2. Environmental effects

The environmental effects of disolids controlharging cuttings to sea are well understood. The practical significance of such effects is determined by the nature and composition of contaminants in the discharge, which determine the rate at which organisynthetic muds are able to re-colonise impacted areas. For water based muds, re colonisation typically proceeds rapidly - generally beginning when discharge has ceased.

OBM discharges have longer term effects, since elevated concentrations of hydrocarbons associated with cuttings and surrounding sediments have severe impacts on marine life - either by direct toxicity or by creating anoxic conditions. The rate at with the oil degrades determines the duration of effects. Degradation is typically slow under North Sea conditions, and effects can last for decades.

Environmental concerns with synthetic muds (synthetic muds) also focus on their persistence in the marine environment, and thus on the duration of environmental effects. The muds were developed in response to increasing restrictions on the discharge of oil based mud (OBM) to sea, with their use and discharge supported by claims from mud companies that their products degraded significantly faster in the marine environment than OBM. These claims are based on limited - and sometimes questionable - data sets.

Results from sea bed surveys and other environmental studies have provided increasing evidence that synthetic muds do not degrade rapidly under field conditions. This has been confirmed by results of laboratory biodegradation tests, carried out by SOAEFD, which indicate that synthetic mud base oils (other than the ester, Petrofree) cannot be differentiated from mineral oils on grounds of persistence.

Following on from this, discharges of OBM and synthetic muds also contribute to overall levels of contamination of the sediments. The significance of this last points needs to be considered against a broader background of reducing inputs of contaminants to the Sea, particularly from land based sources.