Noble Gas and Hydrocarbon Geochemistry of Coalbed Methane Fields from the Illinois Basin
Thesis
Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University
By
Myles Thomas Moore Graduate Program in Earth Sciences
The Ohio State University 2016
Thesis Committee
Dr. Thomas Darrah (Chair) Dr. John Olesik (Committee) Dr. Frank Schwartz (Committee)
Copyright by Myles T. Moore 2016
Abstract
Research presented in this thesis investigates the hydrocarbon molecular content, major and noble gas composition, the isotopic composition of noble gases and hydrocarbons, and select dissolved ions of gases and fluids from producing coalbed methane (CBM) wells. Samples were collected from the Illinois Basin in Sullivan County, Indiana.
Samples analyzed in this study were compared with previously published data in the
Illinois Basin to gain a greater understanding of fundamental fluid systematics and methane formation in coalbed reservoirs.
Chapter 1: Conventional geochemical fingerprinting methods of hydrocarbon molecular and isotopic composition were used to determine the genetic source of natural gas in coalbed methane basins. Integration of isotopic and molecular hydrocarbon composition with noble gas geochemistry were used to determine the origin and migration of natural gas in the crust and relative role of coal seam waters and/or exogenous fluids in methane generation. Significant fluxes of exogenous thermogenic methane are observed in this coalbed methane reservoir.
Chapter 2: Standard methods that assume steady state modelling and empirical methods for determining the residence time of natural gas and groundwater in coalbed methane fields using radiogenic ingrowth of 4He are compared. Previous age dating methods are corrected by taking into account significantly increased 4He diffusional
ii rates specific to coal seams. By correcting for empirically determined rates of 4He accumulation, the geological time frame on which freshwater recharges into deeper sedimentary sequences, which may play a role in timing in which microbes are injected into coal beds and start to generate methanogenic natural gas, are more accurately constrained.
iii Dedication
Dedicated to my close friends, my parents Daniel Moore and Margaret Ruane-Moore, and my sisters Mary and Kate Moore.
iv Acknowledgements I would like to acknowledge my fellow lab mates Colin Whyte, Benjamin Grove,
Sharon Scott, Erica Maletic, Stephanie Poreda, and Dr. Jeremy Williams for help with sample collection, analysis, and reviews of earlier versions of these manuscripts. I would also like to thank Professors Frank Schwartz, John Olesik, and my advisor Dr.
Thomas Darrah for encouragement and support.
v
Vita
2010…….…...………………………...Mahopac High School
2014...... B.S. Water Resource Management,
State University of New York at Oneonta
2014 to Present……………………….Graduate Teaching Associate, School of Earth
Sciences at The Ohio State University
Publications
Moore, M., & Castendyk, D. 2013, Presence of mercury and comparison to other metals in lakes, rivers, and streams in central New York. Biological Field Station Annual Review 2013.
Field of Study
Major Field: School of Earth Sciences
vi
Table of Contents
Abstract……………………………………………………………………….………...ii
Dedication…………………………………………………………………………………..iv
Acknowledgments……………………………………………………………………...v
Vita…………………………………………………………………………………….vi
List of Tables…………………………………………………………………………....x
List of Figures………………………………………………………………………….xii
Summary……………………………………………………………………………...xiv
Chapter 1: Integrating Hydrocarbon Molecular Content and Isotopic Values of
Carbon and Hydrogen in Methane with Noble Gas Geochemistry.………………...…1
Abstract...... 1
1.1 Introduction...... 3
1.2 Background………..…………………………………………………...…………...6
1.2.1 Geological Background……..……………………………………...……………..6
1.2.2 Geochemical Systematics………………………………………………………....8
1.2.2.1 Formation and Identification of Hydrocarbon Gases……………….………...... 8
1.2.2.2 Noble Gas Systematics………………………………………………………...11
1.3. Materials and Methods……………………………………………………………15
1.3.1 Sample Selection………………………………………………………………....15
vii 1.3.2 Sampling and Analysis………………………………………………….……….16
1.3.3 Numerical Modeling….………………………………………………………….20
1.3.4 Graphical and Statistical Treatment of Data……….…………………………….21
1.4. Results………………………………………………………………………….….22
1.4.1 Gas Composition………………………………………………………………....23
1.4.1.1 Hydrocarbon and Major Gases…...………………………………………...... 23
1.4.1.2 Noble Gases………………………………………………………………….....24
1.4.2 Gas Isotope Composition………………………………………………………...26
1.4.2.1 Stable Isotopic Composition of Methane and Dissolved Inorganic Carbon…...26
1.4.2.2 Noble Gas Isotopic Composition...... 29
1.4.3 Selected Dissolved Ions...... 31
1.5 Discussion...... 32
1.5.1 Genetic Source of Natural Gases in the Springfield and Seelyville Formation.....32
1.5.2 Endogenous vs. Exogenous Thermogenic Gases………………………………....36
1.5.3 Potential Sources of Exogenous Thermogenic Gases…………..…………….…..41
1.6 Conclusions………………………………………………………………………..44
1.7 Future Work……………..………………….……………………………………...46
1.8 Acknowledgements……..………….………...………………….…………………48
References……………………………………...... …………………………………….49
Chapter 2: Constraining the Timing of Fluid and Gas Interactions in the Illinois Basin using the ingrowth of 4He in coal seams with thermogenic contributions...... 94
Abstract………………………………………………………………………..……….94
2.1 Introduction……...…………...………………………………………………….....96
viii 2.1.1 Geological Background…….…………………………………………………...100
2.2 Estimating Groundwater Residence Time Using Radiogenic 4He………………..103
2.3 Materials and Methods……………….……………………………...……………109
2.3.1 Sample Selection……...……………………….………………………………...109
2.3.2 Sampling and Analysis…………………………...……………………………..110
2.3.2.1 Gas Samples…………………………………………..…...………..………....110
2.3.2.2 Coal Seam Solids….…………………………………………………………...111
2.3.2.3 Calibrating the Diffusional Release of 4He from Mineral Grains….……..…...112
2.3.3 Graphical and Statistical Treatment of Data…….………….……………….…...113
2.4 Results………………………………………………………………...... ….114
2.4.1 Composition of Coal Seam Solids…...…………………………………….…….114
2.4.1.1 Radioactive Elements.……………………………………………...... ….114
2.4.1.2 Noble Gases in Coal Seam Solids..………………………………………..…..115
2.4.2 Stepwise Heating of Coal Samples to Determine Diffusional Release Rates ...... 116
2.4.3 Calculating Initial Water Volume………………………………………………..117
2.4.4 Residence Time Calculations……………………………………….…………...118
2.5 Discussion...…….………………………………………………………………….121
2.6 Conclusions..………………………………………………………………….…...126
2.7 Acknowledgements…..………………………………………………………..…...127
References……………….……………………………………………………………..128
Complete List of References.....………………………………………………………..152
ix
List of Tables
Chapter 1
Table 1.1 Major gas composition...…………...……………………….……………….68
Table 1.2 Statistical summary of major gas composition…..………….……………....69
Table 1.3 Noble gas elemental composition...………………………….……………...70
Table 1.4 Statistical summary of noble gas elemental composition..….……………....71
Table 1.5 Noble gas isotopic composition...…………………………………………...72
Table 1.6 Statistical summary of noble gas isotopic composition...…………………...73
Table 1.7 Stable isotopic composition of methane and dissolved inorganic carbon...... 74
Table 1.8 Statistical summary of the stable isotopic compositions of methane and dissolved inorganic carbon...………………………………………………………….75
Table 1.9 Select major anions...……………………………………………………….76
Table 1.10 Statistical summary of select major anions.……………………………….77
Table 1.11 Molecular and isotopic gas ratios.……………………………….………...78
Table 1.12 Statistical summary of molecular and isotopic gas ratios.……….………...79
Table 1.13 Correlation matrix of data…………..…………………………….……..…80
Chapter 2
Table 2.1 Location and depths of sampled coalbed methane wells…………..………144
Table 2.2 Concentrations of U, Th, 4He, and 21Ne* in coal samples from the
x Illinois Basin……….……………………………...……………………………….....145
Table 2.3 Statistical summary of noble gas isotopic composition..………...……...... 146
Table 2.4 Results of stepwise heating experiments on coal solid drillings from the
Illinois Basin………………………………………………………………………….147
Table 2.5 Concentrations of tritium and selected noble gas elemental and isotopic abundances………………………………………………….………………………....148
Table 2.6 Statistical summary of noble gas isotopic compositions.....……………...... 149
Table 2.7 Calculated 4He concentrations in groundwater and residence times using standard and empirical models….…...…………………………………………….…..150
Table 2.8 Statistical summary of residence time calculations...…...……...……...…....151
xi
List of Figures
Chapter 1:
Figure 1.1 Stratigraphic column, base map, and cross section of Illinois Basin…....…58
Figure 1.2 Locations of coalbed methane wells sampled in this study and previous studies………………………………………………………………………………….59
Figure 1.3 Comparison of isotopic composition of hydrogen and carbon in methane...60
Figure 1.4 Comparison of isotopic composition of the molecular hydrocarbon composition and stable carbon isotopes in methane …………………………………61
Figure 1.5 Comparison of gas compositions to the proportion of methane……………62
Figure 1.6 Comparison of gas compositions to [36Ar]…………………………………63
Figure 1.7 4He/20Ne compared to molecular and isotopic values of hydrocarbon…….64
3 4 4 20 4 13 4 Figure 1.8 Comparison of He/ He vs. He/ Ne, He/CH4 vs. δ C-CH4, and He/CH4 vs. C1/C2+………………………………………………………………………………….65
4 20 36 4 13 Figure 1.9 Comparison of He/CH4 vs. Ne/ Ar and He/CH4 vs. δ C-CH4…..……..66
20 36 13 Figure 1.10 Comparison of Ne/ Ar vs. [Cl] and δ C-CH4 …………………………67
Chapter 2
Figure 2.1 Stratigraphic column, base map, and cross section of Illinois Basin………136
Figure 2.2 Locations of CBM wells sampled in this study and previous studies……...137
Figure 2.3 Schematic of production and diffusive loss of radiogenic 4He...... ……...... 138
Figure 2.4 Comparison of log[4He] vs. 1000/Temperature (Kelvin) for step heating of
xii coal solids…………...…………………….………………………..……………..…..139
Figure 2.5 Comparison of 4He and 21Ne* that are measured, expected, and the fraction that are retained in coal seam solids....……………………...………….…..140
Figure 2.6 Comparison of the standard age model using empirical diffusional constants in coal seam solids vs. the standard age model………………………………..…….141
Figure 2.7 Comparison of an age model using the empirical diffusional constants plus the exogenous components in coal seam solids vs. the standard age model…….142
Figure 2.8 Comparison of age models corrected for the empirical diffusional constants plus the exogenous components in coal seam solids vs. the empirical diffusional constants in coal seam solids …….…………………………………….143
xiii
Summary
The need to generate cleaner burning fuels have placed a renewed interested in unconventional energy resources such as coalbed methane (CBM) in the last decade.
Despite increased natural gas production from CBM reservoirs, there are still many poorly understood aspects of CBM reserves. These include uncertainty in our ability to resolve the genetic source (biogenic vs. thermogenic) of natural gases found in CBM reservoirs and the potential for exogenous fluids to alter CBM composition. Data including hydrocarbon, major, and noble gas composition and the isotopic composition of hydrocarbons and noble gases from this study indicate that CBM production gases are dominated by biogenic methane, but contain clear contributions from a thermogenic endmember. The thermogenic endmember is distinguished by a positive relationship between the proportion of methane, ethane, 4He, exogenous 20Ne,
20 36 13 2 enriched Ne/ Ar, enriched δ C-CH4 and δ H-CH4, a higher proportion of excess N2
(i.e., non-atmospherically-derived N2) and elevated [Cl] and [Br]. By comparison, the
13 2 more biogenic end-member contained more negative δ C-CH4 and δ H-CH4, is significantly more enriched in gases derived from air-saturated water (e.g., 36Ar and
N2), and had lower [Cl] and [Br]. Based on strong correlations between elevated
20 36 40 36 13 2 4 Ne/ Ar, Ar/ Ar, and enriched δ C-CH4 and δ H-CH4, I conclude that the [ He] is dominated by an exogenous (i.e., migrated) thermogenic endmember.
xiv Groundwater plays a critical role in the post-genetic degradation, alteration, migration, and generation of all hydrocarbon fluids. The importance of groundwater in biogenic coalbed methane (CBM) systems is perhaps even more significant. In CBM systems, groundwater can transport and introduce microbial communities in areas previously pasteurized or devoid of life, deliver essential nutrients, or remove brine components that are deleterious to the formation of biogenic methane. Nonetheless, the timing of the introduction of fresh groundwater into coal beds that produced coalbed methane is poorly constrained because of the inherent challenges in common groundwater dating methods. Herein, I attempt to address this issue by determining the residence time of fluids using the ingrowth of 4He. By determining the empirical rate of radiogenic 4He flux and exogenous sources of thermogenic methane that are rich in helium, I estimate that the average residence times for groundwater in coalbed methane reservoirs from the Illinois Basin on the magnitude of approximately ~9.5 x103 years.
These estimates are approximately 12 times lower than the ages obtained using standard models and are consistent with an influx of groundwater following the
Illinoian glacial period.
xv
Chapter 1. Integrating Hydrocarbon Molecular Content and Isotopic Values of Carbon and Hydrogen in Methane with Noble Gas Geochemistry
Abstract Increased demands for cleaner burning fuels have placed a renewed interest in unconventional energy resources such as coalbed methane (CBM) in the last decade.
Despite increased natural gas production from CBM reservoirs, there are still many poorly understood aspects of CBM reserves. These include uncertainty in our ability to resolve the genetic source (biogenic vs. thermogenic) of natural gases found in CBM reservoirs and the potential for exogenous fluids to alter CBM composition. To address these issues, I analyzed the hydrocarbon, major, and noble gas composition, the isotopic composition of hydrocarbons and noble gases, and select dissolved ions of 20 producing
CBM wells from the Illinois Basin, in Sullivan County, Indiana, USA. While these data indicate that CBM production gases are dominated by biogenic gas, I identify clear contributions from a thermogenic endmember. The thermogenic endmember is distinguished by a positive relationship between the proportion of methane, ethane, 4He,
20 20 36 13 2 exogenous Ne, enriched Ne/ Ar, enriched δ C-CH4 and δ H-CH4, a higher proportion of excess N2 (i.e., non- atmospherically-derived N2) and elevated [Cl] and
13 [Br]. By comparison, the more biogenic end-member contained more negative δ C-CH4
2 and δ H-CH4, is significantly more enriched in gases derived from air-saturated water
36 (e.g., Ar and N2), and had lower [Cl] and [Br]. Based on strong correlations between
20 36 40 36 13 2 elevated Ne/ Ar, Ar/ Ar, and enriched δ C-CH4 and δ H-CH4, I conclude that
1 the [4He] is dominated by an exogenous (i.e., migrated) thermogenic endmember. Our
20 36 2 13 new noble gas and hydrocarbon isotopic data (e.g., Ne/ Ar, C2+/C1, δ H-CH4, δ C-
CH4) suggest that a dual-phase (gas + liquid) component of thermogenic hydrocarbon gases, most likely derived from the New Albany Shale, migrated to and was emplaced within the Pennsylvanian-aged coals examined as part of this study. I hypothesize that after these New Albany Shale gases migrated to the coal seam traps, later stages of biogenic methane formation diluted the geochemical signature of the thermogenic methane.
Key Words: coalbed methane, stable isotopes, natural gas, fluid migration, noble gases, and post-genetic modification
2 1.1 Introduction
Increased demands for cleaner burning fuels have placed a renewed interest in unconventional energy resources throughout the last decade. Coalbed methane (CBM) has been developed as an unconventional source of natural gas in the US since the
1950’s with increased utilization occurring from the late 1980’s to the present (Strąpoć et al., 2007; Strapoc et al., 2010; USEIA, 2010; USEIA, 2012). Today, natural gas production from CBM is approximately 40 million cubic meters (McM) per day or nearly 10% of the total natural gas production in the US. The United States Energy
Information Administration predicts an increased demand for CBM production in the coming years (USEIA, 2010; USEIA, 2012).
Despite the numerous environmental and economic advantages associated with
CBM production, there remains three significant research endeavors associated with
CBM formation. The first being the genetic source (biogenic vs. thermogenic) of natural gas found in productive CBM reservoirs. The second concern is the choice of geochemical approaches to distinguish the relative contributions of these genetic sources.
And lastly, the relative role and geochemistry of coal seam waters and/or exogenous fluids in methane generation also remains poorly constrained (Ritter et al., 2015).
In order to develop a fundamental understanding of CBM systematics, the genetic source of produced hydrocarbons must be determined. Conventionally, the origin of
CBM hydrocarbon gases has been inferred by the use of geochemical fingerprints from
2 13 hydrocarbon molecular (e.g., C1/C2+) and isotopic compositions (e.g., δ H-CH4, δ C-
CH4). The majority of studies, including several from the Illinois Basin, conclude that
CBM forming in coal seams is biogenic in nature (McIntosh et al., 2002; Schlegel et 3 al., 2011a; Strąpoć et al., 2007).
Nonetheless, a subset of producing CBM wells (e.g., Illinois Basin, San Juan Basin,
Black Warrior Basin) show molecular and isotope geochemistry datasets that are inconsistent with conventional indicators of purely microbial gases (C1/C2+=>>2000;
13 δ C-CH4=>-60 per mil (‰)) (McIntosh et al., 2002; Schlegel et al., 2011b; Strąpoć et al.,
2007; Strapoc et al., 2010; Zhou and Ballentine, 2006; Zhou et al., 2002; Zhou et al.,
2005). These datasets can be interpreted as either a) an ambiguous, complex, multi- component mixture of biogenic and thermogenic natural gas or b) biogenic methane that experienced post-genetic alteration.
To date, most workers dismiss these subtle differences in these datasets. Thereby overlooking how post-genetic modification by methanotrophs (e.g., SO4 reduction, methane oxidizers), methanogens (CO2 reduction, fermentation (e.g., acetate)), or the introduction of an exogenous natural gas (e.g., biogenic and thermogenic natural gas) can impact the interpretation of the genetic source of methane in CBM reservoirs.
For example, a significant amount of “knowledge” about the exotic processes of microbes in the subsurface is based on interpretations of samples retrieved from CBM reservoirs, shales, and deep crustal fluids (Martini et al., 1996; Martini et al., 2003;
Martini et al., 2008; Onstott et al., 2006; Sherwood Lollar et al., 2008; Ward et al., 2004;
Zhou et al., 2005). Similarly, estimates of the residence time of fluids associated with the biogenic production of methane within coal seams and the migration of hydrocarbons in the shallow and deep crust can only be determined if the role of various genetic sources are established (Darrah et al., 2014; Darrah et al., 2015). Accurately characterizing the
timing and contributions from exogenous sources is critical for determining a) the 4 sustainability of groundwater pumping for CBM extraction (i.e., reducing hydrostatic pressure); b) the driving forces of basin-scale fluid flow and solute transport; and c) the rates of biogenic gas generation, followed by determining the plausibility of bio- stimulation for methane regeneration (Garven et al., 1993; Gupta et al., 2015; Person et al., 1996; Ritter et al., 2015; Schlegel et al., 2011b). Therefore, I suggest that these processes must be fully explored through the use of diverse geochemical gas isotope signatures, including those from noble gases.
Because noble gases are non-reactive and therefore are unaffected by microbial alteration or oxidation, they represent geochemical tracers that may provide additional insights into these processes (Ballentine et al., 2002; Darrah et al., 2014; Darrah et al.,
2015; Schlegel et al., 2011b; Zhou and Ballentine, 2006; Zhou et al., 2005). Thus, I hypothesize that by integrating noble gas geochemistry with hydrocarbon, major gas
- - (e.g., N2, CO2), and dissolved ion (Br , Cl ) compositions, one can provide greater resolution and certainty as to the relative contributions of biogenic and thermogenic methane, evaluate the emplacement history of natural gas in the crust, and better constrain the relative fluid contributions of in situ coalbed methane vs. natural gases introduced to coal seams from exogenous sources.
5 1.2 Background
1.2.1 Geological Background
The Illinois Basin is an oval-shaped syncline spanning about 1.55 x104 square kilometers and extending from central Illinois to western Indiana and northwestern
Kentucky (Figure 1.1) (Buschbach and Kolata, 1990; Karacan et al., 2014; Mastalerz et al., 2004a; Mastalerz et al., 2013). It is bounded by the Mississippi River Arch to the northwest, the Kankakee Arch to the northeast, the Ozark dome to the southwest, and the New Madrid Rift Complex to the south (Buschbach and Kolata, 1990). These structural features separate the Illinois Basin from adjacent basins such as the
Appalachian Basin (to the east), the Forest City Basin (to the west), and the Michigan
Basin (to the northeast) (Buschbach and Kolata, 1990; Tedesco, 2003).
The Illinois Basin is dominantly a foredeep, intracratonic basin that, like the
Michigan Basin, formed its structure during the evolution of Appalachian tectonics approximately 530 to 280 million years ago (McIntosh et al., 2002; Strąpoć et al., 2007).
Sedimentation in the Illinois Basin occurred during transgressive phases and led to infills up to 3.7 x103 meters thick near the depocenter, which largely consisted of a gradation from shallow to deep marine sediments (McIntosh et al., 2002; Strąpoć et al., 2007).
During the Middle to Upper Devonian, sedimentation occurred within a semi- restricted basin that produced a stratified, anoxic, marine environment that led to the burial of organic-rich sediments (Cluff, 1980). The burial of these organic-rich sediments lead to the formation of the New Albany Shale (Strapoc et al., 2010).
Currently, depths to the New Albany Shale range from surface outcrop at the edges of
3 the Illinois Basin to near 1.5 x10 meters at the depocenter. Thermal maturities of the 6 New Albany Shale range from approximately 0.54% vitrinite reflectance (Ro) on the margins of the basin to 1.5% Ro near the center of the basin (Cluff, 1980; Strapoc et al.,
2010).
The Pennsylvanian-aged coal-bearing strata in the Illinois Basin were deposited from ~318 to 299 million years ago and are divided into three major units: the Raccoon
Creek, the Carbondale, and the McLeansboro Groups (Strąpoć et al., 2007). Two coal intervals for coalbed methane (CBM) production today are the Springfield and
Seelyville coal seams, which are members of the Petersburg and Linton Formations, respectively, and are contained within the Carbondale Group (Strąpoć et al., 2007).
The Springfield and Seelyville coal seams have thicknesses of 1.37-1.83 meters and 0.3-3 meters, respectively (Drobniak et al., 2004; Hatch and Affolter, 2002). Both were deposited in a near shore to marginal marine environment characterized by tidal coastal plains (Pashin et al., 2004; Strąpoć et al., 2007). The Springfield and Seelyville coal seams outcrop on the western and eastern portions of the Illinois Basin and reach depths of 270 and 305 meters, respectively, near the depocenter of the first order synclinal structural depression (Figure 1.1) (Drobniak et al., 2004; Hatch and Affolter,
2002). The highest thermal maturities are indicated by vitrinite reflectance values of
0.7-0.8% Ro, respectively. This range is consistent with high-volatile bituminous A coals (Strąpoć et al., 2007), which transition to lower ranked coals (e.g., high volatile bituminous B and C) toward the basin margins (Green et al., 2003).
Production of natural gas from coalbed methane (CBM) reserves in the Illinois
Basin began in 2000 and increased significantly within the last decade (Tedesco,
2003). Currently, CBM production in the Illinois Basin is approximately 11 McM per 7 day, with total estimated reserves of 1.5-6 billion cubic meters (BcM) (Drobniak et al.,
2004; Karacan et al., 2014; Mastalerz et al., 2004a; Mastalerz et al., 2004b; Mastalerz et al., 2013).
1.2.2 Geochemical Systematics
1.2.2.1Formation and Identification of Hydrocarbon Gases
Methane can be formed via biogenic (catalyzed by microbes) or thermogenic
(induced by increasing temperature and pressure) processes (Tissot and Welte, 1984).
Commonly the source of the natural gas is determined based on the hydrocarbon
13 molecular content (C1/C2+) and isotopic values of carbon (δ C-CH4) and hydrogen
2 (δ H-CH4) in methane, ethane, and propane (Bernard, 1978; Clayton, 1991; Rice and
Claypool, 1981; Schoell, 1980; Schoell, 1983; Schoell, 1988).
Biogenic methane is formed when methanogens ferment or decompose acetate, long chain fatty acids, alkanes, low molecular weight aromatics and/or reduce CO2 (e.g.,
Rice and Claypool, 1981; Schoell, 1980; Whiticar et al., 1986) in anaerobic conditions.
These processes can occur within coal seams, shales, or in the presence of high concentrations of dissolved organic matter under lower temperatures (<~120○C) in shallow aquifers and fractures (Ritter et al., 2015; Rowe and Muehlenbachs, 1999; Tilley and Muehlenbachs, 2006; Whiticar, 1999; Whiticar et al., 1986). The pathways of microbial methane production are often described as either near-surface or sub-surface microbial methane, which are differentiatedby acetate fermentation and CO2 reduction, respectively. Methanogens almost exclusively produce methane (>99.9%) with
13 2 isotopically light carbon and hydrogen signatures (δ C-CH4 ~<-60 ‰ and δ H-CH4 ~<-
8 180 ‰; (Schoell, 1983; Whiticar et al., 1985)).
In comparison to biogenic methane, thermogenic methane forms from the thermocatalytic decomposition of kerogen with increasing pressures and temperatures associated with greater burial depths (i.e., termed catagenesis) (Tilley and Muehlenbachs,
2013; Tissot et al., 1987; Tissot and Welte, 1984; Whiticar et al., 1985). The hydrocarbon composition of thermogenic gases change as the organic source (i.e., kerogen or liquid hydrocarbons) degrades.
Initially, the first byproducts of catagenesis are liquid petroleum and “wet” oil- associated gases with comparatively high ratios of higher-ordered aliphatic hydrocarbon chains to methane (C2+/C1> ~5) and relatively depleted values of carbon and hydrogen in
13 2 methane (δ C-CH4 >~-55 ‰ and δ H-CH4 >~-260 ‰) (Bates et al., 2011; Green et al.,
2008; Rowe and Muehlenbachs, 1999; Schoell, 1983; Schoell, 1988; Whiticar, 1999).
As thermal maturation continues, the C2+/C1 ratio decreases because of the catalytic
13 2 breakdown of heavier aliphatic hydrocarbons, while the δ C-CH4 and δ H-CH4 become progressively more enriched. Thermally mature natural gases commonly have C2+/C1
13 2 <0.02 and δ C-CH4 >-30 ‰ and δ H-CH4 >-140 ‰ (Bates et al., 2011; Green et al.,
2008; Rowe and Muehlenbachs, 1999; Tilley and Muehlenbachs, 2006; Tilley and
Muehlenbachs, 2013; Whiticar, 1999).
13 2 Plots of C1/C2+ vs. δ C-CH4 (i.e., commonly termed “Bernard Plots”) or δ H-CH4
13 vs. δ C-CH4 (i.e., commonly termed “Schoell” or “Whiticar Plots”) are useful in discerning biogenic or thermogenic natural gas origins and relative contributions in mixed gases (Bernard, 1978; Clayton, 1991; Rice and Claypool, 1981; Schoell, 1980;
Schoell, 1983; Schoell, 1988; Whiticar et al., 1985). In these plots, biogenic natural
9 13 gas will have C1/C2+ >~2000 and a δ C-CH4 <~-60 ‰, while thermogenic gases will
13 typically fall along a trend line from C1/C2+ = 0.25 to 100 and δ C-CH4 ~-50 to -25 ‰
(Shown in Figures 1.3 and 1.4).
Following the formation of biogenic and thermogenic hydrocarbon gases, additional post-genetic processes can alter the original composition of natural gases
(Darrah et al., 2015; Kessler et al., 2006; Pape et al., 2010). These processes can include a) mixing with other biogenic or thermogenic natural gases as well as b) secondary microbial or chemical alteration, which can either produce or destroy methane and other hydrocarbon gases. The latter process influences hydrocarbon composition of gases in the subsurface by a) methanogenesis in which CO2 reduction or acetate fermentation produce additional methane or b) methanotrophy, in which bacterial or thermal sulfate reduction can oxidize and destroy hydrocarbon gases.
Additional methanogenic production of methane would progressively enrich the natural gasmixture in methane relative to higher order aliphatic hydrocarbons (higher
13 C1/C2+) and lead to a more depleted δ C-CH4 signature (Bernard, 1978; Schoell, 1983;
Whiticar et al., 1985). In contrast, although the microbial oxidation by methanotrophs or sulfate reduction along bacterial or thermal pathways would similarly increase the C1/C2+ in the natural gas mixture (i.e., higher aliphatic hydrocarbons are oxidized preferentially
13 13 to methane). The resulting natural gas would be enriched in C-CH4 and C-C2H6
(Darrah et al., 2015; Kessler et al., 2006; Pape et al., 2010).
Natural gases can also experience post-genetic alteration during transport in the subsurface. For example, diffusion and two-phase advection can alter the original composition of natural gases (Darrah et al., 2014; Darrah et al., 2015; Dubacq et al.,
10 2012; Gilfillan et al., 2009). Natural gas migration can cause enrichment of 12C and 1H relative to their original hydrocarbon composition (Darrah et al., 2015; Kessler et al.,
2006; Pape et al., 2010; Prinzhofer and Huc, 1995; Xia and Tang, 2012) because of the faster diffusion and/or lower solubility of lower molecular weight compounds.
1.2.2.2 Noble Gas Systematics
Noble gases are non-reactive elements that exist naturally in low abundance relative to hydrocarbons within the crust. They can be used to discern the source of natural gas, determine the residence time of fluids in the crust, and resolve the relative contributions of thermogenic and biogenic methane (Ballentine et al., 2002; Ballentine and
Burnard, 2002; Darrah et al., 2014; Darrah et al., 2015; Hunt et al., 2012; Schlegel et al., 2011b; Solomon et al., 1996; Zhou and Ballentine, 2006). As a result of these characteristics, the composition of noble gases in the crust are not altered by microbial activity, chemical reactions (e.g., sulfate reduction), or oxidation (Ballentine et al.,
2002; Ballentine and Burnard, 2002). The elemental concentration and isotopic composition of noble gases are also well constrained in the atmosphere, hydrosphere, crust, and mantle, which further enhances their functionality as geochemical tracers of crustal fluids and their interactions (Ballentine et al., 2002; Ballentine and Burnard,
2002).
The noble gases associated with hydrocarbons and other geological fluids come from three primary sources: the mantle, atmosphere, and the crust (Ballentine et al., 2002).
The noble gases found with most fluids in the crust represent a binary mixture of inert gases from two sources: the atmosphere (air-saturated water (ASW): e.g., 20Ne, 36Ar,
38Ar, 84Kr) and the crust (U + Th4He, 21Ne*, 136Xe* and 40K40Ar*, where the *
11 denotes the proportion derived from radioactive decay) (e.g., Ballentine et al., 2002).
Noble gases present in the atmosphere and are incorporated into precipitation by
Henry’s Law of solubility (i.e., solubility increases with atomic mass: He (Weiss, 1971a; Weiss, 1971b). These dissolved gases end up in the groundwater as meteoric water recharges the aquifer system. Because the meteoric source for ASW is constant globally, the concentrations of ASW components in subsurface fluids are a well- constrained function of temperature, salinity, and atmospheric pressure (elevation) (Weiss, 1971a; Weiss, 1971b). Typical values for ASW elemental abundances are shown in Table 1.1. Radiogenic and nucleogenic noble gases are produced in the Earth’s crust by the decay of U, Th (e.g., 4He and 21Ne*, 136Xe*), and K (40Ar*) (e.g., Ballentine and Burnard, 2002). As fluid-rock interactions occur within the Earth’s crust, the noble gas composition changes according to the radiogenic nature and geothermal conditions of the rock in which the fluids form and through which they migrate (Ballentine et al., 2002). In bituminous coals, typical ranges for radioactive components are U (~0.5-10 mg/kg), Th (~1-15 mg/kg), and 40K (total K: ~10,000 mg/kg, with [40K]/K ratio of 1.2 x 10-4 = ~1 mg/kg of 40K of which 11% decays to 40Ar*), respectively (Taylor and McLennan, 1995). Typical isotopic ratios of crustal noble gases are as follows 3He/4He= 3 4 (~0.01-0.02RA, where RA is the constrained ratio of He/ Heair in atmospheric air; RA= 1.39 x 10-6), 20Ne/22Ne (~9.60-10.0), 21Ne/22Ne (~0.029-0.060), and 40Ar/36Ar (~295.5- 1100) (e.g., Ballentine et al., 2002). 3 3 4 The occurrence of elevated [ He] and R/RA (where R = He/ Hesample) can indicate 12 the presence and/or proportion of relatively small contributions (~1%) from mantle- derived components in crustal fluids (Oxburgh et al., 1986; Poreda et al., 1986). Therefore, noble gas composition can be used as a sensitive tracer for mantle-derived fluids. Mantle helium isotopic end-members can range from ~2-8RA for mid-ocean ridge basalt-like (MORB) contributions or lower for continental volcanism. In addition to the R/RA value, the relative abundance of helium and other heavier noble gases (e.g., 20Ne, 36Ar) can provide important insights on the source of fluids and be used to better constrain mantle contributions (Ballentine and Hall, 1999; Hilton, 1996; Saar et al., 2005). Air-saturated water and excess atmospheric air have relatively low He/Ne that range from 0.219-0.247 and ~0.288, respectively. By comparison, mantle- and crustal- derived fluids typically have He/Ne >1,000 (e.g., Craig et al., 1978; Hilton, 1996). In addition to distinguishing between ASW and crustal sources, noble gases may be useful in distinguishing post-genetic processes that alter hydrocarbon composition, as well as resolving the relative contributions of thermogenic and biogenic methane. The process of fluid migration (e.g., diffusion, single-phase advection, multiple-phase advection) can fractionate hydrocarbons and noble gases in predictable manners (Darrah et al., 2014; Darrah et al., 2015; Dubacq et al., 2012; Gilfillan et al., 2009; 4 20 36 Zhou et al., 2012). For example, fractionation of He/CH4 (increasing), Ne/ Ar 84 36 (increasing), CH4/C2H6+ (increasing), and Kr/ Ar (decreasing) are diagnostic of two- phase solubility fractionation, while one-phase migration is associated exclusively 4 with enrichment of He/CH4. These fractionation processes can significantly impact the composition of migrating natural gases and lead to marked increases in sensitive 13 parameters such as 4He or 20Ne in stratigraphic coal seam traps (Darrah et al., 2014; Darrah et al., 2015). The strong enrichment of 4He or 20Ne during fluid migration can also help discern contributions form thermogenic sources. Although microbial methane emplaced in the crust would accumulate small quantities of 4He from α-decay or from the release of 4He that has accumulated in sedimentary grains, microbial production of natural gas is not associated with 4He generation (Darrah et al., 2014; Darrah et al., 2015). By comparison, post-genetic fractionation during fluid transport can enrich the migrating fluid in 4He by orders of magnitude, and thus, provide a sensitive tracer for exogenous inputs of thermogenic methane in coal seams (Darrah et al., 2014; Darrah et al., 2015). 14 1.3 Materials and Methods 1.3.1 Sample Selection This study examines the noble gas, hydrocarbon geochemistry (molecular and stable 13 2 isotopic composition: δ C-CH4 and δ H-CH4), and dissolved ion composition (i.e., Cl and Br) of 20 actively producing coalbed methane (CBM) wells in Sullivan County, Indiana, USA (Figures 1.1; 1.2). Samples were collected from the eastern margin of the synclinal Illinois Basin (Figure 1.1), which is underlain by the New Albany Shale. CBM natural gas is produced from Middle-Pennsylvanian-aged Springfield and Seelyville coal seams. The typical depths of the Springfield and Seelyville coal seams range from about 76-140 and 150-210 meters below land surface, respectively. Gas samples were collected from CBM wells at screened intervals ranging from 76 to 210 meters in depth (Figure 1.1C; Table 1.1). Five wells were producing natural gas from the Springfield coal seam, nine from the Seelyville coal seam, and six wells have comingled natural gas production from both coal seams (denoted as “comingled” production in the graphical figures). Data from this study are shown in red symbols with symbol shape denoting sample type. Red diamonds and circles represent samples collected from CBM wells producing from Springfield and Seelyville coal seams, respectively, while comingled production are denoted by red triangles. I also present data from this study area within the context of published reports of natural gas data from actively producing CBM wells (n=20) (Schlegel et al., 2011a; Strąpoć et al., 2007) and the New Albany Shale (n=62) (McIntosh et al., 2002; Schlegel et al., 2011a). 15 Data from published reports on the Springfield and Seelyville coal seams are denoted by green squares (Schlegel et al., 2011a) and blue squares (Strąpoć et al., 2007). Data from published reports from samples collected from the New Albany Shale Formation are denoted by yellow squares (McIntosh et al., 2002) and purple squares (Schlegel et al., 2011a). 1.3.2 Sampling and Analysis Nine of the 20 samples collected from actively producing CBM wells were analyzed for select dissolved ions (i.e., Cl, Br) based on whether or not the CBM well was actively pumping fluids to the surface. It should be noted here that CBM wells produce natural gas by reducing hydrostatic pressure at depth to exsolve natural gas that is dissolved in fluids or absorbed to coal seam solids. Hydrostatic pressure is reduced by pumping coal seam fluids from depth to the surface. Therefore, if the hydrostatic pressure is already low enough for a CBM well to produce natural gas it will not pump fluids to the surface (this had occurred in the 11 samples that could not be analyzed for select dissolved ions). All 20 samples collected from actively producing wells were analyzed for their major gas abundance (e.g., H2, CH4, C2H6, C3H8, normal and iso-C4H10, normal and iso-C5H12, N2, and O2) and noble gas elemental and isotopic composition (He, Ne, Ar, Kr, Xe, and their associated isotopes) according to methods reported previously (Darrah et al., 2014; Darrah et al., 13 2015). The stable isotopic composition of carbon in methane (δ C-CH4) were determined for all 20 samples collected from producing CBM wells. Stable hydrogen 2 isotopes of methane (δ H-CH4) were analyzed in 17 samples. 16 Before sampling, wells were purged of stagnant fluids by one of two methods. Producing wells that were pumping coal seam fluids to the surface were sampled for fluids before production gases. These CBM wells discharged water from the separator spigot into a sampling bucket. In the sampling bucket, pH, temperature, and electrical conductivity were simultaneously measured using a YSI probe in the field (YSI Inc., Yellow Springs, OH). After stable values were maintained for at least five minutes, water samples were collected in acid-washed, high density polyethylene (HDPE) samples vials. Samples were collected directly from the discharging spigot, filtered, and stored on ice with strict adherence to the US Geological Survey water collection protocols (USGS, 2011). Next, production gas samples were collected from actively producing wells for noble gases, hydrocarbon gases, and stable isotopes using 0.95 cm. diameter and 40.6 cm. long refrigeration-grade copper tubes. Copper tubes were connected in-line of the CBM well and after flowing production gas for approximately fifteen minutes (>>50 copper tube volumes) through the copper tubes, gas samples were sealed within the copper tube using brass or stainless steel clamps. Producing wells that were not pumping coal seam fluids to the surface were also sampled for noble gases, hydrocarbon gases, and stable isotopes using the same sample procedure. In the laboratory, the gas samples in the copper tube were prepared for analysis by cold welding approximately one inch splits of the copper tubing using stainless steel clamps. Next, the copper tube was attached to an ultra-high vacuum steel line (total pressure= 1-3 x10-9 torr), which is monitored continuously using a four digit (accurate 17 to the nearest thousandths) 0-20 torr MKS capacitance monometer, using a 0.95 cm. Swagelok ferruled connection. After the sample connection had been sufficiently evacuated and pressure was verified, an aliquot of the gas sample was introduced into the vacuum line by re-rounding the copper. This process was repeated sequentially on vacuum introduction lines for the gas chromatograph and the isotope ratio mass spectrometer (IR-MS). The isotopic analyses of noble gases were performed using a Thermo Fisher Helix SFT MS at The Ohio State University Noble Gas Laboratory. Noble gas procedures for analysis and purification followed methods summarized in (Darrah and Poreda, 2012; Darrah et al., 2013; Hunt et al., 2012; Poreda and Farley, 1992). The average external precision based on "known-unknown" standards were all less than +/- 1.72% for noble gas concentrations with values reported in parentheses ([4He] (0.63%), [22Ne] (1.27%), [40Ar] (0.32%), [84Kr] (1.64%), [132Xe] (1.72%)). These values were determined by measuring referenced and cross-validated laboratory standards including an established atmospheric standard (Columbus, Ohio Air) and a series of synthetic natural gas standards obtained from Praxair including known and validated concentrations of C1 to C5 hydrocarbons, N2, CO2, CO, H2, O2, Ar, and each of the noble gases. Noble gas isotopic standard errors were approximately ±0.0091 times the ratio of air (or 1.26 x10-8) for 3He/4He ratio, <±0.402% and <±0.689% for 20Ne/22Ne and 21Ne/22Ne, respectively, less than ± 0.643% and 0.427% for 38Ar/36Ar and 40 36 Ar/ Ar, respectively (higher than typical because of interferences from C3H8 on mass=36 and 38), less than ±1.26% for 82Kr/84Kr, and less than ±1.57% for 130Xe/132Xe 18 based on daily replicate measurements. Major gas components were measured on a SRS Quadrupole MS and the SRI 8610C multi gas chromatograph (GC) equipped with a flame ionization detector (FID) and thermal conductivity detector (TCD) at The Ohio State University’s Noble Gas Laboratory (Darrah et al., 2013; Hunt et al., 2012). Standard analytical errors were all less than ± 3.41% for major gas concentrations above the detection limit. The average external precision was determined by “known-unknown” standard experimentation using an atmospheric air standard (Columbus, Ohio Air) and a series of synthetic natural gas standards obtained from Praxair. The results of the “known-unknown” average external precision analysis are as follows: CH4 (2.14%), C2H6 (2.78%), N2 (1.25%), CO2 (1.06%), H2 (3.41%), O2 (1.39%), and Ar (0.59%) based on daily replicate measurements during analysis. Stable isotopic values of carbon and hydrogen in methane were measured at Isotech Laboratories (Champaign, Illinois). Procedures for analysis of stable isotopic values of carbon and hydrogen in methane at Isotech were summarized previously (Darrah et al., 2 2014; Darrah et al., 2015; Jackson et al., 2013; Osborn et al., 2011). The δ H-CH4 values are expressed in per mil versus Vienna standard means ocean water (VSMOW) with an approximate standard deviation of ± 0.5 ‰ (Gonfiantini et al., 1995). The 13 δ C-CH4 values are expressed in per mil versus Vienna Peedee belemnite (VDPD), with a standard deviation of ± 0.2 ‰ (Gonfiantini et al., 1995). Using chromatographic separation followed by combustion and dual-inlet isotope ratio mass spectrometry, the 13 2 detection limits for δ C-CH4 and δ H-CH4 were 0.001 and 0.001, respectively based on 19 a 99% confidence that analyte concentration is greater than zero (Isotech laboratories, 2012). The analysis of Br- and Cl- were performed by ion chromatography at the University of North Carolina, Charlotte. The methods for the analysis of Br- and Cl- were identical to those reported previously (Darrah et al., 2015; Warner et al., 2012). 1.3.3 Numerical Modeling When combined, noble gases and the composition of gas-phase hydrocarbons (i.e., molecular and stable isotopic compositions) provide powerful tracers of gas migration processes. Based on the hypothesis for an exogenous source of natural gas in CBM wells, I applied previously developed numerical models to investigate and constrain the subsurface conditions and viable mechanisms of gas transport to shallow aquifers. These mechanisms include: 1) single-phase advection of methane-rich brine (gas dissolved in water); 2) "buoyant" advection of a gas-phase natural gas; and 3) two- phase advection (i.e., free gas + brine); and 4) mixing with biogenic methane. Mechanisms 1 (grey), 2 and 3 (red), and 4 (blue) (Figure 1.9) following methods described previously (Darrah et al., 2014; Darrah et al., 2015). All models assume: 1) that the initial composition of groundwater from producing CBM wells are consistent with ASW that has recently been recharged by meteoric water. Groundwater recharged under these conditions is assumed to have a salinity of zero and to have equilibrated at ~10oC at sea level. Under these conditions, the 20Ne and 36Ar in ASW are 176 x10-6 cm3 STP/L and 1261 x10-6 cm3 STP/L, respectively; 2) the starting natural gas composition of migrated hydrocarbon gases are consistent with 20 20 36 4 -6 New Albany Shale production gas: Ne/ Ar=0.13 and He/CH4=175 x 10 generated at an initial reservoir depth of ~1000 m and ~1 molar NaCl. I use a New Albany-like starting composition because it is the shallowest major hydrocarbon-producing unit in proximity to the Springfield and Seelyville coal seams the current study area (Figures 1.1 and 1.2). All assumptions about the degree of fractionation (i.e., α value) inherent to each migration mechanism are in agreement with Darrah et al., (2015). 1.3.4 Graphical and Statistical Treatment of Data All maps, cross-sections, and well coordinates are plotted using ArcMap GIS 10.2.2. All graphics are plotted using SigmaPlot version 12.3. Statistical evaluations including mean, minimum, maximums, Pearson correlations, standard deviations, and analysis of variance (ANOVA) are performed using SPSS version 22.0. 21 1.4 Results Data are available for two producing coalbed methane reservoirs in the Illinois Basin (Springfield and Seelyville coal seams) as well as co-mingled production from both units. For the analysis, I treat these units as one large group for several reasons. First, there is noted hydraulic communication between the formations (pers. coms. Mr. Larry Neely, Maverick Drilling Co.). Secondly, workers who have analyzed samples from this region have assumed that these thin coalbed units are similar and treated them equivalently (Mastalerz et al., 2004b; McIntosh et al., 2002; Schlegel et al., 2011a; Strąpoć et al., 2007). Lastly, despite a comprehensive statistical evaluation of our study area, I identify no statistically meaningfully differences among any of our three study groups (The three groups being the Springfield coal seam samples, Seelyville coal seam samples, and co-mingled production samples). For example, neither the differences in the means (p= 0.569), medians (p= 0.613), nor the 95% confidence intervals (p= 0.514) of the methane abundances were statistically significant. These determinations were made using a variety of statistical tests including: a) direct student’s t-test comparison of data from the Springfield and Seelyville coal seams (following verification of normality); b) direct non- parametric Mann-Whitney comparison of data from the Springfield and Seelyville coal seams; and c) simultaneous analysis of variance (ANOVA) for the Springfield and Seelyville coal seams and co-mingled production (Table 1.1-1.7B). A statistical summary of all comparisons is shown in Table 1.1- 1.7B. Based on previous considerations and statistical evaluations conducted herein, I make the decision to treat the samples as one coherent dataset throughout the paper. 22 1.4.1 Gas Composition 1.4.1.1 Hydrocarbon and Major Gases Methane (CH4 or C1) is the dominant species of gas in the CBM reservoirs from the current study area. Methane concentrations ranged from 0.875 to 0.973 ccSTP/cc with 0.944 ccSTP/cc on average (Table 1.1A). Secondary gases detected in samples from CBM wells nitrogen (N2), carbon dioxide (CO2), and ethane (C2H6 or C2) (Table 1.1). Nitrogen was consistently the second most abundant gas in all samples. Nitrogen concentrations ranged from 0.020 to 0.097 ccSTP/cc with 0.045 ccSTP/cc on average (Table 1.1).Carbon dioxide was the third most abundant gas in all samples and contained 0.004 to 0.017 ccSTP/cc and 0.009 ccSTP/cc on average (Table 1.1). Ethane was consistently the fourth most abundant gas and second most abundant hydrocarbon species. Ethane concentrations ranged from 7.15 x10-5 to 1.09 x10-3 ccSTP/cc with 3.6 x10-4 ccSTP/cc on average (Table 1.1). Hydrogen, oxygen, propane (C3), normal-butane (C4n), iso-butane (C4i), normal- -5 pentane (C5n), and iso-pentane (C5i) were below detection limits (<1 x 10 ccSTP/cc) in all samples. However, it is important to note that small quantities of oxygen can be removed by the copper tubing, therefore oxygen concentrations in this study must be considered a minimum. There are statistically significant negative correlations between the abundance of 2 2 methane and the levels of N2 (r = -0.98; p= <0.001) and the ratio of C1/C2+ (r = -0.54; 2 p= 0.014). Similarly, [N2] correlates strongly with C1/C2+ (r = 0.61; p= 0.004). These 23 data suggest that as the proportion of methane increases, there is a decreasing abundance of N2, which is typically thought of as an indicator of contributions from the atmosphere, and a higher proportion of ethane. Because ethane is not formed by microbial processes (Jackson et al., 2013), the enrichment of ethane with decreasing [N2] suggests the potential for increasing contributions from thermogenic gases with an increasing proportion of methane and a lower proportion of air-saturated water. Natural gas compositions are characterized according to their a) “wet gas” content, which consists of ethane, propane, butane, and pentane, and b) energy potential (shown here in kilojoules: kJ). The “wet gas” content is typically determined by measuring the C1/C2+ (or the inverse: C2+/C1) in which C1/C2+ < 50 is considered wet gas. The C1/C2+ for samples from this dataset ranges from 867 to 13,256 with an average of 4,220. This range is consistent with “dry gas” (Table 1.6). The major gas composition of these samples suggests an energy potential that ranges from 935 to 1040 kJ. Although the range in energy potential is impacted by the addition of non-combustible gases, specifically N2 and CO2, this range is dominated by relatively large abundances of N2 in these gases. Thus, these levels will remain largely unaffected by dehydration or cryogenic cycling. 1.4.1.2 Noble Gases Helium concentrations ranged from 11.610 to 1,464.6 µccSTP/cc with 216.02 µccSTP/cc on average (Table 1.2). Argon concentrations ranged from 96.030 to 1,092.4 µccSTP/cc with an average of 330.80 µccSTP/cc (Table 1.2). Neon, Krypton, and Xenon were all present in trace concentrations. Neon ranged from 0.127 to 1.715 µccSTP/cc 24 with an average of 0.515 µccSTP/cc (Table 1.2). Krypton ranged from 5.7300 to 255.45 nccSTP/cc with an average of 56.666 nccSTP/cc (Table 1.2). Xenon ranged from 0.3560 to 16.30 nccSTP/cc with an average of 3.738 nccSTP/cc (Table 1.2). The most abundant species of noble gases are helium and argon, as is expected in most crustal fluids (Ballentine et al., 2002; Darrah et al., 2014; Darrah et al., 2015; Darrah et al., 2013; Hunt, 2000). There is a statistically significant correlation between primordial [3He] and crustal [4He] (r2= 0.95; p= <0.001). These values reflect the nearly uniform isotopic composition of helium discussed below (Ballentine et al., 2002; Kipfer et al., 2002). Both 3He and 4He correlate significantly to [20Ne] (r2= 0.53; p= 0.017 and r2= 0.51; p= 0.022, respectively). There are also many significant correlations between major and noble gases. Methane concentrations are inversely correlated with atmospheric noble gas isotopes [20Ne] (r2= -0.52; p= 0.020), [36Ar] (r2= -0.85; p= <0.001), [84Kr] (r2= -0.86; p= <0.001), and [132Xe] (r2= -0.84; p= <0.001) (Figure 1.5; Table 1.7). These data suggest that higher proportions of methane are associated with lower abundances of atmospheric gases or a higher relative natural gas to water ratio. By comparison, increasing [N2] correspond to increasing levels of lower molecular weight air-saturated water gases [20Ne] (r2= 0.51; p= 0.023) and [36Ar] (r2= 0.82; p= <0.001) (Figure 1.5-1.6; Table 1.7) suggesting that a major source of N2 is derived from air-saturated water. The N2/CH4 ratio is positively correlated with the abundance of atmospheric gases (represented here as [36Ar]) (Figures 1.5-1.6). These data suggest that the proportion of 25 methane decreases with increasing amounts of gas derived from air-saturated water. By comparison, the N2/Ar shows significant negative correlations with gases derived from air-saturated water, including [20Ne] (r2= -0.47; p= 0.037), [36Ar] (r2= -0.64; p= 0.002), [84Kr] (r2= -0.61; p= 0.005), and [132Xe] (r2= -0.62; p= 0.004) (Table 1.7; Figure 1.6). The elevated N2/Ar ratio, which is well above air- saturated water (N2/Ar=37.03), suggests the potential for the addition of a non-atmospheric source of N2. Thus, although N2 is typically thought of as atmospheric in origin, it appears that some proportion of the nitrogen is derived from a non-atmospheric source such as denitrification or another unidentified exogenous source. Because argon in the crust may consist of air- saturated water and radiogenic argon, I calculated excess nitrogen based on [36Ar]. The amount of excess nitrogen can be calculated following Equation 1.1. Note that the proportion of non-atmospheric [N2] (i.e., N2excess) decreases with increasing contributions from air-saturated water. 36 36 36 Eq. 1.1 [N2excess]= (N2/ Armeasured-N2/ Arair-saturated water) x [ Ar] 1.4.2 Gas Isotope Composition 1.4.2.1Stable Isotopic Compositions of Methane and Dissolved Inorganic Carbon 13 Stable isotopic values of carbon in methane (δ C-CH4) ranged from -69.80 to - 49.87 ‰ with -58.39 ‰ on average (Figures 1.3-1.5; Table 1.4). Stable isotopic values 2 of hydrogen (δ H- CH4) in methane ranged from -214.9 to -201.4 ‰ with -207.1 ‰ on average (Figures 1.3 and 1.5; Table 1.4). Stable isotopic values of carbon in dissolved inorganic carbon ranged from +17.0 to +27.0‰ with +24.2‰ on average (Table 1.4). These stable isotope values for DIC reflect significant microbial reduction of CO2. 2 13 The stable isotopic compositions of methane (i.e., δ H-CH4 and δ C-CH4) can 26 provide insights into the origin of natural gases in the subsurface (Figure 1.3). The δ13C- 2 CH4 and δ H-CH4 values for CBM reservoirs in this study area are strongly correlated to each other and are statistically indistinguishable (p=>0.614) from previously published data from the same field (Strąpoć et al., 2007). While the C1/C2+, 2 13 δ H-CH4, and δ C-CH4 data for a subset of the production gases from this study are consistent with a biogenic origin, the majority of data do not fall exclusively within the traditional range for subsurface microbial gas. Instead, these data appear to fall along a mixing trend between a microbial component (i.e., subsurface microbial) and an unidentified thermogenic component. These data suggest the possibility for thermogenic contributions discussed further below. In addition to stable isotope data, I also observe significant correlations between 13 13 2 δ C-CH4 and molecular and isotopic gas composition. The δ C-CH4 and δ H-CH4 show significant positive correlations with methane concentration (r2= 0.78; p= <0.001), 2 2 2 ethane concentration (r = 0.71; p= <0.001), N2/Ar (r = 0.49; p= 0.030), and He/Ne (r = 0.70; p= 0.001) (Figure 1.7; Table 1.6). These data suggest that increased enrichments of stable isotope values of carbon and hydrogen in methane correspond to increased abundances of ethane, helium, and lower relative abundances of gases derived from air- saturated water. Because ethane is not produced by biogenic sources, these data suggest the presence of a resolvable thermogenic natural gas component in all samples from this 13 2 area. The δ C-CH4 also shows significant negative correlations with [N2] (r = -0.80; p= <0.001), [20Ne] (r2= -0.54; p= 0.013), and [36Ar] (r2= -0.87; p= <0.001) (Table 1.6). These trends reinforce the observations for significantly higher gas to water ratios in the thermogenic end-member. 27 1.4.2.2 Noble Gas Isotopic Composition 3 4 The helium isotope ratios ( He/ He) in this study range from 0.043RA to 0.901RA 3 with an average of 0.117RA (Table 1.3). The term R/RA represents the ratio of He to 4 3 4 He in a sample compared to the ratio of He to He in the atmosphere, where RA=1.39 x10-6. This range of data is unexpectedly higher than the anticipated range of crustal helium isotope ratios (0.02RA) in the midcontinent and indicates the presence of a resolvable mantle-derived component in these fluids. By comparing 3He/4He and 4He/20Ne, one can easily discern mantle vs. air-saturated water contributions (Figure 1.8). The 4He/20Ne ratio in this dataset range from 11.100 to 1685.9 with an average of 590.00 (Table 1.6A). Each of these levels reflect significant, non-atmospheric excesses in helium derived from crustal or mantle contributions. In combination with the 3He/4He, these data also suggest that non-atmospheric helium represents a mixture between crustal helium and mantle-derived fluids (Figure 1.8). The calculated range for the mixture of mantle-derived helium spans from 0.700 to 15.3 %. The neon isotope ratios of 20Ne/22Ne and 21Ne/22Ne range from 9.761 to 9.787 with 9.775 on average and 0.0279 to 0.0320 with 0.0301 on average, respectively (Table 1.3). These values are consistent with the normal range of air-saturated waters with small additions of nucleogenic 21Ne* and 22Ne*. The nucleogenic contribution of 21Ne* can be calculated following Equation 1.2 and compared to other radiogenic isotopes. For example, the 4He/21Ne* can be a diagnostic indicator for the temperature, fluid-flow dependent production, and retention of radiogenic and nucleogenic gases in the crust (Darrah and Poreda, 2013; Hunt et al., 2012). The 4He/21Ne* can be calculated following 28 Equation 1.3. The 4He/21Ne* in this study ranged from 0.6000 to 35.41 x106 with an average of 6.980 x106 (Table 1.6). Because crustal production is approximately 22 x106, these values suggest that the majority of samples have lost ~70% or more of their 4He relative to the initial production of 21Ne* indicating that these may represent a residual phase that has lost gas volume over time. 21 21 22 21 22 22 Eq. 1.2. Ne*= ( Ne/ Nemeasured - Ne/ Neair-saturated water) x [ Nemeasured] 4 21 4 21 22 21 22 Eq. 1.3. He/ Ne*= He/(( Ne/ Nemeasured - Ne/ Neair-saturated water) x 22 [ Nemeasured]) The argon isotopic ratios of 38Ar/36Ar and 40Ar/36Ar ranged from 0.1828 to 0.2060 with 0.1883 on average and 289.61 to 334.35 with 317.66 on average, respectively (Table 1.3). The upper limit of 40Ar/36Ar is significantly above the air-saturated water ratio (295.5) reflecting excesses in radiogenic argon in the majority of samples. The nucleogenic contribution of 40Ar* can be calculated following Equation 1.4. The 4He/40Ar* can be a diagnostic indicator for the source of natural gas and a thermometer for past temperatures of fluid-rock interactions (Darrah and Poreda, 2013; Hunt et al., 2012). The 4He/40Ar* was calculated following Equation 1.5. The 4He/40Ar* ratio ranged from 1.080 to 76.38 with 17.16 on average (Table 1.6). The ratios ranged from normal crustal production values (4-8) to significant excesses of 4He with respect to 40Ar* produced from temperatures below argon closure temperatures (~250oC) or long-range migration. The 40Ar*/36Ar values correlate significantly with other radiogenic isotope ratios, including the 4He/3He (r2= 0.61; p= 0.004), 21Ne*/22Ne (r2= 0.592; p= 0.006) and 136Xe*/132Xe (r2= 0.65; p= 0.002), and ratios of radiogenic to air-saturated water gases (4He/20Ne) (r2= 0.72; p= <0.001) (Table 1.7). A more detailed listing of krypton 29 and xenon isotope ratios are recorded in Table 1.3. 40 40 36 40 36 36 Eq. 1.4. Ar*= ( Ar/ Armeasured - Ar/ Arair-saturated water) x [ Armeasured] 4 40 4 40 36 40 36 36 Eq. 1.5. He/ Ar*= He/(( Ar/ Armeasured - Ar/ Arair-saturated water) x [ Armeasured]) The ratios of major and noble gases can provide valuable insights on the behavior of 4 6 gases in the crust. The He/CH4 ratios ranged from 12.900 to 1527.6 x10 with 226.5 x106 on average (Table 1.6). The 20Ne/36Ar ratios ranged from 0.2080 to 2.936 with 0.5670 on average (Table 1.6). The 4He/36Ar ratios ranged from 3.1000 to 2773.1 with 4 419.30 on average (Table 1.6). The He/CH4 ratios show significant positive correlations with 4He/20Ne (r2= 0.50; p= 0.026), 4He/36Ar (r2= 0.98; p= <0.001), and 20Ne/36Ar (r2= 0.96; p= <0.001), and negative correlations with 84Ke/36Ar (r2= -0.47; p= 0.039) (Table 4 1.7). While He/CH4 can be increased by a) extended residence time of fluid in the crust, b) oxidation of hydrocarbon gases, or c) long-range fluid migration, the 20Ne/36Ar ratio can only be elevated to the extent that I observe by the advection of a two-phase fluid, specifically at a low gas to water ratio (Vgas/Vwater), in the subsurface. As a 4 20 36 result, I interpret elevated levels of both He/CH4 and Ne/ Ar as a proxy for long- range, multiple phase fluid migration. Methane correlates significantly to diagnostic noble gas isotopes 4He/20Ne (r2= 0.57; p= 0.009) and 40Ar/36Ar (r2= 0.69; p= <0.001) (Table 1.7). These values reflect a significant increase in thermogenic contributions with an increasing proportion of methane in the produced gas samples. Ethane correlates significantly to 4He/20Ne (r2= 0.51; p= 0.023), which suggests that wet gases are associated with higher ratios of thermogenic to air-saturated water gases. The C1/C2+ ratio also shows significant 30 2 positive correlations with [N2] (r = 0.61; p= 0.004) and gases derived from air-saturated water [Ar] (r2= 0.45; p= 0.049), [Kr] (r2= 0.46; p= 0.042), while proxies for deeper crustal fluids are negatively correlated (i.e., 4He/20Ne (r2= -0.54; p= 0.015), 21Ne/22Ne (r2= -0.45; p= 0.044), and 40Ar/36Ar (r2= -0.49; p= 0.027)) (Table 1.7). 36 2 2 The CH4/ Ar correlates negatively to [N2] (r = -0.76; p= <0.001), C1/C2+ (r = - 0.54; p= 0.014), and proxies for air-saturated water (i.e., [Ne] r2= -0.61; p= 0.004), and positively for thermogenic/crustal gas ratios, including 4He/20Ne (r2= 0.58; 40 36 2 2 p=0.007), Ar/ Ar (r = 0.84; p= <0.001), and N2/Ar (r = 0.70; p= 0.001) (Table 1.7). The N2/Ar shows significant negative correlations with air-saturated water derived gases, including [20Ne] (r2= -0.47; p=0.037), [36Ar] (r2= -0.64; p=0.002), [84Kr] (r2= - 0.61; p= 0.005), [132Xe] (r2= -0.62; p= 0.004), and significant positive correlations with 36 2 21 22 2 CH4/ Ar (r = 0.70; p= 0.001), radiogenic neon ( Ne/ Ne, r =0.61; p=0.004), argon (40Ar/36Ar, r2= 0.62; p= 0.003), and xenon isotopes (i.e., 129Xe/132Xe (r2= 0.47; p=0.038); 131Xe/132Xe (r2= 0.49; p= 0.029); 136Xe/132Xe (r2= 0.48; p= 0.032)) (Table 1.7). 1.4.3 Select Dissolved Ions The abundance of dissolved ions and the ratio of bromide (Br) to chloride (Cl) in the formation water can be a diagnostic indicator of the source of salinity. The [Cl] and [Br] ranged from 1067 to 7436 mg/L with 4653 mg/L on average and 6.30 to 21.9 mg/L with 12.60 mg/L on average, respectively, which reflect ~5.60 to ~39.1 % of seawater values (18980 mg/L and 65.000 mg/L, respectively). The Br/Cl ratios ranged from 8.65 x10-4 to 1.46 x10-3 with 1.14 x10-3 on average, which are also all below seawater values (1.52 x 10-3) (Warner et al. 2012). These ratios reflect additional sources of Cl 31 beyond seawater trapped in pore fluids. 1.5 Discussion 36 The elemental (He, Ne, Ar, Kr, Xe), molecular (e.g., C1/C2+, N2/Ar, CH4/ Ar, 4 4 20 20 36 2 13 3 4 He/CH4, He/ Ne, Ne / Ar), and isotopic (e.g., δ H-CH4, δ C-CH4, He/ He, 21Ne/22Ne, 40Ar/36Ar) composition of natural gases can be used to determine the source, mixtures, history of migration, and interactions that occur between fluids (e.g., gas and water) in the Earth’s crust (Darrah et al., 2014; Darrah et al., 2015; Gilfillan et al., 2009; Zhou et al., 2012). Here, I attempt to use these parameters to determine the relative contributions from each genetic source (i.e., biogenic or thermogenic) of hydrocarbon gases in CBM reservoirs from the Illinois Basin. One can then determine whether the distribution of natural gas composition results from the emplacement of exogenous fluids or if these components are native to Pennsylvanian-aged coal seams. 1.5.1 Genetic Source of Natural Gases in the Springfield and Seelyville Formations The molecular composition of hydrocarbons (i.e., C1/C2+) and the stable 2 13 isotopic compositions of methane (i.e., δ H-CH4 and δ C-CH4) can often discern the genetic origin of natural gases in the subsurface (Figures 1.3-1.4). The traditional 2 13 interpretation of Figures 1.3 and 1.4, which display δ H-CH4 vs. δ C-CH4 and C1/C2+ 13 vs. δ C-CH4, respectively, relate the isotopic composition of methane to the degree of thermal maturity. Thermogenic gases typically fall along the thermal maturation trends (dashed red arrow in Figures 1.3-1.4). In Figure 1.3, biogenic gases plot as two distinct fields 13 distinguished by their “light” δ C-CH4 end-members. The biogenic endmembers are 2 largely distinguished by their δ H-CH4 values; shallow "near-surface" (CO2 reduction) 32 2 microbial gases (green box) have significantly depleted δ H-CH4 signatures as compared to "subsurface microbial" (fermentation) gases (blue box; Figure 1.3) (Schoell, 1980; Schoell, 1988). Similarly, in Figure 1.4, biogenic gases are constrained by C1/C2+= 13 > 2,000 and δ C-CH4= <-60 ‰. The majority of production gas data from CBM wells in the Illinois Basin display 13 relatively negative δ C-CH4 values as compared to most primary thermogenic gases (Bernard et al., 1978; Schoell, 1988; Whiticar, 1999). For this reason, many workers interpret these natural gases as having an exclusively biogenic origin. Indeed, there are several lines of evidence that support the formation of microbial gas including elevated 13 13 δ C-DIC and δ C-CO2, high cell counts of methanogenic bacteria (Schlegel et al., 13 2011a), and correspondingly elevated C1/C2+ and negative δ C-CH4 (Table 1.4-1.7). At a glance, data from Figures 1.3 and 1.4 are consistent with the interpretation of biogenic production for this methane. These plots show that the majority of samples plot near the subsurface microbial end-member, although a subset of the data displays 13 13 more enriched δ C-CH4 (δ C-CH4 > -60 ‰; Figures 1.3-1.4) and higher levels of ethane (C1/C2+ as low as 867; Figure 1.4) than would be anticipated for purely 13 microbial sources (i.e., δ C-CH4 < -60 ‰, no quantifiable levels of ethane). Because ethane is not produced by biogenic sources in any sufficient quantities in the subsurface (Jackson et al., 2013), these data suggest that a resolvable component of thermogenic gas is present in all samples. Additionally, in Figures 1.3 and 1.4 the data fall along an apparent mixing trend between subsurface microbial and a thermogenic component, suggesting the possibility for contributions from both biogenic and thermogenic sources in these 33 CBM natural gases. The distribution of major gas compositions provides additional support for the hypothesis of mixing between biogenic and thermogenic gases. To illustrate these 13 2 36 trends, I plot δ C-CH4, [C2H6], N2/Ar, δ H-CH4, [ Ar], and [N2]excess versus [CH4] (Figure 1.5). Note that as the proportion of methane increases, there is general trend of 4 13 4 increasing He and ethane concentrations, a marked increase in δ C-CH4 and He/CH4, and significantly lower concentrations of gases derived from air-saturated water (i.e., 36 36 higher CH4/ Ar and lower Ar and N2) (Figures 1.6-1.7). Because methanogens almost exclusively produce methane, and negligible amounts of ethane or higher chained aliphatic hydrocarbons in the sub-surface (Bernard, 1978; Schoell, 1980), the presence of ethane can serve as clear evidence for thermogenic gas inputs (Jackson et al., 2013). Similarly, because 4He is abundant in thermogenic gases and recently formed microbial gases are nearly devoid of 4He, I interpret elevated [4He] and 4 He/CH4 as a clear indication of thermogenic contributions (Darrah et al., 2014; Darrah et al., 2015). Using the relative concentrations of methane and ethane, I estimate that the proportion of exogenous thermogenic gas ranges from 4.60% to 17.1%. Despite these observations, the implications of decreasing [N2] are ambiguous because I note that all samples from the current study displayed marked excess of non-atmospheric [N2] (Figures 1.5-1.7). Additionally, one could envision a scenario in 4 which methanotrophic microbes would oxidize methane and increase the He/CH4 ratios 13 and δ C-CH4 values in the remaining gas (Darrah et al., 2015; Kessler et al., 2006; Pape et al., 2010). In fact, this hypothesis has been used previously to explain the relative 34 13 enrichment of δ C-CH4 in other CBM formations (Pashin et al., 2014; Zhou et al., 2005). 4 13 While the trends in He/CH4 and δ C-CH4 could be dismissed as a result of methanotrophic oxidation of biogenic methane, comparisons of the relative molecular 4 13 hydrocarbon ratios precludes this explanation. I note that as the He/CH4 and δ C- CH4 increase, there is a trend of decreasing C1/C2+, which results from increasing ethane concentrations (Figure 1.9). If CBM production gases acquired elevated 4 13 He/CH4 and enriched δ C-CH4 through oxidation by methanotrophs (or other mechanisms e.g., thermal sulfate reduction), one would expect to observe an increase in 4 13 the C1/C2+ ratio with increasing He/CH4 and δ C-CH4 (Figure 1.9). This trend occurs because methanotrophs would preferentially degrade higher order aliphatic hydrocarbons (C2+) as compared to methane. These hypothetical trends for oxidation are the opposite of what is observed in our current dataset. Because noble gases are inert and provide an externally defined end-member to calculate hydrocarbon mixing, combining both noble gas and stable isotope tracers may provide additional insight into the argument over thermogenic contributions, mixing, or the impacts of post-genetic modification. The composition of gases derived from air- saturated water (i.e., 36Ar, 84Kr) are particularly useful for this purpose because their initial composition is uniform globally and are unaltered by oxidation or other chemical reactions (Ballentine et al., 2002; Kipfer et al., 2002). Thus, I plot a series of gas parameters vs. [36Ar] (Figure 1.6-1.7). As 36Ar (i.e., a proxy for the proportion of gases derived from meteoric water in the sample) increases, I observe significantly more 13 negative δ C-CH4, higher abundances of [N2], but lower excess N2, lower concentrations 35 4 4 of CH4, C2H6, He, He/CH4, and higher C1/C2+ (lower total ethane); these samples also display significantly lower 21Ne/22Ne, 40Ar/36Ar, 136Xe/132Xe that approach air- saturated water values. In general, these data are consistent with a decrease in thermogenic contributions with decreasing ratios of natural gas to water (Vgas/Vwater). By comparison, I note that samples with lower abundances of 36Ar show the opposite trends. For example, one can observe that increasing ratios of 4He/20Ne, 4He/36Ar, more 13 enriched δ C-CH4, lower abundances of [N2], but higher amounts of excess N2, higher 4 4 concentrations of CH4, C2H6, He, He/CH4, and lower C1/C2+ (higher total ethane) 36 36 with decreasing [ Ar] and higher CH4/ Ar. These samples also show significant increases in radiogenic noble gas isotopes (21Ne*/22Ne, 40Ar*/36Ar, 136Xe*/132Xe) reflecting contributions from gases that have experienced elevated temperatures (at least about ~250oC) to permit the release of heavier radiogenic noble gases (Darrah et al., 2014; Darrah et al., 2015; Darrah and Poreda, 2013; Hunt, 2000). Using the 4 20 36 abundance of ethane, He/CH4, and Ne/ Ar to estimate mixing, indicates that the proportion of exogenous thermogenic gas ranges from 6.30% to 19.2% (slightly higher than, but roughly consistent with hydrocarbon mixing values). Thus, one can conclude that CBM production gases from this study area display a clear and resolvable contribution from thermogenic gases. 1.5.2 Endogenous vs. Exogenous Thermogenic Gases Although multiple lines of geochemical evidence support the presence of a thermogenic component in natural gases from producing CBM reservoirs in the Illinois Basin, the ultimate source of the thermogenic gas remains unknown. The thermogenic gases could be derived endogenously within the coal seams during 36 periods of increased geothermal conditions (e.g., during lithification or burial). Alternatively, the thermogenic gases could be derived from an exogenous source of natural gas that later on migrated into the coal seams. Because the occurrence, distribution, and composition of hydrocarbons in the Earth's crust, including hydrocarbon-bearing formations in the Illinois Basin (Figure 1.1), result from the complex interplay between fluid migration and aquifer rock mechanics (e.g., Ballentine et al., 1991; Bethke and Marshak, 1990; Cathles, 1990), I envision two scenarios that can introduce exogenous fluids into the Springfield or Seelyville coal seams. The most obvious scenario involves the entrapment of hydrocarbon gases that have migrated from nearby source rocks to Pennsylvanian-aged coal seams, where the Springfield or Seelyville may act as stratigraphic traps. Additionally, although the migration of mantle-derived fluids in the mid-continent is not considered likely, one cannot a priori rule out the emplacement of mantle-derived fluids within stratigraphic traps within Springfield or Seelyville coal seams because of the non-crustal helium isotope ratios (Table 1.3). First, I examine the potential for mantle-derived exogenous fluids. Elevated 3He/4He ratios (above radiogenic production values: 0.02RA) provide unequivocal evidence for the presence of mantle-derived fluids in crustal and hydrological systems (Ballentine et al., 2002; Craig et al., 1978). Nonetheless, in shallow crustal systems, fluids with variable 3He/4He ratios can be mixed in the subsurface, there can be variable amounts of air-saturated components, and in shallow aquifers some addition of tritiogenic 3He cannot be discounted. 37 Various approaches have been used to apportion the abundance of mantle-derived components in the shallow crust (Ballentine et al., 2002; Craig et al., 1978; Crossey et al., 2009; Hilton, 1996; Karlstrom et al., 2013; Poreda et al., 1986; Saar et al., 2005). Here, I evaluate mantle contributions by examining the relative distribution of 3He/4He to non-air-like gas components (e.g., 4He/20Ne, Figure 1.8). This approach is appropriate because of the similarity in solubility between He and Ne, which removes the need to correct for variable fractionation factors that result from differing Vgas/Vwater. Our mixing models assume both ASW: R/Ra=0.985, 4He/20Ne= 0.255; ASW with 10 4 20 tritium units (10 T.U.): R/Ra=1.4, He/ Ne=0.255; crustal: R/RA=0.02RA, 4 20 He/ Ne=1000; and a mantle-derived component: R/RA=2 to 8RA for 25 to 100% mantle fraction and 4He/20Ne=1000 (Figure 1.8) (Craig et al., 1978; Crossey et al., 2009; Hilton, 1996). CBM gases from the Illinois Basin produce unexpectedly elevated 3He/4He ratios (0.043 to 0.90RA), which are significantly above radiogenic production values (0.02RA) even with elevated 4He/20Ne. These values reflect approximately 0.7 to 15.3 % mantle contributions of 3He in natural gases from producing CBM wells in this area. Initially, these values seemed difficult to explain, but recent work identifies a correlation between mantle-derived helium in passive continental margins above areas of low velocity seismic anomalies (Whyte et al., 2015). This study area overlies zones of low velocity anomalies associated with the New Madrid Fault system (Schmandt and Lin, 2014). I also note the presence of similarly elevated 3He/4He ratios in New Albany Shale production gases from the same region 38 (Schlegel et al., 2011a). While these data provide clear evidence for the emplacement of exogenous mantle-derived fluids in in the Springfield and Seelyville coal seams and the New Albany Shale, I consider mantle-derived fluids as unlikely source for the increased methane and ethane concentrations that I observe in the thermogenic endmember although one cannot rule out the potential role of thermally driven fluid migration in inducing cross-formational fluid flow. Conversely, the emplacement of an exogenous thermogenic natural gas source from another formation could readily account for the observations of elevated 4He and ethane. The 4He in any crustal fluid results from the combination of: 1) atmospheric inputs, 2) in-situ production of 4He from α-decay of U-Th, 3) the release of 4He that previously accumulated in detrital grains, and 4) the flux from exogenous sources (Solomon et al., 1996; Zhou and Ballentine, 2006). Based on the abundance of 20Ne, which is derived from air-saturated water, I can estimate the atmospheric contributions of 4He. Even in the sample with the lowest [4He], ASW can conservatively account for less than 1/30 of the total [4He]. Using the [U] and [Th] of the Springfield and Seelyville coal seams to estimate the potential in-situ production of [4He], I find an estimate of steady-state production and accumulation of <1.030 x10-9 ccSTP/L of water/yr, which accounts for 0.005% of the total 4He per year at maximum. Although the release of 4He from detrital mineral grains in coals into groundwater can significantly exceed steady-state production (Sheldon et al., 2003; Solomon et al., 1996), the calculated maximum release within these coal seams is only ~0.5 x10-6 ccSTP/L/yr or about 1.5% of the measured [4He] at maximum. 39 Thus, I conclude that the [4He] observed (up to 1460 µccSTP/cc) in methane-rich 4 samples greatly exceeds the viable combined concentrations from [ He]ASW, the 4 4 maximum [ He]in situ, and the release from He that previously accumulated in sedimentary grains within the formation. Therefore, I conclude that the excess [4He] I have observed in producing CBM wells requires the migration of an exogenous 4 source into these shallow aquifers. Based on the correlations between He, CH4, and C2H6, I suggest that an exogenous hydrocarbon-rich source is the most likely reason for elevated 4He in this area. Diagnostic ratios of thermogenic and air-saturated water derived gases provide additional supporting evidence for the hypothesis of a migrated thermogenic gas. Because isotopic ratios of atmospheric components in shallow groundwater are largely consistent globally, with only minor variations that result from salinity, temperature, and elevation (atmospheric pressure) (Ballentine et al., 2002), the isotopic ratios of ASW gases provides additional insight into the history of gas- water interactions and post-genetic modification processes (Darrah et al., 2014; Darrah et al., 2015; Gilfillan et al., 2009; Zhou et al., 2012). Similarly, the relative concentration of exogenous 4He in 4 4 crustal fluids (e.g., He/CH4) results from a combination of the He released within the original thermogenic natural gas source and the fractionation that occurs during fluid migration processes (Ballentine et al., 2002; Ballentine and Sherwood Lollar, 2002; 4 Darrah et al., 2014; Darrah et al., 2015; Hunt et al., 2012). As a result, the He/CH4 and 20Ne/36Ar of crustal fluids are particularly useful for fingerprinting the source of natural gas and evaluating the processes of gas migration in the subsurface (e.g., diffusion or 4 solubility fractionation) (Darrah et al., 2014; Darrah et al., 2015). The He/CH4 and 40 20Ne/36Ar ratios record important clues about the transport mechanisms by which exogenous the hydrocarbon-rich brine could reach superior formations (Darrah et al., 2014; Darrah et al., 2015). Producing CBM wells, specifically in the methane-rich end-member have 20Ne/36Ar well above ASW equilibrium (~0.156). In fact, these values range up to 2.94 in the methane-rich endmember (Figure 1.9). I note that the increase in 20Ne/36Ar relates almost exclusively to an increase of [20Ne] concomitantly 4 20 36 with [CH4], [C2H6], and [ He]. These data suggest that the elevated Ne/ Ar ratios are indicative of an exogenous source of natural gas in the thermogenic endmember. I 20 36 4 also notice a positive correlation between Ne/ Ar and He/CH4 and hypothesize that 4 highly elevated He/CH4 values likely reflect significant post-genetic modification of a thermogenic natural gases during transport through the crust. 1.5.3 Potential Sources of Exogenous Thermogenic Gases The collection of data evaluated above suggests that a) natural gas in producing CBM reservoirs from the Illinois Basin are derived from a mixture of biogenic and thermogenic gas and b) the source of thermogenic gas is derived from an exogenous source. I briefly discuss the plausible scenarios for these thermogenic contributions. A thorough examination of petroleum geology of the Illinois Basin (Figure 1.1) suggests that the Upper Devonian-aged New Albany Shale constitutes one potential hydrocarbon source that could contribute thermogenic methane to the superior, Pennsylvanian-aged Springfield and Seelyville Formations. Although I view the New Albany Shale as a likely candidate, predominantly because of its location in the sedimentary column and its noted gas production, the ad hoc interpretation that New 41 Albany Shale-derived gases may contribute to CBM in this area is supported by the gas geochemistry. For comparative purposes, I plot previously published New Albany Shale data in Figures 1.3C and 1.4C (Schlegel et al., 2011a). Note that in Figure 1.3C, the thermogenic- rich endmember falls along the same mixing line as published New Albany Shale production gas data supporting the possibility for this thermogenic source. An examination of Figure 1.4C produces a less clear trend. However, I note that by applying the gas fractionation model developed in Darrah et al., (2014; 2015) to the New Albany Shale gas data, I can a) account for the majority of New Albany Shale data despite the relatively large range in composition and b) provide a plausible endmember for the previously unidentified thermogenic gas source (Figure 1.4C). Additionally, the occurrence of elevated 3He/4He in the Springfield and Seelyville 4 coal seams is consistent with the New Albany Shale gas data, while the range of He/CH4, when input into the gas fractionation model account for the noble gas observations for thermogenic-rich endmember in the producing CBM wells in this study area. If I assume that the New Albany Shale is a viable source for thermogenic gas in this region, I envision that the natural gas composition of fluids produced from the CBM reservoir evolved in three steps: 1. Thermogenic natural gas, which had likely been impregnated previously with a component of mantle-derived fluids, migrated as a two- phase fluid from the New Albany Shale to superior formations; 2. The thermogenic natural gases migrated into the Pennsylvania-aged coal seams, which serve as a stratigraphic trap for the hydrocarbon gases; 3. At some point in time, possibly 42 following the erosion, uplift, denudation, and recharge of glacial meltwater (Schlegel et al., 2011a), biogenic methane production increases and leads to the observed mixtures of dominantly biogenic methane with resolvable and quantifiable mixtures of thermogenic methane. Although clearly more work is needed to evaluate the feasibility of these processes, it is worth nothing that the gas molecular and isotopic tracers correspond to each other and select dissolved ions (i.e., Cl, Br) (Figure 1.10). Thus, I suggest that the rapid increase in freshwater recharge during interglacial periods could reduce the abundance of salts and thermogenic gases and stimulate biogenic methane production. 4 20 36 Notice that in Figure 1.9, the enrichment of He/CH4 and Ne/ Ar requires the formation and transport of a dual phase fluid. If I assume that thermogenic New Albany Shale gas migrated and was emplaced in the Springfield and Seelyville coal seams, I can interpret 4 20 36 the correlation of He/CH4 and Ne/ Ar as a result of the dilution of thermogenic gas by biogenic methane with ASW-like 20Ne/36Ar that is devoid in 4He. 43 1.6 Conclusions The integration of hydrocarbon, major, and noble gas composition, the isotopic composition of hydrocarbon and noble gases, and select dissolved ion composition of 20 producing CBM wells from the Illinois Basin, in Sullivan County, Indiana, USA were used to develop a geochemical framework for evaluating the relative contributions of biogenic and thermogenic methane in CBM reservoirs. Our observations suggest that in this setting biogenic methane is dominant, but there are resolvable contributions from thermogenic sources, potentially emplaced prior to the onset biogenic methane formation. Our observations from this study area indicate that previous studies in the Illinois and other basins may overestimate the proportion of biogenic methane. Thus, the implications of standard approaches such as the usage of isotopic and molecular content of hydrocarbons must be explored in other basins. I determine that the thermogenic endmember is distinguished by a positive relationship between the occurrence of ethane, 4He, exogenous 20Ne, enriched 20 36 13 2 Ne/ Ar, enriched δ C-CH4 and δ H-CH4, a higher proportion of non- atmospherically-derived N2. By comparison, the more biogenic end-member contained 13 2 more negative δ C-CH4 and δ H-CH4, is significantly more enriched in gases derived 36 from air-saturated water (e.g., Ar and N2), and contains lower concentrations of ethane. Although all samples displayed a surprising excess of resolvable, mantle- derived 3He (0.7-15.3%), the [4He] is dominated by an exogenous (i.e., migrated) crustal source associated with the thermogenic endmember. 20 36 2 Our new noble gas and hydrocarbon isotopic data (e.g., Ne/ Ar, C2+/C1, δ H- 13 CH4, δ C- CH4) suggest that a component of dual-phase (gas + liquid) thermogenic 44 hydrocarbon gases (up to ~17 to 19%), potentially derived from the New Albany Shale, migrated to and was emplaced within the stratigraphic coal seam traps (i.e., Springfield and Seelyville coal seams). I hypothesize that after these New Albany Shale gases migrated to the coal seam traps, later stages of interglacial meltwater recharge and biogenic methane formation diluted the geochemical signature of the thermogenic methane and brines over time. I conclude that the integration of noble gas geochemistry with hydrocarbon and dissolved ion chemistry permits a more robust evaluation of the source and migration processes of natural gas in the Earth’s crust, which is essential for understanding the genetic source of hydrocarbon gases in coalbed methane reservoirs as well as the roles of microbes in the deep subsurface. 45 1.7 Future Work The current study revealed several new observations about production gases from CBM wells in the Illinois Basin. Although previous studies have suggested that natural gases from CBM reservoirs may contain thermogenic contributions, there have been very few systematic studies that have quantified the genetic sources of natural gas and no known previous studies that employed a multi-component approach that included the molecular and isotopic composition of hydrocarbons, major gases, noble gases, and dissolved ions. Despite these advancements, future work is needed to resolve the relative roles of in situ (i.e., derived from coals) and exogenous thermogenic natural gases in more diverse geographic areas. The potential sources of endogenous thermogenic natural gas within coals remains poorly constrained and have not been studied through the use of a suite of multiple gas geochemical parameters. I identified marked excesses in N2 throughout the current dataset, which have been identified in other basins (e.g., Powder River and Black Warrior Basins) (Ritter et al., 2015). Although these markedly high nitrogen levels have been identified in many basins, they have been largely dismissed as having been derived air-saturated water or gas-water interactions. Future work should examine the nitrogen isotopic values of N2 and the potential pathways for N2 generation to determine the potential roles of microbes and coal seam fluid chemistry in these processes. Specific to noble gases, it remains unclear why apparently low thermal maturity coals would contain such obvious excesses of 40Ar* or how oxygen-deficient minerals 46 could produce 21Ne* at rates similar to average crustal production rates. In order to reliably constrain in situ and exogenous sources of thermogenic gas, I must better constrain how noble gases will interact with high surface area, organic-rich coals. Noble gas geochemistry should be applied more broadly to other CBM reservoirs (e.g., Black Warrior Basin, Powder River Basin, San Juan Basin, Raton Basin). I anticipate that the use of these additional parameters will provide better resolution on the role of exogenous fluids and provide additional constraints on the different genetic sources of natural gas. In this particular study area, further work is needed to evaluate the proposed role of the gases that were derived from the New Albany Shale. While the New Albany Shale was selected as a potential exogenous fluid source based on the geology in the Illinois Basin and the proximity of the New Albany Shale to the Springfield and Seelyville coal seam formations, it is was originally only shown here for comparison. Future work should more fully consider other possibilities that have not been explored herein. Additionally, throughout the next year, I plan to collect more gas samples from producing CBM wells in a more broad geographic area throughout the Illinois Basin to further test some of the ad hoc hypotheses generated as part of this study. 47 1.8 Acknowledgements I acknowledge financial support from NSF EAGER (EAR-1249255) and NSF SusChem (EAR-1441497) to T.H.D and salary support for M.T.M from the School of Earth Sciences at The Ohio State University. I thank Professors Jennifer McIntosh (U. Arizona), Karlis Muehlenbachs (U. Alberta), John Olesik, Frank Schwartz, W. Berry Lyons (OSU), and Robert Poreda (University of Rochester) for stimulating discussions on the geology and geochemistry of coalbed methane reservoirs in the Illinois Basin and elsewhere. I also thank Colin Whyte, Benjamin Grove, Sharon Scott, Erica Maletic, Stephanie Poreda, Dr. Jeremy C. Williams, and Yohei Matsui (OSU) for field and analytical support and friendly reviews of earlier versions of this manuscript. I also thank Larry Neely and Jason Neely (Maverick Energy) for their assistance in sampling, sharing of information, and their knowledge about the study area. 48 References Ballentine, C.J., Burgess, R., Marty, B., 2002. Tracing fluid origin, transport and interaction in the crust. In: Porcelli, D., Ballentine, C.J., Wieler, R. (Eds.), Noble Gases in Geochemistry and Cosmochemistry. Reviews in Mineralogy & Geochemistry, pp. 539-614. Ballentine, C.J., Burnard, P.G., 2002. Production, release and transport of noble gases in the continental crust. 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Identifying and quantifying natural CO2 sequestration processes over geological timescales: The Jackson Dome CO2 Deposit, USA. Geochimica Et Cosmochimica Acta, 86: 257-275. 57 Chapter 1. Figures Figure 1.1 A generalized stratigraphic column (A), areal extent of the Illinois Basin (B), and a simplified structural cross section (C) (reproduced from Strąpoć et al., 2007) of the synclinal Illinois Basin. The stratigraphic column displays the Middle Pennsylvanian-aged Springfield and Seelyville coal seams (of the Carbondale Group) and the upper to middle Devonian-aged New Albany Shale unit. It is important to note that the Dekovan or Davis Formations are equivalent units of the Seelyville Formation. Samples were collected from producing coalbed methane (CBM) wells in the area denoted by the red box on the eastern portion of the Illinois Basin (1C). 58 Figure 1.2 An inset map of sampling locations denoted by the red box (A) and a topographic map (B) showing the locations of producing CBM wells sampled as part of this study (n=20) in Sullivan County, Indiana denoted in red symbols. The green squares denote CBM well locations from previous studies (Schlegel et al., 2011). Purple and yellow boxes denote New Albany Shale well locations from previous studies (Schlegel et al., 2011, McIntosh et al., 2002). 59 2 Figure 1.3 A comparison of the stable isotopic values of hydrogen (δ H-CH4) and 13 carbon (δ C-CH4) in methane. The hatched oval represents the typical range of thermogenic natural gases, with the dashed red line indicating the trend of increasing thermal maturity up and to the right. The blue box represents subsurface microbial methane and the green box represents near-surface microbial methane (A). Samples collected from producing CBM wells from this study (red symbols); from previous reports (Schlegel et al., 2011 and Strąpoć et al., 2007 in green and blue symbols, respectively) (B); and from gases produced from the New Albany Shale (McIntosh, et al., 2002 and Schlegel et al., 2011 in purple and yellow symbols, respectively) (C). The standard deviation is for samples collected in this study. The sample data appear to fall along a two-component mixing line between low maturity thermogenic methane and subsurface microbial methane. 60 Figure 1.4 A comparison of the relative abundances of methane to higher-order aliphatic hydrocarbons (C1/C2+) vs. the stable isotopic composition of carbon in 13 methane (δ C-CH4) from producing CBM wells from this study (red symbols); from previous reports (Schlegel et al., 2011 and Strąpoć et al., 2007 in green and blue symbols, respectively) (A); and from gases produced from the New Albany Shale (McIntosh et al., 2002 and Schlegel et al., 2011 in purple and yellow symbols, respectively) (B). The standard deviation is for samples collected in this study. The typical ranges for the composition of thermogenic and biogenic methane are shown in the green and blue hatched boxes, respectively, while the dashed red arrow in the thermogenic box reflects the trend of increasing thermal maturity. The brown trend depicts hypothetical mixing between the New Albany Shale and biogenic methane; the green trend shows the pathway of oxidation of thermogenic hydrocarbon gases from the New Albany Shale by methanotrophs; and the blue trend displays post-genetic alteration of natural gas from the New Albany Shale following fractionation by GGS-R (adapted from Darrah et al., 2015) (C). 61 13 Figure 1.5 The stable isotopic values of carbon in methane (δ C-CH4) (A), the concentration of ethane [C2H6] (B), the ratio of N2/Ar (C), the stable isotopic values 2 36 of hydrogen in methane (δ H-CH4) (D), the concentration of [ Ar] (E), and the concentration of excess nitrogen [N2] vs. the proportion of [CH4] in producing CBM wells sampled in this study. 62 13 Figure 1.6 The stable isotopic values of carbon in methane (δ C-CH4) (A), 4 the ratio of He/CH4 (B), the proportion of nitrogen [N2] (C), and the ratio 36 of N2/CH4 (D) vs. the concentration of [ Ar] (a proxy for the contributions from air-saturated water gases in the Earth’s crust) in producing CBM wells sampled in this study. 63 4 20 36 Figure 1.7 Comparison of the ratio He/ Ne vs. CH4/ Ar (A), stable isotopic values 13 of carbon in methane (δ C-CH4) (B), the ratio of methane to higher order hydrocarbons (C1/C2+) (C), and a comparison of [N2] vs. stable isotopic values 13 of carbon in methane (δ C-CH4) (D) in producing CBM wells sampled in this study. 64 Figure 1.8 Comparison of the ratio of 3He/4He vs. 4He/20Ne in producing CBM wells sampled in this study. The yellow box represents the composition for globally constrained ASW and the blue box represents tritiated ASW composition. 65 4 20 36 Figure 1.9 Comparison of He/CH4 vs. Ne/ Ar from producing CBM wells sampled in this study (A). The green square represents the previously reported composition of producing gases from the New Albany Shale (Schlegel et al., 2011). The dashed grey line represents one-phase advection of a New Albany-like gas source. The blue line represents mixing of New Albany Shale production gas with a biogenic source. The dashed red trend lines represent a model fractionation by two-phase advection of New Albany Shale to the Springfield and Seelyville coal 4 13 seams. Also displayed is a comparison of He/CH4 vs. δ C-CH4 (B). 66 Figure 1.10 Comparison of the ratio 20Ne/36Ar versus Cl (A) and stable isotopic 13 values of carbon in methane (δ C-CH4) (B) from producing CBM wells sampled in this study. Chloride was only measured in wells that had produced waters when sampling. 67 Chapter 1. Tables Table 1.1 Major Gas Composition Well Max H2 CH4 C2H6 C3H8 C4H10n C4H10i C5H12n C5H12i N2 O2 CO2 GROSS kJ Coal Gas depth GROSS kJ (AFTER CO2 Sample ID Production Screened (BEFORE REMOVAL) Unit (m.) CO2 µccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc REMOVAL) Creed Mine Springfield 76 <0.02 0.922 1.27x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.066 <0.002 0.012 984.8 997.1 -4 -5 -5 -5 -5 -5 Stultz Springfield 72 <0.02 0.961 2.05x10 <1x10 <1x10 <1x10 <1x10 <1x10 0.031 <0.002 0.008 1026.61026.6 1035.3 -4 -5 -5 -5 -5 -5 Mayfield-1 Springfield 91 <0.02 0.965 4.50x10 <1x10 <1x10 <1x10 <1x10 <1x10 0.023 <0.002 0.013 1030.71030.7 1044.3 Alexander- Springfield 107 <0.02 0.953 5.07x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.043 <0.002 0.004 1018.4 1022.5 1 1018.4 Creed-2 Springfield 76 <0.02 0.950 1.73x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.044 <0.002 0.006 1014.6 1021.2 1014.6 Bolenbaugh Seelyville 173 <0.02 0.939 4.85x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.048 <0.002 0.008 1003.3 1011.5 1003.3 T.Cole Seelyville 177 <0.02 0.959 5.04x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.034 <0.002 0.007 1024.6 1031.8 1024.6 Seelyville 213 <0.02 0.943 4.38x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.043 <0.003 0.008 1007.6 1015.2 Alexander- 2 1007.6 Vic Seelyville 171 <0.02 0.963 3.73x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.021 <0.002 0.017 1028.7 1046.1 1028.7 Doherty-1 Seelyville 176 <0.02 0.959 2.47x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.032 <0.002 0.010 1024.1 1034.5 1024.1 Arnett-1 Seelyville 153 <0.02 0.961 3.82x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.030 <0.002 0.009 1027.2 1036.8 1027.2 Arnett-3 Seelyville 167 <0.02 0.954 2.38x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.040 <0.002 0.005 1019.4 1025.0 1019.4 McCain Seelyville 175 <0.02 0.899 9.25x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.085 <0.002 0.006 960.2 965.9 960.2 Wheeler Seelyville 175 <0.02 0.942 1.09x10-3 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.041 <0.002 0.007 1008.9 1015.2 Co-mingled 1008.0 Hancock-1 158 <0.02 0.948 7.15x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.049 <0.002 0.004 1011.8 1015.8 Co-mingled 1011.8 Coulson-1 174 <0.02 0.973 4.73x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.021 <0.002 0.006 1039.9 1046.5 Co-mingled 1039.9 F. Willis No-info <0.02 0.902 4.25x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.075 <0.002 0.010 964.0 974.1 Co-mingled 964.0 Unger 185 <0.02 0.875 7.84x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.097 <0.002 0.009 934.7 942.9 Co-mingled -4 -5 -5 -5 -5 -5 934.7 E.Hobbs-1 No-info <0.02 0.938 3.12x10 <1x10 <1x10 <1x10 <1x10 <1x10 0.052 <0.002 0.011 1001.8 1012.5 Co-mingled Gimoson No-info <0.02 0.971 5.40x10-4 <1x10-5 <1x10-5 <1x10-5 <1x10-5 <1x10-5 0.020 <0.002 0.009 1001.81037.7 1047.1 1037.7 1.2 Statistical Summary of Major Gas Composition GROSS kJ GROSS kJ H2 CH4 C2H6 C3H8 C4H10n C4H10i C5H12n C5H12i N2 O2 CO2 (BEFORE (AFTER CO2 CO2 REMOVAL) REMOVAL) All ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc ccSTP/cc Samples Average - 0.944 3.6x10-4 - - - - - 0.045 - 0.009 1008.4 1017.1 Minimum - 0.875 7.1x10-5 - - - - - 0.020 - 0.004 934.7 942.9 Maximum - 0.973 1.1x10-3 - - - - - 0.097 - 0.017 1039.9 1047.1 St. Dev. - 0.026 2.3x10-4 - - - - - 0.021 - 0.003 27.7 28.2 Springfield Average - 0.950 2.9x10-4 - - - - - 0.041 - 0.009 1015.0 1024.1 Minimum - 0.922 1.3x10-4 - - - - - 0.023 - 0.004 984.8 997.1 Maximum - 0.965 5.1x10-4 - - - - - 0.066 - 0.013 1030.7 1044.3 St. Dev. - 0.017 1.7x10-4 - - - - - 0.017 - 0.004 18.1 17.8 69 Seelyville Average - 0.947 4.3x10-4 - - - - - 0.041 - 0.009 1011.5 1020.2 Minimum - 0.899 9.2x10-5 - - - - - 0.021 - 0.005 960.2 965.9 Maximum - 0.963 1.1x10-3 - - - - - 0.085 - 0.017 1028.7 1046.1 St. Dev. - 0.020 2.8x10-4 - - - - - 0.018 - 0.003 21.4 23.4 Co- mingled Average - 0.934 3.2x10-4 - - - - - 0.052 - 0.008 998.3 1006.5 Minimum - 0.875 7.1x10-5 - - - - - 0.020 - 0.004 934.7 942.9 Maximum - 0.973 5.4x10-4 - - - - - 0.097 - 0.011 1039.9 1047.1 St. Dev. - 0.039 2.0x10-4 - - - - - 0.030 - 0.003 41.7 41.1 1.3 Noble Gas Elemental Composition 3He 4He 20Ne 21Ne 22Ne 20Ne 22Ne Ne 36Ar 38Ar 40Ar Ar 84Kr Kr 132Xe Xe Sample ID pcc/cc µcc/cc µcc/cc µcc/cc µcc/cc ncc/cc ncc/cc µcc/cc µcc/cc µcc/cc µcc/cc µcc/cc ncc/cc ncc/cc ncc/cc ncc/cc Creed Mine 4.55 29.63 1.04 2.98x10-3 0.11 1043.71 106.66 1.15 2.72 0.51 830.2 833.45 98.49 173.10 3.41 12.68 Stultz 5.32 74.18 0.16 5.28x10-4 0.02 164.33 16.81 0.18 0.51 0.09 165.5 166.11 8.49 14.93 0.30 1.12 Mayfield-1 1.34 18.85 0.11 3.56x10-4 0.01 114.71 11.74 0.13 0.40 0.08 122.7 123.18 8.70 15.28 0.36 1.33 Alexander- 29.85 423.42 0.28 8.64x10-4 0.03 280.34 28.69 0.31 0.44 0.08 144.1 144.63 5.54 9.74 0.18 0.69 1 Creed-2 19.34 244.68 0.77 2.44x10-3 0.08 766.65 78.45 0.85 1.08 0.20 333.1 334.37 15.82 27.81 0.42 1.57 Bolenbaugh 25.48 421.27 0.60 1.82x10-3 0.06 601.14 61.48 0.66 0.60 0.12 201.2 201.89 6.61 11.62 0.19 0.69 T.Cole 27.53 460.78 0.27 8.21x10-4 0.03 273.31 27.94 0.30 0.51 0.10 166.2 166.86 7.70 13.52 0.22 0.82 Alexander- 29.64 23.67 0.42 1.27x10-3 0.04 415.89 42.56 0.46 2.00 0.37 579.2 581.55 65.91 115.83 2.20 8.17 2 Vic 11.01 174.84 0.15 4.79x10-4 0.02 150.95 15.44 0.17 0.29 0.06 95.7 96.03 3.26 5.74 0.13 0.47 Doherty-1 88.67 1464.60 1.55 5.02x10-3 0.16 1550.82 158.82 1.71 0.53 0.10 175.2 175.87 5.03 8.85 0.10 0.36 70 Arnett-1 12.00 149.63 0.19 5.76x10-4 0.02 185.37 18.99 0.20 0.38 0.07 124.4 124.81 4.96 8.71 0.10 0.39 Arnett-3 5.96 70.32 0.16 4.65x10-4 0.02 155.32 15.90 0.17 0.34 0.06 112.4 112.85 4.16 7.31 0.10 0.36 McCain 4.48 31.27 0.47 1.38x10-3 0.05 466.38 47.66 0.52 1.60 0.29 473.7 475.57 61.81 108.62 1.76 6.54 Wheeler 22.03 286.71 0.29 9.31x10-4 0.03 290.78 29.74 0.32 0.70 0.13 225.0 225.88 10.68 18.77 0.50 1.86 Hancock-1 6.17 46.99 0.35 1.04x10-3 0.04 349.31 35.69 0.39 1.20 0.23 370.0 371.42 37.88 66.57 1.15 4.29 Coulson-1 11.90 192.04 0.14 4.49x10-4 0.01 143.77 14.70 0.16 0.40 0.08 133.1 133.59 5.42 9.52 0.22 0.81 F. Willis 5.14 11.61 1.04 3.01x10-3 0.11 1043.72 106.66 1.15 3.69 0.70 1088.0 1092.37 145.35 255.45 4.38 16.30 Unger 5.93 37.23 0.99 2.94x10-3 0.10 994.89 101.67 1.10 3.42 0.63 1011.9 1015.93 139.82 245.73 4.04 15.04 E.Hobbs-1 4.36 62.53 0.16 5.06x10-4 0.02 155.70 15.95 0.17 0.34 0.06 112.3 112.68 4.07 7.15 0.16 0.58 Gimoson 6.52 96.11 0.18 5.75x10-4 0.02 175.68 17.99 0.19 0.38 0.07 125.8 126.22 5.15 9.05 0.19 0.71 5 5 (ASW) 62.42 44.91 176.33 0.521 18.03 1.76x10 1.80x10 194.88 1261 237 3.73x10 0.374 50.33 88.33 3.52 13.10 4 (10oC) 1.4 Statistical Summary of Noble Gas Elemental Composition 3He 4He 20Ne 21Ne 22Ne 20Ne 22Ne Ne 36Ar 38Ar 40Ar Ar 84Kr Kr 132Xe Xe All pcc/cc µcc/cc µcc/cc µcc/cc µcc/cc ncc/cc ncc/cc µcc/cc µcc/cc µcc/cc µcc/cc µcc/cc ncc/cc ncc/cc ncc/cc ncc/cc Samples Average 16.361 216.019 0.466 1.42x10-3 0.048 466.138 47.677 0.515 1.076 0.202 329.485 330.763 32.243 56.666 1.006 3.738 Minimum 1.338 11.610 0.115 3.56x10-4 0.012 114.708 11.740 0.127 0.287 0.059 95.685 96.031 3.264 5.736 0.096 0.356 Maximum 88.670 1464.600 1.551 5.02x10-3 0.159 1550.818 158.816 1.715 3.688 0.695 1087.990 1092.374 145.353 255.454 4.385 16.300 St. Dev. 19.493 327.901 0.406 1.25x10-3 0.041 405.521 41.483 0.448 1.062 0.199 310.298 311.559 45.873 80.620 1.399 5.200 Springfield Average 12.081 158.153 0.474 1.43x10-3 0.048 473.947 48.470 0.524 1.028 0.193 319.126 320.346 27.410 48.173 0.935 3.477 Minimum 1.338 18.851 0.115 3.56x10-4 0.012 114.708 11.740 0.127 0.397 0.075 122.707 123.180 5.543 9.741 0.184 0.685 Maximum 29.855 423.425 1.044 2.98x10-3 0.107 1043.711 106.660 1.153 2.717 0.513 830.220 833.449 98.494 173.100 3.411 12.681 St. Dev. 12.109 173.804 0.410 1.20x10-3 0.042 410.095 41.915 0.453 0.984 0.186 297.583 298.753 39.917 70.152 1.387 5.155 71 Seelyville Average 25.199 342.567 0.454 1.42x10-3 0.047 454.439 46.503 0.502 0.772 0.145 239.228 240.145 18.901 33.219 0.587 2.184 Minimum 4.476 23.670 0.151 4.65x10-4 0.015 150.951 15.440 0.167 0.287 0.059 95.685 96.031 3.264 5.736 0.096 0.356 Maximum 88.670 1464.600 1.551 5.02x10-3 0.159 1550.818 158.816 1.715 2.000 0.373 579.180 581.552 65.910 115.834 2.199 8.173 St. Dev. 25.590 450.045 0.439 1.43x10-3 0.045 438.572 44.915 0.485 0.605 0.111 170.101 170.817 25.602 44.994 0.806 2.996 Co-mingled Average 6.669 74.419 0.477 1.42x10-3 0.049 477.179 48.777 0.527 1.573 0.295 473.501 475.369 56.283 98.915 1.691 6.287 Minimum 4.356 11.610 0.144 4.49x10-4 0.015 143.771 14.703 0.159 0.343 0.064 112.278 112.685 4.071 7.155 0.155 0.578 Maximum 11.896 192.043 1.044 3.01x10-3 0.107 1043.715 106.660 1.153 3.688 0.695 1087.990 1092.374 145.353 255.454 4.385 16.300 St. Dev. 2.677 64.074 0.427 1.22x10-3 0.044 426.790 43.602 0.472 1.570 0.294 457.257 459.121 68.086 119.660 1.993 7.409 1.5 Noble Gas Isotopic Composition Sample ID 3He 3He (He/Ne) (He/Ne) 20Ne 21Ne 38Ar 40Ar 78Kr 80Kr 82Kr 83Kr 86Kr 126Xe 128Xe 129Xe 130Xe 131Xe 134Xe 136Xe 4He 4He 22Ne 22Ne 36Ar 36Ar 84Kr 84Kr 84Kr 84Kr 84Kr 132Xe 132Xe 132Xe 132Xe 132Xe 132Xe 132Xe ASW R/RA RC/RA Creed Mine 0.110 0.110 25.7 89.2 9.785 0.0279 0.1887 305.61 0.0067 0.076 0.206 0.202 0.305 0.006 0.081 0.968 0.158 0.791 0.395 0.335 Stultz 0.052 0.052 408.3 1417.8 9.776 0.0314 0.1830 327.34 0.0066 0.091 0.207 0.201 0.303 0.009 0.085 1.002 0.165 0.797 0.395 0.353 Mayfield-1 0.051 0.051 148.7 516.2 9.771 0.0304 0.1897 308.73 0.0072 0.076 0.208 0.206 0.309 0.007 0.078 0.963 0.158 0.786 0.396 0.355 Alexander-1 0.051 0.051 1366.4 4744.4 9.772 0.0301 0.1849 328.61 0.0067 0.114 0.204 0.201 0.305 0.007 0.085 0.999 0.180 0.803 0.406 0.351 Creed-2 0.057 0.057 288.7 1002.4 9.772 0.0312 0.1864 307.84 0.0071 0.107 0.203 0.203 0.303 0.007 0.083 0.982 0.166 0.781 0.388 0.333 Bolenbaugh 0.044 0.044 634.0 2201.5 9.778 0.0297 0.1934 334.35 0.0068 0.085 0.205 0.206 0.305 0.007 0.082 1.014 0.172 0.796 0.414 0.339 T.Cole 0.043 0.043 1525.4 5296.5 9.780 0.0294 0.1920 325.14 0.0076 0.122 0.209 0.201 0.303 0.009 0.086 0.968 0.175 0.807 0.396 0.345 Alexander-2 0.901 0.901 51.5 178.8 9.771 0.0298 0.1863 289.61 0.0072 0.106 0.207 0.204 0.306 0.008 0.082 0.991 0.175 0.802 0.398 0.337 Vic 0.045 0.045 1047.8 3638.0 9.776 0.0310 0.2060 333.38 0.0077 0.069 0.207 0.212 0.297 0.020 0.089 1.010 0.189 0.831 0.477 0.377 Doherty-1 0.044 0.044 854.2 2965.8 9.765 0.0316 0.1874 331.80 0.0075 0.134 0.204 0.202 0.306 0.010 0.085 0.974 0.192 0.770 0.398 0.374 72 Arnett-1 0.058 0.058 730.1 2535.2 9.761 0.0303 0.1902 331.18 0.0069 0.105 0.203 0.204 0.301 0.012 0.090 0.970 0.163 0.821 0.376 0.373 Arnett-3 0.061 0.061 409.6 1422.3 9.769 0.0292 0.1828 327.40 0.0069 0.114 0.210 0.206 0.301 0.011 0.087 0.993 0.172 0.810 0.407 0.387 McCain 0.103 0.103 60.7 210.7 9.786 0.0289 0.1837 296.66 0.0068 0.132 0.209 0.204 0.305 0.012 0.090 1.008 0.166 0.790 0.395 0.307 Wheeler 0.055 0.055 891.9 3097.0 9.777 0.0313 0.1859 319.33 0.0068 0.106 0.206 0.202 0.303 0.006 0.080 0.987 0.170 0.808 0.395 0.346 Hancock-1 0.094 0.094 121.7 422.6 9.787 0.0291 0.1895 307.50 0.0068 0.095 0.204 0.204 0.305 0.006 0.084 0.985 0.167 0.810 0.397 0.335 Coulson-1 0.045 0.045 1208.4 4195.9 9.778 0.0305 0.1870 328.98 0.0069 0.104 0.204 0.205 0.303 0.006 0.083 1.008 0.162 0.784 0.396 0.344 F. Willis 0.318 0.318 10.1 35.0 9.785 0.0282 0.1885 294.99 0.0067 0.133 0.208 0.205 0.300 0.008 0.084 1.000 0.171 0.813 0.429 0.332 Unger 0.115 0.115 33.9 117.6 9.786 0.0289 0.1855 295.87 0.0067 0.133 0.208 0.205 0.303 0.008 0.094 0.981 0.168 0.787 0.401 0.338 E.Hobbs-1 0.050 0.050 363.2 1261.2 9.762 0.0317 0.1861 327.58 0.0078 0.107 0.207 0.207 0.305 0.008 0.089 1.033 0.176 0.833 0.422 0.349 Gimoson 0.049 0.049 494.8 1717.9 9.766 0.0320 0.1889 331.29 0.0069 0.109 0.207 0.204 0.308 0.008 0.089 0.956 0.166 0.777 0.378 0.344 Air-saturated 0.985 0.985 0.288 1.00 9.780 0.029 0.188 295.50 0.006 0.040 0.203 0.202 0.303 0.003 0.071 0.981 0.151 0.789 0.388 0.329 Water (ASW) Values Table 1.6 Statistical Summary of Noble Gas Isotopic Composition (He/Ne) (He/Ne) 3He 3He 20Ne 21Ne 38Ar 40Ar 78Kr 80Kr 82Kr 83Kr 86Kr 126Xe 128Xe 129Xe 130Xe 131Xe 134Xe 136Xe 4He 4He ASW 22Ne 22Ne 36Ar 36Ar 84Kr 84Kr 84Kr 84Kr 84Kr 132Xe 132Xe 132Xe 132Xe 132Xe 132Xe 132Xe All Samples Average 0.117 0.117 533.7 1853.29 9.775 0.0301 0.1883 317.66 0.0070 0.106 0.206 0.204 0.304 0.009 0.085 0.990 0.170 0.800 0.403 0.348 Minimum 0.043 0.043 10.1 34.95 9.761 0.0279 0.1828 289.61 0.0066 0.069 0.203 0.201 0.297 0.006 0.078 0.956 0.158 0.770 0.376 0.307 Maximum 0.901 0.901 1525.4 5296.54 9.787 0.0320 0.2060 334.35 0.0078 0.134 0.210 0.212 0.309 0.020 0.094 1.033 0.192 0.833 0.477 0.387 St. Dev. 0.194 0.194 478.7 1662.18 0.008 0.0012 0.0050 15.10 0.0004 0.020 0.002 0.002 0.003 0.003 0.004 0.020 0.009 0.017 0.021 0.019 Springfield Average 0.064 0.064 447.5 1553.99 9.775 0.0302 0.1865 315.63 0.0069 0.093 0.205 0.203 0.305 0.007 0.082 0.983 0.165 0.791 0.396 0.346 Minimum 0.051 0.051 25.7 89.20 9.771 0.0279 0.1830 305.61 0.0066 0.076 0.203 0.201 0.303 0.006 0.078 0.963 0.158 0.781 0.388 0.333 Maximum 0.110 0.110 1366.4 4744.36 9.785 0.0314 0.1897 328.61 0.0072 0.114 0.208 0.206 0.309 0.009 0.085 1.002 0.180 0.803 0.406 0.355 St. Dev. 0.026 0.026 533.5 1852.29 0.006 0.0014 0.0027 11.34 0.0003 0.017 0.002 0.002 0.002 0.001 0.003 0.018 0.009 0.009 0.006 0.011 73 Seelyville Average 0.150 0.150 689.5 2393.97 9.774 0.0301 0.1897 320.98 0.0071 0.108 0.207 0.205 0.303 0.011 0.086 0.991 0.175 0.804 0.406 0.354 Minimum 0.043 0.043 51.5 178.78 9.761 0.0289 0.1828 289.61 0.0068 0.069 0.203 0.201 0.297 0.006 0.080 0.968 0.163 0.770 0.376 0.307 Maximum 0.901 0.901 1525.4 5296.54 9.786 0.0316 0.2060 334.35 0.0077 0.134 0.210 0.212 0.306 0.020 0.090 1.014 0.192 0.831 0.477 0.387 St. Dev. 0.282 0.282 471.8 1638.18 0.008 0.0010 0.0070 16.55 0.0004 0.021 0.002 0.003 0.003 0.004 0.004 0.018 0.010 0.018 0.028 0.026 Co-mingled Average 0.112 0.112 372.0 1291.69 9.777 0.0301 0.1876 314.37 0.0070 0.114 0.206 0.205 0.304 0.007 0.087 0.994 0.168 0.801 0.404 0.340 Minimum 0.045 0.045 10.1 34.95 9.762 0.0282 0.1855 294.99 0.0067 0.095 0.204 0.204 0.300 0.006 0.083 0.956 0.162 0.777 0.378 0.332 Maximum 0.318 0.318 1208.4 4195.86 9.787 0.0320 0.1895 331.29 0.0078 0.133 0.208 0.207 0.308 0.008 0.094 1.033 0.176 0.833 0.429 0.349 St. Dev. 0.105 0.105 452.3 1570.35 0.011 0.0016 0.0016 16.97 0.0004 0.016 0.002 0.001 0.002 0.001 0.004 0.026 0.005 0.021 0.019 0.007 Table 1.7 Stable Isotopic Composition of Methane and Dissolved Inorganic Carbon Coal Gas Production Well Max depth Sample ID 13 2 13 Unit Screened (m.) δ C-CH4 δ H-CH4 δ C-DIC per mil per mil per mil Creed Mine Springfield 76 -64.10 -209.7 n.r. Stultz Springfield 73 -58.10 n.r. 17 Mayfield-1 Springfield 91 -53.90 -202.3 n.r. Alexander-1 Springfield 107 -54.60 -206.4 26 Creed-2 Springfield 76 -59.58 -214.9 n.r. Bolenbaugh Seelyville 173 -55.31 -210.6 27 T.Cole Seelyville 177 -55.20 -203.9 24 74 Alexander-2 Seelyville 213 -63.14 -208.7 n.r. Vic Seelyville 171 -55.87 -202.6 26 Doherty-1 Seelyville 176 -57.30 n.r. 27 Arnett-1 Seelyville 153 -54.68 -201.4 21 Arnett-3 Seelyville 167 -58.64 -203.5 24 McCain Seelyville 175 -63.24 -203.1 n.r. Wheeler Seelyville 175 -49.87 -203.6 n.r. Hancock-1 Co-mingled 158 -62.32 -209.8 23 Coulson-1 Co-mingled 174 -54.77 n.r. 27 F. Willis Co-mingled No-info -65.67 -213.6 n.r. Unger Co-mingled 185 -69.80 -208.7 n.r. E.Hobbs-1 Co-mingled No-info -56.80 -208.6 n.r. Gimoson Co-mingled No-info -54.90 -208.9 n.r. Table 1.8 Statistical Summary of Stable Isotopic Composition of Methane and Dissolved Inorganic Carbon 13 2 13 δ C-CH4 δ H-CH4 δ C-DIC per mil per mil per mil All Samples Average -58.39 -207.1 24.2 Minimum -69.80 -214.9 17.0 Maximum -49.87 -201.4 27.0 St. Dev. 4.89 4.1 3.2 Springfield Average -58.06 -208.3 21.5 Minimum -64.10 -214.9 17.0 Maximum -53.90 -202.3 26.0 St. Dev. 4.13 5.3 6.4 75 Seelyville Average -57.03 -204.7 24.8 Minimum -63.24 -210.6 21.0 Maximum -49.87 -201.4 27.0 St. Dev. 4.23 3.2 2.3 Co-mingled Average -60.71 -209.9 25.0 Minimum -69.80 -213.6 23.0 Maximum -54.77 -208.6 27.0 St. Dev. 6.23 2.1 2.8 Table 1.9 Select Major Anions Cl Br Br/Cl Coal Gas Well Max Sample ID Production depth Unit Screened mg/L mg/L (m.) Creed Mine Springfield 76 n.r. n.r. n.a. Stultz Springfield 72 1067 n.r. n.a. Mayfield-1 Springfield 91 n.r. n.r. n.a. Alexander-1 Springfield 107 4023 9.3 2.31x10-3 Creed-2 Springfield 76 n.r. n.r. n.a. Bolenbaugh Seelyville 173 6462 14.9 2.31x10-3 T.Cole Seelyville 177 7436 21.9 2.95x10-3 Alexander-2 Seelyville 213 n.r. n.r. n.a. 76 Vic Seelyville 171 4819 12.1 2.51x10-3 Doherty-1 Seelyville 176 6064 11.7 1.93x10-3 Arnett-1 Seelyville 153 2031 6.3 3.10x10-3 Arnett-3 Seelyville 167 4070 13.2 3.24x10-3 McCain Seelyville 175 n.r. n.r. n.a. Wheeler Seelyville 175 n.r. n.r. n.a. Hancock-1 Co-mingled 158 5613 10.8 1.92x10-3 Coulson-1 Co-mingled 174 4944 12.9 2.61x10-3 F. Willis Co-mingled No-info n.r. n.r. n.a. Unger Co-mingled 185 n.r. n.r. n.a. E.Hobbs-1 Co-mingled No-info n.r. n.r. n.a. Gimoson Co-mingled No-info n.r. n.r. n.a. Table 1.10 Statistical Summary of Select Major Anions Cl Br Br/Cl mg/L All Samples mg/L Average 4653 12.6 2.54x10-3 Minimum 1067 6.3 1.92x10-3 Maximum 7436 21.9 3.24 x10-3 St. Dev. 1958 4.3 4.79 x10-4 Springfield Average 2545 9.3 2.31x10-3 Minimum 1067 9.3 2.31x10-3 Maximum 4023 9.3 2.31x10-3 St. Dev. 2090 - - 77 Seelyville Average 5147 13.4 2.67x10-3 Minimum 2031 6.3 1.93x10-3 Maximum 7436 21.9 3.24x10-3 St. Dev. 1938 5.1 5.09x10-4 Co-mingled Average 5279 11.9 2.27x10-3 Minimum 4944 10.8 1.92x10-3 Maximum 5613 12.9 2.61x10-3 St. Dev. 473 1.5 4.84x10-4 Table 1.11 Molecular and Isotopic Gas Ratios 4 4 4 4 4 CO 2 CH 4 CH 4 CH 4 He N2 CH 4 C2 H6+ CH 4 CO 2 He 20 He 84 132 He He Ne Kr Xe Sample ID 3 3 4 20 36 21 40 He He 36Ar He CH4 Ar C2H6+ CH4 CO2 CH4 Ne 36Ar Ar 36Ar 84Kr Ne* Ar* 6 x10 x10-6 Creed Mine 1.24x1010 2.03x1011 3.39x105 3.11x104 32.1 79.6 7256.6 1.38x10-4 74.3 0.0135 28.4 0.384 10.9 0.036 0.035 n.a. 1.1 Stultz 8.38x109 1.81x1011 1.90x106 1.30x104 77.2 185.2 4687.6 2.13x10-4 114.6 0.0087 451.4 0.325 146.7 0.017 0.036 1.77 4.6 Mayfield-1 1.30x1010 7.21x1011 2.43x106 5.12x104 19.5 184.5 2145.6 4.66x10-4 74.0 0.0135 164.3 0.289 47.4 0.022 0.041 1.10 3.6 Alexander-1 3.95109 3.19x1010 2.17x106 2.25x103 444.3 299.2 1879.6 5.32x10-4 241.5 0.0041 1510.4 0.639 965.5 0.013 0.033 12.17 29.2 Creed-2 6.48x109 4.91x1010 8.78x105 3.88x103 257.6 131.3 5489.4 1.82x10-4 146.5 0.0068 319.2 0.709 226.1 0.015 0.027 1.38 18.3 Bolenbaugh 8.10x109 3.69x1010 1.56x106 2.23x103 448.7 235.4 1935.1 5.17x10-4 115.9 0.0086 700.8 0.999 700.1 0.011 0.028 9.12 18.0 T.Cole 6.95x109 3.48x1010 1.87x106 2.08x103 480.6 201.0 1901.1 5.26x10-4 137.9 0.0073 1685.9 0.535 901.2 0.015 0.029 35.41 30.4 78 Alexander-2 7.50x109 3.18x1010 4.71x105 3.98x104 25.1 74.2 2154.6 4.64x10-4 125.7 0.0080 56.9 0.208 11.8 0.033 0.033 0.60 n.a. Vic 1.67x1010 8.74x1010 3.35x106 5.51x103 181.6 217.4 2578.9 3.88x10-4 57.7 0.0173 1158.2 0.526 609.2 0.011 0.039 5.34 16.1 Doherty-1 1.00x1010 1.08x1010 1.82x106 6.55x102 1527.6 179.6 3879.6 2.58x10-4 95.8 0.0104 944.4 2.936 2773.1 0.010 0.019 3.37 76.4 Arnett-1 9.25x109 8.01x1010 2.56x106 6.42x103 155.6 237.8 2513.4 3.98x10-4 103.9 0.0096 807.2 0.494 398.5 0.013 0.021 5.56 11.2 Arnett-3 5.46x109 1.60x1011 2.78x106 1.36x104 73.7 358.5 4002.1 2.50x10-4 174.8 0.0057 452.8 0.452 204.8 0.012 0.023 13.38 6.4 McCain 5.90x109 2.01x1011 5.63x105 2.88x104 34.8 178.4 9725.6 1.03x10-4 152.4 0.0066 67.0 0.292 19.6 0.039 0.028 n.a. 16.9 Wheeler 7.11x109 4.28x1010 1.34x106 3.29x103 304.3 179.6 867.6 1.15x10-5 132.5 0.0075 986.0 0.413 406.8 0.015 0.047 4.04 17.1 Hancock-1 3.91x109 1.54x1011 7.87x105 2.02x104 49.6 130.9 13256.6 7.54x10-5 242.3 0.0041 134.5 0.290 39.1 0.031 0.030 7.31 3.3 Coulson-1 6.30x109 8.18x1010 2.41x106 5.07x103 197.4 155.2 2057.9 4.86x10-4 154.3 0.0065 1335.8 0.355 474.6 0.013 0.040 7.94 14.2 F. Willis 1.04x1010 1.76x1011 2.45x105 7.77x104 12.9 68.9 2124.5 4.71x10-4 86.7 0.0115 11.1 0.283 3.1 0.039 0.030 n.a. n.a. Unger 8.70x109 1.48x1011 2.56x105 2.35x104 42.5 95.0 11164.4 8.96x10-5 100.6 0.0099 37.4 0.291 10.9 0.041 0.029 n.a. 29.4 E.Hobbs-1 1.05x1010 2.15x1011 2.74x106 1.50x104 66.7 464.3 3001.6 3.33x10-4 89.2 0.0112 401.6 0.454 182.4 0.012 0.038 1.39 5.7 Gimoson 8.97x109 1.49x1011 2.56x106 1.01x104 99.0 161.0 1796.6 5.57x10-4 108.2 0.0092 547.0 0.463 253.1 0.014 0.037 1.73 7.1 ASW (10oC) 37.03 0.255 0.140 0.036 0.040 0.070 1.12 Statistical Summary of Molecular and Isotopic Gas Ratios 4 4 4 4 4 CO2 CH4 CH4 CH4 He N2 CH4 C2H6+ CH4 CO2 He 20 He 84 132 He He Ne Kr Xe 3 3 4 20 36 21 40 He He 36 He Ar C H + CH CO CH Ne 36 Ar 36 84 All Ar CH4 2 6 4 2 4 Ar Ar Kr Ne* Ar* Samples 6 x10 x10-6 Average 8.50x109 1.40x1011 1.65x106 1.78x104 226.5 190.8 4220.9 3.80x10-4 126.5 9.01x10-3 590.0 0.567 419.3 0.021 0.032 6.98 17.16 Minimum 3.91x109 1.08x1010 2.45x105 6.55x102 12.9 68.9 867.6 7.54x10-5 57.7 4.13x10-3 11.1 0.208 3.1 0.010 0.019 0.60 1.08 Maximum 1.67x1010 7.21x1011 3.35x106 7.77x104 1527.6 464.3 13256.6 1.15x10-3 242.3 1.73x10-2 1685.9 2.936 2773.1 0.041 0.047 35.41 76.38 St. Dev. 3.13x109 1.53x1011 9.80x105 1.99x104 342.2 97.2 3474.1 2.45x10-4 49.7 3.29x10-3 529.2 0.587 630.2 0.011 0.007 8.57 17.44 Springfield Average 8.85x109 2.37x1011 1.54x106 2.03x104 166.2 176.0 4291.7 3.06x10-4 130.2 9.33x10-3 494.7 0.469 279.3 0.020 0.034 4.10 11.35 Minimum 3.95x109 3.19x1010 3.39x105 2.25x103 19.5 79.6 1879.6 1.38x10-4 74.0 4.14x10-3 28.4 0.289 10.9 0.013 0.027 1.10 1.08 Maximum 1.30x1010 7.21x1011 2.43x106 5.12x104 444.3 299.2 7256.6 5.32x10-4 241.5 1.35x10-2 1510.4 0.709 965.5 0.036 0.041 12.17 29.17 St. Dev. 3.88x109 2.81x1011 8.94x105 2.07x104 182.4 81.6 2280.7 1.80x10-4 69.3 4.13x10-3 589.7 0.192 392.8 0.009 0.005 5.38 12.01 79 Seelyville Average 8.55x109 7.62x1010 1.81x106 1.14x104 359.1 206.9 3284.2 4.51x10-4 121.8 9.01x10-3 762.1 0.762 669.4 0.018 0.030 9.60 24.05 Minimum 5.46x109 1.08x1010 4.71x105 6.55x102 25.1 74.2 867.6 1.03x10-4 57.7 5.72x10-3 56.9 0.208 11.8 0.010 0.019 0.60 6.42 Maximum 1.67x1010 2.01x1011 3.35x106 3.98x104 1527.6 358.5 9725.6 1.15x10-3 174.8 1.73x10-2 1685.9 2.936 2773.1 0.039 0.047 35.41 76.38 St. Dev. 3.37x109 6.46x1010 9.70x105 1.38x104 469.4 74.8 2605.3 2.98x10-4 34.0 3.44x10-3 521.5 0.845 843.8 0.011 0.009 11.12 22.22 Co-mingled Average 8.13x109 1.54x1011 1.50x106 2.53x104 78.0 179.2 5566.9 3.35x10-4 130.2 8.75x10-3 411.2 0.356 160.6 0.025 0.034 4.59 11.92 Minimum 3.91x109 8.18x1010 2.45x105 5.07x103 12.9 68.9 1796.6 7.54x10-5 86.7 4.13x10-3 11.1 0.283 3.1 0.012 0.029 1.39 3.26 Maximum 1.05x1010 2.15x1011 2.74x106 7.77x104 197.4 464.3 13256.6 5.57x10-4 242.3 1.15x10-2 1335.8 0.463 474.6 0.041 0.040 7.94 29.42 St. Dev. 2.57x109 4.36x1010 1.19x106 2.65x104 65.0 144.1 5204.3 2.09x10-4 60.1 2.90x10-3 499.9 0.084 184.2 0.014 0.005 3.51 10.59 Table 1.13 Correlation Matrix of Data Gross Gross 3 4 20 21 CH4 C2H6 N2 CO2 TOTAL BTU BTU He He Ne Ne before After 2 ** ** ** ** * * r 1.000 0.336 -.981 0.024 .853 1.000 .993 .224 .266 -.515 -.466 CH4 Sig. .147 .000 .921 .000 .000 .000 .343 .256 .020 .038 N 20 20 20 20 20 20 20 20 20 20 20 r2 0.336 1 -.421 .001 -.021 0.35 .347 .139 .113 -.331 -.316 C2H6 Sig. .147 .065 .997 .929 .130 .134 .558 .636 .155 .174 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** * * r -.981 -.421 1 -.151 -.771 -.983 -.991 -.225 -.263 .506 .457 N2 Sig. .000 .065 .526 .000 .000 .000 .339 .262 .023 .043 N 20 20 20 20 20 20 20 20 20 20 20 r2 .024 .001 -.151 1 .088 .024 .138 -.081 -.026 .123 .116 CO2 Sig. .921 .997 .526 .713 .921 .561 .735 .912 .605 .627 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** r .853 -.021 -.771 .088 1 .848 .850 .125 .202 -.370 -.336 TOTAL Sig. .000 .929 .000 .713 .000 .000 .601 .393 .109 .147 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** * * r 1.000 .350 -.983 .024 .848 1 .993 .225 .267 -.517 -.469 Gross kJ Sig. .000 .130 .000 .921 .000 .000 .341 .256 .020 .037 before N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** * * r .993 .347 -.991 .138 .850 .993 1 .213 .261 -.499 -.452 Gross kJ Sig. .000 .134 .000 .561 .000 .000 .366 .266 .025 .046 Aftrer N 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** r .224 .139 -.225 -.081 .125 .225 .213 1 .952 .529 .583 3He Sig. .343 .558 .339 .735 .601 .341 .366 .000 .017 .007 N 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** r .266 .113 -.263 -.026 .202 .267 .261 .952 1 .507 .562 4He Sig. .256 .636 .262 .912 .393 .256 .266 .000 .023 .010 N 20 20 20 20 20 20 20 20 20 20 20 2 * * * * * * ** r -.515 -.331 .506 .123 -.370 -.517 -.499 .529 .507 1 .997 20Ne Sig. .020 .155 .023 .605 .109 .020 .025 .017 .023 .000 N 20 20 20 20 20 20 20 20 20 20 20 2 * * * * ** ** ** r -.466 -.316 .457 .116 -.336 -.469 -.452 .583 .562 .997 1 21Ne Sig. .038 .174 .043 .627 .147 .037 .046 .007 .010 .000 N 20 20 20 20 20 20 20 20 20 20 20 2 * * * * * * ** ** r -.514 -.330 .505 .123 -.369 -.516 -.498 .530 .508 1.000 .997 22Ne Sig. .020 .155 .023 .605 .110 .020 .025 .016 .022 .000 .000 N 20 20 20 20 20 20 20 20 20 20 20 2 * * * * * * ** ** r -.515 -.331 .505 .123 -.369 -.517 -.499 .529 .507 1.000 .997 Ne Sig. .020 .155 .023 .605 .109 .020 .025 .017 .022 .000 .000 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** * r -.847 -.319 .817 .072 -.727 -.848 -.832 -.201 -.305 .611 .555 36Ar Sig. .000 .170 .000 .763 .000 .000 .000 .395 .191 .004 .011 N 20 20 20 20 20 20 20 20 20 20 20 (Continued) 80 Table 1.13 (Continued) (He/Ne) 22Ne Ne 36Ar 38Ar 40Ar Ar 84Kr Kr 132Xe Xe 3He/4He (He/Ne) asw 2 * * ** ** ** ** ** ** ** ** ** r -.514 -.515 -.847 -.843 m -.847 -.862 -.862 -.838 -.838 -.210 .568 .568 CH4 Sig. .020 .020 .000 .000 .000 .000 .000 .000 .000 .000 .374 .009 .009 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * r -.330 -.331 -.319 -.317 -.321 -.321 -.336 -.336 -.309 -.309 .027 .506 .506 C2H6 Sig. .155 .155 .170 .174 .168 .168 .147 .147 .185 .185 .911 .023 .023 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * ** ** * ** ** ** ** ** ** ** r .505 .505 .817 .812 .818 .818 .827 .827 .804 .804 .178 -.569 -.569 * N2 Sig. .023 .023 .000 .000 .000 .000 .000 .000 .000 .000 .454 .009 .009 N 20 20 20 20 20 20 20 20 20 20 20 20 20 r2 .123 .123 .072 .079 .074 .074 .097 .097 .121 .121 -.044 -.113 -.113 CO2 Sig. .605 .605 .763 .740 .758 .758 .684 .684 .610 .610 .855 .635 .635 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** r -.369 -.369 -.727 -.722 - -.721 -.743 -.743 -.710 -.710 -.303 .382 .382 ** .721 TOTAL Sig. .110 .109 .000 .000 .000 .000 .000 .000 .000 .000 .195 .097 .097 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * ** ** ** ** ** ** ** ** ** ** r -.516 -.517 -.848 -.843 -.847 -.847 -.863 -.863 -.838 -.838 -.208 .573 .573 Gross Si .020 .020 .000 .000 .000 .000 .000 .000 .000 .000 .378 .008 .008 kJ g. before 20 20 20 20 20 20 20 20 20 20 20 20 20 N 2 * * ** ** ** ** ** ** ** ** * * r -.498 -.499 -.832 -.827 -.831 -.831 -.844 -.844 -.817 -.817 -.212 .554 .554 Gross Si .025 .025 .000 .000 .000 .000 .000 .000 .000 .000 .370 .011 .011 kJ g. Aftrer 20 20 20 20 20 20 20 20 20 20 20 20 20 N 2 * * r .530 .529 -.201 -.201 -.198 -.198 -.249 -.249 -.257 -.257 .071 .409 .409 3 He Sig. .016 .017 .395 .394 .402 .402 .289 .289 .274 .274 .765 .074 .074 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * * * r .508 .507 -.305 -.304 -.298 -.298 -.340 -.340 -.355 -.355 -.224 .499 .499 4 He Sig. .022 .022 .191 .192 .203 .203 .143 .143 .125 .125 .343 .025 .025 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** * ** ** ** * * r 1.000 1.000 .611 .612 .620 .620 .566 .566 .557 .557 .112 -.290 -.290 20 * Ne Sig. .000 .000 .004 .004 .004 .004 .009 .009 .011 .011 .638 .216 .216 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** * * * ** * * * * r .997 .997 .555 .556 .564 .564 .508 .508 .497 .497 .096 -.256 -.256 21 * Ne Sig. .000 .000 .011 .011 .010 .010 .022 .022 .026 .026 .687 .276 .276 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** * ** ** ** * * r 1 1.000 .610 .611 .619 .619 .565 .565 .555 .555 .112 -.289 -.289 22 * Ne Sig. .000 .004 .004 .004 .004 .009 .009 .011 .011 .639 .217 .217 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** * ** ** ** * * r 1.000 1 .611 .612 .620 .620 .565 .565 .556 .556 .112 -.289 -.289 * Ne Sig. .000 .004 .004 .004 .004 .009 .009 .011 .011 .638 .216 .216 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** * ** ** ** ** ** * ** ** r .610 .611 1 1.000 1.000 1.000 .992 .992 .992 .992 .451 -.619 -.619 36 * Ar Sig. .004 .004 .000 .000 .000 .000 .000 .000 .000 .046 .004 .004 N 20 20 20 20 20 20 20 20 20 20 20 20 20 (Continued) 81 Table 1.13 (Continued) 13 20 21 38 40 130 132 131 132 136 132 δ C- 3 3 36 4 4 4 Ne/ Ne/ Ar/ Ar/ Xe/ Xe Xe/ Xe Xe/ Xe CO2/ He CH4/ He CH4/ Ar CH4/ He He/CH CH 22Ne 22Ne 36Ar 36Ar 4 ** ** ** * r2 - .63 .243 .69 .106 .002 .566 .783 .024 -.017 .742 -.485 .263 ** ** CH4 Sig. .006.58 .0030 .302 .0018 .656 .994 .009 .000 .921 .942 .000 .030 .263 ** N 208 20 20 20 20 20 20 20 20 20 20 20 20 2 ** r - .360 .125 .306 .101 .151 .129 .708 .001 -.138 .274 -.161 .114 C2H6 Sig. .320.2 .119 .598 .190 .672 .525 .589 .000 .997 .561 .242 .499 .632 N 2035 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** r .59 - - - -.138 -.014 -.599 -.801 -.151 -.013 -.761 .440 -.260 ** N2 Sig. .0060 .001.667 .150.3 .001.68 .563 .954 .005 .000 .526 .957 .000 .052 .268 ** ** N 20 20 2034 209 20 20 20 20 20 20 20 20 20 2 ** r - .143 .64 .083 .155 .186 .311 .024 1.000 .374 .259 .257 -.028 ** CO2 Sig. .592.1 .548 .0024 .728 .515 .434 .182 .919 0.000 .104 .271 .273 .907 N 2028 20 20 20 20 20 20 20 20 20 20 20 20 2 * ** ** r - .428 .198 .61 .051 .065 .481 .566 .088 .071 .645 -.404 .198 ** TOTAL Sig. .019.51 .060 .402 .0047 .831 .787 .032 .009 .713 .765 .002 .077 .402 * N 207 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** * Gross r - .63 .244 .69 .107 .004 .565 .790 .024 -.020 .743 -.485 .263 ** ** kJ Sig. .006.58 .0032 .300 .0019 .653 .986 .009 .000 .921 .935 .000 .030 .263 ** before N 209 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** * Gross r - .64 .316 .70 .125 .026 .595 .785 .138 .024 .766 -.452 .257 ** ** kJ Sig. .005.59 .0023 .174 .0012 .601 .914 .006 .000 .561 .920 .000 .046 .273 ** After N 208 20 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** r - .302 .009 .263 .673 -.344 .264 .206 -.081 -.474 .011 -.376 .952 3He Sig. .192.3 .196 .971 .263 .001 .138 .261 .383 .735 .035 .964 .103 .000 N 2004 20 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** r - .343 .066 .434 .645 -.355 .330 .302 -.026 -.401 .145 -.467 1.000 4He Sig. .209.2 .139 .782 .056 .002 .125 .156 .196 .912 .080 .543 .038 .000 N 2094 20 20 20 20 20 20 20 20 20 20 20 20 2 * * ** * r .263 - - - .237 -.448 -.196 -.544 .123 -.217 -.614 .214 .508 20Ne Sig. .262 .210.29 .667.1 .134.3 .315 .048 .408 .013 .605 .357 .004 .364 .022 N 20 203 2003 2047 20 20 20 20 20 20 20 20 20 2 * * ** ** r .211 - - - .276 -.467 -.161 -.499 .116 -.235 -.575 .167 .564 21Ne Sig. .373 .333.22 .665.1 .191.3 .239 .038 .499 .025 .627 .319 .008 .482 .010 N 20 208 2003 2005 20 20 20 20 20 20 20 20 20 2 * * ** * r .262 - - - .238 -.448 -.195 -.543 .123 -.218 -.613 .214 .510 22Ne Sig. .264 .212.29 .667.1 .135.3 .313 .048 .410 .013 .605 .357 .004 .366 .022 N 20 202 2003 2046 20 20 20 20 20 20 20 20 20 2 * * ** * r .263 - - - .237 -.448 -.196 -.544 .123 -.217 -.613 .214 .509 Ne Sig. .262 .210.29 .667.1 .134.3 .314 .048 .408 .013 .605 .357 .004 .364 .022 N 20 203 2003 2047 20 20 20 20 20 20 20 20 20 2 * ** ** ** r .63 - - - -.205 -.105 -.536 -.867 .072 .019 -.842 .688 -.304 ** 36Ar Sig. .0030 .001.693 .470.1 .000.81 .385 .661 .015 .000 .763 .936 .000 .001 .193 ** ** N 20 20 2071 206 20 20 20 20 20 20 20 20 20 (Continued) 82 Table 1.13 (Continued) 4 20 20 36 4 36 84 36 132 84 N2/Ar CH4/C2H6+ C2H6+/CH4 CH4/CO2 CO2/CH4 He/ Ne Ne/ Ar He/ Ar Kr/ Ar Xe/ Kr 2 * ** ** r .299 -.541 .311 .116 -.056 .568 .206 .333 -.796 .159 CH4 Sig. .200 .014 .182 .626 .814 .009 .384 .151 .000 .503 N 20 20 20 20 20 20 20 20 20 20 2 ** ** * * r .099 -.753 .999 -.049 -.025 .506 -.051 .122 -.407 .538 C2H6 Sig. .676 .000 .000 .837 .917 .023 .832 .609 .075 .014 N 20 20 20 20 20 20 20 20 20 20 2 ** ** ** r -.245 .612 -.396 .022 -.072 -.570 -.204 -.335 .788 -.228 N2 Sig. .298 .004 .084 .928 .764 .009 .389 .149 .000 .334 N 20 20 20 20 20 20 20 20 20 20 2 ** ** r -.059 -.242 .001 -.889 .997 -.113 .086 .032 -.016 .249 CO2 Sig. .804 .303 .998 .000 .000 .635 .718 .893 .947 .289 N 20 20 20 20 20 20 20 20 20 20 2 ** r .401 -.304 -.044 .117 .021 .382 .209 .268 -.658 .019 TOTAL Sig. .080 .193 .854 .623 .930 .097 .377 .254 .002 .937 N 20 20 20 20 20 20 20 20 20 20 2 * ** ** Gross r .299 -.550 .325 .115 -.056 .573 .204 .333 -.798 .167 BTU Sig. .200 .012 .162 .630 .814 .008 .388 .151 .000 .483 before N 20 20 20 20 20 20 20 20 20 20 2 ** * ** Gross r .290 -.572 .322 .012 .059 .554 .212 .334 -.793 .194 BTU Sig. .215 .008 .167 .960 .806 .011 .370 .150 .000 .413 Aftrer N 20 20 20 20 20 20 20 20 20 20 2 ** ** r -.026 -.229 .137 .037 -.099 .409 .906 .925 -.356 -.407 3He Sig. .912 .330 .565 .878 .678 .073 .000 .000 .124 .075 N 20 20 20 20 20 20 20 20 20 20 2 * ** ** * r .084 -.212 .108 .006 -.048 .499 .958 .984 -.466 -.408 4He Sig. .724 .369 .651 .979 .841 .025 .000 .000 .038 .074 N 20 20 20 20 20 20 20 20 20 20 2 * ** * r -.469 .294 -.314 -.237 .169 -.289 .597 .421 .377 -.480 20Ne Sig. .037 .208 .177 .314 .476 .216 .005 .065 .102 .032 N 20 20 20 20 20 20 20 20 20 20 2 ** * * r -.443 .271 -.301 -.230 .158 -.256 .651 .476 .320 -.493 21Ne Sig. .050 .248 .197 .328 .507 .276 .002 .034 .169 .027 N 20 20 20 20 20 20 20 20 20 20 2 * ** * r -.469 .293 -.314 -.237 .169 -.289 .598 .422 .376 -.481 22Ne Sig. .037 .209 .177 .314 .476 .217 .005 .064 .103 .032 N 20 20 20 20 20 20 20 20 20 20 2 * ** * r -.469 .294 -.314 -.237 .169 -.289 .597 .421 .376 -.481 Ne Sig. .037 .209 .177 .314 .476 .216 .005 .065 .102 .032 N 20 20 20 20 20 20 20 20 20 20 2 - ** ** r ** .443 -.295 -.184 .146 -.619 -.243 -.370 .890 -.120 .641 36Ar Sig. .002 .051 .207 .438 .540 .004 .302 .109 .000 .614 N 20 20 20 20 20 20 20 20 20 20 (Continued) 83 Table 1.13 (Continued) Gross Gross 3 4 20 21 CH4 C2H6 N2 CO2 TOTAL BTU BTU He He Ne Ne before After ** ** ** ** ** ** * r2 -.843 -.317 .812 .079 -.722 -.843 -.827 -.201 -.304 .612 .556 38Ar Sig. .000 .174 .000 .740 .000 .000 .000 .394 .192 .004 .011 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** r -.847 -.321 .818 .074 -.721 -.847 -.831 -.198 -.298 .620 .564 40Ar Sig. .000 .168 .000 .758 .000 .000 .000 .402 .203 .004 .010 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** r -.847 -.321 .818 .074 -.721 -.847 -.831 -.198 -.298 .620 .564 Ar Sig. .000 .168 .000 .758 .000 .000 .000 .402 .203 .004 .010 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** * r -.862 -.336 .827 .097 -.743 -.863 -.844 -.249 -.340 .566 .508 84Kr Sig. .000 .147 .000 .684 .000 .000 .000 .289 .143 .009 .022 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** * r -.862 -.336 .827 .097 -.743 -.863 -.844 -.249 -.340 .566 .508 Kr Sig. .000 .147 .000 .684 .000 .000 .000 .289 .143 .009 .022 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** * * r -.838 -.309 .804 .121 -.710 -.838 -.817 -.257 -.355 .557 .497 132Xe Sig. .000 .185 .000 .610 .000 .000 .000 .274 .125 .011 .026 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** * * r -.838 -.309 .804 .121 -.710 -.838 -.817 -.257 -.355 .557 .497 Xe Sig. .000 .185 .000 .610 .000 .000 .000 .274 .125 .011 .026 N 20 20 20 20 20 20 20 20 20 20 20 r2 -.210 .027 .178 -.044 -.303 -.208 -.212 .071 -.224 .112 .096 3He/4He Sig. .374 .911 .454 .855 .195 .378 .370 .765 .343 .638 .687 N 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** ** * * r .568 .506 -.569 -.113 .382 .573 .554 .409 .499 -.290 -.256 (He/Ne) Sig. .009 .023 .009 .635 .097 .008 .011 .074 .025 .216 .276 N 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** ** * * r .568 .506 -.569 -.113 .382 .573 .554 .409 .499 -.290 -.256 (He/Ne) asw Sig. .009 .023 .009 .635 .097 .008 .011 .074 .025 .216 .276 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** * ** ** r -.588 -.235 .590 -.128 -.517 -.589 -.598 -.304 -.294 .263 .211 20Ne/ 22Ne Sig. .006 .320 .006 .592 .019 .006 .005 .192 .209 .262 .373 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** r .630 .360 -.667 .143 .428 .632 .643 .302 .343 -.293 -.228 21Ne/ 22Ne Sig. .003 .119 .001 .548 .060 .003 .002 .196 .139 .210 .333 N 20 20 20 20 20 20 20 20 20 20 20 2 ** r .243 .125 -.334 .644 .198 .244 .316 .009 .066 -.103 -.103 38Ar/ 36Ar Sig. .302 .598 .150 .002 .402 .300 .174 .971 .782 .667 .665 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** r .698 .306 -.689 .083 .617 .699 .702 .263 .434 -.347 -.305 40Ar/ 36Ar Sig. .001 .190 .001 .728 .004 .001 .001 .263 .056 .134 .191 N 20 20 20 20 20 20 20 20 20 20 20 (Continued) 84 Table 1.13 (Continued) (He/Ne) 22Ne Ne 36Ar 38Ar 40Ar Ar 84Kr Kr 132Xe Xe 3He/4He (He/Ne) asw ** * ** ** ** ** ** ** ** * ** ** r2 .611 .612 1.000 1 1.000 1.000 .992 .992 .992 .992 .450 -.617 -.617 * 38Ar Sig. .004 .004 .000 .000 .000 .000 .000 .000 .000 .046 .004 .004 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** ** ** ** ** ** ** ** ** r .619 .620 1.000 1.000 1 1.000 .991 .991 .991 .991 .436 -.615 -.615 * 40Ar Sig. .004 .004 .000 .000 .000 .000 .000 .000 .000 .054 .004 .004 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** ** ** ** ** ** ** ** ** r .619 .620 1.000 1.000 1.000 1 .991 .991 .991 .991 .436 -.615 -.615 * Ar Sig. .004 .004 .000 .000 .000 .000 .000 .000 .000 .054 .004 .004 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** ** ** ** ** ** ** ** ** r .565 .565 .992 .992 .991 .991 1 1.000 .996 .996 .424 -.618 -.618 * 84Kr Sig. .009 .009 .000 .000 .000 .000 0.000 .000 .000 .063 .004 .004 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** ** ** ** ** ** ** ** ** r .565 .565 .992 .992 .991 .991 1.000 1 .996 .996 .424 -.618 -.618 * Kr Sig. .009 .009 .000 .000 .000 .000 0.000 .000 .000 .063 .004 .004 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * ** ** ** ** ** ** ** * ** ** r .555 .556 .992 .992 .991 .991 .996 .996 1 1.000 .447 -.622 -.622 132Xe Sig. .011 .011 .000 .000 .000 .000 .000 .000 0.000 .048 .003 .003 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * ** ** ** ** ** ** ** * ** ** r .555 .556 .992 .992 .991 .991 .996 .996 1.000 1 .447 -.622 -.622 Xe Sig. .011 .011 .000 .000 .000 .000 .000 .000 0.000 .048 .003 .003 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * * * r .112 .112 .451 .450 .436 .436 .424 .424 .447 .447 1 -.380 -.380 3He/4He Sig. .639 .638 .046 .046 .054 .054 .063 .063 .048 .048 .098 .098 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** ** ** r -.289 -.289 -.619 -.617 -.615 -.615 -.618 -.618 -.622 -.622 -.380 1 1.000 (He/Ne) Sig. .217 .216 .004 .004 .004 .004 .004 .004 .003 .003 .098 .000 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** ** ** r -.289 -.289 -.619 -.617 -.615 -.615 -.618 -.618 -.622 -.622 -.380 1.000 1 (He/Ne) Sig. .217 .216 .004 .004 .004 .004 .004 .004 .003 .003 .098 .000 asw N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** ** r .262 .263 .630 .632 .636 .636 .633 .633 .634 .634 .056 -.245 -.245 20Ne/ 22Ne Sig. .264 .262 .003 .003 .003 .003 .003 .003 .003 .003 .814 .299 .299 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** ** r -.292 -.293 -.693 -.695 -.696 -.696 -.708 -.708 -.712 -.712 -.246 .367 .367 21Ne/ 22Ne Sig. .212 .210 .001 .001 .001 .001 .000 .000 .000 .000 .295 .112 .112 N 20 20 20 20 20 20 20 20 20 20 20 20 20 r2 -.103 -.103 -.171 -.161 -.169 -.169 -.160 -.160 -.153 -.153 -.118 .309 .309 38Ar/ 36Ar Sig. .667 .667 .470 .499 .476 .476 .500 .500 .518 .518 .621 .185 .185 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** ** ** ** ** r -.346 -.347 -.816 -.812 -.807 -.807 -.803 -.803 -.806 -.806 -.608 .724 .724 40Ar/ 36Ar Sig. .135 .134 .000 .000 .000 .000 .000 .000 .000 .000 .004 .000 .000 N 20 20 20 20 20 20 20 20 20 20 20 20 20 (Continued) 85 Table 1.13 (Continued) 20 21 38 40 130 131 136 132 13 3 3 36 4 4 4 Ne/ Ne/ Ar/ Ar/ Xe/ Xe/ Xe/ Xe δ C-CH4 CO2/ He CH4/ He CH4/ Ar CH4/ He He/CH 22Ne 22Ne 36Ar 36Ar 132Xe 132Xe * ** ** ** r2 .63 - - - - -.100 -.533 -.864 .079 .019 -.840 .690 -.303 ** 38Ar Sig. .0032 .001.695 .499.1 .000.81 .390.20 .676 .016 .000 .740 .936 .000 .001 .194 ** 61 ** 3 N 20 20 20 202 20 20 20 20 20 20 20 20 20 2 * ** ** ** r .63 - - - - -.109 -.536 -.864 .074 .014 -.844 .678 -.296 ** 40Ar Sig. .0036 .001.696 .476.1 .000.80 .378.20 .646 .015 .000 .758 .953 .000 .001 .205 ** ** N 20 20 2069 207 208 20 20 20 20 20 20 20 20 2 * ** ** ** r .63 - - - - -.109 -.536 -.864 .074 .014 -.844 .678 -.296 ** Ar Sig. .0036 .001.696 .476.1 .000.80 .378.20 .647 .015 .000 .758 .953 .000 .001 .205 ** ** N 20 20 2069 207 208 20 20 20 20 20 20 20 20 2 * ** ** ** r .63 - - - - -.074 -.512 -.873 .097 .072 -.796 .710 -.338 ** 84Kr Sig. .0033 .000.708 .500.1 .000.80 .376.20 .756 .021 .000 .684 .763 .000 .000 .144 ** ** N 20 20 2060 203 209 20 20 20 20 20 20 20 20 2 * ** ** ** r .63 - - - - -.074 -.512 -.873 .097 .072 -.796 .710 -.338 ** Kr Sig. .0033 .000.708 .500.1 .000.80 .376.20 .756 .021 .000 .684 .763 .000 .000 .144 ** ** N 20 20 2060 203 209 20 20 20 20 20 20 20 20 2 * ** ** ** r .63 - - - - -.070 -.513 -.855 .121 .084 -.800 .721 -.354 ** 132Xe Sig. .0034 .000.712 .518.1 .000.80 .328.23 .771 .021 .000 .610 .726 .000 .000 .126 ** ** N 20 20 2053 206 201 20 20 20 20 20 20 20 20 2 * ** ** ** r .63 - - - - -.070 -.513 -.855 .121 .084 -.800 .721 -.354 ** Xe Sig. .0034 .000.712 .518.1 .000.80 .328.23 .771 .021 .000 .610 .726 .000 .000 .126 ** ** N 20 20 2053 206 201 20 20 20 20 20 20 20 20 2 * * r .056 - - - .067 .068 -.248 -.416 -.044 -.127 -.455 .503 -.224 3He/4He Sig. .814 .295.24 .621.1 .004.60 .778 .776 .292 .068 .855 .592 .044 .024 .342 ** N 20 206 2018 208 20 20 20 20 20 20 20 20 20 2 ** * ** ** * r - .367 .309 .72 .440 .126 .403 .703 -.113 -.444 .582 -.682 .498 ** (He/Ne) Sig. .299.2 .112 .185 .0004 .052 .598 .078 .001 .635 .050 .007 .001 .026 N 2045 20 20 20 20 20 20 20 20 20 20 20 20 ** * ** ** * r2 - .367 .309 .72 .440 .126 .403 .703 -.113 -.444 .582 -.682 .498 ** (He/N Sig. .299.2 .112 .185 .0004 .052 .598 .078 .001 .635 .050 .007 .001 .026 e) 45 asw N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** * ** r 1 -.719 .067 -.547 -.252 -.083 -.620 -.553 -.128 .000 -.668 .346 -.292 20Ne/ Sig. .000 .780 .013 .284 .729 .004 .011 .592 1.000 .001 .135 .212 22 Ne N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** * r -.719 1 .067 .592 .294 -.071 .382 .656 .143 -.092 .612 -.530 .341 21Ne/ Sig. .000 .778 .006 .208 .765 .097 .002 .548 .701 .004 .016 .141 22 Ne N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** r .067 .067 1 .296 .357 .364 .278 .218 .644 -.049 .348 -.117 .066 38Ar/ Sig. .780 .778 .205 .122 .115 .235 .356 .002 .837 .132 .623 .783 36 Ar N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * ** ** ** ** ** r -.547 .592 .296 1 .335 .151 .651 .763 .083 -.249 .837 -.737 .433 40Ar/ Sig. .013 .006 .205 .149 .524 .002 .000 .728 .289 .000 .000 .057 36 Ar N 20 20 20 20 20 20 20 20 20 20 20 20 20 (Continued) 86 Table 1.13 (Continued) 4 20 20 36 4 36 84 36 132 84 N2/Ar CH4/C2H6+ C2H6+/CH4 CH4/CO2 CO2/CH4 He/ Ne Ne/ Ar He/ Ar Kr/ Ar Xe/ Kr 2 - ** ** r ** .438 -.292 -.188 .153 -.617 -.242 -.368 .888 -.119 .643 38Ar Sig. .002 .053 .211 .428 .521 .004 .304 .110 .000 .617 N 20 20 20 20 20 20 20 20 20 20 2 - * ** ** r ** .446 -.297 -.184 .147 -.615 -.235 -.363 .886 -.122 .642 40Ar Sig. .002 .049 .204 .436 .536 .004 .318 .115 .000 .608 N 20 20 20 20 20 20 20 20 20 20 2 - * ** ** r ** .446 -.297 -.184 .147 -.615 -.235 -.363 .886 -.122 .642 Ar Sig. .002 .049 .204 .436 .536 .004 .318 .115 .000 .608 N 20 20 20 20 20 20 20 20 20 20 2 - * ** ** r ** .459 -.313 -.196 .171 -.618 -.276 -.390 .907 -.106 .605 84Kr Sig. .005 .042 .179 .408 .470 .004 .240 .090 .000 .658 N 20 20 20 20 20 20 20 20 20 20 2 - * ** ** r ** .459 -.313 -.196 .171 -.618 -.276 -.390 .907 -.106 .605 Kr Sig. .005 .042 .179 .408 .470 .004 .240 .090 .000 .658 N 20 20 20 20 20 20 20 20 20 20 2 - ** ** r ** .435 -.286 -.213 .194 -.622 -.292 -.405 .910 -.058 .620 132Xe Sig. .004 .055 .222 .368 .412 .003 .211 .077 .000 .809 N 20 20 20 20 20 20 20 20 20 20 2 - ** ** r ** .435 -.286 -.213 .194 -.622 -.292 -.405 .910 -.058 .620 Xe Sig. .004 .055 .222 .368 .412 .003 .211 .077 .000 .809 N 20 20 20 20 20 20 20 20 20 20 2 * r -.408 -.075 .037 -.047 -.026 -.380 -.210 -.246 .466 .001 3He/4He Sig. .074 .752 .876 .843 .914 .098 .374 .295 .038 .996 N 20 20 20 20 20 20 20 20 20 20 2 * * ** ** ** r .342 -.535 .490 .212 -.158 1.000 .287 .578 -.709 .083 (He/Ne) Sig. .140 .015 .028 .369 .507 .000 .219 .008 .000 .729 N 20 20 20 20 20 20 20 20 20 20 * * ** ** ** r2 .342 -.535 .490 .212 -.158 1.000 .287 .578 -.709 .083 (He/Ne) Sig. .140 .015 .028 .369 .507 .000 .219 .008 .000 .729 asw N 20 20 20 20 20 20 20 20 20 20 2 - ** ** r ** .562 -.220 .163 -.080 -.245 -.348 -.344 .699 .108 20Ne/ .583 22Ne Sig. .007 .010 .352 .492 .738 .299 .132 .137 .001 .649 N 20 20 20 20 20 20 20 20 20 20 2 * ** r .369 -.454 .344 -.153 .089 .367 .343 .368 -.738 .278 21Ne/ Sig. .110 .044 .138 .520 .710 .111 .139 .110 .000 .236 22 Ne N 20 20 20 20 20 20 20 20 20 20 2 ** r -.048 -.204 .119 -.394 .619 .309 .059 .142 -.218 .134 38Ar/ Sig. .840 .389 .616 .086 .004 .185 .806 .549 .357 .573 36 Ar N 20 20 20 20 20 20 20 20 20 20 2 ** * ** * ** r .622 -.493 .287 .005 .028 .724 .388 .518 -.911 -.001 40Ar/ Sig. .003 .027 .220 .982 .907 .000 .091 .019 .000 .998 36 Ar N 20 20 20 20 20 20 20 20 20 20 (Continued) 87 Table 1.13 (Continued) Gross Net Gross Net 3 4 20 21 CH4 C2H6 N2 CO2 TOTAL BTU BTU BTU BTU He He Ne Ne before Before After after r2 -.179 -.043 .193 -.059 -.117 -.179 -.179 -.184 -.184 -.145 -.140 -.195 -.199 129Xe/ 132Xe Sig. .450 .858 .414 .805 .624 .451 .451 .438 .438 .541 .555 .409 .401 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** r .106 .101 -.138 .155 .051 .107 .107 .125 .125 .673 .645 .237 .276 130Xe/ 132Xe Sig. .656 .672 .563 .515 .831 .653 .653 .601 .601 .001 .002 .315 .239 N 20 20 20 20 20 20 20 20 20 20 20 20 20 ** ** * ** ** ** ** r2 .566 .129 -.599 .311 .481 .565 .565 .595 .595 .264 .330 -.196 -.161 136Xe/ 132Xe Sig. .009 .589 .005 .182 .032 .009 .009 .006 .006 .261 .156 .408 .499 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** ** * * r .783 .708 -.801 .024 .566 .790 .790 .785 .785 .206 .302 -.544 -.499 13 C-CH4 Sig. .000 .000 .000 .919 .009 .000 .000 .000 .000 .383 .196 .013 .025 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** r .024 .001 -.151 1.000 .088 .024 .024 .138 .138 -.081 -.026 .123 .116 3 CO2/ He Sig. .921 .997 .526 0.000 .713 .921 .921 .561 .561 .735 .912 .605 .627 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * r -.017 -.138 -.013 .374 .071 -.020 -.020 .024 .024 -.474 -.401 -.217 -.235 3 CH4/ He Sig. .942 .561 .957 .104 .765 .935 .935 .920 .920 .035 .080 .357 .319 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** ** ** r .742 .274 -.761 .259 .645 .743 .743 .766 .766 .011 .145 -.614 -.575 36 CH4/ Ar Sig. .000 .242 .000 .271 .002 .000 .000 .000 .000 .964 .543 .004 .008 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * * * * * r -.485 -.161 .440 .257 -.404 -.485 -.485 -.452 -.452 -.376 -.467 .214 .167 4 CH4/ He Sig. .030 .499 .052 .273 .077 .030 .030 .046 .046 .103 .038 .364 .482 88 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** * ** r .263 .114 -.260 -.028 .198 .263 .263 .257 .257 .952 1.000 .508 .564 4 He/CH4 Sig. .263 .632 .268 .907 .402 .263 .262 .273 .273 .000 .000 .022 .010 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * r .299 .099 -.245 -.059 .401 .299 .299 .290 .290 -.026 .084 -.469 -.443 N2/Ar Sig. .200 .676 .298 .804 .080 .200 .200 .215 .215 .912 .724 .037 .050 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * ** ** * * ** ** r -.541 -.753 .612 -.242 -.304 -.550 -.550 -.572 -.572 -.229 -.212 .294 .271 CH4/C2H6+ Sig. .014 .000 .004 .303 .193 .012 .012 .008 .008 .330 .369 .208 .248 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** r .311 .999 -.396 .001 -.044 .325 .325 .322 .322 .137 .108 -.314 -.301 C2H6+/CH4 Sig. .182 .000 .084 .998 .854 .162 .162 .167 .167 .565 .651 .177 .197 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** r .116 -.049 .022 -.889 .117 .115 .115 .012 .012 .037 .006 -.237 -.230 CH4/CO2 Sig. .626 .837 .928 .000 .623 .630 .630 .960 .960 .878 .979 .314 .328 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** r -.056 -.025 -.072 .997 .021 -.056 -.056 .059 .059 -.099 -.048 .169 .158 CO2/CH4 Sig. .814 .917 .764 .000 .930 .814 .814 .806 .806 .678 .841 .476 .507 N 20 20 20 20 20 20 20 20 20 20 20 20 20 (Continued) Table 1.13 (Continued) (He/Ne) 22Ne Ne 36Ar 38Ar 40Ar Ar 84Kr Kr 132Xe Xe 3He/4He (He/Ne) asw r2 -.196 -.195 -.074 -.075 -.078 -.078 -.058 -.058 -.073 -.073 .031 .047 .047 129Xe/ 132Xe Sig. .409 .409 .758 .754 .744 .744 .808 .808 .759 .759 .895 .843 .843 N 20 20 20 20 20 20 20 20 20 20 20 20 20 r2 .238 .237 -.205 -.203 -.208 -.208 -.209 -.209 -.231 -.231 .067 .440 .440 130Xe/ 132Xe Sig. .313 .314 .385 .390 .378 .378 .376 .376 .328 .328 .778 .052 .052 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * * * * * * * r -.195 -.196 -.536 -.533 -.536 -.536 -.512 -.512 -.513 -.513 -.248 .403 .403 136Xe/ 132Xe Sig. .410 .408 .015 .016 .015 .015 .021 .021 .021 .021 .292 .078 .078 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * ** ** ** ** ** ** ** ** ** ** r -.543 -.544 -.867 -.864 -.864 -.864 -.873 -.873 -.855 -.855 -.416 .703 .703 13 Sig. .013 .013 .000 .000 .000 .000 .000 .000 .000 .000 .068 .001 .001 C-CH4 N 20 20 20 20 20 20 20 20 20 20 20 20 20 r2 .123 .123 .072 .079 .074 .074 .097 .097 .121 .121 -.044 -.113 -.113 3 CO2/ He Sig. .605 .605 .763 .740 .758 .758 .684 .684 .610 .610 .855 .635 .635 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * r -.218 -.217 .019 .019 .014 .014 .072 .072 .084 .084 -.127 -.444 -.444 3 Sig. .357 .357 .936 .936 .953 .953 .763 .763 .726 .726 .592 .050 .050 CH4/ He N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** ** ** ** * ** ** r -.613 -.613 -.842 -.840 -.844 -.844 -.796 -.796 -.800 -.800 -.455 .582 .582 36 CH4/ Ar Sig. .004 .004 .000 .000 .000 .000 .000 .000 .000 .000 .044 .007 .007 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** ** * ** ** r .214 .214 .688 .690 .678 .678 .710 .710 .721 .721 .503 -.682 -.682 4 Sig. .366 .364 .001 .001 .001 .001 .000 .000 .000 .000 .024 .001 .001 CH4/ He N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * * * r .510 .509 -.304 -.303 -.296 -.296 -.338 -.338 -.354 -.354 -.224 .498 .498 4 He/CH4 Sig. .022 .022 .193 .194 .205 .205 .144 .144 .126 .126 .342 .026 .026 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * ** ** ** ** ** ** ** ** r -.469 -.469 -.641 -.643 -.642 -.642 -.605 -.605 -.620 -.620 -.408 .342 .342 Sig. .037 .037 .002 .002 .002 .002 .005 .005 .004 .004 .074 .140 .140 N2/Ar N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * * * * * r .293 .294 .443 .438 .446 .446 .459 .459 .435 .435 -.075 -.535 -.535 CH4/C2H6+ Sig. .209 .209 .051 .053 .049 .049 .042 .042 .055 .055 .752 .015 .015 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * r -.314 -.314 -.295 -.292 -.297 -.297 -.313 -.313 -.286 -.286 .037 .490 .490 C2H6+/CH4 Sig. .177 .177 .207 .211 .204 .204 .179 .179 .222 .222 .876 .028 .028 N 20 20 20 20 20 20 20 20 20 20 20 20 20 r2 -.237 -.237 -.184 -.188 -.184 -.184 -.196 -.196 -.213 -.213 -.047 .212 .212 CH4/CO2 Sig. .314 .314 .438 .428 .436 .436 .408 .408 .368 .368 .843 .369 .369 N 20 20 20 20 20 20 20 20 20 20 20 20 20 r2 .169 .169 .146 .153 .147 .147 .171 .171 .194 .194 -.026 -.158 -.158 CO2/CH4 Sig. .476 .476 .540 .521 .536 .536 .470 .470 .412 .412 .914 .507 .507 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** ** ** ** r -.289 -.289 -.619 -.617 -.615 -.615 -.618 -.618 -.622 -.622 -.380 1.000 1.000 4He/20Ne Sig. .217 .216 .004 .004 .004 .004 .004 .004 .003 .003 .098 .000 .000 N 20 20 20 20 20 20 20 20 20 20 20 20 20 (Continued) 89 Table 1.13 (Continued) 13 20 21 38 40 36 130 132 131 132 136 132 δ C- 3 3 36 4 4 4 Ne/ Ne/ Ar/ Ar/ Ar Xe/ Xe Xe/ Xe Xe/ Xe CO2/ He CH4/ He CH4/ Ar CH4/ He He/CH CH 22Ne 22Ne 36Ar 4 2 * r .072 .052 .018 .120 .301 .481 -.097 -.020 -.059 -.196 .122 -.049 -.138 129Xe/ Sig .762 .828 .939 .614 .198 .032 .684 .932 .805 .408 .607 .838 .561 132 Xe N. 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * ** r -.252 .294 .357 .335 1 .245 .414 .129 .155 -.490 .267 -.314 .645 130Xe/ Sig .284 .208 .122 .149 .297 .070 .587 .515 .028 .255 .177 .002 132Xe N. 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** r - .382 .278 .651 .414 .288 1 .446 .311 -.020 .748 -.349 .327 136Xe/ Sig .004.62 .097 .235 .002 .070 .218 .049 .182 .932 .000 .132 .159 ** 132 0 Xe N. 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** * ** * r - .65 .218 .763 .129 .115 .446 1 .024 -.018 .739 -.557 .302 ** 13 Sig .011.55 .0026 .356 .000 .587 .629 .049 .919 .939 .000 .011 .196 C- * . 3 CH4 N 20 20 20 20 20 20 20 20 20 20 20 20 20 r2 -.128 .143 .64 .083 .155 .186 .311 .024 1 .374 .259 .257 -.028 ** 4 CO2/ Sig .592 .548 .002 .728 .515 .434 .182 .919 .104 .271 .273 .907 3He N. 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * r .000 -.092 - -.249 -.490 -.095 -.020 -.018 .374 1 .106 .555 -.402 .04 CH4/ Sig 1. .701 .837 .289 .028 .691 .932 .939 .104 .657 .011 .079 3 9 He N. 20 00 20 20 20 20 20 20 20 20 20 20 20 20 0 2 ** ** ** * r - .61 .348 .837 .267 .302 .748 .739 .259 .106 1 -.482 .142 ** CH / Sig .001.66 .0042 .132 .000 .255 .195 .000 .000 .271 .657 .031 .551 4 ** 36 8 Ar N. 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** * * * * r .346 - - -.737 -.314 .040 -.349 -.557 .257 .555 -.482 1 -.468 .53 .11 CH4/ Sig .135 .016 .623 .000 .177 .868 .132 .011 .273 .011 .031 .037 * 4 0 7 He N. 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** * r -.292 .341 .066 .433 .645 -.354 .327 .302 -.028 -.402 .142 -.468 1 4He/ Sig .212 .141 .783 .057 .002 .125 .159 .196 .907 .079 .551 .037 . CH4 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** * * * ** r - .369 - .622 .302 .487 .481 .485 -.059 .026 .702 -.419 .085 Sig .007.58 .110 .840.04 .003 .196 .029 .032 .030 .804 .915 .001 .066 .722 N2/Ar ** 3 8 N. 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * ** * r .56 - - -.493 -.236 -.158 -.398 -.698 -.242 .084 -.538 .118 -.211 ** Sig .0102 .044.45 .389.20 .027 .316 .507 .082 .001 .303 .725 .014 .621 .371 CH4/C * . 4 4 2H6+ N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** r -.220 .344 .119 .287 .103 .159 .115 .690 .001 -.141 .252 -.142 .109 C2H6+/ Sig .352 .138 .616 .220 .667 .503 .629 .001 .998 .552 .284 .550 .647 . CH4 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** r .163 -.153 - .005 -.025 -.022 -.164 .045 -.889 -.293 -.096 -.279 .007 .39 CH4/C Sig .492 .520 .086 .982 .916 .926 .490 .850 .000 .210 .688 .234 .977 . 4 O2 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** r -.080 .089 .61 .028 .142 .184 .266 -.041 .997 .373 .196 .299 -.049 ** 9 CO2/C Sig .738 .710 .004 .907 .550 .437 .256 .864 .000 .106 .407 .201 .837 . H4 N 20 20 20 20 20 20 20 20 20 20 20 20 20 (Continued) 90 Table 1.13 (Continued) 4 20 20 36 4 36 84 36 132 84 N2/Ar CH4/C2H6+ C2H6+/CH4 CH4/CO2 CO2/CH4 He/ Ne Ne/ Ar He/ Ar Kr/ Ar Xe/ Kr 2 * r .467 -.049 -.032 .095 -.048 .047 -.123 -.107 -.097 .167 129Xe/ 132Xe Sig. .038 .837 .893 .692 .842 .843 .604 .654 .684 .482 N 20 20 20 20 20 20 20 20 20 20 2 ** ** r .302 -.236 .103 -.025 .142 .440 .613 .699 -.363 -.218 130Xe/ 132Xe Sig. .196 .316 .667 .916 .550 .052 .004 .001 .116 .355 N 20 20 20 20 20 20 20 20 20 20 2 * ** r .481 -.398 .115 -.164 .266 .403 .356 .427 -.648 -.171 136Xe/ 132Xe Sig. .032 .082 .629 .490 .256 .078 .123 .060 .002 .472 N 20 20 20 20 20 20 20 20 20 20 2 * ** ** ** ** r .485 -.698 .690 .045 -.041 .703 .183 .350 -.848 .348 13 Sig. .030 .001 .001 .850 .864 .001 .439 .130 .000 .132 C-CH4 N 20 20 20 20 20 20 20 20 20 20 2 ** ** r -.059 -.242 .001 -.889 .997 -.113 .086 .032 -.016 .249 3 CO2/ He Sig. .804 .303 .998 .000 .000 .635 .718 .893 .947 .289 N 20 20 20 20 20 20 20 20 20 20 2 * r .026 .084 -.141 -.293 .373 -.444 -.307 -.391 .237 .322 3 CH4/ He Sig. .915 .725 .552 .210 .106 .050 .188 .088 .315 .166 N 20 20 20 20 20 20 20 20 20 20 2 ** * ** ** r .702 -.538 .252 -.096 .196 .582 .127 .271 -.825 .168 36 91 Sig. .001 .014 .284 .688 .407 .007 .594 .248 .000 .480 CH4/ Ar N 20 20 20 20 20 20 20 20 20 20 2 ** * ** r -.419 .118 -.142 -.279 .299 -.682 -.373 -.487 .738 .102 4 Sig. .066 .621 .550 .234 .201 .001 .105 .029 .000 .668 CH4/ He N 20 20 20 20 20 20 20 20 20 20 2 * ** ** * r .085 -.211 .109 .007 -.049 .498 .958 .983 -.465 -.408 4 He/CH4 Sig. .722 .371 .647 .977 .837 .026 .000 .000 .039 .074 N 20 20 20 20 20 20 20 20 20 20 2 ** r 1 -.290 .093 .132 -.086 .342 .088 .157 -.629 -.014 Sig. .214 .698 .578 .719 .140 .711 .509 .003 .952 N2/Ar N 20 20 20 20 20 20 20 20 20 20 2 ** * ** r -.290 1 -.747 .291 -.202 -.535 -.124 -.266 .619 -.278 CH4/C2H6+ Sig. .214 .000 .213 .392 .015 .602 .257 .004 .236 N 20 20 20 20 20 20 20 20 20 20 2 ** * * r .093 -.747 1 -.052 -.023 .490 -.054 .114 -.388 .535 C2H6+/CH4 Sig. .698 .000 .826 .922 .028 .820 .632 .091 .015 N 20 20 20 20 20 20 20 20 20 20 2 ** r .132 .291 -.052 1 -.899 .212 -.112 -.006 -.041 -.148 CH4/CO2 Sig. .578 .213 .826 .000 .369 .640 .981 .862 .533 N 20 20 20 20 20 20 20 20 20 20 2 ** r -.086 -.202 -.023 -.899 1 -.158 .069 .005 .048 .236 CO2/CH4 Sig. .719 .392 .922 .000 .507 .772 .984 .840 .316 N 20 20 20 20 20 20 20 20 20 20 2 * * ** ** r .342 -.535 .490 .212 -.158 1 .287 .578 -.709 .083 4He/20Ne Sig. .140 .015 .028 .369 .507 .219 .008 .000 .729 N 20 20 20 20 20 20 20 20 20 20 (Continued) Table 1.13 (Continued) Gross Gross 3 4 20 21 CH4 C2H6 N2 CO2 TOTAL BTU BTU He He Ne Ne before After 2 ** ** ** ** r .206 -.051 -.204 .086 .209 .204 .212 .906 .958 .597 .651 20Ne/36Ar Sig. .384 .832 .389 .718 .377 .388 .370 .000 .000 .005 .002 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** * r .333 .122 -.335 .032 .268 .333 .334 .925 .984 .421 .476 4He/36Ar Sig. .151 .609 .149 .893 .254 .151 .150 .000 .000 .065 .034 N 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** * r -.796 -.407 .788 -.016 -.658 -.798 -.793 -.356 -.466 .377 .320 84Kr/36Ar Sig. .000 .075 .000 .947 .002 .000 .000 .124 .038 .102 .169 N 20 20 20 20 20 20 20 20 20 20 20 2 * * * r .159 .538 -.228 .249 .019 .167 .194 -.407 -.408 -.480 -.493 132Xe/84Kr Sig. .503 .014 .334 .289 .937 .483 .413 .075 .074 .032 .027 N 20 20 20 20 20 20 20 20 20 20 20 92 Table 1.13 (Continued) (He/Ne) 22Ne Ne 36Ar 38Ar 40Ar Ar 84Kr Kr 132Xe Xe 3He/4He (He/Ne) asw 2 ** ** r .598 .597 -.243 -.242 -.235 -.235 -.276 -.276 -.292 -.292 -.210 .287 .287 20Ne/36Ar Sig. .005 .005 .302 .304 .318 .318 .240 .240 .211 .211 .374 .219 .219 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** r .422 .421 -.370 -.368 -.363 -.363 -.390 -.390 -.405 -.405 -.246 .578 .578 4He/36Ar Sig. .064 .065 .109 .110 .115 .115 .090 .090 .077 .077 .295 .008 .008 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** ** * ** ** r .376 .376 .890 .888 .886 .886 .907 .907 .910 .910 .466 -.709 -.709 84Kr/36Ar Sig. .103 .102 .000 .000 .000 .000 .000 .000 .000 .000 .038 .000 .000 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * * r -.481 -.481 -.120 -.119 -.122 -.122 -.106 -.106 -.058 -.058 .001 .083 .083 132Xe/84Kr Sig. .032 .032 .614 .617 .608 .608 .658 .658 .809 .809 .996 .729 .729 N 20 20 20 20 20 20 20 20 20 20 20 20 20 (Continued) Table 1.13 (Continued) 13 20 22 21 22 38 36 40 36 130 132 131 132 136 132 δ C- 3 3 36 4 4 4 Ne/ Ne Ne/ Ne Ar/ Ar Ar/ Ar Xe/ Xe Xe/ Xe Xe/ Xe CO2/ He CH4/ He CH4/ Ar CH4/ He He/CH CH4 ** ** r2 -.348 .343 .059 .388 .613 -.384 .356 .183 .086 -.307 .127 -.373 .958 20Ne/36Ar Sig. .132 .139 .806 .091 .004 .095 .123 .439 .718 .188 .594 .105 .000 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 * ** * ** r -.344 .368 .142 .518 .699 -.274 .427 .350 .032 -.391 .271 -.487 .983 4He/36Ar Sig. .137 .110 .549 .019 .001 .242 .060 .130 .893 .088 .248 .029 .000 N 20 20 20 20 20 20 20 20 20 20 20 20 20 2 ** ** ** ** ** ** ** * r .699 -.738 -.218 -.911 -.363 -.104 -.648 -.848 -.016 .237 -.825 .738 -.465 84Kr/36Ar Sig. .001 .000 .357 .000 .116 .663 .002 .000 .947 .315 .000 .000 .039 N 20 20 20 20 20 20 20 20 20 20 20 20 20 r2 .108 .278 .134 -.001 -.218 .142 -.171 .348 .249 .322 .168 .102 -.408 132Xe/84Kr Sig. .649 .236 .573 .998 .355 .551 .472 .132 .289 .166 .480 .668 .074 N 20 20 20 20 20 20 20 20 20 20 20 20 20 93 Table 1.13 (Continued) 4 20 20 36 4 36 84 36 132 84 N2/Ar CH4/C2H6+ C2H6+/CH4 CH4/CO2 CO2/CH4 He/ Ne Ne/ Ar He/ Ar Kr/ Ar Xe/ Kr ** * r2 .088 -.124 -.054 -.112 .069 .287 1 .937 -.410 -.486 20Ne/36Ar Sig. .711 .602 .820 .640 .772 .219 .000 .072 .030 N 20 20 20 20 20 20 20 20 20 20 2 ** ** * r .157 -.266 .114 -.006 .005 .578 .937 1 -.520 -.380 4He/36Ar Sig. .509 .257 .632 .981 .984 .008 .000 .019 .098 N 20 20 20 20 20 20 20 20 20 20 2 - ** ** * r ** .619 -.388 -.041 .048 -.709 -.410 -.520 1 -.026 .629 84 36 Kr/ Ar Sig. .003 .004 .091 .862 .840 .000 .072 .019 .914 N 20 20 20 20 20 20 20 20 20 20 * * r2 -.014 -.278 .535 -.148 .236 .083 -.486 -.380 -.026 1 132Xe/84Kr Sig. .952 .236 .015 .533 .316 .729 .030 .098 .914 N 20 20 20 20 20 20 20 20 20 20 Chapter 2: Constraining the Timing of Fluid and Gas Interactions in the Illinois Basin using the ingrowth of 4He in coal seams with thermogenic contributions Abstract Groundwater plays a fundamental role in the generation, post-genetic degradation, alteration, and migration of all hydrocarbon fluids. Groundwater is particularly important in biogenic coalbed methane (CBM) systems. In CBM systems, groundwater can transport and introduce microbial communities into areas previously pasteurized or devoid of life, deliver essential nutrients to stimulate biogenic production, modulate redox conditions, and remove brine components that are deleterious to the formation of biogenic methane. Nonetheless, the time scales of fresh groundwater recharge into coal seams, which stimulates the formation of coalbed methane, remains poorly constrained; these factors relate to the inherent challenges of using common groundwater dating methods to determine the residence times. Herein, I attempt to address this issue by determining the residence time of fluids using the ingrowth of radiogenic 4He. Due to the lack of previous studies on the abundance of 4He and the rate of diffusional release of 4He from coal seam solids, it was imperative to constrain the abundance of 4He in coal seam solids and quantify the rate of diffusional release by stepwise heating before I can employ this technique. Following this approach, I identify significantly higher levels of [4He] in coal seam solids than anticipated (2.1 to 4.4 x 104 µcc/kg), as well as significantly higher rates for the diffusional release (~0.81 94 µcc/kg/yr on average) of 4He from coal seam solids as compared to standard release estimates (0.15 µcc/kg/yr) for the continental crust. By correcting for these rapid rates of release, as well as the exogenous thermogenic sources that are rich in helium, I identify average residence times for groundwater in coalbed methane reservoirs from the Illinois Basin on the magnitude of approximately 9.6 x 104 to 9.8 x 104 years on average. These estimates are approximately 10 to 12 times lower than standard residence time models and are consistent with a significant influx of groundwater during the interglacial period following the Illinoian glacial episode. Key Words: coalbed methane, residence time, crustal helium flux, exogenous fluids, thermogenic gas, helium 95 2.1 Introduction The occurrence, distribution, and composition of hydrocarbons in the Earth's crust are inextricably linked to the tectonic and hydrologic histories (e.g., Ballentine et al., 1991; Bethke and Marshak, 1990; Cathles, 1990). For example, tectonic processes lead to catagenesis, which expels hydrocarbons and "deep" crustal brines into the shallower water-saturated crust, where regional groundwater flow and buoyancy forces can lead to trapping in favorable stratigraphic or tectonically-induced structural settings (Ballentine et al., 1991; Cathles, 1990; Sherwood Lollar and Ballentine, 2009). As a result, characterizing the interactions between hydrocarbon fluids and groundwater has long been an important aspect of petroleum geology (Selley, 1998). Groundwater can also play a critical role in the post-genetic degradation, alteration, and incipient generation of biogenic hydrocarbon fluids (Martini et al., 1998; Osborn and McIntosh, 2010; Pashin et al., 2014; Schlegel et al., 2011b; Van Stempvoort et al., 2005; Whiticar, 1999; Zhou and Ballentine, 2006). For example, the dissolution of more soluble components into groundwater during hydrocarbon transport can reduce the mass of hydrocarbons. While keeping in mind the introduction of microbes into the subsurface by groundwater can have profound implications for crustal carbon budgets and the economic potential of hydrocarbon reserves. Microbes transported into previously isolated or pasteurized (i.e., formations heated beyond the temperatures that support microbial life) subsurface settings can reduce hydrocarbon reserves through biodegradation, leading to significant biogenic methane production in organic substrates (Ritter et al., 2015; Zhou and Ballentine, 2006). In fact, biogenic methane now accounts for at least 20% of the world’s economic 96 natural gas reservoirs (Martini et al., 1998). The role of groundwater in biogenic coalbed methane (CBM) formation, may be even more profound (Martini et al., 1996; Martini et al., 1998; Pashin et al., 2014; Schlegel et al., 2011b). The timing and method of migration of fresh groundwater is critical to the formation of biogenic methane (Ritter et al., 2015). For example the introduction of fresh groundwater can transport and introduce microbial communities capable of catalyzing the reaction of fossil carbon to methane. The introduction of fresh groundwater provides sufficient fresh water (neutral pH, <2mM of SO2- or Cl-, respectively) to “flush” high-saline formational brines from organic-rich formations (e.g., shales, coalbeds), to control redox conditions, and also to provide the nutrient fluxes (e.g., acetate, nitrate from shallower regions in the aquifer) necessary to permit methanogenic bacteria to thrive (Bates et al., 2011; Martini et al., 2008; McIntosh et al., 2012; Orem et al., 2014; Osborn and McIntosh, 2010; Pashin, 1998; Pashin et al., 2014; Ritter et al., 2015; Schlegel et al., 2011a). Due to the importance of fresh groundwater, constraining the residence time and migration of fluids associated with these processes and the occurrence of biogenic gas accumulations in sedimentary basins are critical to understanding the role of groundwater recharge in microbial methane generation (McIntosh et al., 2012; Pashin, 1998; Pashin et al., 2014; Schlegel et al., 2011a; Schlegel et al., 2011b). Nonetheless, relatively little is known regarding a) the source of fluids that stimulate microbial methane generation, b) the rates of methanogenic bacterial transport to organic-rich formations in shallow groundwater systems, or c) the rates of in situ biogenic methane production (Ritter et al., 2015; Schlegel et al., 2011b). In fact, only a handful of studies have examined the residence time of groundwater in areas of microbial 97 methane production (Bates et al., 2011; Nakagawa et al., 2002; Schlegel et al., 2011b; Zhou and Ballentine, 2006; Zhou et al., 2005). Several approaches are used to constrain the residence time of groundwater in subsurface hydrocarbon reservoirs. These include hydrological assessments and modelling based on Darcy’s Law and various geochemical approaches, such as the use of cosmogenic, radiogenic, and anthropogenic isotopic tracers. The most common isotopic tracers used for groundwater residence time estimates include, tritium (3H), 14C of dissolved inorganic carbon (DIC), 129I, 36Cl, 39Ar, 81Kr, 85Kr, and the accumulation of stable, radiogenic isotopes (e.g., 4He) (Bentley et al., 1986; Bethke et al., 1999; Cook et al., 1996; Park et al., 2002; Sheldon et al., 2003; Snyder et al., 2003; Solomon et al., 1996; Torgersen and Clarke, 1985; Zhou et al., 2005). Each of these approaches has their limitations in sedimentary basins with accumulated hydrocarbon gases. For example, modelling the flow of groundwater in cleated (fractured) coal seams, or other fractured media, remains challenging. As to the use of isotopic methods, fluids contained in coalbed methane formations are often too old for tritium (< ~80 years) or 14C (<~4.0 x 103 years) methods. Also, the admixture of background, dead (fossil) 14C reduces the reliability of 14C dating methods and limit the applicability of this approach. Similarly, 36Cl and 129I age estimates are altered by the presence of residual formational brines retained in low porosity and permeability shales or coalbeds (Bates et al., 2011; McIntosh et al., 2012; Schlegel et al., 2011b; Zhou and Ballentine, 2006). Because of these limitations, many recent workers have found that the use of inert noble gases techniques (e.g., 4He, 39Ar, 40Ar, 81Kr, 85Kr) provide the most realistic residence times of water and hydrocarbons in 98 organic-rich formations (Schlegel et al., 2011b; Zhou and Ballentine, 2006). Herein, I will attempt to use noble gas tracers, specifically the accumulation of radiogenic 4He within the context of other air-saturated water noble gases, to determine the residence time of water in coalbed methane reservoirs from the Illinois Basin. This technique has previously been useful to determining the residence time of groundwater on timescales ranging from thousands to millions of years (Bates et al., 2011; Lowenstern et al., 2014; Plummer et al., 2012; Schlegel et al., 2011b; Sheldon et al., 2003; Solomon et al., 1996). 99 2.1.1 Geological Background The Illinois Basin is located in the midcontinent of the United States, extending from Illinois to western Indiana and northwestern Kentucky (Figure 2.1; 2.2) (Buschbach and Kolata, 1990; Karacan et al., 2014; Mastalerz et al., 2004a; Mastalerz et al., 2013). CBM production occurs from Pennsylvanian-aged coal-bearing strata (Springfield and Seelyville coal seams). The typical depths of the Springfield and Seelyville coal seams range from about 76-140 and 150-210 meters below land surface, respectively. The highest thermal maturities observed for coal seams sampled are indicated by vitrinite reflectance values of 0.7-0.8% Ro. CBM production began in the Illinois Basin in ~2000 with significant increases in production within the last decade (Tedesco, 2003). CBM fields currently produce approximately 11 million cubic meters per day (McM/day), with total estimated reserves of 1.5-6.0 billion cubic meters (BcM) (Drobniak et al., 2004; Karacan et al., 2014; Mastalerz et al., 2004a; Mastalerz et al., 2004b; Mastalerz et al., 2013). Although coalbed methane formation in the Illinois Basin is traditionally considered biogenic in origin, previous studies have documented significant contributions from an exogenous, thermogenic source, which complicates residence determinations as discussed below (Moore et al., 2016). A more complete geological description of the Illinois Basin is presented in (Moore et al., 2016). The Pennsylvanian-aged sedimentary units, including the Springfield and Seelyville coal seams, and most other stratigraphic units in the synclinal Illinois Basin constitute continuous-type regional stratigraphic traps due to their extensive lateral continuity and documented capacity for long-range fluid transport (Bethke and 100 Marshak, 1990; Garven et al., 1993; McIntosh and Walter, 2006; Stueber and Walter, 1991; Stueber and Walter, 1994). These coal seams have a low primary porosity, but contain variable degrees of secondary porosity within cleats. These fractures provide for extensive permeability development and facilitate fluid migration. Hydraulic conductivity within the Springfield and Seelyvillle coal seams, as measured with various aquifer tests, range from 0.092 to 0.121 m/day (Pers. Coms., Mr. Larry Neely). On geological timescales, the Illinois Basin has been shaped by episodic, regional- scale stages (>600km) of volumetrically large pulses of brine and hydrocarbon fluid migration. These events are associated with the tectonic stages that deformed the Ouachitas and Appalachian mountains, and are thought to have been the drivers of long-distance migration of brines and hydrocarbon fluids away from the deforming fold- thrust belts within the Illinois Basin (Bethke and Marshak, 1990; Garven et al., 1993; McIntosh and Walter, 2006; Stueber and Walter, 1991; Stueber and Walter, 1994). Throughout the last three million years, multiple cycles of continental glaciation and interglaciation have also significantly impacted the hydrogeology of the Illinois Basin. Interglacial periods provide ice-free conditions much the same as today. Precipitation on topographically high uplands provided freshwater recharge and flow into deeper sedimentary strata. This creation of flow systems is thought to have been aided by erosion, uplift, denudation, and neotectonic fracturing associated with glacial cycles (Bates et al., 2011; McIntosh et al., 2012; Schlegel et al., 2011b; Stueber and Walter, 1991; Stueber and Walter, 1994; Walter et al., 1990). Late-stage flow of groundwater into the underlying New Albany Shale probably occurred as recently as the last 100,000 to one million years (Schlegel et al., 2011b). Today, groundwater flow is thought to 101 be driven by recharge in local topographic highs, or along the basin margins, with groundwater generally flowing toward the center of the synclinal basin (east to west in the current study area) (Labotka et al., 2015; Panno et al., 2013; Schlegel et al., 2011b). 102 2.2 Estimating Groundwater Residence Time Using Radiogenic 4He The non-reactive nature, low terrestrial abundance, and well-characterized isotopic composition of noble gases (e.g., helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe)) constrained in various reservoirs (mantle, crust, hydrosphere, and lithosphere) make them powerful tracers of subsurface fluid migration (Ballentine et al., 2002; Ballentine and Burnard, 2002). Importantly, noble gas elemental and isotopic compositions are preserved in shallow groundwater independent of microbial activity, mineral reactions, and changes in redox conditions (Ballentine et al., 2002; Ballentine and Burnard, 2002). Noble gases in subsurface aquifers are primarily derived from three sources: the mantle, the atmosphere, and the crust (Ballentine et al., 2002). In most shallow aquifers, the noble gas composition is a reflection of a mixture from two distinct sources: the atmosphere (air saturated water (ASW); e.g., 20Ne, 36Ar, 38Ar, 84Kr) and the crust (4He and 21Ne* derived from the decay of uranium and thorium, and 40Ar* derived from the decay of 40K, where the * represents the proportion of gas derived from radioactive decay) (Ballentine et al., 2002). Noble gas signatures in crustal fluids are well constrained because they only fractionate by well understood physical processes such as multiple-phase advection or diffusion (Darrah et al., 2015; Darrah et al., 2014; Gilfillan et al., 2009; Zhou et al., 2005; Zhou et al., 2012). Groundwater residence time can be estimated using noble gases by measuring the abundance of [4He] (Bethke et al., 1999; Cook et al., 1996; Darrah et al., 2015; Hunt, 2000; Lowenstern et al., 2014; Solomon et al., 1996; Torgersen et al., 1992). The [4He] in groundwater reflects a combination of: 1) atmospheric inputs, 2) in-situ production 103 of 4He from U-Th (α-decay), 3) the diffusional release of 4He that previously accumulated in detrital grains, and 4) the flux from exogenous sources (Ballentine and Burnard, 2002; Bethke et al., 1999; Cook et al., 1996; Darrah et al., 2015; Sheldon et al., 2003; Solomon et al., 1996; Torgersen and Clarke, 1985; Torgersen et al., 1992; Zhou and Ballentine, 2006). The atmospheric inputs of helium can be estimated from measurements of other noble gases within air-saturated water components (e.g., 20Ne, 36Ar, 84Kr), while the in situ production of [4He] can be calculated from the measured [U] and [Th] in the porous medium (Eq. 2.1) (Ballentine and Burnard, 2002). In the majority of hydrocarbon-rich aquifer fluids, the atmospheric and in situ production of [4He] is negligible when compared to the transfer of 4He from the solid to the water phase by the diffusional release of 4He that has accumulated in aquifer rock/minerals over over geologic time (Eq. 2.2) and/or the exogenous sources of 4He (Darrah et al., 2015; Hunt, 2000). Thus, quantifying the rate of transfer of 4He from the mineral grain to groundwater and resolving the magnitude of exogenous sources of 4He is critical to determining the residence time of the water in the crust, especially in CBM reservoirs (Cook et al., 1996; Darrah et al., 2015; Hunt, 2000; Lowenstern et al., 2014; Plummer et al., 2012; Schlegel et al., 2011b; Sheldon et al., 2003; Solomon et al., 1996; Zhou and Ballentine, 2006) (Figure 2.3). Because aquifer materials are typically not available for measurement, ρ (defined below), φ (defined below), [U], and [Th] are frequently estimated by taking the average of published values. In cases where the aquifer solids have not been thoroughly studied, it is important to collect and analyze aquifer solid samples in order to quantify [4He] and the diffusional release rates in order to determine the contributions from endogenous 104 sources (Cook et al., 1996; Darrah et al., 2015; Hunt, 2000; Plummer et al., 2012; Sheldon et al., 2003; Solomon et al., 1996). Because there is a limited amount of data available for coal samples, specifically in the Illinois Basin, direct measurement of aquifers solids became a critical component of the current study. Similarly, quantifying the summation of exogenous fluxes that have reached the shallow aquifers, specifically coalbed methane reservoirs over time, presents unique challenges (Darrah et al., 2015; Schlegel et al., 2011b; Solomon et al., 1996; Zhou and Ballentine, 2006). In order to mitigate these issues and to attempt to account for the external flux of 4He, some workers have developed and adopted a steady state 4He degassing model (Eq. 2.3) (Ballentine et al., 2002; Ballentine and Burnard, 2002; Bethke et al., 1999; Castro and Goblet, 2003; Castro et al., 1998a; Castro et al., 2000; Torgersen and Clarke, 1985; Torgersen et al., 1992). For the purposes of this paper, I define this as the standard model. In the standard model, the amount of 4He generated by in situ production is typically calculated using the equation (Ballentine and Burnard, 2002): Eq. 2.1 4 퐻푒푖n situ production = in which ρ is the aquifer density, Λ is a parameter defining the efficiency of 4He transfer 4 from the solid to the water, φ is the porosity, t is time, and J4 is the source function of He produced by U and Th decay in the aquifer defined as: Eq. 2.2 105 in which [U] and [Th] are the concentrations in aquifer rocks in mg/kg. The amount of 4He accumulated from an external flux based on steady state assumptions is calculated using the equation (Zhou and Ballentine, 2006): Eq. 2.3 where J4 is the same as defined in equation 2.2, ρcrust is the density of the crust, H is the thickness of the crust, t is time, φ is aquifer porosity, and h is aquifer thickness. A major assumption in these steady state estimates is that there is a uniform crustal 4He flux across a basin throughout time. Typically these assumptions are used, even when it is recognized that major episodic pulses in fluid migration are controlled by periodic tectonic events (Castro et al., 1998a; Castro et al., 1998b; Schlegel et al., 2011b; Torgersen and Clarke, 1985; Zhou and Ballentine, 2006; Zhou et al., 2005; Solomon et al., 1996; and Darrah et al., (2014; 2015)), which in turn have demonstrated that the steady state assumptions for 4He transport are often not valid because exogenous fluxes are often episodic. For these reasons, in combination with the fact that the migration of small amounts of exogenous thermogenic methane can dramatically augment [4He] and hence age estimates (Darrah et al., 2015), it is essential to develop methods to better quantify the flux of exogenous, thermogenic sources of methane when possible. In the latter scenario, I hypothesize that the relative abundance of air-saturated water noble gases (e.g., 106 20Ne/36Ar, 84Kr/36Ar) may provide important insight as to the presence and magnitude of exogenous gases (Darrah et al., 2015; Darrah et al., 2014) and can potentially minimize the errors associated with the steady state assumptions of the standard model. For these reasons, I suggest that it is imperative to use measurements of other air-saturated water noble gases, such as Ne (e.g., 20Ne, 22Ne), Ar (i.e., 36Ar), Kr (i.e., 84Kr), and Xe (i.e., 132Xe) in combination with [4He] to better constrain residence times. One key factor that must be parameterized in order to determine the residence time of water based on [4He] is the original concentration of 4He in groundwater based on the measured values in producing gases (Schlegel et al., 2011b; Zhou and Ballentine, 2006). Because noble gases obey Henry’s laws of solubility in water (He < Ne < Ar < Kr < Xe) and the partitioning of specific gases between the water and gas phase is a function of Volumegas/Volumewater (Vgas/Vwater), one cannot simply assume that the abundance of air- saturated water isotopes (20Ne, 36Ar, 84Kr, 132Xe) can be directly related to their original abundances in groundwater. Unless the original volume of gas is sufficiently high with respect to the volume water (Vgas/Vwater ∞) (Ballentine et al., 2002; Ballentine and Burnard, 2002; Darrah et al., 2015; Darrah et al., 2014; Gilfillan et al., 2009; Zhou and Ballentine, 2006; Zhou et al., 2005). By first using the air-saturated water noble gases to calculate the original Vgas/Vwater, (Eq. 2.4) I can insert the Vgas/Vwater into a Rayleigh fractionation model and estimate the original concentration of 4He in the water phase (Zhou and Ballentine, 2006; Zhou et al., 2005). Based on previous work, I anticipate that excesses of 4He and 20Ne may have significant exogenous contributions from the migration of thermogenic methane. Thus, 107 although the enrichment in 20Ne can be used to help constrain the exogenous component, it may not be a suitable proxy for gas-water interaction in the subsurface. For these reasons, I estimate groundwater volumes using the 84Kr/36Ar and assuming that all of the 36Ar and 84Kr are derived from air-saturated water in the coal seam. Eq. 2.4 α-1 (A/B)water = (A/B)0f ; Where: groundwater groundwater = [(rA/ϕA)KA ]/[(rB/ϕB)KB ]; (A/B)water= A/B ratio in the groundwater and A and B are different noble gases; (A/B)0= the original groundwater phase A/B ratio; f = fraction of B remaining in the groundwater phase; α = fractional coefficient for gas/groundwater system; KA, KB= Henry’s constants for gases A and B; rA, rB= groundwater phase activity coefficients; ϕA, ϕB= gas phase fugacity coefficients. All Henry’s constants were calculated from empirical equations (Ballentine et al., 2002). Fugacity coefficients and activity coefficients were calculated following (Ballentine et al., 2002). From these calculations, I estimate the original Vgas/Vwater for each sample and hence the original volume of water (Table 2.4). 108 2.3. Materials and Methods 2.3.1 Sample Selection This study examines the noble gas (e.g., 4He, 20Ne, 36Ar, and 84Kr) geochemistry of 20 actively producing coalbed methane wells in Sullivan County, Indiana, USA (Table 2.1; Figures 2.1; 2.2). The study area is located in the eastern margin of the synclinal Illinois Basin (Figure 2.1), which is underlain by the New Albany Shale. CBM natural gas production in this area occurs in the Middle-Pennsylvanian-aged Springfield or Seelyville coal seams. Gas samples collected as part of this study were obtained from CBM wells screened at intervals ranging from 76 to 210 meters in depth (Figure 2.1C; Table 2.1). Five wells were producing from the Springfield coal seam, nine from the Seelyville coal seam, and six wells have comingled production (denoted as “comingled” production in the graphical figures). Data from our study are shown in red symbols with symbol shape denoting sample type. Red diamonds and circles represent samples collected from the Springfield and Seelyville coal seams, respectively, while comingled production from both the Springfield and Seelyville coal seams are denoted by red triangles. 109 2.3.2 Sampling and Analysis 2.3.2.1 Gas Samples Gas samples from twenty actively producing CBM (coalbed methane) wells were collected using 0.95 cm. in diameter and 40.6 cm. in length refrigeration-grade copper tubes. Before sampling, actively producing wells were purged for approximately fifteen minutes (>>50 copper tube volumes). After flushing, gas samples were sealed with brass or stainless steel clamps. Each sample was then analyzed for their noble gas elemental and isotopic composition (He, Ne, Ar, Kr, Xe) according to methods reported previously (Darrah et al., 2015; Darrah et al., 2014). In the laboratory, copper tube samples were attached using a 0.95 cm Swagelok ferruled connection to an ultra-high vacuum steel line (total pressure= 1-3 x10-9 torr), which is monitored continuously using a four digit (accurate to the nearest thousandths) 0-20 torr MKS capacitance monometer. After the sample connection had been sufficiently evacuated and pressure was verified, an aliquot of the gas sample was let into the vacuum line by re-rounding the copper. The isotopic analyses of noble gases were performed using a Thermo Fisher Helix SFT MS at The Ohio State University Noble Gas Laboratory. Noble gas procedures for analysis and purification followed methods summarized in (Darrah and Poreda, 2012; Darrah et al., 2013; Hunt et al., 2012; Poreda and Farley, 1992). The average external precision based on "known-unknown" standards were all less than +/- 1.72% for noble gas concentrations with values reported in parentheses ([4He] (0.63%), [22Ne] (1.27%), [40Ar] (0.32%), [84Kr] (1.64%), [132Xe] (1.72%)). 110 These values were determined by measuring referenced and cross-validated laboratory standards including an established atmospheric standard (Columbus, OH Air) and a series of synthetic natural gas standards obtained from Praxair including known and validated concentrations of C1.to C5 hydrocarbons, N2, CO2, CO, H2, O2, Ar, and each of the noble gases. Noble gas isotopic standard errors were approximately ±0.0091 times the ratio of air (or 1.26 x10-8) for 3He/4He ratio, <±0.402% and <±0.689% for 20Ne/22Ne and 21Ne/22Ne, respectively, less than ± 0.643% and 0.427% for 38Ar/36Ar and 40Ar/36Ar, respectively (higher than typical because of interferences from 82 84 C3H8 on mass=36 and 38), less than ±1.26% for Kr/ Kr, and less than ±1.07% for 130Xe/132Xe. 2.3.2.2 Coal Seam Solids The abundances of 4He, 22Ne and 21Ne* in coal seam solids were evaluated using six coal samples (two from the Springfield and four from the Seelyville) at depths ranging from ~73 to 213 meters. These samples were collected from drilling cuttings and cores of coal seams in Sullivan County, Indiana. Approximately 25 grams of each sample were oven dried, lightly crushed, and sieved through a 63-micron sieve. The >63-micron fraction was retained, dried, weighed, then rinsed fully with deionized water and then dried again at 25oC overnight following methods reported in (Hunt, 2000). The helium elemental and isotopic abundances (e.g., 4He, 21Ne, and 22Ne) were determined using a Thermo Fisher Helix SFT noble gas mass spectrometer by peak height comparison to a calibrated air standard. In order to correct helium concentrations 111 for air leakage, it was assumed that all 3He came from air, and the air component was subtracted from the overall helium concentration. The vastly different ratios of crustal (~1x10-8) versus atmospheric helium (1.39x10-6) ratios of helium isotopes is 3 4 confirmed by the high temperature release of helium with a He/ He ratio <0.03 RA. Excess 21Ne (21Ne*) was determined by subtracting the atmospheric ratio of 21Ne/22Ne from the measured ratio and multiplying it by the measured concentration of 22Ne following Eq. 2.5. Eq. 2.5 21 21 22 21 22 22 21 22 [ Ne*]= ( Ne/ Nemeasured – Ne/ NeAir) * [ Ne]measured , where Ne/ NeAir= 0.0289 The U and Th concentrations were measured using splits of coal seam solid samples by laser ablation ICP-MS. Analyses of U and Th concentrations were completed using a Thermo Finnigan Element 2 ICP-Sector Field MS and a Photon Machines Excite Laser at the Trace Element Research Laboratory at The Ohio State University following methods developed previously (Walsh, 2015). 2.3.2.3 Calibrating the Diffusional Release of 4He from Mineral Grains In order to determine the diffusional release rates of 4He from coal samples, a step heating procedure was used following the methods of Hunt (2000). For each sample (n=4) used for the diffusional release experiment, ~25 milligrams (mg) of dried rock was placed into an “on-line” stainless steel tube furnace and heated using an external resistive heater. Temperature was measured with 2 external thermocouples at the top and bottom of the chamber and maintained using a variable transformer. The average 112 temperature between the two thermocouples was used, with an estimated temperature error of ±5oC. The diffusional release experiment was conducted by step-wise heating samples at intervals of 50oC, 75oC, 100oC, 150oC, 200oC, 250oC, 300oC, and 400oC. Timing for each temperature step was long enough to allow helium to accumulate at measureable concentrations. The lowest temperature step (50oC) accumulated helium for 10 days, while each successive step remained closed for ~2 hours (with exact times recorded). Incremental 4He, 21Ne, and 22Ne measurements were made on a Thermo Fisher Helix SFT noble gas mass spectrometer by peak height comparison to a calibrated air standard (Columbus, OH Air). Error for [4He] analysis was limited to less than 5%. 2.3.3 Graphical and Statistical Treatment of Data All maps, cross-sections, and well coordinates are plotted using ArcMap GIS 10.2.2. All graphics are plotted using Sigma Plot v. 12.3. Statistical evaluations including mean, minimum, maximums, Pearson correlations, standard deviations, and analysis of variance (ANOVA) are performed using SPSS v. 22.0. 113 2.4. Results The current study provides data from six coal seam solid samples and gas data from twenty producing CBM wells in the Springfield and Seelyville coal seams. Four of the coal seam solid samples underwent stepwise heating experiments. The full complement of natural gas elemental, molecular, and isotopic compositions were presented in (Moore et al., 2016). 2.4.1 Composition of Coal Seam Solids 2.4.1.1 Radioactive Elements The concentrations of alpha-producing (U, Th) elements, in tandem with the age of the formation can be used to determine the amount of 4He that is expected to accumulate in coal seam solids throughout geological time. A comparison of the amount of helium that is retained in coal seam solids to these estimates can provide a qualitative comparison of the behavior of radiogenic 4He in mineral grains and fluid flow histories in the subsurface. Constraining the concentrations of α-producing elements is also essential to evaluating the in situ production of 4He today. For the six coal seam solid samples analyzed in this study, the [U] and [Th] ranged from 0.85 to 1.54 mg/kg with 1.2 mg/kg on average and 2.95 to 5.35 mg/kg with 4.0 mg/kg on average, respectively (Table 2.2). The Th/U ratios ranged from 2.5 to 4.2 with an average of 3.4 (Table 2.2). Assuming the values from six samples are representative of the coal formation on the macroscopic level, these data suggest that the maximum amount of α-production within one million years would only yield 5.86 µcc of He per liter. The one million year production interval is arbitrary, but are within the range of 114 previously published research on interglacial meteoric recharge pulses in this area (McIntosh and Walter, 2006; Stueber and Walter, 1991; Stueber and Walter, 1994; Walter et al., 1990). 2.4.1.2 Noble Gases in Coal Seam Solids Measured [4He] and [21Ne*] in coal samples ranged from 21,700 to 44,060 cc/kg and 1,210 to 3040 pcc/kg, respectively (Table 2.2; Figure 2.5). Based on the measured concentrations of U and Th, described above, we calculated the estimated total of [4He] and [21Ne*] based on the age of the formation (i.e., the amount of radiogenic gas that was produced since deposition). Again, assuming the values from six samples are representative of the coal seam solids on the macroscopic level, these data suggest that through the time that has elapsed since the deposition of the Springfield and Seelyville coal seams (~300 million years) approximately 5.3 to 9.3 x104 µcc of 4He would have been produced per gram of coal seam solids with 7.3 x104 µcc/g on average. By comparison, the estimated production of 21Ne* ranged between 2.4 to 4.2 x103 pcc/g with 3.3 x103 pcc/g on average. These data suggest that the percentage of 4He that is retained ranged from 25 to 53% with 43% on average, while the amount of 21Ne* that is retained ranges from 47-80% with 59% on average. In combination, these data suggest that the 4He/21Ne* ratios ranged from 9.61 x106 to 21.2 x106 with 16.4 x106 on average as compared to the average crustal production ratio of 22 x106 (Table 2.2; Figure 2.5). At first glance, the 4He/21Ne* data seem surprising because average 21Ne* production rates are directly proportional to the generation of 4He and the nearly ubiquitous presence of oxygen 115 in silicate minerals. Because coal is dominantly carbon, one should not anticipate the generation of 21Ne*, and thus, the source of 21Ne* remains uncertain. 2.4.2 Stepwise Heating of Coal Samples to Determine Diffusional Release Rates In order to provide reliable estimates for the rate of 4He diffusional loss from coal seam solids into coal seam waters, one must have robust constraints on the transfer coefficients (from solids to fluids) for 4He that has accumulated in coal seam solids over time (Darrah et al., 2015; Hunt, 2000; Sheldon et al., 2003; Solomon et al., 1996). Although the rates of helium diffusion are reasonably well-constrained for most crustal aquifer rocks (Ballentine and Burnard, 2002), there is little to no published data available on diffusional release constants for bituminous coal (or coal in general). Thus, I needed to perform a step-wise heating experiment to calculate the helium diffusion release rate for coal seam solids in the Illinois Basin as part of this study (Table 2.3; Figure 2.4). Previous studies have determined diffusional release constants by performing step-wise heating experiments for known intervals of time to develop an Arrhenius Plot (log[4He] vs. 1000/(temperature in Kelvin), and subsequently using the regression of that data to determine the diffusional release of helium at modern in situ aquifer temperatures (~15oC) (Figure 2.4) (Darrah et al., 2015; Hunt, 2000; Sheldon et al., 2003; Solomon et al., 1996). The step-wise heating experiment showed a steady increase in [4He] in the 50oC, 75oC, 100oC, 150oC, and 200oC heating steps (Table 2.3). However, beyond these temperatures, the cumulative loss of 4He began to stop increasing as temperature increased (rollover). I interpret these data to suggest that the majority of 4He is degassed by approximately the 200oC temperature interval (Figure 2.4). As a result, I elected to estimate the 116 diffusional loss rate by regressing values only up to the 200oC temperature step. The calculated 4He diffusional release rates at 15 oC based on these estimates ranged from 0.77 to 1.03 µcc/kg/yr and averaged 0.81 µcc/kg/yr with a standard deviation of 0.15 µcc/kg/yr. Although I plan to do future work to better constrain the robustness of these estimates, I use a diffusional loss rate of 0.81 µcc/kg/yr to calculate the residence of groundwater in this study. 2.4.3 Calculating Initial Water Volume In order to determine the initial concentration of 4He in the groundwater phase, I must first estimate the volume of water that was degassed to generate the gas phase and in turn determine the original concentration of 4He in the groundwater phase. Because the 20Ne/36Ar can be impacted by the introduction of exogenous 20Ne, I use the degree of 84Kr/36Ar fractionation from air-saturated water values to estimate the original concentration of 4He in groundwater. This is done after determining the fraction of residual water remaining based on the measured [36Ar] and [84Kr]. While the 84 36 36 Volumegas/Volumewater, the Kr/ Ar, the [ Ar], and volumes of water were calculated for each individual sample (Tables 2.4-2.5), I present the range and averages for comparative purposes. The air-saturated water value for 84Kr/36Ar estimated for atmospheric pressure, temperature of recharge, and salinity is 0.041. The measured 84Kr/36Ar ranged from 0.0095 to 0.0409 with 0.0206 on average (Table 2.4). This range suggests variable amounts of mass-dependent gas fractionation in the majority of samples reflecting variable initial Volumegas/Volumewater. The Volumegas/Volumewater was calculated using 117 the recently adapted two-stage groundwater gas stripping and re-dissolution (GGS-R) model (Darrah et al., 2015; Darrah et al., 2014; Gilfillan et al., 2008; Gilfillan et al., 2009; Zhou et al., 2012). The measured [36Ar] ranged from 0.29 to 3.69 µcc/cc with 1.08 µcc/cc on average (Table 2.4). In combination with these water and gas fraction calculations, I estimate that 5.21 x10-4 to 8.65 x10-3 liters of water with 2.87 x10-3 liters of water on average were degassed per cubic centimeter at standard temperature and pressure of produced natural gas. The initial concentration of 4He in groundwaters from coal seams in the Illinois Basin range from 9,520 to 179,900 µcc/L (Table 2.5). 2.4.4 Residence Time Calculations Using the initial estimated [4He] in groundwater, I calculate residence by three methods. The first method uses the standard approach based on previous publications (Schlegel et al., 2011b; Zhou and Ballentine, 2006). This method incorporates the 4He contributions from air-saturated water, contributions from in situ α-decay, and an average external flux, which model the release of radiogenic gases from detrital grains and external sources, and is estimated by the methods described above (Section 2); this model parameterizes the flux of 4He from coal seam solids to fluids at a rate of 0.15 µcc/kg/yr. Based on these constraints, the residence time ranges from 1.42 x105 to 2.70 x106 years with an average of 9.02 x105 years. The second method adapts an empirical approach (i.e., measure instead of model). Our approach relies upon directly quantifying the concentration of 4He in coal seam solids from the Springfield and Seelyville coal seams (Table 2.3; Figure 2.5) and the rate of diffusive loss from the mineral grains (Table 2.3; Figure 2.4). Based on this 118 approach (described in detail in Sections 2 and 3), I estimate that the flux of 4He from minerals grains to fluids in the coal seams and use measured [4He] in coal seam solids to estimate the diffusional boundary conditions; this model parameterizes the flux of 4He from coal seam solids to fluids at a rate of 0.81 µcc/kg/yr at 15oC (Table 2.3). Using the standard approach that incorporates the 4He contributions from air-saturated water and in situ α-decay, but uses the measured and calculated rates for helium release from mineral grains, I estimate the residence time to be 1.54 x104 to 2.93 x105 years with 9.80 x104 years on average (Table 2.5; Figure 2.6). Note that these values are approximately an order of magnitude lower than the average residence time calculated using the standard model (Table 2.5; Figure 2.6). Our previous work shows that coalbed methane reservoirs in our study receive quantifiable exogenous contributions of thermogenic gases, possibly from the New Albany Shale (Moore et al., 2016). While standard methods are left to assume external fluxes are continuous and occur at steady state, our previous observations suggest that the external flux is likely episodic and occurs at larger magnitudes than previously anticipated. Thus, I develop an additional model that accounts for both the rates of diffusional loss from coal seam solids and the exogenous sources. I estimate the exogenous sources based on the thermogenic contributions for each sample calculated in (Moore et al., 2016) and verified here using the relative contributions of excess 20Ne. Based on these components, I calculate the residence time to be 1.21 x104 to 2.92 x105 years with 9.54 x104 years on average (Table 2.5; Figures 2.6-2.8). I note that the model that corrects for coal diffusional constants and exogenous sources is approximately 119 12 times lower than the standard model and 20% below the standard approach that incorporates the empirically derived helium diffusional release constants (Figure 2.8). 120 2.5 Discussion In many studies, it is not feasible to obtain core samples or cuttings from producing gas wells in order to quantify the abundance of 4He that resides in mineral grains, the rates of diffusional loss of 4He, or even the U and Th concentrations. In these situations, it is necessary to use estimated rates for helium release from sediment grains and steady state assumptions for exogenous inputs from the crust. Nonetheless, I previously identified and quantified exogenous contributions of 4He (and even some mantle 3He) to fluids produced from the CBM reservoirs in this study (Moore et al., 2016). Similarly, the rates of 4He production within and release from coal seam solids is entirely unconstrained. Herein, both factors were determined to occur at significantly larger magnitudes than previously estimated by standard models. For these reasons, I suggest that it is essential to reliably constrain these parameters using a) the full complement of gas isotope geochemistry to evaluate magnitude and composition of exogenous sources; b) stepwise heating experiments and Arrhenius calculations to quantify the rate at which helium is transferred from coal seam solids to the fluids; and c) direct measurements of the abundance of 4He retained in coal grains (Tables 2.2-2.3; Figures 2.3; 2.5). These total fusion and stepwise heating methods produced some surprising results. Although the total amount of [4He] in coal seam solids ranged significantly, the concentrations of 4He in these samples were much higher than expected. For example, based on modelled results, radiogenic 4He was anticipated to be removed (“flushed”) from mineral grains in shallow aquifers on the timescale of ~10 x 103 years (Hunt, 2000). Despite these predictions and the noted introduction of fresh meteoric water 121 that has diluted formational brines throughout this region (McIntosh et al., 2012; McIntosh et al., 2004; Schlegel et al., 2011a; Schlegel et al., 2011b; Stueber and Walter, 1991; Stueber and Walter, 1994; Walter et al., 1990), I find that the coal seam minerals have retained >40% of the radiogenic 4He assuming an ingrowth time of ~300 million years. As a result, standard models dramatically underestimate the amount of 4He that already resides within coal seams and that can be released from coal seam solids into pore waters. Obviously the significant errors in these underestimates would be propagated through residence time calculations and produce unreliable results if the standard method were employed (discussed further below). The exceptionally high [4He] in coal seam solids suggest one of several possibilities. One possibility might be that because the release of helium from mineral grains to pore fluids is a function of porosity, low porosity coals could be exceptionally “helium tight” for the majority of their geological history and only release helium at faster rates in modern times following neotectonic fracturing or fracking by coalbed methane production. Because of its small atomic radius, helium can freely equilibrate between mineral phases and pore fluids. Thus, another possibility is that the elevated helium measured in the coal seam solids relates to helium that was more recently introduced from exogenous sources and later dissolved into mineral grains. Even if this mechanism did account for elevated [4He] in coal seam solids, the release rate from grains could still be used for residence time calculations if the helium concentrations and transfer rates can be validated in additional studies. While the current dataset does not allow us to uniquely constrain these possibilities or other options that I do not consider, it is worth noting that 122 the 4He/21Ne* is ~50% below the crustal production value, but well above anticipated rates of relative 4He/21Ne* production in oxygen-deficient coals. This result is troubling because one would not anticipate significant in situ production of 21Ne* in coal seams in light of the absence of oxygen atoms in mineral lattices. At the present time the source of 21Ne* is unknown. The second surprising result relates to the elevated rate for the empirically determined transfer of 4He from coal seam solids to pore fluids. Compared to the average continental crust, I observe significantly higher rates of 4He transfer from the coal grains to CBM fluids. These diffusional constants are approximately 5.4 times greater than the rates observed for typical siliclastic or quartz grains at relevant temperatures (5-25oC). Based on these measurements, which demonstrate that modelled values systematically underestimate 4He transfer rates, I conclude that assuming standard transfer rates for helium would systematically overestimate the residence of fluids in coalbed methane reservoirs from this study area. Preliminary work in the Powder River Basin suggests similarly high rates of diffusional helium loss from coal solids (Ritter et al., 2015), which suggest this problem may be a fundamental property of coal solids. For these reasons, I conclude that the standard approach for estimating helium diffusional loss rates would systematically bias the residence times by more than an order of magnitude and suggest that the time elapsed since freshwater recharge in this study area is in on the scale of millions of years. While this area has experienced numerous glacial and interglacial periods throughout the last ~3 million years (McIntosh et al., 2012; McIntosh et al., 2004; Schlegel et al., 2011b; Stueber and Walter, 1991; Stueber and Walter, 1994; Walter et al., 1990), the residence times estimated 123 based on the standard model suggest that recharge occurred in the middle of the Illinoian glacial period. Further, if the standard model ages are correct, these residence time calculations for relatively shallow coal seams in this study area would be significantly longer than estimates of residence time for freshwater that recharged in the New Albany Shale (located ~>610 meters below the Seelyville coal seam) (Schlegel et al., 2011b). By quantitatively correcting for the amount of 4He that is introduced into CBM reservoirs via the release of 4He that has accumulated in coal seam solids, I estimate residence times on the order of 9.80 x104 years (with a range of plus or minus 3.90 x 103 years based on the standard deviations of calculated helium diffusion constants). It is worth noting that these estimates place the timing of recharge during the interglacial period following the Illinoian glacial cycle. Additionally, these residence time calculations are within the error bars of residence time calculations for the underlying New Albany Shale (Schlegel et al., 2011b). Based on the combination of empirical data for [4He] in mineral grains, empirically determined diffusional release rates of 4He from coal seam solids, and the hydrological feasibility of residence time interpretations, I conclude that the standard model overestimates residence times. The standard model that uses the empirical values for the [4He] in mineral grains and empirically determined diffusional release rates of 4He from coal seam solids produces a more hydrological realistic value that is more consistent with other estimates of residence times for underlying formations. Nonetheless, by additionally correcting the improved model for contributions from exogenous thermogenic sources, the estimated groundwater residence times are further reduced by an additional ~20%. I 124 determine average residence times by this method of ~9.59 x 104 years (plus or minus 3.90 x 103 years based on the standard deviations of calculated helium diffusion constants). I note that these average residence time estimates are also within error bounds predicted by previously age models for the New Albany Shale (Schlegel et al., 2011b) and occur during interglacial periods following the Illinoian glacial cycle. Although the correction for exogenous sources reduces age estimates by 20% on average (and up to 38% in some samples), the largest source of uncertainty in the residence time calculations is the magnitude of 4He that is retained in coal seam solids and the rate of 4He transport from coals to fluids within coal seams. Thus, future work should attempt to better constrain the rates of diffusional loss for 4He from coals and other complex, organic-rich rock matrices (e.g., shales) in order to better refine residence time calculations. Though, the corrections for the exogenous inputs of 4He reduce the groundwater residence time by 20%, based on a standard deviation of 3.90 x103, the value of 9.8 x 104 years calculated using the diffusional release of 4He from coals is not statistically indistinguishable from 9.54 x 104 years using both the diffusional release of 4He and exogenous inputs of 4He. This further exemplifies the importance of constraining the 4He diffusional release from coal seam solids. 125 2.6 Conclusions Understanding the timescales on which biogenic methane is produced in coalbed methane is a critical step towards evaluating the roles of groundwater in methanogenesis. Here I attempted to determine the residence time of groundwater in the Springfield and Seelyville coal seams from the Illinois Basin using the ingrowth of 4He. The utilization of noble gases to determine residence time and flow paths of groundwater requires assumptions about the production and diffusion rate of helium in aquifer materials. While these assumptions may be valid for many systems, excess amounts of helium and significantly higher rates for the diffusional loss of helium from coal seam solids determined in this study underscore the need to test these assumptions when applying this technique to unique aquifer systems. Without properly understanding aquifer material properties, noble gas residence time estimates are underconstrained. Our data suggest that standard models for the transfer of 4He from coal seam solids to pore fluids is systematically underestimated, which yield systematically overestimated values of groundwater age. Additionally, I identify significantly higher levels of 4He in coal seam solids than was anticipated based on typical crustal sediments and the marked presence of an exogenous source of 4He. By taking these factors into account, I estimate the average residence times for groundwater in coalbed methane reservoirs from the Illinois Basin on the magnitude of approximately 9.59 x 104 years. These estimates are approximately 10 to 12 times lower than standard models and consistent with an influx of fresh groundwater following the Illinoian glacial period as has been observed previously in the underlying New Albany Shale. 126 2.7 Acknowledgements I acknowledge financial support from NSF EAGER (EAR-1249255) and NSF SusChem (EAR-1441497) to T.H.D and salary support for M.T.M from the School of Earth Sciences at The Ohio State University. I thank Professors Jennifer McIntosh (U. Arizona), John Olesik, Frank Schwartz, W Berry Lyons (OSU), Robert Poreda (University of Rochester), and Dr. Andrew Hunt (USGS) for stimulating discussions on groundwater age dating techniques and the hydrogeology and geochemistry of coalbed methane reservoirs in the Illinois Basin. I also thank Anthony Lutton, Colin Whyte, Benjamin Grove, Sharon Scott, Erica Maletic, Dr. Jeremy C. Williams, and Yohei Matsui (OSU) for field and analytical support and friendly reviews of earlier versions of this manuscript. I also thank Larry Neely and Jason Neely (Maverick Energy) for their assistance in sampling, sharing of information, and their knowledge about the study area. 127 References Ballentine, C.J., Burgess, R., Marty, B., 2002. Tracing fluid origin, transport and interaction in the crust. In: Porcelli, D., Ballentine, C.J., Wieler, R. (Eds.), Noble Gases in Geochemistry and Cosmochemistry. Reviews in Mineralogy & Geochemistry, pp. 539-614. Ballentine, C.J., Burnard, P.G., 2002. Production, release and transport of noble gases in the continental crust. In: Porcelli, D., Ballentine, C.J., Wieler, R. (Eds.), Noble Gases in Geochemistry and Cosmochemistry. Reviews in Mineralogy & Geochemistry, pp. 481-538. 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Identifying and quantifying natural CO2 sequestration processes over geological timescales: The Jackson Dome CO2 Deposit, USA. Geochimica Et Cosmochimica Acta, 86: 257-275. 135 Chapter 2. Figures: Figure 2.1. A generalized stratigraphic column (A), areal extent of the Illinois Basin (B), and a simplified structural cross section (C) (reproduced from Strąpoć et al., 2007) of the synclinal Illinois Basin. The stratigraphic column displays the Middle Pennsylvanian-aged Springfield and Seelyville coal seams (of the Carbondale Group) and the upper to middle Devonian-aged New Albany Shale unit. It is important to note that the Dekovan or Davis Formations are equivalent units of the Seelyville Formation. Samples were collected from producing coalbed methane (CBM) wells in the area denoted by the red box on the eastern portion of the Illinois Basin (1C). 136 Figure 2.2. An inset map of sampling locations denoted by the red box (A) and a topographic map (B) showing the locations of producing CBM wells sampled as part of this study (n=20) in Sullivan County, Indiana denoted in red symbols. The green squares denote CBM well locations from previous studies (Schlegel et al., 2011). Purple and yellow boxes denote New Albany Shale well locations from previous studies (Schlegel et al., 2011, McIntosh et al., 2002). 137 Figure 2.3. A schematic of the production and diffusive loss of radiogenic noble gases in quartz or other crustal minerals (Adapted from: Darrah & Poreda, 2013). The simplified cross-section of the Appalachian Plateau Province shows an 4 example of how migration of He and CH4 can occur through an aquifer from depths. 138 Figure 2.4. Results of a step heating procedure for diffusional release rate of 4He from coal samples. Stultz is a coal sample from a well producing in the Springfield coal seam and the other three are coal samples are from the Seelyville coal seam. The step-wise heating was at intervals of 50oC, 75oC, 100oC, 150oC, 200oC, 250oC, 300oC, and 400oC. 139 21 4 Figure 2.5. Comparison of [ Ne*]measured (pcc/kg) vs. [ He]measured (cc/kg) (A), 21 4 4 fraction of Neretained vs. fraction of Heretained (B), [ He]measured (cc/kg) vs. 4 21 21 [ He]expected (cc/kg) (C), and [ Ne*]measured (pcc/kg) vs. [ Ne*]expected (pcc/kg) for six coal samples collected in this study. 140 Figure 2.6. Comparison of standard corrected model for coal diffusion (years) vs. standard age model (years) for 20 fluid samples collected in this study. 141 Figure 2.7. Comparison of exogenous model corrected for coal diffusion (years) vs. standard age model (years) for 20 fluid samples collected in this study. 142 Figure 2.8. Comparison of exogenous model corrected for coal diffusion (years) vs. standard corrected model for coal diffusion (years) for 20 fluid samples collected in this study. 143 Chapter 2. Tables: Table 2.1 Location and depths of sampled coalbed methane wells Coal Gas Well Max depth Sample ID Latitude Longitude Production Unit Screened (m.) Creed Mine Springfield 76 39.03743 -87.48148 Stultz Springfield 73 39.03273 -87.42898 Mayfield-1 Springfield 91 39.01942 -87.42932 Alexander-1 Springfield 107 39.05428 -87.41125 Creed-2 Springfield 76 39.03188 -87.42554 Bolenbaugh Seelyville 173 39.02953 -87.49162 T.Cole Seelyville 177 39.0285 -87.48657 Alexander-2 Seelyville 213 39.03045 -87.4851 Vic Seelyville 171 39.04068 -87.48675 Doherty-1 Seelyville 176 39.0411 -87.48355 Arnett-1 Seelyville 153 39.03818 -87.43818 Arnett-3 Seelyville 167 39.04065 -87.44732 McCain Seelyville 175 39.01677 -87.48395 Wheeler Seelyville 175 39.01861 -87.49787 Hancock-1 Co-mingled 158 39.02785 -87.50045 Coulson-1 Co-mingled 174 39.041 -87.47672 F. Willis Co-mingled No-info 39.03164 -87.47223 Unger Co-mingled 185 39.02106 -87.48782 E.Hobbs-1 Co-mingled No-info 39.01777 -87.5061 Gimoson Co-mingled No-info 39.02388 -87.48392 144 Table 2.2 Concentrations of U, Th, 4He, and 21Ne* in coal samples from the Illinois Basin. Well Coal Gas Max Measured Measured Expected Expected 4 21 U Th 4 21 4 4 % He % Ne Sample ID Production depth Th He Ne* He He 21 (mg/kg) (mg/kg) Ne Retained Retained Unit Screened U (ucc/kg) (pcc/kg) (µcc/g) (pcc/g) 21Ne* (m.) Assuming Assuming 300Ma 300Ma Stultz Springfield 73 1.06 3.65 3.44 27861.4 1548.0 18.00 66034 2988 42.19% 51.81% Creed-2 Springfield 76 1.24 4.15 3.34 34335.4 1619.9 21.20 76250 3450 45.03% 46.95% T.Cole Seelyville 177 0.85 2.95 3.48 21749.0 1211.7 17.95 53035 2400 41.01% 50.49% Alexander- 2 Seelyville 213 0.98 4.06 4.16 35079.4 2081.9 16.85 66679 3017 52.61% 69.00% Doherty-1 Seelyville 176 1.47 5.35 3.65 23649.1 2460.9 9.61 93880 4248 25.19% 57.93% 145 Wheeler Seelyville 175 1.54 3.90 2.53 44060.8 3040.8 14.49 84418 3820 52.19% 79.60% Table 2.3 Statistical summary of noble gas isotopic composition Measured Measured 4 Expected Fraction Fraction Th He Expected U Th/U 4He 21Ne* 21Ne 4He 21Ne (mg/kg) 4He (µcc/g) (mg/kg) (ucc/kg) (pcc/kg) 21Ne* (pcc/g) Retained Retained Average 1.19 4.01 3.43 31122.52 1993.86 16.35 73382.78 3320.49 0.43 0.59 Minimum 0.85 2.95 2.53 21748.97 1211.71 9.61 53035.44 2399.79 0.25 0.47 Maximum 1.54 5.35 4.16 44060.81 3040.77 21.20 93879.83 4247.96 0.53 0.80 146 St. Dev. 0.28 0.79 0.53 8339.40 674.13 3.95 14581.41 659.79 0.10 0.13 147 148 Table 2.6 statistical summary of noble gas isotopic composition 4 20 36 fract. He Ne Ar 3He 21Ne 4He 4He 4He 20Ne 4He 84Kr 132Xe resid. 21 40 20 36 36 36 84 4 22 Ne* Ar* Ne Ar Ar Ar Kr µcc/cc µcc/cc µcc/cc 36Ar He Ne Avg. 216.02 0.47 1.08 0.27 0.12 0.03 6.98 17.16 590.03 0.57 419.25 0.0206 0.03 Min. 11.61 0.11 0.29 0.02 0.04 0.03 0.60 1.08 11.12 0.21 3.15 0.0095 0.02 Max. 1464.60 1.55 3.69 0.95 0.90 0.03 35.41 76.38 1685.95 2.94 2773.07 0.0409 0.05 St. 327.901 0.406 1.062 0.354 0.194 0.001 8.566 17.436 529.156 0.587 630.213 0.011 0.007 Dev. 149 150 151 References Chapter 1: Ballentine, C.J., Burgess, R., Marty, B., 2002. Tracing fluid origin, transport and interaction in the crust. In: Porcelli, D., Ballentine, C.J., Wieler, R. (Eds.), Noble Gases in Geochemistry and Cosmochemistry. Reviews in Mineralogy & Geochemistry, pp. 539-614. Ballentine, C.J., Burnard, P.G., 2002. Production, release and transport of noble gases in the continental crust. In: Porcelli, D., Ballentine, C.J., Wieler, R. (Eds.), Noble Gases in Geochemistry and Cosmochemistry. Reviews in Mineralogy & Geochemistry, pp. 481-538. Ballentine, C.J., Onions, R.K., Oxburgh, E.R., Horvath, F., Deak, J., 1991. Rare-gas constraints on hydrocarbon accumulation, crustal degassing, and groundwater-flow in the Pannonian. Basin Earth and Planetary Science Letters, 105(1-3): 229-246. Bates, B.L., McIntosh, J.C., Lohse, K.A., Brooks, P.D., 2011. Influence of groundwater flowpaths, residence times and nutrients on the extent of microbial methanogenesis in coal beds: Powder River Basin, USA. Chemical Geology, 284(1-2): 45-61. Bentley, H.W. et al., 1986. CL-36 dating of very old groundwater. 1. The Great Artesian Basin, Australia. Water Resources Research, 22(13): 1991-2001. Bethke, C.M., Marshak, S., 1990. Brine migrations across North America-The plate- tectonics of groundwater. Annual Review of Earth and Planetary Sciences, 18: 287-315. Bethke, C.M., Zhao, X., Torgersen, T., 1999. Groundwater flow and the He-4 distribution in the Great Artesian Basin of Australia. Journal of Geophysical Research-Solid Earth, 104(B6): 12999-13011. Buschbach, T.C., Kolata, D.R., 1990. Regional Setting of Illinois Basin: Chapter 1: Part I. Illinois Basin: Regional Setting. Castro, M.C., 2004. Helium sources in passive margin aquifers - new evidence for a significant mantle He-3 source in aquifers with unexpectedly low in situ He- 3/He-4 production. Earth and Planetary Science Letters, 222(3-4): 897-913. 152 Castro, M.C., Goblet, P., 2003. Calibration of regional groundwater flow models: Working toward a better understanding of site-specific systems. Water Resources Research, 39(6). Castro, M.C., Goblet, P., Ledoux, E., Violette, S., de Marsily, G., 1998a. Noble gases as natural tracers of water circulation in the Paris Basin 2. Calibration of a groundwater flow model using noble gas isotope data. Water Resources Research, 34(10): 2467-2483. Castro, M.C., Jambon, A., de Marsily, G., Schlosser, P., 1998b. Noble gases as natural tracers of water circulation in the Paris Basin 1. Measurements and discussion of their origin and mechanisms of vertical transport in the basin. Water Resources Research, 34(10): 2443- 2466. Castro, M.C., Stute, M., Schlosser, P., 2000. Comparison of He-4 ages and C-14 ages in simple aquifer systems: implications for groundwater flow and chronologies. Applied Geochemistry, 15(8): 1137-1167. Cathles, L.M., 1990. Scales and effects of fluid-flow in the upper crust. Science, 248(4953): 323- 329. Cook, P.G. et al., 1996. Inferring shallow groundwater flow in saprolite and fractured rock using environmental tracers. Water Resources Research, 32: 1501-1509. Cuoco, E. et al., 2013. Impact of volcanic plume emissions on rain water chemistry during the January 2010 Nyamuragira eruptive event: Implications for essential potable water resources. Journal of Hazardous Materials, 244: 570- 581. Darrah, T.H. et al., 2015. The evolution of Devonian hydrocarbon gases in shallow aquifers of the northern Appalachian Basin: Insights from integrating noble gas and hydrocarbon geochemistry. Geochimica Et Cosmochimica Acta, 170: 321-355. Darrah, T.H., Poreda, R.J., 2012. Evaluating the accretion of meteoritic debris and interplanetary dust particles in the GPC-3 sediment core using noble gas and mineralogical tracers. Geochimica et Cosmochimica Acta, 84: 329-352. 153 Darrah, T.H. et al., 2013. Gas chemistry of the Dallol region of the Danakil Depression in the Afar region of the northern-most East African Rift. Chemical Geology, 339: 16-29. Darrah, T.H., Vengosh, A., Jackson, R.B., Warner, N.R., Poreda, R.J., 2014. Noble gases identify the mechanisms of fugitive gas contamination in drinking-water wells overlying the Marcellus and Barnett Shales. Proceedings of the National Academy of Sciences of the United States of America, 111(39): 14076-14081. Drobniak, A., Mastalerz, M., Rupp, J., Eaton, N., 2004. Evaluation of coalbed gas potential of the Seelyville coal member, Indiana, USA. International Journal of Coal Geology, 57(3-4): 265-282. Etiope, G. et al., 2009. Evidence of subsurface anaerobic biodegradation of hydrocarbons and potential secondary methanogenesis in terrestrial mud volcanoes. Marine and Petroleum Geology, 26(9): 1692-1703. Garven, G., Ge, S., Person, M.A., Sverjensky, D.A., 1993. Genesis of stratabound ore deposits in the midcontinent basins of North America 1. The role of regional groundwater flow. American Journal of Science, 293(6): 497-568. Gilfillan, S.M. et al., 2008. The noble gas geochemistry of natural CO2 gas reservoirs from the Colorado Plateau and Rocky Mountain provinces, USA. Geochimica Et Cosmochimica Acta, 72(4): 1174-1198. Gilfillan, S.M.V. et al., 2009. Solubility trapping in formation water as dominant CO2 sink in natural gas fields. Nature, 458(7238): 614-618. Hunt, A.G., 2000. Diffusional release of helium-4 from mineral phases as indicators of groundwater age and depositional history. Hunt, A.G., Darrah, T.H., Poreda, R.J., 2012. Determining the source and genetic fingerprint of natural gases using noble gas geochemistry: A northern Appalachian Basin case study. AAPG bulletin, 96(10): 1785-1811. James, A.T., Burns, B.J., 1984. Microbial alteration of subsurface natural-gas accumulations Aapg Bulletin-American Association of Petroleum Geologists, 68(8): 957-960. Karacan, C.O., Drobniak, A., Mastalerz, M., 2014. Coal bed reservoir simulation 154 with geostatistical property realizations for simultaneous multi-well production history matching: A case study from Illinois Basin, Indiana, USA. International Journal of Coal Geology, 131: 71-89. Labotka, D.M., Panno, S.V., Locke, R.A., Freiburg, J.T., 2015. Isotopic and geochemical characterization of fossil brines of the Cambrian Mt. Simon Sandstone and Ironton- Galesville Formation from the Illinois Basin, USA. Geochimica Et Cosmochimica Acta, 165: 342-360. Lowenstern, J.B., Evans, W.C., Bergfeld, D., Hunt, A.G., 2014. Prodigious degassing of a billion years of accumulated radiogenic helium at Yellowstone. Nature, 506(7488): 355-360. Martini, A.M., Budai, J.M., Walter, L.M., Schoell, M., 1996. Microbial generation of economic accumulations of methane within a shallow organic-rich shale. Nature, 383(6596): 155- 158. Martini, A.M. et al., 1998. Genetic and temporal relations between formation waters and biogenic methane: Upper Devonian Antrim Shale, Michigan Basin, USA. Geochimica Et Cosmochimica Acta, 62(10): 1699-1720. Martini, A.M., Walter, L.M., McIntosh, J.C., 2008. Identification of microbial and thermogenic gas components from Upper Devonian black shale cores, Illinois and Michigan basins. Aapg Bulletin, 92(3): 327-339. Mastalerz, M., Drobniak, A., Rupp, J.A., Shaffer, N.R., 2004a. Characterization of Indiana's coal resource: availability of the reserves, physical and chemical properties of coal, and present and potential uses. Indiana Geological Survey, Indianapolis, Indiana. Mastalerz, M., Gluskoter, H., Rupp, J., 2004b. Carbon dioxide and methane sorption in high volatile bituminous coals from Indiana, USA. International Journal of Coal Geology, 60(1): 43-55. Mastalerz, M., Schimmelmann, A., Drobniak, A., Chen, Y., 2013. Porosity of Devonian and Mississippian New Albany Shale across a maturation gradient: Insights from organic petrology, gas adsorption, and mercuty intrusion. Aapg Bulletin, 97(10): 1621-1643. 155 McIntosh, J.C., Schlegel, M.E., Person, M., 2012. Glacial impacts on hydrologic processes in sedimentary basins: evidence from natural tracer studies. Geofluids, 12(1): 7-21. McIntosh, J.C., Walter, L.M., 2006. Paleowaters in Silurian-Devonian carbonate aquifers: Geochemical evolution of groundwater in the Great Lakes region since the Late Pleistocene. Geochimica Et Cosmochimica Acta, 70(10): 2454-2479. McIntosh, J.C., Walter, L.M., Martini, A.M., 2004. Extensive microbial modification of formation water geochemistry: Case study from a Midcontinent sedimentary basin, United States. Geological Society of America Bulletin, 116(5-6): 743- 759. Moore, M.T., Vinson, D.S., Darrah, T.H., 2016. Noble gas and hydrocarbon geochemistry of coalbed methane fields from the Illinois Basin. Chemical Geology, submitted. Nakagawa, F., Yoshida, N., Nojiri, Y., Makarov, V.N., 2002. Production of methane from alassesin eastern Siberia: Implications from its C-14 and stable isotopic compositions. Global Biogeochemical Cycles, 16(3). Orem, W. et al., 2014. Organic substances in produced and formation water from unconventional natural gas extraction in coal and shale. International Journal of Coal Geology, 126: 20-31. Osborn, S.G., McIntosh, J.C., 2010. Chemical and isotopic tracers of the contribution of microbial gas in Devonian organic-rich shales and reservoir sandstones, northern Appalachian Basin. Applied Geochemistry, 25(3):456-471. Panno, S.V. et al., 2013. Formation waters from Cambrian-age strata, Illinois Basin, USA: Constraints on their origin and evolution. Geochimica Et Cosmochimica Acta, 122: 184- 197. Park, J., Bethke, C.M., Torgersen, T., Johnson, T.M., 2002. Transport modeling applied to the interpretation of groundwater Cl-36 age. Water Resources Research, 38(5). Pashin, J.C., 1998. Stratigraphy and structure of coalbed methane reservoirs in the United States: An overview. International Journal of Coal Geology, 35(1-4): 156 209-240. Pashin, J.C. et al., 2014. Relationships between water and gas chemistry in mature coalbed methane reservoirs of the Black Warrior Basin. International Journal of Coal Geology, 126: 92-105. Plummer, L.N. et al., 2012. Old groundwater in parts of the upper Patapsco aquifer, Atlantic Coastal Plain, Maryland, USA: evidence from radiocarbon, chlorine-36 and helium-4. Hydrogeology Journal, 20(7): 1269-1294. Poreda, R.J., Farley, K.A., 1992. Rare gases in Samoan xenoliths. Earth and Planetary Science Letters, 113(1-2): 129-144. Ritter, D. et al., 2015. Enhanced microbial coalbed methane generation: A review of research, commercial activity, and remaining challenges. International Journal of Coal Geology, 146: 28-41. Schlegel, M.E., McIntosh, J.C., Bates, B.L., Kirk, M.F., Martini, A.M., 2011a. Comparison of fluid geochemistry and microbiology of multiple organic- rich reservoirs in the Illinois Basin, USA: Evidence for controls on methanogenesis and microbial transport. Geochimica Et Cosmochimica Acta, 75(7): 1903-1919. Schlegel, M.E., Zhou, Z., McIntosh, J.C., Ballentine, C.J., Person, M.A., 2011b. Constraining the timing of microbial methane generation in an organic-rich shale using noble gases, Illinois Basin, USA. Chemical Geology, 287(1-2): 27- 40. Selley, R.C., 1998. Elements of Petroleum Geology 2. Academic Press, London, UK. Sheldon, A.L., Solomon, D.K., Poreda, R.J., Hunt, A., 2003. Radiogenic helium in shallow groundwater within a clay till, southwestern Ontario. Water Resources Research, 39(12). Sherwood Lollar, B., Ballentine, C.J., 2009. Insights into deep carbon derived from noble gases. Nature Geoscience, 2(8): 543-547. Snyder, G.T. et al., 2003. Origin and history of waters associated with coalbed methane: I-129, Cl- 36, and stable isotope results from the Fruitland Formation, CO and NM. Geochimica Et Cosmochimica Acta, 67(23): 4529-4544. 157 Solomon, D.K., Hunt, A., Poreda, R.J., 1996. Source of radiogenic helium 4 in shallow aquifers: Implications for dating young groundwater. Water Resources Research, 32(6): 1805-1813. Solomon, D.K., Poreda, R.J., Cook, P.G., Hunt, A., 1995. Site characerization using H-3/He-3 groundwater ages, Cape Cod, MA. Ground Water, 33(6): 988-996. Solomon, D.K., Poreda, R.J., Schiff, S.L., Cherry, J.A., 1992. Tritium and He-3 as groundwater age tracers in the Borden aquifer. Water Resources Research, 28(3): 741-755. Solomon, D.K., Schiff, S.L., Poreda, R.J., Clarke, W.B., 1993. A validation of H-3/He- 3 method for determining groundwater recharge. Water Resources Research, 29(9): 2951-2962. Stueber, A.M., Walter, L.M., 1991. Origin and chemical evolution of formation waters from Silurian-Devonian strata in the Illinois Basin, USA. Geochimica Et Cosmochimica Acta, 55(1): 309-325. Stueber, A.M., Walter, L.M., 1994. Glacial recharge and peleohydrologic flow systems in the Illinois Basin- Evidence from chemistry of Ordovician carbonate (Galena) formation waters. Geological Society of America Bulletin, 106(11): 1430-1439. Tedesco, S., 2003. Coalbed Methane Potential and Activity of the Western Interior Basin, AAPG Annual Convention, Salt Lake City, Utah. Torgersen, T., Clarke, W.B., 1985. Helium accumulation in groundwater. 1. An evaluation of sources and the continental flux of crustal He-4 in the Great Artesian Basin, Australia Geochimica Et Cosmochimica Acta, 49(5): 1211- 1218. Torgersen, T., Habermehl, M.A., Clarke, W.B., 1992. Crustal helium fluxes and heat flow in the Great Artesian Basin, Australia. Chemical Geology, 102(1-4): 139- 152. Van Stempvoort, D., Maathuis, H., Jaworski, E., Mayer, B., Rich, K., 2005. Oxidation of fugitive methane in ground water linked to bacterial sulfate reduction. Ground Water, 43(2): 187- 199. 158 Walsh, T.B., 2015. The role of faults and fractures on subsurface fluids flow in the Marcellus Shale of the Appalachian Plateau in western New York, University of Rochester, Rochester, NY. Walter, L.M., Stueber, A.M., Huston, T.J., 1990. Br-Cl-Na systematics in Illinois Basin fluids- Constraints on fluid origin and evolution. Geology, 18(4): 315-318. Whiticar, M.J., 1999. Carbon and hydrogen isotope systematics of bacterial formation and oxidation of methane. Chemical Geology, 161(1-3): 291-314. Whiticar, M.J., Faber, E., Schoell, M., 1986. Biogenic methane formation in marine and fresh- water environments- CO2 reduction vs. acetate fermentation isotope evidence. Geochimica Et Cosmochimica Acta, 50(5): 693-709. Zhou, Z., Ballentine, C.J., 2006. He-4 dating of groundwater associated with hydrocarbon reservoirs. Chemical Geology, 226(3-4): 309-327. Zhou, Z., Ballentine, C.J., Kipfer, R., Schoell, M., Thibodeaux, S., 2005. Noble gas tracing of groundwater/coalbed methane interaction in the San Juan Basin, USA. Geochimica Et Cosmochimica Acta, 69(23): 5413-5428. Zhou, Z., Ballentine, C.J., Schoell, M., Stevens, S.H., 2012. Identifying and quantifying natural CO2 sequestration processes over geological timescales: The Jackson Dome CO2 Deposit, USA. Geochimica Et Cosmochimica Acta, 86: 257-275. References Chapter 2 Ballentine, C.J., Burgess, R., Marty, B., 2002. Tracing fluid origin, transport and interaction in the crust. In: Porcelli, D., Ballentine, C.J., Wieler, R. (Eds.), Noble Gases in Geochemistry and Cosmochemistry. Reviews in Mineralogy & Geochemistry, pp. 539-614. Ballentine, C.J., Burnard, P.G., 2002. Production, release and transport of noble gases in the continental crust. In: Porcelli, D., Ballentine, C.J., Wieler, R. (Eds.), Noble Gases in Geochemistry and Cosmochemistry. Reviews in Mineralogy & Geochemistry, pp. 481-538. Ballentine, C.J., Onions, R.K., Oxburgh, E.R., Horvath, F., Deak, J., 1991. Rare-gas constraints on hydrocarbon accumulation, 159 crustal degassing, and groundwater-flow in the Pannonian. Basin Earth and Planetary Science Letters, 105(1-3): 229-246. Bates, B.L., McIntosh, J.C., Lohse, K.A., Brooks, P.D., 2011. Influence of groundwater flowpaths, residence times and nutrients on the extent of microbial methanogenesis in coal beds: Powder River Basin, USA. Chemical Geology, 284(1-2): 45-61. Bentley, H.W. et al., 1986. CL-36 dating of very old groundwater. 1. The Great Artesian Basin, Australia. Water Resources Research, 22(13): 1991-2001. Bethke, C.M., Marshak, S., 1990. Brine migrations across North America-The plate- tectonics of groundwater. Annual Review of Earth and Planetary Sciences, 18: 287-315. Bethke, C.M., Zhao, X., Torgersen, T., 1999. Groundwater flow and the He-4 distribution in the Great Artesian Basin of Australia. Journal of Geophysical Research-Solid Earth, 104(B6): 12999-13011. Buschbach, T.C., Kolata, D.R., 1990. Regional Setting of Illinois Basin: Chapter 1: Part I. Illinois Basin: Regional Setting. Castro, M.C., 2004. Helium sources in passive margin aquifers - new evidence for a significant mantle He-3 source in aquifers with unexpectedly low in situ He- 3/He-4 production. Earth and Planetary Science Letters, 222(3-4): 897-913. Castro, M.C., Goblet, P., 2003. Calibration of regional groundwater flow models: Working toward a better understanding of site-specific systems. Water Resources Research, 39(6). Castro, M.C., Goblet, P., Ledoux, E., Violette, S., de Marsily, G., 1998a. Noble gases as natural tracers of water circulation in the Paris Basin 2. Calibration of a groundwater flow model using noble gas isotope data. Water Resources Research, 34(10): 2467-2483. Castro, M.C., Jambon, A., de Marsily, G., Schlosser, P., 1998b. Noble gases as natural tracers of water circulation in the Paris Basin 1. Measurements and discussion of their origin and mechanisms of vertical transport in the basin. Water Resources Research, 34(10): 2443- 2466. 160 Castro, M.C., Stute, M., Schlosser, P., 2000. Comparison of He-4 ages and C-14 ages in simple aquifer systems: implications for groundwater flow and chronologies. Applied Geochemistry, 15(8): 1137-1167. Cathles, L.M., 1990. Scales and effects of fluid-flow in the upper crust. Science, 248(4953): 323- 329. Cook, P.G. et al., 1996. Inferring shallow groundwater flow in saprolite and fractured rock using environmental tracers. Water Resources Research, 32: 1501-1509. Cuoco, E. et al., 2013. Impact of volcanic plume emissions on rain water chemistry during the January 2010 Nyamuragira eruptive event: Implications for essential potable water resources. Journal of Hazardous Materials, 244: 570- 581. Darrah, T.H. et al., 2015. The evolution of Devonian hydrocarbon gases in shallow aquifers of the northern Appalachian Basin: Insights from integrating noble gas and hydrocarbon geochemistry. Geochimica Et Cosmochimica Acta, 170: 321-355. Darrah, T.H., Poreda, R.J., 2012. Evaluating the accretion of meteoritic debris and interplanetary dust particles in the GPC-3 sediment core using noble gas and mineralogical tracers. Geochimica et Cosmochimica Acta, 84: 329-352. Darrah, T.H. et al., 2013. Gas chemistry of the Dallol region of the Danakil Depression in the Afar region of the northern-most East African Rift. Chemical Geology, 339: 16-29. Darrah, T.H., Vengosh, A., Jackson, R.B., Warner, N.R., Poreda, R.J., 2014. Noble gases identify the mechanisms of fugitive gas contamination in drinking-water wells overlying the Marcellus and Barnett Shales. Proceedings of the National Academy of Sciences of the United States of America, 111(39): 14076-14081. Drobniak, A., Mastalerz, M., Rupp, J., Eaton, N., 2004. Evaluation of coalbed gas potential of the Seelyville coal member, Indiana, USA. International Journal of Coal Geology, 57(3-4): 265-282. Etiope, G. et al., 2009. Evidence of subsurface anaerobic biodegradation of hydrocarbons and potential secondary methanogenesis in terrestrial mud 161 volcanoes. Marine and Petroleum Geology, 26(9): 1692-1703. Garven, G., Ge, S., Person, M.A., Sverjensky, D.A., 1993. Genesis of stratabound ore deposits in the midcontinent basins of North America 1. The role of regional groundwater flow. American Journal of Science, 293(6): 497-568. Gilfillan, S.M. et al., 2008. The noble gas geochemistry of natural CO2 gas reservoirs from the Colorado Plateau and Rocky Mountain provinces, USA. Geochimica Et Cosmochimica Acta, 72(4): 1174-1198. Gilfillan, S.M.V. et al., 2009. Solubility trapping in formation water as dominant CO2 sink in natural gas fields. Nature, 458(7238): 614-618. Hunt, A.G., 2000. Diffusional release of helium-4 from mineral phases as indicators of groundwater age and depositional history. Hunt, A.G., Darrah, T.H., Poreda, R.J., 2012. Determining the source and genetic fingerprint of natural gases using noble gas geochemistry: A northern Appalachian Basin case study. AAPG bulletin, 96(10): 1785-1811. James, A.T., Burns, B.J., 1984. Microbial alteration of subsurface natural-gas accumulations Aapg Bulletin-American Association of Petroleum Geologists, 68(8): 957-960. Karacan, C.O., Drobniak, A., Mastalerz, M., 2014. Coal bed reservoir simulation with geostatistical property realizations for simultaneous multi-well production history matching: A case study from Illinois Basin, Indiana, USA. International Journal of Coal Geology, 131: 71-89. Labotka, D.M., Panno, S.V., Locke, R.A., Freiburg, J.T., 2015. Isotopic and geochemical characterization of fossil brines of the Cambrian Mt. Simon Sandstone and Ironton- Galesville Formation from the Illinois Basin, USA. Geochimica Et Cosmochimica Acta, 165: 342-360. Lowenstern, J.B., Evans, W.C., Bergfeld, D., Hunt, A.G., 2014. Prodigious degassing of a billion years of accumulated radiogenic helium at Yellowstone. Nature, 506(7488): 355-360. Martini, A.M., Budai, J.M., Walter, L.M., Schoell, M., 1996. Microbial generation of economic accumulations of methane within a shallow organic-rich shale. 162 Nature, 383(6596): 155- 158. Martini, A.M. et al., 1998. Genetic and temporal relations between formation waters and biogenic methane: Upper Devonian Antrim Shale, Michigan Basin, USA. Geochimica Et Cosmochimica Acta, 62(10): 1699-1720. Martini, A.M., Walter, L.M., McIntosh, J.C., 2008. Identification of microbial and thermogenic gas components from Upper Devonian black shale cores, Illinois and Michigan basins. Aapg Bulletin, 92(3): 327-339. Mastalerz, M., Drobniak, A., Rupp, J.A., Shaffer, N.R., 2004a. Characterization of Indiana's coal resource: availability of the reserves, physical and chemical properties of coal, and present and potential uses. Indiana Geological Survey, Indianapolis, Indiana. Mastalerz, M., Gluskoter, H., Rupp, J., 2004b. Carbon dioxide and methane sorption in high volatile bituminous coals from Indiana, USA. International Journal of Coal Geology, 60(1): 43-55. Mastalerz, M., Schimmelmann, A., Drobniak, A., Chen, Y., 2013. Porosity of Devonian and Mississippian New Albany Shale across a maturation gradient: Insights from organic petrology, gas adsorption, and mercuty intrusion. Aapg Bulletin, 97(10): 1621-1643. McIntosh, J.C., Schlegel, M.E., Person, M., 2012. Glacial impacts on hydrologic processes in sedimentary basins: evidence from natural tracer studies. Geofluids, 12(1): 7-21. McIntosh, J.C., Walter, L.M., 2006. Paleowaters in Silurian-Devonian carbonate aquifers: Geochemical evolution of groundwater in the Great Lakes region since the Late Pleistocene. Geochimica Et Cosmochimica Acta, 70(10): 2454-2479. McIntosh, J.C., Walter, L.M., Martini, A.M., 2004. Extensive microbial modification of formation water geochemistry: Case study from a Midcontinent sedimentary basin, United States. Geological Society of America Bulletin, 116(5-6): 743- 759. Moore, M.T., Vinson, D.S., Darrah, T.H., 2016. Noble gas and hydrocarbon geochemistry of coalbed methane fields from the Illinois Basin. Chemical 163 Geology, submitted. Nakagawa, F., Yoshida, N., Nojiri, Y., Makarov, V.N., 2002. Production of methane from alassesin eastern Siberia: Implications from its C-14 and stable isotopic compositions. Global Biogeochemical Cycles, 16(3). Orem, W. et al., 2014. Organic substances in produced and formation water from unconventional natural gas extraction in coal and shale. International Journal of Coal Geology, 126: 20-31. Osborn, S.G., McIntosh, J.C., 2010. Chemical and isotopic tracers of the contribution of microbial gas in Devonian organic-rich shales and reservoir sandstones, northern Appalachian Basin. Applied Geochemistry, 25(3):456-471. Panno, S.V. et al., 2013. Formation waters from Cambrian-age strata, Illinois Basin, USA: Constraints on their origin and evolution. Geochimica Et Cosmochimica Acta, 122: 184- 197. Park, J., Bethke, C.M., Torgersen, T., Johnson, T.M., 2002. Transport modeling applied to the interpretation of groundwater Cl-36 age. Water Resources Research, 38(5). Pashin, J.C., 1998. Stratigraphy and structure of coalbed methane reservoirs in the United States: An overview. International Journal of Coal Geology, 35(1-4): 209-240. Pashin, J.C. et al., 2014. Relationships between water and gas chemistry in mature coalbed methane reservoirs of the Black Warrior Basin. International Journal of Coal Geology, 126: 92-105. Plummer, L.N. et al., 2012. Old groundwater in parts of the upper Patapsco aquifer, Atlantic Coastal Plain, Maryland, USA: evidence from radiocarbon, chlorine-36 and helium-4. Hydrogeology Journal, 20(7): 1269-1294. Poreda, R.J., Farley, K.A., 1992. Rare gases in Samoan xenoliths. Earth and Planetary Science Letters, 113(1-2): 129-144. Ritter, D. et al., 2015. Enhanced microbial coalbed methane generation: A review of research, commercial activity, and remaining challenges. International Journal of Coal Geology, 146: 28-41. 164 Schlegel, M.E., McIntosh, J.C., Bates, B.L., Kirk, M.F., Martini, A.M., 2011a. Comparison of fluid geochemistry and microbiology of multiple organic- rich reservoirs in the Illinois Basin, USA: Evidence for controls on methanogenesis and microbial transport. Geochimica Et Cosmochimica Acta, 75(7): 1903-1919. Schlegel, M.E., Zhou, Z., McIntosh, J.C., Ballentine, C.J., Person, M.A., 2011b. Constraining the timing of microbial methane generation in an organic-rich shale using noble gases, Illinois Basin, USA. Chemical Geology, 287(1-2): 27- 40. Selley, R.C., 1998. Elements of Petroleum Geology 2. Academic Press, London, UK. Sheldon, A.L., Solomon, D.K., Poreda, R.J., Hunt, A., 2003. 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