sound wave search for oil & gas Seismic surveys provide detailed information
No other geophysical method has influenced and changed the search for oil and gas as much as seismic surveys: of all the measurement methods, they provide the most detailed information about the subsurface and are essential in oil and gas exploration. Seismic surveys are used when the data analysis and investigations of the geologists on-site are promising, and when measurements of the earth’s magnetic field and gravity have provided the first indications of possible natural gas or crude oil bearing structures. The probability of finding hydrocarbons can be significantly increased with the results of seismic surveys.
With this technique, sound waves are generated at the earth’s surface. They are reflected in different ways by the deeper rock strata depending on the characteristics of the subsurface. Geophones in the ground record the reflections. Our team of geologists, geophysicists, petrophysicists and engineers then constructs two and three-dimensional models of the subsurface based on the information gathered. Using these models, the Wintershall specialists can tell where crude oil and natural gas bearing structures might be and how large they could be.
Seismic surveys are now the main technique for scouting for reservoirs – both on land and at sea. Just as doctors examine human bodies with ultrasound, geophysicists and geologists use seismic images to examine the earth.
This enables them to discover rock formations that formed millions of years ago. Not infrequently, their expert eyes find indications of oil and gas reservoirs. The interactive diagram shows how reflection seismology works.
On land special vehicles, so-called “seismic vibration trucks”, or “vibro trucks” are deployed to generate the sound waves underground. They are a key element of every seismic campaign – and the most easily recognizable element thanks to their size.
It requires true teamwork to produce seismic images of the subsurface. When Wintershall conducts seismic surveys, as well as the vibro trucks, numerous colleagues are out on site making sure the seismic campaign is successful. As well as looking after the trucks themselves, they collect and evaluate the data.
The countless geophones have to be anchored in the ground again each time the trucks move on – that’s really hard work! Our video explains how a seismic campaign is conducted.
Although reflection seismology has been developed further and refined frequently in the last few decades, improvements are still possible sometimes. One example of this is the development of wireless seismic surveys by Wintershall. This makes carrying out seismic campaigns even easier.
Seismic at sea Creating sound waves with air guns
About a quarter of the world’s oil and gas reservoirs are located in layers of rock under water – in Europe it’s even 90 percent. Hence, oil companies began searching for reservoirs off the mainland early on. Seismic surveys are also the main instrument used for exploration on the high seas. But at sea seismic ships are used instead of vibro trucks. The sound waves are generated from the vessel using so-called “air guns”. The sound waves from the air guns travel through the water, penetrate the rock strata under the seabed and are reflected – in exactly the same way as exploration on land. To capture the reflections, the vessel pulls a large number of hydrophones behind it on long cables. This system is also called “towed array sonar”.
To analyze the seismic data, the Wintershall experts use the same methods used for exploration on land. With the help of state-of-the-art technology, they constantly manage to acquire new information about undiscovered reservoirs from old data sets. This was the deciding factor in allowing Wintershall to participate in some important hydrocarbon discoveries in Norway in recent years – even though the North Sea has for a long time been considered to a large extent exhausted.
Being a good neighbor close relations are crucial
But the Wintershall teams on the ground are not just responsible for carrying out the seismic surveys; they are also tasked with maintaining a direct dialog with our neighbors. Providing the residents of the areas affected with comprehensive and transparent information early on is important for maintaining public acceptance for a technologically and logistically demanding project of this nature.
One example of this is the seismic campaign that Wintershall conducted in the Norwegian North Sea – while doing so, it took into account the interests of the Norwegian fishermen. The relationship between oil and gas companies and fishermen is not always easy. While the former fear that they will not be able to search for natural resources in promising regions, the latter are concerned about their equipment and catches.
The solution: Wintershall approached the largest Norwegian fishing association at the planning phase. Together the two sides discussed the plans for the seismic surveys and decided on the best possible time frame. Wintershall also informed the fishermen about the project early on – this way there were no complaints.
In 2014 Wintershall conducted seismic surveys in Germany in Bockstedt, Lower Saxony. The experts at the site informed the local residents and neighbors about the project early and comprehensively. They did so without lengthy presentations and chose a dialog instead – this way they were able to respond to questions directly.