Advanced organic characterization of hydraulic fracturing wastewaters

Abstract

Advancements in technology have allowed for the utilization of previously unattainable natural gas resources. Hydraulic fracturing (HF) is a process used in the extraction of underground resources to increase oil, natural gas, and water production rates when these resources are located in rock formations with a naturally low permeability. Horizontal fracturing, often referred to as high volume fracturing, is the preferred method for removing natural gas from shale facies. After the fracturing event is complete, injection water returns to the surface as HF wastewater (HFWW). In the beginning of the flowback period, this wastewater is thought to be more representative of the injection water and is referred to as flowback water. As the flowback period continues, this water is more influenced by the shale facies and are referred to as produced water. The United States produces 870 billion gallons of produced water annually. Produced water is comprised of a geogenic portion, consisting of compounds native to the geologic formation, and additives, which contain chemicals used to stimulate the fracturing formation and aid in production. Recently there has been an increased push from industry, the scientific community, and the public, suggesting produced water from oil and gas (O&G) operations could potentially represent a new water source for areas with water scarcity problems, such as Colorado. Although alternative uses for this water could greatly benefit communities, careful consideration of the chemical composition must be given before reuse or treatment. The objective of this dissertation was to characterize HFWW throughout the fracturing process and their interaction in the environment in the event of a spill. Four research efforts were undertaken to evaluate this topic: identify new analytical methods needed for complete chemical characterization (Chapter 2), describe the temporal variability known chemical constituents of HFWW (Chapter 3), identify and describe the unknown chemical variation (Chapter 4), and simulate a HFWW surface spill in an agricultural soil under environmentally relevant conditions (Chapter 5). Chapter 2 focused exclusively on the organic fraction of this wastewater. It was found that many organic chemicals remain unidentified, and targeted approaches for organic chemical analysis alone will be insufficient for complete organic chemical characterization. This dissertation presents applications of under-utilized approaches that may serve as potential solutions to address the issues created by the complex matrices inherent to flowback and produced water. The temporal variation identified in Chapter 3 found the presence of numerous surfactant homologs, including biocides, with the highest levels at the beginning of the flowback period. It was also discovered that three different stages exist in the flowback period: the flowback stage, the transition stage, and the produced water stage. The results from Chapter 4 found that numerous homologous series were present. The increase in homologous series during the transition stage corresponded with variability described in the principal component analysis of nontargeted high resolution mass spectrometry data. Finally, Chapter 5 demonstrated that no surfactants or their transformation products were found in leachate samples. Thus, in this environment, under these time constraints, these compounds are unlikely to travel far from the initial spill site. However, the leaching of trace metals due to salts was observed and could pose a threat to ground and surface waters. The results of this dissertation motivate further efforts for complete characterization of HFWW; these efforts may lead to significant improvements in HFWW treatment, potentially leading to the beneficial reuse of these waters.