In this blog post, we’ll explore the principles of seismic surveying—a core technology in oil exploration—and the process of locating oil in a way that’s easy to understand.
Conflicts within the international community over oil have been ongoing for a long time. From the Gulf War and the Iraq War to more recent international conflicts, energy security and securing resources have consistently been cited as key underlying factors. For a long time, oil has served as a key energy source sustaining modern industrial society, and even today, it plays a vital role in the global economy and industry. However, despite the recent expansion of the energy transition, oil continues to be utilized as a major energy source, and securing a stable energy supply chain remains a critical challenge for countries around the world. Consequently, nations worldwide are continuing their technological, political, and economic efforts to secure oil. South Korea, too, is continuing to make various investments to develop resources and strengthen energy security at the national level, and public interest in these matters is also growing. Against this backdrop, the principles of oil exploration—which will be introduced below—can serve as important foundational knowledge not only for those majoring in related fields but also for the general public seeking to understand energy and resource issues.
Oil mostly exists in liquid form thousands of meters underground. So, how can we locate oil buried so deep underground? The answer may not come to mind immediately, but in fact, the principle is not much different from methods we encounter in everyday life. Let’s imagine there is a sealed black box right in front of you. If you had to guess what was inside without opening it, how would you go about it? There are several ways, but the first thing you’d likely do is shake the box and listen to the sound it makes. This is because the sound of objects colliding inside the box allows you to make a reasonable guess about what kind of objects are inside. If you thought of this, you’ve already grasped the core principle used in actual oil exploration. If you replace the black box with the Earth’s crust, this is the core technology of oil exploration, known as “seismic survey.”
To understand seismic survey, we first need to know what seismic waves are. The sounds we hear with our ears are phenomena transmitted by the vibration of tiny particles in the air. These vibrations are transmitted not only through air but also through liquids and solids. For example, the phenomenon of noise from the apartment above being transmitted through the floor and walls operates on the same principle. The transmission of sound and the transmission of vibrations within a solid are essentially the same phenomenon; the only difference is whether the medium transmitting the vibrations is air or a solid. Scientists distinguish these vibrations traveling through solids from ordinary “sound” and call them “elastic waves.”
If vibrations traveling through solids are called elastic waves, what is elastic wave exploration? Let’s return to the example of the black box. Now, the box has become the Earth’s crust, and two new problems arise. First, the crust is far too massive to be shaken by hand. Second, the crust is solid, so we cannot directly hear sounds coming from inside it. To solve this, engineers have devised methods to generate strong shocks or artificial vibrations at the Earth’s surface. In the past, explosions were often used, but today, methods that generate seismic waves more safely and precisely—such as using equipment like vibroseis vehicles—are also widely used. The vibrations generated in this way travel through the solid interior in the form of seismic waves and are measured by various sensors installed on the Earth’s surface. By analyzing the measured seismic waves, it is possible to estimate what materials exist underground. We will examine this estimation process in more detail below. This technology—which involves generating artificial vibrations in the Earth’s crust and measuring the resulting seismic waves to analyze the subsurface structure—is known as “seismic exploration.”
Engineers already know from experience the sounds produced by various objects when trying to identify what is inside a box. Therefore, by comparing the sounds they know with the sounds they actually hear, they can make a reasonable guess about what is inside the box. So, what principle allows seismic exploration to identify materials within the Earth’s crust? Engineers utilize the phenomenon of “reflection,” an important property shared by both seismic waves and sound.
You’ve probably experienced at least once that when you shout or sing near a wall, the sound seems louder. This is due to the phenomenon of sound reflection. As sound travels, when it encounters the boundary between different materials, some of it passes through while some is reflected back. The reason sound seems louder in front of a wall is that both the sound that travels directly and the sound that is reflected back reach your ears simultaneously. This principle applies equally to elastic waves. When elastic waves generated at the Earth’s surface travel underground and encounter boundaries between different materials, some continue onward while others are reflected. By measuring the reflected waves that return to the surface, it is possible to estimate the presence of different rock layers or oil underground and calculate their locations.
The basic principle of seismic exploration is as follows: When an artificial vibration is generated at a point on the Earth’s surface, elastic waves are created and propagate in all directions. As these waves travel through the subsurface, they continue downward unless they encounter a boundary between different materials. However, when they encounter a boundary between different rock layers or fluids, some of the waves are reflected and return to the Earth’s surface. These reflected waves are recorded by numerous receivers installed on the surface. By analyzing these recordings, it is possible to estimate the structure of the subsurface and identify structures where oil or natural gas may be present. In actual oil exploration, these measurements are repeated hundreds to thousands of times to generate highly precise subsurface images.We have now examined the principles of seismic exploration, a core technology in oil exploration. Seismic exploration remains one of the most widely used technologies for exploring for oil and natural gas, and it has established itself as a core technology for energy exploration worldwide, both offshore and onshore. In particular, as 3-dimensional (3D) and 4-dimensional (4D) seismic survey technologies, high-performance computing, and artificial intelligence (AI)-based data interpretation technologies advance, exploration accuracy continues to improve, and research to reduce exploration costs and risks is actively underway.Although carbon neutrality and the expansion of renewable energy are being promoted globally, various organizations, including the International Energy Agency (IEA), project that oil and natural gas will continue to account for a significant share of the global energy supply for quite some time. Accordingly, the importance of securing stable resources and efficient exploration technologies is likely to remain high. Humankind is developing new technologies to locate underground resources more accurately and at lower cost, and seismic exploration is also expected to become increasingly sophisticated in the future, driven by advances in artificial intelligence and cutting-edge data processing technologies.
