Probing the Influence of Reactions between Fracture Fluids and Marcellus Shale on the Composition of Major Ion and Trace Element Fluid Chemistry in Flowback Waters

Hakala, Alexandra; Joseph, Craig; Marcon, Virginia; Bank, Tracy; Hedges, Sheila; Malizia, Thomas R.; Mouser, Paula; Liu, Shuai

Increased natural gas production from shales is due to the deployment of hydraulic fracturing technologies. Current practices employ large volumes of water with chemical additives, and also result in the production of flowback waters that require treatment before reuse or disposal. An understanding of changes in fluid chemistry due to fracturing fluid-shale reactions provides direct input for reservoir design, and also may guide development of strategies for managing and disposal of solid and liquid wastes.

In this study we investigated Marcellus Shale metal extractability and reactivity with fracturing fluids through bulk extractions, and fracture fluid-shale reactions in high pressure, high temperature autoclave systems. The primary goals for this study are to evaluate the role of shale-fluid reactions on controlling flowback water chemistry, and to evaluate the potential for metals to be extracted from organic-rich shales under various environmental conditions.

Metal extractability studies focused on Marcellus Shale core and outcrop powders and rock chips were performed under different temperature and pressure conditions with a variety of extractants. Reactions between synthetic fracturing fluids (designed based on information from FracFocus) and Marcellus Shale core are ongoing in high pressure, high temperature autoclave systems to evaluate changes to both trace element and total dissolved solids composition of the fluid, and changes to rock morphology and mineralogy, over time. Experimental results will be used to identify the primary solid phases controlling changes to fluid chemistry.

Our results to date show that, despite no statistical differences in trace metal concentrations in core and outcrop samples, extractability varies as a function of sample type and, generally, metal extractability is higher in outcrop samples. For example, in batch extractions using powdered rock samples the extractability of U by oxidation of the organic matter with H2O2 is higher in outcrops (~10%) compared to cores (~0%) . For our rocking autoclave experiments, we anticipate that reactions between synthetic fracturing fluid and natural carbonate and clay minerals present in our samples will result in observable geochemical changes. Ongoing studies will 1) determine the rate of metal leaching and the influence of increased surface area on metal extractability, and 2) identify the primary reactions that occur between fracturing fluids and shales.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013