HOW CAN WE MANAGE PRODUCED WATER ASSOCIATED WITH UNCONVENTIONAL OIL TO REDUCE POTENTIAL HAZARDS?

Although large volumes of water have been produced with oil for decades, changes in production within the past decade have resulted in increased hazards from over-pressuring and induced seismicity in some regions. Here we examine spatiotemporal variability in produced water volumes and related management issues in the major U.S. unconventional/conventional oil plays (Bakken, Permian, and Eagle Ford plays, and Oklahoma). Results show that although we produce less water with oil in many unconventional plays, the biggest difference is that we can no longer inject the produced water back into the pressure-depleted reservoirs as we did when water flooding conventional reservoirs. Disposal into non-oil producing horizons is linked to over-pressuring in shallow geologic units in the Bakken play and Permian Basin and to induced seismicity in Oklahoma. Various approaches can be adopted to mitigate produced water management issues, including (1) reuse/recycling of produced water for hydraulic fracturing, (2) establishing synergies between unconventional and co-located conventional reservoirs, (3) water flooding, and (4) treatment of produced water that is put to a beneficial use in another sector. Challenges to these practices include matching produced water quantity and quality with hydraulic fracturing demands, chemical compatibility issues with disposal in conventional reservoirs, and treatment costs. This assessment of spatiotemporal variability in produced water volumes from the various plays within the context of conventional reservoir development and water demand for other sectors should advance our understanding of options for managing produced water to reduce adverse environmental impacts.