Sealing out the sand

A mixture of environmentally friendly, inorganic components and a chemical catalyst in water can be used to prevent sand getting into oil production works, seal tunnel wall fissures and stop erosion.

The method, developed at the NorwegianUniversity of Science and Technology (NTNU), involves pumping water containing the additives into the relevant subsea oil well or tunnel wall.

‘The system consists of two solutions – one carbonate source and one calcium source – which are mixed half and half. Gradually, over 24 hours, calcite, or limestone, precipitates from the mixture,’ explained Prof. Terje Østvold at the Department of Materials Science and Engineering.

This calcite is a type of calcium carbonate which is highly insoluble in water and will seal fissures in rocks and bind grains of sand.

Oil fields are depleted gradually, which results in lower pressure. To recover more oil, the producers pump in water to increase the pressure, which can occasionally transport sand into the production plant. The solution currently being used to minimise the problem is mechanical – a grid is placed in front of the drill pipe exit to prevent sand from entering, but it is not particularly effective.

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 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.

The method could also be used to reduce soil erosion caused by wind and water.

‘It turns out that soil can be stabilised in the same way as sand, with environmentally friendly minerals that also function as fertilisers. 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,’ said Østvold.