Offshore environmental impact surveys have been carried out by oil and gas operators in the North Sea since 1975, initially as part of corporate environmental management programmes and latterly as regulatory requirement. Routine monitoring of the area around installations to confirm impact hypotheses of the seabed and check the general health of the marine environment is now endorsed in UK Regulations notably under the under The Offshore Chemicals Regulations 2002.
Monitoring surveys have traditionally been carried out along one or more transects leading away from the installations and following the prevailing current direction. Collection of sediment samples were taken at stations set at varying distances, 500, 800, 1200, 2500 and 5000 metres from the platform along the transects. Samples from reference stations located at 8 to 10 kilometres from the installations would also be collected. The samples would then been analysed for hydrocarbons and metals content and to investigate the seabed biological communities.
This monitoring strategy is designed to measure gradients of environmental effects in the vicinity of the platform. Between 1975 and 1998, it is estimated that some 520 seabed survey were carried out. However, a lack of consistency and standardisation in the way these surveys were conducted has led to difficulty in establishing long-term environmental effects.
To that purpose, Oil & Gas UK (UKOOA at the time) funded a project with the aim of collating and reviewing all seabed monitoring data collected by the UK oil and gas industry from 1975 to 1998. The Oil & Gas UK seabed environmental review was carried out in three phases:
Phase 1: compilation of an inventory of surveys carried out in the UK sector.
Phase 2: production of database files containing detailed biological, chemical and geographical data.
Phase 3: examination the extent of contamination from offshore exploration and appraisal activities and impacts on the biota, and attempt to determine any large-scale trends over wider geographical areas. This final phase was completed in April 2001.
Today, techniques have evolved and the focus is more on wide-scale baseline environmental monitoring at a pre-operational stage. This involves screening the development area for any potential ecologically important habitats and species using side-scan and/or multi beam sonar and swathe bathymetry techniques.