POTENTIAL EFFECTS OF DRILLING EFFLUENTS ON MARINE ORGANISMS 



Dr. Jerry M. Neff 



Batten e Ocean Sciences Laboratory 



Duxbury, MA 



Of more than 25,000 offshore wells drilled in U.S. waters in the past 90 

 years, more than 10,000 are still in production. During drilling and 

 production, there are several possible discharges to the ocean and physical 

 alterations of the bottom that may have adverse effects on the marine 

 environment. Some discharges are authorized by permit; others are accidental. 

 The permitted discharges of greatest environmental concern are drilling muds, 

 drill cuttings, and produced water. The most important accidental discharge 

 is petroleum through operational spills or blowouts. Physical impacts may be 

 caused by the mere presence of the platform or by emplacement of pipelines on 

 the bottom. The major concern in this report is the impact of drilling muds 

 and cuttings discharges. 



Such discharges are diluted very rapidly by dispersion and fractionation. 

 The heavier solids (representing about 90 percent of the mass of the mud) 

 settle rapidly to the bottom, usually within 200 to 1,000 m of the rig, 

 depending upon water depth and current speed. The liquids, soluble materials, 

 and fine clay-sized particles are carried away from the rig in a near-surface 

 plume and are diluted rapidly by mixing with seawater. In a typical current 

 of around 10 cm/s, a dilution of ten-thousand fold--well below toxic or even 

 sublethal levels--is accomplished within 200 m of the rig in less than half an 

 hour. Small wonder the National Academy of Science report concluded there is 

 essentially zero likelihood of any adverse effect within the water column. 



The ingredients of greatest concern in drilling muds on the sea floor are 

 metals, notably barium, chromium, lead, and zinc. Cadmium and mercury are 

 regulated by the Environmental Protection Agency but are found above 

 background levels only in association with high concentrations of barium. 

 Minor ingredients sometimes added to drilling mud that may contribute to its 



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