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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 (continued)

The Effects of Discharges of Produced Water

Almost all offshore oilfields produce large quantities of contaminated water that can have significant environmental effects if not handled properly. The UK Offshore Operators' Association explains the phenomenon as follows:

Oil and gas reservoirs have a natural water layer (called formation water) that, being denser, lies under the hydrocarbons. Oil reservoirs frequently contain large volumes of water, while gas reservoirs tend to produce only small quantities. To achieve maximum oil recovery, additional water is usually injected into the reservoirs to help force the oil to the surface. Both formation and injected water are eventually produced along with the hydrocarbons and, as an oil field becomes depleted, the amount of produced water increases as the reservoir fills with injected seawater.

At the surface, produced water is separated from the hydrocarbons, treated to remove as much oil as possible, and then either discharged into the sea or injected back into the wells. In addition, some installations are able to inject produced water into other suitable geological formations.

After treatment, produced water still contains traces of oil and, because of this, discharge into the sea is strictly controlled by legislation. Under the terms of an international convention ( At its first meeting (The Hague, 1978), the Paris Commission (later the Oslo-Paris or OSPAR Commission) confirmed its acceptance of the provisional target standard for discharges from offshore oil installations of 40 ppm (PARCOM 1/17/1, 101). The Commission recalled that in interpreting this standard, it was important that all new platforms be equipped with the best practicable means for separating oil from discharged water and reducing the average oil content of a discharge to within the range of 30 to 50 ppm. The 40 ppm was therefore a mean to be aimed at - not a maximum to be complied with. The Commission adopted (PARCOM 1/17/1, 104) the following recommendation from the Oil Working Group to supplement the provisional target standard: "Each national authority should set limits on the total amount of waste water permitted to be discharged from each platform. This limit should be fixed for each platform individually, taking into account its known treatment capacity." [emphasis added].) which takes into account the need to safeguard the marine environment, the permitted level of oil in produced water that can be discharged from an installation is 40 ppm, averaged over a month. Operators must analyse the oil-in-water level twice each day and report the results to the regulatory authorities. (United Kingdom Offshore Operators' Association. 1999b. 1999 Environmental Report. Website: London)

Anything above 100ppm must be reported as an oil spill. Interviewed for this study, a UKOOA spokesman said: "Regular scientific reviews have concluded environmental impacts are insignificant from discharges at these concentrations."

The UK Department of Trade and Industry explains the legal mechanism: "In the UK we regulate oil discharges through the Prevention of Oil Pollution Act, 1971, which requires operators of offshore installations to apply for an exemption to allow the discharge of produced water. Any exemption granted stipulates that overboard discharge must not exceed 40 parts per million. Additionally, the UK offshore industry has voluntarily accepted a target of 30 parts per million on a company annual average basis from January 1999." (DTI spokesman, Aberdeen, 2 May 2000, pers. comm.)

It is clear that the figure of 40ppm was what was technically feasible when the limit was agreed, as distinct from what may be environmentally desirable. At onshore installations, such as the Sullom Voe oil and gas terminal in Shetland, the oil companies have more space for large, heavy equipment, sand filters, settlement ponds and long process times to reduce the oil in water concentration of dirty ballast and other effluents to as low as 4ppm. At Sullom Voe, however, the receiving water is a tidal sound with strong currents, making mixing and dispersion much more rapid than, for example, the Sakhalin Shelf, where currents are slower, as they are in most seabed areas around the world.

UKOOA says performance has improved over the years:

Currently UKOOA has a 30ppm company annual average commitment (This came into effect in January 1999 as a voluntary target agreed with between the oil companies and the UK Department of Trade and Industry. JWGW. ) that is being achieved. Whilst industry was able to achieve an average for 1998 of 22ppm (and 1999 provisional figures are slightly lower) the problems experienced by some installations suggests technology has not advanced significantly since the OSPAR decision was taken. Also, one of the methods of achieving the reduction has been to increase the use of chemicals which also brings its own environmental issues, in both the creation and disposal of the material. Some facilities are re-injecting produced water but care needs to be taken to ensure the environmental balance is correct as this increases the energy consumed and results in increased atmospheric emissions. UK requires two measurements (using a prescribed test method) each day and up to 3% of the measurements can be above the 40ppm but must be below 100ppm. Anything above 100ppm must be reported as an oil spill. Regular scientific reviews have concluded environmental impacts are insignificant from discharges at these concentrations. (UKOOA spokesman. April 2000. pers. comm.)

It should be noted that although the UK Government specifies the test methods and makes periodic checks on calibration of equipment and the qualifications of inspection contractors and their personnel, there is no regular system of random, unannounced visits by Government inspectors to offshore installations in the UK sector and therefore no truly independent verification of these measurements. As is the norm in other relationships between the petroleum industry and the UK Government, a great deal is taken on trust. It is impossible for the lay person to determine whether or not that trust is justified.

A similar industry/government relationship exists in US coastal waters, where the EPA set toxicity limits in 1993 that prescribed a 29ppm monthly average "oil and grease" content for produced water, with a daily maximum of 42ppm (For discussion of this, see: American Petroleum Institute. 1995. Proceedings: Workshop to Identify Promising Technologies for the Treatment of Produced Water Toxicity. Health and Environmental Sciences Departmental Report No. DR351. Parsons Engineering Science, Fairfax, Virginia).

UKOOA's view is: "Discharges of oil in produced water cannot be compared with large oil spills because the small amounts of oil are dispersed within the sea and do not form a surface slick" (Ibid) but it is a commonplace observation among people who have flown regularly over the North Sea that nearly all installations usually have faint but visible streaks of sheen extending for hundreds of meters downwind of them, even when their water treatment plants are the best available. On calm water a visible sheen can form at 25ppm. Offshore, the flow of produced water must be almost continuous, whereas at an onshore tanker terminal it can be intermittent, allowing batch treatment and recirculation. As a result, offshore water treatment must rely on equipment such as electrostatic precipitators, plate separators, gas flotation units, centrifuges, hydrocyclones, filter membranes and skim piles to get as much oil as possible out of the water. Gravity treatment is still the main part of the process (American Petroleum Institute. 1995. op. cit.) but there is neither space (For example, see ibid.: "a footprint of 3 feet by 3 feet was suggested as a site that would not require major structural changes to existing facilities [in the Gulf of Mexico]. Offshore platforms are also limited to a maximum weight capacity of approximately 250 lbs per square foot." North Sea platforms are generally larger and have more space but the restrictions are still real. JWGW) nor time to allow treated water to lie for days in settlement ponds where oil can be skimmed off and biological agents can help to purify it. Produced water discharged offshore may therefore be up to 10 times oilier than the discharges from Sullom Voe or the Valdez Marine Terminal in Alaska.

On Floating Production, Storage and Offloading vessels (FSOs or FPSOs) the movement of the anchored ship in the swell can upset water treatment processes and lead to discharges considerably above the average levels. This problem is particularly acute when storms generate very large waves, which happens on average for at least 60 days a year in the northern North Sea.

There is more in produced water than water and oil. In 1987, Neff (Neff, 1987, op. cit.) described produced water for ocean discharge as containing up to 48 parts per million (ppm) of petroleum, because it had usually been in contact with crude oil in the reservoir rocks. There were also elevated concentrations of barium, beryllium, cadmium, chromium, copper, iron, lead, nickel, silver and zinc, and "small amounts of the natural radionucleides, radium226 and radium228 ("very little" of which became attached to nearby sediments) and "up to several hundred ppm of non-volatile dissolved organic material of unknown composition". Produced water was "diluted very rapidly", with higher salinity or concentrations of hydrocarbons or metals, or decreases in dissolved oxygen, usually not seen more than 100-200m from the point of discharge.

Neff was unequivocal about the risks, or lack of them: "Because of rapid mixing with seawater, most physical/chemical features of produced water (low dissolved oxygen and pH, elevated salinity and metals) do not pose a hazard to water column biota." He added, however, "in shallow, turbid waters, elevated concentrations of hydrocarbons may be detected in surficial sediments up to about 1,000m from the discharge"; that the aromatic hydrocarbons and metals in produced water were toxic; and that "the toxicity of the soluble organic fraction of produced water is not known".

He continued: "More than 88% of the 54 bioassays performed to date... gave results indicating that the produced water was practically non-toxic. The most toxic produced water samples had been treated with biocides." Neff noted that, although there were "practically no laboratory studies on Sublethal or chronic effects of produced water in marine organisms", eight experimental field studies around development and production platforms had demonstrated accumulation of petroleum hydrocarbons bottom sediments and "severely depressed" benthic fauna within 150-200m of the platforms. The cause was oil in produced water.

Throughout the 1990s evidence accumulated that produced water might be less benign than it appeared. For example, a 1992 conference on produced water showed clear effects on sea urchins (Krause, P. R., Osenberg, C. W. and Schmitt, R. J. 1992. Effects of Produced Water on Early Life Stages of a Sea Urchin: Stage-Specific Responses and Delayed Expression. . In Ray, J. P. and Engelhardt, F. R. (eds.) 1992. Produced Water - Technological/ Environmental Issues and Solutions. Plenum Press. New York) and abalone (Raimondi, P. T. and Schmidtt, R. J. 1992. Effects of Produced Water on Settlement of Larvae: Field Tests Using Red Abalone. In Ray, J. P. and Engelhardt, F. R. (eds.) 1992. Produced Water - Technological/ Environmental Issues and Solutions. Plenum Press. New York) and in the same year a Dutch study raised concerns about produced water effects in the shallow waters of the Netherlands coastal shelf (Slager, L. K. et al. 1992. Environmental Aspects of Produced Water Discharges from Oil and Gas Production on the Dutch Continental Shelf. Part III. Environmental Effects. Free University of Amsterdam. ISBN 90-5192-021-0).

In 1994 the London-based Oil Industry International Exploration & Production Forum (E&P Forum) published a detailed report, North Sea Produced Water: Fate and Effects in the Marine Environment. The European Environment Sub-committee responsible for the report included two representatives of Exxon and one each from Amerada Hess, Amoco, BP, Chevron, Conoco, Elf and Texaco. They calculated that the average oil content of produced water discharged in 1991 from all North Sea production platforms was 34mg/l, less than the Paris Commission (PARCOM) target monthly average of 40mg/l. In that year the total discharge volume was 160 million cubic metres, 95% of it from oil installations and 5% from gas. These discharges were estimated to contain about 52,600 tonnes of organic compounds and about 1,000 tonnes of heavy metals.

The E&P Forum figure for 1988's dispersed oil in produced water was "approximately 4,100 tonnes" compared with an estimated total of 136,000 tonnes of oil discharged into the North Sea from all sources. The study gave no 1991 figure for the total of dispersed oil in produced water but at the stated 34mg/l it would be about 5,440 tonnes. In 1994 produced water volumes were "expected to increase steadily and then level out in 1998 to about 340 million cubic metres per year". In the past, some authors have questioned the accuracy of the total oil-in-water figures provided by the industry and the UK Government (e.g. Vik, E. A., Berg, J.D., Bakke, S. & Lundh, T., 1991. Review of Offshore Chemical Selection, Use and Operating Procedure to Minimise Environmental Impact. Water Science and Technology 24 (10) 135-142. and Reddy et al. 1995. op. cit. ) but, if we extrapolate these E&P Forum figures and assume that the industry managed to keep average oil content down to 34mg/l or less, this means that the total quantity of oil discharged with North Sea produced water could have increased to about 11,560 tonnes by 1998, a 182% increase in 10 years. However, produced water volumes tend to increase dramatically as older oilfields (like those in the northern North Sea) pass their peak production, so the actual total was considerably lower. As UKOOA puts it, (United Kingdom Offshore Operators' Association. 1999b. 1999 Environmental Report. Website: London) "the gradual decrease in the concentration of oil in water arises mainly from improvements in the technology used for separating small quantities of oil from water".

Greenpeace authors would dispute this and have quoted a figure of 45%, in some Norwegian waters, for the proportion of oil in the sea that comes from offshore installations. They contend that, because produced water volumes increase as oilfields age, the total amount of oil discharged with it will also increase. (Reddy, S., et al. 1995. op. cit.)

Despite this, the most recent UKOOA summary says: "In 1998, the industry total average oil in produced water was 22ppm, reflecting a trend of improvement since 1992." UKOOA has also published the following table for the UK sector of the North Sea:

Table 10: Produced Water Discharges, North Sea

(See also Appendix 8, which includes displacement water)

Year Number of installations Water quantity (millions of tonnes) Oil levels (ppm) Oil quantity (tonnes)
1996 59 210 27 5,706
1997 64 234 25 5,764
1998 67 253 22 5,690

It is important to note that the reporting and monitoring system for discharges of produced water (and, indeed, all other offshore discharges) is based almost entirely on self-reporting, at least in the UK sector of the North Sea. Unannounced visits by government inspectors to platforms are almost unheard of and, because helicopter access to the installations is controlled by the oil industry, almost impossible to arrange. Some inspectors may be stationed on individual platforms for periods of time, but permanent on-site inspection does not happen. The monitoring and reporting of discharges therefore fails the most elementary test of scientific impartiality and independence. This is not intended as a criticism of the oil industry; it is simply to state the facts. All data collected under such circumstances must of necessity be regarded as unverifiable, to say the least. This central problem has not been addressed by OSPAR, nor indeed by the British Government, whose Department of Trade and Industry is responsible for regulating the oil industry, and also for commercial promotion of the industry and its suppliers. Not surprisingly, there are extremely close contacts between oil company staff and civil servants. These relationships, it is assumed, stop well short of corruption but it is noticeable that there is a "revolving door syndrome" in the UK offshore industry, whereby national and local government officials formerly responsible for regulating and promoting the oil industry leave the public service and appear shortly afterwards as highly-paid employees of the oil industry and its trade associations (The author has personal knowledge of several such "reincarnations" over the past 28 years and can supply names in confidence).

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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

Everyday News
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Impact of Offshore Oil&Gas Industry


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