Application of forward osmosis for reducing volume of produced/Process water from oil and gas operations

Produced water management is one of the key challenges faced by the oil and gas industry globally. Specifically, the gas industry in Qatar is challenged to minimize the produced/process water (PPW) volumes injected into disposal wells to ensure long term sustainability of the reservoirs. This research evaluated a novel application of forward osmosis (FO) to reduce the volumes of PPW disposed of by deep well injection using brine from thermal desalination plants or seawater as draw solutions. In the case of brines, this process also provides some environmentally beneficial dilution before discharge. In order to verify the PPW volume reduction concept, bench-scale FO experiments were carried out using commercial flat sheet membranes. FO performance was evaluated using PPW with and without pretreatment and results confirm that pretreatment is key to the successful implementation of FO for the treatment of PPW. Experimental results indicate that FO is effective in achieving 50% volume reduction of pretreated PPW with stable flux of 12 LMH. Lab analyses show that the TOC in the diluted draw solution was below the detection limit indicating that the TOC from the feed did not appear in the draw solution and hence would not be discharged to the environment. © 2015 Elsevier B.V. All rights reserved.

This research highlights a novel application of forward osmosis to reduce the volumes of produced/process water (PPW) disposed of by deep well injection using brine from thermal desalination plants or seawater as a draw solution. Results show that FO is effective in achieving 50% volume reduction of PPW with an average stable flux of 12 LMH. A significant increase in flux was observed when the feed and draw solution temperatures were increased from 20 °C to 40 °C with deionized water as the feed solution and 1 M NaCl as the draw solution. This increase was attributed to several factors, including a decrease on water viscosity, a slight increase in the draw solution osmotic pressure, and potential enhancement of some membrane properties. The draw solution concentration also had an impact on the flux since it increases the effective osmotic pressure across the membrane. FO performance was evaluated using PPW with and without pretreatment and results show that pretreatment is key to the successful implementation of FO to treat PPW. Experiments with the untreated PPW showed fouling on the FO membranes, which was attributed to the organics present in the feed water. Different pretreatment options were evaluated and the results showed that powdered activated carbon, at a dosage of 500 mg/L, reduced the TOC from 132 to 47 mg/L, and stable water flux and no fouling were observed. Further optimization of pretreatment is required. The water quality analysis showed that the initial TOC in the PPW was 132 mg/L and the TOC in the draw solution after being treated by Fig. 8. Comparison of FO performance with PPW as feed with and without pretreatment. PPW: CFV: 20 cm/s, temp: 25 °C, AL-FS. DS: 70 g/L NaCl.