Origin, fate and detection of methane leaking from the deep subsurface into groundwater and soil

Abstract

Oil and gas development can cause unintended connectivity between the deep subsurface and shallow aquifers. Methane leaking through such connections can result in groundwater contamination, greenhouse gas emissions, and can constitute an explosion hazard. When leaking methane enters into groundwater and soil systems it is subject to a number of processes that can retain it, degrade it, and alter its molecular and isotopic signature. This signature is used for environmental fingerprinting of methane origin, and can be further changed by mixing of leaking methane with naturally occurring biogenic sources. Together, the combination of those processes makes detection of leakage through surficial flux measurements or groundwater sampling challenging.

In this work, the fate of methane leaking from oil and gas reservoirs into the environment was studied using a combination of scientific approaches, including groundwater sampling and analysis of dissolved gasses and isotopic tracers, soil gas flux measurements, and multiphase numerical modelling. Additionally, the occurrence of methane leakage at legacy gas wells in the Netherlands was investigated, together with a characterization of the natural distribution and origin of methane in groundwater in the Netherlands. Based on this combined hydrogeochemical investigation, the study provides further insight into the risks of methane leakage, and the processes that control its migration through the subsurface.