Thin Coals Research Articles

Geological Assessment of Turonian - Coniacian terrestrial sedimentation records during climatic recovery, Moreno Hill Formation, Zuni Basin

Understanding of Upper Cretaceous terrestrial sediments within the Western Interior Basin is advancing; however, the Turonian–Coniacian transition remains enigmatic. Recent chronometry of the Moreno Hill Formation indicates that sediment deposition took place during this interval of geodynamic upheaval and climatic recovery immediately following the peak of the Cretaceous Thermal Maximum (CTM). To decipher these effects, the sedimentary record of the Moreno Hill Formation was reassessed near the type section, and near Quemado, New Mexico (USA) using facies analysis and architectural reconstruction. Seven facies types (thirteen lithofacies codes), eleven architectural elements, and three facies associations were identified. Sedimentation within the floodplain of the lower Moreno Hill Formation was affected by the east-migrating forebulge of the Western Interior Basin. Furthermore, increasingly bedload-rich multi-story channel complexes and a transition from near-coastal to alluvial coals reflect gradual climatic cooling and overall regression of the Western Interior Seaway (with interruption by a regional [T2–R2] transgressive-regressive sequence). This is consistent with more subaerial conditions indicative of continued regression reflected within the floodplain sediments of the upper Moreno Hill Formation. Whilst diversion of westerly fluvial feeder systems by ongoing forebulge migration also affected sediment transport and deposition, a return to more suspended-load-rich single-story channels and thin coals are tied to an intervening (T3) transgression. Repetitive paleosol sequences throughout the Moreno Hill Formation indicate groundwater fluctuation in response to these base level changes. Together with detrital zircon-based geochronology, these slight sedimentary differences support a revised subdivision from three into two members: lower and upper. Beyond feeding the seaward Gallup Delta, the newly defined lower member correlates to the Toreva, Straight Cliffs (Smoky Hollow member), Ferron Sandstone, Funk Valley and Frontier formations (Dry Hollow Member) and the upper member to the Wepo and Straight Cliffs (John Henry Member) formations within the Kaiparowits, Notom, Last Chance and Vernal fluvio-deltaic systems. Landward sediments of the Cardium Formation (Canada) correlate with the lower and upper members of the Moreno Hill Formation.

Toward the Threshold of Radiation Hazards of U in Chinese Coal through the CART Algorithm.

The high volume of coal used for combustion usually leads to a large amount of coal combustion residues (CCRs), which contain the naturally occurring radioactive materials (NORMs) decayed from U and Th in coals. The high radioactivity of NORMs can cause potential harm to humans if the CCRs are used as building materials. The activities of CCRs not only depend on the concentrations of radionuclides but also largely depend on the variations of ash yields of coal. On the other hand, ash yields significantly vary in coal from less than 1-50%. This indicates that similar concentrations of radionuclides in coal with different ash yields generally do not result in similar activities in CCRs. Therefore, it is significant to build a threshold of U in coals with different ash yield levels. In this research, based on the data of 945 coal samples from China and the selected optimal model using the classification and regression tree algorithm, the threshold of U for the radiation hazard is determined to be 7.98 mg/kg for coals with ash yields higher than 20%, while the threshold of U for the radiation hazard is 5.28 mg/kg for coals with ash yields lower than 20%.

Carboniferous Manning Canyon Formation, northern Utah, USA: A carbonate-mud-dominated cyclothem motif recording the main onset of the late Paleozoic Ice Age

A poorly understood Mississippian to basal Pennsylvanian succession is preserved in parts of northern Utah, western USA. The mudrock- and carbonate-dominated Manning Canyon Formation and lateral equivalents have been referred to as “cyclothems” and might therefore be expected to preserve a record of repeated, late Paleozoic sea-level excursions similar to cyclothemic successions elsewhere in the paleotropics. In this paper, we document the sedimentology and stratigraphy of the Serpukhovian to earliest Bashkirian Manning Canyon Formation, focusing on surface exposures in the Oquirrh and Uinta Mountains and a cored subsurface intersection from central Utah. Four facies associations were identified in the Manning Canyon Formation: Mid-Shelf, Muddy Inner Shelf, Deltaic, and Coastal Plain, which are herein interpreted in the context of a muddy, semi-enclosed, epicontinental carbonate shelf fringed by a low-relief coastal plain. These facies associations are broadly comparable to recent and extant environments from a range of equatorial, clay-rich, deltaic, coastal plain, and offshore carbonate-producing environments in the Caribbean Sea, northern Australia, and SE Asia, which can be used as first-order analogues for the Manning Canyon Formation. These modern analogues suggest that several relative sea-level excursions of <40 m are recorded in the unit. The stratigraphically oldest records of substantial relative sea-level oscillations are in the lowermost Manning Canyon Formation. These preceded a more sustained pattern recorded by at least nine 4th-order, high-frequency and high-magnitude (≥40 m) sea-level cycles that characterize the upper two-thirds of the formation. Sea-level highstands are recorded by open marine shelf facies, whereas lowstands are recorded by incised channel and valley fills, and (presumed) laterally equivalent paleosols and thin coals. No record of high frequency/high magnitude relative sea-level oscillations comparable in character to those preserved in the Manning Canyon Formation was documented in the underlying stratigraphy. It is concluded that the Manning Canyon Formation may record the main onset of the eustatic signal associated with the main phase of the late Paleozoic Ice Age at ~330 Ma.

Can thin coals be resolved in seismic data? An example of the challenges for Carboniferous (Visean to Westphalian) source-rock definition across the Elbow Spit Platform (Netherlands) and the Mid North Sea High (UK) through well synthetic modelling

Abstract The ability to predict coal units from seismic data has become important for hydrocarbon exploration, especially in areas away from traditional play sweetspots. An understanding of coal distribution/thickness from seismic data can influence the risking of basin source-rock presence/charge efficiency. A selection of wells is presented from the Carboniferous of the Elbow Spit Platform (Netherlands), the Mid North Sea High (UK) and adjacent areas. These wells penetrated various coal thicknesses, as well as sandstones, mudstones and thin limestones in different stratigraphic configurations. For each well, full-stack synthetic seismograms (acoustic impedance domain) using a conventional seismic wavelet are generated along with supporting rock physics. This analysis suggests, as a guideline, that coal thickness needs to meet a threshold of 25–35% of loop thickness to be uniquely distinguishable from the surrounding lithologies (discernible soft kick). If the coals are thinner than this threshold, they will be comparable to soft sandstone-related kicks, although some exceptions exist where thin coals directly overlie soft sandstone intervals. The exact percentage value will depend on seismic-data quality and rock properties. This study highlights the need for careful consideration of thin-coal seismic expression when devising interpretation strategies and risking source-rock presence.

Palynologic, petrographic and geochemical composition of the Vancleve coal bed in its type area, Eastern Kentucky Coal Field, Central Appalachian Basin

The Vancleve coal bed was studied geochemically, palynologically, and petrographically near the type area of the Vancleve coal bed, where new road construction has provided fresh exposures. In the study area, the Vancleve coal is relatively thin (<76cm), low in ash yield (avg. 7.0%, dry basis), and high in overall total sulfur content (avg. 3.3%, dry basis). Three very thin (<10cm thick) leader coals are present at two of the six sample locations. The leader coals are high in ash yield (avg. 29.4%, dry basis), and high, but variable, total sulfur content (avg. 5.0%, range 1.1 to 8.8%, dry basis).Palynologically, the coal is dominated by Lycospora (avg. 80.4%), the dispersed spore genus of Lepidophloios, Lepidodendron, and Paralycopodites. Lycospora micropapillata and Lycospora orbicula, both of which were produced by Paralycopodites, an ecotonal, colonizing lycopod, are more prevalent near the base of the coal bed. Lycospora pellucida, Lycospora granulata (produced by Lepidophloios), and Lycospora pusilla (produced by Lepidodendron) are more abundant in the middle and upper portions of the bed. Spores and pollen from other Pennsylvanian plant groups are minor in occurrence. Biostratigraphically, the coal is transitional Westphalian A/B in age, containing both Late Langsettian, and Early Duckmantian elements. Petrographically, the coal is high in vitrinite content (avg. 80.5%, mmf), with telovitrinite occurring more commonly than detrovitrinite and gelovitrinite (avg. TV/DV+GV=3.3). Liptinite (avg. 9.4%, mmf) and inertinite (10.2%, mmf) occur in minor amounts by comparison. The average random vitrinite reflectance of the Vancleve coal is 0.54%, and the average calculated maximum vitrinite reflectance is 0.58%, indicating the Vancleve coal to be high volatile C/B bituminous in rank, in the study area.Low ash yields are often considered indicative, at least in part, of ombrotrophic (raised) mire origins in Pennsylvanian coal beds. However, the dominance of Lycospora, vitrinite macerals, and high sulfur contents indicates that the Vancleve coal bed is most likely formed from a planar, rheothrophic mire, with a consistently high water table. Low ash yields indicate that the paleomire was not subjected to any large influxes of sediment during peat accumulation from extra-mire sources.Palynologically, the very thin (<10cm thick) leader coals, more diverse in composition, though remain Lycospora dominant. Petrographically, they are high in vitrinite content, but have lower TV/DV+GV ratios (avg. 2.0). Collectively, these data indicate that the leader coals also formed from planar, rheotrophic mires, though with substantially more influence from extra mire sediment sources.The coal is locally capped and cutout by paleochannels. Sediments from a heterolithic, laterally accreting channel appear to have locally loaded the peat when it was still pliable resulting in sandstone dikes and injection structures. Loading on pliable peat may also have led to slumping in the overlying channel fill.

Pre-Cenozoic geology of the Latrobe Valley Area—onshore Gippsland Basin, S.E. Australia

In 2010–2011, a well on the uplifted northern edge of the Latrobe Valley (Yallourn North-1A) cored a 550 m section of mostly arenaceous sediments from the Lower Cretaceous Tyers River Subgroup. A follow-up core-hole (Yallourn Power-1) aimed at extending the Tyers River Subgroup section some 5 km south into the Latrobe Valley instead encountered Paleozoic basement rocks immediately below Cenozoic coal measures. From a re-examination of earlier coal and groundwater bore results, and new interpretations from gravity, seismic and magneto-telluric (MT) surveys, there is a significant area of Paleozoic basement rock that may underlie the whole northern Latrobe Valley area. The uplifted Yallourn North Lower Cretaceous sediments are a separate basin entity herein named the Monash trough. It appears they are separate from the main Lower Cretaceous Strzelecki Group Basin sediments on the southern side of the Latrobe Valley. Attributes of the Monash trough may underlie the main Strzelecki Basin, but this remains to be substantiated by further drilling. The intervening subcrop of Paleozoic basement rocks is herein named the Glengarry basement block. It shows characteristic gravity, MT and seismic features covering some 200 km2 of the northern Latrobe Valley area. The boundary between the Glengarry basement block and Strzelecki Basin approximates to the Princes Highway. It is uncertain whether structural separation of the Monash trough from the main Strzelecki Basin always existed, or whether uplift and stripping of Cretaceous rocks over the Glengarry basement block occurred in post-Cretaceous but pre-Cenozoic times. Comparative rank and maturity indices indicate a greater depth of burial of the Glengarry basement block than what exists today, whereas less stripping and loss of section have occurred to the Monash trough. Cretaceous sediments of the Tyers River Subgroup (Rintouls Creek Formation, Tyers Conglomerate) in the Monash trough are dominated by mudstones, siltstones with lesser quartzose sandstones, conglomerates and thin coals. The sediments are over 300 m thick and are conformably overlain by 100 m of volcaniclastic sediments typical of the main Strzelecki Group, in turn overlain by nearly 100 m of Cenozoic coal measures. New detailed spore–pollen dating of Yallourn North-1A cores indicates that all Cretaceous sediments in the Monash trough are Barremian in age. This revises the traditional Neocomian age assigned to the formation. High total organic carbon levels in the 100 m-thick mudstones of the Locmany Member in the Rintouls Creek Formation constitute a mature petroleum source rock worthy of future hydrocarbon exploration.

The Pennsylvanian Springhill Mines Formation: sedimentological framework for a portion of the Joggins Fossil Cliffs UNESCO World Heritage Site

This is the first detailed study of the coastal exposure of the Springhill Mines Formation within the Joggins Fossil Cliffs World Heritage Site. A 16.9-m-thick interval of dark laminated mudrocks and sharpbased sandstones at the base of our section is reassigned to the top of the Joggins Formation. This interval records a rapid, presumably widespread flooding event and the temporary establishment of a marginalmarine to brackish bay. The overlying 697 m of strata represent deposition in poorly drained and well-drained environments, and are assigned to the Springhill Mines Formation. Strata reflecting poorly drained environments contain green and grey mudrocks, thin coals, sheet sandstones, and channel bodies interpreted to have been deposited in coastal swamps and low-lying parts of a floodplain. Intervals reflecting well-drained conditions contain reddish brown mudrocks, sheet sandstones, and channel bodies interpreted to have been deposited on a vegetated floodplain that was periodically exposed to oxidizing conditions. Strata reflecting poorly drained conditions are thick and abundant in the lower half of the formation and well-drained intervals become thick and more abundant in the upper half. The shift in facies abundance is accompanied by an interpreted evolution in fluvial style from predominantly anastomosed channels (below 376 m) to sheet-like channel bodies (376–449 m) and ultimately to predominantly meandering-channel bodies (449–697 m). The formation-scale changes in drainage conditions and fluvial style records decreased halokinetic subsidence and aggradation of the alluvial surface as sediments shed from the Caledonia Highlands prograded into this part of the basin.

Selection of monitoring techniques for a carbon storage and enhanced coalbed methane recovery pilot test in the Central Appalachian Basin

The goals of monitoring, verification, and accounting (MVA) for carbon capture, utilization, and storage (CCUS) studies include improved understanding of injection and storage processes, evaluation of interactions among carbon dioxide (CO2), reservoir fluids, and formation solids, and assessment and minimization of environmental impacts (DOE and NETL, 2009). Site-specific selection of tools for a well-rounded MVA program may include technologies for atmospheric, near-surface, and subsurface monitoring.An upcoming small-scale CCUS study in an active coalbed methane field in Buchanan County, Virginia, presents a unique application for several established, effective MVA methods. The study will involve injecting up to 20,000tonnes of CO2 into three injection wells over a one-year period in order to test the injection and storage potential of the coal seams and to assess the potential for enhanced coalbed methane (ECBM) recovery at offset production wells. The reservoir consists of approximately 15 to 20 coal seams, averaging 0.3m (1.0ft) in thickness and distributed over 300m (1000ft) of vertical section. This reservoir geometry creates an unusual target for CO2 injection and also a challenging one for many monitoring and imaging techniques. MVA for the Buchanan County test will include gas content measurements at offset wells, groundwater monitoring, injectate tracer analysis, well logging, surface deformation measurement, passive microseismic monitoring, and tomographic fracture imaging. Multiple monitoring wells will be drilled in order to facilitate the MVA efforts. Surface deformation measurement, microseismic monitoring, and tomographic fracture imaging are state-of-the art tools that have potential to define the subsurface CO2 plume beyond the borehole scale. The results of the MVA program for the Buchanan County injection demonstration can be used to improve design for potential future studies of CCUS in thin coals.

New evidence concerning the thermal history of Devonian and Carboniferous rocks in the South Portuguese Zone

The Late Palaeozoic rocks of southern Portugal have a complex thermal history. Vitrinite reflectance determinations from 90 samples confirm that the organic maturity of Late Palaeozoic rocks in SW Portugal is very high, mainly corresponding to meta-anthracite coal rank. The optic fabric of vitrinite in oriented coal samples from the Brejeira Formation suggests maturation under simple, non-tectonic, burial conditions with peak temperatures being attained prior to Variscan deformation. The lack of any increase in vitrinite reflectance with depth through c . 1 km of section in borehole AC-1 is not consistent with conductive heat transfer and is interpreted as the result of late synorogenic to post-orogenic advective heating. This heating episode generated temperatures sufficiently high to produce levels of maturity corresponding to meta-anthracite coal rank through much of the terrane now exposed, but not high enough to result in overprinting of the pre-deformation optic fabric of vitrinite in the thin coals. The slightly lower maturity of older, platform-facies rocks in the Aljezur–Bordeira area may reflect either deposition on a basement high followed by less burial than adjacent parts of the basin, or the area being the site of a sink for descending relatively cool fluids.

Emerging continuous gas plays in the Cooper Basin, South Australia

Recent off-structure drilling in the Nappamerri Trough has confirmed the presence of gas saturation through most of the Permian succession, including the Roseneath and Murteree shales. Basin-centred gas, shale gas and deep CSG plays in the Cooper Basin are now the focus of an escalating drilling and evaluation campaign. The Permian succession in the Nappamerri Trough is up to 1,000 m thick, comprising very thermally mature, gas-prone source rocks with interbedded sands—ideal for the creation of a basin-centred gas accumulation. Excluding the Murteree and Roseneath shales, the succession comprises up to 45% carbonaceous and silty shales and thin coals deposited in flood plain, lacustrine and coal swamp environments. The Early Permian Murteree and Roseneath shales are thick, generally flat lying, and laterally extensive, comprising siltstones and mudstones deposited in large and relatively deep freshwater lakes. Total organic carbon values average 3.9% in the Roseneath Shale and 2.4% in the Murteree Shale. The shales lie in the wet gas window (0.95–1.7% Ro) or dry gas window (&gt;1.7% Ro) over much of the Cooper Basin. Thick Permian coals in the deepest parts of the Patchawarra Trough and over the Moomba high on the margin of the Nappamerri Trough are targets for deep CSG. Gas desorption analysis of a thick Patchawarra coal seam returned excellent total raw gas results averaging 21.2 scc/g (680 scf/ton) across 10 m. Scanning electron microscopy has shown that the coals contain significant microporosity.

A review and technical summary of the AAPG Hedberg Research Conference “Variations in fluvial-deltaic and coastal reservoirs deposited in tropical environments”

This conference addressed the question of whether fluvial-deltaic and coastal reservoirs deposited in tropical environments exhibit different facies relationships than those of temperate systems. Although this conference concluded that there is nothing distinctly unique about clastic depositional systems in tropical environments, the magnitude of the processes that operate in these environments differs from nontropical environments. Because these processes influence the distribution of reservoir and nonreservoir facies, geologists need a fundamental understanding of the contrasts between tropical and nontropical environments when interpreting subsurface data and building depositional models. We highlight the following features that seem to be more favorably developed in tropical environments. (1) Many tropical systems exhibit complexly stacked channel and overbank deposits. Although some fluvial deposits have the classic meandering pattern, seismic attributes indicate that many tropical channel belts are anastomosing systems that intersect each other at large angles. Subsurface correlation without the benefit of three-dimensional seismic data is all but impossible. (2) In contrast to deltaic deposits in temperate climates, which exhibit high sand/shale ratios near the delta with sand content decreasing basinward and laterally away from the delta, tropical deltas tend to be muddier near the river mouth and have cleaner, well-sorted sand bodies better developed laterally in the shoreface and shallow-marine environments. (3) Modern tropical coasts are home to large estuarine environments dominated by mangroves. Estuarine deposits interpreted in the subsurface and observed in outcrop are sand rich, yet little sand is observed in modern mangrove estuaries. Mangrove estuarine deposits also contain abundant organic-rich layers, thin coals, and dispersed organic matter that may favor the development of a self-sourced petroleum system. The flushing of these systems during relative low stands may be an important mechanism not only for reservoir development, but also for dispersing organic matter into deep-water systems. This conference was dominated by discussions of depositional systems in Southeast Asia, which have a strong tectonic overprint. Further research on tropical systems from the South American and African conjugate margin could provide important tests for the ideas highlighted above.

Geochemistry of Late Triassic coals in the Changhe Mine, Sichuan Basin, southwestern China: Evidence for authigenic lanthanide enrichment

Abstract Five thin coals of Late Triassic age occur in the Changhe Mine, Sichuan Basin, southwestern China. Petrology and geochemistry of these coals and their roof, parting, and floor samples were studied. The results show that the Changhe coals are enriched in As (8.9–11.8 μg/g), W (2.2–11.2 μg/g), Pb (20.8–48.2 μg/g), and Th (7.5–18.8 μg/g). The source of these elements is possibly the Xuefeng old land which is an early Paleozoic source area southeast of the Sichuan Basin. Two tonsteins were found in the Changhe Mine. One is the roof (K8R) of the K8 coal which is a pure kaolinitic claystone. The other is the claystone (K9C) above the roof of the K9 coal which is mainly made up of mixed illite–smectite minerals. The REE content (287.9 μg/g) of the K8 coal is much higher than that of its roof (153.6 μg/g). SEM-EDX results show that authigenic monazite and kaolinite are the main carriers of REE in the K8 coal. On the basis of coal chemistry and occurrence of the precipitated minerals, it is likely that leaching of the K8R tonstein occurred. It is possible that trace elements including Be (8.4 μg/g), Zr (302 μg/g), Nb (26 μg/g), Hf (9.7 μg/g), Th (18.8 μg/g), U (5.8 μg/g), Ga (16.1 μg/g), and Pb (48.2 μg/g) in the K8 coal were also elevated by the leachate of its overlying tonstein (K8R). The K9C tonstein with a total thickness of 16 cm is widely distributed in the Changhe Mine and serves as a distinct marker bed for correlation of coal seams. Besides mixed illite–smectite minerals, trace amounts of euhedral zircon, anatase, apatite, and massive silica with vesicular structure were also examined, these constitute strong evidence for its felsic volcanic ash origin.

U and Th in some brown coals of Serbia and Montenegro and their environmental impact

The objective of this paper is to determine and compare the concentrations of U and Th in soft to hard brown (lignite to sub-bituminous) coals of Serbia and Montenegro. It also presents comparison of the obtained data on U and Th concentrations with the published data on coals located in some other countries of the world. Almost the whole coal production of Serbia and Montenegro is used as feed coals for combustion in thermal power plants. Channel samples from open pit and underground mines and core samples were collected for hard and soft brown coals. For the analysis the samples were decomposed using microwave technique. Obtained solutions containing U and Th were analyzed by inductively coupled plasma mass spectroscopy (ICP-MS) using NIST standards. Concentration of U from the investigated basins and the corresponding mine fields ranges within 0.60-70.10 mg/kg, 0.65-3.20 mg/kg, 0.95-6.59 mg/kg, 1.20-6.05 mg/kg, 0.80-6.66 mg/kg, 0.18-89.90 mg/kg, 0.19-4.14 mg/kg, and 0.28-3.52 mg/kg for the Kostolac, Kolubara, Krepoljin, Sjenica, Soko Banja, Bogovina East field, Senje-Resavica and Pljevlja basins, respectively. Concentration of Th ranges within 0.20-2.60 mg/kg, 0.84-6.57 mg/kg, 1.48-6.48 mg/kg, 0.12-2.71 mg/kg, 0.13-4.95 mg/kg, 0.14-3.48 mg/kg, 0.29-3.56 mg/kg, and 0.17-1.89 mg/kg for the Kostolac, Kolubara, Krepoljin, Sjenica, Soko Banja, Bogovina East field, Senje-Resavica and Pljevlja basins, respectively. Brown coal from Senje-Resavica, Kolubara, Kostolac and Pljevlja is characterized by low U concentration. Coals form the Krepoljin, Soko Banja and Sjenica basins have slightly higher U concentrations than the mentioned group. The highest concentration of U is characteristic for the coal from the Bogovina East field. Concentration of Th in coals from Serbia and Montenegro has proved to be low. Out of all investigated coal basins, only the coal from the Krepoljin and Kolubara basins has high concentration of Th. The hydrothermally altered rocks of the Timok dacite-andesite complex, representing the basement of the Bogovina basin, could be a potential source of U, especially at the bottom part of the Lower seam of the Bogovina East field. This study shows that brown coals in Serbia and Montenegro (soft to hard brown coals or lignite to sub-bituminous) contain low levels of U (5.30 mg/kg, average value and 2.10 mg/kg geometric mean value) and Th (1.80 mg/kg, average value and 1.12 mg/kg geometric mean value). There are some obvious differences in concentration of U and Th in coals from different basins in Serbia and Montenegro. The approximate value for U and Th release mainly from power plants was 644.33 t and 983.46 t, respectively within the period 1965-2000 for the studied mines in Serbia, and 23.76 t and 15.05 t for the Potrlica mine (Montenegro) within the period 1965-1997. The coals in Serbia and Montenegro show no identifiable unfavourable impact on the surrounding environment, due to low natural radioactive concentration of U and Th, but further investigations concerning human health should be performed. Preliminary research revealed that in some Serbian coals (and, particularly, parts of the coal seam) U and Th content are rather high. Such coals should be carefully studied, as well as U and Th concentrations in ash, fly ash, waste disposals, nearby soil and ground water. Further studies should include determination of the radioactivity of all these products, and estimation of possible health impact.

Late Carboniferous palaeobotany of the upper Bideford Formation, north Devon: a coastal setting for a Coal Measures flora

The Culm Seams are thin coals in the Upper Carboniferous upper Bideford Formation of north Devon. Clastic sedimentary rocks associated with the coals have yielded a fossil macroflora dominated by the remains of the Calamostachyales and Medullosales, together with subsidiary lycophytes, sphenophylls, ferns, lagenostomaleans, rare cordaites, and a possible early cycad. The flora is probably early Langsettian in age, which is in agreement with the evidence of the non-marine bivalves and marine bands. It is broadly similar in composition to contemporaneous macrofloras from South Wales. It is unlikely to represent an assemblage formed from plant remains subject to longdistance transportation. Rather, it was probably preserved in the lower reaches of a ‘bird-foot’ delta that had temporarily transgressed into the Culm Basin. The distal margin of this delta would represent a comparable habitat to the levees of the rivers further inland, and thus would have supported vegetation similar to that which generated the more usual Coal Measures macrofloras.

Groundwater flow associated with coalbed gas production, Ferron Sandstone, east-central Utah

The flow and distribution of water associated with coalbed gas production in the Ferron Sandstone was characterized utilizing a discrete fracture network model and a porous media model. A discrete fracture network model calculated fluid flux through volumes of various scales to determine scale effects, directional bulk permeability, and connectivity. The mean directional permeabilities varied by less than a factor of 6, with the northwest–southeast direction (face cleat direction) as the most conductive. Northwest southeast directed hydrofracture simulations increased permeability in all directions except the northeast–southwest, although the permeability increase was not more than a factor of 3. Cluster analysis showed that the simulated cleat network was very well connected at all simulated scales. For thick coals, the entire cleat network formed one compartment, whereas thin coals formed several compartments. Convex hulls of the compartments confirmed that the directional bulk permeability was nearly isotropic. Volumetric calculations of the Ferron coal indicated that all the water produced to date can be accounted for from the coal cleat porosity system and does not depend on contributions of water from contiguous units.Flow paths, determined from porous media modeling from recharge to discharge, indicate that the three coalbed gas (CBG) fields assessed in this study could have different groundwater chemical compositions as confirmed by geochemical data. Simulated water production from 185 wells from 1993 to 1998 showed that in 1998 the maximum head drawdown from the Drunkards Wash field was more than 365 m, and the cone of depression extended to within a short distance of the Ferron outcrop. Maximum drawdown in the Helper field was 120 m, and the maximum drawdown in the Buzzards Bench field was just over 60 m. The cone of depression for the Helper field was half the size of the Drunkards Wash field, and the cone of depression for the Buzzards Bench field was limited to just outside the field unit. Water budget calculations from the simulation indicate that none of the stream flows are affected by coalbed gas associated water production.

A Completion Solution for the Paddy Reservoir in Northeast British Columbia: A Case Study

Abstract The Paddy reservoir, located near the Foothills of the Rocky Mountains in northeast British Columbia, Canada, is a fluvioestuarine valley-filled sandstone that has moderate to high permeability. Evidence of tectonic stress has been observed during hydraulic fracture treatments in the form of excessive wellbore friction and net pressures. Historically, attempts to fracture-stimulate these wells has been difficult due to the inability to generate sufficient fracture width necessary for proppant placement. This paper presents a completion solution for the Paddy reservoir in northeast British Columbia that enabled successful placement of propped fracture treatments. Pressure response of past fracture treatments were analysed to understand the cause of past failures, and to quantify the influence of tectonicallyinduced stress. A recommended completion solution is presented which includes orientated perforating to reduce near-wellbore friction and a process for designing fracture treatments to enable successful placement of proppant. Field examples of the new completion technique are presented which show that near-wellbore friction was reduced by 50%, and that up to four times the amount of proppant was placed in the formation compared to previous treatments. Pressure match simulation results from the fracture treatments are also presented. Geologic Summary The Paddy Member forms the upper portion of the Peace River Formation and is distributed over the Peace River area of northwest Alberta and northeast British Columbia. It is underlain by dominantly coarse-grained shoreface deposits of the Cadotte Member and overlain by marine shales of the Shaftesbury Formation. The Paddy Member is made up of thinly bedded sandstones and shales with occasional thin coals. In the study area, the Paddy is approximately 40 m thick. Reservoir quality, incised valley sandstones located in the upper part of the unit are up to 18 m thick. They are dominantly fine to medium and occasionally coarse grained, fairly quartz-rich sandstones with 10 - 30% chert and other lithic grains. Beds are from centimetre to metre scale in thickness and show small to large-scale trough cross lamination. Where bedding thickness is reduced, millimetre scale wavy shale laminae are common and are often incorporated into stylolitic concentrations, which greatly reduce vertical permeability. The cleaner sandstones were probably deposited under fluvial conditions with some tidal influence where thin shale laminae are common. The dominant cement in these sandstones is quartz, which substantially occludes intergranular porosity in the study area. Small amounts of carbonate cements also occur but are rarely volumetrically important. In addition to intergranular porosity, a significant amount of microporosity has been generated through the dissolution of detrital grains, primarily chert. The abundance of microporosity in these sandstones, together with low water saturations indicated by wireline log analysis, may be the origin of the widely held concern that the Paddy reservoir is susceptible to formation damage through water blocking. Core from the study area indicates that porosity in the Paddy reservoir ranges up to 20%, with associated permeability to air at minimal confining pressure of several hundred millidarcies. A minimum porosity cutoff for pay is taken at approximately 8 - 9%, which is typically associated with 1 md permeability.

From Cyclothems to Sequences: The Record of Eustasy and Climate on an Icehouse Epeiric Platform (Pennsylvanian-Permian, North American Midcontinent)

The stratigraphic succession of the North American Midcontinent contains a high-resolution (< 100,000 year) record of sea level and climate change spanning the Pennsylvanian-Permian boundary. Outcrop-based sequence stratigraphic analysis on the upper Wabaunsee, Admire, and lower Council Grove groups in Kansas and Nebraska reveals a hierarchy of fifty-one fifth-order meter-scale cycles grouped into five fourth-order composite sequences. Fifth-order cycles are bounded by subaerial unconformities in nearshore settings and correlative conformities in offshore settings, and are therefore very thin depositional sequences. Lowstand systems tracts, observed only in nearshore deposits, are expressed as sandy, incised-valley fills in these meter-scale cycles. Transgressive systems tracts, which are dominated by carbonate deposition, include coastal evaporites indicating arid climatic conditions. Highstand systems tracts, which are dominated by siliciclastic deposition, include thin but persistent coals in muddy coastal successions indicating humid climatic conditions. Paleosols at sequence boundaries evolve from vertic to calcic, indicating climate change from relatively humid to relatively arid conditions during subaerial exposure. This indicates that relatively arid climate coincided with eustatic lows while relatively humid climate coincided with eustatic highs on this low-latitude platform. Composite sequences are bounded by subaerial, angular unconformities and display a transgressive-regressive stacking pattern of meter-scale cycles. The high-resolution stratigraphic record of the Midcontinent helps constrain the rate and magnitude of environmental change in ancient icehouse conditions and can serve as a baseline of environmental change for comparison with other coeval successions.

Controls on boron and germanium distribution in the low-sulfur Amos coal bed, Western Kentucky coalfield, USA

The Duckmantian-aged Amos coal bed is a thin (<51 cm) coal bed that occurs in lobate southwest-trending pods separated by thin sandstones in the Western Kentucky coalfield. The coal bed, which is comprised of up to two benches and a rider coal, is low in ash yield (<6%) and sulfur content (<1%). The coal tends to be thin (<40 cm), but it was heavily mined in the 1980s because it could be combusted as mined. Geochemical analysis of the Amos coal bed shows higher concentrations of B and Ge than other Western Kentucky coal beds. High total B concentrations as well as high B/Be, both considered to be indicators of marine environments, increase toward the top of the coal bed. Most of the B values for the Amos samples range from 66 to 103 ppm (whole coal basis) indicating deposition in a brackish environment. High Ge concentrations in coals have been considered to be a function of seam thickness and proximity to the top and bottom of the coal bed. Thin coals, such as the Amos, are dominated by the coal bed margins and, therefore, have a tendency to have relatively high Ge concentrations. In the case of the Amos coal bed, the lower bench has a higher Ge content, suggesting that the substrate was a more important source of Ge than the roof rock.

The Upper Hance coal bed in southeastern Kentucky: palynologic, geochemical, and petrographic evidence for environmental succession

The Upper Hance coal bed in Bell County, eastern Kentucky exhibits considerable variation in depositional setting on a mine scale. Palynology and geochemistry of the coal are examined in order to supplement previous petrographic examinations. The various depositional settings of the Upper Hance mire progress from the pioneer, possibly partially allochthonous, settings at the mire margins and base; to the well-developed, planar to domed main body of the mire; and finally to the terminal events of flooding, clastic influx, and temporary reestablishment of mires now seen as the thin rider coals. Palynologic diversity generally decreases upwards from the basal lithotype through the main body of the coal bed. The cannel and rider lithologies represent distinct depositional events.

Peat accumulation on a drowned coastal braidplain: the Mullins Coal (Upper Carboniferous), Sydney Basin, Nova Scotia

The Mullins Coal lies within the braided-fluvial South Bar Formation. The lateral extent (15 km) and thickness (2 m) of the coal suggest that controls for peat accumulation were allogenic. Marine inundation of the distal braidplain, as indicated by the high-sulphur content of the coal and the occurrence of agglutinated foraminifera in associated shales, caused ponding of freshwater near maximum marine transgression, with accumulation of thick paralic peat across a stable platform of sandy fluvial sediments. Highstand parasequences with thin capping coals were subsequently incised beneath a sequence boundary as the braidplain readvanced. The Mullins Coal thins and splits in association with muddy bayfill deposits eastward towards the Glace Bay Syncline, a long-lived palaeotopographic element related to fault-bounded basement blocks. Although relative sea-level change controlled the stratigraphic position of the precursor peats, differential tectonic subsidence and/or compaction modified their extent, thickness and quality.