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.