Laboratory study of trace element release and environmental risks from shale-fracturing fluid interactions

Area of Science:

• Geochemistry
• Environmental Science
• Earth Science

Background:

• Hydraulic fracturing (fracking) is a key natural gas extraction method.
• Black shales, like the Marcellus, are targeted for extraction.
• Fracking fluid interacts with shale, altering mineralogy and mobilizing trace elements.

Purpose of the Study:

• Investigate trace element release and redistribution during fracking.
• Analyze geochemical reactions between fracking fluid and shale.
• Assess long-term environmental mobility of mobilized elements.

Main Methods:

• Laboratory experiments simulating fracking stages (shut-in, flowback, production, closure).
• Analysis of geochemical reactions and mineralogical changes in shale.
• Monitoring of trace element mobilization and redistribution.

Main Results:

• Acid additions during shut-in dissolve carbonates and sulfides, leading to sulfide oxidation and mineral transformations.
• Trace elements are released via acid dissolution during initial production.
• Some elements (lanthanides, Zn, Sr) are lost from the solid phase.
• Elements like As, Mo, and U are converted to more mobile mineral forms.

Conclusions:

• Fracking processes significantly alter shale geochemistry.
• Mobilized trace elements, particularly As, Mo, and U, pose risks for long-term environmental mobility.
• Potential for drinking water contamination increases with aging well networks.