Alkaline earth metals such as barium (Ba2+), strontium (Sr2+), and radium (Ra2+) were found in the shale gas produced hypersaline brine (i.e., flowback and produced water). During the operation of the hydraulic fracturing (fracking), brine was produced and flow back to the surface. Spills of the produced water may occur during operation, handling, and storage with potential negative impact on shallow potable aquifers. However, it is not well understood the fate of the hazardous elements within the brines upon a leakage into a reactive porous medium of various mineralogy. Here, we present experimental and modeling work to describe the transport of the major cations in both natural and synthetic produced water, namely: Ba2+, Ca2+, Mg2+, and Sr2+ (congeners of Ra2+). We selected porous media containing either sand, hydrous ferric oxide-coated sand (HCS), resin-coated sand (RCS), or activated alumina (as an analog for clay). Transport experiments were performed with both natural produced water (NPW) and synthetic produced water (SPW). SPW was synthesized with the same major cation concentration as the NPW to understand the effect of the organics in the metal transport. Experiment results show that all the alkaline earth metals tested moved with negligible retardation, i.e., breakthrough around 1 pore volume (PV), in NPW through all the porous media (Figure 1). Only activated alumina showed some reactivity towards the cations of interest. It was, therefore, selected and tested further with SPW and SPW at various dilution ratios. The transport of Ba2+, Ca2+, Mg2+, and Sr2+ behaves similarly with and without the presence of organics, and it is affected significantly by the salinity. Dilution of SPW determines larger retardation of the cations opening the possibility to engineer the process. To this aim, a reactive transport model was developed with PHREEQC in order to design the characteristics of the fluid and of the solid to optimize the retention.

Transport of alkaline earth metals in natural and synthetic produced water through porous media

2019 Spring National Meeting

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