Large methane release from abandoned hydrocarbon wells in Italy

Abandoned hydrocarbon wells (AHWs) represent an understudied anthropogenic source of atmospheric fossil methane (CH4). To date, CH4 flux measurements from AHWs have been extensively conducted in North America, highlighting the important role of unplugged wells, especially those that can be defined as high-emitters (releasing at least 0.9 t CH4 y−1). In Europe, only a few plugged wells have been measured, in the Netherlands, United Kingdom, and Germany; in all other countries, globally hosting likely several millions AHWs, inventories and CH4 emission data are unavailable. Here, we report the first data of CH4 emission from unplugged and plugged AHWs in Italy, a major historic hydrocarbon producer in Europe. Based on the official Italian dataset of hydrocarbon wells, we developed an inventory of 3,427 onshore AHWs, predominantly located in the central and eastern Po Plain, with additional clusters along the Apennine chain and associated foredeep basins. The current number of onshore AHWs may be underestimated due to undocumented exploratory wells drilled during early historical phases. Field investigations conducted at 19 historic wells using static chambers, digital flow meters, and infrared detection combined with image analysis, together with additional flux calculations performed on one site previously documented in the geochemical literature, revealed gas leakage at 13 sites, with emission rates ranging from 0.0003 to 57.3 t CH4 y−1. Eight unplugged wells were found to be high-emitters, collectively accounting for approximately 98% of total CH4 output, whereas the investigated plugged wells did not show detectable CH4 emissions. Plugging status, well age, and historical circumstances of the abandonment seem to be crucial in determining the gas leakage potential. Such factors should be considered to derive statistically robust AHW emission factors and related global CH4 emission to the atmosphere.

Atmospheric methane · Current (fluid) · Flux (metallurgy) · Fossil fuel · Hydrocarbon · Methane · Natural gas · Petroleum seep · Water well · Atmospheric and Environmental Gas Dynamics · CO2 Sequestration and Geologic Interactions · Methane Hydrates and Related Phenomena