A FIELD-SCALE SIMULATION OF BARIUM TRANSPORT IN CLASS II WASTEWATER INJECTION WELLS

Barium is the most common and abundant heavy metal present in hydraulic fracturing wastewater. Based on new findings regarding the variables controlling the transport of barium in deep saline aquifers where hydraulic fracturing wastewater is commonly disposed in the USA, a reactive transport model has been developed to assess the long-term risk of underground sources of drinking water (USDW) contamination by barium. The developed reactive transport model, which has been implemented using TOUGHREACT program as framework, accounts for important reactions such as the kinetic dissolution/precipitation of minerals and aqueous phase and surface complexation reactions of barium and competing cations (calcium and magnesium). Different to most heavy metal reactive transport models, the developed model includes the pH dependence of barium on surface complexation (sorption) reactions. The model has been verified using core-scale experimental results of barium transport in dolomite and sandstone cores. For the sake of practicality, a 3-dimensional geological model that corresponds to the Cushing oil field of Oklahoma has been used to conduct field-scale simulations of hydraulic fracturing wastewater injection into a Class II wastewater disposal well. The implications of the obtained simulation results will be discussed in the context of the long-term risk of hydraulic fracturing wastewater disposal into depleted oil reservoirs and deep saline aquifers.