4,000 meters deep in the sea! my country's first inter-oceanic ridge deep-sea electromagnetic joint exploration geological experiment was successful!

On September 5, the South China Sea Institute of Oceanology, Chinese Academy of Sciences, reported that the team of Sun Zhen, a researcher at the institute, cooperated with researchers from China University of Geosciences (Beijing) to conduct the first cross-ocean ridge deep-sea artificial source electromagnetic and magnetotelluric joint detection profile experiment in China at a depth of about 4,000 meters in the central basin of the South China Sea, using independently developed electromagnetic transmitting and receiving equipment. The entire profile is nearly 100 kilometers long, with a total of 16 receiving measurement points, and obtained electromagnetic data of good quality. This experiment marks a further breakthrough in China's high-power artificial source electromagnetic detection technology under complex deep-sea terrain conditions.

01 The working principle of ocean electromagnetism

Marine electromagnetics is actually one of the methods of marine geophysics . It is based on the physical basis of a difference in electrical conductivity . It transmits high-voltage electricity underwater through an excitation field source (such as lightning, or an artificially excited generator), and then emits it to the seawater on the seabed, which will generate an electromagnetic signal . When the electromagnetic signal encounters a place with electrical differences underground (that is, the intersection of good conductivity and non-conductivity), it will be reflected back, and then brought back to the underground. By analyzing the detection target information and interpreting the response, we can obtain relevant information such as the underground structural form, such as whether the form contains minerals? Or does it contain oil and gas? Or is there a large structural belt, etc.

Marine electromagnetic method is an important method for detecting seabed geological structures. At present, only a few units from the United States and Europe have mature technology and equipment for conducting joint detection of artificial sources and magnetotelluric methods in the deep sea. Over the past 20 years, through long-term and unremitting efforts, China has made important progress in the fields of seabed electromagnetic field observation, high-power artificial source emission, electromagnetic offshore operation technology, data analysis and processing, etc.

02 Current status of foreign marine exploration technology

Foreign countries have been developing marine electromagnetic exploration technology since the end of the last century. After more than ten years of development, this technology has become an essential means of marine geophysical exploration. At present, when major oil companies conduct marine oil and gas exploration, the traditional method is to use marine seismic seawater to shoot, and then use seismic waves to explore the seabed oil and gas based on elastic differences. However, this method has an obvious problem: after the structural exploration, it is known that it may contain oil, but it may also contain water, and marine seismic cannot distinguish the two. But the marine electromagnetic method can solve this problem. Early marine electromagnetic technology emerged in this context. However, with the development of technology, marine electromagnetics has now become an independent exploration technology with an independent set of theoretical methods and technologies that can be used for independent exploration. At present, major oil companies still use marine seismic as the main method and use marine electromagnetics as an auxiliary means. These two methods can also be organically combined. In this way, the exploration efficiency of marine oil and gas is improved, especially the accuracy of exploration.

03 Current status of development of artificial source ocean exploration technology in my country

Artificial sources use a device called armored cables to convert electricity generated from ships into high voltage (like high-voltage transmission lines) and transmit it to the seawater, and then use two electrodes about 300 meters long to transmit it to the seabed. Receivers are like small spiders, arranged on the seabed according to a certain web, and then the transmitter is towed by a ship to tow the receiver back to receive the electromagnetic signal, thus achieving exploration.

04 my country's marine electromagnetic detection of seabed geological structure and resources has reached a new level

According to Sun Zhen, a researcher at the South China Sea Institute of Oceanology, Chinese Academy of Sciences, all the electromagnetic transmitting and receiving equipment used in this voyage was independently developed by Chinese scientists. In order to conduct this experiment, the project team spent 4 years preparing. The experiment was held from July to August this year. The entire profile was nearly 100 kilometers long, with a total of 16 receiving points, and obtained good quality electromagnetic data. This cross-ocean ridge ocean electromagnetic method joint exploration operation was carried out by the comprehensive geophysical research vessel "Experiment 6" of the South China Sea Institute of Oceanology, Chinese Academy of Sciences.

Wang Meng, associate professor at China University of Geosciences (Beijing), said that this joint exploration achieved long-term observation of multi-component natural source electromagnetic fields on the deep seabed, and also successfully realized the near-seabed towed high-power artificial electromagnetic source transmission operation, effectively supplementing the high-frequency natural source electromagnetic field signals absorbed by the extremely thick and highly conductive seawater layer.

Dr. Jiang Feng, head of the electromagnetic joint exploration voyage, said that this exploration achieved the goal of simultaneously detecting the resistivity structure of the shallow crust and deep mantle with one geophysical profile, which will significantly enhance China's ability to use marine electromagnetic methods to detect seabed geological structures and resources.

Comprehensive sources: CCTV News, Science and Technology Daily, Xinhua News Agency