Abstract
The combination of advances in hydraulic-fracturing and horizontal-drilling technologies has led to a resurgence in oil and gas activity in multiple regions across the United States. To minimize the impact of the increased water use, many oil and gas companies are pursuing fracture-flowback-water and produced-water recycling for subsequent drilling and fracturing operations. Common processes in a recycling strategy include metal precipitation to minimize scaling potential and electrocoagulation for removing solids that may foul a well when water is reused. In this study, precipitation of calcium, magnesium, barium, and strontium were examined experimentally by adding target ligands followed by solids separation with electrocoagulation. In addition, removal efficacy was modeled using commercially available chemical-equilibrium software (OLI Systems). The experimental results were compared with the predicted data at pH values of 9.5 and 10.2. The differences between the modeled data and the experimental data indicated a deficiency in the solid/liquid-separation process in the laboratory. Results also showed that the pH value did not affect the treatment efficiency, except in the case of magnesium; however, sequencing of softening relative to coagulation was important. An additional finding was that, on the basis of the target metal, either sulfate or carbonate needs to be greater than a threshold concentration to achieve precipitation goals. Chemical consumption at pH values of 9.5 and 10.2 was significantly different. Chemical-equilibrium modeling predicts that the average base usage was 30% lower at a pH of 9.5 compared with a pH of 10.2 and 34% lower for acid usage. The reduction in use experimentally was 27% for base and 43% for acid.
Published Version
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