(646c) Transport of Earth Alkaline Elements in Produced Water through Reactive Porous Media

Hydraulic fracturing (or fracking) is a well stimulation technique used to extract oil and gas from a low permeability formation. During the operation large volumes of fracking fluid containing chemical, water, and propping agent (proppant) is injected and a hypersaline brine which contains high concentration of hazardous elements is produced. Generally, a proppant is injected during the operation to maintain the fractures open allowing oil and gas to flow back. Conventional proppants have only a mechanical function. Here, we present a work aimed at designing a proppant that has also a chemical function to treat in situ the produced water. We are specifically interested in the adsorption of earth alkaline metals, i.e. radium (Ra²⁺), which has long half-life and high radiotoxicity. In this study, earth alkaline metals, i.e. Ba²⁺, Ca²⁺, Mg²⁺, Sr²⁺ (the congener of Ra²⁺) are tested through a porous media such as goethite-coated beads, sand, activated alumina, and hydrous manganese oxide (HMO)-coated sand. Column flood tests were carried out at conditions of natural and synthetic produced water. The measurements were described with the triple layer surface complexation model coupled with the Pitzer activity coefficient method and a reactive transport model.

The experimental results show that Ba²⁺, Ca²⁺, Mg²⁺, and Sr²⁺ travels with negligible retardation (Pore volume injected ~ 1) through the FeO(OH) and sand porous media. While, selective adsorption was observed with the activated alumina porous medium, i.e. Ba²⁺ was the most retarded metals, then, Sr²⁺> Ca²⁺> Mg²⁺. The goal of this research is to test and design a smart material that adsorbs hazardous metals at high salinity.