Agnieszka Drobniak

Porosity of Devonian and Mississippian New Albany Shale across a maturation gradient: Insights from organic petrology, gas adsorption, and mercury intrusion

The evolution of porosity in shales with increasing maturity was examined in a suite of five New Albany Shale samples spanning a maturity range from immature (vitrinite reflectance, Ro 0.35%) to postmature (Ro 1.41%). Devonian to lower Mississippian New Albany Shale samples from the Illinois Basin used in this study contain marine type II kerogen having total organic carbon contents from 1.2 to 13.0 wt. %. Organic petrology, CO2 and N2 low-pressure adsorption, and mercury intrusion capillary pressure techniques were used to quantify pore volumes, pore sizes, and pore-size distributions. Increasing maturity of the New Albany Shale is paralleled by many changes in the characteristics of porosity. The total porosity of 9.1 vol. % in immature New Albany Shale decreases to 1.5 vol. % in the late mature sample, whereas total pore volumes decrease from 0.0365 to 0.0059 cm3/g in the same sequence. Reversing the trend at even higher maturity, the postmature New Albany Shale exhibits higher porosity and larger total pore volumes compared to the late mature sample. With increasing maturity, changes in total porosity and total pore volumes are accompanied by changes in pore-size distributions and relative proportions of micropores, mesopores, and macropores. Porosity-related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition, but maturity exerts the dominant control upon these characteristics. We conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences.

Geochemical constraints on the origin and volume of gas in the New Albany Shale (Devonian–Mississippian), eastern Illinois Basin

This study involved analyses of kerogen petrography, gas desorption, geochemistry, microporosity, and mesoporosity of the New Albany Shale (Devonian–Mississippian) in the eastern part of the Illinois Basin. Specifically, detailed core analysis from two locations, one in Owen County, Indiana, and one in Pike County, Indiana, has been conducted. The gas content in the locations studied was primarily dependent on total organic carbon content and the micropore volume of the shales. Gas origin was assessed using stable isotope geochemistry. Measured and modeled vitrinite reflectance values were compared. Depth of burial and formation water salinity dictated different dominant origins of the gas in place in the two locations studied in detail. The shallower Owen County location (415–433 m [1362–1421 ft] deep) contained significant additions of microbial methane, whereas the Pike County location (832–860 m [2730–2822 ft] deep) was characterized exclusively by thermogenic gas. Despite differences in the gas origin, the total gas in both locations was similar, reaching up to 2.1 cm3/g (66 scf/ton). Lower thermogenic gas content in the shallower location (lower maturity and higher loss of gas related to uplift and leakage via relaxed fractures) was compensated for by the additional generation of microbial methane, which was stimulated by an influx of glacial melt water, inducing brine dilution and microbial inoculation. The characteristics of the shale of the Maquoketa Group (Ordovician) in the Pike County location are briefly discussed to provide a comparison to the New Albany Shale.

Spontaneous Combustion and Coal Petrology

This chapter presents the basic concepts of coal petrology and discusses coal parameters that have been noted as potential triggers for spontaneous combustion. Macerals, the microscopically identifiable organic constituents of coal, are one of three basic parameters that define coal. The other two parameters are the coal rank, the measure of metamorphism of the organic constituents, and the inorganic content of the coal, most visibly seen as the minerals associated with coal. Among many factors that trigger spontaneous combustion, oxidation of coal at ambient temperature is the major one. It is an exothermic reaction, the exact mechanisms of which are not fully understood. At very low temperatures, reaction between coal and oxygen is physical (adsorption), and it changes into chemisorptions starting at ambient temperature. Particle size and available surface area are important because adsorption is an important process in coal oxidation. Higher adsorption, and the monolayer capacity in particular, influences the amount of moisture that can be retained in the coal and moisture is frequently cited as the main control on spontaneous combustion. Fractured and faulted thick coal seams with pyrite and organic shale partings are particularly susceptible to spontaneous combustion.

Diversity and composition of cave methanotrophic communities

Methane oxidizing microorganisms (methanotrophs) are a major sink for the greenhouse gas methane (CH4), and have been investigated in several environments. Recent studies show that CH4 consumption in caves is pervasive and is a result of active methanotrophy. However, little is known about what controls the distribution and abundance of methanotrophs in caves. We sampled 42 sediments from 21 caves in North America to elucidate the factors shaping cave methanotroph communities. We hypothesized that cave methanotroph communities should be related to cave-air CH4 concentrations and exhibit dispersal-limited biogeographical patterns due to the insular nature of caves. Using 16S rRNA sequencing, we recovered methanotrophs from 88 % of samples collected, including locations in caves where CH4 concentrations were at or below detection limits (≤ 0.3 ppmv). Methanotrophs from the Methylocystaceae (Type II) were the dominant methanotrophs as has been seen in other environments with low CH4 concentrations. Despite being insular ecosystems, we found that the composition of methanotrophs did not vary with distance, both within and among caves. Instead, we found evidence for a core microbiome, perhaps suggesting that high-affinity methanotrophs are not dispersal limited. Additionally, we observed that the relative abundance of methanotrophs was positively related the proportion of gravel in cave sediments and the relative abundance of methylotrophs. Last, we found that the relative abundance of methanotrophs was inversely correlated with cave-air CH4 concentrations. Our results suggest that methanotrophs in caves have influences on cave biogeochemistry beyond CH4 oxidation and that high-affinity methanotrophs may disperse easily into caves. IMPORTANCE Recent observations have shown that the atmospheric greenhouse gas methane (CH4) is consumed by microorganisms (methanotrophs) in caves at rates comparable to CH4 oxidation in surface soils. Caves are abundant in karst landscapes that comprise 14 % of Earth’s land surface area, and therefore may be acting as a substantial CH4 sink. A detailed ecological understanding of the forces that shape methanotrophic communities in caves is lacking. We sampled cave sediments to better understand the community composition and structure of cave methanotrophs. Our results show that the relative abundance of methanotrophs was negatively correlated with CH4 concentrations in cave air and that methanotrophic communities were similar to each other over distances of 10s of m to 100s of km.

ILLUSTRATING GEOLOGY OF INDIANA WITH ESRI STORY MAPS

Esris Story Maps are a powerful yet easy way to illustrate geologic research. These interactive web applications that combine maps, data, links, photographs, videos, and narrative text are an excellent tool to create dynamic publications and highlight research. More importantly, the end user does not require expensive software or training in cartography and GIS. Easy access to geological data through Story Maps can engage, educate, and hopefully inspire viewers to further research and create their own Story Maps.