Innovative Methods for Methane Leakage Monitoring Near Oil and Gas Installations

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In recent years, there has been an increased focus on environmental issues near oil and gas production sites and pipelines. The trend is likely to continue as future oil and gas production is commencing in environmentally vulnerable areas, and farther north near the polar ice cap. The exploration in more remote areas implies that online in situ monitoring has great advantages over expedition based monitoring. The Norwegian Geotechnical Institute (NGI) is an independent research and consultancy foundation having over 40 years of worldwide offshore instrumentation experience. NGI has recently launched a research initiative to develop new methods for in situ and on line environmental monitoring offshore. In 2012, NGI designed and installed an integrated environmental monitoring system for subsea leakage detection. It was installed on the seabed beneath an operating oil and gas platform in the North Sea. We give here an overview of the instrumentation system and the motivation for the different design choices. The system is an example of an integrated monitoring system, where different types of sensors complement each other and gives a more thorough understanding of methane transport at the site of interest. After installation, NGI has analyzed monitoring data and provided decision support to operator personnel. Nearly two years of production site data collection represents a unique data set that enables a comprehensive analysis of methane transport. From the operator side, the motivation for environmental monitoring usually arises from the need to answer clearly defined questions such as ‘Is there a gas leakage in the production system? Where is it? How large is the leakage?’ The leakage detection system is expected to answer these questions, preferrably in an unambiguous manner. However, natural gas can be released to the water phase from several sources e.g. organic matter on the seabed. If the leakage detection monitoring data shall be interpreted in a control room that operates with alarm states, these sources of background noise must be identified and separated from a real leak situation. We look at which circumstances to be aware of and how to maximize the operational value of a leakage detection system.