Biodegradation of Anco Green Novaplus Drilling Muds on Cuttings Deposited in Benthic Chambers

Abstract

Discharge of drilling fluids attached to bore hole cuttings may affect the benthic environment on the deposition sites in the North Sea. The effects may vary according to dose and properties of the base fluid and other components of the mud recipe. In the present study, biodegradation and environmental effects of two new drilling muds, Anco Green (based on an ester produced from fish oil fatty acids) and Novaplus (based on a linear olefin), was investigated in a six months simulated seabed experiment performed in benthic chambers at Marine Research Station Solbergstrand. Exponential regression analyses yielded the following rank of half-lives: Anco Green < Petrofree (reference ester) < Ultidrill (reference olefin) < Novaplus < Safemul (reference mineral oil). Effects of the ester based cuttings on redox-potentials and macrobenthic communities were more servere than the effects of olefin based cuttings. The most servere effects were observed in the Petrofree treatment. All chambers treated with olefin cuttings or low-organic control sediment, maintained diverse benthic communities classified by the end of the six months enclosure, as good or fair according to general criteria for fjord and coastal environments. Concentrations of drilling fluids, barium and two biomarker enzymes were measured in the polychaete Hediste diversicolor after six months exposure in the chambers. Several indications were found on bioaccumulation of olefins and mineral oil. Different levels of enzyme activities between control and treated chambers, showed that the polychaete had been affected by components present in some of the cuttings.