Oil & Natural Gas Corporation (ONGC) has been exploring and producing Oil and Gas on the western continental shelf of the Arabian Sea since mid 1970's. There are about 150 production platforms (including 13 major complexes) and approximately 3,000 km of sub-sea pipeline producing over 20 million tonnes of crude oil and about 20 billion cubic metres of natural gas per annum from this region.

ONGC has established an Institute of Petroleum Safety, Health and Environment Management (IPSHEM) as its commitment towards promoting higher standards of Health, Safety and Environment for the Petroleum Sector in India. The Institute apart from imparting training in HSE has regularly undertaken a two-season offshore monitoring study since 1994 for its Offshore Installations.

Offshore Environment Monitoring may have many meanings but generally, it means repeated measurement of pollutants for their effects, and changes over a time frame. In a more regulatory sense, monitoring includes collection of data in relation to some standards or guidelines imposed on the project authorities.

This paper describes the strategies, procedures, methodologies adopted in the design of the monitoring program, surveys, analysis etc. and the salient findings during the study period 1994-2001.

The parameters of interest covering environmental impact of offshore operations are identified. From the study, it is clear that there is little or no effect of offshore operations on the general hydrography of water column, and availability of nutrients for phyto-plankton growth in the marine environment. Environmental Impact of offshore operations on the biological productivity was found to be insignificant from the recorded observations. Most pollutants were well within the background levels in this offshore region of the Arabian Sea.

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