Produced waters from oil and gas recovery typically contain a broad array of dissolved contaminants, including Ba2+ and Sr2+ (present not only as divalent ions but in various other complexed forms). Removal of these compounds may be necessary prior to re-injection of this water (to prevent down-well scale formation), prior to its disposal as waste (e.g., discharge to a treatment facility incapable of removing Ba2+ and Sr2+), or prior to treatment processes such as reverse osmosis that may be used to recover and reuse the water. Sr2+ and Ba2+ removal, however, is complicated by the high concentrations of dissolved ions present in most produced waters (which can dramatically alter their ionic speciation) and by the relatively high solubility of Sr precipitates. Polyelectrolyte additives can complex with and form around target metals directly in the produced water, functioning as nanosized entrapment agents. By tailoring a polyelectrolyte for a specific environment, a stable complex can be formed that can then be separated from the produced water through filtration or gravity separation, thereby minimizing the need for additional treatment for the purposes noted above. This study presents the results of experiments on the removal of Sr2+ and Ba2+ from produced waters with varying ionic strengths and background water chemistries, through complexation with polyelectrolytes containing sulfonate functional groups. Several polysulfonate compounds displayed Sr removal rates from produced waters in excess of removals obtainable through co-precipitation of (Ba,Sr)SO4, the most common treatment method currently in use. In addition, these polymers were selective for Sr2+ and Ba2+ over the lower-MW divalent cations Ca2+ and Mg2+. Ongoing investigations of these polyelectrolyte-metal complexes (PECs) as a treatment process for scale forming cations in produced waters are focused on improving polyelectrolyte selectivity in high salt brines. The most promising polymers and treatment conditions will be further evaluated with respect to the possibility of polymer regeneration, after separation of the PEC from the produced water environment, and their potential to be scaled up to full-scale treatment systems.

Use of polyelectrolyte complexes in Sr and Ba removal from produced waters

251st National Meeting (2016)

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