(644e) Advanced Supercritical Water-Based Process Concepts for Treatment and Beneficial Reuse of Produced Water Generated By Oil/Gas Production

Both U.S. energy and economic security rely upon continued development of U.S. unconventional shale plays, which require access to suitably clean water resources. Produced water (brine) is the nation’s largest industrial waste stream, with approximately 22 billion barrels generated annually by the U.S. oil and gas sector. The recent surge and continued development of unconventional U.S. shale plays will result in greater volumes of produced water. In addition, an additional brine waste stream will be created by future sequestration of CO₂ emissions generated by fossil-based power plants into saline aquifers. Utilizing this brine in development of unconventional shale resources represents a beneficial reuse of this waste stream. This approach can not only lower stress on local watersheds but can also address public/local government concerns regarding long-term ground water contamination potential and seismic activity associated with Class II salt water disposal wells (SWDs).

However, direct reuse of brines in shale development activities currently is limited due to constituents found in this waste stream. Specifically, the high levels of dissolved solids found in the brine may cause scaling within the shale or within production casings, reducing well productivity. Current brine treatment technologies including membrane- and thermal-based processes are ineffective in treating brine containing concentrations of dissolved solids greater than 80,000 ppm due to fouling or cost/sizing, respectively.

To address these limitations, Ohio University (OHIO) with funding from the U.S. Department of Energy’s (DOE) National Energy Technology Laboratory (DE-FE0026315), has been developing an advanced supercritical water (SCW)-based process for treatment and beneficial reuse of brine waste streams. This SCW process offers an advantageous media for brine treatment, as its lower fluid density and decreased hydrogen bond strength provides a means to simultaneously remove dissolved solids and hydrocarbons.

Previous SCW-based brine treatment systems have been plagued by internal scaling, resulting in inefficient heat transfer, plugging, and process downtime. To address this issue OHIO has been developing both externally- and internally-heated SCW reactor design concepts, which utilize advantageous fluid dynamics and electrically driven Joule-heating mechanisms, respectively. OHIO’s new SCW reactor designs offer the potential to provide a field deployable brine treatment process and a resultant product which may be reused in shale development or other beneficial reuse applications, thereby supporting goals of NETL’s Strategic Center for Oil and Natural Gas.

To evaluate process potential, OHIO has been conducting both experimental investigations using prototype SCW reactors and process simulations/techno-economic assessments using Aspen Plus^TM. Removal of dissolved solids has been investigated at pressures ranging from 23-28 MPa, respectively, demonstrating clean water product with dissolved solids content ranging from 500-2,800 mg/L from feedstock containing up to 180 g/L. Tests have also been conducted with produced water generated from an unconventional well located in the Point Pleasant Shale play in eastern Ohio. This presentation will review experimental and techno-economic study results from this U.S. DOE supported project.