Knowledge Centre
Chemical Discharges
Source of emissions
Drilling for hydrocarbons and their subsequent production would not be possible without the use of chemicals. Uses include:
- rig and turbine washes
- pipe dopes used to lubricate drill pipe joints
- hydraulic fluids used to control subsea valves
- biocides, corrosion inhibitors, demulsifiers
- water-based and organic phase drilling fluids
- cementing chemicals
- work-over chemicals
- stimulation chemicals
- completion chemicals
- water injection chemicals
- water and gas tracers
- jacking grease
During drilling the main source of chemicals reaching the marine environment is the discharge of drilling fluids. Drilling fluids are used to lubricate the drill bit and drilling assembly and to facilitate removal of rock fragments. Drilling fluids also provide pressure control in the well and to stabilise the formation. The largest quantities of chemicals discharged during drilling operations are water-based drilling fluid additives and weighting agents, much of which are chemically inert.
Specialist chemicals are used during the production of hydrocarbons to maintain process efficiency. Demulsifiers improve the separation of oil and water; corrosion inhibitors protect the plant; scale inhibitors slow down the build up of scale in pipework and valves; biocides reduce microbial growth. Depending on their properties these chemicals will partition between the oil and the water in the process. The reaction products and residual chemicals from those that partition to the water phase will be released to the marine environment with the produced water discharge.
Chemicals are also used to maintain pipelines and ensure pipeline integrity; including biocides and oxygen scavengers.
Accidental releases of chemicals can arise from a number of different sources, including equipment failure and human error.
Potential environmental impacts
Chemicals discharged into the marine environment have the potential for acute or long term effects on marine organisms. Whether these effects are realised depends on a number of factors such as the inherent toxicity of the material, the quantities discharged and resulting concentrations in the water column, the length of time biota are exposed to that concentration and the sensitivity of the organisms to the particular chemical.
Chemicals discharged from offshore operations are immediately diluted in the sea – the amount of dilution depends on the water depth and water currents but is at least 1000 times at a distance of 500metres from the discharge point. This dilution reduces the discharge to levels which are not acutely toxic to marine organisms.
Several extensive studies have been carried out to assess the environmental impact of chemical discharges from offshore operations, none of which have identified any impact.
Key control and mitigation measures
The use and discharge of chemicals in offshore operations is tightly controlled by the operators and by the regulators.
The regulatory control stems from a variety of OSPAR requirements, particularly Recommendation 2000/2 on a harmonised mandatory control system for the use and reduction of the discharge of offshore chemicals (HMCS) (as amended by OSPAR Decision 2005/1) which has the objective to protect the marine environment by identifying those chemicals used in offshore oil and gas operations with the potential for causing an adverse environmental impact and restricting their use and discharge to the sea. This involves the generation of an environmental data set (i.e. toxicity, persistence and bioaccumulation potential) and its evaluation using pre-screening criteria and a decision-support tool called CHARM (Chemical Hazard Assessment and Risk Management).
In the UK, the OSPAR requirements are implemented through the Offshore Chemical Regulations 2002 which require operators to obtain a permit prior to the use and discharge of any chemicals offshore. Only chemicals which have been registered with Cefas can be used. The operator must undertake a risk assessment for the use and discharge of each chemical in order to obtain the permit.
The effect of these regulatory controls has been to phase out the use of the most hazardous chemicals and to put in place a programme to replace those remaining chemicals which represent a lower but still undesirable hazrd.
The European Community Regulation on chemicals and their safe use (EC 1907/2006) are now in force. The Registration, Evaluation, Authorisation and restriction of Chemicals (REACH) regulations are intended to eliminate the differences in assessment between existing and new chemicals and cover the potential effects of exposure to chemicals on human health and the environment. Discussions are currently ongoing as to how the OSPAR HMCS and REACH requirements can be harmonized.
The cost of chemicals is also a mitigation measure – they are expensive and are used in controlled amounts to avoid wastage. In drilling operations significant quantities are recovered for reuse where technically possible.
Updated: November 2009
