Around 2010, the issue of oil and gas contamination of shallow groundwaters and of methane emissions jumped into the public domain with the application of hydraulic fracture stimulation or ‘fracking’ in North America and later elsewhere. Fracking became a political issue that few outside the oil and gas industry understood technically and even fewer understood the geoenvironmental consequences of. Over time,it became clear that there were only a few cases of groundwater contamination by fracking itself but many from the inadequate cementing of oil and gas wells, some which had been recently completed by fracking.
This monograph addresses a void in the hydrogeological literature so that the reader may appreciate how and why groundwater contamination and gas emissions from oil and gas wells occur so frequently. It begins with a description of oil and gas well construction and completion,including hydraulic fracture stimulation. It then describes how these wells have been plugged and abandoned, often inadequately. The monograph proceeds to identify geoenvironmental pathways by which natural gas migrates along the wellbore annulus and either escapes to the ground surface or enters and contaminates shallow groundwaters. Discussions follow of the chemical effects on groundwater, laboratory and field experiments of gas migration in the subsurface and the numerical simulation of these processes.