THE ROLE OF WATER IN RECOVERY OF ENERGY RESOURCES

Water is a crucial component in existing and emerging in-situ extraction technologies such as borehole hydraulic mining, in-situ retorting, in-situ recovery, and hydraulic fracturing, used to recover oil, gas, coal, and uranium resources. In-situ technologies are revolutionizing the access, economics and (or) safety of recovering oil and gas from deep, low permeability reservoirs and uranium resources from deep, low-grade deposits. In situ technologies typically involve the injection of large amounts of water, usually fresh or brackish, into the subsurface. During hydraulic fracturing, water is injected under pressure high enough to create fracture networks in the reservoir rock and dramatically increase the permeability of very tight rock. This process allows previously inaccessible oil and gas resources to be extracted. In-situ recovery (ISR) of uranium involves the injection of leaching solutions directly into aquifer- and sandstone-hosted uranium deposits to dissolve the uranium in-place, allowing the uranium-rich water to be pumped to the surface. The ISR uranium production phase is followed by aquifer remediation that often involves the direct flushing of the host aquifer with additional water. Although not as common, hydraulic borehole mining involves breaking up target commodities, such as coal or uranium ore, with a high-pressure jet and pumping the broken rock to the surface as slurry. In-situ retorting uses large amounts of water to heat the oil shale in the subsurface and for subsequent flushing of the formation with water to remove residual labile organic and inorganic contaminants during remediation. These in-situ subsurface water injections and extractions generate large volumes of wastewater that are of poor quality due to high salinity, trace metal contaminants, organic constituents, and (or) radionuclides. Water demand by these technologies can also challenge local and regional water supplies. The role of water in in-situ technologies for the recovery of energy-related resources encompasses both hydrogeology and geochemistry. These in-situ technology innovations present opportunities in enhanced energy resource extraction and challenges in water quality, use, management, treatment, availability, reuse, and recycling.