Mechanical degradation of polyacrylamide at ultra high deformation rates during hydraulic fracturing

Boya Xiong, Prakash Purswani, Taylor Pawlik, Laxmicharan Samineni, Zuleima T. Karpyn, Andrew L. Zydney, Manish Kumar

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Degradation of drag reducer polyacrylamide under high volume hydraulic fracturing (HVHF) conditions alters its polymer size, distribution and chemical composition, potentially affecting the toxicity and treatability of the resulting wastewater. This study focused on a non-chemical pathway-mechanical degradation of polyacrylamide under ultra-high fluid strain conditions (∼107 s-1) that uniquely exist during HVHF but has not yet been explored experimentally. PAM solutions were subjected to an abrupt contraction into a narrow capillary driven by a high-pressure precision pump (∼10 000 psi). The change in polyacrylamide size distribution was evaluated by size exclusion chromatography. The peak polymer molecular weight (MW) after a single-pass through the capillary decreased from 107 to 7 × 105 Da at deformation rate = 4 × 106 s-1. The extent of degradation increased with , approximately following an empirical scaling relationship of for the polyacrylamide with an initial MW ≈ 107 Da. Degraded PAM with lower MW (<106 Da) showed minimal degradation during multiple flow passes even at high deformation rates, suggesting that most mechanical degradation occurs at the first entrance into the fracture. Relative to chemical degradation, mechanical degradation caused a narrowing of the MW distribution due to greater degradation of the larger MW polymers and preferential mid-chain polymer scission. In addition, we saw no detectable change in chemical composition during mechanical scission, in contrast to the generation of carbonyl groups during oxygenic radical induced chemical degradation. Combining both chemical and mechanical mechanisms during HVHF operation, we propose an initial mechanical breakage of polymer chain by fluid strain, followed by chemical degradation under the high temperature and appropriate mineralogical conditions. These findings provide critical information for understanding the nature of degradation byproducts from polyacrylamide, and the treatability of polyacrylamide fragment-containing wastewaters.

Original languageEnglish (US)
Pages (from-to)166-172
Number of pages7
JournalEnvironmental Science: Water Research and Technology
Volume6
Issue number1
DOIs
StatePublished - Jan 2020

All Science Journal Classification (ASJC) codes

  • Environmental Engineering
  • Water Science and Technology

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