Questions and answers
Below we have gathered and answered frequently asked questions about our seismic surveys.
It is a type of geophysical exploration technique that uses sound waves to produce images of the rocks beneath the Earth’s surface. The images of the subsurface produced by the survey are used to identify possible oil and gas deposits. Seismic surveys are one of the first steps in the exploration for oil and gas, being used in practically all Oil & Gas exploration projects across the world in both onshore and offshore locations.
A seismic survey is a crucial early step in oil and gas exploration. The subsurface images that the survey produces are used to identify potential deposits of oil and gas and then to decide where, if anywhere, to drill an exploration well. A geophysical survey employing seismic energy sources is the only feasible technology available to accurately image the subsurface before a well is drilled.
Equinor has made a commitment to the Argentinian government to carry out 3D seismic surveys in our operated blocks offshore Argentina within the first exploration period. Actually, acquiring seismic data was a minimum committment imposed by the authorities in all offshore licences offered in the 2019 Licence Round.
The 3D seismic acquisition will be carried out by a seismic vessel equipped with a sound source, which uses compressed air to generate acoustic waves that are directed at the seabed. The sound waves are reflected from different layers of rock from the subsurface. They are then recorded by a series of sensors that are fitted along thick cables (streamers) that are dragged along by the seismic vessel.
This process is repeated along the survey area and the information recorded is processed by computers to produce images of the underground where possible deposits of oil or gas can be identified.
The acoustic waves are emitted in regular intervals by the seismic vessel. For our surveys in Argentina, the interval is five to seven seconds and the emitted sound lasts for less than 0,5 second.
The sources are not operated during periods of bad weather or technical downtime, or when the vessel is transiting between survey lines (line changes). This means that for a typical survey, the total duration of the tiem that the source is actually active is less than 5% of the total survey duratio
To collect seismic data short bursts of compressed air are released from a sound source into the water towards the seafloor.
This creates low frequency sound waves that pass through the water, the sea floor and into the subsurface layers. Then the sound waves are reflected up to the sea surface where they are recorded by the sensors.
The sound waves are emitted in regular intervals. For our surveys in Argentina, the interval is five to seven seconds.
In the North the survey will be carried out in our licences in the Northern Argentina Basin (CAN_114, CAN_108 and extending slightly into CAN_100).
In the south the survey will be covering most of MLO_121, and parts of the AUS_105 and AUS_106 licences, in the Austral and Western Malvinas basins.
For the northern licences (CAN_114, CAN_108 and CAN_100), the plan is to start operations in November 2022 and complete the survey in Q1 2023.
For the southern licences (MLO_121, AUS_105 and AUS_106), the plan is to start operations around September 2023 and to complete them in Q1 2024.
We estimate about 70% of acquisition days, out of the total survey time.
To guarantee that the seismic vessel with the towed equipment is able to navigate safely and without interference with other vessels in the acquisition area, the seismic vessel and all her in-sea equipment will be visible on radar screens on other ships.
Furthermore, the seismic vessel will be accompanied by a support vessel that will ensure that other ships in the area do not get too close. For this work, a safety zone for shipping will be established of up to five km from the front and side of the seismic vessel and up to 13 km behind it (five km behind the end of the streamers).
The survey vessel shall be equipped with an Integrated Navigation System (INS), Automatic Identification System (AIS), and will have VHF and UHF radio for communication. The vessel is also fitted with satellite communications for telephone and emails.
The Master (Captain) of the Vessel will issue regular Navigation warnings and provide communications on a regular basis with relevant marine/port authorities to indicate the actual and future areas of operations. Fishing associations and industrial fishermen will also be notified of the prospective seismic survey activities, dates, location, and the issued safety awareness zone.
Several Equinor representatives, some of whom will be Argentinian, will be onboard the seismic vessel to supervise the work and to ensure that it is carried out in accordance with Equinor standards.
Since the 1950s, dozens of seismic surveys and acquisitions have been conducted offshore Argentina. Most recently TGS acquired 3D seismic data in the Western Malvinas Basin during Q4 2020 and Q1 2021
Since the company was founded in 1972, we have conducted hundreds of surveys all over the world. Since 2000 we have acquired more than a dozen seismic surveys in the Americas, particularly offshore Canada, Brazil, Nicaragua and Suriname.
We always focus on the co-existence with other industries or stakeholders that are affected by our operations, such as fisheries and local communities. Being one of the world’s largest offshore operators, safety is our number one priority, for both people and the environment.
The sound from seismic sound sources is a strong sound impulse, but not unique in its strength. Natural sounds like lightning striking into the water, ice bergs calving and even sound from marine organisms can have similar amplitudes. Like with noise in air, under water sound gets weaker as the distance increases from the sound source.
All comparisons to noise from nuclear explosions or comparisons to the take-off of a space rocket or an airplane are wrong. They are not based on accurate research. Rather on misunderstandings of noise measurements in water and air and other factors. It is impossible to compare the energy released in a nuclear explosion to the one emitted by a seismic sound source.
There is no doubt that sound from seismic sound sources is a strong sound impulse, but it is not unique in its strength. Natural sounds like lightning striking into the water, ice bergs calving and even sound from marine mammals can have similar, or even higher, amplitudes. Like with noise in air, noise in water will weaken with distance to the sound source.
During our seismic operations offshore Argentina, we will have dedicated mammal observers onboard the seismic vessel to monitor and record marine life, such as whales and dolphins. Their task is to ensure that animals sensitive to low frequency sounds are not nearby prior to starting the sound source. Once the sound source is started, the sound output is increased slowly to give animals time to move away.
If animals are observed nearby during the seismic acquisition, the sound output will be paused until they are well outside the exclusion zone defined by the Argentinian authorities.