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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 (continued)

The Synthetic-based Drilling Muds (SBM) Controversy

Because of the widely recognised problems with OBMs, governments and environmentalists at first welcomed proposals to formulate alternative muds, based on emulsions and polymers of various kinds, that could do the essential heavy work of OBMs but not cause gross pollution of the environment. The thinking behind these synthetic-based drilling fluids, or SBMs, was summed up by the American oil company Unocal's promotional material on "Environmental Stewardship" in its Health, Environment and Safety Report for 1995:

In an effort to minimize drilling impacts on the environment, Unocal engineers have developed an innovative drilling fluid using synthetic-based fluids... Oil-based and synthetic-based fluids are preferred over water-based fluids in most applications for their ability to drill a gauge hole, thereby minimizing drilling problems.

In an effort to minimize impacts on the environment, Unocal's engineers are testing various fluid systems in their drilling operations. Unocal's drilling department in the Gulf of Thailand has successfully utilized an economical synthetic-based drilling fluid developed in-house by Unocal scientists. Plans are underway to apply the fluid in drilling all oil and gas wells in Thailand and Indonesia. This same drilling fluid meets current permit guidelines for discharge of drill cuttings in the Gulf of Mexico, and has been accepted by EPA and the Department of Interior's Minerals Management Service. The synthetic drilling fluid that Unocal is testing has several distinct environmental advantages over conventional diesel and mineral oil-based drilling fluids. Synthetic-based fluids are free of inherent contaminants, unlike conventional oil-based drilling fluids. As a result, they are more benign environmentally, as demonstrated by aquatic toxicity testing. A health-based risk assessment was recently performed to further confirm the reduced environmental impact of this innovative drilling fluid. (Unocal. 1996. Environmentally sensitive drilling fluids. 1995 Health, Environment and Safety Report. Website: El Segundo, CA)

The "inherent contaminants" referred to were the traces of radioactivity and toxic heavy metals in barite and other minerals, which can vary according to the mine producing the material and the extent of processing prior to packaging and sale.

Making no reference to current European thinking on synthetic-based fluids, the EPA recently summarised its own views on synthetic substitutes for OBMs (United States Environmental Protection Agency (EPA). 2000 (April) Notice of Data Availability; Effluent Limitations Guidelines for the Oil and Gas Extraction Point Source Category [draft public consultation document on proposed new rules governing offshore discharges of SBM/SBF]. CFR Part 435. Washington, D.C. See also: United States Department of the Interior (DOI), Minerals Management Service (MMS). 2000. Clean Water Act - Technological Advancements. Website: Washington D.C.):

Since about 1990, the oil and gas extraction industry developed SBFs with synthetic and non-synthetic oleaginous (oil-like) materials as the base fluid to provide the drilling performance characteristics of traditional oil-based fluids (OBFs) based on diesel and mineral oil, but with lower environmental impact and greater worker safety through lower toxicity, elimination of polynuclear aromatic hydrocarbons (PAHs), faster biodegradability, lower bioaccumulation potential, and, in some drilling situations, less drilling waste volume.

EPA's information to date, including limited seabed surveys in the Gulf of Mexico, indicate that the effect zone of the discharge of certain SBFs is within a few hundred meters of the discharge point. These surveys also indicate that the sea floor may significantly recover in one to two years. EPA believes that impacts are primarily due to smothering by the drill cuttings, changes in sediment grain size and composition (physical alteration of habitat), and anoxia (absence of oxygen) caused by the decomposition of the organic base fluid. The benthic smothering and changes in grain size and composition from the cuttings are effects that are also associated with the discharge of WBFs and associated cuttings. Based on the record to date, EPA finds that these impacts, which are believed to be of limited duration, are less harmful to the environment than the non-water quality environmental impacts associated with the zero discharge requirement applicable to OBFs. Moreover, EPA prefers SBFs over OBFs as there are operational accidents that lead to spills and loss of drilling fluid to the environment.
[emphasis added. JWGW]

The EPA SBF Proposal, published on February 3, 1999 (64 FR 5488), identified possible methods to control SBF discharges associated with cuttings (SBF-cuttings) in a way that reflects the appropriate level of technology. EPA proposed using stock limitations on the base fluids from which the drilling fluids are formulated. This would ensure that substitution of synthetic and other oleaginous base fluids for traditional mineral oil and diesel oil reflects the appropriate level of technology. In other words, EPA wants to ensure that only the SBFs formulated from the "best" base fluids are allowed for discharge. Parameters that distinguish the various base fluids are the polynuclear aromatic hydrocarbon (PAH) content, sediment toxicity, rate of biodegradation, and potential for bioaccumulation.

EPA also proposed that SBF-cuttings should be controlled with discharge limitations, such as a limitation on the toxicity of the SBF at the point of discharge, and a limitation on the mass (as volume) or concentration of SBFs discharged. The latter type of limitation would take advantage of the solids separation efficiencies achievable with SBFs, and consequently minimize the discharge of organic and toxic components. Additionally, EPA proposed that SBF discharges not associated with cuttings (e.g., incidental spills, accumulated solids, deck drainage) should meet zero discharge requirements, as this is the current industry practice due to the value of these drilling fluids.
[emphasis added. JWGW]

Research by Norwegian and British Government scientists and by the UK Offshore Operators' Association, UKOOA (which includes Exxon's UK subsidiary, Esso) suggests, however, that the early promise of most SBMs has not been fulfilled:

SBM tests in the UK suggested these fluids, with the possible exception of one, were no better than OBM and seabed studies confirmed this. UK industry voluntarily agreed a reduction strategy and phase out to allow time for infrastructure to be developed to dispose of the cuttings. This phase-out stops at the end of 2000, after which no SBM's will be discharged [in UKCS waters]. There is still some uncertainty over one of the SBMs (esters), which may biodegrade quite quickly, but it is looking as though the UK will phase it out also... The PARCOM sea based activities committee (SEBA) made a recommendation that is more relaxed than the UK position as it continues to allow discharge of SBMs in some circumstances. The technical aspects are very similar to OBM in terms of disposal options. (UKOOA spokesman, pers. comm..April 2000)

The view of the British Government's Centre for Environment, Fisheries & Aquaculture Science (CEFAS) is summarised in their latest (March 2000) guidelines (CEFAS. 2000a. Guidelines for the UK Revised Offshore Chemical Notification Scheme in Accordance with the OSPARCOM Harmonised Offshore Chemical Notification Format. London):

Since the biodegradation of most synthetic drilling fluids was found to be unacceptably low, the Department of Trade and Industry, in conjunction with other Government departments, acted with operators to reduce discharges of these fluids to zero by 31 December 2000. In order to achieve this, all operators were asked to draw up a company specific phase-out strategy demonstrating how each company intended to reduce its SM discharges by approximately 20% each year, using a 1996 baseline. Companies are making greater reductions than targeted and the objective of zero discharge by end 2000 should be achieved.

The same point was made by OSPAR's Working Group on Sea-Based Activities (SEBA), meeting in Amsterdam on 14 - 18 February 2000 (OSPAR. 2000. Draft Measures Proposed by the OSPAR Working Group on Sea-based Activities (SEBA), February 2000. Amsterdam.), which noted "the report (SEBA 96/5/1) that recently developed synthetic drilling fluids are likely to persist when discharged into the marine environment at high concentration on drill cuttings where anaerobic conditions develop."

This highlights a major difference of opinion between Europe and the US, where the Environmental Protection Agency is currently proposing to allow limited discharges of treated SBM, on the grounds that, overall, this will cause less pollution than re-injection or shipping ashore for treatment, partial reclamation and landfill disposal - all of which involve high energy demands for transport and processing. (United States Environmental Protection Agency (EPA). 2000 (April) Notice of Data Availability; Effluent Limitations Guidelines for the Oil and Gas Extraction Point Source Category [draft public consultation document on proposed new rules governing offshore discharges of SBM/SBF]. CFR Part 435. Washington, D.C.)

Like UNOCAL, the US Department of Energy (DOE) is still extremely positive about the supposed environmental benefits of Synthetic-based muds. In a DOE-funded paper (Veil, J.A., Daly, J.M., Johnson, N. 1999. EPA Speeds Regs for Offshore Synthetic-based Mud. Oil and Gas Journal, 97(37):78-85) for the Society of Petroleum Engineers/EPA Exploration and Production Environmental Conference in Austin, Texas, as recently as March 1999, John Veil of the Argonne National Laboratory and his co-authors from the EPA and DOE said: "SBMs contain no polynuclear aromatic hydrocarbons, exhibit lower toxicity and bio-accumulation potential, and biodegrade faster than OBMs". They also believed SBM cuttings were "less likely that OBM cuttings to cause adverse sea-floor impact".

The language used in the paper suggests that Veil and his colleagues were asked to consider economic as well as environmental factors. For example: "...although SBMs cost more than OBMs, the nature of SBM-based drilling fluids may permit associated cuttings to be discharged onsite". They also reported: "The industry has been eager to use SBMs, particularly in the Gulf of Mexico, where drilling has moved into deep water. Current federal regulatory requirements, however, do not adequately address the discharge issue of SBM-based cuttings, and some SBMs continue to be hauled onshore for processing and reuse after the well is drilled." (The unstated implication is that this is expensive and thus a problem. It is, but is it an environmental science problem?)

The EPA's main concern appears to be not that SBM/SBF is undesirable, as European research concluded several years ago, but that the American methods used to measure and detect its toxicity, bio-degradability and bio-accumulation potential are not sufficiently refined. The problem identified here is that the toxicity tests currently prescribed by the US Government for testing WBMs do not give accurate results for SBMs: because oil can dissolve in SBM, the "sheen test" used to determine whether a discharge is or is not causing a slick, may be ineffective; when WBM bio-assay tests are used, "most SBMs demonstrate very low toxicity, due to the inability of SBM to disperse in water"; and, because SBMs tend to concentrate in seabed sediments rather than remaining suspended in the water, standard tests on particles suspended in the water column do not show up the contaminants in SBM.

The authors concluded that if independent research were available on the toxicity of the components in SBMs, "it may be unnecessary to perform sediment toxicity tests at the point of discharge, and toxicity levels may be controlled through the base fluid and controls on crude oil contamination".

Whether the EPA will come to similar conclusions as the UK and Norway, once it has developed new monitoring techniques, remains to be seen. But it is noteworthy that the same corporations currently discharging synthetics offshore US are simultaneously moving very rapidly to meet the phase-out deadline for SBM offshore UK.

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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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