Natural gas production from Marcellus Shale formation has significantly changed the energy landscape in recent years. It is important to understand the reactive transport of chemical species in Marcellus Shale waters (MSW) released into groundwater aquifers. These systems are typically heterogeneous with large spatial variation on physical and geochemical properties. To understand the impact of mineral spatial distribution on the reactive transport of chemicals from MSW, three 2D flow-cell (40.0 cm×12.0 cm×1.0 cm) experiments were carried out with a pulse of MSW release. All flow cells have the same clay content (vermiculite, 23% volume) within quartz matrix but different spatial patterns characterized by the relative length of the clay zone versus the total length of the flow cell (L). The uniform flow cell contains well-mixed clay and quartz and therefore has the highest clay-quartz contact area. The 1/4-Zone flow cell has five clay zones of one-quarter of the flow-cell length distributed evenly within the quartz matrix, while the 1/2-Zone flow cell has two clay zones with one-half of flow-cell length. Results showed that dominant reactions differ in the flow cells. In uniform flow cell, ion exchange reaction dominates so that most Ba goes to the solid phase, to an extent Ba cannot precipitate out with SO4 as barite (BaSO4) . In the 1/2-Zone flow cell, however, Ba concentration decreases mostly due to barite precipitation. In 1/4-Zone flow cell, both ion exchange and mineral precipitation contributed to Ba concentration decrease. In general, the 1/2-Zone flow cell has the smallest ion exchange capacity for other species including Na, Ca, Mg, K and heavy metals (Mn, Cu, Zn, Cd and Pb) as well. Our work emphasizes the importance of mineral spatial pattern in regulating not only reaction rates but also the type of reactions in controlling that the reactive transport and fate of MSW chemicals.

Effects of mineral spatial distribution on the reactive transport of Marcellus shale waters

254th National Meeting (2017)

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