(432c) Treatment of Flowback/Produced Water From Gas Shale Plays with Membrane Distillation

To reduce the amount of freshwater used in hydraulic fracturing and the overall cost of water management in a well field, shale gas development companies are striving to reuse most of the hydraulic fracturing flowback water. However, there are numerous instances when the flowback and produced water cannot be reused and must be disposed. Furthermore, flowback and produced water reuse is feasible only as long as there is sufficient number of new wells where this water can be utilized for hydraulic fracturing, which is not necessarily the case for mature fields. It has become increasingly evident that the future of the unconventional onshore gas industry is critically dependent on technical solutions that would enable efficient and cost effective management of flowback and produced waters. This study is designed to evaluate the promise of membrane distillation (MD) technology to meet this objective.

The total dissolved solids content of flowback and produced water can reach nearly 350,000 mg/L, ten times the average TDS concentration in seawater. Sodium and chloride are the primary ions present, followed by calcium, barium, strontium and magnesium. The water also contains some heavy metals at low concentrations. The extremely high TDS concentrations render the most prevalent desalination technologies employed today for seawater desalination ineffective. Even with favorable energy prices, reverse osmosis (RO) treatment of brine water becomes economically infeasible above 40,000 mg/L TDS (Cline et al., 2009). High salinity of the feed water decreases the driving force for mass transport in RO considerably but has minimal impact on MD because of the limited impact on vapor pressure of water, which is the driving force in MD, (Cath et al., 2004). Complete rejection of ions and dissolved non-volatile organics is achieved with MD as long as the membrane pores are not wetted (Nghiem et al., 2011). The other principal advantage of MD over other treatment technologies is a much lower expected energy demand because MD can operate at near atmospheric pressure and in the temperature range of 50-100 ^oC, which is significantly lower than typical temperatures used in conventional thermal treatment processes (e.g., distillation, mechanical vapor recompression). As a result, associated costs are predicted to be drastically lower than their thermal and membrane processes counter-parts, (Al-Obaidani et al., 2008).

In this present study, a flat sheet DCMD module with a membrane contact surface area of 0.004 m² was constructed to test the feasibility of MD technology for treating flowback and produced water from unconventional shale plays. Acrylic copolymer membrane with a mean pore size of 0.45µm was used in these experiments. Initial tests were conducted with this module using feed NaCl concentrations up to 30% at temperatures between 40-65°C and the results in terms of permeate flux and quality were similar to those found in the literature. Further testing was conducted using concentrated synthetic and actual flowback water from a well located in Westmoreland County, PA. The results are promising in that the permeate fluxes obtained are comparable to those obtained with NaCl only. The test with real flowback water, which had a TDS of 3.9%, yielded a permeate flux of 33.8 kg/(hr m²) for an operating temperature gradient of just 31.5°C. In addition, no serious irreversible fouling or wetting of the membrane was observed during the 70-minute test with real flowback water and clean water permeability was restored after membrane rinsing with clean water. The results of ongoing studies to further demonstrate the feasibility of MD for flowback/produced water treatment at different feed compositions and temperature gradients will be presented at the conference.

References:

1. Al-Obaidani, S., Curcio, E., Macedonio, F., Profio,  G.D., Al-Hinai, H., Drioli, E., (2008). “Potential of membrane distillation in seawater desalination: thermal efficiency, sensitivity study and cost estimation.” Journal of Membrane Science 323: 85–98.
2. Cath, T.Y., Adams, V.D., Childress, A.E., (2004). "Experimental study of desalination using direct contact membrane distillation: a new approach to flux enhancement." Journal of Membrane Science 228(1): 5-16.
3. Cline JT, Kimball BJ, Klinko KA, Nolen CH.  (2009). Advances in Water Treatment Technology and Potential Affect on Application of USDW.  GWPC: 2009 Underground Injection Control Conference. San Antonio, TX January 26-29, 2009.
4. Nghiem, L.D., Cath, T.Y., (2011). "A scaling mitigation approach during direct contact membrane distillation." Separation and Purification Technology 80(2): 315-322.