RE-EXAMINING SALTWATER MANAGEMENT PRACTICES IN OKLAHOMA

Oklahoma’s climate is characterized by extended dry periods embedded within wet periods, so thousands of reservoirs were built in the early 20^th century to store surface water during wet years. Because wet years are few and far between, especially in western Oklahoma, groundwater resources are also utilized to meet water demand. Water supply infrastructure has evolved to meet Oklahoma’s annual freshwater demand of about 1.7 million ac-ft. Proportions of freshwater demand are attributed to agriculture (41.5%), public supply (31.7%), livestock and aquaculture (11.6%), thermoelectric (10.5%), domestic and commercial (3.0%), and industrial and mining (1.7%).

During extended droughts, the proportion of groundwater withdrawals will typically increase to meet demand while not drawing reservoirs down below their conservation storage levels. This practice is not sustainable because groundwater is also a limited resource. Long-term trends in groundwater systems, such as the High Plains or Rush Springs Aquifers of Oklahoma, indicate that annual withdrawals far exceed annual recharge. Wastewaters from all sectors could be considered as alternative water sources that can be treated and re-used to supplement existing freshwater supplies.

The energy industry, in particular, has an abundance of wastewater that is currently disposed of into saltwater disposal wells. Brine that is co-produced with oil and gas exceeds 135,000 ac-ft per year in Oklahoma, and often is produced in locations that are experiencing water supply shortages. Co-produced water can be reused for makeup water in hydraulic fracturing operations (internal reuse) with little or no treatment. However, external reuse such as for irrigated agriculture would require desalination to reduce total dissolved solids concentrations of co-produced water from a median of about 150,000 ppm to less than 3000 ppm. Multi-stage treatment with membrane and distillation technologies can achieve these desalination goals, and must continue to be developed for cost-effective recycle and reuse of co-produced water. This line of research examines options for jointly sustainable energy production and water supply scenarios that include a component of co-produced water recycle and reuse.