What happens to the soil after oil production?
What happens to the soil after oil production?
Deep pumps for oil production are located on the Wintershall Dea site.
© Source: Mohssen Assanimoghaddam/dpa/Montage RND
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Oil and natural gas are both formed in a similar way and are of prehistoric origin. That is why one also speaks of fossil raw materials. Plankton or algae fall to the sea floor, where they are covered with sediment. This means that the biomass cannot be completely decomposed. Their chemistry changes as a result of high pressure and temperatures, and over the course of millions of years, crude oil or natural gas are formed – these two raw materials often occur in close proximity to each other.
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That’s where the similarities end: As a liquid, oil doesn’t reside in large chambers underground, but tends to fill many, small spaces in porous rock. If this layer is drilled into, the oil presses upwards. This creates black fountains that shoot out of the ground. The reason for this is the high pressure that arises from impenetrable layers of earth and the property of liquids to strive upwards. If the pressure drops at some point, the extraction companies pump water or gas into the ground. The pressure rises again, more oil comes out.
Ground can become unstable
However, this is not unlimited. Groundwater gradually penetrates from neighboring layers of rock, and the high proportion of water eventually makes oil production uneconomical. The oil reservoirs can therefore not be completely emptied. The density in the soil is maintained by residual oil and groundwater. The soil can still suffer from the extraction and become more unstable. Especially when natural gas is still being produced in the region.
This occurs more often in compressed chambers. If the gas is extracted from these chambers, the subsurface pressure changes more significantly and the ground is more likely to collapse. The traces that gas production can leave behind can be seen in Groningen in the Netherlands. Underneath the region lies a large gas field with an original capacity of more than 2800 billion cubic meters. Gas has been mined for more than 60 years.
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The earth is now very porous. In addition, the different densities cause many weak earthquakes. They rarely score more than three points on the Richter scale, but the tremors occur just below the surface. This increases damage to roads and houses. The resistance of the population grew so much that in the meantime it was decided to end gas production. After 60 years of production, the natural gas field is significantly emptier anyway. However, the region still has to struggle with the long-term effects for years to come.
Similar phenomenon when mining coal
The same applies to coal mining. The damage to houses is also clearly visible in mining regions. The ground in the Ruhr area, for example, is criss-crossed by more than 60,000 shafts, tunnels and cavities, many of which are in danger of collapsing. The cavities and tunnels gradually collapse, the ground sinks.
Because this rarely happens evenly, there are sloping positions in the statics of buildings. Roads and railway tracks are also at risk. Rising groundwater and frequent earthquakes also cause problems in these regions. The cost of repairing the damage is immense. The imbalances have to be leveled out with new concrete foundations and cracks in the walls have to be closed.
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