Exploring the hydraulic fracturing parameter space: a novel high-pressure, high-throughput reactor system for investigating subsurface chemical transformations

Abstract

Hydraulic fracturing coupled with horizontal drilling (HDHF) involves the deep-well injection of a fracturing fluid composed of diverse and numerous chemical additives designed to facilitate the release and collection of natural gas from shale plays. Analyses of flowback wastewaters have revealed organic contamination from both geogenic and anthropogenic sources. The additional detections of undisclosed halogenated chemicals suggest unintended in situ transformation of reactive additives, but the formation pathways for these are unclear in subsurface brines. To develop an efficient experimental framework for investigating the complex shale-well parameter space, we have reviewed and synthesized geospatial well data detailing temperature, pressure, pH, and halide ion values as well as industrial chemical disclosure and concentration data. Our findings showed subsurface conditions can reach pressures up to 4500 psi (310 bars) and temperatures up to 95 °C, while at least 588 unique chemicals have been disclosed by industry, including reactive oxidants and acids. Given the extreme conditions necessary to simulate the subsurface, we briefly highlighted existing geochemical reactor systems rated to the necessary pressures and temperatures, identifying throughput as a key limitation. In response, we designed and developed a custom reactor system capable of achieving 5000 psi (345 bars) and 90 °C at low cost with 15 individual reactors that are readily turned over. To demonstrate the system's throughput, we simultaneously tested 12 disclosed HDHF chemicals against a radical initiator compound in simulated subsurface conditions, ruling out a dozen potential transformation pathways in a single experiment. This review outlines the dynamic and diverse parameter range experienced by HDHF chemical additives and provides an optimized framework and novel reactor system for the methodical study of subsurface transformation pathways. Ultimately, enabling such studies will provide urgently needed clarity for water treatment downstream or releases to the environment.

Halogen Radicals Contribute to the Halogenation and Degradation of Chemical Additives Used in Hydraulic Fracturing

“…Although the role of halogen radicals in the degradation and halogenation of additives in hydraulic fracturing fluids has not yet been investigated, there are two primary reasons to suspect that they may be involved in these reactions. First, hydraulic fracturing fluids frequently have even higher halide concentrations (e.g., median Cl – and Br – concentrations of up to 4.6 M and 5.0 mM, respectively) than seawater or brines previously shown to be conducive to halogen radical formation. − ,,, Second, oxidative breakers (e.g., persulfate, S 2 O 8 2– ) are widely used to generate radicals (in particular, sulfate radical) at high temperatures (i.e., 40–100 °C) to break down polymer gels (i.e., guar). , The use of persulfate as an oxidative breaker is associated with the formation of halogenated products in hydraulic fracturing fluids, − and water treatment with sulfate radical in the presence of halides can lead to the halogenation of organic compounds. − Notably, sulfate radical generated from thermally activated persulfate is likely to generate halogen radicals because it can be scavenged directly by either Cl – or Br – (eqs and , ). In comparison, halogen radical formation from hydroxyl radicals is limited by the rapid reverse reaction of the intermediate ClOH •– (eq ), which limits its accumulation .…”

Emerging Trends in Biological Treatment of Wastewater From Unconventional Oil and Gas Extraction

“…(Luek et al, 2018). Formation of halogenated compounds of common fracking additives (cinnamaldehyde, epichlorohydrin and 2,2-dibromo-3-nitrilopropionamide) has been experimentally confirmed under simulated conditions of high pressure, high temperature, presence of oxidizing agents (ammonium persulfate) and salinity (Sumner and Plata, 2018). These halogenated compounds may need further monitoring as they are likely to be recalcitrant to biodegradation and pose health risks.…”

Effects of Carbonate Minerals on Shale-Hydraulic Fracturing Fluid Interactions in the Marcellus Shale

“…During hydraulic fracturing operations, the mixture of water and chemical additives that comprise HFF is in contact with the target shale formation for weeks and reacts with the brine and shale in the formation at high temperature and pressure. During this time, numerous interactions can take place that significantly alter HFF fluid chemistry, the mineral composition and petrophysical properties of shale, and the release of organic and inorganic contaminants (Hoelzer et al, 2016;Harrison et al, 2017;Paukert Vankeuren et al, 2017;Sumner and Plata, 2018aPilewski et al, 2019;Hakala et al, 2021). Studies conducted using benchtop reactors showed that multiple shale-HFF reactions could occur, such as mineral precipitation and dissolution, organo-metallic complex formation, ion adsorption onto shale organic matter and clay minerals, and organic matter degradation (Jew et al, 2017;Sumner and Plata, 2018a;Pilewski et al, 2019;Hakala et al, 2021).…”

“…During this time, numerous interactions can take place that significantly alter HFF fluid chemistry, the mineral composition and petrophysical properties of shale, and the release of organic and inorganic contaminants (Hoelzer et al, 2016;Harrison et al, 2017;Paukert Vankeuren et al, 2017;Sumner and Plata, 2018aPilewski et al, 2019;Hakala et al, 2021). Studies conducted using benchtop reactors showed that multiple shale-HFF reactions could occur, such as mineral precipitation and dissolution, organo-metallic complex formation, ion adsorption onto shale organic matter and clay minerals, and organic matter degradation (Jew et al, 2017;Sumner and Plata, 2018a;Pilewski et al, 2019;Hakala et al, 2021). Among these, mineral dissolution and precipitation reactions impact the porosity and permeability of shale the most.…”