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Lookup NU author(s): Dr Shannon FlynnORCiD
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND).
© 2022. The combination of hydraulic fracturing with horizontal drilling has revolutionized oil and gas production. However, most of our understanding of the subsurface mechanisms and chemical interactions that occur during the process come from analyses of flowback and produced water (FPW). While the chemical composition of FPW can provide some information to understand water-rock interactions in the subsurface, the mechanisms by which dissolved species, including potentially toxic heavy metals (PTHM), are mobilized remain poorly constrained. In this study, we used stirred benchtop reactors to simulate the geochemical processes that occur when injected hydraulic fracturing fluid (HFF) interacts with reservoir rock formations of the Upper Devonian Duvernay Formation, a mudstone formation that is an important hydraulic fracturing target in west-central Alberta, Canada. Our aims were to: (1) assess whether our laboratory methods can be used to predict the inorganic chemistry of FPW, including concentrations of PTHM, and (2) to ascertain the reaction kinetics and mechanisms of the release of inorganic components from reservoir rocks. Our results indicate that elemental concentration data from reactor experiments coupled with saturation indices modelling can be used to predict the assemblage of solid phases that precipitates downhole, such as barite + celestine + gypsum. High salinity experiments (0.5 M NaCl), simulating FPW reuse, showed increased concentrations of many dissolved species with increasing salinity. Our findings were corroborated with geochemical modelling of FPW samples collected from operating unconventional wells in the Duvernay Formation. FPW from wells using a mixture of recycled produced water (RPW) and fresh source water to make up the injected HFF had higher concentrations of many elements, including the PTHM, Ba, Sr, and As. Our work illustrates the potential environmental risks of using RPW in hydraulic fracturing operations in the event of a spill and it provides a robust benchtop approach to predict the leaching of elements from the host rock during hydraulic fracturing.
Author(s): Snihur KN, Swaren LR, von Gunten K, Harris NB, Wilson SA, Gingras MK, Konhauser KO, Flynn SL, Alessi DS
Publication type: Article
Publication status: Published
Journal: Chemical Geology
Year: 2022
Volume: 591
Print publication date: 05/03/2022
Online publication date: 06/01/2022
Acceptance date: 04/01/2022
Date deposited: 24/03/2022
ISSN (print): 0009-2541
ISSN (electronic): 1872-6836
Publisher: Elsevier BV
URL: https://doi.org/10.1016/j.chemgeo.2022.120718
DOI: 10.1016/j.chemgeo.2022.120718
ePrints DOI: 10.57711/fm2v-r824
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