Source of emissions
The extraction, stabilisation and export of hydrocarbons involve several processes that give rise to atmospheric emissions. These include combustion to provide electrical power and to drive compressors and pumps; flaring of excess gas for safety and during well testing; venting during tank loading and incidental releases from fire fighting and refrigeration plant.
Combustion and flaring result in emissions of carbon dioxide (CO2), carbon monoxide (CO), methane (CH4) and oxides of nitrogen (NOx) and sulphur (SOx). Small amounts of nitrous oxide (N2O) are also released. Venting releases Volatile Organic Compounds (VOCs) and methane, whilst firefighting and refrigeration releases Halon and chlorofluorocarbons (CFCs).
Potential environmental impacts
Atmospheric emissions from offshore operations are implicated in several potential impacts:
- Anthropogenic global warming - which is attributable to greenhouse gas emissions notably CO2 and CH4
- Stratospheric ozone depletion – caused by halon and CFCs which are known collectively as Ozone Depleting Substances (ODS)
- Ground level ozone formation – caused by reactions between VOCs and NOx
- Acidification – caused by emissions of acid gases such as NOx and SOx
Emissions from combustion and flaring are most significant because of their global impact. Although ODS have the potential for global impact they are used in relatively small amounts offshore. The potential for ozone formation and acidification is minimised by the geographic location of most offshore installations.
Key control and mitigation measures
Atmospheric emissions offshore are tightly controlled by international, European and national regulations.
The International Maritime Organisation regulates emissions of ODS, NOx, SOx and VOCS from ships through MARPOL 73/78 Annexe VI. MARPOL defines offshore installations and drilling rigs as ships and the Merchant Shipping (Prevention of Air Pollution from Ships) Regulations 2008 implement the requirements in the UK.
The European Union Greenhouse Gas Emission Trading Scheme, Directive 2003/87/EC (EU ETS) is implemented in the UK by The Greenhouse Gas Emissions Trading Scheme 2005 (the 2005 Regulations) as amended which apply the scheme to offshore installations having combustion facilities with a combined rated thermal input of above 20 MW (th).
EC Directive 96/61 on Integrated Pollution Prevention and Control which is implemented in the UK through the Offshore Combustion Installations (Prevention and Control of Pollution) Regulations 2001 (amended in 2007). No offshore combustion installation can be operated except in accordance with a permit issued under the PPC Regulations.
EU Regulation EC 1005/2009 on Ozone Depleting Substances will be implemented by the Environmental Protection (Controls on Ozone Depleting Substances) Regulations 2010.
Gas venting and flaring are both subject to consent under the Petroleum Act 1998 which has the objective to conserve gas, a finite energy resource, by avoiding unnecessary wastage during the production of hydrocarbons. Consent to Vent is required under the Energy Act 1976. Consents to vent includes venting of gases from onboard crude oil storage tanks e.g. for FPSOs during crude oil filling operations.
EEMS, the upstream oil and gas industry environmental database, provides the vehicle for offshore oil and gas industry emissions to be incorporated into annual UK inventories of atmospheric emissions that are required under a number of international conventions and EU instruments. In addition to atmospheric reporting through EEMS there are other statutory reporting requirements under the EU Emissions Trading Scheme.
Updated: November 2009