Fuzzy clustering analysis of hydraulic fracturing additives for environmental and human health risk mitigation

Chemical additives used in hydraulic fracturing (HF) for unconventional natural gas production can be a risk to environmental and human health (EHH). The EHH risk is affected by three factors: the chemical hazard measured, the certainty of the measured hazard, and the use frequencies of additives. Limited studies have holistically assessed the EHH risks of HF additives. This study qualitatively analyzed the EHH risks of 105 representative HF additives used in British Columbia, Canada, based on the three previously listed factors using a fuzzy clustering analysis approach. The performance of additives on these factors was converted into indices using an indexing system. The indices were grouped into seven clusters according to their relative similarities. The EHH risk of each cluster was interpreted based on the resulting indices. Results show that additives grouped in clusters 7 and 2 have relatively high EHH risks, which require special attention in HF operations. Clusters 4, 1, and 5 were identified as having moderate EHH risks, while clusters 6 and 3 are of low EHH risk concerns. Many iron control agents were classified into cluster 7, indicating that this type of additives is associated with a high EHH risk. Many friction reducers and gelling agents were classified into cluster 4 characterized by the highest hazard uncertainty. Assessment of hypothetical fracturing fluids shows that using additives grouped in clusters with a low risk could help mitigate the EHH impacts posed by HF chemicals.