Coal Accumulations Research Articles

Study of a Low-Cost Method for Estimating Energy Fuel Resources in Anthropogenic Sediments

Abstract In 2021, at the request of PJSC “Dnepropetrovsk Coke Plant”, city Kamianske, we conducted research at the facility where coke-chemical waste is stored on one of the coal waste collectors. The study area was 9.37 ha. The research subject was anthropogenic formations, which were formed due to the storage of coal-floated sediments on the company’s premises. The research aimed to determine the characteristics and analysis of the quantity and quality of coal accumulations, determine the retention of the insulating layer and its composition, and create maps of the quality and capacity of accumulated anthropogenic sediments. The ordering company decided to use both – the latest ground penetration technology and the traditional methods of drilling and laboratory, thanks to which an unusually large number of parameters were obtained and processed during the research process. Similar research was conducted on other industrial facilities, but to a much lesser extent; since we have implemented a combined, comprehensive methodology for the assessment of anthropogenic deposits, because of which the effectiveness of geological research and economic assessment increased, the time of conducting research shortened to 40-45 calendar days, and the cost of such tests decreased five times. At this stage, some things could be improved in the methodology, such as imperfection of the mathematical model and methodology of statistical data processing. These errors will be eliminated during further modelling work under the prepared implementation plan for the tested methodology.

Sequence paleogeography and coal accumulation model in the fluvio-lacustrine rift basin: The Lower Cretaceous of the Huhehu Sag of Hailar Basin, Inner Mongolia (NE China)

Significant volumes of coals can be preserved in fluvio-lacustrine rift basins but prediction of occurrence and geometry within a sequence-stratigraphic framework is always a challenge. The Huhehu Sag is a continental rift basin in Hailar Basin of NE China, with the Damoguaihe and Yimin formations of Lower Cretaceous as the main coal-bearing strata. In this study, the sedimentary facies, sequence stratigraphy, paleogeography, and coal accumulation characteristics in the Huhehu Sag are analyzed. Data used includes boreholes, geophysical well logs and seismic profiles. The coal-bearing strata are mainly composed of conglomerates, sandstones, siltstones, mudstones, and coals. Alluvial fan, braided fluvial, fan delta, braided fluvial delta and lacustrine depositional systems are identified. Coal seams were mainly formed in lacustrine and delta depositional systems. Six third-order sequences were subdivided according to sequence boundaries represented by regional unconformities, basal surfaces of incised valley fills, facies-reversal surfaces, and abrupt color changes related to the base level changes. Sequence 1 corresponds to the Tongbomiao Formation formed in the early syn-rift phase, Sequence 2 corresponds to the Nantun Formation formed in the syn-rift climax phase, Sequence 3 and 4 span the Damoguaihe Formation, with Sequence 3 formed in the syn-rift climax phase and Sequence 4 formed in the late syn-rift phase, and Sequence 5 and 6 span the Yimin Formation which were formed in the post-rift stage. All six sequences were developed with littoral-sublittoral lake, delta front and delta plain paleogeographic units. Sequence 1 to Sequence 2, Sequence 3 to Sequence 4 and Sequence 5 to Sequence 6 are of progradational patterns, while Sequence 2 to Sequence 3 and Sequence 4 to Sequence 5 display retrogradational features. From Sequence 1 to Sequence 4, the syn-rift led to the thickening of strata as well as the coal seams towards the eastern side of the sag. In Sequence 5 and 6, post-rift thermal sagging caused the wide distribution of the strata with the depositional centers as well as the thick coals being distributed in the central belt of the sag. Coals were mainly developed in the transgressive systems tract (TST) and highstand systems tract (HST) of Sequences 4 and 5. The favorable paleogeographic units for thick coal accumulations were mainly littoral-sublittoral lacustrine and delta. The Huhehu Sag is interpreted as an overfilled basin, we further divided the overfilled basin into three subtype basins by accommodation space, including the low, moderate, and high accommodation overfilled basins. In the low accommodation overfilled basin, the relatively thick coals were developed near the maximum flooding surface, while in the moderate accommodation overfilled basin, the relatively thick coals were developed in the lower-middle part of TST and the middle part of HST. These results could be used to predict the preferred depositional environments and favorable areas for coal and coalbed methane exploration in the fluvio-lacustrine rift basins.

САМОВОЗГОРАНИЕ УГЛЕЙ В УСЛОВИЯХ КРИ0ЛИТ030НЫ

Taking into account the prospects for the growth of coal production in the conditions of the North-East, the countries require further development of research to more reliably justify measures to prevent endogenous fires in the permafrost zone, which cause serious economic damage and worsen the environmental situation due to the release of large amounts of toxic gases. The authors have studied the chemical activity and tendency to spontaneous combustion of coals in the permafrost zone. The effect of ambient temperature on the dynamics of oxidative processes in coal accumulations is shown. These studies have identified the main factor in preventing the endogenous fire hazard of coal deposits in the North-East of the country, which consists in maintaining negative or low air temperatures to prevent the intensification of oxidative processes in the coals of the permafrost zone. In laboratory conditions, the influence of physical and chemical factors on the process of spontaneous combustion of frozen coals was studied. Field experiments were carried out on many coal mines in the permafrost area. A system analysis and generalization of domestic and foreign methods of prevention of spontaneous combustion of coals has been carried out. Antipyrogenic compositions have been proposed to reduce the oxidizing ability of coals

Effects of Void Scale of Coal Accumulation on Methane-Air Flame Propagation and Overpressure Dynamics

ABSTRACT With the coal mining toward depth, there is an increased probability of gas explosion accidents. While the propagation characteristics of gas explosion on account of goaf environment have not been determined yet, which has great significance for the prevention of the goaf fire spreading to working face. This paper investigates the critical void scale of coal piles that allowed for the propagation of gas explosion flames using a closed duct with the dimensions of 100 × 20 × 10 cm. The void ratios of the stacked coals varied in 0.554, 0.521, 0.492, and 0.471. The results show that the increased flame speed in the coal accumulations poses a greater explosion hazard. While the smaller coal particle sizes are more advantageous for the suppression effect on flame velocity. The explosion duration is inversely proportional to the void ratio, which mainly depends on the void diffusion stage and the flame extinction stage. Moreover, the maximum overpressure and (dP/dt)max of the explosions attenuate with the decrease in the void scale. The critical void ratio of coal accumulation is between 0.47 and0.49 for premixed methane-air flame with an equivalence ratio of 1. The irregular coal geometry makes flame quenching easier. The void-scale effect of accumulations on flame propagation should be fully considered in the explosion prevention works.

The evolution of nanopores and surface roughness in naturally matured coals in South China: An atomic force microscopy and image processing study

The coals in South China has not been well investigated because the coal mines are small in volume compared with the well-known large-scale coal accumulations in North China, thus the nature of such coals is of significance to study. The nanopore characteristics and surface roughness of 14 coal samples that have experienced low degrees of tectonic deformation as a naturally matured coal series in South China were addressed. Atomic force microscopy (AFM) and image processing were applied in a study of relationships between nanopore development, surface roughness, and thermal maturity (indicated by vitrinite reflectance; Ro = 0.65%–4.43%) in the naturally matured coal series. The results show that areal porosities of the coal samples are 0.78%–9.33%, with mean pore sizes of 7.9–27.9 nm. There were three main stages of pore evolution related to thermal maturity, with Ro values of <1.3%, 1.3%–3.7%, and >3.7%. Pore number, areal porosity, and mean pore size follow a cyclical downward/upward trend across the three stages. Arithmetical mean (Ra) and root-mean-square (Rq) surface roughness values are 1.69–17.74 nm and 2.24–28.81 nm, respectively. Ra and Rq values of coal samples with relatively low thermal maturity (Ro < 1.3%) are controlled mainly by coal maceral and mineral composition, whereas values for coals with relatively high thermal maturity (Ro > 1.3%) are controlled by nanopore development. Thermal maturity is an important factor that influences the nanopore and surface roughness characteristics of naturally matured coals in South China.

Developing methanogenic microbial consortia from diverse coal sources and environments

Biogenic gas production is a promising alternative or supplement to conventional methane extraction from coalbeds. Adsorbed and free gas, generated over geologic time, can be supplemented with biogenic gas during short-term engineering operations. There are two generic protocols for doing this. The first is to contact the coal with nutrients to support native bacterial development. The second approach is to inject appropriately cultured ex-situ consortia into subsurface coal accumulations. Research has mainly focused on the former: in-situ stimulation of native microbial communities with added nutrients. Relatively few studies have been conducted on the strategies for enriching ex-situ microbial populations under initial atmospheric exposure for subsequent injection into coal seams to stimulate biodegradation, and methanogenesis. To evaluate the feasibility of ex-situ cultivation, natural microbial populations were collected from various hydrocarbon-rich environments and locations characterized by natural methanogenesis. Different rank coals (i.e., lignite, sub-bituminous, bituminous), complex hydrocarbon sources (i.e., oil shale, waxy crude), hydrocarbon seeps, and natural biogenic environments were incorporated in the sampling. Three levels of screening (down-selection to high grade the most productive consortia) allowed selection of microbial populations, favorable nutrient amendments, sources of the microbial community, and quantification of methane produced from various coal types. Incubation periods of up to twenty-four weeks were evaluated at 23 °C. Headspace concentrations of CH4 and CO2 were analyzed by gas chromatography. After a two-week incubation period of the most promising microbes, generated headspace gas concentrations reached 873,400 ppm (154 sft3/ton or 4.8 scm3/g) for methane and 176,370 ppm (31 sft3/ton or 0.9 scm3/g) for carbon dioxide. Rudimentary statistical assessments – variance analysis (ANOVA) of a single factor - were used to identify trends and levels of significance or impact of the consortia enrichment. It was demonstrated that microbial communities from coal and lake sediments can be enriched and adapted to effectively generate methane under initial atmospheric exposure. The development and enrichment of these methanogenic consortia is described.

Coal-forming through time in North America

Coal-forming through time in North America

Iron sulfide precipitation sequence in Albian coals from the Maestrazgo Basin, southeastern Iberian Range, northeastern Spain

Deposition of important coal accumulations in the proximal areas of a delta-estuary, occurred in the Maestrazgo Basin during the middle Albian (late Lower Cretaceous). These coals are characterized by high sulfur contents: 4.18% in coal from the Castellote subbasin, and 7.16% in coal from the Calanda subbasin (dry basis). A petrographic study of iron sulfide was carried out on the subject coals, to deduce an iron sulfide precipitation sequence for five principal stages: (a) early syngenetic stage; (b) late syngenetic stage; (c) syngenetic-diagenetic stage; (d) early epigenetic stage; and (e) late epigenetic stage. A sulfide precipitation control during the syngenetic stage, carried out by different compounds liberated from organic matter during its coalification stages, is deduced from the confrontation with other studies on coal differing in rank, depositional environment and geographical location.

Depositional environments and resource potential of cretaceous coal-bearing strata at Chignik and Herendeen bay, Alaska Peninsula

Cretaceous (Campanian to Maestrichtian) coal-bearing strata occur on the Alaska Peninsula southwest of Wide Bay and extend to Pavlof Bay. The depositional succession consists of the lower member of the Chignik Formation, the Coal Valley Member (middle member, Chignik Formation), the upper member of the Chignik Formation, and the Hoodoo Formation. Previous interpretations of the depositional environments of these formations suggest that deposition of nonmarine sands of the Coal Valley Member through the nearshore sediments of the Chignik Formation and the deep-water marine Hoodoo Formation represents a marine transgression. Other researchers have interpreted these units as coeval sedimentary facies deposited in different environments: (1) alluvial fan to flood plain (Coal Valley Member); (2) inner-neritic (upper and lower shoreface) continental shelf (Chignik Formation); and (3) outer-neritic continental shelf to bathyal continental slope (Hoodoo Formation). Additional field work by the authors suggests that both previous interpretations should be combined. Upper and lower shallow-marine facies of the Chignik Formation represent transgressive events separated by the nonmarine Coal Valley Member, a regressive phase. The interrelationship of these units indicates that the Coal Valley Member was deposited simultaneously with individual marine facies of the Chignik and Hoodoo Formations in three different environments. This simultaneous, intermediate depositional phase was followed by onlap (transgression) by the upper member Chignik and Hoodoo Formations. This interpretation is supported by field evidence of lateral interfingering of the sediments and by gradational vertical contacts. The depositional environment for the sediments of the Coal Valley Member is nonmarine flood plain and alluvial fan. There are indications that marine conditions were nearby and salt-marsh and delta deposition may have taken place. If depositional environments were the same or similar elsewhere in the Late Cretaceous, thick coal accumulations probably cannot be expected to occur in covered areas on the Alaska Peninsula. Coal resource estimates were computed for two areas within the Coal Valley Member trend. These areas, Herendeen Bay and Chignik Bay, contain most of the known potential for commercial coals on the Alaska Peninsula. Resource estimates approach 360 × 10 6 MT in beds 0.9 m or more in thickness.

Controls on Late Cretaceous--Paleocene Sedimentation in Wyoming: ABSTRACT

Recent developments in the time-stratigraphic interpretation of seismic record sections have indicated the need for separating tectonic and eustatic processes. The combination of a eustatic rise with a major orogenic episode during the Paleocene in Wyoming resulted in a stratigraphic sequence of economic importance. This sequence was deposited during a period of worldwide onlap, and a period of thrusting and foreland uplift. More than 5,000 ft (1,500 m) of stratigraphic fill of intermontane basins record these processes. Lithologic, environmental, and petrographic observations indicate sea-level changes, strandline positions, paleocurrent patterns, and areas of provenance. Authigenic glauconite suggests an area of brackish to marine transgression within the Cannonball sea. Supporting this observation, specific vertebrae faunas indicate that central Wyoming was inundated by the worldwide post-Danian transgressive onlap. Other environmental criteria support the paleogeographic reconstruction of a broad interior sea invading an area of rising uplifts, encroaching thrust plates, and subsiding basins. These boundary conditions provided the framework for the development of commercial hydrocarbon and coal accumulations. Lacustrine and marine source and reservoir rocks, coastal swamps, and thick subbituminous coals were developed in response to the climatic, tectonic, and eustatic history. These aspects are interpreted from the mineralogy, palynology, petrophysical responses, and the facies patterns in outcrop and subsurface sections. End_of_Article - Last_Page 546------------

Continental Drift, III: Late Paleozoic Glacial Centers, and Devonian-Eocene Coal Distribution

Glaciation and large-scale coal deposition cannot take place without an adequate water supply. If the supercontinents of Gondwanaland and Laurasia ever existed, Proterozoic and Paleozoic glaciations would not have been possible deep in the supercontinents' interiors, nor could the major Carboniferous, Permian, and younger coal fields of eastern North and South America, and of eastern Africa and India have formed. The presence of major late Paleozoic ice centers in Western Australia, central India and northern West Pakistan, Africa, Brazil, and the Atlantic-Indian Ocean margins of Antarctica, and of large Paleozoic coal fields in eastern Africa, eastern India, Brazil, and eastern North America indicates that large water supplies actually were present close to the places where the glaciations took place, and where the coal fields formed. This in turn suggests that currently popular reconstructions of Gondwanaland and Laurasia are wrong. Coal accumulations took place in areas where plant decay was slight, average annual temperature ranged from cool to warm, and annual rainfall exceeded 1,500-2,000 mm. The great amount of rain required could not have been precipitated unless late Paleozoic Atlantic and Indian Oceans had existed. The possibility that these late Paleozoic oceans were inland seas is eliminated by the circulation requirements of these oceans. For example, the surface waters of the North Atlantic and Arctic Oceans are derived ultimately from the Southern Ocean. This surface water is returned to the Southern Ocean by intermediate-to abyssal-depth currents. This mechanism for returning water to the Southern Ocean appears to eliminate any possibility that the late Paleozoic inland seas were epeirogenic water bodies. Therefore, until advocates of the new global tectonics find an alternate explanation for tillite and coal distribution, the spreading sea-floor, mobile-plate, and polar-wandering hypotheses will have to be regarded as interesting speculations which are supported by only a fraction of the known geological, paleontological, and paleoclimatological data.