Numerical and Data Analysis of Methane Leakage through Petroleum Wells

Abstract

Subsurface methane leakage around oil and gas wells contributes to fugitive greenhouse gas emissions and contamination of freshwater aquifers. The leakage can occur through natural or induced permeable pathways or due to poor cementation or degradation of the cement around petroleum wells. Accurate prediction of methane migration in the subsurface depends on knowledge of porosity and permeability of the conduits as well as flow system conditions. A two-dimensional, two-phase numerical model is employed using DuMux to simulate subsurface methane migration through the cemented wellbore that experienced temporal degradation. The simulations showed that methane migration patterns are affected by cement quality around boreholes, which dictates the rate and duration of methane leakage. Cement degradation accelerates methane upward migration, allowing it to travel faster and farther. In contrary, high-quality cement acts as a barrier to prevent methane migration to freshwater aquifers or to the surface. Moreover, the analysis of published data from petroleum wells in Alberta, Canada confirm that poor annular cementing is a possible contributor to methane leakage and migration to the atmosphere, and thus major contributor to climate change.