Gas Emissions from Energy Wells and the Groundwater Monitoring Problem

English Abstract:

There is accumulating evidence from the drilling and completion of some energy wells of free-phase gas emissions migrating considerable distances away from such wells (500 m or more) in structurally complex terrain. This information was obtained by regulatory agencies and geological surveys in structurally complex regions such as the Appalachian belt of eastern North American. Such migration distances pose real problems with respect to the monitoring of gas emissions that may affect shallow potable groundwaters. Information on wellbore leakage is only recently appearing in the technical literature reflecting what industry has long acknowledged, i.e., the difficulty of wellbore sealing with cement slurries when numerous strata contain hydrocarbon and hydrogen sulfide gases under varying in-situ pressures. Given (i) the transient nature of natural gas emissions from energy wells, (ii) the spatial and temporal variability of groundwater quality and (iii) the uncertain integrity of landowner wells, there is clearly a burden of proof on those sampling landowner wells to demonstrate that the ‘pre-drill’ data collected are robust and provide reliable information for use in dispute resolution. Not only can we expect gas emissions to be pulses, but we must anticipate that the discharge area, in which such gas ‘daylights’, might be distant from the energy well pad and its location therefore uncertain. For these reasons there is a clear need to link research concerning wellbore integrity with gas migration through fractured-rock networks. Similarly, groundwater monitoring has to be focused on potential gas-discharge areas that contain public groundwater supply wells. Such research and monitoring requires recognition from research-funding institutions, regulatory agencies and geological surveys.