POTENTIAL EFFECTS OF DRILLING EFFLUENTS 



ON MARINE ORGANISMS 



Jerry M. Neff 



Battelle Ocean Sciences 



Duxbury, Massachusetts 02332 



During drilling and production from an offshore platform, 

 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 most 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 and by emplacement of 

 pipelines on the bottom. The focus of this talk will be on 

 impacts of drilling mud and cuttings discharges. 



When discharged to the ocean, drilling muds and cuttings 

 are diluted very rapidly by dispersion and fractionation. 

 The heavier solids (representing about 9 percent of the 

 mass of the mud) settle rapidly to the bottom, usually 

 within 200 to 1000 meters of the rig, depending on water 

 current speed and water depth. The liquids, soluble 

 materials, and fine clay-sized particles in the drilling 

 mud are carried away from the rig in a near-surface plume 

 and are diluted rapidly by mixing with seawater. 



Because of the rapid dilution of drilling mud in surface 

 waters, significant biological impacts have not been 

 detected in the water column. However, drilling mud and 

 cuttings solids may cause adverse impacts in bottom living 

 (benthic) biological communities wherever the mud and 

 cuttings solids accumulate on the bottom. These impacts 

 could be due to physical burial, changes in sediment 

 texture making the habitat less suitable for some species, 

 or chemical toxicity of some drilling mud ingredients. 



The ingredients in water-based drilling muds of greatest 

 environmental concern are metals. The metals most likely to 

 be present in drilling muds at concentrations significantly 

 higher than their concentrations in marine sediments are 

 barium, chromium, lead, and zinc. Minor ingredients 

 sometimes added to drilling muds that may contribute to its 

 impact include diesel fuel or mineral oil, surfactants, and 

 biocides. Many hundreds of acute toxicity bioassays have 

 been performed with water-based drilling muds. Nearly 90 

 percent of the samples were found to be non-toxic or 

 practically non-toxic to marine organisms. 



Several large field studies have been performed in this 

 country and abroad by the oil industry and the government 



B-11 



