Examining the Feasibility of using Coal Mine Drainage as a Hydraulic Fracturing Fluid

Abstract

Much of the current concern about hydraulic fracturing revolves around the treatment and disposal of wastewaters that come up out of the well after fracturing has occurred. These “produced waters” and “flowback waters” in some cases are high in concentrations of total dissolved solids (TDS), naturally occurring radioactive material (NORM), and metals. There are currently many ways these wastewaters are managed including being recycled on site, treated at commercial waste water treatment plants, or shipped away for storage in federally permitted underground injection wells. This study suggests that by supplementing wastewater with high-sulfate coal mine drainage (CMD), on site recycling can be even more effective through the removal of high metal concentrations and NORM from the wastewater. This could potentially allow for 100% waste water recycling, saving local water resources, while a legacy environmental problem may be remediated. This study was focused on the idea that by mixing coal mine drainage with flowback or produced water, many of the negative characteristics of both fluids can be remediated. The sulfate can be removed from the coal mine drainage, and with it, the barium and radium can be removed from the coal mine drainage. Mix ratios of 1:4, 1:2, and 3:4 were used for this study and in almost every case a majority of the radium (100% for each ratio), barium (75, 90, and 80% respectively), and sulfate (90, 75, and 40% respectively) precipitated out of the mixture. Barium and radium concentrations were found to be strongly correlated within each the sample (r2 of .815). In addition to that, the removal of those solutes was also found to be correlated (r2 of .75). Finally, using spatial analysis and a number of input factors, it was found that on average the use of coal mine drainage is between $30 and $200 thousand more expensive to use per well than fresh water. These results indicate that mixing AMD and flowback water is an effect means of water treatment for re-use as hydraulic fracturing fluid. Although not currently cost effective, the potential to clean up a legacy environmental problem has inspired policy makers to begin the process of making the use of coal mine drainage more cost effective with less legal consequence.