Illinois Basin Research Articles

Orenia metallireducens sp. nov. Strain Z6, a Novel Metal-Reducing Member of the Phylum Firmicutes from the Deep Subsurface.

A novel iron-reducing species, Orenia metallireducens sp. nov., strain Z6, was isolated from groundwater collected from a geological formation located 2.02 km below land surface in the Illinois Basin, USA. Phylogenetic, physiologic, and genomic analyses of strain Z6 found it to have unique properties for iron reducers, including (i) active microbial iron-reducing capacity under broad ranges of temperatures (20 to 60°C), pHs (6 to 9.6), and salinities (0.4 to 3.5 M NaCl), (ii) lack of c-type cytochromes typically affiliated with iron reduction in Geobacter and Shewanella species, and (iii) being the only member of the Halanaerobiales capable of reducing crystalline goethite and hematite. This study expands the scope of phylogenetic affiliations, metabolic capacities, and catalytic mechanisms for iron-reducing microbes.

Geochemical and petrographic alteration of rapidly heated coals from the Herrin (No. 6) Coal Seam, Illinois Basin

Coals altered by rapid heating events (i.e., those intruded by dikes and sills) are thought to follow a different geochemical maturation pathway than coals altered through diagenesis. If an igneous intrusion alters the petrographic and geochemical properties of a coal, the effect should also be observable in the coal's molecular structure. In this study, we evaluate whether coals altered by rapid heating follow distinct maturation trends from coals that were altered by slower heating (burial maturation). Petrographic, geochemical, and micro-FTIR analyses were performed on a series of Pennsylvanian Illinois Basin coal samples, collected at various distances from a Permian igneous dike. Standard coal characterization techniques including vitrinite reflectance and proximate and ultimate analyses provide valuable insights on the maturation pathways experienced by rapidly heated coals. These techniques were coupled with reflectance micro-FTIR to provide a better understanding of the molecular changes that occur in the coal structure during relatively short-lived, intensive heating events.With decreasing distance to the intrusion, coals have higher mean random vitrinite reflectance values (Rr) within the dike alteration zone. Coking textures similar to those observed in industrial cokes are observed within 2m of the intrusion. Geochemical data for HCl-treated coals indicate an overall loss of H, O, and N and an increase in C approaching the dike. Intruded coals have higher volatile matter (VM) yields at high rank than coals of similar rank that result from normal burial maturation. When plotted on a van Krevelen diagram or Seyler chart, intruded coals follow different coalification trends than coals matured through normal burial diagenesis.Reflectance micro-FTIR analysis of collotelinite shows increased aromaticity with rank: both the ratio of the aromatic CH stretching band at ~3100–3000cm−1 versus the aliphatic CHx stretching bands between 3000 and 2800cm−1 (AR1), and the ratio of the aromatic out-of-plane deformation bands between ~900–700cm−1 versus the aliphatic CHx band (AR2) increase with increasing Rr. Within the 3000–2800cm−1 region, there is an increase in the area under the asymmetric CH3 peak at ~2960cm−1 relative to the asymmetric CH2 peak at ~2920cm−1 with increased rank. Within the 900–700cm−1 region, the overall intensity of the ~750cm−1 peak (aromatic rings with four adjacent H atoms) relative to the ~870cm−1 peak (aromatic rings with one isolated H atom) increases up to 2.5% Rr, likely reflecting a lower degree of substitution (DOS) of alkyl groups on aromatic ring sites. The prevalence of the 750cm−1 peak at high rank may represent a lower degree of condensation of aromatic rings in the structure of intruded coals compared to normally matured coals.

A Quality Control Method for TeleseismicP‐Wave Receiver Functions

We introduce a new semiautomated quality control (QC) method for teleseismic P ‐wave receiver functions consisting of 13 editing procedures. These procedures are categorized into three groups based on (1) deconvolution attributes, (2) characteristics of each receiver function, and (3) the statistical attributes of a station gather. We evaluated the efficacy of individual procedure and combination of multiple procedures by applying them to receiver functions estimated from the EarthScope Ozark–Illinois–Indiana–Kentucky experiment for the Illinois basin area, and 10 years of USArray Transportable Array data for the contiguous United States. The method developed in this study significantly improves the efficiency and accuracy of receiver function QC. Our approach has three useful properties: (1) unlike a manual editing method, our approach produces reproducible results defined by a finite set of tunable parameters; (2) it provides an effective and efficient tool for processing large datasets containing millions of receiver functions; (3) the QC procedures are less dependent on phase similarities comparing to the automated scheme used by the EarthScope Automated Receiver Survey while producing comparable common conversion point stacking images.

Tepidibacillus decaturensis sp. nov., a microaerophilic, moderately thermophilic iron-reducing bacterium isolated from 1.7 km depth groundwater.

A Gram-stain-negative, microaerophilic rod-shaped organism designated as strain Z9T was isolated from groundwater of 1.7 km depth from the Mt. Simon Sandstone of the Illinois Basin, Illinois, USA. Cells of strain Z9T were rod shaped with dimensions of 0.3×(1-10) µm and stained Gram-negative. Strain Z9T grew within the temperature range 20-60 °C (optimum at 30-40 °C), between pH 5 and 8 (optimum 5.2-5.8) and under salt concentrations of 1-5 % (w/v) NaCl (optimum 2.5 % NaCl). In addition to growth by fermentation and nitrate reduction, this strain was able to reduce Fe(III), Mn(IV), Co(III) and Cr(VI) when H2 or organic carbon was available as the electron donor, but did not actively reduce oxidized sulfur compounds (e.g. sulfate, thiosulfate or S0). The G+C content of the DNA from strain Z9T was 36.1 mol%. Phylogenetic analysis of the 16S rRNA gene from strain Z9T showed that it belongs to the class Bacilli and shares 97 % sequence similarity with the only currently characterized member of the genus Tepidibacillus, T.fermentans. Based on the physiological distinctness and phylogenetic information, strain Z9T represents a novel species within the genus Tepidibacillus, for which the name Tepidibacillus decaturensis sp. nov. is proposed. The type strain is Z9T (=ATCC BAA-2644T=DSM 103037T).

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.

A sulfate conundrum: Dissolved sulfates of deep-saline brines and carbonate-associated sulfates

Sulfates in deeply circulating brines and carbonate-associated sulfates (CAS) within sedimentary units of the Cambrian strata in the Illinois Basin record a complex history. Dissolved sulfate within the Mt. Simon Sandstone brines exhibits average δ34SSO4 values of 35.4‰ and δ18OSO4 values of 14.6‰ and appears to be related to Cambrian seawater sulfate, either original seawater or sourced from evaporite deposits such as those in the Michigan Basin. Theoretical and empirical relationships based on stable oxygen isotope fractionation suggest that sulfate within the lower depths of the Mt. Simon brines has experienced a long period of isolation, possibly several tens of millions of years. Comparison with brines from other stratigraphic units shows the Mt. Simon brines are geochemically unique. Dissolved sulfate from brines within the Ironton-Galesville Sandstone averages 22.7‰ for δ34SSO4 values and 13.0‰ for δ18OSO4 values. The Ironton-Galesville brine has mixed with younger groundwater, possibly of Ordovician to Devonian age and younger. The Eau Claire Formation lies between the Mt. Simon and Ironton-Galesville Sandstones. The carbonate units of the Eau Claire and stratigraphically equivalent Bonneterre Formation contain CAS that appears isotopically related to the Late Pennsylvanian-Early Permian Mississippi Valley-type ore pulses that deposited large sulfide minerals in the Viburnum Trend/Old Lead Belt ore districts. The δ34SCAS values range from 21.3‰ to 9.3‰, and δ18OCAS values range from +1.4‰ to −2.6‰ and show a strong covariance (R2=0.94). The largely wholesale replacement of Cambrian seawater sulfate signatures in these dolomites does not appear to have affected the sulfate signatures in the Mt. Simon brines even though these sulfide deposits are found in the stratigraphically equivalent Lamotte Sandstone to the southwest. On the basis of this and previous studies, greater fluid densities of the Mt. Simon brines may have prevented the less dense Mississippi Valley-type fluids from interacting with these deeply circulating brines. Progressive in situ quartz cementation that occurred in the Mt. Simon Sandstone contemporaneous to the ore pulses may also have precluded fluid migration. The Mt. Simon brines appear to be a mixture of evaporated connate Cambrian seawater, recirculating deep-seated crystalline basement brines, and meteoric water.

A Middle Pennsylvanian macrofloral assemblage from wetland deposits in Indiana (Illinois Basin): a taxonomic contribution with biostratigraphic, paleobiogeographic, and paleoecologic implications

AbstractTaxonomic analysis is provided for a Middle Pennsylvanian macrofloral assemblage collected from clastic wetland deposits in Clay County, Indiana, on the eastern margin of the Illinois Basin. Adpressed plant fossils were recovered from four distinct beds in the lowermost Staunton Formation, positioned above the Minshall Coal (uppermost Brazil Formation), part of a succession deposited near the Atokan-Desmoinesian boundary. The assemblage of 22 fossil-taxa is dominated by pteridosperms (includingNeuropteris flexuosa,Macroneuropteris scheuchzeri,Alethopteris densinervosa,Neuropteris ovata,Eusphenopteris neuropteroides, andNeuropteris missouriensis) with lesser cordaitaleans (Cordaitesspp. indet.) and sphenopsids (particularlySphenophyllum cuneifolium). Lycopsids are uncommon, and ferns are rare. In contrast, the microfloral assemblage from the Minshall Coal and overlying clastic units is dominated by lycopsid and tree fern spores. Comparisons with established biozonation schemes yield different ages depending on the regional biostratigraphic framework used: (1) latest Bolsovian (Radiizonates difformisBiozone, American microfloras); (2) latest Bolsovian or earliest Asturian (‘Neuropteris’ rarinervisBiozone, Appalachian Basin macrofloras); or (3) earliest Asturian (Linopteris obliquaBiozone, European macrofloras). The placement and correlation of the Bolsovian-Asturian and Atokan-Desmoinesian boundaries, which have traditionally been equated by palynology, are evaluated in the context of this discordance. Several revised stratigraphic scenarios are proposed for this interval in the Illinois Basin, which is being increasingly recognized as a time of significant environmental change throughout Euramerica. Homotaxial comparisons with European macrofloral assemblages indicate that, of the 18 biological taxa recorded, between 14 and 17 (78–94%) also are common in coeval wetland deposits in Europe. The similarities exemplify the spatial conservatism and low diversity of wetland plant communities over vast areas of tropical Euramerica, a manifestation of the intrinsically stressful conditions that characterize such habitats, and indicates that neither the Laurentian Shield nor the Appalachian-Variscan Mountains were an insurmountable barrier to plant dispersal during the Middle Pennsylvanian.

U–Pb detrital zircon evidence of transcontinental sediment dispersal: provenance of Late Mississippian Wedington Sandstone member, NW Arkansas

ABSTRACTU–Pb ages of detrital zircons from the Wedington Sandstone member in northwest Arkansas provide evidence for Late Mississippian westward transcontinental sediment transport from the Appalachian foreland. The Late Mississippian Wedington Sandstone member of the Fayetteville Shale is a fine- to medium-grained quartzarenite. It separates the Fayetteville Shale into informal lower and upper intervals, and was deposited as a small constructive delta complex that prograded towards the south and southeast during the Late Mississippian. As a major influx of clastic sediments, the Wedington Sandstone member records the sediment source and dispersal in the mid-continent during the Late Mississippian. A total of 559 detrital zircon grains from six Wedington samples were recovered for U–Pb detrital zircon geochronological analysis. Results show that age distributions can be subdivided into six groups: ~350–500, ~900–1350, ~1360–1500, ~1600–1800, ~1800–2300, and > ~2500 Ma, and are characterized by a prominent peak for the age group of ~900–1350 Ma, a major peak at ~1600–1800 Ma, and a few other minor age clusters. Regional correlation and geological evidence from surrounding areas suggest that the transcontinental sediment dispersal started as early as the Late Mississippian. U–Pb detrital zircon age distribution suggests that the Wedington Sandstone member was likely derived from the Appalachian foreland with contributions from the Nemaha Ridge to the west where the Yavapai–Mazatzal sources were exposed during the Late Mississippian. Sediment was likely transported westward through or around the Illinois Basin, merged with mid-continent sediment, and then entered into its current location in northwest Arkansas. Transportation of this sediment from mixed sources continued along its course to the south, forming a delta on the Northern Arkansas Structural Platform.

Microanalysis of carbonate cement δ18O in a CO2-storage system seal: Insights into the diagenetic history of the Eau Claire Formation (Upper Cambrian), Illinois Basin

Oxygen isotope (δ18O) zonation in carbonate mineral cements is often employed as a proxy record (typically with millimeter-scale resolution) of changing temperature regimes during different stages of sediment diagenesis. Recent advances in secondary ion mass spectrometry allow for highly precise and accurate determinations of cement δ18O values to be made in situ on a micrometer scale, thus significantly increasing the spatial resolution available to studies of diagenesis in sandstone–shale and carbonate systems. Chemo-isotopically zoned dolomite–ankerite cements within shaly sandstone beds of the predominantly silty–shaly Eau Claire Formation (Cambrian, Illinois Basin) were investigated, revealing the following: with increasing depth of burial (from <0.5 to ∼2 km [<1500 to 6500 ft]), cement δ18O values decrease from a high of approximately 24‰ down to approximately 14‰ (on the Vienna standard mean ocean water [VSMOW] scale, equivalent to −6.5‰ to −16.5‰ on the Vienna Peedee belemnite [VPDB] scale). The observed cross-basin trend is largely consistent with cements having formed in response to progressive sediment burial and heating. Within the context of independent burial and thermal history models for the Illinois Basin, cementation began soon after deposition and continued intermittently into the mid-Permian. However, temperatures in excess of burial model predictions are inferred at the time of latest ankerite cement precipitation, which we propose overlapped in time with conductive heating of the Eau Claire Formation (a closed system) from under- and overlying sandstone aquifers that channeled the flow of hot, Mississippi Valley–type mineralizing brines during the mid-Permian (ca. 270 Ma).

Treatment of produced water from an oilfield and selected coal mines in the Illinois Basin

If large-scale CO2 sequestration operations are implemented in oilfields or coal mines, large volumes of water (i.e., produced water) could potentially be generated that would need to be properly managed. In this work, produced water samples with total dissolved solids (TDS) values of 18,000–102,000mg/L (ppm) were collected from an oilfield, a coal-bed methane field, and a coal mine in the Illinois Basin of the United States and were treated by selected conventional pretreatment processes followed by a reverse osmosis desalination process. Pretreatment processes included coagulation by lime, ferric chloride, or aluminum sulfate; filtration by sand, walnut shells, anthracite coal, or microfiltration; and adsorption by organoclay, activated carbon, or ion-exchange resins. Selected pretreatment processes were sufficient for removing most of the contaminants, but the high sodium background of the high-TDS produced water (102,000ppm) limited the effectiveness of the ion-exchange pretreatment in removing scale-forming species. Reverse osmosis was a practical process for desalination of pretreated produced water samples tested (by reducing the TDS more than 96%) except for the high-TDS produced water. Reported bench-scale produced water treatment data might be beneficial for the design and operation of pilot-scale plants for treating produced waters with similar properties.

Microseismic data acquisition, processing, and event characterization at the Illinois Basin – Decatur Project

Microseismic monitoring at the Illinois Basin – Decatur Project (IBDP) is accomplished using a combination of commercially available components that are integrated to provide real-time analysis and remote processing capabilities by means of a purpose-built data management system and secure web portal. The processing workflow consists of real-time, remote access, and in-house processing components, which provides a seamless path from in-field quality control to final locations with short turn-around times. Event location is performed using an adaptation of the Geiger method, which is designed to be robust for the sparse but localized observation sets typically encountered with injection monitoring. Observed microseismicity displayed distinct linear clustering and increased in distance from the injection well over time, presenting challenges for location accuracy of more distal events. The velocity model, a key component in event location and characterization, evolved through early stages of the project as new wells were drilled providing the opportunity for improved observation geometry and acquisition of additional controlled energy source points for model calibration. The experience gained at IBDP highlights the importance of field systems and processing flows that allow adaptation to evolving operational conditions and microseismic event activity.

Draft Genome Sequence of Tepidibacillus decaturensis Strain Z9, an Anaerobic, Moderately Thermophilic, and Heterotrophic Bacterium from the Deep Subsurface of the Illinois Basin, USA.

The genome of the moderately thermophilic and halotolerant bacterium Tepidibacillus decaturensis strain Z9 was sequenced. The draft genome comprises three scaffolds, for a total of 2.95 Mb. As the first sequenced genome within the genus Tepidibacillus, 2,895 protein-coding genes, 52 tRNA genes, and 3 rRNA operons were predicted.

Mineral changes in cement-sandstone matrices induced by biocementation

Prevention of wellbore CO2 leakage is a critical component of any successful carbon capture, utilization, and storage program. Sporosarcina pasteurii is a bacterium that has demonstrated the potential ability to seal a compromised wellbore through the enzymatic precipitation of CaCO3. Here we investigate the growth of S. pasteurii in a synthetic brine that mimics the Illinois Basin and on Mt. Simon sandstone encased in Class H Portland cement under high pressure and supercritical CO2 (PCO2) conditions. The bacterium grew optimum at 30°C compared to 40°C under ambient and high pressure (10MPa) conditions; and growth was comparable in experiments at high PCO2. Sporosarcina pasteurii actively induced the biomineralization of CaCO3 polymorphs and MgCa(CO3)2 in both ambient and high pressure conditions as observed in electron microscopy. In contrast, abiotic (non-biological) samples exposed to CO2 resulted in the formation of surficial vaterite and calcite. The ability of S. pasteurii to grow under subsurface conditions may be a promising mechanism to enhance wellbore integrity.

Changes in gas storage and transport properties of coal as a result of enhanced microbial methane generation

This study was aimed at identifying the changes in coal storage and transport properties affecting gas production from coal-gas reservoirs, when treated with microbial consortia to generate/enhance production of methane. The work expanded on the technology of bio-conversion, first proposed in order to imitate the natural/microbial process of biogenic gasification leading to recharging coalbed methane reservoirs or, setting up natural gas reservoirs in non-producing coalbeds or, to coal waste, typically in the form of fines/ultra-fines. The pressure parameter was considered critical since, with continued production of methane, the produced gas would first diffuse into the coal matrix and get adsorbed with increasing pressure. During production, the pressure would decrease and the process would be reversed, gas diffusing out of the coal matrix and arriving at the cleat system.The experimental work tested the variation in the sorption and diffusion properties of treated coal, post continued bio-conversion since these are the first two physical phenomena in CBM production. During the first phase, single component sorption–diffusion experiments were carried out using methane and CO2 on virgin coals retrieved from the Illinois basin. Coals were then treated with nutrient amended microbial consortia for different periods. Gas production was monitored over thirty and sixty day periods of treatment after which, sorption–diffusion experiments were repeated on treated coals, thus establishing a trend over the sixty-day period. The sorption data was characterized using the Langmuir model. The variation trend in the value of diffusion coefficient, D, was also established as a function of pore pressure.The results indicated an increase in the sorption capacity of coal as a result of continued bioconversion. This was attributed to increased pore surface area due to microbial actions resulting in changes in the pore size or, creation of new pores. It was further shown that the rate of diffusion increased, especially for methane, which exhibited rates higher than that for CO2. These findings clearly support improved gas storage capacity with continued bio-conversion as well as significantly enhanced diffusion rates. As a continuation of this effort, change in permeability, the second gas transport phenomenon in coal-gas production, is currently being evaluated.

Data integration, reservoir response, and application

The microseismic activity observed in and around a geologic formation undergoing carbon dioxide (CO2) injection is a combination of natural, or “background”, microseismicity plus that activity which is induced by injection operations. Since injection pressure within storage target formations are maintained safely below fracture pressure this induced activity typically originates at natural pre-existing zones of mechanical weakness presented by structural or stratigraphic features. The combination of mechanical properties and in situ stresses dictate the focal mechanism for microseismic emissions, an understanding of which facilitates the use of observed microseismicity for regulatory compliance and project management.Under favorable conditions microseismic activity may be unambiguously correlated with structural and/or stratigraphic features directly observed in seismic data, thus providing strong constraints to interpretation of observed microseismicity for focal mechanisms. However, in many cases, such as at the Illinois Basin–Decatur Project (IBDP), this direct correlation is elusive and other indirect support is required. Analysis of microseismicity at IBDP has been performed within the context of the integrated reservoir and mechanical earth models developed as part of the site characterization and monitoring program. The IBDP integrated modeling workflow involved continuous and geotechnically consistent data integration for geologic modeling, calibrated flow simulation, three-dimensional (3D) mechanical earth model, and coupled hydro-mechanical simulation. Using the coupled model, scenario-based forward modeling of microseismicity was performed for hypothetical focal mechanisms inferred from observed data.The experience gained at IBDP illustrates the importance of integrated modeling in the interpretation of microseismic activity for focal mechanisms and provides valuable insights into critical data gaps which could be the target of future basic research efforts.

Fine-scale structure of the Precambrian beneath the Illinois Basin

Increasing our understanding of the heterogeneity of Precambrian crust continues to be a focus for deep seismic reflection studies. High-resolution two-dimensional (2D) seismic profiles and a high-resolution 3D seismic volume, all centered on Decatur (Illinois, USA), provide new insights on the structure and composition of Precambrian basement beneath the Illinois Basin of the central USA midcontinent. The new data reveal a pattern of strong and coherent reflections and associated diffractions deeply buried within the eastern Granite-Rhyolite Province. This pattern is dominated by a thick seismic stratigraphic sequence, which is wedge or bowl shaped in cross section and has an angular unconformity with the overlying Paleozoic section. Deeper intrabasement bowl-shaped sequences or series are also observed in the same area. We interpret these features to be a northward continuation of analogous basement sequences located 75 km to the south below the southern part of the Illinois Basin. This correlation indicates a vast Precambrian province with a north-south dimension of >200 km. Although multiple explanations are admissible for the Precambrian reflectivity, the most likely for our study area is igneous intrusion of broad mafic igneous (diabase?) sills possibly underlain by small plutons. The concentration of such mafic (or bimodal) igneous activity within or coeval with the eastern Granite-Rhyolite Province suggests an episode of Proterozoic crustal extension and rifting.

Shear velocity structure beneath the central United States: implications for the origin of the Illinois Basin and intraplate seismicity

AbstractWe present new estimates of lithospheric shear velocities for the intraplate seismic zones and the Illinois Basin in the U.S. midcontinent by analyzing teleseismic Rayleigh waves. We find that relatively high crustal shear velocities (VS) characterize the southern Illinois Basin, while relatively low crustal velocities characterize the middle and lower crust of the central and northern Illinois Basin. The observed high crustal velocities may correspond to high‐density mafic intrusions emplaced into the crust during the development of the Reelfoot Rift, which may have contributed to the subsidence of the Illinois Basin. The low crustal VS beneath the central and northern basin follow the La Salle deformation belt. We also observe relatively low velocities in the mantle beneath the New Madrid seismic zone where VS decreases by about 7% compared to those outside of the rift. The low VS in the upper mantle also extends beneath the Wabash Valley and Ste. Genevieve seismic zones. Testing expected VS reductions based on plausible thermal heterogeneities for the midcontinent indicates that the 7% velocity reduction would not result from elevated temperatures alone. Instead this scale of anomaly requires a contribution from some combination of increased iron and water content. Both rifting and interaction with a mantle plume could introduce these compositional heterogeneities. Similar orientations for the NE‐SW low‐velocity zone and the Reelfoot Rift suggest a rift origin to the reduced velocities. The low VS upper mantle represents a weak region and the intraplate seismic zones would correspond to concentrated crustal deformation above weak mantle.

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.

Illinois Basin – Decatur Project pre-injection microseismic analysis

The Illinois Basin – Decatur Project (IBDP) is a large-scale carbon dioxide (CO2) injection and storage demonstration project. Over a three-year period one million metric tons of CO2 were injected deep into the Mt. Simon Sandstone, a deep saline reservoir in the Illinois Basin. This study examines the microseismic data gathered for the period from May 2010 to November 2011, which preceded the CO2 injection.Microseismic events are detected through permanent geophone arrays installed in two wells. A CO2 injection well drilled to the depth of 7236 feet (2205m) is outfitted with a 4-component geophone array. Situated approximately 185ft away (56m), the 3502 feet (1067m) deep geophysical monitoring well contains a 3-component geophone array.During the pre-injection period, a total of 7894 microseismic events were detected and 99% of these correlate with drilling and other well-related operations. Eight local microseismic events were identified that appear unrelated to well activity and appear representative of the background level of microseismicity.Regional seismicity was also examined by changing triggering parameters and producing a second dataset. Under this configuration, the system detected twelve regional seismic events that correlate to the United States Geological Survey (USGS) earthquake record, and approximately 1100 distant events are believed associated with quarry-related blasting operations.

Finding cost-effective nutrient solutions and evaluating environmental conditions for biogasifying bituminous coal to methane ex situ

Biostimulation through providing nutrients to microorganisms has been proven to be highly effective in enhancing methane yield from bituminous coals in the Illinois basin. In light of the extremely cheap natural gas price at present, it is critically important to decrease the cost of nutrient solutions used to stimulate microbial gasification of coal and improve the cost-effectiveness of the biostimulation approach. To lower cost of a nutrient solution reported in previous studies, the three most expensive components, yeast extract, peptone and mercaptoethanesulfonic acid (Coenzyme M, CoM) were evaluated. Regarding the first two, decreasing their concentrations resulted in decreased methane production. In terms of CoM, its concentration could be reduced to at least half without affecting methane yield negatively. Complete elimination of CoM led to a methane yield of 85% of those with the presence of this compound in the original medium. Two complex media, trypticase soy broth (TSB) and corn steep liquor (CSL) were intended to replace yeast extract and peptone. TSB had increasingly positive effect with increasing its concentration while CSL had opposite trend. TSB at 100% (v/v) was then investigated under different cultivation conditions. Among the four parameters tested, TSB concentration and agitation were found to exert positive effect while coal loading and temperature had negative impact on methane production. The highest methane yield of 828.9ft3/ton in 30days was obtained under temperature of 28°C with a coal loading of 200g/L and agitation at 100rpm. This yield is four-time higher than those observed with the original medium. These results clearly demonstrated that biostimulation is a viable method for enhancing methane production from coal and the ingredients of nutrient solutions need to be evaluated in detail in order to make biostimulation cost-effectively at commercial scales.