(646b) Advanced Supercritical Water-Based Process Concepts for Treatment and Beneficial Reuse of Brine 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 14 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 likely 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 National Energy Technology Laboratory (NETL) Crosscutting Research Program Project 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 naturally occurring radioactive materials (NORM) using commercial ion exchange resins and natural adsorbent has been investigated. Further, removal of dissolved solids from simulated and field-derived produced water has been investigated at pressures ranging from 23-28 MPa, respectively, demonstrating the ability to recover greater than 99 percent of salts from brines containing dissolved solid concentrations greater than 240,000 mg∙L^-1. Techno-economic summaries have identified important brine treatment cost sensitivity parameters and heat recovery schemes to lower brine treatment costs. This presentation will review experimental and techno-economic study results from both U.S. DOE supported projects.