Halogenation Chemistry of Hydraulic Fracturing Additives under Highly Saline Simulated Subsurface Conditions

Abstract

Unconventional natural gas extraction via hydraulic fracturing coupled with horizontal drilling (HDHF) has generated disruptive growth in the domestic energy sector. Field analyses of residual HDHF fluids have detected halogenated species, potentially the product of unexplored reactions between authigenic halides and HDHF additives. Utilizing a custom high-pressure reactor system, we simultaneously screened 12 frequently disclosed, functionally diverse HDHF additives to uncover transformation chemistry. One emergent pathway, the halogenation of cinnamaldehyde in the presence of ammonium persulfate, demonstrated the potential for oxidative breakers to react with halides to yield reactive halogen species. Halogenated product formation, product distribution, and kinetics were evaluated with respect to shale well subsurface condition, linking transformation risk to measurable well-dependent characteristics (e.g., halide compositions, well temperatures, and pH). In a representative flowback brine, the brominated product dominated on a molar percent basis (6 ± 2%, as normalized by initial cinnamaldehyde loading) over chlorinated (1.4 ± 0.4%) and iodinated forms (2.5 ± 0.9%), reflecting relative halide abundance and propensity for oxidation. This work demonstrates that relevant subsurface reactions between natural brines and hydraulic fracturing additives can result in the unintended formation of halogenated products.

Flowback verses first-flush: new information on the geochemistry of produced water from mandatory reporting

“…3,5,7 To our knowledge, this is the rst time that halogenated aromatic compounds have been identied as additives to hydraulic fracturing uids in California, although previous studies have reported halogenated reaction products in owback and wastewaters from oil and gas extraction. [57][58][59] Chemical use and water use was found to vary with factors such as the geological reservoir (as identied by FAP) and the companies conducting the stimulation treatment. Although water use intensity varied by reservoir geology, large differences in water use were observed between practitioners in the same geological deposit.…”

A geospatially resolved database of hydraulic fracturing wells for chemical transformation assessment

“…These higher temperatures can activate persulfate (disclosed as a "breaker") to sulfate radical, which is capable of oxidizing concentrated halides to reactive species that can go on to halogenate other additives. 39,50,[65][66][67] Thus, we classied codisclosures of persulfate at the same site (n ¼ 6352) as being of higher halogenation forming potentials. Finally, to isolate the wells with the highest likelihood of halogenation, we highlighted wells with disclosed persulfate usage in the top 25 th percentile of reported concentrations and satised the other reaction conditions.…”

“…To demonstrate the utility of the dataset for evaluating qualitative transformation predictions (i.e., the likelihood a transformation will occur based on known "rules" or criteria for the transformation related to geochemical and geophysical conditions), we conducted a case study drawing on existing knowledge of cinnamaldehyde halogenation pathways. 28,38,39,50 Beginning with a generated list of wells containing cinnamaldehyde disclosures, we set criteria for subsurface conditions reported to encourage cinnamaldehyde halogenation; e.g., high temperature (greater than or equal to 60 C) and halide concentrations (greater than or equal to 50 000, 500, and 25 mg L À1 chloride, bromide, and iodide, respectively), plus high values of persulfate breaker disclosed (i.e., masses in the top quartile of disclosures for this oxidant). For comparison purposes, we also highlighted wells where the reaction criteria were met except for high oxidant usage.…”

“…Across all historical FracFocus reporting, cinnamaldehyde appeared in disclosures for 14 175 out of 107 144 distinct wells (13.2%). To isolate wells in which reactive halogen species might form and add to cinnamaldehyde (a probe chemical for other a-unsaturated aldehydes), we screened for wells with subsurface conditions that met or exceeded the experimental "requirements" determined in Sumner and Plata: 39 Cl À and Br À concentrations of at least 50 000 and 500 mg L À , respectively, and a temperature of at least 60 C. Of the total cinnamaldehyde wells, 1726 met those reaction criteria, notably in the Williston (n ¼ 494), Anadarko (220), Permian (513), and Gulf Coast (344) basins ( Fig. 1), which tend to have elevated temperatures.…”

“…26,27 Equipped with an understanding of subsurface conditions, 38 researchers have simulated the shale well parameter space in laboratory systems to interrogate and characterize subsurface reaction pathways, demonstrating conditions or additives that can either mitigate or encourage transformation. Analyses of cinnamaldehyde (a corrosion inhibitor), 39 glutaraldehyde (a biocide), 40 and polyacrylamide (a friction reducing polymer) 41 have elucidated problematic halogenation, agglomeration, and degradation pathways, respectively. However, without predictive well models these results serve only to explain past detections in the eld, ultimately a reactive response to an emerging issue.…”