Ohio Shale Research Articles

Accumulation of Organic Matter in the Rome Trough of the Appalachian Basin and Its Subsequent Thermal History: Discussion

666 This discussion is intended to correct a major error of fact concerning the organic carbon concentration of the lower Huron Member of the Ohio Shale in eastern Kentucky. Figure 2 of Curtis and Faure (1997) showed a map of total organic carbon concentrations in the lower Huron Shale, based on data collected for the Gas Research Institute. This map is essentially identical to those previously published by Curtis (1988, his plate II) and Curtis (1990, his figure

Accumulation of Organic Matter in the Rome Trough  of the Appalachian Basin and Its Subsequent Thermal History

We used geochemical data to examine the origin and preservation of organic matter contained in the lower part of the Huron Member of the Ohio Shale formation and the Rhinestreet Shale Member of the West Falls Formation (Devonian) in Kentucky, Ohio, West Virginia, and Virginia. The thermal history of the organic matter was determined by relating relative temperatures experienced by the organic matter to the geologic setting. The organic matter in these formations is predominantly marine in origin and was most probably derived largely from algal organisms. Although the rate of production of marine organic matter may have been uniform within the basin, its preservation apparently was controlled by the existence of a set of fault-bounded anoxic subbasins associated with the Rome trough, a Cambrian structural complex. These subbasins apparently were anoxic because they limited oxygen recharge by circulating waters. Preservation of organic matter was also enhanced by periodic blooms of the alga Tasmanites and similar organisms in the waters above the subbasins during both early Huron and Rhinestreet deposition. A significant negative correlation was identified between the vitrinite reflectance peak temperature, an integrated measure of the thermal history of a rock, and the hydrogen index, a measure of the remaining hydrocarbon-generation potential of kerogen. Although peak temperatures were controlled by burial depth, excess heating occurred locally, perhaps by hot brines rising from depth through fractures associated with major structures in the study area.

Clevelandodendron ohioensis, gen. et sp. nov., a slender upright lycopsid from the late Devonian Cleveland Shale of Ohio

Clevelandodendron ohioensis Chitaley & Pigg gen. et sp. nov. is an almost entire lycopsid plant known from a single compressed specimen from the Cleveland Shale member of the Upper Devonian Ohio Shale. This unique specimen is 125 cm long, consisting of an unbranched, slender, monopodial axis with a partially preserved plant base bearing thick appendages at one end, and a compact, terminal ovoid bisporangiate strobilus at the other. The stem is 2 cm wide for most of its length. Visible on the decorticated stem surface are helically arranged, elongate leaf traces and laterally compressed, slender leaves along the stem margin. The plant base bears 4‐6 thick appendages. The terminal strobilus is compact, ovoid, 9 cm long and up to 6 cm wide, morphologically similar to those of some Lepidodendrales, and bears helically arranged sporophyll/sporangium complexes with narrow bases and distal laminae up to 18 mm long, turned upward. Megaspores are 320‐360 μm, trilete and laevigate, lacking a gula; microspores are 30‐42 μm, trilete, indistinctly punctate and possibly assignable to Calamospora or Punctatisporites. Clevelandodendron demonstrates that slender unbranched lycopsids with an isoetalean plant habit similar to the Carboniferous genera Chaloneria and Sporangiostrobus and Triassic Pleuromeia‐like forms were present as early as the Late Devonian. The early occurrence of this unique habit suggests that diversification within the isoetalean clade sensu Rothwell and Erwin (including both Isoetales and Lepidodendrales) was well established prior to the Carboniferous.

Fractured Shale Reservoirs: Towards a Realistic Model: ABSTRACT

Fractured shale reservoirs are fundamentally unconventional, which is to say that their behavior is qualitatively different from reservoirs characterized by intergranular pore space. Attempts to analyze fractured shale reservoirs are essentially misleading. Reliance on such models can have only negative results for fractured shale oil and gas exploration and development. A realistic model of fractured shale reservoirs begins with the history of the shale as a hydrocarbon source rock. Minimum levels of both kerogen concentration and thermal maturity are required for effective hydrocarbon generation. Hydrocarbon generation results in overpressuring of the shale. At some critical level of repressuring, the shale fractures in the ambient stress field. This primary natural fracture system is fundamental to the future behavior of the fractured shale gas reservoir. The fractures facilitate primary migration of oil and gas out of the shale and into the basin. In this process, all connate water is expelled, leaving the fractured shale oil-wet and saturated with oil and gas. What fluids are eventually produced from the fractured shale depends on the consequent structural and geochemical history. As long as the shale remains hot, oil production may be obtained. (e.g. Bakken Shale, Green River Shale). If the shale is significantly cooled,more » mainly gas will be produced (e.g. Antrim Shale, Ohio Shale, New Albany Shale). Where secondary natural fracture systems are developed and connect the shale to aquifers or to surface recharge, the fractured shale will also produce water (e.g. Antrim Shale, Indiana New Albany Shale).« less

Exceptionally Preserved Arthropod from the Ohio Shale (Upper Devonian) of Ohio

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The Correlation Between Bedrock Uranium and Dissolved Radon in Ground Water of a Fractured Carbonate Aquifer in Southwestern Ohio

AbstractTwo hypotheses have previously been proposed for the source of elevated radon in ground water of southwestern Ohio: (1) penecontemporaneous uranium at the Silurian‐Ordovician unconformity, and/or (2) parent radionuclides transported from fragments of uranium‐rich Ohio Shale within the glacial drift above the aquifer. To further test the first hypothesis, vertical profiles of dissolved radon in ground water and uranium in rock cores were obtained at two locations immediately underlain by the Silurian/Ordovician unconformity. Radon concentrations exceeding 1000 pCi/l occurred in zones where the bedrock had uranium concentrations greater than 1.5 ppm. Radon concentrations of less than 500 pCi/l occurred in zones where the rock had uranium concentrations below 0.25 ppm. A log‐linear regression model between uranium and radon had a correlation coefficient of 0.82. Three aspects of the results support the hypothesis that the source is transported, although not necessarily from fragments of Ohio Shale. First, the high uranium‐radon zones did not occur consistently or exclusively at the Silurian/Ordovician unconformity. Second, the high uranium‐radon zones are correlated to fracture zones having a higher hydraulic conductivity and thus appear to be related to the zones of greater flow and transport. Third, the amount of uranium‐radon disequilibrium increases exponentially with increasing hydraulic conductivity. The hypothesis of a penecontemporaneous source, not supported by our study, arose when previous investigators conducted regional surveys of domestic wells and springs and found a correspondence between elevated radon and the location of the Silurian‐Ordovician unconformity. The observations of the previous investigators can be explained by the fact that the basal Silurian is in some places a horizon of higher hydraulic conductivity that facilitates transport. The two most probable external sources of uranium would be uranium‐containing detritus in the glacial drift or uranium‐containing phosphate fertilizers spread on the surface. Given that the uranium was transported into the aquifer during the Holocene, it could not have generated enough radium in the time elapsed since entering the aquifer to produce the radon levels that were measured. This observation indicates that radium was cotransported with uranium into the zones of high radon.

Comparison of kinetic analysis of source rocks and kerogen concentrates

Shales and kerogen concentrates from the Green River, Rundel, Ohio, Draupne, and Phosphoria formations were examined by Pyromat II micropyrolysis and kinetic parameters were determined by the shift-in- T max, discrete distribution, modified Friedman, and modified Coats-Redfern methods. Overall, the shales and corresponding kerogens exhibited very similar kinetic parameters. Green River, Rundel, and Ohio shales and kerogens exhibited principal discrete activation energies of 54–57 kcal/mol, narrow distributions, and T max at 25°C/min heating rate around 480°C. Draupne and Phosphoria shales and kerogens exhibited kinetic parameters typical of Type II source rocks—principal discrete activation energies of 54–57 kcal/mol, broad distributions, and T max at 25°C/min around 459°C. The discrete distribution kinetic parameters were used to calculate oil generation at laboratory and geological heating rates. Each shale and corresponding kerogen exhibited generation curves and 50% generation temperatures that were very similar. The principal difference was that the kerogens exhibited slightly more oil generation at low temperatures compared to the corresponding shales. Some kerogens exhibited curves which were also shifted to slightly lower temperatures than those of the corresponding shales. For these specific shales and kerogens, the results indicate that kerogen isolation does little to affect the pyrolysis kinetic parameters. Although from a limited number of samples, these results suggest kerogen isolation may not be necessary to derive valid kinetic parameters.

Opportunity knocked and no one was home: Aspinothoracid arthrodires (Placodermi) from the Ohio Shale Formation (Upper Devonian, North America)

The vertebrate fauna from the Ohio Shale formation is a key element to our understanding of aspinothoracid arthrodires. Many of the original descriptions for taxa from this important fauna are based on incomplete material or lack phylogenetic analyses. An ongoing study already has provided redescriptions of a number of these taxa based on a wealth of new material recovered from the Interstate 71 Paleontological Salvage Project. Continuing work centers on remaining problematic taxa from the Ohio Shale. Further analysis of this fauna will provide important information for phylogenetic studies and our understanding of the complex history of the Upper Devonian.

The significance of oil shale fabric in primary hydrocarbon migration

Scanning electron microscopy (SEM) and thin-section analysis of the fabrics (particle orientation) of some well known ‘oil shales’ reveal they all share two common characteristics: (1) even though preferred platy particles dominate, there is present an open network of numerous interconnecting pores; and (2) fine lamination of alternating silt and organic clay-rich zones is common. Shales selected for analysis include the Woodford Shale, Sunbury Shale, torbanite, Rundle Shale and Ohio Shale (Huron Member), West Falls Formation (Rhinestreet Member), New Albany Shale (Clegg Creek Member) and the Exshaw Formation. A model is proposed, based upon fabric information, for the migration of hydrocarbons from source rocks. Hydrocarbons generated in organic-rich zones migrate through the micropores until reaching adjacent silt laminae, which act as ‘pipelines’ to facilitate further migration out of the source rock.

Rock-eval pyrolysis and vitrinite reflectance trends in the Cleveland Shale Member of the Ohio Shale, eastern Kentucky

Within eastern Kentucky, organic petrographic and geochemical data indicate a southeastwards increase in maturation of the Cleveland Shale Member of the Ohio Shale (Devonian-Mississippian). Reflectance levels of dispersed organic material in the Cleveland Shale increase from 0.5% in the outcrop belt in central Kentucky, to slightly over 1.0% in Pike County, eastern Kentucky. A decrease in fluorescence intensity of liptinitic components, such as Tasmanites, accompanies this reflectance increase, as does a shift in fluorescence color of the alginite towards the red. In the highest rank areas, fluorescence is almost absent. Groundmass fluorescence is observed also, and follows trends similar to those shown by the alginite. Kerogen in the Cleveland Shale is primarily Type II, as indicated by petrographic observations and Rock-Eval data. Total organic carbon contents of this shale decrease from over 12% in the outcrop belt, to less than 2% in the eastern-most part of the study area. Source rock potential ranges from good to very good, with the highest potentials occurring in the outcrop belt. T max values for this unit increase from under 430°C in the outcrop belt to over 450°C in the southeast, confirming the increase in maturation trends indicated by vitrinite reflectance data. Both petrographic and geochemical maturation parameters place the Cleveland Shale of eastern Kentucky within the oil window. Comparison with maturation data for Pennsylvanian-age coals upsection suggests that maturation indices are retarded, or suppressed, in the Devonian shales. The level of maturation indicated for the Cleveland may be problematical considering that the Ohio Shale is a major gas-producer in this area.

Geologic and Production Comparisons of the New Albany Shale of the Illinois Basin With the Michigan Basin's Antrim Shale and the Appalachian Basin's Ohio Shale

Geologic and Production Comparisons of the New Albany Shale of the Illinois Basin With the Michigan Basin's Antrim Shale and the Appalachian Basin's Ohio Shale

Testing of an Irati oil shale in a multi-stage fluidized bed retorting process

A Permian Irati oil shale from Brazil was tested in a 7.6cm diameter prototype of the Kentort II process which is a multi-stage fluidized bed retort containing pyrolysis, gasification and combustion zones. To facilitate comparisons, test conditions were maintained similar to those from a recent study utilizing a Devonian shale (Cleveland Member of the Ohio Shale) from Kentucky. The Irati shale was processed with all three zones of the process in operation and solid recirculation was used to transfer heat throughout the reactor. Generally, the Irati shale performed well in the process, but generation of fines was more prevalent. Oil yields averaged 112% of the modified Fischer assay despite the use of recycled solids to transfer heat to the pyrolyser. Due to the more aliphatic nature of the kerogen, carbon conversion to oil was significantly greater for the Irati shale compared to the Cleveland shale. Otherwise, gasification and combustion kinetics and hydrocarbon gas production were similar for the two shales.

CHEMICAL COMPOSITION OF SHALE OIL I. DEPENDENCE ON OIL SHALE ORIGIN

ABSTRACT Shale oils obtained by nitrogen retorting of North Carolina, Cleveland, Ohio, Colorado, Rundle, Stuart, and Condor oil shales have been chemically characterized by g.c.-m.s. techniques. After species identification, chemical compositions of the shale oils have been related to the geological origins of the parent shales. Based on the characteristics observed in the chromatograms, eight semi-quantitative parameters have been used to describe the chromatograms. Six of these parameters describe the relative abundance and distribution of straight chain alkanes and alkenes in the chromatograms. The other two parameters represent the abundance, relative to the total amount of volatiles in the oil, of alkylbenzenes and alkylphenols.

Radon hazards associated with outcrops of Ohio Shale in Ohio

The indoor (basement) radon concentrations and the uranium, organic carbon, and radon contents of samples from the underlying Ohio Shale (Upper Devonian) were investigated in six approximately 100 square kilometer areas of Ashtabula, Cuyahoga, Erie-Huron, Franklin, Pike, and Logan counties. The thickness and lithology of the sediment overburden above the Ohio Shale in these areas also was investigated. Results show that the amount of radon gas emanating from the Ohio Shale is a direct function of the uranium concentration in this geologic unit and that the uranium itself is ultimately controlled by the amount of organic matter. Uranium, organic matter (as measured by total organic carbon), and radon in the Ohio Shale outcrops all increase in a westward direction across Ohio. Similarly, the indoor radon concentration in houses increases from east to west across the state. Where the average thickness of the sediment overburden exceeds 27 m (Franklin and Logan counties), much of the radon in houses may be derived from Ohio Shale clasts in the glacial till. In other areas where the average overburden thickness is 6 m or less (Ashtabula, Cuyahoga, Erie-Huron, and Pike counties), the indoor radon levels appear to be directly controlled by emanations from the underlying Ohio Shale bedrock.

Fractured Gas Reservoirs in the Devonian Shale of the Illinois and Appalachian Basins

The Devonian and Lower Mississippian black shale sequence of Kentucky includes the New Albany Shale of Illinois basin and the Ohio Shale of the Appalachian basin. Fractured reservoirs in the Ohio Shale contain a major gas resource, but have not been so prolific in the New Albany Shale. The authors propose two models of fractured shale reservoirs in both the Illinois and the Appalachian basins, to be tested with gas production data. (1) Where reactivated basement faults have propagated to the surface, the lack of an effective seal has prevented the development of overpressure. The resulting fracture system is entirely tectonic is origin, and served mainly as a conduit for gas migration from the basin to the surface. Gas accumulations in such reservoirs typically are small and underpressured. (2) Where basement faults have been reactivated but have not reached the surface, a seal on the fractured reservoir is preserved. In areas where thermal maturity has been adequate, overpressuring due to gas generation resulted in a major extension of the fracture system, as well as enhanced gas compression and adsorption. Such gas accumulations are relatively large. Original overpressuring has been largely lost, due both to natural depletion and to uncontrolled production. more » The relative thermal immaturity of the Illinois basin accounts for the scarcity of the second type of fractured reservoir and the small magnitude of the New Albany Shale gas resource. « less

Seismic Evaluation of the Devonian Ohio Shale in the Big Ugly Area, Southwestern West Virginia

The Devonian Ohio Shale was studied in the Big Ugly area of southwestern West Virginia by reprocessing and interpreting existing seismic and geologic data. These data suggest the presence of detached structures above three decollement zones and cross-strike discontinuities associated with the Alleghanian deformation west of Mann Mountain anticline. A basement growth structure, the Griffithsville basement high, localized detached structures along its southeast flank. High producing trends of gas from the Devonian Ohio Shale occur either near northwest-trending cross-strike structural discontinuities or in the northeast-trending detached structures where fracture density should be increased.

Characterization of Devonian Ohio Shale SDO‐1 as a USGS Geochemical Reference Sample

Recommended concentrations for 38 elements in the U.S. Geological Survey reference sample, Ohio Shale (Devonian) SDO‐1, are presented here. For an additional 25 elements, average concentrations or ranges are reported for information. Also presented are the supporting analytical data and a description of the statistical procedure used in deriving recommended concentrations from that data. The sample is a brownish‐black, fissile, platy shale containing flattened pyrite nodules and a high organic content. It is typical of “eastern gas shale”, in contrast to the USGS reference sample SGR‐1, which typifies oil shale from the Green River Formation. SDO‐1 was collected from the Huron Member of the Late Devonian Ohio Shale in western Rowan County, Kentucky. The sample is available as fine splits for detailed chemical analysis and as coarse splits for hand, microscopic, and microfossil examination.

Stratigraphic Traps in Silurian Lockport Dolomite of Kentucky

The Lockport Dolomite has yielded commercial quantities of petroleum of nearly 100 years and continues to be an exploration target in eastern Kentucky. Reservoirs are largely confined to porous buildups and to erosional truncation along the Cincinnati arch. These stratigraphic traps developed under the influence of (1) sea level fluctuations, which controlled the development of reefal, skeletal-bank, and ooid-shoal facies across the carbonate shelf, (2) relict topographic highs in the underlying Keefer Sandstone and in the lower Lockport, which provided optimum sites for deposition of boundstones and grainstones, and (3) syndepositional movement of fault blocks, which localized skeletal buildups. Isopach thicks along the western edge of the study area represent erosional remnants beneath the Middle to Upper Devonian unconformity, rather than carbonate buildups. Porosity originated during subaerial weathering in the Devonian, and reservoirs were capped by the impermeable organic-rich Ohio Shale. Away from the unconformity, patch reefs and skeletal banks can be identified by thicks on isopach maps, by their clean gamma-ray signature, and by a relatively high log porosity. The distribution of buildups generally parallels earlier topographic highs or basement faults. Secondary porosity (intercrystalline dolomite and moldic vuggy) formed in the eogenetic zone during lowered sea level, and impermeable lagoonal and tidal-flat carbonates serve as seals. Because of the stacking of poro s Lockport units, eastern Kentucky has good potential for multiple pay zones.

Porosity and Permeability of Eastern Devonian Gas Shale

Summary High-precision core analysis has been performed on eight Devonian gas shale samples from the Appalachian basin. Seven of the core samples consist of the Upper Devonian Age Huron member of the Ohio shale, six of which came from wells in the Ohio River valley, and the seventh from a well in east-central Kentucky. The eighth core sample consists of Middle Devonian Age Marcellus shale obtained from a well in Morgantown, WV. The core analysis was originally intended to supply accurate input data for Devonian shale numerical reservoir simulation. Unexpectedly, the work has identified a number of geological factors that influence gas production from organic-rich shales. The presence of petroleum as a mobile liquid phase in the pores of all seven Huron shale samples effectively limits the gas porosity of this formation to less than 0.2%, and gas permeability of the rock matrix is commonly less than 0.1 μd at reservoir stress. The Marcellus shale core, on the other hand, was free of a mobile liquid phase and had a measured gas porosity of approximately 10%, and a surprisingly high permeability of 20 μd. Gas permeability of the Marcellus was highly stress-dependent, however; doubling the net confining stress reduced the permeability by nearly 70%. The conclusion reached from this study is that the gas productivity potential of Devonian shale in the Appalachian basin is influenced by a wide range of geologic factors. Organic content, thermal maturity, natural fracture spacing, and stratigraphic relationships between gray and black shales all affect gas content and mobility. Understanding these factors can improve the exploration and development of Devonian shale gas.

Subdivision of Lower Portion of Huron Member of Ohio Shale, Kanawha and Boone Counties, West Virginia, and Applications to Gas Production: ABSTRACT

Current work funded by the Gas Research Institute indicates that, in Kanawha and Boone Counties, West Virginia, most gas wells completed in the Devonian shales produce from the lower part of the Upper Devonian Huron Member of the Ohio Shale. Discrete assemblages of black shale emplacement in this part of the Appalachian basin can be discerned and are mappable using log data from wells that penetrate the lower Huron section. Black shale isolith maps across the two-county area show discrete elongate trends of black shale, thinning predominantly from northeast to southwest. These elongate black shale minima are interpreted herein as sites where newly deposited, black organic mud substrates were scoured by the action of relatively high-velocity turbidite plumes entering this part of the basin from shallower regions toward the east and northeast. Turbidite-transported muds and silts were then laid in the newly scoured areas in close vertical and lateral contact with the surrounding black muds. This interfingering of organic black shales with the gray silty shales and siltstones is significant to gas production from the Devonian shales in that the interbedded nature of these rocks provides a mechanism whereby gas generated and held by absorption in the black shales canmore » migrate into the more porous and permeable gray shales and siltstones, hence from there into a fracture system or a well bore.« less