Use of the ALARP Principle for Evaluating Environmental Risks and Impacts of Produced-Water Discharged to Sea

Abstract

Summary When produced water from offshore production is discharged to sea, itcontains some oil (aliphatic and aromatic components), production chemicals,and naturally occurring radioactive materials (NORM). These groups of materialsare traditionally treated in different ways in the regulations andstandards. Regulations of oil in produced water are mainly related to maximumconcentrations and the total discharge of the aliphatic (dispersed) fraction.Regulation of chemicals is based on the environmental risk profile of eachproduction chemical, although efforts are made toward regulations based on riskassessment of the discharge of the mixture of substances. For discharge of NORMdissolved in the produced water, no limit values are imposed. For NORM solids(scale, sludge, sand) from process equipment, discharge to sea is in generalnot allowed--it is reinjected or taken to a deposit onshore. Management of safety risks takes place on the basis of the principle thatrisks shall be reduced to a level as low as reasonably practicable (ALARP). Theconcept of environmental risk is not as unambiguously defined as safety risks.With respect to accidental environmental impacts, the parallel is relativelystraightforward, but with respect to planned environmental impacts (e.g.,emissions/discharges during operation), the parallel to the safety ALARP levelis not so clear; the consequence (the environmental impact) is not linked to acertain frequency (i.e., we cannot talk about risk as likelihood timesconsequence). Costs are normally defined as money, effort, and time. But what if the costof a reduced health, safety, and environmental (HSE) risk or impact is anincrease in another HSE risk or impact? Produced-water reinjection might causeincreased carbon dioxide (CO2) emissions. Handling solid NORM duringshipping to shore causes health risks to the people handling the NORM. Can thatrisk be justified on the basis of the possible reduction in environmentalimpact by not discharging the solid NORM to sea instead? This paper highlights the aforementioned issues and proposes a method called’integrated HSE ALARP assessment’ for supporting such analysis. Theenvironmental risks and impacts of discharge of oil, chemicals, and NORM,respectively, with produced water to sea are used to illustrate theseprinciples.