Carnegie Institute of Technology

Abstract

The Marcellus shale is one of the world’s largest unconventional natural gas reserves. Recovery of this deep-subsurface resource is enabled by hydraulic fracturing, a technology that increases the permeability of source rock and greatly improves the economics o f natural gas development. Hydraulic fracturing of deep, unconventional shale produces large volumes o f a brine solution known as produced water that is laden with metals, aqueous and non-aqueous organic matter and naturally-occurring radioactive material that can lead to challenging water management issues for the industry. The produced fluids recovered at the wellhead are typically stored in surface impoundments for a period of weeks or months prior to re-use or disposal. Microbial activity in produced water from different stages of natural gas development, and during impoundment can lead to adverse environmental impacts and an increase in gas production costs due production of odorous and toxic compounds, bio-corrosion and natural gas souring. Despite the importance of microorganisms in the management of produced water, there is little information about the microbial populations and their metabolic capabilities at the wellhead following hydraulic fracturing or in the impoundments during storage. With this in mind, the overarching objective of this work is to introduce a better understanding of the microbial populations and their metabolic capabilities in produced fluids from hydraulic fracturing in the Marcellus shale region. Four independent tasks were designed and completed that improve the understanding of microbial communities in produced water from hydraulic fracturing. Tasks 1 and 2 focus on determining changes in microbial community structure and functions in hydraulic fracturing fluids and produced water samples from the well head. Tasks 3 and 4 focus on the impact of impoundment and associated treatment on microbial communities and geochemistry in natural gas associated wastewaters. Task 1 determined dominant microbial communities in hydraulic fracturing fluids and produced water from shale gas extraction using 16S rRNA gene based clone libraries and tagencoded pyrosequencing. Results showed that distinct bacterial populations were observed in fracturing fluids and in produced water samples over time. While majority of the bacterial community in fracturing fluids constituted aerobic species, their relative abundance decreased in produced water with an increase in halotolerant, anaerobic/facultative anaerobic fermentative and sulfidogenic species. This task provides evidence of long term subsurface selection of the microbial community induced through hydraulic fracturing. Task 2 determined the functional potential of microbial communities in hydraulic fracturing source water and produced water using metagenomic sequencing. The metabolic profile revealed quantitative and qualitative differences in genes responsible for carbohydrate metabolism, respiration, sporulation and dormancy, iron acquisition and metabolism, stress response and sulfur metabolism in the produced water samples as compared to the fracturing source water sample. These results suggest that microbial communities and their functional capabilities are responsive to environmental and geochemical changes induced through hydraulic fracturing. Task 3 determined the changes in microbial community composition at different depths of flowback water impoundments that utilized different water management strategies using 16S rRNA clone libraries. Results showed that microbial communities in the untreated impoundment and the biocide amended impoundment were depth dependent, diverse and most similar to anaerobic, sulfidogenic, methanogenic and fermentative species. The bacterial community in the pretreated and aerated impoundment was uniform with depth, less diverse and most similar to known iodide oxidizing bacteria. This study provides evidence for emergence o f deleterious microbial communities in that can create environmental and health concerns due to emission of hydrogen sulfide, methane and volatile organic carbons in open impoundments. Task 4 determined the impact of aeration on the microbial community composition and geochemical parameters in a produced water impoundment. The microbial ecology at different depths of the impoundment was characterized before and after aeration using 16S rRNA gene based clone libraries and pyrosequencing. Prior to aeration, the surface water of the impoundment was relatively more oxidizing compared to deeper waters that were characterized by sulfidic, anoxic, and reducing conditions. The microbial community was also stratified, with the deeper waters dominated by anaerobic halophilic microorganisms such as sulfidogenic and fermentative bacteria, and methanogenic archaea. Identification of sulfidogenic bacteria and the presence of sulfide in the deeper waters provided evidence of biogenic sulfide production. Shortterm aeration (9 days) did not cause a major shift in microbial community composition, but resulted in oxidizing conditions that are likely to suppress metabolic activities of sulfidogenic and fermentative microorganisms. This body of work improves understanding of microbial populations in produced fluids from different stages of natural gas development. Results from this dissertation will enable development of more informed and sustainable produced water management practices.