It is almost one o’clock at night when a car from Smart Seismic Solutions drives into Amsterdam’s Hobbemastraat. The lights at the German consulate are already off, the nearby Museum Square is deserted. While traffic controllers take their place on the access roads, the car comes to a stop in the middle of the street. Apart from the large tires and chunky front bumper, you could mistake the vehicle for a normal, somewhat noisy garbage truck.
Then a rubber-protected plate drops down between the large wheels down to the paving stones. A deep arrhythmic rumbling spreads under the road surface and a slight tremor can still be clearly felt under the sidewalk at the end of the street. After one minute the metal plate rises again, the car drives twenty meters further, lowers the plate again and starts again. Some passers-by walk by without looking up.
In November and December – unnoticed by most Amsterdam residents – geological research of staggering proportions took place in the capital. Trucks with seismic equipment drove meticulously along the streets, stopping every twenty meters to cause vibrations that penetrated up to three kilometers deep into the ground. The research took place at night to limit environmental noise from passing trams and construction work as much as possible.
About twenty thousand orange-gray boxes, spread across the city and attached to lampposts or bicycle racks. With this data, in combination with information from previous drillings, geologists can create a three-dimensional image of the subsurface. The technique is comparable to a pregnancy ultrasound in the hospital, but instead of an unborn child, layers of earth that were formed millions of years ago emerge.
A rubber-protected plate causes vibrations up to three kilometers deep underground.
Photo Simon Lenskens
Oil in Papua New Guinea
Petru Luhos from Smart Seismic Solutions will guide the car along Museumplein tonight. “I prefer to work outside the city,” says Luhos, directing his colleagues via walkie-talkie. “We were just standing in front of a bridge again that we did not dare to drive over with this weight. Then we had to take a complete detour.”
Luhos and his colleagues speak Romanian to each other, their native language. But the company is French and active all over the world. In most places they are asked to map fossil reserves. “For example, a few years ago we were in Papua New Guinea,” says Luhos. “That was for oil and gas.”
The research in Amsterdam focuses on another energy source hidden in the earth’s surface: geothermal heat. Geothermal energy may play an important role in future energy supply. It produces no emissions and is also inexhaustible, like the sun and the wind. But just like with oil and gas, geothermal energy requires a detailed picture of the soil.
Geothermal heat extraction uses the high temperatures that are naturally present in the inner part of the earth. The Earth’s core has a temperature of about six thousand degrees, as hot as the surface of the sun. As you get closer to the Earth’s surface, that temperature drops. At a depth of three kilometers, the bottom is still about ninety degrees, almost enough to boil water.
Tens of thousands of households
Geothermal heat producers want to know whether a porous, water-permeable sandstone layer is present at that depth. If that layer is there, they can pump cold water in there and bring the heated water up again through a second nearby well. That is something significantly different from the normal ground heat pump that some people have at home, which only goes a few tens of meters deep. The hot water from one geothermal well can be enough to heat tens of thousands of households.
In 28 places in the Netherlands this happens already. Geothermal heat heats dozens of greenhouses in Westland and a number of residential areas throughout the country. The existing geothermal projects are usually in places where oil and gas have previously been found, because the earth’s layers have already been mapped. In places in the Netherlands where oil or gas has never been explored, it is not yet known whether the suitable sandstone layer is present.
“Above the ground, the Netherlands is flat,” says geophysicist Johannes van den Akker, who is out this night on behalf of the public company Energie Beheer Nederland (EBN). “But underneath, the geology is quite interesting. The height of an earth layer can vary considerably per neighborhood in Amsterdam. You have to imagine that in some places in the Netherlands you really encounter the Himalayas or the Alps underground.”
Sensors measure the vibrations on the facade to limit nuisance as much as possible.
Photos Simon Lenskens
140,000 letters to local residents
EBN was commissioned to fill in the “blank spots” on the Dutch geological map and has partly outsourced this to Smart Seismic Solutions. The public company then makes the results of the research freely available, so that other companies can set up production locations themselves in the future.
The geology is already visible in two dimensions in many places, says Van Den Akker. “You should see that as a cross-section of a cake, on which you can clearly see the different layers. With the three-dimensional image that we are creating now, we will soon have the entire cake in our hands.”
As the research vehicle moves through the street, two of Luhos’ colleagues walk along on either side of the street. Every time the car stops, they place square sensors against the nearest facades.
“These sensors measure the vibrations in the building,” says Van Den Akker. “If the vibrations are too high, we turn the level down. The level is now a lot lower than we use on the edges of the city.” In this way, the researchers try to limit the nuisance to local residents as much as possible. “But I am not going to deny that it can wake people up,” says Van den Akker. “People sometimes come outside.”
People who carry flyers and can provide local residents with explanations also accompany the research vehicle. EBN has sent 140,000 information letters in advance, says Van den Akker. “That helps to prepare people for it. But the most important message is: we are only here once. The vibrations we cause one night are enough to get a complete picture of the geology. It was created millions of years ago and will remain the same for millions of years.”
Van Den Akker can see on a digital map where the car has already been and where it has not.
Photo Simon Lenskens
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