The Nederlandse Aardolie Maatschappij (NAM) had not expected the damage at a depth of more than a kilometer in the well. During the last major internal inspection in 2012, there was still nothing wrong. The crack was discovered in 2019 and the injection of wastewater via this well was immediately stopped. In the seven other injection wells in Rossum, waste water is still injected into the deep soil.
Repair of the well is almost impossible. In order to be able to continue to inject wastewater, the NAM would have to build a new well or create a new side corridor from the old well. Such an operation costs too much money and would put pressure on the profit margins of the wastewater injection.
Plan of action
NAM drew up an action plan and now that it has been approved, the company can resume work in Rossum. There has been a large drilling tower on the Tramweg in Rossum for several weeks now. That derrick was needed to pull the inner tube out of the double-walled injection well. When the inner tube turned out to be deformed and a crack was discovered in the outer tube, the work was halted.
Now that SSM has given permission to shut things down permanently, the derrick can be restarted to get the job done. The drilling tower costs millions a day and NAM is pleased that the machines and the operational team can now get back to work.
The action plan states that NAM intends to install a 100-meter-long cement plug in the injection well at a depth of approximately 1 kilometer.
Milling away steel outer tube
First, the derrick will cut away the entire steel outer tube at the height of the salt layer (1 kilometer) over a length of 50 meters. The space that this creates? will be completely filled with cement that will adhere to the original rock layer. In addition, the steel outer tube on top of this 50-meter-long cement plug will be further filled with a column of another 50-meter cement.
According to NAM, this new cement plug creates an impermeable barrier between the old gas field into which waste water was pumped and the overlying rock layers. According to them, this means that wastewater injection well ROW2 is safely closed off.
I assume we are now also getting evidence of what the NAM found down there
In parliamentary questions posed by GroenLinks on 19 February, it is stated that the minister’s party wants to know what exactly was found in ROW2. The party wants an independent investigation into the damage. The same is also demanded by the municipal council of Dinkelland and by the Provincial Council of Overijssel.
It is believed that clarity will come before the well is permanently closed. Once the cement plug has been applied, an independent research agency can no longer perform measurements. This independent investigation is necessary to find out what risks Northeast Twente runs in the other injection wells.
Because those wells are constructed differently from the broken ROW2, the state of the outer pipe can be measured much less deeply. Municipal council, province and GroenLinks want the risks to be properly mapped out.
NAM will start with the milling work next Monday and that work is expected to take a week. The milling of the 50-meter steel outer pipe in particular will cause noise pollution above ground. Another week later, the job should be done and the derrick can be dismantled and disposed of.
Since there are no quieter methods available, NAM asks local residents to understand the noise nuisance. The work will last from eight in the morning to nine in the evening.