Date of Award:

5-2017

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Geosciences

Department name when degree awarded

Geology

Committee Chair(s)

Benjamin Burger

Committee

Benjamin Burger

Committee

Seth Lyman

Committee

Dennis Newell

Abstract

What effect does the development of oil and gas have on the observed air quality (i.e., increased ozone, carbon dioxide (CO2), volatile organic compounds (VOCs), and/or methane emissions) in northeastern Utah? What percentage of these gases is natural background emissions, and what percentage is due to the recent oil and gas development in the region? Emissions in this text refer to gases released from the earth’s surface to the atmosphere. Methane is the primary compound in natural gas. Natural gas is a naturally occurring hydrocarbon gas mixture. Emissions of methane, non-methane hydrocarbons (NMHC), and CO2 at 27 natural gas well pads, 11 non-well locations in oil and gas fields, and seven hydrocarbon-bearing outcrops in eastern Utah between 2013 and 2016 were measured. Emission measurements were collected using a dynamic flux chamber (DFC). Methane emissions were the focus of this study, but emissions of other compounds were also measured to better understand the sources and characteristics of methane emissions. Background methane fluxes were all (mg) meter (m)-2 hour (h)-1. Methane emissions from well pad soils were commonly higher closer to the wellhead, though exceptions existed. Methane flux from well pad soils ranged from -5.6 to 70,000 mg m-2 h-1 , though 81% of sampled well pad soils had fluxes < 10 mg m-2 h-1. Based on analysis of non-methane hydrocarbons (NMHC) emission data, emissions from 68% of the sampled well pad soils were due to leaks of raw natural gas. The sources of emissions from the remaining well pad soils were likely a combination of raw gas leaks, liquid hydrocarbon spills, and/or methanogenic processes. CO2 emissions were higher than methane emissions 92% of the time at well sites. CO2 emissions could have originated from leaking CO2 in natural gas, or CO2 emitted from bacterial decomposition of organic matter in the soil. Total combustible soil gas is the amount of hydrocarbon gases that are present in the interstitial space of soil. Total combustible soil gas concentrations were measured at 21 wells. Combustible soil gas concentrations and methane emissions were poorly correlated. Soil gas and emissions measurement locations were nearby but not identical, and the poor correlations could be due to non-uniform distributions of measured gases in the soil. In summer 2015, soil properties were also analyzed to understand emissions better. At well sites, low soil pH and high total organic carbon content were associated with increased methane emissions. Wells categorized as shut-in had the highest average methane flux. Measured methane soil emissions were scaled-up for the entire Uinta Basin to estimate the overall emission from well pad soils, and to compare soil emissions with other natural gas-related sources. Methane emissions from natural gas facilities have been previously quantified. Emission measurements from this study were compared against other emission sources at natural gas facilities to estimate the significance leaking wells have on air quality. The status of the well can change throughout the lifetime of a well. Producing and shut-in gas wells were estimated to emit 16.1 ± 4.3 and 8.6 ± 3.2 (90% confidence interval) t y-1 (tonne/year) of methane in the Uinta Basin, respectively, which is < 0.1% of total methane emissions from all natural gas sources.

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