Temporal characterization and statistical analysis of flowback and produced waters and their potential for reuse

Hydraulic fracturing (HF) has allowed for the utilization of previously unattainable shale oil and gas (O&G) resources. After HF is complete, the waters used to increase the facies' permeability return uphole as wastewaters. When these waters return to the surface, they are characterized by complex organic and inorganic chemistry, and can pose a health risk if not handled correctly. Therefore, these waters must be treated or disposed of properly. However, the variability of these waters' chemical composition over time is poorly understood and likely limits the applicability of their reuse. This study examines the water chemistry of a hydraulically fractured site in the Niobrara formation throughout the flowback period. Samples were collected every other day for the first 18days, then on a regular basis for three months. We identified HF fluid additives, including benzalkonium chlorides (BACs), alkyl ethoxylates (AEOs), and polyethylene glycols (PEGs), as well as geogenic components present in flowback and produced waters, their overall temporal pattern, and variables affecting the reuse of these waters. Observations indicate that alkalinity and iron may limit the reuse of these waters in HF, while chloride and alkalinity may limit the use of these waters for well-casing cement. The presence of numerous surfactant homologs, including biocides, was also observed, with the highest levels at the beginning of the flowback period. Principal component analysis identified three unique groupings in the chemical data that correspond to different stages in the flowback period: (1) the flowback stage (days 1-2); (2) the transition stage (days 6-21); and (3) the produced water stage (days 21-87). Results from this study will be important when designing decision frameworks for assessing water treatment options, particularly if onsite treatment is attempted. Successful reclamation of these waters may alleviate stress on water resources that continues to negatively impact the U. S.