Shales Of Devonian Age Research Articles

Spatial and Temporal Correlation of Water Quality Parameters of Produced Waters from Devonian-Age Shale following Hydraulic Fracturing

The exponential increase in fossil energy production from Devonian-age shale in the Northeastern United States has highlighted the management challenges for produced waters from hydraulically fractured wells. Confounding these challenges is a scant availability of critical water quality parameters for this wastewater. Chemical analyses of 160 flowback and produced water samples collected from hydraulically fractured Marcellus Shale gas wells in Pennsylvania were correlated with spatial and temporal information to reveal underlying trends. Chloride was used as a reference for the comparison as its concentration varies with time of contact with the shale. Most major cations (i.e., Ca, Mg, Sr) were well-correlated with chloride concentration while barium exhibited strong influence of geographic location (i.e., higher levels in the northeast than in southwest). Comparisons against brines from adjacent formations provide insight into the origin of salinity in produced waters from Marcellus Shale. Major cations exhibited variations that cannot be explained by simple dilution of existing formation brine with the fracturing fluid, especially during the early flowback water production when the composition of the fracturing fluid and solid-liquid interactions influence the quality of the produced water. Water quality analysis in this study may help guide water management strategies for development of unconventional gas resources.

ELDRAGONITE, Cu6BiSe4(Se2), A NEW MINERAL SPECIES FROM THE EL DRAGON MINE, POTOSI, BOLIVIA, AND ITS CRYSTAL STRUCTURE

Eldragonite, with the simplified formula Cu 6 BiSe 4 (Se 2 ), is a new mineral species discovered in a telethermal vein-type deposit with selenides at the El Dragon mine, Province of Quijarro, Department of Potosi, Bolivia. It forms inclusions in krut’aite, and is associated with clausthalite, klockmannite, umangite and tiemannite, as well as with watkinsonite, petrovicite and two unnamed phases in the system Cu–Pb–Hg–Bi–Se. The unique vein of eldragonite-bearing krut’aite is hosted within sandstones and shales of Devonian age. Eldragonite occurs in anhedral grains and polycrystalline aggregates attaining a size of up to 100 × 80 μm. Megascopically, the mineral has a brownish to light-maroon color, is opaque and lacks internal reflections. It has a metallic luster and a brownish black streak, is brittle with an uneven to conchoidal fracture, without observable cleavage. The VHN 15 values range between 212 and 243 (mean 225) kg/mm 2 , corresponding to a Mohs hardness of ~3 ½. In plane-polarized light, eldragonite is distinctly bireflectant and pleochroic, from light grayish brown to cream; it is strongly anisotropic with rotation tints in shades of orange and blue-black. The reflectances (in air and oil, respectively) for the COM standard wavelengths are: 32.5–34.5, 17.7–19.7 (470 nm), 32.95–36.3, 18.0–21.4 (546 nm), 33.3–36.8, 18.3–21.6 (589 nm), 34.0–36.9, 19.1–21.7 (650 nm). Electron-microprobe analyses gave (mean of 24 analyses): Cu 35.9, Fe 1.25, Ni 0.35, Bi 20.3, Se 42.5, total 100.3 wt.%, corresponding to (Cu 5.98 Fe 0.24 Ni 0.06 ) ∑6.28 Bi 1.03 Se 5.70 . The ideal formula is Cu 6 BiSe 4 (Se 2 ), which requires Cu 35.84, Bi 19.64, Se 44.52 wt.%. Eldragonite has an orthorhombic cell, space group Pmcn , with a 4.0341(4), b 27.056(3), c 9.5559(9) A, V 1043.0(3) A 3 , and Z = 4. The calculated density is 6.76 g/cm 3 . The strongest X-ray powder-diffraction lines [ d in A ( I ) hkl ] are: 6.547(58)031, 3.579(100)052, 3.253(48)141, 3.180(77)081, 3.165(56)013, 3.075(84)102, 3.065(75)151,112, 2.011(53)200, 1.920(76)154, 1.846(52)1103. The crystal structure was solved from single-crystal data, and was refined to R 1 = 0.026 on the basis of 1731 unique reflections. There are one Bi and six Cu positions. Among the six Se positions, two Se atoms form a Se 2 pair [d(Se–Se) = 2.413 A]; eldragonite is thus a mixed selenide–diselenide compound. The crystal structure is organized according to two slabs alternating along a . The thin slab with formula Cu 6 Se 6 is a zigzag layer derived from the CaF 2 archetype; the thick slab, Cu 6 Bi 2 Se 6 , is similar to that of wittichenite, Cu 3 BiS 3 . The Se 2 pair is at the junction between these two slabs. This new mineral species is named after the location where it was discovered.

Variability of chlorinated-solvent sorption associated with oxidative weathering of kerogen

The perchloroethylene (PCE) sorption distribution coefficient ( K d, measured at 40–100 μg/l solution concentration in batch experiments) ranged from 4.0 to 134 l/kg over the sampled thickness (1.0–6.0 m depth) of a moderately-low organic carbon (0.002–0.005), fractured and weathered diamict (poorly sorted, glacially deposited) aquitard. The organic carbon-normalized K d ( K oc) for deeper, unoxidized (reduced) samples from this deposit (log K oc=4.4–4.59) were generally consistent with the kerogen in the underlying Devonian-age shale (log K oc=4.57), a likely source rock for these sediments. The similarities between these samples suggest that the sorption capacity of the kerogen was minimally altered during transport and deposition, and that humic substances were not co-deposited with the kerogen in the glacially-deposited sediments. The K oc within the diamict was correlated to the oxidation state of the organic matter, characterized by the H/O ratio through elemental analysis. The K oc for more oxidized samples from shallower depth samples (log K oc=3.35–3.65) were approximately an order of magnitude less than those determined for the reduced samples. The K oc for 1.5- to 2.5-cm thick oxidation haloes surrounding fractures and characterized by visible Fe-oxidation, were approximately 20–30% lower than the adjacent unaltered matrix samples. The linear trend observed between log K oc and log H/O is similar to, but steeper than, the relation reported previously, which represents increasing sorption magnitude with increasing diagenesis in coal and shale samples. The spatial distribution of the K oc within this aquitard, in concert with qualitative geologic observations, suggests that oxidative weathering of the native kerogen exerts an important control on hydrophobic organic compound sorption.

AN EVALUATION OF THE HYDROCARBON POTENTIAL OF THE SEDIMENTARY BASINS OF LIBYA

Distinctive structural and stratigraphic styles, together with the timely development of source rocks, reservoirs and seals, have produced in Libya the richest hydrocarbon habitats on the African continent. These habitats are located in the Sirte Basin (29,000 MM brl of proved reserves), and Ghadames Basins and Pelagian Shelf (3,000 MM brls of proved reserves). Significant oil discoveries have also been made in the Murzuk Basin (1,500 MM brl of proved reserves) and the offshore Cyrenaica Platform.Four major potential source rocks have been identified in Libya: the Sirte shales (Campanian), the Hagfa shales (Palaeocene), the Tanezzuft shales (Silurian), and shales of Devonian age. The Sirte and Hagfa shales have generated hydrocarbons for most of the prolific reservoirs in the Sirte Basin. The Sirte shales supply hydrocarbons to clastic reservoirs of Cambro‐Ordovician age (the Gargaf Group) and Lower Cretaceous age (Nubian sandstones), and also to Upper Cretaceous carbonates. The Hagfa shales source most of the Tertiary reservoirs in the Sirte Basin and possibly the Cyrenaica Platform. Silurian (Tanezzuft) and Devonian shales supply hydrocarbons to reservoirs of Palaeozoic and Mesozoic ages, particularly Silurian and Devonian sandstones in the Ghadames and Murzuk Basins, and the Cyrenaica Platform.The principal seals in the Sirte Basin are Late Cretaceous and Tertiary shales and anhydrites. Palaeozoic and Mesozoic shales, impermeable carbonates, and occasional anhydrites form the major seals in the Ghadames and Murzuk Basins and the Cyrenaica Platform.

Kohlenstoff- und Sauerstoff-Isotopenuntersuchungen an Karbonatkonkretionen und umgebendem Gestein

The composition of the carbon and oxygen isotopes has been determined in about 40 carbonate concretions and surrounding clays and shales of different geological ages. Two different areas and stratigraphic levels in Northwestern Germany have been sampled: 1. concretions in shales of Lower Cretaceous age fromt he area between Hildesheim and Hannover; 2. concretions in shales of Devonian age from the Harz mountains (and the foreland).

Arthropods and Ancient Man

In spite of any knowledge, recognition, or lack of these, man has had both benefit and serious harm from insects from his appearance on earth. Remains somewhat doubtfully identified as insects, have been recovered from Silurian rocks 200 to 300 million years old while unquestioned insects are known from the Old Red Sandstone and from shales of Devonian age, somewhat more recent. By Carboniferous times, 200 million years or so ago, insects were abundant. All the orders and many present-day genera are known from Tertiary deposits-many of which are 50 million years old. I think it may be assumed from this that many, if not most, of the present day insect species had already acquired their characteristic habits by Recent geological time when man appeared 500,000 or, at most, 1,000,000 years ago. Thus, man and undoubtedly his immediate progenitors, had insect competitors for much of his food and clothing, when he started to use it; pestiferous insects interfered with his activities and disturbed his primitive peace of mind, disease vectors spread pestilence and misery, and parasites infested his person. In fact, “Adam had ‘em” and our ancestors were, without exception, lousy, literally, if not figuratively. On the other hand insects furnished honey, the only sweet known to man until almost modern times, and whenever insect epidemics destroyed the harvest of ancient Agriculture, man was able to subsist for a little while on the insects themselves. Caterpillars, fat grubs and many other insects were delicacies in the dietary of almost all primitive people and of many tribes attaining barbaric or even higher cultural status.