THE ROLE OF SHALE KEROGEN – HYDRAULIC FRACTURING FLUID INTERACTIONS IN HYDROCARBON TRANSPORT AND CONTAMINANT RELEASE

The recent increase in unconventional oil and gas exploration and production has
stimulated significant research on hydraulic fracturing, but the many possible chemical
reactions between the fracturing fluids and the minerals and organic matter comprising the
shale host rocks are not well understood. In particular, there is a lack of information
concerning the evolution of organic matter in shale reservoirs during hydraulic fracturing
operations. Organic matter, primarily in the form of kerogen, is the dominant source of
hydrocarbons in shale plays and is therefore critical to productivity. In addition, kerogen is
enriched in metals, making it a potential source of contaminants to produced waters. In the
present study, two different kerogens of contrasting types and maturities (Green River and
Marcellus) were reacted with a variety of fluids, including a commonly used synthetic
hydraulic fracturing fluid, in order to determine the effect of these fluids on shale minerals
and organic matter before and after exposure and solid-fluid partitioning. No trends in the
concentrations or speciation of carbon, hydrogen, or oxygen were quantifiable, due to
either the absence of reactions or difficulties in detecting such trends because of significant
natural heterogeneity in the kerogen samples. However, solubilization of organic
compounds occurred in the more immature Green River kerogen when it was exposed to
fracturing fluid. The same effect was not observed in experiments involving Marcellus
kerogen. The organic compounds released from the Green River kerogen to solution
impacted Fe speciation in particular. Additionally, experiments with Green River and
Marcellus kerogens and either fracturing fluid or pH 2 water mobilized metal contaminants.
The source of contaminants varies between the two kerogens, with metals in the Marcellus
largely sourced from associated pyrite, and with metals within the Green River sourced
from a combination of accessory mineral dissolution and desorption from kerogen. These
results suggest that chemical reactions between fracturing fluid and more immature
kerogens can impact reservoir geochemistry, potentially affecting production. However,
the apparent stability of kerogenic pores based on the lack of observable changes in
functional group chemistry of either kerogen studied suggests that important transport and
storage parameters such as wettability and gas sorption capacity should remain constant
throughout the lifetime of a well.

Dustin, Megan. (2017). THE ROLE OF SHALE KEROGEN – HYDRAULIC
FRACTURING FLUID INTERACTIONS IN HYDROCARBON
TRANSPORT AND CONTAMINANT RELEASE. Stanford Digital Repository. Available at: http://purl.stanford.edu/qf258sx1103