The method has been developed at the Norwegian University of Science and Technology (NTNU), and involves pumping water with various additives into the relevant area. It could be a well at a subsea oil field, or a tunnel wall. These additives are environmentally-friendly, inorganic components and a chemical catalyst.
”The system consists of two solutions – one carbonate source and one calcium source – which are mixed half and half. Gradually, over 24 hours, calcite – limestone – precipitates from the mixture,” explains the man behind the method, Professor Terje Østvold at the Department of Materials Science and Engineering.
This limestone will seal fissures in rocks and bind grains of sand.
Calcite is a type of calcium carbonate. Calcium carbonate is highly insoluble in water – which is wonderfully demonstrated by the magnificent formations in stalactite caves.
Oil fields are depleted gradually, which results in lower pressure. To recover more oil, the producers pump in water to increase the pressure. This method has a significant problem attached to it: In many reservoirs, the water will transport sand into the production plant. The solution currently being used to minimize the problem is mechanical: Some sort of grid is placed in front of the drill pipe exit to prevent sand from entering, but it is not particularly effective.
”Gradually, the amount of sand makes the recovery impossible and unprofitable. New wells must be drilled, but that could be so expensive that recovering the remaining oil does not pay off," says Professor Østvold.
However, when Østvold’s chemical water mixture enters the oil reservoir, calcium carbonate crystals will come between the grains of sand and bind them together. That makes the sand unable to move. The oil may flow through the sand without bringing it into the pipe.
The water mixture can also be used to seal tunnels more efficiently and environmentally-friendly than today.
”The current method involves injecting concrete into fissures in the rock while working the tunnels. The carbonate and calcium water is a lot more liquid than concrete. By injecting this mixture into the rock wall on the inside of the tunnel, the calcium carbonate crystals will fill the narrow, water-bearing fissures in the rock and seal them," says Professor Østvold.
“It is too soon to say whether the new method will be less expensive than the current one, but it is definitely a possibility,” claims Østvold.
The Norwegian Public Roads Administration is particularly interested in the discovery, and recently invited the researchers from NTNU to test the method in the Eiksund tunnel in Møre.
”It worked perfectly,” confirms Professor Østvold. ”We achieved a leakage reduction of more than eighty per cent.”
Binding the soil
It appears that this method could also be used to reduce soil erosion caused by wind and water. Soil erosion is an enormous global problem.
”It turns out that soil can be stabilized in the same way as sand, with environmentally-friendly minerals that also function as fertilizers. If we water the soil in autumn with water containing chemicals and a catalyst, we may produce minerals that bind the soil particles together. That way we may protect the soil from erosion while waiting for the next growth period,” says Professor Østvold.
Østvold has developed the new method in cooperation with the spin-off firm Impermeable AS that he established a few years ago. Together with research fellows and students at NTNU and the University of Patras, Greece, he further developed the method.
He says that commercial actors are planning to test the method at oil fields in the North Sea. The worldwide engineering company M-I provides technology services for oil companies all over the world. Its Norwegian subsidiary M-I Production Chemicals is genuinely interested in adopting the method, and Østvold has also met with British Petroleum in London for the same reason.
By Tore Oksholen
Nina Tveter | alfa
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