Nontarget Screening and Identification of Organic Additives and Transformation Products in Drilling Cutting and Flowback Water Related to Shale Gas Extraction

Abstract

With the rapid development of shale gas exploitation, large quantities of drilling cuttings (DCs) and flowback waters (FWs) laden with organics are produced. These organics, whose chemical compositions are largely unknown, could be toxic to organisms in the receiving environment. This study collected two time series of DCs and FWs from different shale gas exploitation platforms in the Sichuan Basin, China. We developed a nontarget analytical method to identify organic additives as well as their degradation products in these DCs and FWs and observed variable compositions and levels of organic additives in the DCs and FWs. The variation could be ascribed to the varied geological shale formations and unique drilling techniques. Alcohol ethoxylates (AEOs) and quaternary ammonium compounds (QACs) were identified as the main additives in the DCs from water-based drilling cutting with AEOs and alkylbenzenesulfonate in the related FWs. Meanwhile, nonylphenol ethoxylates (NPEOs) and QACs were the predominant surfactants in oil-based drilling cutting, with polyethylene glycols (PEGs) and AEOs dominating in related FWs. Carboxylated products of PEGs, polypropylene glycols, NPEOs, and octylphenol ethoxylates were widely identified in DCs and FWs, evincing biotic/abiotic transformation and chain-shortening of these surfactants downhole.