Reactive transport modeling of produced water disposal into dolomite saline aquifers: Controls of barium transport

Experimental results on barium transport in dolomite are used to formulate, calibrate, and validate a reactive transport model of produced water disposal into dolomite saline aquifers. The model accounts for sorption, dissolution/precipitation reactions of minerals (dolomite, calcite, barite, gypsum, and witherite) and complexation and acid-base reactions of most abundant ionic species (H⁺, HCO₃⁻, SO₄²⁻, Ca²⁺, Mg²⁺, and Cl⁻) in produced waters including Ba²⁺ which is the most common and abundant heavy metal present in produced water from oil and gas reservoirs. The model is applied to determine the chemical controls of barium transport in Arbuckle dolomite aquifers. The simulated scenario corresponds to produced water disposal through a Class II injection well located near an abandoned well that can facilitate the transport of barium to underground sources of drinking water (USDW). Simulation results reveal that most suitable dolomite aquifers to prevent the contamination of USDW by barium are dolomite aquifers of high SO₄²⁻ content (>1000 mg/L). The mobility of barium which is promoted by the formation of Ba(Cl)⁺ and competition of cations (Ca²⁺ and Mg²⁺) for hydration sites of dolomite can be suppressed by the precipitation of barium as barite in dolomite saline aquifers of high SO₄²⁻ content. A sensitivity analysis conducted using a two-level factorial design of experiments indicates that barium transport can be controlled by the initial concentration of a single ionic specie (mostly SO₄²⁻) or the concentration of various ionic species (e.g., SO₄²⁻, Cl⁻, and Mg²⁺). This depends on the chemical composition of both the dolomite saline aquifer and injection produced water. This work highlights the potentiality of a reactive transport simulation approach to conduct compatibility analysis of dolomite saline aquifers and produced waters to select dolomite aquifers and/or decide on treatment methods to prevent the contamination of USDW by barium.