Coal-bearing Sandstones Research Articles

Control of microstructural and mineralogical characteristics on thermo-elastic behaviour of coal-bearing sandstone under mild to high-temperature regimes: Experimental investigation and development of AI prediction models

Control of microstructural and mineralogical characteristics on thermo-elastic behaviour of coal-bearing sandstone under mild to high-temperature regimes: Experimental investigation and development of AI prediction models

Study on the Influence of Sample Size on the Mechanical and Integrity Characteristics of Coal Measure Sandstone under High Strain Rate

In order to explore the size effect of the mechanical and damage characteristics of coal measure sand stones under dynamic load, uniaxial impact compression tests were carried out on coal-bearing sand stones with a diameter of 50 mm and a length–diameter ratio of L/R = 0.5, 0.8, 1, 1.2, 1.5, 1.8, and 2 by using the Hopkinson pressure bar test system. The size effect law of the mechanical properties and energy dissipation of coal-bearing sandstone under a high strain rate were investigated. Then, the mercury injection test was carried out on the fragments at different positions, and the electron microscope scanning test was carried out on the fragments near the end of the transmission rod. Based on the area damage definition method and normalization treatment, the integrity model of coal measure sandstone, considering the influence of the length–diameter ratio, was established. The results showed that the peak strength and dynamic elastic modulus of coal measure sandstone increased first and then decreased with the increase in length–diameter ratio under impact compression load, and they reached the maximum when the length–diameter ratio was 1.2. The dynamic peak strain increased gradually with the increase in length–diameter ratio. The energy of coal-bearing sandstone showed strong size effect, that is, the total absorbed energy, elastic energy, and dissipated energy increased with the increase in length–diameter ratio, and the size effect of total absorbed energy was the most obvious. Under the same impact pressure, the porosity of coal-bearing sand stones with seven kinds of length–diameter ratios near the incident end was roughly the same. But when the length–diameter ratio was greater than 0.5, the porosity decreased gradually with the increase in the distance from the incident end. And the larger the length–diameter ratio, the more obvious the decreasing trend. When the length–diameter ratio was smaller, the size of the holes and cracks and the cluster density were larger. The integrity model of coal measure sandstone, considering the influence of the length–diameter ratio, showed that the larger the length–diameter ratio, the better the relative integrity of coal-bearing sandstone.

Hydrogeochemical modelling of groundwater in a fractured Carboniferous sandstone aquifer

Deep groundwater monitoring in tight bedrock is not commonly performed and rarely documented. For a case study in Bochum, NRW, deep monitoring wells allow groundwater investigation in the outcropping Carboniferous down to a depth of 186 m. Groundwater monitoring was carried out by combining sampling of the monitoring wells and local springs at the site. Inverse models were developed using the hydrogeochemical code PHREEQC to understand the natural geochemical processes of deep groundwater in the coal-bearing sandstone. The identified hydrogeochemical processes are pyrite oxidation in shallow fracture systems and Na-Ca/Mg cation exchange in deep fracture systems. Core samples reveal fractures containing Fe-dolomite and calcite cements. A freshening process dominates the deep fractured rocks, where fresh water is flushing a saline aquifer. The data presented here support the planning of further monitoring wells and help to improve future modelling approaches.

Pollution Characteristics and Spatial Distribution of Heavy Metals in Coal-Bearing Sandstone Soil: A Case Study of Coal Mine Area in Southwest China.

Soil pollution in coal mining areas is a serious environmental problem in China and elsewhere. In this study, surface and vertical profile soil samples were collected from a coal mine area in Dazhu, Southwestern China. Microscopic observation, concentrations, chemical speciation, statistical analysis, spatial distribution, and risk assessment were used to assess heavy metal pollution. The results show that the weathering of coal-bearing sandstone and mining activities substantially contributed to soil pollution. The concentrations of Fe, Ni, Cu, Zn, Mn, Cd, Hg, and Pb exceeded their background values. Cd caused the most intense pollution and was associated with heavily–extremely contaminated soils. The residual fraction was dominant for most metals, except Cd and Mn, for which the reducible fraction was dominant (Cd: 55.17%; Mn: 81.16%). Zn, Ni, Cd, and Cu presented similar distribution patterns, and Hg and As also shared similar distribution characteristics. Factor 1 represented anthropogenic and lithologic sources, which were affected by mining activities; Factor 2 represented anthropogenic sources, e.g., fertilizers and traffic pollution; and Factor 3 represented the contribution of metals from soil-forming parent material. More than half of the study area had high pollution risk and was not suitable for vegetable cultivation.

Temporal variation of hydrogeochemical characteristics and processes of aquifers in the Liuqiao coal mine

Studying the characteristics and hydrogeochemical evolution processes of groundwater can contribute to the prevention of water-related hazards and ensure sustainable management of groundwater resources. In this study, the hydrogeochemical characteristics and evolution processes of the coal-bearing sandstone aquifer and Carboniferous limestone aquifer of the Taiyuan formation in the Liuqiao coal mine in Huaibei coalfield were assessed using piper diagram, Gibbs diagrams, ionic proportion ratios, and principal component analysis (PCA). The results showed that Na+ + K+ and SO42− were the dominant cations and anion, respectively, in both aquifers. The coefficients of variation of six hydrochemical parameters increased gradually, reflecting the formation of different water chemical compositions. The formation of hydrochemical compositions was dominated by water-rock interaction, including the dissolution of rock salt, cation exchange adsorption and pyrite oxidation. In addition, the PCA revealed two first components, explaining the highest proportion of variance. Over time, the water sample points were mostly found in the second and third quadrants, indicating the groundwater salinization effect as a result of the gradual increase in the cation alternating adsorption.

The effects of micro- and meso-scale characteristics on the mechanical properties of coal-bearing sandstone

Studying the effects of the micro- and meso-scale characteristics of coal-bearing sandstone on its mechanical properties can provide basic data and accumulated experience for the development of technology for the in situ testing of the strength of rock masses. In this paper, the micro- and meso-structures, mineral composition, and elemental contents of 16 kinds of sandstone from three coal mines were studied through X-ray diffraction and polarizing microscope analysis. The stress–strain evolutional characteristics of different sandstone samples were obtained through uniaxial compression, tension, and shear tests under acoustic emission monitoring, and the effect of various micro- and meso-characteristics on the mechanical properties and failure characteristics of the sandstones was investigated. The results show that the strength, elastic modulus, cohesion, and friction coefficient all increase with increasing quartz content and degree of particle contact, and decrease with increasing plagioclase and clay mineral content, especially kaolinite content. The failure mode of sandstone samples is mainly shear failure during uniaxial compression, the larger the particles and the lower the quartz content, the higher the RA value generated near the peak, indicating that more tensile failure occurs. Furthermore, the strength damage model and damage constitutive model are established by acoustic emission measurement data. These results could provide useful reference for the development of intelligent systems for the in situ testing of the mechanical properties of coal and rock masses.

Occurrence, Classification and Formation Mechanisms of the Organic-Rich Clasts in the Upper Paleozoic Coal-Bearing Tight Sandstone, Northeastern Margin of the Ordos Basin, China

The detailed characteristics and formation mechanisms of organic-rich clasts (ORCs) in the Upper Paleozoic tight sandstone in the northeastern margin of the Ordos Basin were analyzed through 818-m-long drilling cores and logging data from 28 wells. In general, compared with soft-sediment clasts documented in other sedimentary environments, organic-rich clasts in coal-bearing tight sandstone have not been adequately investigated in the literature. ORCs are widely developed in various sedimentary environments of coal-bearing sandstone, including fluvial channels, crevasse splays, tidal channels, sand flats, and subaqueous debris flow deposits. In addition to being controlled by the water flow energy and transportation processes, the fragmentation degree and morphology of ORCs are also related to their content of higher plants organic matter. The change in water flow energy during transportation makes the ORCs show obvious mechanical depositional differentiation. Four main types of ORC can be recognized in the deposits: diamictic organic-rich clasts, floating organic-rich clasts, loaded lamellar organic-rich clasts, and thin interlayer organic-rich clasts. The relationship between energy variation and ORCs deposition continuity is rarely studied so far. Based on the different handling processes under the control of water flow energy changes, we propose two ORCs formation mechanisms: the long-term altering of continuous water flow and the short-term water flow acting triggered by sudden events.

Porosity evolution of two Upper Carboniferous tight-gas-fluvial sandstone reservoirs: Impact of fractures and total cement volumes on reservoir quality

Abstract Cyclic fluvial, coal-bearing sandstones from the Upper Carboniferous are important tight-gas reservoirs in the Lower Saxony Basin, NW Germany. Two wells from two fields located 10 km apart, both comprising of Westphalian C/D fluvial sandstones were studied. Well A was affected by approximately 1.2 km and well B of approximately 2.8 km of basin inversion after maximum burial depths larger than 5 km. Both fields display significant differences in recovered resources. An integrated core study combining sedimentological, petrographic and petrophysical data illustrates the impact of different diagenetic pathways. While permeability values appear in the same range of 0.01–1 mD for both fields, lithologies from well A of field A have average matrix porosities of 6% in a generally unfractured reservoir, whereas lithologies from well B of field B have matrix porosities of 10% in an overall fractured reservoir. Intense siderite/ankerite cementation in matrix and fractures is present in sandstones from both fields and can be related to fluid migration during basin inversion. In contrast, the strong alpine tectonic inversion affecting field B results in a lower thermal exposure since the late Cretaceous, resulting in smaller quartz cement volumes than in field A and larger matrix porosities in field B. Thus, matrix porosity is overall better due to smaller total cement volumes in field B. The study indicates a strong impact of fractures on tight sandstone reservoir quality and quartz cementation on hydrocarbon production performance from the sandstone matrix. Observations may be applicable to similar, strongly inverted tight gas sandstone fields and may directly affect exploration strategies.

Foraminiferal-based paleobiogeographic reconstructions in the Carboniferous of Iran and its implications for the Neo-Tethys opening time: a synthesis

The biogeographic distribution of foraminifers and their belonging to either the southern or northern margins of the Paleo-Tethys are used here for paleogeographic reconstructions of Iran during the Carboniferous. Lower Carboniferous foraminiferal assemblages from northern and central Iran show a cosmopolitan character and affinities to both the southern and northern borders of the Paleo-Tethys. Hence, in the Early Carboniferous Iran occupied an intermediate southern latitude position, forming part of Gondwana. This conclusion is consistent with the Late Ordovician to Early Carboniferous drift history of Iran based on paleomagnetic data. In the Late Carboniferous, the foraminiferal affinities of northern and central Iran with the northern part of Paleo-Tethys suggest that Iran separated from Gondwana and moved northwards to a lower latitude. This separation is also evidenced by the Upper Carboniferous coal-bearing sandstones of the Sardar Formation and sandstones with high degree of chemical weathering, which would indicate warm and humid conditions. Considering the composition of foraminiferal fauna along with the evidence of magmatic activities in northwest Iran, it can be inferred that the commencement of the Neo-Tethys opening and continental break-up in Iran occurred sometime in the Late Carboniferous, which contradicts the previous claims that the separation of Iran from Gondwana occurred in Permian and/or Triassic times.

OUTBURST HAZARD OF SANDSTONES OF THE TYAGLIV FIELD OF THE SOUTH-WESTERN COAL REGION OF THE LVIV-VOLYN BASIN

We have investigated coal-bearing sandstones of the Tyagliv field of the Lviv-Volyn Basin (LVB). The complex of investigations on prediction of their outburst hazards has been conducted on the basis of geologicalprospecting and geological-geophysical data. A special attention was paid to the wells that expose rocks occurred at a depth of over 700 m because it was proved that in the conditions of the LVB outbursts are absent at lesser depths. We have determined main petrographic indications that have an influence upon outburst hazard of sandstones (the amount of clastic and regenerative quartz, micaceous-clayed minerals, the size of clastic grains and extension and the type of contacts between the graines). On the basis of the calculated complex criterion of outburst hazard “B” it was possible to construct transverse profiles of the coal-bearing series with singling out of outburst-safe («В» < 0.4), low degree of outburst hazard (0.4 < «В» < 0.6), outbursthazardous (0.6 < «В» < 1.0) sandstones. The Tyagliv field is the most gas producing one within the limits of the Lviv-Volyn Basin. While studying we have determined that sandstones n 6 1 Sn 7 , n 8 Sn 9 , n 9 Sb 4 are potentially outburst-hazardous ones and at the same time they may be good collectors of accompanying gas-methane.

Reconnaissance study of organic geochemistry and petrology of Paleozoic-Cenozoic potential hydrocarbon source rocks from the New Siberian Islands, Arctic Russia

A reconnaissance study of potential hydrocarbon source rocks of Paleozoic to Cenozoic age from the highly remote New Siberian Islands Archipelago (Russian Arctic) was carried out. 101 samples were collected from outcrops representing the principal Paleozoic-Cenozoic units across the entire archipelago. Organic petrological and geochemical analyses (vitrinite reflectance measurements, Rock-Eval pyrolysis, GC-MS) were undertaken in order to screen the maturity, quality and quantity of the organic matter in the outcrop samples. The lithology varies from continental sedimentary rocks with coal particles to shallow marine carbonates and deep marine black shales. Several organic-rich intervals were identified in the Upper Paleozoic to Lower Cenozoic succession. Lower Devonian shales were found to have the highest source rock potential of all Paleozoic units. Middle Carboniferous-Permian and Triassic units appear to have a good potential for natural gas formation. Late Mesozoic (Cretaceous) and Cenozoic low-rank coals, lignites, and coal-bearing sandstones also display a potential for gas generation. Kerogen type III (humic, gas-prone) dominates in most of the samples, and indicates deposition in lacustrine to coastal paleoenvironments. Most of the samples (except some of Cretaceous and Paleogene age) reached oil window maturities, whereas the Devonian to Carboniferous units shared a maturity mainly within the gas window.

Geochemical and environmental baseline of major and trace elements in Zarand coals, southeastern Iran

In order to establish a geochemical baseline for environmental impacts of coal measures in Rhaeto-Jurassic Zarand coalfields, multielement geochemistry of 22 host rocks, 26 coal seams and 9 coal ashes was determined by ICP-MS, ICP-AES, XRF, PGM-ICP24 and CV-ASS methods at ALS Chemex, Canada. The discrimination diagrams of major trace elements show a continental margin granitoid arc provenance for coal-bearing sandstones and shales. Compared to the crustal abundance, world coals and American coals, the geochemical baseline for most of the elements is within the limits of safeguard background values. However, higher contents of Li (49.31–185 mg/kg), Rb (71.12–131.73 mg/kg), Cs (7.13–16.12 mg/kg), V (72.19–213.1 mg/kg), Th (7.63–11.8 mg/kg), As (10.1–31.31 mg/kg), Nb (5.4–15.07 mg/kg),Ta (0.4–1 mg/kg), Hf (1.89 mg/kg), Ga (12.63–32.16 mg/kg), Ce (37.31–64.28 mg/kg), Pb (40.23–55.76 mg/kg), Cr (48.23–133 mg/kg), Zr (60.39 mg/kg), and Hg (0.24 mg/kg), are of some environmental as well as economic concerns. The low values of B (0.12–12 mg/kg), S (7,839–10,567 mg/kg) and Zn (63.25–157.6 mg/kg) in Zarand coals may indicate a fluvial freshwater environment of coal deposition. Au, Pt and Pd contents are slightly higher than the crustal abundance and further studies are required for their possible environmental and economic evaluation. As the mean Hg value in ash (0.0075 mg/kg) is almost 32 times lower than the mercury content of the coal seams (0.24 mg/kg), it is noteworthy that much of Hg is released by coal combustion to the atmosphere, which has certainly a detrimental environmental impact. The Ce, Cs, Ga, La, Li, Rb and V values are much higher than the average world and American coals and merit further investigations for being the economic by-products.

ABSTRACT: Sequence Stratigraphic Analyses of the Upper Cretaceous Deposits, Rio Grande Embayment, Using Well Logs, Cores and Outcrops

ABSTRACT The present study is an attempt to solve problems of stratigraphic correlation in the Upper Cretaceous strata, Rio Grande Embayment, using sequence stratigraphic principles applied to cores, outcrops and wireline log information. Well-defined log signatures, supplemented by core and outcrop data, were observed and correlated between boreholes. Chronostratigraphically significant surfaces, especially transgressive surfaces, were correlated. Upward-coarsening sand units within the three Upper Cretaceous progradational wedges, San Miguel, Olmos and Escondido formations, encased in prodelta and shelf mudstones were laterally correlated through the study area. Observations indicate a basinward decrease in number of sand units and net sandstone thickness. Outcrop studies in Maverick County indicate deposition of the coal-bearing Olmos Formation in the lower deltaic plain whose upper part is eroded and unconformably overlain by transgressive units of the Escondido Formation. Cored intervals through reservoir-quality clean and mature sandstones from the San Miguel Formation confirm long reworking history by wave action and longshore currents forming strand plain deposits within a wave dominated deltaic setting. Cores sampled in the updip position indicate more tight and argillaceous sandstones with more fluvial influence and low reservoir potential. Downdip Olmos and Escondido formations were interpreted to belong to a transgressive systems tract. Updip Olmos, a coal-bearing sandstone and shale sequence of coastal-plain and deltaic origin, is more argillaceous and low reservoir quality and belongs to a highstand systems tract. End_of_Record - Last_Page 4-------

Chapter 20 Paleogene history

The Paleogene chapter of Svalbard history is a quite distinct one. It begins with an unconformity, albeit a sub-parallel one representing a late Cretaceous hiatus. Resting on Albian and older strata, the Van Mijenfjorden Group of six formations totals a thickness of about 2500 m in the Central Basin of Spitsbergen. The outcrop is ringed by Early Cretaceous strata in a broad syncline (Fig. 20.1). The strata are largely non-marine, coal-bearing sandstones, with interbedded marine shales and they range in age through Paleocene and Eocene. From latest Paleocene through Eocene time the West Spitsbergen Orogeny caused (Spitsbergian) deformation along the western border of the Central Basin, but it is most conspicuous in the folding and thrusting of Carboniferous through Early Cretaceous rocks. The orogen extended westwards to and beyond the western coast of central and southern Spitsbergen including Precambrian and Early Paleozoic rocks, which had already been involved in earlier tectogenesis. The eastward-verging thrusting extended beneath the Tertiary basin and reactivated older faults to the east. In the wider context Svalbard, adjacent to the north coast of Greenland, had been an integral part of Pangea from Carboniferous through Cretaceous time. The northward extension of the Atlantic opening reached and initiated the spreading of the Arctic Eurasia Basin at the beginning of the Paleogene Period. This led to the separation of Svalbard together with the Barents Shelf and northern Europe from Greenland by dextral strike-slip transform faulting. In the course of this progression, oblique collision between northeast Greenland and Svalbard caused

Mineralogy and phase-chemistry of an Ir-enriched pre-K/T layer from the Lattengebirge, Bavarian Alps, and significance for the KTB problem

Three distinct iridium anomalies are exposed in the Cretaceous-Tertiary boundary (KTB) section of the Lattengebirge, Bavarian Alps, comprising a pelagic calcareous sequence from below a continental slope. Multiple Ir anomalies are in contrast to most reported K/T sections which are characterized by a single Ir peak. Two of these Ir spikes are contained in the 20 cm thick actual KTB termed “clayey interval” with the main peak of 4.4 ppb precisely at the boundary, and the second peak of 2.8 ppb 10 cm above. A third peak of 3.6 ppb was detected at 16 cm below the KTB in a thin, turbiditic and coal-bearing sandstone layer of Upper Maastrichtian age. The distribution of Ir anomalies provides evidence of episodic Ir-delivering events over an extended period of time. Whereas the worldwide distributed single-spiked KTB layers are composed entirely of diagenetically altered materials, various phases are discernible in the well preserved Ir-bearing pre-K/T layer: (1) sandstone clastic minerals in a carbonate matrix, (2) coal which is partly burned, (3) sulfides (chalcopyrite) included in coal, and (4) silicate melt glasses. The glasses represent the first ones reported from a K/T section, and were formed by combustion metamorphism from sedimentary parent rocks of the coal as indicated by their major element chemistry and REE patterns. Phase-chemistry of the layer components reveals Ir concentrations of up to 110 ppb indicating that Ir and chalcophile trace elements (TRE) are primarily contained in the sulfides. This carrier-phase points to Ir enrichment by processes unrelated to impact, and its stratigraphic position demonstrates availability of Ir for incorporation into sediments before the KTB. The uptake of Ir and chalcophile TRE into the coal and subsequent combustion-metamorphism occurred on the continent during a time interval of 14,000–9000 yr prior to the KTB as constrained by radiometric age determinations, stratigraphy, and sedimentation rates. In the Lattengebirge K/T sediments no indications of shock are found. The results suggest a volcanic origin for the multiple Ir-bearing horizons. Like the worldwide KTB layers, they are concomitantly enriched in Ir and chalcophile TRE and, hence, have a common source. The Lattengebirge K/T profile is largely continuous, and was recently reexamined by micropaleontological methods (contribution by D. Herm and K.F. Weidich). The preservation of multiple Ir anomalies is attributed to high sedimentation rates of 1.75 cm/kyr and the absence of carbonate dissolution and condensation of sediments usually encountered in the worldwide KTB layers.

Lower Carboniferous Palynomorphs from Um Bogma, Sinai (Egypt)

Abstract Thirty-two species of spores and acritarchs were recovered from the Carboniferous coal-bearing sandstones (Abu Thora Formation) of southwestern Sinai (Egypt). The obtained microflora restricts the formation to the Upper Viséan Stage. These sporomorphs exhibit apparent similarity to late Viséan palynomorphs recently recorded from the subsurface of the extreme western part of Egypt. Three acritarchs and the miospore genera Dibolisporites, Acinosporites, Apiculatisporites, Apiculatisporis and Anaplanisporites are identified for the first time from the paralic Carboniferous rocks of Sinai.

Palynostratigraphy of the sedimentary formations of Assam, India:4. Age of the laitryngew-mawkma coal-bearing sandstones and their relationship with the Charra formation

The present paper deals with the age of the coal-bearing sandstones of the Laitryngew-Mawkma area and their relationship with the Cherra Formation. Climatic condition and depositional environment at the time of deposition have been summarized. Since Medlicott first distinguished the coal-bearing sandstones of Laitryngew-Mawkma area, the age of these rock units have tacitly been accepted as the “Lakadong Sandstone Stage" (Lower-Middle Eocene). On the basis of stratigraphical similarity, they have been equated with the coal-bearing sandstone of Mawmluh (Lower Cherrapunji; Longitude 91°42'30" E: Latitude 25°15'15"N). Recent palynological and palaeontological studies of the sedimentary formations of the South Shillong Plateau have shown that these coal-bearing sandstones may be slightly older than what they were previously regarded. The results of the heavy mineral studies also seem to conform to palynological dating.&#x0D; Since these sandstones apparently seem to be older than the Lakadong Sandstone, they may be a continuation of the sedimentary succession developed at Cherrapunji, and hence Palaeocene in age. The fossils suggest the prevalence of subtropical climate and a shallow, fresh-water or lagoonal environment of deposition.

Paleocurrent analysis of Lower Gondwana sedimentary rocks, Pench Valley coalfield, Madhya Pradesh (India)

The Lower Gondwana sequence (mostly Permian) of the Pench Valley coalfield in central India includes three formations as follows in ascending order: Talchir, comprising diamict/?tillite, sandstone and shale; Barakar, largely an assemblage of coal-bearing sandstone; and Motur, representing a sequence mostly of sandstone and mudstone. The paleocurrent study of these formations is based on dimensional pebble fabric of diamicts and cross-bedding dip azimuths of sandstone. The study reveals that the sediment transport during deposition of the Lower Gondwana formations in this area was persistently from the southeast to the northwest direction. Analysis of cross-bedding dip azimuthal data at various levels of sampling reveals that streams which deposited the Barakar and Motur sediments in the Pench Valley Basin had a sinuous regimen. Total variance values of foreset dip azimuth further suggest that the variability was low for streams which deposited the Barakar sand but high for those which laid down the Motur sediments; the former implying, probably, a “braided” pattern, whereas the latter a “meandering” pattern, an inference appropriately supported by the lithology and bedding types of the two formations.