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Identification of Geochemical Processes During Hydraulic Fracturing of a Shale Gas Reservoir: A Controlled Field and Laboratory Water‐Rock Interaction Experiment

A detailed study on geochemical processes following hydraulic fracturing can provide important information on the origin of solutes and potential improvement of fracturing technology. However, this remains difficult due to the low resolution of flowback water and high salinity of formation water. To fill this knowledge gap, a shale‐gas well was drilled and freshwater was used to fracture the shale. In parallel, laboratory water‐rock interaction experiments were conducted. The intensive sampling for flowback water and the use of multiple isotopes provided novel and detailed insights into the water‐rock interactions after hydraulic fracturing. The results showed that beyond mixing processes, cation exchange, adsorption/desorption, and barite precipitation were observed both in the laboratory and field studies. Although oxidation of pyrite was observed in most of the laboratory experiments, our findings demonstrate that this process was not evident in field flowback samples that were dominated by mixing of fracturing fluids and formation water.