Source: Matthew Reagan and Dan Hawkes
Hydrocarbon production from unconventional resources and the use of reservoir stimulation techniques, such as hydraulic fracturing, has grown explosively over the last decade. However, concerns have arisen that reservoir stimulation may create significant environmental threats through the creation of permeable pathways connecting the stimulated reservoir with shallower fresh-water aquifers, thus resulting in the contamination of potable groundwater by escaping hydrocarbons or other reservoir fluids.
In a study recently published (March 25, 2015) in Water Resources Research, a team of ESD scientists—including Matthew Reagan, George Moridis (Hydrocarbon Resources Program Head), Noel Keen, and Jeff Johnson—used numerical simulation to investigate potential gas and water transport between a tight-gas reservoir and an overlying fresh-water aquifer following hydraulic fracturing operations. They focused on two general failure scenarios: (1) communication between the reservoir and aquifer via a connecting fracture or fault and (2) communication via a compromised well ( i.e., a deteriorated, preexisting nearby well or an imperfectly completed newer well, including the gas well itself).
They concluded that the key factors driving short-term transport of gas include high permeability for the connecting pathway and the overall volume of the connecting feature—assuming that such connecting features do occur. Production from the reservoir is likely to mitigate release through reduction of available free gas and lowering of reservoir pressure, and cessation of gas production may increase the potential for release. They also found that hydrostatic (not overpressurized) reservoirs are unlikely to act as a continuing source of migrating gas, because gas contained within the newly formed hydraulic fractures is the primary source for potential contamination. Such incidents of gas escape are likely to be limited in duration and scope. Follow-up research will examine overpressured reservoirs, the potential escape of brines from the reservoir, and additional subsurface geometries.
This work was a part of an EPA-funded study, led by George Moridis, to assess the potential impacts of hydraulic fracturing on drinking water resources and to identify the driving factors (geomechanical and transport) that affect the potential, severity, and frequency. This research was funded by the U.S. Environmental Protection Agency’s Hydraulic Fracturing Drinking Water Assessment through Interagency Agreement (DW-89-92235901-C, Stephen Kraemer, EPA Project Officer).
To read the paper, go here»
Citation: Reagan, M.T., G.J. Moridis, N.D. Keen, and J.N. Johnson (2015), Numerical simulation of the environmental impact of hydraulic fracturing of tight/shale gas reservoirs on near surface groundwater: Background, base cases, shallow reservoirs, short-term gas and water transport. Water Resources Research, DOI: 10.1002/2014WR016086.