Dr. Peter Fokker
- reservoir engineering
- data assimilation
- induced seismicity
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Many of the activities that take place below the surface, such as reducing the groundwater level and extracting oil and gas, ultimately lead to soil subsidence. TNO has developed models which combine accurate satellite measurements of the Earth's surface with subsurface data. This results in more accurate assessment of the causes and effects of soil subsidence.
Operators that produce oil and gas go to great lengths to understand what is going on in the reservoir. They monitor the situation based on seismic research, geophysical measurements and a continuous flow of production data. Producing safely and efficiently is of great importance, both for the community and the oil and gas industry. The same applies to limiting the impact on the surrounding area. In spite of all these efforts to collect measurements and monitor operations, researcher Peter Fokker still sees room for improvement, for example by combining subsurface data with accurate satellite measurements.
Peter Fokker, who is a geo-scientist, cites a topical example in illustration of the potential improvements that can be achieved: “Extracting gas from the gas field in Groningen has subjected the rock formations to greater pressure, a process known as compaction. The gas reservoir rock is covered by elastic layers of salt, shale, sand, clay and peat. They form a mattress that is a number of kilometres thick. This ensures that the changes caused by gas extraction in the deep underground environment can spread across a large surface area, which extends for approximately the same distance as the depth of the gas field. Radar signals from space are used to measure subsidence with an accuracy of 1 mm.”
Satellites orbiting the Earth at a distance of 700 km have measured gradual surface changes since 1992. Some of those surface changes can be attributed to oil or gas extraction at great depths. Other causes, such as settlement in the peat layer or compaction of the clay due to a reduction in the groundwater level, occur at a shallower level. And this is where TNO's expertise comes into play: detecting the causes that have led to the observed surface changes. Because the effect is already known, but the cause still has to be determined, experts refer to this process as inverse modelling. In these models, TNO combines data about the underlying soil and rock structures with satellite measurements relating to the surface topography.
Fokker explains the social benefits: “Our expertise makes it possible to accurately identify the perpetrator in debates about who is responsible for possible damage caused by soil subsidence. That is an important issue. And we help operators to gain a better understanding of how the pressure profile in the reservoir changes during production. If our measurements show that gas at high pressure has been left behind somewhere, the operator can target drilling operations on that specific compartment. The result is extra economic value for the operator and the Treasury. In addition, this information allows operators to avoid major pressure differences and reduce the risk of stresses below the surface causing earthquakes. TNO is also involved in research into storing gas in empty gas fields. Our discovery that the uplift above the Bergermeer gas storage field was smaller than the previous level of subsidence may lead to a different understanding of the risks of earthquakes in the long term. Again, an unexpected result.”
Please contact Peter Fokker
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