Large-scale changes in subsurface water budgets from oil and gas production

Water management is a key issue for the oil and gas industry. Much of the recent attention has been on water use and subsequent handling of flowback and produced water for unconventional oil and gas developments (i.e. high volume hydraulic fracturing (HVHF)). Much less attention has been paid to decades of conventional oil and gas production and potential environmental impacts. The volume of water produced and injected with conventional oil production are much larger than for unconventional oil production via HVHF, and changes in hydraulic head are expected to occur over much larger areas for greater periods of time. We postulate that operation of wells for produced water disposal for conventional oil and injection for enhanced oil recovery projects are more likely to drive upward migration of solutes to shallow aquifers where high permeability pathways exist. This is particularly problematic in areas where injection wells exist in shallower strata, such as those in exempt aquifers. Evidence of changes in groundwater chemistry from operation of deep injection wells is scarce due to a lack of monitoring. However, changes in salinity in the Williston, Powder River and Paradox basins suggest that disposal of produced water and injection associated with enhanced oil recovery are having effects on groundwater chemistry (e.g., freshening subsurface reservoirs, introducing contaminants into brackish aquifers) and removing freshwater resources from the active hydrologic cycle.