Reducing the Scaling Potential of Oil and Gas Produced Waters with Integrated Accelerated Precipitation Softening and Microfiltration

Development of unconventional oil and natural gas resources is inexplicitly tied to the generation of saline waste waters commonly referred to as produced water. Produced waters can contain high concentrations of sparingly soluble salts, making mineral scaling an important problem for desalination processes. This investigation evaluated the removal of dissolved and particulate forms of calcium, a common mineral scaling element, using accelerated precipitation softening (APS) combined with microfiltration (MF). Filtration of APS effluent produced filtrate with a 3% lower dissolved calcium concentration and 8xlower turbidity than filtrate from water softened without seeds. An optimum calcium carbonate seed concentration of 7 g/L was identified for the produced water. The particulate seeds are well-rejected by polymeric and ceramic membranes. In a cross-flow configuration the particulates did not significantly foul the ceramic MF membrane until a solids concentration of 15 g/L was reached indicating that the APS-MF system is capable of treating high-solids content water. In addition, it could be operated without settling the water after the APS reaction, while maintaining a reasonable operating filtrate flux and TMP.