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NAM Dutch Environmental Legacy not just Groningen Earthquakes

In February 1965 there was a explosive blowout at a NAM gas field in Sleen, East Drenthe – an agricultural area of the Netherlands. A whole drilling rig was swallowed in a quicksand lake created by the explosion.

Afterwards, NAM, the company responsible for the explosion all those years ago and the earthquakes now plaguing Groningen, converted the area into a park.

Unfortunately, scientists have discovered to their consternation that methane leaks have contaminated the local groundwater and there is a risk of further explosions.

It would have been a disaster if this had all happened in a residential area.

(The Dutch Petroleum Company (NAM) is a 50/50 joint venture between Shell and Exxon.)

Text below is translated from an article by Marlies ter Voorde published in Dutch on 26 Dec 2017 by de Volkskrant.

Gas leak in the bottom of East Drenthe, groundwater at Sleen contains methane

In 1965 it all went wrong at Sleen in East Drenthe at a gas drilling. An explosion created a lake of quicksand that swallowed the entire derrick. Half a century later, geologists are worried about the crash site.

By: Marlies ter Voorde December 26, 2017, 10:31

There is a gas leak in the bottom of East Drenthe. The groundwater at the village of Sleen contains methane, originating from the gas field that is located in the subsurface at a depth of two kilometers. This is the conclusion drawn by earth scientists from Utrecht University and the water research institute KWR from the chemical analysis of water. The natural gas seeps through cracks that occurred 52 years ago in a drilling accident, the geologists think.

It is agricultural area, so the gas can go away. That would have been different if they had built a residential area

Geohydrologist Niels Hartog

Methane is non-toxic, but vigilance is required at high concentrations such as at Sleen. If the gas is released from the water in a poorly ventilated room there is a risk of explosions, possibly followed by fire. Scientists still have to figure out whether the natural gas at Sleen escapes the earth’s surface. ‘If that is the case, it can do no harm at this location’, says geohydrologist Niels Hartog of KWR, who worked on the research. ‘It is agricultural land, so the gas can go away. It would have been different if they had built a residential area with cellars and crawl spaces. ‘

The province says it knows the groundwater for all kinds of polluting substances, but not so far methane.

This is not a problem for drinking water, says Nico van der Moot, geohydrologist at the WMD water company that provides drinking water for Drenthe. Methane is removed from the water as standard and with a simple procedure for purification, says Van der Moot, who is not involved in the study.

‘That methane from a natural gas field is in the groundwater is exceptional’, he explains, ‘but methane from other sources is common.’ Soil bacteria that break down dead plant material also produce the gas, often in high concentrations. ‘Marsh gas, is it called. In Spannenburg in Friesland it is even extracted from drinking water as fuel ‘, says Van der Moot.

Jasper Griffioen, geochemist at Utrecht University who also cooperated with the research, agrees. ‘I know from India and Nepal sacred sources where an everlasting little flame burns on the surface of the water’, says Griffioen. ‘Hindus find that a sacred place, we see it as an earth science phenomenon.’



The discovery of the leaky natural gas field in Sleen was no coincidence, stressed earth scientist Gilian Schout of Utrecht University, lead author of the PNAS article. ‘We were looking for leaks, even with natural fractures and former wells.’

The search for suitable locations to store CO2 or waste water in the soil is in full swing, and then it is important to know if there are weak spots to keep an eye on, he explains. ‘If methane can leak away, other gases and liquids can in principle also pass through.’

The gas field at Sleen was a logical place to include in this study. In February 1965 it went wrong with a gas drilling. The high pressure in the gas field caused an explosion in which quicksand was formed, and the entire 50-meter high derrick in the soil disappeared. For a few months, a mixture of natural gas, mud and stones spurted out of the ground, only then did the NAM regain control of the situation.

The fact that natural gas is still leaking is evident from the chemical signature of the methane in the groundwater – which is the same as the composition of the methane from the Sleen gas field. However, the methane is broken down in the groundwater, the researchers discovered. The methane concentration decreases rapidly as the distance to the crash site increases.

Other leakages than those at Sleen have not yet been found by the researchers in the Netherlands.

‘It is agricultural land, so the gas can go away. That would have been different if they had built a residential area

Geohydrologist Niels Hartog

If methane can leak away, other gases and liquids can in principle also pass through

Earth scientist Gilian Schout


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