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Dieren en planten

Water en land

Mens en Milieu

Pollution   Drilling mud   Drilling cuttings   
Cuttings, Ecomare

Drilling mud and cuttings

When drilling for oil or gas, hundreds of tons of pulverized seabed materials are released in the water. One uses a kind of paste, the drilling mud, to pump these cuttings to the surface. The mud also serves as a lubricant and a cooling agent for the drill bit and offers counter-pressure when a pressurized oil or gas field is drilled. One used to use an oil-bearing liquid for this purpose, which strongly polluted the cuttings with oil. Nowadays, drilling muds based on water are used whenever possible. This mud contains no oil, though it does contain chemicals. The oil-bearing cuttings were dumped in sea till 1993, polluting the sea bottom within a radius of 200 meters around the platform.

  • With or without oil

    The amount of cuttings released by drilling is tremendous. The diameter of a drilling shaft varies from 90 centimeters at the surface to around 15 centimeters at the end depth (300 to 4500 meters under the sea surface). Around 500 to 1000 tons of cuttings are released when a shaft is drilled.
    Presently, the use of drilling mud is more or less a closed system. The released cuttings are sifted on the floor of the drilling rig where they are separated from the drilling mud, which can be reused. The cuttings that are processed when using water-based drilling mud are allowed to be thrown overboard as long as the oil level is less than 1%. Remnants of drilling fluids sometimes hang onto these cuttings.
    After the drilling mud has been used several times, its usefulness declines. Around 95% of the oil is then first filtered from the drilling fluid, after which the rest of the fluid becomes waste.
    Using drilling mud based on oil (or oil-based mud, OBM) has decreased significantly in the past several years since dumping oil bearing cuttings anywhere on the Dutch section of the Continental Plate (NCP) was forbidden in 1993.
    The type of drilling mud most commonly applied is based on water, the so-called water-based mud (WBM). Due to its particular characteristics, OBM is still applied for drilling in exceptional and difficult areas. Companies which drill with oil-based drilling muds are required to bring the oil bearing cuttings to land for processing.