Geology and characterisation of the Pecket coal deposit, Magellan Region, Chile

The geology, petrography and chemical variation of the Pecket coal sequence, Magellan Region (52°57′S, 71°10′W), the only Chilean coal used for electricity generation on a large scale, has been studied in order to predict their combustion behaviour, especially in coal blends. The depositional environment of formation of the coal seams was a swamp rarely exposed to subaerial conditions and was associated with the development of the folded foreland of the Magellan basin during the Tertiary (Oligo–Miocene). The general tectonic regime of the collision of the Antarctic and South American plates is reflected by a system of joints with 40°N–50°W strike. The maceral composition of all six seams studied indicates high contents of vitrinite (>90%), minor content of liptinite (4.7%) and inertinite (<2%). Occurrence of tonstein horizons altered to kaolinite indicates a distal volcanism during peat accumulation. Coal rank varies between lignite and subbituminous (Ro=0.28–0.42%) with an average dry basis calorific value of 5450 kcal/kg, 17 wt.% moisture, 41 wt.% volatile matter, and sulphur content below 0.5 wt.%. The mineral matter (LTA) associated with the coal shows a dominance of kaolinite with quartz, smectite, and minor basanite. SiO₂/Al₂O₃ and Fe₂O₃/CaO ratios of the ashes diminish towards the lower seams. With respect to the utilisation of Pecket coals in combustion, base/acid ratios (B/A) and silica ratios (SR) indicate potential fouling for seams 1, 2, 5, and 6i, with high fouling indexes (Rf) for seams 2 and 5. Pecket coal is excellent for blend combustion due to its low sulphur content.     

An overview of the Permian (Karoo) coal deposits of southern Africa

The coal deposits of southern Africa (Botswana, Malawi, Mozambique, Namibia, South Africa, Swaziland, Tanzania, Zambia and Zimbabwe) are reviewed. The coal seams formed during two periods, the Early Permian (Artinskian–Kungurian) and the Late Permian (Ufimian–Kazanian). The coals are associated with non-marine terrestrial clastic sedimentary sequences, most commonly mudrock and sandstones, assigned to the Karoo Supergroup. The Early Permian coals are most commonly sandstone-hosted while the younger coals typically occur interbedded with mudstones. The sediments were deposited in varying tectono-sedimentary basins such as foreland, intracratonic rifts and intercratonic grabens and half-grabens. The depositional environments that produced the coal-bearing successions were primarily deltaic and fluvial, with some minor shoreline and lacustrine settings. Coals vary in rank from high-volatile bituminous to anthracite and characteristically have a relatively high inertinite component, and medium- to high-ash content. In countries where coal is mined, it is used for power generation, coking coal, synfuel generation, gasification and for (local) domestic household consumption.     

Geochemistry of coals from the Elk Valley coalfield, British Columbia, Canada

The Elk Valley coalfield of British Columbia is one of the major coal producing areas in Canada. The coals are of Cretaceous and Jurassic–Cretaceous age and range in rank from high-volatile to low-volatile bituminous (%Ro_max: 0.8–1.6). Coal seams from outcrops and active mines in this coalfield were analysed for rank and maceral composition using reflected light microscopy, for geochemistry using AAS, INAA, and ICPES, and also by proximate and ultimate analyses. The Elk Valley coal seams contain low average concentrations of hazardous elements such as As, Mo, Pb, and Se. However, there are seams that contain relatively high concentrations of some of these elements, such as 8 mg/kg and 108 mg/kg of arsenic. When the geochemistry of coal seams is compared within the different parts of the coalfield, the elemental composition amongst the seams from various sections located in the central area of the coalfield is similar. Coal seams in the northern area of the coalfield have different geochemistry than coal seams in other areas of the coalfield; seams in the northern area have much higher As, Br, Cr, Cu, Fe, K, and Na content, but contain less Ca.     

Microfacies and depositional environment of Tertiary Tanjung Enim low rank coal, South Sumatra Basin, Indonesia

The South Sumatra basin is among the most important coal producing basins in Indonesia. Results of an organic petrography study on coals from Tanjung Enim, South Sumatra Basin are reported. The studied low rank coals have a mean random huminite reflectance between 0.35% and 0.46% and are dominated by huminite (34.6–94.6 vol.%). Less abundant are liptinite (4.0–61.4 vol.%) and inertinite (0.2–43.9 vol.%). Minerals are found only in small amounts (0–2 vol.%); mostly as iron sulfide.Based on maceral assemblages, the coals can be grouped into five classes: (1) humotelinite-rich group, (2) humodetrinite-rich group, (3) humocollinite-rich group, (4) inertinite-rich group and (5) humodetrinite–liptinite-rich group. Comparing the distribution of maceral assemblages to the maceral or pre-maceral assemblages in modern tropical domed peat in Indonesia reveals many similarities. The basal section of the studied coal seams is represented typically by the humodetrinite–liptinite-rich group. This section might be derived from sapric or fine hemic peat often occurring at the base of modern peats. The middle section of the seams is characterized by humotelinite-rich and humocollinite-rich groups. The precursors of these groups were hemic and fine hemic peats. The top section of the coal seams is typically represented by the humodetrinite-rich or inertinite-rich group. These groups are the counterparts of fibric peat at the top of the modern peats. The sequence of maceral assemblages thus represents the change of topogenous to ombrogenous peat and the development of a raised peat bog.A comparison between the result of detailed maceral assemblage analysis and the paleodepositional environment as established from coal maceral ratio calculation indicates that the use of coal maceral ratio diagrams developed for other coal deposits fails to deduce paleo-peat development for these young tropical coals. In particular, mineral distribution and composition should not be neglected in coal facies interpretations.     

Geochemical and mineralogical anomalies of the late Permian coal in the Zhijin coalfield of southwest China and their volcanic origin

This paper describes the influence of volcanic ash on the concentrations and occurrences of associated elements in coal in the Zhijin Coalfield in western Guizhou Province, China. Our studies reveal that the No. 9 coal seam in the Zhijin Coalfield has very high content of Fe (4.34%), Cu (369.90 μg/g), U (49.6 μg/g), Mo (63.10 μg/g), Zn (33.97 μg/g), and Zr (841.80 μg/g). The studies have also found that elements, such as Fe and Cu, do not occur as sulfides in this coal seam, in sharp contrast to many other coal seams in China. The geochemical and mineralogical anomalies of the coal seam are attributed to synsedimentary volcanic ash. In addition to normal macerals and minerals in coal, a volcanic-influenced material (VIM) derived from volcanic ash, detrital material of terrigenous origin and organic matter was identified under polarized-light reflectance microscopy and scanning electron microscopy equipped with energy-dispersive X-ray (EDX) analyzer. The volcanic-influenced material is the main carrier of the above elements in this coal. Six types of the volcanic-influenced material (VIM-1, VIM-2, VIM-3, VIM-4, VIM-5, and VIM-6) are further distinguished on the basis of their structures and compositions. To the best of our knowledge, this is the first report that presents a detailed classification of coal components with a high content of volcanic ash.     

Metamorphism of mineral matter in coal from the Bukit Asam deposit, south Sumatra, Indonesia

The coal of the Miocene Bukit Asam deposit in south Sumatra is mostly sub-bituminous in rank, consistent with regional trends due to burial processes. However, effects associated with Plio–Pleistocene igneous intrusions have produced coal with vitrinite reflectance up to at least 4.17% (anthracite) in different parts of the deposit. The un-metamorphosed to slightly metamorphosed coals, with Rv_max values of 0.45–0.65%, contain a mineral assemblage made up almost entirely of well-ordered kaolinite and quartz. The more strongly heat-affected coals, with Rv_max values of more than 1.0%, are dominated by irregularly and regularly interstratified illite/smectite, poorly crystallized kaolinite and paragonite (Na mica), with chlorite in some of the anthracite materials. Kaolinite is abundant in the partings of the lower-rank coals, but is absent from the partings in the higher-rank areas, even at similar horizons in the same coal seam. Regularly interstratified illite/smectite, which is totally absent from the partings in the lower-rank coals, dominates the mineralogy in the partings associated with the higher-rank coal beds. A number of reactions involving the alteration of silicate minerals appear to have occurred in both the coal and the associated non-coal lithologies during the thermal metamorphism generated by the intrusions. The most prominent involve the disappearance of kaolinite, the appearance of irregularly interstratified illite/smectite, and the formation of regular I/S, paragonite and chlorite. Although regular I/S is identified in all of the non-coal partings associated with the higher-rank coals, illite/smectite with an ordered structure is only recognised in the coal samples collected from near the bases of the seams. The I/S in the coal samples adjacent to the floor of the highest rank seam also appears to have a greater proportion of illitic components. The availability of sodium and other non-mineral inorganic elements in the original coal to interact with the kaolinite, under different thermal and geochemical conditions, appears to be the significant factor in the formation of these new minerals, and distinguishes the mineralogical changes at Bukit Asam from those developed more generally with rank increases due to burial, and from the effects of intrusions into coals that were already at higher rank levels.     

The use of numerical simulation in predicting coalbed methane producibility from the Gates coals, Alberta Inner Foothills, Canada: Comparison with Mannville coal CBM production in the Alberta Syncline

Two medium to low volatile bituminous rank coals in the Lower Cretaceous Gates Formation (Mannville equivalent), Inner Foothills of Alberta, were cored as part of a coalbed methane exploration program. The target seams (Seam 4 and Seam 10) were intersected at 652 m and 605 m, respectively. The coals were bright banded, relatively competent and reasonably cleated, with cleat spacing between 5–20 mm. The FMI (Formation Micro-Imaging) log identified two primary fracture directions, corresponding to both face and butt cleats, which were developed almost equally in some coal intervals. The amount of shearing was limited, in spite of the presence of numerous thrust faults and fold structures in the corehole vicinity. Total gas content was high, with an average of 17.7 cm³/g (arb; 568.1 scf/t). An adsorption isotherm of the thick Seam 4 showed gas saturation levels of 90% at in-situ reservoir conditions. Methane content was 92–96% and carbon dioxide levels were less than 2%. Isotopic studies on the methane confirmed the thermogenic origin of the gas, as anticipated based on the coal rank. The coal seams were fracture stimulated using 50/50 nitrogen and fresh water along with 9 to 12 tons of 12/20 mesh sand used as a proppant. It is believed that the coals were not stimulated properly because of the small proppant volume and the complex — and often unpredictable — fracture pattern in coals, particularly in the Inner Foothills region that has high stress anisotropy. An injectivity test showed coal absolute permeability to be less than 1 mD, the skin to be −  2 (indicating a slightly damaged coal) and water saturation in the cleats to be 90%. A four-month production test was conducted; gas rates declined from 930 to 310 m³/d (33 to 11 MCFD) and water rates were low (< 5 BWD). Produced water was saline (TDS was 20,000 mg/L) and high in chloride and bicarbonate ions. Production testing was followed by history matching and numerical simulation, which consisted of numerous vertical and horizontal well development scenarios and other parameters. Simulating multiple parallel horizontal wells in the Gates coals resulted in the highest peak gas production rates, cumulative production and recovery efficiencies, in agreement with public data from the Mannville coals in the deeper part of the Alberta Syncline. The positive effect of constructive interference in depressurizing the coal reservoirs and accelerating gas production over short periods of time was demonstrated. Coal quality data from a nearby underground mine shows that drilling horizontal wellbores in the Gates coals would be challenging because of unfavourable geomechanical properties, such as low cohesion and unconfined compressive strength values, and structural complexity.     

The Lower Permian coal seams from Singrauli coalfield (M.P.), India: petrochemical nature, rank, age and sedimentation

Biopetrographic and chemical investigations carried out on the Lower Permian (Barakar Formation) coal seams encountered in two bore-holes (NCSM-3 and CMSA-111) from the Singrauli coalfield, Son Valley, reveal that they are, in general, rich in inertinite and mineral matter towards the eastern part. Whereas, towards the western part they are rich in vitrinite with subordinate amounts of inertinite and mineral matter. The Turra and Purewa Top seams, in the eastern part, consist chiefly of mixed and fusic coal types and the Turra and Purewa Merged seams, in the western part of the basin, are characterized dominantly by vitric and mixed coal types. The basin of deposition was shallower in its major part but deepened towards west. Consequently frequent oxic fluctuations are most common in the coal seams of the eastern part.The rank of these coal seams ranges between subbituminous-A to high-volatile bituminous-C stages. They show normal increase in rank with depth. The coal seams in the western part of the area are higher in rank than their counterparts in the east. The Purewa Bottom seam (NCSM-3) is petro-palynologically correlatable with the Turra seam (CMSA-111) of the western part.It has been presumed that Glossopteridophyta (a complex group of gymnospermous plants), arthrophytes and ferns were the vegetal source for the formation of Barakar coal seams. These plants during the Early Permian grew as thick forests along river valleys and as upland and subaquatic vegetation, and experienced a warm, humid and windy temperate climate. The coal seams were presumably deposited in backwater and lacustrine swamps in fluvial environment from hypoauchthonous source material.An attempt has been made to explain reasons for the high incidence of mineral matter and its apparent relationship with inertinite content in the coal seams while also discussing the depositional history.     

Coal petrology of coal seams from the Leão-Butiá Coalfield, Lower Permian of the Paraná Basin, Brazil — Implications for coal facies interpretations

In the Leão-Butiá Coalfield, Rio Grande do Sul the coal seams occur in the Rio Bonito Formation, Guatá Group, Tubarão Supergroup of the Paraná Basin, Brazil and are of Permian (Artinskian–Kungurian) age.This study is the first detailed investigation on the coal petrographic characterization of the coal-bearing sequence in relation to the depositional settings of the precursor mires, both in terms of whole seam characterization and in-seam variations. The study is based on the analyses of nine coal seams (I2, CI, L4, L3, L2, L1, S3, S2, S1), which were selected from core of borehole D-193, Leão-Butiá and represent the entire coal-bearing sequence.The interpretation of coal facies and depositional environment is based on lithotype, maceral and microlithotype analyses using different facies-critical petrographic indices, which were displayed in coal facies diagrams. The seams are characterized by the predominance of dull lithotypes (dull, banded dull). The dullness of the coal is attributed to relatively high mineral matter, inertinite and liptinite contents. The petrographic composition is dominated by vitrinite (28–70 vol.% mmf) and inertinite (> 30 vol.% mmf) groups. Liptinite contents range from 7 to 30 vol.% (mmf) and mineral matter from 4–30 vol.%. Microlithotypes associations are dominated by vitrite, duroclarite, carbominerite and inertite. It is suggested that the observed vertical variations in petrographic characteristics (lithotypes, microlithotypes, macerals, vitrinite reflectance) were controlled by groundwater level fluctuations in the ancient mires due to different accommodation/peat accumulation rates.Correlation of the borehole strata with the general sequence-stratigraphical setting suggests that the alluvial fan system and the coal-bearing mudstone succession are linked to a late transgressive systems tract of sequence 2. Based on average compositional values obtained from coal facies diagrams, a deposition in a limno-telmatic to limnic coal facies is suggested.     

Supergene and hypogene alteration in the dual-use kaolin-bearing coal deposit Angren, SE Uzbekistan

The Jurassic Angren coal–kaolin deposit, Uzbekistan, is one of the largest producers of coal and kaolin suitable for refractories and industrial ceramics in central Asia. The Major coal seam, attaining a thickness between 4 and 24 m, is encased by kaolin-bearing bedsets which have been derived from supergene pre- and hypogene post coal kaolinization. Joint clay-mineralogical and coal petrographic analyses formed the basis of the environment analysis of this coal–kaolin series and constrained the physico-chemical conditions existing during the Triassic through Jurassic period of time. Massive kaolin I underneath the coal seam is a typical residual kaolin or underclay with arsenic Fe-disulfides and siderite indicative of a reducing swampy depositional environment developing under moderately hot climatic conditions. Towards the top, kaolin I became reworked fluvial by processes. The Major coal seam developed in swamps interfingering with a fluvial drainage system of suspended to mixed-load deposits. The maximum temperature for the post-depositional alteration of the carbonaceous material is 70 °C. Post-coal kaolinization (kaolin II) affecting trachyandesites and trachytes is of low-temperature origin and low-sulphidation-type. The temperature of formation was well below 200 °C, deduced from the absence of dickite in the clay mineral assemblage. Basaltic dykes intersected the coal–kaolin series and account for contact metamorphic reactions in the proximal parts of the aluminum-bearing wall rocks reaching sanidinite-facies conditions with temperatures around 1000 °C.     

Properties of thermally metamorphosed coal from Tanjung Enim Area, South Sumatra Basin, Indonesia with special reference to the coalification path of macerals

Thermally metamorphosed Tertiary age coals from Tanjung Enim in South Sumatra Basin have been investigated by means of petrographic, mineralogical and chemical analyses. These coals were influenced by heat from an andesitic igneous intrusion. The original coal outside the metamorphosed zone is characterized by high moisture content (4.13–11.25 wt.%) and volatile matter content (> 40 wt.%, daf), as well as less than 80 wt.% (daf) carbon and low vitrinite reflectance (VR_max = 0.52–0.76%). Those coals are of subbituminous and high volatile bituminous rank. In contrast the thermally metamorphosed coals are of medium-volatile bituminous to meta-anthracite rank and characterized by low moisture content (only < 3 wt.%) and volatile matter content (< 24 wt.%, daf), as well as high carbon content (> 80 wt.%, daf) and vitrinite reflectance (VR_max = 1.87–6.20%). All the studied coals have a low mineral matter content, except for those which are highly metamorphosed, due to the formation of new minerals.The coalification path of each maceral shows that vitrinite, liptinite and inertinite reflectance converge in a transition zone at VR_max of around 1.5%. Significant decrease of volatile matter occurs in the zone between 0.5% and 2.0% VR_max. A sharp bend occurs at VR_max between 2.0% and 2.5%. Above 2.5%, the volatile matter decreases only very slightly. Between VR_r = 0.5% and 2.0%, the carbon content of the coals is ascending drastically. Above 2.5% VR_r, the carbon content becomes relatively stable (around 95 wt.%, daf).Vitrinite is the most abundant maceral in low rank coal (69.6–86.2 vol.%). Liptinite and inertinite are minor constituents. In the high rank coal, the thermally altered vitrinite composes 82.4–93.8 vol.%. Mosaic structures can be recognized as groundmasss and crack fillings. The most common minerals found are carbonates, pyrite or marcasite and clay minerals. The latter consist of kaolinite in low rank coal and illite and rectorite in high rank coal. Change of functional groups with rank increase is reflected most of all by the increase of the ratio of aromatic C–H to aliphatic C–H absorbances based on FTIR analysis. The Oxygen Index values of all studied coals are low (OI < 5 mg CO₂/g TOC) and the high rank coals have a lower Hydrogen Index (< 130 mg HC/g TOC) than the low rank coals (about 300 mg HC/g TOC). T_max increases with maturity (420–440 °C for low rank coals and 475–551 °C for high rank coals).Based on the above data, it was calculated that the temperature of contact metamorphism reached 700–750 °C in the most metamorphosed coal.     

Clays and other minerals in coal seams of the Moura-Baralaba area, Bowen Basin, Australia

The clays and other minerals in a succession of Late Permian coals of high-volatile bituminous to semi-anthracite rank have been identified, using low-temperature oxygen plasma ashing and X-ray diffraction, and evaluated to identify the relative roles in mineral matter formation of detrital input, early diagenesis in the peat swamp and late diagenesis associated with rank advance. Although well-ordered kaolinite of probable early diagenetic origin is abundant throughout the succession, the uppermost and lowermost seams of the sequence, regardless of rank, contain relatively abundant illite and/or interstratified illite/smectite, along with a small but significant proportion of chlorite. These clays are thought to be essentially of detrital origin, washed or blown into the peat deposit in relative abundance during the establishment and subsequent overwhelming of an extensive and long-lived swampy environment. Quartz is also abundant in the lower seams of the sequence, especially close to the regional sediment source area. Illite is unusually abundant in the topmost seam in both high- and low-rank parts of the succession, and thus appears to represent detrital input from a particular source material. Although significant changes are reported in the clays of the associated strata due to rank advance, the principal effect of rank advance on the minerals in the coal itself appears to be the development of an ammonium illite, and possibly some additional fine-grained chlorite, in the semi-anthracite material. Isolation within the organic matter of the coal is thought to have inhibited access for ions such as K⁺, which might otherwise have become involved in metamorphic reactions and given rise to mineralogical changes commonly found in non-coal sedimentary successions.     

Studies of the relationship between coal petrology and grinding properties

The maceral and microlithotype composition of selected coals has been investigated with respect to the grinding properties, specifically Hardgrove grindability index (HGI), of the coals. The study expands upon previous investigations of HGI and coal petrology by adding the dimension of the amount and composition of the microlithotypes. Coal samples, both lithotypes and whole channels, were selected from restricted rank ranges based on vitrinite maximum reflectance: 0.75–0.80% R_max, 0.85–0.90% R_max and 0.95–1.00% R_max. In this manner, the influence of petrographic composition can be isolated from the influence of rank. Previous investigations of high volatile bituminous coals demonstrated that, while rank is an important factor in coal grindability, the amount of liptinite and liptinite-rich microlithotypes is a more influential factor. In this study, we provide further quantitative evidence for the influence of microlithotypes on HGI and, ultimately, on pulverizer performance.     

The geology, petrology, palynology and geochemistry of Permian coal basins in Tanzania: 2. Songwe-Kiwira Coalfield

This study provides coal quality, petrological, palynological and geochemical (Rock Eval) data on Permian coal seams and associated shales and mudstones of the Karoo Supergroup of the Songwe-Kiwira Coalfield, Tanzania. The coal seams, which have a cumulative thickness of 6.80 m, occur in the shale–coal–sandstone facies of the Mchuchuma Formation of Artinskian to Kungurian(?) age.Coal quality data (calorific values, volatile matter contents) and vitrinite reflectances indicate high volatile C bituminous to high volatile A bituminous coals, having relatively high ash yields (22–49 wt.%) and highly variable sulphur contents (0.17–9.2 wt.%). They could be used to fuel small-scale power generation units thereby providing electricity to nearby towns and villages. Also, the coals could be used as a substitute for wood, which is becoming increasingly scarce. In rural Tanzania, charcoal is still the main energy source for cooking, and wood is used extensively in brick kilns and for making roofing tiles.Petrological analysis indicated that the coals are dominated by dull to banded dull lithotypes, with seams at the base of the Mchuchuma Formation enriched in inertinite macerals (up to 83 vol.%), whereas up-section vitrinite contents increase. Palynological analyses indicated that the assemblage in the lower Mchuchuma Formation (Scheuringipollenites assemblage) is dominated by trilete spores, whereas in the remainder of the section, non-taeniate disaccates dominate (Scheuringipollenites–Protohaploxypinus assemblage). Facies critical macerals suggest for most seams a marsh/wet forest swamp depositional setting, which is consistent with the palynological data.Rock Eval analyses indicate type II/III kerogen, with Tmax (°C) values ranging from 426 to 440, corresponding to the early stage of hydrocarbon generation. Thermal Alteration Indices (2 to 2+) and vitrinite reflectance levels (0.60–0.83 Ro (%) support the Rock Eval maturity assessment, and despite the predominance of terrestrial-derived organic matter, there is evidence of oil generation and expulsion in the form of cavity and fracture filling exsudatinite.     

我国西部低煤级煤的液化性能

我国西部地区中新生代赋存着丰富的低煤级(R_max<0.8%)煤炭资源,且绝大部分为低灰、低硫、低磷的优质煤,这为煤的洁净利用提供了最佳的液化原料。从煤质和煤岩基本性质出发,探讨了研究区低煤级煤的液化性能。通过高压釜在溶剂和催化剂条件下的加氢液化试验可知,在氢耗量5%左右时,煤的液化转化率达90%以上,油产率达55%以上,这表明我国西部低煤级煤可作为重要的液化用煤资源。同时,通过分析影响本区煤液化性能的控制因素,发现煤的挥发分产率、碳氢原子比、活性组分含量和镜质体反射率等指标可直接影响煤的液化性能。      

Geology of Santa Rita Coal Basin, Rio Grande do Sul, Brazil

Data on the sedimentology, stratigraphy, palynology, coal petrography and geochemistry of the Santa Rita Coal Basin, Rio Grande do Sul, Brazil, are presented. The investigations were carried out on samples obtained from drill cores of the sedimentary rocks of Tubarão Supergroup, Lower Permian of Paraná Basin.The sequence comprises more than 10 coal layers, three sets of which — SR₁, SR₂ and SR₃ — are correlated with the SB+MB, I₁F and I₂B+I₃B coal seams, respectively, of the Charqueadas Coal Basin, southwest of Santa Rita. The lower, as well as the upper contacts of the sedimentary sequences are transitional and very difficult to trace.The Itararé sequences (basal group) comprise pelites, conglomerates and sandstones. The pelites are the most representative lithologies. The overlying Rio Bonito Formation comprises pelites and coal seams with subordinate para- conglomerates.Palynological analysis has unravelled a rich microfloristic association with a predominance of specimens related to the Infraturma laevigati, apiculati and cingulicavati of the Turma Triletes (Pteridophyta) either in the coal seams or in the associated rocks. Monosaccites, Disaccites and Striatiti (Gymnospermae) are accessory forms in the palynological assemblage. Botryococcus and algae-like elements are less abundant.Comparative studies of cuticular fragments collected from boreholes N₃ and P₄ showed better preservation and greater concentration in the latter, which may indicate that borehole N₃ is located closer to the margin of the swamp.Reflectance measurements ranging from 0.43 Rr% to 0.50 Rr% allow the coal seams to be classified as sub-bituminous B and A, according to the ASTM classification. Microlithotype analyses have shown the predominance of carbominerite, trimacerite and vitrite. Vitrinite is the most prominent maceral group (20–50%), inertinite and exinite are subordinate. The mineral content is about 40%.Results from geochemical analyses, from either coal or associated pelites, show the association of boron and vanadium with the organic matter; gallium is related to the inorganic material.The available sedimentological, palaeontological and petrographical data suggest a paludal environment related to swamps and the coal seams present characteristics of “reed” moor limnotelmatic facies of an authochthonous/hypautochthonous origin.     

Facies and genesis of Carboniferous coal seams of Northwest Germany

In order to get detailed information about the facies and genesis of Upper Carboniferous coal seams of Northwest Germany, maceral analyses of complete seam profiles (Westphalian B-D, mainly Westphalian C) were carried out. Four main facies and twelve subfacies could be distinguished. The main facies are:

1. (1) The sapropelic-coal facies, consisting of fine-grained inertinite and liptinite, which forms from organic sediments deposited at the bottom of moor lakes.

2. (2) The densosporinite facies which is high in inertinite and liptinite and low in vitrinite. Syngenetic pyrites, clastic layers, thick vitrains and fusains do not occur. This facies originates from peats of ‘open mires’ with higher groundwater table and herbaceous vegetation. The ‘open mire’ was situated in the centre of extensive swamps. Consequently, clastic sedimentation did not affect this swamp type and nutrient supply and pH values were low.

3. (3) The vitrinite-fusinite facies, which is high in vitrinite. This is the result of abundant vitrains. Under the microscope, fusains were mostly identified as fusinite. The vitrinite-fusinite facies originates from a forest mire. More or less abundant seam splits and clastic layers show that rivers flowed in the neighbourhood of this area.

4. (4) The shaly-coal facies, which represents the most marginal part of the former swamp frequently affected by clastic sedimentation.

Within the Carboniferous of the Ruhr Region it seems unlikely that the thin coal seams of the Namurian C and Westphalian A1 contain a densosporinite facies. The swamps were situated in the lower delta plain where they were often affected by marine influences. Consequently, coals are high in minerals and sulfur and they are thin and discontinous. The best conditions for the formation of extensive swamps, with open mires (densosporinite facies) in their central parts, prevailed during Westphalian A2 and B1 times. Low contents of sulfur and minerals and high content of inertinite are typical for these coals. Sedimentation mainly took place in the transitional zone from the lower to the upper delta plain. During the Westphalian B2 and C fluvial sedimentation dominated. Within the coal seams minerals, sulfur and pseudovitrinite increase while inertinite decreases. This is the consequence of coal of the densosporinite facies occurring with increased rarity. The coal seams of the Westphalian C2 contain no densosporinite facies because peat formation was restricted by increasing fluvial sedimentation and by a better drainage. As a consequence, extensive swamps with ‘open mires’ in the centre were no longer formed after the formation of the “Odin” seams. Above the “Odin” seams coal of the vitrinite-fusinite facies contains thick-walled torisporinites. Variations and lowering of the groundwater table caused mild oxidative influences during peat formation. This is documented by an increase in pseudovitrinite, the occurrence of torisporinites and the absence of spheroidal sideritic concretions. Sulfur content increases in the absence of the low-ash and low-sulfur coal of the densosporinite facies.In Upper Carboniferous coal seams of the Ibbenbüren Region the inertinite and telocollinite contents are higher than in those of the Ruhr Region. Therefore, variations of the groundwater table have been more pronounced and resulting oxidative influences must have been more severe. Seldom occurring marine and brackish horizons and a higher fusinite (fusain) content indicate a slight elevation of this area. From Early Westphalian D times onward, peat formation was no longer possible because of the better drainage. This resulted in severe oxidative conditions which excluded peat formation.     

液氮溶浸对不同煤阶含水煤样渗流特性的影响

中国包含多种煤阶煤层,由于煤质、地质条件等差异,不同煤层中的水分赋存情况也具有较大差异性。煤阶、饱水度作为影响液氮低温致裂效果的两个重要因素,有必要对其进行深入研究。为此,分别选择褐煤、烟煤与无烟煤3种煤阶煤样,并制备得出饱水度分别为0%、33%与99%的煤样进行液氮溶浸处理,使用摄像机定点拍摄、观察煤样表面宏观裂隙处理前后的演化规律,并对煤样进行氮气渗流试验。试验结果表明：液氮溶浸后褐煤因产生的一条与多条贯穿裂隙发生整体结构上的断裂,烟煤表面有新裂隙产生,原生宏观裂隙有一定的扩展与延伸,无烟煤表面宏观裂隙无明显发育;煤样饱水度越高,液氮的致裂增透效果越显著;液氮溶浸对3种煤阶煤样的致裂增透效果关系为：褐煤>烟煤>无烟煤,在完全干燥状态下,由于热应力不足以破坏颗粒间链接,烟煤与无烟煤的增透效果近似相等;对于褐煤,液氮溶浸处理对完全干燥状态下的煤体即产生有效致裂,渗透率平均增幅高达559.35%,对于烟煤,在饱水度为33%和99%的状态下,液氮溶浸对煤体具有明显致裂效果,渗透率平均增幅分别为330.60%和448.77%,对于无烟煤,在饱水度为99%的状态下液氮溶浸处理才能对煤体产生有效致裂,渗透率平均增幅为185.53%。     

Development of the first coal seam gas exploration program in Indonesia: Reservoir properties of the Muaraenim Formation, south Sumatra

The Late Miocene Muaraenim Formation in southern Sumatra contains thick coal sequences, mostly of low rank ranging from lignite to sub-bituminous, and it is believed that these thick low rank coals are the most prospective for the production of coal seam gas (CSG), otherwise known as coalbed methane (CBM), in Indonesia.As part of a major CSG exploration project, gas exploration drilling operations are being undertaken in Rambutan Gasfields in the Muaraenim Formation to characterize the CSG potential of the coals. The first stage of the project, which is described here, was designed to examine the gas reservoir properties with a focus on coal gas storage capacity and compositional properties. Some five CSG exploration boreholes were drilled in the Rambutan Gasfield, south of Palembang. The exploration boreholes were drilled to depths of ~ 1000 m into the Muaraenim Formation. Five major coal seams were intersected by these holes between the depths of 450 and 1000 m. The petrography of coal samples collected from these seams showed that they are vitrinite rich, with vitrinite contents of more than 75% (on a mineral and moisture free basis). Gas contents of up to 5.8 m³/t were measured for the coal samples. The gas desorbed from coal samples contain mainly methane (CH₄) ranging from 80 to 93% and carbon dioxide (CO₂) ranging from 6 to 19%. The composition of the gas released into the production borehole/well is, however, much richer in CH₄ with about 94 to 98% CH₄ and less than 5% CO₂.The initial results of drilling and reservoir characterization studies indicate suitable gas recovery parameters for three of the five coal seams with a total thickness of more than 30 m.     

Geological controls on the formation and distribution of gas in British coal measure strata

The methane, ethane, higher alkanes and nitrogen found in British coal seams are residual products of coalification occasionally complemented by petroleum-derived hydrocarbons. Carbon dioxide, a minor constituent of coal seam gas, may have been introduced during the phase of cleat mineralisation following uplift. Helium and argon are considered to be radiogenic in origin.Variations in seam methane content with depth, geographic location and rank can be interpreted in terms of the coalification and erosion history of a coalfield. However, the limitations inherent in an analysis in which coal rank is represented by a single parameter must be recognised.There are indications that the methane content of a seam is not likely to exceed the methane sorption capacity of the coal determined at a temperature commensurate with that obtaining at the maximum burial depth.Research in the East Midlands coalfield suggests that structurally controlled migration of coalification gas was contemporaneous with folding. During the Permo-Carboniferous erosion period gas was lost from outcropping seams. Subsequently, the bulk permeability of the seams must have been reduced, perhaps as a result of cleat mineralisation, because no re-distribution of methane appears to have occurred in response to later (Tertiary) deformation and gas contents of seams at incrop below the base of the Permo-Triassic have remained zero.Data on the effects of faulting on seam gas contents are few but the expectation is that faults, of appropriate age and orientation, whilst inhibiting in-seam migration may, in some instances have aided cross-measures movement of gas. Elevated seam ethane and propane contents are frequently encountered in seams disturbed by oil-bearing faults.