Springfield Coal Research Articles

Mesophase pitch-based high performance carbon fiber production using coal extracts from mild direct coal liquefaction

Mild direct coal liquefaction (autogenous pressure, no catalyst, no H2 gas) of Springfield coal in fluid catalytic cracking decant oil is shown to effectively produce coal extract precursors to spinnable mesophase pitch. This work demonstrates that the coal extract can be thermally treated to obtain mesophase pitch in a facile one-step process, bypassing the production of an intermediate isotropic pitch. Furthermore, the presence of 25 wt.% coal in the initial slurry can increase the yield to mesophase pitch nearly twofold and yield to carbon fiber by approximately 70%. The coal extract-derived mesophase pitch was melt-spun and heat treated to produce carbon fiber with graphitic texture, high modulus (>400 GPa) and tensile strength up to 943 MPa. Overall, this work demonstrates that coal can be effectively utilized to markedly amplify the mesophase pitch and carbon fiber yield from fluid catalytic cracking decant oil by relatively simple processing, while conserving utility as a precursor to high performance carbon fiber and potentially other high value graphitic products.

Was coal metamorphism an influence on the minor element chemistry of the Middle Pennsylvanian Springfield (No. 9) coal in Western Kentucky?

Coal rank in the Middle Pennsylvanian Carbondale Formation Springfield coal in the Western Kentucky coalfield, part of the Illinois Basin, ranges from high volatile A bituminous in southern Union and Webster counties to high volatile C bituminous in the rest of the region. The chlorine content closely follows the coal rank, being highest in the high volatile A bituminous coals. High concentrations of V and Cr are evident in the top benches at all sites and is particularly strong in the higher rank sites. Zinc and other elements (Ni, Mo, among others) are enriched in some benches, but the trend is not as consistent as with V and Cr. Zirconium (+ Nb) and TiO2, both serving as proxies for a detrital influx, show differentiation among the quadrangles, with the high volatile C bituminous Spottsville quadrangle coals having the highest Zr + Nb content. The correlation between Y and Zr indicates that the highest Y occurs in the Spottsville samples. The Spottsville samples have highest REE. Principal components analysis using both a rank parameter (vitrinite maximum reflectance) and the set of geochemical parameters showed that the coal rank axis (Rmax) (with the highest rank being in the Providence quadrangle) is orthogonal to the overlapping LREE/HREE and GdN/GdN* axes and is opposite to the REE, Zr + Nb, and Zn axes. Hydrothermal metamorphism certainly influenced coal rank, the chlorine content of the coals, and, perhaps, some aspects of the minor element chemistry. Coal metamorphism, however, was not the sole influence and not even the dominant influence on the concentration of REE in the Springfield coal in western Kentucky since other factors, such as the greater concentrations of detrital minerals in the Spottsville quadrangle samples, seem to have had a greater influence on the REE chemistry.

Microstructural diversity and digestion yields of select bituminous and subbituminous coals as raw material candidates for carbon fiber precursor production

This work investigates the use of coals as raw materials for carbon fiber precursor production as a new alternative to coal utilization. Coal being a highly complex and heterogeneous material with different macerals and minerals complicates this task. Extensive microstructural characterization as well as preliminary digestion studies are performed on three bituminous coals (Herrin and Springfield from the Illinois Basin and the Blue Gem from the Central Appalachians) and one subbituminous coal from the Powder River Basin (Monarch), as raw material candidates. The subbituminous coal was richer in oxygen, lower in sulfur, and had a higher volatile matter yield. Microstructural investigations were performed using X-ray diffraction, X-ray/neutron computed tomography, scanning electron microscopy with energy dispersive spectroscopy, and petrology. Mild solvent extraction studies were conducted using creosote and decant oil as solvents in microreactors. The extraction yield was sensitive to temperature and time (350 to 450 °C between 30 and 120 mins.) for both creosote and decant oil digestions. While the Blue Gem coal had more desirable microstructural properties with less mineral content and cleaner macerals, it had the lowest coal conversion to quinoline soluble ‘liquid’ (of the bituminous coals). The lower coal conversion yield was hypothesized to be connected to the lack of FeS2 which could act as a catalyst when Fe is liberated from the structure under solvent extraction conditions. The Herrin and Springfield coals revealed similar microstructures and coal conversion efficiencies (higher than Blue Gem). These coals were the most promising candidates for further examination from this first approximations study. The subbituminous Monarch coal, however, was deemed less suitable due to poor coal conversion and less desirable microstructures. Additionally, the presented results with combined microstructural data from multiple length scales established a framework necessary for a first approximations study in this new coal utilization approach.

Geocatalytically generated methane from low-maturity coal and shale source rocks at low temperatures (80–120 °C) over 52 months

Geocatalytic methanogenesis has been proposed to contribute to methane generation from low-maturity coal and shale source rocks. This study contributes further evidence for geocatalytic methanogenesis from low-maturity source rocks based on long-term experiments lasting up to 52 months. Samples from the Upper Devonian New Albany Shale (Ro 0.54 %) and Springfield Coal No. 2 (Pennsylvanian; Ro 0.54 %) were heated in glass tubes at 80, 100, and 120 °C for 52 months. Sample aliquots from the Upper Cretaceous Second White Specks Formation (Ro 0.42 %) were heated in gold tubes at 80 and 100 °C for 42 months at elevated hydrostatic pressures of 100 to 300 MPa. The product gases — methane (CH4) and carbon dioxide (CO2) — were collected and quantified, and gas yields were corrected for leakage from imperfectly closed pores in samples during heating. The results show that longer heating produced more CH4. The average CH4 yields from New Albany Shale and Springfield Coal No. 2 are 0.47 and 3.0 μmol CH4 per gram of total organic carbon (TOC) over 52 months of heating. Elevated hydrostatic pressure caused lower CH4 yields from the Second White Specks Formation (3.82 to 1.20 μmol g−1 TOC), suggesting that pressure can retard methanogenesis. Maceral type critically controls the methanogenesis potential of low-maturity coal and shale source rocks. Results of this study provide important insights to the origin of natural gas in low-maturity sedimentary basins.

Bulk and intramolecular carbon isotopic compositions of hydrocarbon gases from laboratory pyrolysis of oil shale of the Green River Formation: Implications for isotope structures of kerogens

Evaluation of intramolecular isotope distributions within organic compounds can provide important insights into gas formation processes and structural properties of gas-generating precursors, such as kerogen, bitumen, and oil, in natural reservoirs. Until recently, little has been known about the intramolecular isotope distributions within kerogens. In this study, we conducted systematic pyrolysis experiments of gas generation from a lacustrine oil shale of the Eocene Green River Formation under hydrous and anhydrous conditions (equivalent maturity or Easy %Ro: 0.76 to 3.27 at 310 to 480 °C for 3 to 50 days), measuring gas yields and compositions, as well as bulk and position-specific (PS) carbon isotope compositions. Gas generation processes were investigated in combination with kinetic Monte Carlo (kMC) simulations on a model Type I kerogen based on the chemical structures of oil shale of the Green River Formation. The comparison of our experimental results with kMC modelling indicates a series of β-scission, radical isomerization, and recombination reactions better represent the bulk isotope compositions of propane in the pyrolysis of the oil shale of the Green River Formation, but the ΔCc-t (= δ13Ccen – δ13Cter) values of propane at Easy %Ro > 1.5 can be better simulated by a simple combination of propyl groups with H radicals. Combining our previous works on marine shale of the Woodford Formation and Springfield Coal Member of the Carbondale Formation, PS carbon isotopes of propane indicate that in the lacustrine shales of the Green River Formation and the marine Woodford Shale, propane is sourced from CC bond cleavage, while CO bond cracking generates propane from coal at the initial kerogen cracking stage. At high maturity, the differences of late-stage propane production among the source rocks lead to the different bulk and PS C kinetic isotope effects of propane. Our findings suggest that the δ13C at the terminal position of propane precursors is likely up to 3.6‰ higher than at the central position in the Green River kerogen, while they are similar in the marine shale of Woodford Formation. In addition, the δ13C at the central position of propyl groups attached to heteroatom compounds is relatively more positive in the Springfield Coal Member of the Carbondale Formation than in Green River kerogen. A comparison of intramolecular C isotopes of propyl groups in the kerogens with their bulk δ13C, based on the PS δ13C of early-generated propane, contributes to our understanding of heterogeneities of isotopic structures of sedimentary organic matter.

Gas generation and intramolecular isotope study in laboratory pyrolysis of the Springfield coal from the Illinois Basin

Position-specific (PS) isotopes of propane have been proposed as a potential geochemical tool to decipher various geological processes (e.g., thermal cracking, biodegradation, H exchange) in natural reservoirs. The limited studies have been conducted on the PS isotopes of propane from the pyrolysis gases from marine shales, and natural gases sourced from lacustrine and marine kerogens, but little is known on gases produced from the humic kerogen. This study investigated the PS δ13C of propane in the closed-system pyrolysis of the Springfield coal, Illinois Basin, Indiana, at 310 to 470 °C (Easy %Ro: 0.76 to 3.07). The C kinetic isotope effect (KIE) of CH4 produced in both this study and previous low-temperature pyrolysis of the same coal indicates the cleavage of CO bonds is the main generation pathway at the early kerogen cracking stage, followed by the breakdown of alkyl groups. At the wet-gas cracking stage, C3H8 production from thermally stable compounds has a significant influence on the bulk and position-specific C KIE in the pyrolysis of marine Woodford kerogen and Springfield coal. According to the PS δ13C of propane, the central site is likely more enriched in 13C and the δ13C of the terminal site is relatively heterogeneous within the propyl group attached to different functional groups of the gas-prone kerogen. Our findings based on the pyrolysis experiments and natural gas samples indicate thermal cracking and biodegradation appear to alter the δ13Ccen values more significantly than the δ13Cter values of propane. The larger magnitude of ΔCc-t in the kMC simulations (Peterson et al., 2018) compared with those from the marine shale and coal possibly implies the non-random distributions of 13C of propane precursors in the kerogens. As a new dimension of intramolecular isotopic information of propane, the PS δ13C values can contribute to fingerprinting the gas origins and identifying the various geological processes (e.g., kerogen cracking, wet-gas cracking, microbial activities) in sedimentary basins.

Mechanism and Controlling Factors on Methane Yields Catalytically Generated From Low-Mature Source Rocks at Low Temperatures (60–140°C) in Laboratory and Sedimentary Basins

Various studies have shown that geo-catalytically mediated methanogenesis could happen in immature to early-mature source rocks at temperatures ranging from 60 to 140°C based on a series of long-term laboratory heating experimental evidences. The results of those studies show that methane yields at the given temperature are 5–11 orders of magnitude higher than the theoretically predicted yields from early thermogenic methane generation kinetic models. However, different types of source rocks in these laboratory simulation experiments generated varied CH4 and CO2 yields, which suggest that controls on CH4 generation during catalytic methanogenesis are complex. This study summarizes and compares gas yield results from laboratory low-temperature heating simulation experiments. Pre-existing trapped methane in rock chips could mimic newly generated gas during heating. The yields of catalytically generated CH4 from individual source rocks were re-quantified by subtracting the amounts of pre-existing CH4 in the closed pores of the original source rocks from the total methane amounts released from heating experiments and pre-existing CH4 in the closed pores in heated source rocks. The results show that heating temperature and time exert a positive influence on methane catalytic methanogenesis. Mowry and Second White Specks Formation Shale generated approximately ten times more CH4 than New Albany Shale and Mahogany Shale per gram of total organic carbon (TOC). Samples of Springfield Coal #1 and #2 exhibited ten times yield difference from one another at the same heating temperature. Those yield differences are not strongly associated with TOC content, heating time, temperature, metal content, or kerogen type but appear to be more influenced by maceral composition and also maceral–mineral contact area within the source rocks. We conclude that macerals in the liptinite group have a propensity for methanogenesis. Specifically, amorphous organic matter undergoes transformation into hydrocarbons earlier than alginite at low-temperature heating conditions. Sporinite also contributes to higher yields of methane released from the coal source rock. Vitrinite and inertinite show a positive influence on carbon dioxide but no significant effect on increasing methane yields compared to other macerals. The strongest catalytic methanogenesis in the studied sample produced methane yields at 60°C, which amounted to ∼2.5 μmol per gram of organic carbon during one year of heating. We suggest that geocatalytic methanogenesis could generate economically sizeable gas plays from immature to early-mature source rocks over geologic time.

Methane generation from low-maturity coals and shale source rocks at low temperatures (80–120 °C) over 14–38 months

This study contributes long-term (14 to 38 months) experimental evidence for geocatalytically mediated methanogenesis in immature to early mature shale and coal source rocks at temperatures from 80 to 120 °C. Borosilicate glass tubes with pre-outgassed coal and shale source rock chips and water were sealed under vacuum, sterilized, heated isothermally, and finally opened in connection with a vacuum line where headspace gases methane (CH4) and carbon dioxide (CO2) were collected. The possibility of admitting pre-existing CH4 from closed pores into product gases during heating experiments was evaluated by comparative ball milling of original and heated rock chips, followed by quantitation of released gases with a novel closed-circuit laser-based SARAD RTM2200 gas detector system with sub-µmol sensitivity. The yields of produced CH4 from individual source rocks were corrected by subtracting the amounts of pre-existing CH4 from formerly closed pores in original source rocks that had leaked during long-term heating. Different shales and coals express contrasting propensities to geocatalytically generate CH4 and CO2, with CH4 yields ranging from 0.1 to 5.5 µmol g−1 total organic carbon (TOC). CH4 yields from two petrographically different samples of Springfield Coal with comparable thermal maturity suggest that liptinite expresses a far higher propensity for methanogenesis, but liberates less CO2 than vitrinite. Shale from the Second White Specks Formation generated approximately 10 times more CH4 than New Albany Shale per g of TOC, further suggesting complex controls on CH4 generation during catalytic methanogenesis. Higher temperature can enhance the activities of catalytic methanogenesis. The extrapolation of laboratory-based reaction rates to natural conditions in organic-rich buried sediments suggests that geocatalytic methanogenesis can be fast enough in some source rocks to generate economically sizeable gas plays from immature to early mature source rocks over geologic time.

Catalytic generation of methane at 60–100 °C and 0.1–300 MPa from source rocks containing kerogen Types I, II, and III

Low temperature (60 and 100 °C) and long-term (6 months to 5 years) heating of pre-evacuated and sterilized shales and coals containing kerogen Types I (Mahogany Shale), II (Mowry Shale and New Albany Shale), and III (Springfield Coal and Wilcox Lignite) with low initial maturities (vitrinite reflectance Ro 0.39–0.62%) demonstrates that catalytically generated hydrocarbons may explain the occurrence of some non-biogenic natural gas accumulations where insufficient thermal maturity contradicts the conventional thermal cracking paradigm. Extrapolation of the observed rate of catalytic methanogenesis in the laboratory suggests that significant amounts of sedimentary organic carbon can be converted to relatively dry natural gas over tens of thousands of years in sedimentary basins at temperatures as low as 60 °C.Our laboratory experiments utilized source rock (shale and coal) chips sealed in gold and Pyrex® glass tubes in the presence of hydrogen-isotopically contrasting waters. Parallel heating experiments applied hydrostatic pressures from 0.1 to 300 MPa. Control experiments constrained the influence of pre-existing and residual methane in closed pores of rock chips that was unrelated to newly generated methane.This study’s experimental methane yields at 60 and 100 °C are 5–11 orders of magnitude higher than the theoretically predicted yields from kinetic models of thermogenic methane generation, which strongly suggests a contribution of catalytic methanogenesis. Higher temperature, longer heating time, and lower hydrostatic pressure enhanced catalytic methanogenesis. No clear relationships were observed between kerogen type or total organic carbon content and methane yields via catalysis. Catalytic methanogenesis was strongest in Mowry Shale where methane yields at 60 °C amounted to ∼2.5 μmol per gram of organic carbon after one year of hydrous heating at ambient pressure.In stark contrast to the earlier findings of hydrogen isotopic exchange between water and thermogenic methane in hydrous pyrolysis experiments above 300 °C, the hydrogen isotopic composition of added water exerted limited influence on the δ2H value of methane generated catalytically at low temperatures. We hypothesize that the catalytic sites responsible for methanogenesis are located in hydrophobic microenvironments with limited access to water. The δ13CCH4 values of methane generated catalytically at 60–100 °C range from ∼−57.6 to −41.4‰ and are thus similar to typical thermogenic methane (δ13CCH4 >−50‰) and microbially generated methane (<−55‰). Future studies need to evaluate the possibility that clumped isotope characteristics of catalytically generated methane can diagnose the low-temperature regime of catalytic methanogenesis. Furthermore, testing of freshly cored anoxic rocks is needed to determine whether the use of archived, oxygen-exposed rocks in geochemical maturation/catalysis studies introduces artifacts in experimental hydrocarbon yields.

Mapping of compositional properties of coal using isometric log-ratio transformation and sequential Gaussian simulation – A comparative study for spatial ultimate analyses data

Chemical properties of coal largely determine coal handling, processing, beneficiation methods, and design of coal-fired power plants. Furthermore, these properties impact coal strength, coal blending during mining, as well as coal's gas content, which is important for mining safety. In order for these processes and quantitative predictions to be successful, safer, and economically feasible, it is important to determine and map chemical properties of coals accurately in order to infer these properties prior to mining.Ultimate analysis quantifies principal chemical elements in coal. These elements are C, H, N, S, O, and, depending on the basis, ash, and/or moisture. The basis for the data is determined by the condition of the sample at the time of analysis, with an “as-received” basis being the closest to sampling conditions and thus to the in-situ conditions of the coal. The parts determined or calculated as the result of ultimate analyses are compositions, reported in weight percent, and pose the challenges of statistical analyses of compositional data. The treatment of parts using proper compositional methods may be even more important in mapping them, as most mapping methods carry uncertainty due to partial sampling as well.In this work, we map the ultimate analyses parts of the Springfield coal from an Indiana section of the Illinois basin, USA, using sequential Gaussian simulation of isometric log-ratio transformed compositions. We compare the results with those of direct simulations of compositional parts. We also compare the implications of these approaches in calculating other properties using correlations to identify the differences and consequences. Although the study here is for coal, the methods described in the paper are applicable to any situation involving compositional data and its mapping.

Geochemical, petrographic and palynologic characteristics of two late middle Pennsylvanian (Asturian) coal-to-shale sequences in the eastern Interior Basin, USA

Two coal-to-shale sequences of late Middle Pennsylvanian (Asturian) age from the southern portion of the Eastern Interior (Illinois) Basin, USA were examined geochemically, petrographically and palynologically. The Springfield coal was found to be moderately low in ash yield and high in total sulfur content. Petrographically, the coal is high in vitrinite content and low in liptinite and inertinite. Palynologically, the bed is co-dominated by spores of arborescent lycopod and tree fern affinities. The examination of closely-spaced bench samples revealed vertical species variation within both of these plant groups. Lycospora micropapillata+L. orbicula, both of which were produced by Paralycopodites, are most abundant in basal coal benches, whereas Lycospora granulata, produced by Lepidophloios is the dominant arborescent lycopod spore throughout the rest of the bed. Thymospora pseudothiessenii is the dominant tree fern spore throughout most of the coal, with Laevigatosporites globosus becoming dominant in the top-most coal benches.The Herrin coal bed is also moderately low in ash yield and high in total sulfur content. Unlike the Springfield coal, it contains two distinct inorganic partings that have regional extent. The Herrin coal also has several coal benches with increased ash and sulfur that were not present in the Springfield coal bed. Petrographically, it is dominated by vitrinite, with the partings and high ash coal benches containing more inertinite, and liptinite. Palynologically, the Herrin coal is dominated by arborescent lycopod spores with subdominant tree fern spores. As with the Springfield coal, Lycospora micropapillata+L. orbicula are the dominant arborescent lycopod spores at the base of the coal, with Lycospora granulata dominating the rest of the bed. Granasporites medius, which was produced by Diaphorodendron and Synchysidendron, occurs more frequently in the Herrin coal bed, and are most abundant in, and in proximity to, the two inorganic partings. Tree fern spores are less abundant in the Herrin coal, and do not display any discernable vertical species variation.Collectively, both the Springfield and Herrin coal beds are interpreted to have formed in extensive planar, topogenous mires. Consistently saturated peat conditions throughout the development of both paleomires are indicated by the high vitrinite contents, and prevalence of arborescent lycopods. The deposition of widespread inorganic partings in the Herrin coal represents significant events in peat accumulation, with high ash coal benches representing smaller, more local events.Both of the coals are overlain by black, very organic-rich (avg. TOC±20%) marine shales. The Turner Mine Shale, which directly overlies the Springfield coal, has layers at the coal/shale contact with fairly abundant vitrinite, primarily in the form of vitrodetrinite, near the base of the shale, but the majority of the shale is dominated by the liptinite macerals bituminite, lamalginite and amorphinite. Micrinite is a major organic component of the shale. The Anna Shale, which directly overlies the Herrin coal, is similar in overall maceral composition, but contains less vitrinite, and more solid bitumen and micrinite. Trace element ratios (Ni/Co, V/Cr, V/V+Ni), indicative of paleoredox conditions, indicate that both shales were deposited under mainly dysoxic to suboxic/anoxic conditions. The shales are interpreted to represent a progressively rising water table, caused by an increase in eustatic sea levels. Vitrinite reflectance values in the shales are lower than corresponding values measured from the coal, indicating some degree of vitrinite suppression occurring in the Turner Mine and Anna Shales.

Characteristics of Microbial Coalbed Gas during Production; Example from Pennsylvanian Coals in Indiana, USA

Coalbed gases from 11 wells producing from the Springfield and Seelyville Coal Members (Pennsylvanian) were analyzed for composition and carbon and hydrogen stable isotope ratios in four sampling events to investigate short-term variation trends. Nine wells in the Seelyville Coal Member produce coalbed gases from the virgin seam, whereas two wells in the Springfield Coal Member produce gas from mine voids. Methane dominates gas composition in all wells, and its content ranges from ~94% to almost 98%, with ethane typically accounting for less than 0.01%. Carbon dioxide content in most samples is below 1%, whereas N2 content ranges from less than 2% to 4.8%. Methane δ13C values range from −55.3‰ to −61.1‰, and δ2H values range from −201‰ to −219‰. Isotopic values of methane and C1/(C2 + C3) ratios indicate a biogenic origin along the CO2-reduction pathway, consistent with previous studies in this area. Our results demonstrate that gas properties may change significantly during a period of one year of production history. Compositional trends (e.g., C1/(C2 + C3), CH4/CO2 ratios) are specific for each well and often irregular. These changes result from a combined influence of numerous factors and, therefore, are difficult to predict.

Carbon isotope analysis of whole-coal and vitrinite from intruded coals from the Illinois Basin: No isotopic evidence for thermogenic methane generation

Igneous intrusions into coals and organic-rich rocks may have contributed to global warming in the geologic past through the release of greenhouse gases. Evidence for a large release of thermogenic CH4 from the organics would include significant δ13Corg enrichment in the residual organic matter (OM). However, δ13Corg values of thermally altered OM in coals and shales adjacent to intrusions often show negative trends or, in some cases, ambiguous or positive trends. Previous studies have evaluated the δ13Corg of whole-coal samples rather than that of individual organic components, or macerals. As different macerals have different isotopic compositions, maceral-specific trends may be masked by variations in maceral composition of the bulk samples. This study evaluates the hypothesis that, if a large-scale release of 13C-depleted thermogenic CH4 resulted from intrusion of the coal, then it should have produced 13C-enriched coal residuum and, specifically, vitrinite (the most abundant component of the coal) adjacent to the intrusion. This study reports geochemical and petrographic data for whole-coal samples and vitrinite macerals (separated via density-gradient centrifugation, DGC) from a transect of thermally altered Springfield (No. 5) Coal (Pennsylvanian) in the Illinois Basin.Approaching the dike contact, mean vitrinite reflectance (Rr) increases from background levels of 0.55% up to ~4.8% and liptinites become indistinguishable from vitrinite. Isotropic and fine-grained circular mosaic coke is observed in samples within ~1.3m of the coal/intrusion contact. Approaching the intrusion, volatile matter (VM) decreases and fixed carbon (FC) and %C increase, whereas %H decreases. Total organic carbon (TOC) for whole coal decreases from 77% to 34%, whereas TOC for separated vitrinite fractions increases from ~66% to 93% toward the coal/intrusion contact. Density of DGC-separated vitrinites ranges from 1.27g/mL in the unaltered coal to 1.52g/mL in the sample adjacent to the coal/intrusion contact. Vitrinite density increases with increased Rr and %C, and decreases with increased %H and H/C.Despite these marked geochemical and petrographic changes, no significant changes in δ13Corg values of the whole coal (−25.3‰ to −24.9‰) or the separated vitrinites (−25.3‰ to −25.0‰) occur proximal to the intrusion. Changes in the isotopic signatures are not of a magnitude that would be expected if significant quantities of isotopically depleted thermogenic CH4 had been generated by the intrusive event. Moreover, no petrographic evidence supports the occurrence of condensed or immobilized thermal products due to rapid pyrolysis (such as 12C-rich pyrolytic carbon) close to the intrusion that could have moderated any changes in δ13Corg. Geochemical and petrographic results suggest that only minimal loss of CH4 was associated with the rapid heating of the Springfield (No. 5) Coal by the intrusion. These findings have significant implications for models linking past global warming to the intrusion of coals and carbonaceous shales.

Maceral controls on porosity characteristics of lithotypes of Pennsylvanian high volatile bituminous coal: Example from the Illinois Basin

Porosity characteristics of vitrain, clarain, durain, and fusain lithotypes of the Springfield Coal Member of the Petersburg Formation and the Danville and Hymera Coal Members of the Dugger Formation from the Illinois Basin were investigated with a special emphasis on the control of coal macerals on pore-size distribution. These Pennsylvanian coals are of high volatile bituminous rank and have vitrinite reflectance ranging from 0.51 to 0.60%. The lithotypes studied show decreasing values of Brunauer-Emmett-Teller surface area, and micro- and mesopore volumes from vitrain through clarain and durain to fusain. Within the mesopore size range, vitrain and clarain are dominated by pore-size widths of 4 to 10nm, whereas durain and fusain have more volume for pores larger than 20nm. In contrast to mesopores, micropore sizes are very similar for all lithotypes, averaging 1.37 to 1.39nm. In addition to differences among lithotypes, there are significant differences in pore characteristics among the three coals studied, with largest surface areas and pore volumes documented for the Hymera, followed by the Danville and the Springfield. A strong relationship exists between surface area, mesoporosity, and microporosity and maceral composition, with vitrinite having a very strong positive correlation, liptinite having a weak positive correlation, and inertinite having a strong negative correlation. Negative correlations of total porosity with vitrinite and liptinite and positive correlations with inertinite suggest that among the maceral groups, pores in inertinite contribute most to the total porosity. The Fourier transform infrared spectrometry technique demonstrates that fusains from the three coals studied have higher aromaticity and a higher degree of aromatic ring condensation and lower hydrocarbon potential than the other lithotypes, whereas chemical differences between vitrain, clarain, and durain are less distinct. In addition, there is a relationship between aromaticity of the lithotypes and surface area and mesopore and micropore volumes.

Dike-induced thermal alteration of the Springfield Coal Member (Pennsylvanian) and adjacent clastic rocks, Illinois Basin, USA

A basaltic dike intrusion caused a short-term and short-distance contact aureole in the vitrinite-rich Springfield Coal Member of the Carbondale Formation (Pennsylvanian) and in the underlying paleosol and overlying black shale in the Illinois Basin. Parallel series of samples from all three horizons were analyzed for vitrinite reflectance (Ro, %) and other parameters to evaluate the lateral extension of the thermal aureole. Ro values in the porous and fluid-permeable coal increase from a background value of ~0.66% at ≥4.0m distance from the dike to more than 5.0% at the intrusive contact. Ro values in the underlying paleosol increase from a background of ~0.65% at ≥3m distance to 1.74% at the dike contact. In contrast, roof rock shale close to the contact had a higher Ro value than the paleosol (Ro=2.56%). These differences cannot be explained by thermal conductivity of heat alone, or the coal having lower thermal conductivity would show lower vitrinite reflectance values. Apparently, the coal having much higher Ro values experienced enhanced lateral convective heat transfer in comparison to the denser and less permeable, but more conductive, rocks in the paleosol and overlying black shale. The advection of relatively cold fluid in the lower part of the coal seam streaming towards the dike may have provided cooling for floor rock close to the coal near the contact. In contrast, roof rock close to the contact had a higher Ro value than the paleosol (Ro=2.56%) in the absence of cooling.

Anatomy of an intruded coal, II: effect of contact metamorphism on organic δ13C and implications for the release of thermogenic methane, Springfield (No. 5) Coal, Illinois Basin

Concerns about the present-day accelerated rate of carbon input to the atmosphere have prompted the search for comparable events throughout Earth's history. Recent research has attempted to determine the cause of such events, represented as negative δ13C excursions within the sedimentary record, and their subsequent effect on the Earth. It has been suggested that such excursions could be the result of the large-scale release of 13C-depleted thermogenic methane produced by the intrusion of large igneous provinces (LIPs) into organic-rich rocks and/or coal (e.g., McElwain et al., 2005; Svensen et al., 2004, 2007). Our study asserts that if intrusions result in significant release of 13C-depleted thermogenic methane from intruded coals, 13C-enriched coal should be observed adjacent to the intrusions.In this study, values of bulk organic δ13C (δ13Corg) are reported for fifteen samples along a coal transect in the Illinois Basin where a Pennsylvanian-age coal (the Springfield or No. 5 Coal) is intruded by a Permian ultramafic dike. The samples reveal significant bulk geochemical and petrographic changes within the alteration halo; for example, volatile matter (VM) decreases towards the intrusion, whereas fixed carbon (FC) and vitrinite reflectance (Rr) both increase, accompanied by the development of natural coke (both isotropic and anisotropic), mosaic structure, devolatilization vacuoles, and carbonate mineralization. Reflectance levels and coke development are consistent with exposure to temperatures >450–500°C. Despite the high level of alteration of the organic matter, no significant change is observed in δ13Corg; values across the transect vary by less than 0.5‰. Along this transect, δ13Corg does not correlate with Rr and does not appear to be influenced by maceral composition. The intruded coals show no evidence of pyrolytic carbon that could influence δ13Corg.The relatively high VM contents of the intruded coals (compared to coals that have undergone normal burial maturation) and the lack of any trend in δ13Corg approaching the intrusion raises questions about previously published models of the effects of large-scale igneous intrusions on atmospheric composition and δ13Corg excursions associated with oceanic anoxic events. This study underscores the importance of the use of organic petrography in combination with isotope geochemistry to determine if contact metamorphosed coals and organic-rich shales could have released a significant amount of 13Corg-depleted volatiles leading to negative δ13Corg excursions in the sedimentary record.

Modeling and analysis of gas capture from sealed sections of abandoned coal mines

All coal mines eventually complete their economic life, stop production, and are abandoned completely. Ventilation shafts and access drifts of these mines are usually sealed by plugging with concrete to isolate the mine environment from the outside atmosphere (surface) and also to prevent unauthorized access to old workings. Although large areas of access to the mine can be isolated, the void space left behind can never be isolated from surrounding coal and other formations. The void spaces act as a huge sink and start accumulating gas, perhaps groundwater as well, over time to form a methane reservoir. Understanding methane emission into old workings from surrounding strata, and the leakage characteristics of in-place mine seals, and analyzing gas production potential from such areas can improve ventilation designs in mines operating in similar settings, and can also enable the possibility of using abandoned mine methane (AMM) as an energy source. To meet these objectives, data acquired from different sources and utilized in the context of flow modeling and reservoir simulation, along with productions of AMM wells, can be invaluable tools. However, modeling of abandoned mines for gas emission and capture may not be an easy task. The difficulties in estimating spatial variability in various properties of the surrounding coal and mine environment, the complex geometry of the mine boundary and its details, and the initial conditions at the time of abandonment and when analysis begins all add to the challenge.In this paper, a reservoir modeling study that aims to characterize methane extraction from an abandoned room-and-pillar mine in the Springfield coal, Indiana, is demonstrated. The analyses related to interactions of surrounding coal with the abandoned mine environment were performed though history matching, initially, of two AMM wells drilled into two sealed sections. Analyses were then extended to evaluate different well locations to understand potential changes in gas emission from the coal, as well as leakage from the seals. Data required for establishing a detailed reservoir environment were obtained from mine maps, analysis of well productions by using a composite model, and by geostatistical modeling of point-wise data to create property maps.Results showed that wells drilled in larger sealed sections of the mine and away from previous workings performed better. Furthermore, the location of the well in the sealed section can be important as locations close to surrounding coal can have a better chance of promoting more gas in-flow from the coal seam, whereas locations close to the seal can take advantage of leakage through the seal and can benefit from higher rates of the gas contributed from other parts of the mine. Since gas emissions from coal and leakage through seals vary with the pressure differential, simulations of AMM can also be used in ventilation design of mines operating in similar settings as estimates and thus can also help improving safety of mines with quantified understanding of leakage.

Effects of rapid thermal alteration on coal: Geochemical and petrographic signatures in the Springfield (No. 5) Coal, Illinois Basin

Igneous intrusion into a coal bed can change the geochemical and petrographic properties of the coal including vitrinite reflectance, maceral petrographic composition, optical texture, mineralogy, stable isotope composition, trace element composition, and bulk geochemistry. The intent of this study was to evaluate petrographic and geochemical changes in an intruded coal and compare them to trends seen in coals altered by normal burial maturation, thereby evaluating whether or not the intruded coals followed a different maturation pathway. The current study reports petrographic, bulk geochemical (proximate, ultimate), Leco total organic carbon (TOC), and Rock-Eval pyrolysis data for a suite of samples from the Springfield (No. 5) Coal (Pennsylvanian, Desmoinesian) in the southern part of the Illinois Basin where the coal had been intruded by a Permian-age peridotite dike.Petrographic analysis shows an increase in vitrinite reflectance (Rm) from background levels of 0.55–0.63% up to ~4.80%, a loss in ability to differentiate liptinite macerals, formation of isotropic coke and, at the dike/coal contact, development of fine-grained mosaic anisotropic coke texture. Volatile matter (VM) content decreases and fixed carbon (FC) content, ash, and mineral matter (Parr formula) increase approaching the intrusion contact. Carbon increases whereas nitrogen, hydrogen, and oxygen decrease approaching the intrusion. The presence of carbonate minerals (confirmed by X-ray diffraction and petrographic analysis) has a significant impact on proximate and ultimate data. However, even after removal of carbonates, trends for VM vs. Rm, %C vs. Rm, and H vs. C do not follow typical trends associated with normal burial coalification. Approaching the contact, Leco TOC, Rock-Eval free oil content (S1), remaining hydrocarbon potential (S2), CO2 from pyrolysis of the organic matter (S3), and hydrogen (HI) and oxygen (OI) indices decrease whereas thermal maturity (Tmax, °C) increases. S2 vs. Rm and Tmax vs. Rm diverge from the pathways seen in previous studies of coals that have undergone normal burial maturation.Geochemical data from this study suggest that the intruded Springfield (No. 5) Coal may have followed a maturation track that differed from that seen under normal burial maturation, perhaps due to the geologically rapid, high heating event associated with the emplacement of the intrusion. It is also suggested here that the natural coke textures produced by this rapid geological heating may differ from those observed for metallurgical cokes produced under standard industrial coking conditions. Typically, in an industrial coke oven, a coal of this initial rank (Ro=~0.6%) would produce an isotropic coke, rather than the fine-grained circular anisotropic coke seen here. However, as variations in heating rate, duration of heating, maximum temperatures attained, hydrothermal conditions, and pressure are mostly unknown for the intrusive event, it is not unreasonable to suggest that differences in these variables contributed to the higher anisotropy of the coke. Alternatively, the development of this texture may reflect “pre-heating” of the coal during the intrusion event.

Extractability of biomarkers from high- and low-vitrinite coals and its effect on the porosity of coal

The influence of two solvents on the degree of bitumen extractability and the porosity of the extracted coals was investigated using two high-volatile bituminous coals with different petrographic composition. The Springfield Coal (vitrinite-rich) and the Lower Block Coal (vitrinite-poor) from the Illinois Basin were Soxhlet-extracted with methanol (CH3OH) and dichloromethane (CH2Cl2). The abundances of three selected groups of biomarkers extracted from both coals were compared: (1) n-alkanes plus pristane and phytane; (2) hopanes; and (3) 3- and 4-ring aromatic hydrocarbons (phenanthrene, anthracene, fluoranthene, and pyrene). Overall, the extracts of the vitrinite-poor Lower Block Coal contained greater amounts of n-alkanes and hopanes, whereas aromatic hydrocarbons were extracted in greater quantities from the vitrinite-rich Springfield Coal. Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography/Mass Spectrometry (GC/MS) confirmed that the average lengths of aliphatic chains were greater in CH2Cl2 extracts from both coals. For the Lower Block Coal, the aromaticity of extracted organic matter was greater in the CH2Cl2 extract than in the CH3OH extract. Both coals showed an increase in microporosity (<2nm; measured by CO2 adsorption) after solvent treatments. In addition, the mesopore surface area (2–50nm, measured by N2 adsorption) was reduced likely because of a shift in the size distribution of mesopore diameters towards those of macropores (i.e. >50nm). Our analyses of compound classes present in the extracts and resultant porosity changes in the extracted coals provide useful insights into the structural and molecular differences in two bituminous coals of different maceral compositions.

Chemical compound classes supporting microbial methanogenesis in coal

Microbial generation of coalbed methane (CBM) occurs in numerous basins worldwide. This study identifies specific classes of chemical compounds in two high volatile bituminous coals from the Illinois Basin in southwestern Indiana, USA that are being degraded during methanogenesis. Springfield Coal is rich in vitrinite (92.2vol.% vitrinite in coal) whereas Lower Block Coal contains larger contributions of liptinite and inertinite and contains only 66.2vol.% vitrinite. Anaerobic bioreactors used in the experiments contained a mineral-salts medium, operationally-defined coal extracts, and a microbial inoculum composed of an endemic microbial consortium that was obtained from co-produced water from an active CBM well. Our experiments investigated degradation of organic matter (OM) and concurrent methanogenesis using water-soluble, methanol (CH3OH)-soluble, and dichloromethane (CH2Cl2)-soluble fractions of extracted OM from coal as the sole carbon sources. Only methanol and dichloromethane were found to be effective solvents to extract sufficient OM from coals for biodegradation. The methane yield over time was small (1.7 to 8.7μmol in total headspace) and less than 1% of carbon added to bioreactors in organic extracts was converted into methane. Extracts of vitrinite-rich Springfield Coal yielded relatively more methane than extracts of Lower Block Coal. The preference of methanogenic microbial consortia for extracts from vitrinite-rich Springfield Coal may be related to the fact that the organic matter in vitrinite is rich in functional groups containing organic nitrogen, sulfur and oxygen (NSO) that provide chemical sites with low activation energies to initiate biodegradation. A comparison of the molecular compositions of the initial organic extracts with their biodegraded residues after incubation of the bioreactors for 24weeks indicated that biodegradation of n-alkanes and aromatic hydrocarbons occurred concurrently, whereas hopanes proved to be far more refractory. Our study documents significant biodegradation of n-alkanes (14 to 91% by GC/MS peak intensity) from coal extracts. It is particularly noteworthy that biodegradation also eliminated 6 to 58% of aromatic biomarkers, although the pool of n-alkanes was not exhausted. This significant early biodegradation of aromatic hydrocarbons in coal extracts contrasts starkly with the biodegradation pattern of petroleum where similar aromatic compounds are degraded only after n-alkanes have been severely depleted. This evidence may support the hypothesis that microbial communities engaged in coal biodegradation do not express a strong preference for either aliphatic or aromatic carbon sources, in contrast to biodegradation patterns typical of petroleum. CH3OH‐extracted organic matter from coal was generally more biodegradable than CH2Cl2-extracted organic matter from the same coal, probably because CH3OH extracts contained lower concentrations of longer straight aliphatic chains allowing faster microbial degradation.