TRANSPORT OF HEAVY METALS THROUGH SHALE ROCK FRACTURES DUE TO THE INJECTION OF FRACTURING FLUIDS: MODELING AND SIMULATION

We are studying the impact of fracturing fluid organic additives (guar gum, polyacrylamide and glutaraldehyde) on the transport of commonly encountered heavy metals (Ba, Sr, As, and Se) in fractured shale gas reservoirs. Little is currently known regarding the effect of fracturing fluid organic additives on the transport of heavy metals through fractures under downhole conditions of shale gas reservoirs. In order to determine the feasibility of shallow aquifers contamination by heavy metals soured from shale gas reservoirs, a reactive transport model is being developed using TOUGHREACT open source program as a framework. The model accounts for the effect of pH changes on the sorption of heavy metals on the surface of shale rocks, the effect of minerals dissolution/precipitation on pH, as well as advective and dispersive mass transport processes through fractured and porous media. The model is being verified and calibrated by conducting core-flooding experiments at shale gas reservoir conditions. Our preliminary results indicate that the presence of fracturing fluid organic additives, as well as changes in the pH of the fluid due to dissolution/precipitation of minerals greatly affect the transport of heavy metals. The implications toward potential contamination of shallow aquifers over long periods of time will be discussed.