Oxidative Breakers Can Stimulate Halogenation and Competitive Oxidation in Guar-Gelled Hydraulic Fracturing Fluids

Abstract

A number of flowback samples derived from horizontally drilled hydraulic fracturing (HDHF) operations reveal consistent detections of halogenated organic species , yet the source of these compounds remains uncertain. Studies simulating subsurface conditions have found that oxidative “breakers” can halogenate certain additives, but these pathways are unverified in the presence of cross-linked-gels, common features of HDHF operations. Using a high-throughput custom reactor system, we implemented a reaction matrix to test the capacity for halogenation of two frequently disclosed compounds with demonstrated halogenation pathways (cinnamaldehyde and citric acid) across guar gels with varied types and concentrations of cross-linkers and oxidative breakers. Cinnamaldehyde halogenation proceeded most readily in borate cross-linked gels at high ammonium persulfate dosages. Citric acid formed trihalomethanes (THMs) broadly across the matrix, generating brominated THMs at higher levels of hypochlorite breaker. Isolated removals of cross-linker or guar enhanced or diminished certain product formations, highlighting additional capacities for relevant ingredients to influence halogenation. Finally, we analyzed flowback samples from the Denver–Julesberg Basin, finding that additions of oxidant enhanced halogenation. As a more realistic subsurface simulation, this work demonstrates strict criteria for the subsurface halogenation of cinnamaldehyde and the broad capacity for THM formation due to systematic oxidant usage as gel breakers in HDHF operations.

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.…”

“…As chlorine-based oxidants, these compounds are directly applicable to disinfecting agents 60,61 but have also been shown to form THMs when applied as breakers to guar-crosslinked fracturing uids. 50 We focused this analysis around ve different regions with the greatest disclosure rates of these breakers for comparison purposes: the Williston Basin, the Permian Basin, the Gulf Coast Basin, the Denver Basin, and the Anadarko Basin. Inputs included the appended pH, temperature, and bromide concentrations for each well location.…”

“…In these basins, DOC measurements were not frequently available and could not be approximated by regional values. Therefore, as a proxy for DOC in this analysis, we used the disclosed concentration of guar (oen the dominant organic chemical additive by mass 26,50 ) and adjusted the value according to the carbon fraction of guar's molecular mass (0.4 based on an average formula of C 6 H 12 O 6 ). Carbohydrates such as guar are known trihalomethane precursors, 63 and measurements of guar gum have been made in owback uids by measuring total carbohydrate content.…”

Synthesis of ammonium persulfate microcapsule with a polyaniline shell and its controlled burst release

“…5,6 Among them, oxidized breakers like ammonium persulfate (APS) are commonly used for water-based fracturing fluids. [7][8][9] Unfortunately, APS is too reactive, even at moderate temperatures, so adding the APS directly to the fracturing fluids will rapidly reduce the viscosity of the fracturing fluid prematurely and result in sand-out during the well construction process. 10 To solve these problems, microencapsulation technology with a controlled burst release is an ideal method.…”