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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

Drilling Waste Streams from Offshore Oil and Gas Installations

Drilling Fluids - What They Are and What They Do

We all depend to a surprising extent on drilling fluids, despite most of the world's population knowing almost nothing about them. Without drilling muds and their additives, corporations could not drill for oil and gas and we would have hardly any of the fuels and lubricants considered essential for modern industrial civilisation.

Drilling fluids, including the various mixtures known as drilling muds, do the following essential jobs in oil and gas wells:

  • Lubricate the drill bit, bearings, mud pump and drill pipe, particularly as it wears against the sides of the well when drilling deviated wells around corners;

  • Provide hydraulic pressure to the motor which drives the drill bit at the bottom of the hole;

  • Clean and cool the drill bit as it cuts into the rock;

  • Lift rock cuttings to the surface and allow cuttings to drop out in the mud pit or shakers to prevent them recirculating;

  • Regulate the chemical and physical characteristics of the mixture arriving back at the drilling rig;

  • Carry cement and other materials to where they are needed in the well;

  • Provide information to the drillers about what is happening downhole - by monitoring the behaviour, flow-rate, pressure and composition of the drilling fluid;

  • Maintain well pressure and lubricate the borehole wall to control cave-ins and wash-outs;

  • Prevent well blow-outs - by including very heavy minerals such as barites to counteract the pressure in the hole.

Drilling muds are made of bentonite and other clays, and/or polymers, mixed with water to the desired viscosity. Muds transport the other components in drilling fluids down the drill pipe and bring cuttings back up the well. By far the largest ingredient of drilling fluids, by weight, is barite (BaSO4), a very heavy mineral of density 4.3 to 4.6. It is also used as an inert filler in some foods and is more familiar in its medical use as the "barium meal" taken before X-raying the intestines.

Over the years individual drilling companies, and their expert drillers have devised proprietary and secret formulations to deal with specific types of drilling job. These mud "recipes" are based on long experience, arcane knowledge and special skills. One of the problems in studying the effects of drilling waste discharges is that the drilling fluids are made from a range of over 1,000 ingredients - many of them known, confusingly, by different trade-names, generic descriptions, chemical formulae and regional or industry slang words.

A Shell Oil Company engineer in the US, James P. Ray (Ray, J. P. 1989. Offshore Drilling Waste Issues. In Engelhardt, F. R. et al. (eds). 1989. Drilling Wastes. pp. 849-860. Elsevier Science Publishers Ltd, Barking, England), has written that, back in 1975, "Most people had little idea of the composition of additives. It was even hard for a mud engineer from one company to really know what another company was calling the same product."

The Public Domain Problem

In addition to the difficulties of identifying and accurately characterising drilling fluid components, and the infinite variety of mixtures used in different situations, many of the recipes are kept secret by particular companies or individuals. It is usually impossible for a member of the public, such as a journalist or a researcher, to obtain from drilling contractors or oil companies a completely accurate description of the constituents of any given drilling fluid (Reddy, S., Santillo, D. and Johnston, P. 1995. Amendments to the London Convention: Discharges from the Offshore Industry - The Environmental Effects of Oil and Gas Exploration and Production. Greenpeace International, London). Even the encyclopaedic list of drilling chemicals published periodically by the US magazine World Oil does not give exact chemical descriptions for all the hundreds of trade-named products listed in its tables (World Oil. 2000. Fluids Tables. Gulf Publishing Company. Houston, Texas. Website:;=4&TECHLINK;=105). Government agencies in the UK and the US are only able to find out exactly what is in drilling fluids if they keep the information secret from the public in whose name they act as guardians of the environment - and sometimes even from the end users of the products.

The Offshore Chemical Notification Scheme (OCNS), currently operating in the UK under the OSPAR (The Oslo-Paris Convention for the Protection of the Marine Environment of the North-East Atlantic - originally the Oslo and Paris Conventions) agreements (see detailed discussion below), imposes the confidentiality rule. This is an extract from the latest "Frequently Asked Questions" section of the OCNS website, designed for the use of offshore operators filling in Harmonised Offshore Chemical Notification Format (HOCNF) paperwork (CEFAS. 2000. Guidelines for the UK Revised Offshore Chemical Notification Scheme in Accordance with the OSPARCOM Harmonised Offshore Chemical Notification Format. London) :

I wish to notify a product but the manufacturer will not give me confidential formulation details, what can I do?

This common problem is easily solved by asking the manufacturer to provide the confidential details directly to CEFAS [the UK Government's Centre for Environment, Fisheries & Aquaculture Science] referencing your submission. The third party has our assurance that the data will be treated as 'Commercial in Confidence' and will not be released to any other party, or used for any other purpose, without their specific written permission.

This categorical assurance of secrecy is elaborated in the Guidelines issued by CEFAS, the laboratory authorized by the UK Government's to administer OCNS under OSPAR rules:

Any details entered onto the HOCNF will be held in COMMERCIAL CONFIDENCE, by named individuals only, in the relevant Government departments. They will not be released under any circumstances to any third party without written permission of the supplier (Ibid. p.18).
[The capital letters are the UK Government's, not the author's]

The most recent List of Notified Chemicals from CEFAS names but does not accurately identify some 2,014 products sold to offshore drillers (CEFAS, 2000b. UK Offshore Chemical Notification Scheme - List of Notified Chemicals. London). Most of these are additives and nearly all are simply given as trade names. As many of them are simply different names for the same substances, the actual number of chemicals and compounds in use offshore UK is probably about 1,000. The point is that no-one outside the UK Department of Trade and Industry knows for sure. Government ministers themselves may not know.

In response to questions about the lack of accurate, public domain, identification data for offshore chemicals, an industry expert who spoke on condition of anonymity recently gave the author this explanation:

In very simple terms the situation is as follows. A manufacturer comes up with a new product, which for example will improve certain drilling procedures. He gets into contact with offshore operators (i.e. those companies which actually run the drilling rigs) and explains to them the advantages of his new product. If they are interested, they will ask the national authorities of Contracting Parties whether they can use (and, if necessary, discharge) this new product. In order to permit the use of this new product, the national authorities need certain information as stipulated in the HOCNF [Harmonised Offshore Chemical Notification Format]. You will note that some of the information required in the HOCNF has to come from the manufacturer (in particular as regards the composition of the new product), whereas some other information comes from the operator (in particular as regards the use of the new product).

The manufacturer will never show the detailed composition to the operator, because most operators have their own chemical laboratories and it would be easy (and much cheaper) for them to synthesise the product on their own, thus cutting out the manufacturer. This also explains the problem of the synonyms. If the detailed composition, names and synonyms of all offshore chemicals would be freely available, operators would obviously choose the one which is the cheapest. Not knowing what is "behind" a certain trade name prevents them from doing so. To a certain extent you can compare this with the situation in the pharmaceutical industry. Also there you have a multitude of drugs which vary considerably in price, although they basically contain the same active ingredients.

From the above you can see that the whole system is a triangle between manufacturer, operator and national authority. OSPAR legislation is basically a circle around these three key players, setting the framework of international legislation to ensure that the decisions to be taken by the national authorities are harmonised. This means that if the UK authorities decide to permit the use of an offshore chemical with certain restrictions, the same restrictions should be imposed by the Norwegian authorities, if a Norwegian operator wants to use the product.

To ensure this harmonised approach, national authorities exchange information informally and during so-called 'HOCNF contact point meetings'. Because confidential information is exchanged during these meetings, the OSPAR Secretariat is not present, but the system nevertheless seems to work satisfactorily. In this context, your understanding that "no-one but the manufacturers and a few UK government officials is allowed to know exactly what is in all the materials" is not totally correct. In theory, this mechanism to exchange HOCNF-related information should ensure that most national authorities know about the relevant data.

The fact remains, however, that the information is not in the public domain and therefore not capable of independent verification by scientific peer review. The reasons for this are clearly neither technical nor environmental but commercial. It would be interesting to know how many other industries are favoured by governments with such confidential indulgence.

Terminology and the Obfuscating Euphemism

So - we are not allowed to know what, exactly, is in the waste dumped over the side of thousands of drilling rigs, production platforms and drillships. The terminology used to describe the main classes of drilling fluids can also be confusing because it has changed over the years, to keep up with changes in mud technology. These are the terms used by the Oslo-Paris Commission (OSPAR) and the UK Department of Trade and Industry, as of March 2000:

a. Water-based muds or fluids (WBM);
b. Organic-phase drilling fluids (OPF), which is the newly-coined collective term (and euphemism) for:
i. Oil-based muds (OBM), including Low-toxicity Oil-based Muds (LTOM) and
ii. Synthetic-based drilling fluid/mud (SBF or SBM) - formerly known as Pseudo Oil-based Mud (POBM) and also including Emulsion-based Mud.

As discussed below in more detail, the term WBM conceals the fact that the water base may contain hydrocarbons in concentrations of parts-per-thousand (Reddy, S., et al. 1995. op. cit.), some from additives and some from crude petroleum with which the mud has been in contact down the hole (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.)

Whatever the base fluid used, nearly all muds contain at least some of the additives in the List of Notified Chemicals and the Fluids Tables mentioned above. These materials come back up the well to the drilling floor (The deck of the drilling rig or platforms where the drilling turntable and drilling crews are located) in a slurry with drill cuttings (rock fragments), crude oil, gas, natural gas liquids, produced water, traces of heavy metals, biocides, surfactants and other, mostly organic, substances. The mixtures entering and leaving a well can be so complicated that the OCNS has a special reporting category called UCMs: "unresolvable complex mixtures" (CEFAS. 2000a. op. cit. p.20). In the early years of offshore drilling, all this material was dumped into the sea.

Pollution problems caused by oil and other contaminants in waste drilling fluids were recognised over 40 years ago in the Gulf of Mexico and, since the development of the North Sea oil and gas fields in the 1970s, have become a major political issue in Western Europe.

Oil-based muds were developed for situations where WBMs could not provide enough lubrication or other desired characteristics. Usually, this would be when a job required directional, or deviated, drilling. In this precision drilling technique, now so essential to the industry, the drill bit can be "steered" downhole so that the well deviates from the vertical by a known and controlled angle. When wells are drilled many thousands of feet below the seabed, the drill bit can end up cutting horizontally through the strata, making accessible isolated pockets of oil and gas that were previously not economic to extract. Such deviated drilling has revolutionised the economics of offshore oil and gas drilling and has become standard procedure on such fields as the Atlantic Margin, off the west coast of Shetland, where many small, discrete reservoirs can now be penetrated with a single well. Although the radii of such curved wells are very large, deviated drilling still requires drilling mud with higher lubrication qualities than the ordinary, water-based mud traditionally used for spudding in and drilling vertical wells - particularly when cutting through layers of very hard rock or when drilling smaller radius holes a long way down. Until the mid-1980s, OBM was routinely used for this kind of difficult drilling.

The realisation that relatively large areas of seabed around hundreds of offshore installations had been smothered, sterilised and/or poisoned, by OBM-contaminated drill cuttings and the crude oil sticking to them, led to a number of international agreements which, by 1996, had outlawed the discharge of oil-based drilling muds containing diesel or mineral oils (OSPAR. 1992a. PARCOM Decision 92/2 on the Use of Oil-based Muds. See also: OSPAR. 1996. PARCOM Decision 96/3 on a Harmonized Mandatory Control System for the Use and Reduction of the Discharge of Offshore Chemicals; OSPAR. 1997. PARCOM Decision 97/1 on Substances/Preparations Used and Discharged Offshore; OSPAR. 1999a. List of Substances / Preparations Used and Discharged Offshore Which Are Considered to Pose Little or No Risk to the Environment (PLONOR)). How far this has been put into effect is the subject of some debate.

Low-toxicity OBMs can be and still are used (See the list of "Z-muds" on the CEFAS website: Group Z Base Fluids), but only in formulations designed for zero-discharge, where all the used mud is either recycled (usually onshore) or re-injected with cuttings into the rocks below the seabed.

Changing the terminology is a technique sometimes used by industries seeking to delay or weaken regulation. Giving something a new, neutral-sounding name can confuse and soothe lawmakers, government officials and the general public. A classic example of the obfuscating euphemism, originating in the US, is the recent re-naming of drilling muds.

The phrase "oil-based mud" was an accurate description of drilling mud containing diesel oil, commonly used 10 years ago, but had obvious negative connotations and was, indeed, a serious source of pollution, as the North Sea drill cuttings piles testify. At first, the term "synthetic-based mud" or "emulsion-based mud" sounded neutral, or even positive, in relation to OBM, but when it proved (at least in Europe) to be no better than OBM then a new wording was required. Therefore, we are now asked to call both OBMs and SBMs "organic-phase drilling fluids", on the grounds that the oils formerly used in OBMs and the esters and vegetable oils used in SBMs all have "organic" origins - in that diesel oil and "mineral oils" are refined from crude oil which, millions of years ago, derived from microscopic sea creatures.

"Organic" conjures up entirely different images to "oil-based" and is therefore preferred by industry apologists. The euphemism sounds scientific but conceals from the ignorant the fact that nothing has changed. Likewise, the industry and its friends in government feel no need to change the name of "water-based muds" because "water-based" implies purity - even though WBMs may contain many "organic" substances and also some pollutants derived from crude oil. This kind of semantic engineering is highly advanced (and highly paid) in the global oil and gas industry. In countries where English is not the first language, the necessity for technical translation (into Russian, for example) introduces further opportunities for subtle linguistic obfuscation.

Table 1: Total number of installations in the OSPAR Convention's maritime area, 1984-1998 (Source: OSPAR, London. May 2000)

Country 1984 1986 1990 1991 1992 1993 1994 1995 1996 1997 1998
Germany 1 1 3 3 4 3 2 2 2 2 2
Spain 1 1 1 1 1 1 1.5 9 9 6 5
Ireland 1 1 2 2 2 2 0 0 4 6 3.2
Denmark 7 11 20 20 20 26 37 39 43 46 47
Nethelands 30 45 63 60 88 97 120 118 116 125 125
Norway 13 18 24 25 34 109 90 83 103 83 85
United Kingdom 90 90 79 79 79 81 187 207 275 252 293
TOTAL 143 167 192 190 228 320 438 459 554 520 560

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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



Articles on Offshore
Oil&Gas; and Environment

Impact of Offshore Oil&Gas; Industry


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