Methane emissions from abandoned hydrocarbon wells in Italy: inventory, measurement techniques and the role of mega-emitters

Abandoned hydrocarbon (oil and gas) wells (AOG) represent a poorly studied source of atmospheric methane, potentially contributing to total anthropogenic fossil methane emission and related climatic impact. Methane leakage from AOG was measured only in a few countries (U.S.A., Canada, the Netherlands, United Kingdom), and available inventories in other countries are incomplete or need quality checks. Methodologies for gas flux measurement are not standardized. New studies have recently started in Italy in order to inventory onshore AOG, design multiple and versatile techniques for methane flux measurement, which can be adaptable to different typologies of well-heads, and to execute first measurements. Preliminary data revealed the existence of several AOW releasing relevant amounts of methane (orders of 10¹ ton yr^-1), which are up to two orders of magnitude above those typically observed in North America. Contextualization of such “mega-emitters” (their percentage with respect to total AOW, technical conditions, possible existence in other countries) is necessary to assess average emission factors and derive bottom-up methane emission estimates at national and global scale.