Unconventional in-situ extraction techniques have become increasingly important in the development of oil, gas, and uranium resources that are generally not recoverable and/or economic using “conventional” extraction methods. These in-situ extraction methods include hydraulic fracturing for shale-gas and tight-oil production, in-situ retorting for oil-shale production, and extraction of uranium using in-situ recovery (ISR), a solution mining technique. Water is both indirectly and directly linked to these in-situ energy development methods because they occur in place (underground) and/or require the injection of water, often fresh, into the subsurface. Although they usually have a relatively small land-surface footprint, there remain uncertainties regarding potential subsurface impacts, particularly to groundwater resources. Possible concerns include: (1) releases of chemical additives, and mining fluids added during the extraction process, and mobilization of naturally occurring trace metals, organics and radionuclides from minerals and formation waters; (2) alteration of groundwater equilibrium such that returning post-extraction groundwater quality conditions back to pre-development conditions is difficult; (3) uncertainties in the likelihood of contaminant migration along newly created fractures in petroleum reservoirs or from uranium mining zones to near-surface groundwater aquifers, especially drinking water sources; and (4) large volumes of surface water or groundwater used during "injection" resulting in significant freshwater consumption. High salinity, organic compounds, and trace metals in wastewaters from oil and gas production and uranium ISR make deep injection wells and recycling popular handling options, depending on treatment. Although wastewaters from uranium ISR operations are not reused in agriculture mainly due to high concentrations of radium, moderate salinity wastewaters from coalbed methane and enhanced oil recovery are being reused in irrigated agriculture in the United States and Australia. These precedents suggest that opportunities can exist under the right circumstances even with other unconventional energy extraction methods that produce wastewaters with compositions more challenging to beneficial reuse. Water is a vital resource for both agriculture and in-situ energy development processes and as pressure on water supplies increases, it is worthwhile to explore innovative new linkages among these industries.

Water challenges in unconventional in situ energy resource extraction technologies

249th National Meeting (2015)

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