Transport of barium in fractured dolomite and sandstone saline aquifers

摘要

To understand the advective-dispersive transport of Ba in fractured dolomite and sandstone saline aquifers, we conducted core-flooding experiments and reactive transport simulations. We used intact and synthetic fractured dolomite and sandstone cores collected from formations where hydraulic fracturing (HF) wastewater is disposed in Oklahoma, USA. The core-flooding experiments were conducted using saline water containing typical concentrations of NaCl (90 g/L), Ca (5 g/L), Mg (1 g/L), and Ba (100 mg/L) in HF wastewaters. At typical concentrations of NaCl, Ca, and Mg in HF wastewater, our experimental results show similar Ba transport rates in both intact and fractured dolomites but faster Ba transport rates in intact than in fractured sandstones. We found a match between measured and simulated breakthrough curves of Ba in intact and fractured sandstones. This supports the hypothesis that the inhibitory effect of salinity on Ba sorption increases Ba transport through matrix pores bordering the fracture while reducing its transport through the fracture. This is reflected by a reduction of the overall rate of Ba transport through fractured dolomites and sandstones. We found that the effect of salinity in retarding Ba transport through fractured dolomites and sandstones increases with increased matrix porosity and/or fracture aperture size. We implemented the multiple interacting continua (MINC) method developed for modeling fluid flow in fractured porous media to successfully capture the effect of salinity, matrix porosity and fracture aperture size on Ba transport in fractured sandstones. The measured and simulated results have significant implications on efforts of field-scale simulations of Ba transport in dolomite and sandstone saline aquifers where HF wastewater is disposed. (c) 2018 Elsevier B.V. All rights reserved.