Deoiled produced water treatment using direct-contact membrane distillation

Deoiled produced water in current produced water treatment facilities for water reclamation from steam-flooded oil exploration (Webb et al. Desalination of oilfield-produced water at the San Ardo water reclamation facility, CA, SPE 121520-PP, 2009) activities is available at temperatures between 160 and 200 F (71-93 C). Desalination of this deoiled produced water is accomplished currently by reverse osmosis after a number of steps including cooling. Membrane distillation processes can utilize this sensible heat to achieve desalination. Direct-contact membrane distillation studies using a hollow-fiber membrane module with brine in the cross-flow have been successfully conducted using a variety of produced waters such as Chevron A [Pre-RO, Post WEMCO; the latter refers to an induced gas/dissolved gas flotation (IGF/DGF) technique], Chevron B1, and Chevron B2 having total dissolved solids (TDS) respectively of 7622, 12040, and 35000 mg/L. The brine feed temperature was varied between 50 and 85 C. The effect of brine feed flow rate variation was also studied. At 80 C, the highest observed water vapor flux at a higher feed brine velocity was 15 kg/m²·h. The permeated waters were substantially pure with a very low TDS value in each case, indicating very high salt rejections. These conclusions held even when the feed deoiled produced water was concentrated via batch recirculation to recover as much as 80% of the feed produced water in the distillate stream.