternative to current seismic acquisition sources in some areas. This new source emits less energy, so it emits sound at lower levels.