A water mixture that prevents sand from gumming up oil production equipment and can also be used to seal cracks in tunnel walls to stop erosion has been developed at the Norwegian University of Science and Technology (NTNU).
The technique involves pumping water with various additives into subsea oil fields or tunnel walls, for example.
“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 Professor Terje Østvold at the Department of Materials Science and Engineering, who devised the technique.
This limestone seals fissures in rocks and bind grains of sand.
Oil fields are depleted gradually, which results in lower pressure. To recover more oil, more water is pumped in to increase the pressure. But in many reservoirs, the water will transports sand into the production equipment. Currently, filters are used to remove the sand, but this method is not particularly effective.
“Gradually, the amount of sand makes recovery impossible and unprofitable. New wells must be drilled, but that may be so expensive that recovering the remaining oil is uneconomic,” says Professor Østvold.
When Østvold’s chemical water mixture enters the oil reservoir, calcium carbonate crystals binds sand grains together, so they cannot move down the pipe. The water mixture can also be used to seal fissures in tunnels.
“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 Østvold.
The Norwegian Public Roads Administration is interested in the discovery, and recently invited the researchers from NTNU to test the method in the Eiksund tunnel in Møre.
“It worked perfectly,” claims Østvold. “We achieved a leakage reduction of more than 80 per cent.”
Østvold developed the new method in cooperation with the spin-off firm Impermeable AS that he founded a few years ago. There are plans to test the technique in oil fields in the North Sea.