Environmental Impacts of the Oil and Gas Industries

the sensitivity of exploration activities including thedefinition of ‘no go’ times or conditions.

DrillingDuring drilling, a drilling mud is continuously circulatedbetween the well and the platform through a ‘riser pipe’.Mud is used to maintain well pressure and wall stability,to cool and lubricate the drill bit and to carry the rockchips (cuttings) generated during the drilling process awayfrom the cutting head to the platform. Here, the cuttingsare partially cleaned and the majority of drill mud re-used.Muds come in a variety of forms, dependent on their fluidbase. Amongst these are water based muds (WBM) andoil based muds (OBM). In the past, the bulk of cleanedOBM cuttings were discharged to the seabed along withtheir residual oily mud contamination. Extensivemonitoring studies showed that this caused changes tothe seabed via a combination of smothering, organicenrichment and toxicity effects. These were seen to bemost severe close to discharging platforms where the ‘pileproper’ formed, but they commonly extended up to adistance of 1 or 2 km. These discharges are no longerallowed.

ProductionDuring production, large amounts of produced water (PW)are recovered with the hydrocarbons. This is cleaned tovery stringent standards and some is re-injected tomaintain reservoir pressure. The bulk, however, hastraditionally been discharged to sea. As fields age and as

IntroductionFor generations the North Sea has been a valuable sourceof food exploited by the UK fishing industry. In the lastquarter of the 20th century it also became a vital energysource following the discovery of significant reserves ofoil and gas (O&G). In the 21st century, it may emerge asa source of renewable energy.

Both the fishing and O&G industries are important to theeconomy of Scotland and the UK generally, and mustcoexist in a marine environment that is sensitive toexploitation and contamination. Fisheries ResearchServices (FRS) has a significant role, providing advice onthe nature and extent of the impact of the O&G industriesto their regulator, the Department of Trade and Industry(DTI).

Environmental Effects of Oil and GasProductionExplorationOperators investigate the likelihood of hydrocarbons beingpresent under the seabed using high intensity sound(seismic surveys). Commercial fish species are sensitiveto sound and, at close range, larval fish might even bekilled by seismic sources. Seismic surveys might thereforedisturb spawning fish away from territory where they havechosen to aggregate for spawning purposes and thiscould, in extreme circumstances, be harmful to stockproductivity. Disturbing fish away from traditional areasmay also affect fishermen’s catches. FRS gives advice on

cuttings piles beneath them are not, they may spread, iffishing over them is allowed. All of these options, namelycomplete installation removal, cuttings piles recovery,and the wisdom of allowing fishing over piles if they areexposed, will be the subject of much discussion in theyears head. To aid these discussions, FRS has conductedstudies where sediment blocks containing fluorescentlabel were placed on the seabed prior to being fishedover (see below).

the amounts of oil remaining fall, the amounts of PWincrease. The turn of the millennium marked the time ofmaximum recovery of oil in the UK North Sea fields. Soalthough the levels of oil in produced water are very low,and despite improvements in technology which havetended to reduce them, the overall total amount of oildischarged with the water by UK industry will continue torise in the next few years; it will then tail off as the industrydeclines. Increased regulatory attention is therefore beingfocussed on the PW discharge, not least because inaddition to oil, it contains residues of naturally occurringheavy metals and radionuclides and oil field chemicals.FRS took part in a recent collaborative research study tolook at PW effects. Such studies will inform the continuingmonitoring needs and regulatory requirements.

A wide variety of chemicals is used to treat the oil, gasand water that is gathered from offshore reservoirs. Theseare regulated under a harmonised mandatory controlscheme (HMCS) negotiated under the auspices of theOslo and Paris Commission (OSPAR). As part of its advisoryservice to DTI, FRS assesses UK operators’ applicationsto use particular amounts of specified chemicals.

MonitoringIn the past, most O&G monitoring concentrated on thenear-field effects of cuttings piles discharges at the majordrill sites. Although monitoring of the impacts of pilesremains a focus of interest, attention is now being directedtowards detecting more subtle changes in contaminationpatterns in the further field. FRS has a resident group ofhydrocarbon analytical experts and is advising stratifiedrandom monitoring approaches to determine ifcontamination is decreasing with time (because OBMcuttings discharges have ceased), or increasing with timebecause other discharges still take place (see producedwater section above). Surveys of this type have beenconducted in recent years in the Fladen Ground and EastShetland Basin areas of the North Sea. These will hopefullyform a snapshot against which changes over time can beassessed.

DecommissioningAlthough the decommissioning phase of the North Seaindustry is now underway, the peak period ofdecommissioning of installations will likely be in theperiod 2010-2020. Some decommissioning operationshave the potential to impact both the environment andfishing activities. FRS is a key advisor on the implicationsof individual plans, and has two major areas of interestin the decommissioning context: cuttings piles; and on-surface large pipelines.

Fishing in the immediate vicinity of installations isprevented by exclusion zones. If installations arecompletely removed at decommissioning and the large

These showed that no significantly increasedenvironmental risk is likely to flow from the spread ofcontamination caused by fishing over piles. Any spreadover time is predicted to be very slow. The extent, if any,to which it occurs will be followed by individual fieldmonitoring studies and by the stratified random surveyapproach described above. The peak period of large trunkpipeline decommissioning may be some time after thatof installations, since key parts of the export system willneed to be retained to service the last producinginstallations. Fishermen have learnt to live with theselarge lines. Indeed, some choose to fish along them,alleging they act as aggregation devices for fish. FRS isconcerned about the eventual fate of these lines oncethey are no longer required and will seek to ensure thattheir potential to interfere with the environment and withfishing activities is minimised.

Accidental EventsFRS provides a 24-hour emergency response service aspart of the National Contingency Plan designed to copewith transport and offshore oil and gas pollution incidentsin UK waters. Significant accidental spills from offshoreinstallations or during refuelling and transport arethankfully very rare events. Were one to happen, advicewould be provided to the primary responders and to anyEnvironment Group established. In addition, FRS maintainsthe sole UK centre for the sensory analysis ofcontamination in fish and shellfish in order to advise thehuman health consequences of spillages of oil orchemicals at sea. (See leaflets ‘Ensuring the Quality ofFish and Shellfish’ and ‘Sensory Assessment of Fish andShellfish Quality’).

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