Specialist Ships Equipped With Hydrophones Collect Data
Discovering new oil and gas deposits under the seabed is by no means the main focus, though. Norman Ettrich explains: »Due to the move away from fossil fuels, there is waning interest from European countries in discovering new oil and gas deposits. They are more concerned with better understanding and examining known reservoirs and those already in use.« After all, the technology can also be used to find suitable locations for greenhouse gases such as CO2 to be deposited underground.
Researching the surface and subsurface of the seabed requires specialist ships that often cover thousands of square kilometers in straight lines. They drag airguns and hydrophones behind them. Typically, the airguns send an acoustic pulse down every 25 meters. In the water, the sound waves travel at a speed of 1,480 m/s, penetrating the rock layers under the seabed. In extreme cases, the acoustic waves can travel through 3,000 meters of water, before passing through another 11,000 meters below the seabed.
The signals reflected are then detected on the sea surface by highly sensitive hydrophones. “In this way, each pulse creates a seismic trace. These traces provide information about how much time elapses between emission and reception. This propagation time is also influenced by the composition and size of each rock layer. Because the acoustic signal is picked up by multiple hydrophones, the seabed can be analyzed from multiple angles. The strength, propagation time and angle of the signal provide crucial information about the features, structure and thickness of the rock formation. This includes information about whether a particular layer is very porous and whether the pores are filled with oil or gas, for example.