During planning of a drilling operation in the North Sea with planned discharges from the top hole section, it was revealed that the drilling location was bordering to a predefined area for sand-eel (Ammodytes marinus). As sand-eel spawning is strongly related to limited habitat, spawning grounds are given high value on the uniqueness, life-historical importance and productivity. Due to the presence of sand-eel, mitigating measures were implemented to minimize the risk of smothering sand-eel areas by: 1) Use of cuttings Transport System (CTS) in order to lead the discharges away from the defined sand-eel area. 2) Use of particle free drilling fluid for minimizing spreading of particles. As a consequence barite is not included in the drilling mud composition. Barite contains high amounts of Ba and may generate particles with a potential of being transported over long distances. Environmental authorities required documentation of drilling discharges not spreading to the sand-eel habitat. The question is then how one can monitor and document the spreading of barium free drilling discharges on seabed?
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