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Environmental Impact of the Offshore Oil and Gas Industry by Stanislav Patin - a unique summary of world-wide studies on the environmental issues associated with offshore oil and gas exploration and development

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Muddied Waters

A Survey of Offshore Oilfield Drilling Wastes and Disposal Techniques to Reduce the Ecological Impact of Sea Dumping

by Jonathan Wills, M.A., Ph.D., M.Inst.Pet., for Ekologicheskaya Vahkta Sakhalina (Sakhalin Environment Watch); 25th May 2000

Environmental Effects of Drilling Waste Discharges

In the 1980s the consensus among Western scientists studying the environmental effects of drilling waste discharges was that effects were mainly local and minor. This view was summarised by the American researcher Jerry Neff of the Battelle Research Laboratory in Duxbury, Massachusetts, with an authoritative paper (Neff, J. M. 1987. Biological Effects of Drilling Fluids, Drill Cuttings and Produced Waters, in Boesch, D. F. and Rabalais N. N. (eds.). 1987. Long-Term Environmental Effects of Offshore Oil and Gas Development, pp. 469-538. Elsevier Applied Science Publishers, London) in Donald Boesch and Nancy Rabelais' influential book, Long-Term Environmental Effects of Offshore Oil and Gas Development, published in 1987:

Most of the major ingredients of drilling fluids have a low toxicity to marine organisms. Only chrome and ferrochrome lignosulphates and sodium hydroxide are slightly toxic. A few specialty chemicals sometimes added to drilling fluids to solve certain problems are toxic. These include diesel fuel, chromate salts, surfactants and paraformaldehyde biocide...

...[tests for] chronic and/or sub-lethal effects of drilling fluids have been performed with at least 40 species of marine animals. In most cases, sublethal responses in marine animals were observed at drilling mud concentrations only slightly lower than those that were acutely lethal. In some species, sublethal responses were observed at drilling fluid concentrations up to two orders of magnitude lower than acutely lethal concentrations. Sensitive species included reef corals, lobster larvae and scallop embryos and larvae. Recruitment of planktonic larvae to sandy sediments in laboratory microcosms was decreased by high concentrations of drilling mud mixed with or layered on the sediments. Based on laboratory studies of acute and chronic/sublethal toxicity of drilling muds and field observations of rates of dilution of drilling muds in the water column, it is concluded that water column organisms will never be exposed to drilling fluids long enough and at sufficiently high concentrations to elicit any acute or sublethal responses. Where drilling fluid solids settle on the bottom, there could be localised adverse impacts on the benthos, through chemical toxicity, change in sediment texture, or burial...
[emphases added. JWGW]

...The severity of the impact of drilling fluids and cuttings on the benthos is directly related to the amount of material accumulating on the substrate, which in turn is related to the amount and physical characteristics of the materials being discharged, and to the environmental conditions at the time and site of discharge, such as current speed and water depth. In high energy environments, little mud and cuttings accumulate and impacts on the benthos are minimal and of short duration. In low energy and depositional environments, more material accumulates and there may be reduction in abundance of some benthic species.

Other authors take a less sanguine view. The Russian scientist Stanislav Patin has recently published a comprehensive study (Patin, S. A. 1999. Environmental Impact of the Offshore Oil & Gas Industry. Eco Monitor Publishing, East Northport, New York. ISBN 0-967 1836-0-X. This work cites numerous Russian sources not usually referred to by Western writers on the subject) which points out that, despite moves to increase re-injection and shipment ashore for disposal, up to 80 per cent of drilling wastes and chemicals still enter the sea, one way or another:

Produced, ballast and injection waters, as well as drilling cuttings and fluids polluted by hundreds of different chemicals, often go directly overboard at the production site. The majority of available studies of liquid and solid wastes of the offshore oil and gas industry give very different estimates of their toxicities. They are difficult to compare, due to the variability of the chemical composition of these discharges. (p.255.)

Patin says water-based drilling muds, while preferred over OBMs or SBMs for obvious environmental reasons, can still damage marine life. Leaving aside the question of toxicity, WBMs deposited on seabed sediments may smother benthic animals and, if in the form of very fine particles suspended in the water, can interfere with respiration in small marine animals and pelagic fish:

...small (pellet) fractions gradually spread over large distances. Particles less than 0.01mm in size can glide in the water column for weeks and months. As a result, large zones of increased turbidity are created around drilling platforms. These phenomena, on an even larger scale, happen during the laying of underwater pipelines, construction of artificial islands, bottom dredging, and some other activities that accompany offshore oil production operations. At the same time, the increased turbidity can pose a certain risk. In Russia, "Rules for water protection" [1991] do not allow increasing the suspended matter in fisheries water bodies over 0.25-0.75mg/l higher than the background natural levels. As direct observation in areas of exploratory drilling on the eastern shelf of Sakhalin showed ( Sapozhnikov, V. V. 1995. Modern Understanding of the Functioning of the Bering Sea Ecosystem. In Complex Studies of the Ecosystem of the Bering Sea. pp. 387-392. VNIRO, Moscow.), the persistent plumes of increased turbidity disturb the balance of production-destruction processes in the surface (photic) layer of seawater. It can also cause disturbances at the ecosystem level. Experimental evidence shows the negative effects of pellet suspension (particles with a size of 0.005-0.01mm) on marine organisms. A short-term increase in concentration of such suspension above the level of 2-4 grams per litre caused quick adverse effects and death to fry of salmon, cod and littoral amphipod (1. Shparkovski, I. A. 1993. Biotesting Water Environment Quality with the Use of Fish. In Arctic Seas: Bioindication of the State of the Environment, Biotesting and Technology of Pollution Destruction. pp. 11-30. Izd-vo KNTS RAN. Apatiti. 2. Matishov, G. G., Shparkovski, I. A. and Nazimov, V. V. 1995. Impact of Bottom Deepening Activities on Barents Sea Biota During the Development of the Shtokmanovskoe Gas Condensate Field. Doklady RAN 345r:138-141. Moscow ).
[emphasis added. JWGW]

Neff characterised water-based drilling fluids used on the US Continental Shelf as "specially formulated mixtures of clays and/or polymers, weighting agents, lignosulfates and other materials suspended in water", with barium, chromium, lead and zinc often present at "substantially higher" levels than in natural marine sediments:

Acute lethal toxicity of more than 70 used water-based drilling fluids has been evaluated in more than 400 bioassays with at least 62 species of marine organisms from the Atlantic and Pacific Oceans, the Gulf of Mexico and Beaufort Sea. Nearly 90% of LC50 values were above 10,000ppm drilling mud added, indicating that the drilling muds are practically non-toxic. Only two LC50 values were below 100ppm. The most toxic drilling muds are those that contain high concentrations of hexavalent chromium, diesel fuel or surfactant. (Neff, J. M. 1987. op. cit. p.520)

Although the main components of WBMs may be relatively harmless when heavily diluted in the sea, Patin says that, like other muds, they commonly contain additives that can be extremely toxic, even in low concentrations:

Using water-based formulations does not fully eliminate the environmental hazards... Some comparative studies showed that water-based fluids do not always meet strict ecological requirements (Sorbye, E. 1989. Technical Performance and Ecological Aspects of Various Drilling Muds. In Proceedings of the First International Conference on Fisheries and Offshore Petroleum Exploitation, pp. 1-18. Bergen). In particular, they can include some toxic biocides and heavy metals in their composition. Besides, in contrast with oil-based muds, these fluids display a higher capacity for dilution in the marine environment. Finally, large volumes of water-based muds are usually disposed of overboard, while muds on the oil base are largely recycled. At the same time, the experimental and field studies show that acute toxic effects of water-based drilling muds can be manifested only at high concentrations (Patin, S. A. 1998. A New Approach to Assessment of the Environmental Impact of the Offshore Oil and Gas Industry: Water Resources. Moscow). Such concentrations can be found only in direct vicinity to the discharge point (within a radius of several meters). (Patin, S. A. 1999. op. cit.)

Comparative studies (1. National Research Council Panel on Assessment of Fates and Effects of Drilling Fluids and Cuttings in the Marine Environment. 1983. Drilling Discharges in the Marine Environment. National Academy Press Marine Board, Commission on Engineering and Technical Systems, National Research Council. Washington, D.C. 2. Neff, 1987, op. cit 3. Swan, J., Neff, J. M. and Young, P. C. (eds.) 1994. Environmental Implications of Offshore Oil and Gas Development in Australia - the Findings of an Independent Scientific Review. Australian Petroleum Exploration Association Ltd., Sydney. ) showed that marine organisms were more sensitive to the suspended particulate phase of drilling muds than to the liquid phase. This indicates that suspended particles in drilling fluids may contribute substantially to their toxicity. [p.259]
[emphasis added. JWGW]

The larger and heavier particles in all drilling muds tend to reach the seabed more quickly, as one would expect, and here the accumulations of this artificially produced sediment alter the ecology in two ways - by changing the particle size of the benthic sediments and by smothering animals that cannot move out of the way in time. As Norwegian researchers put it in a recent paper: "Immediately after discharge, the benthic community is eliminated under the discharge piled and is impoverished in the surrounding area, with the impact decreasing with distance ( Det Norske Veritas. 2000. Technical Report - Drill Cuttings Joint Industry Project. Phase I Summary Report. Revision 2: 20th January 2000. DNV doc. order No. 29003500. Oslo)."

Patin cites research by Kozak and Shparkovski (Kozak, N. V. and Shparkovski, I. A. 1991. Testing Drilling Muds and their Components with the Use of Fish from the Barents Sea. In Theses of the Second All-Union Conference on Fisheries Toxicology. 1:272-273), who found that water-based clay fluids effected changes in respiration rates and heartbeat in salmon fry exposed to concentrations of between 2 and 15 milligrams per litre (mg/l) for a couple of minutes and led to "reduced survival" in cod and flounder exposed to concentrations of 5 mg/l for 10 to 30 days. Shparkovski et al. (Shparkovski, I. A., Petrov, V. S. and Kozak, N. V. 1989. Physiological Criteria [for] Assessment of the Ecological Situation During Drilling on the Shelf. In Theses of the First All-Union Conference on Fisheries Toxicology, 2:199-200. Riga) had earlier reported "threshold changes in respiratory and cardiac activities" in cod, salmon, haddock and rays exposed for two to five minutes to 15-40mg/l concentrations of "water-based clay-bentonite fluids". Another Russian research paper (Borisov, V. P., Osetrova, N. V., Ponomarenko, V. P. and Semenov, V. N. 1994. Impact of Offshore Oil and Gas Developments on the Bioresources of the Barents Sea. VNIRO, Moscow) described 50% mortality in salmon fry and amphipods exposed for between 48 and 96 hours to 5-22mg/l concentrations of water-based lignosulfonate and ammonium drilling fluids. On the other hand, "chronic tests" of copepods, amphipods, bivalves and cod fry exposed to "water-based muds" at 10-103mg/l produced "no observed effect". (Kosheleva, V. V., Novikov, N. A., Migalovski, I. P., Gorbacheva, E. A. and Lapteva, A. N.. 1997. Responses of marine organisms to environmental pollution during oil and gas development on the shelf of the Barents Sea. PINRO, Murmansk)

Patin says the composition of drilling fluids is so variable and the circumstances of their use so different that there is "an extremely wide range of concentrations that cause different toxic effects" ranging from "practical absence of toxic effects to lethal toxicity". He divides drilling fluid components into three main groups, based on their eco-toxicological hazard:

  • Group I includes the main components of water-based drilling muds - such as bentonite and other clays, barite and lignosulfonates. These are of "low and moderate toxicity", declining rapidly in effect with distance from the point of discharge.

  • Group II, of "intermediate toxicity" but much smaller volume, comprises surfactants, lubricants, circulation additives, oil and oil products, solvents, emulsifiers, thinners and spotting fluids.

  • Group III includes highly toxic materials present in small quantities, such as heavy metals, scavenging agents, defoamers, descalers, corrosion inhibitors, bactericides and biocides.

Summarising various toxicological studies on the effects of the components of water-based drilling fluids, Patin supports the view that barite (barium sulphate) has "no observed effects" at concentrations of less than 2mg/l in standard chronic tests.

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"Muddied Waters":



List of Abbreviations

Summary of Conclusions

Drilling Waste Streams from Offshore Oil and Gas Installations

The Law on Offshore Wastes Discharges in Different Jurisdictions:

The OSPAR Convention

United Kingdom



United States

Inviting Regulation

Environmental Effects of Drilling Waste Discharges

The SBM Controversy

"Non-Water Quality Environmental Impacts"


Drill Cuttings

Produced Water

Minimising Waste Discharges and Their Effects

Reinjection Offshore

Cleaning Produced Waters

List of Main Sources

Selected References



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