bluuebunny/crossref_metadata_2025 huggingface dataset:
History of exploration in the southern North Sea
Authors: Glennie K. W.
Published: April 2008

Exploration history in the Southern North Sea Basin extends back to 1858 in Germany, which was the centre of Europe’s oil industry for about a century, with a resurgence in oil discoveries from 1934 to 1945. This changed dramatically in 1963 with the realization of the immense size of the Dutch Groningen gas field. Core data indicated that the Rotliegend reservoir extended westward into the southern North Sea. Between December 1965 and October 1966, five major gas discoveries totalled reserves of almost 20 tcf, sufficient to saturate the UK monopoly market. By 1969, with cheaper seismic ships and a billion barrel oil field in Norwegian waters, UK exploration activity shifted to the central and northern North Sea. The UK southern North Sea became a backwater until about 1981 when, with a pending shortage, British Gas encouraged renewed activity by increasing the price for new gas, the Carboniferous soon becoming an exploration target. Meanwhile, exploration in the Dutch land and offshore, and German land areas resulted in a steady stream of gas discoveries and some oil derived from Liassic source rocks, both enhanced by the later use of 3D seismic data.
Compartmentalization of Rotliegendes gas reservoirs by sealing faults, Jupiter Fields area, southern North Sea
Authors: Leveille Gregory P. , Knipe Rob , More Colin , Ellis Dave , Dudley Graham , Jones Greg , Fisher Quentin J. , Allinson Gareth
Published: April 2008

Rotliegendes gas reservoirs in the Jupiter Fields are compartmentalized by sealing faults. Significant variations in free water levels (i.e. gas-water contacts corrected for capillary pressure effects), hydrocarbon composition and pressure exist between sealed fault blocks. Displacements on many of the sealing faults are low, resulting in ‘clean’, porous and permeable Rotliegendes sandstones being juxtaposed across the faults. Characteristics that are important in determining the sealing potential of intra-Rotliegendes faults include (i) fault-rock cement types and volumes, (ii) intensity of cataclasis, (iii) three-dimensional continuity of the fault and associated damage zone, (iv) authigenic clay content at the time of faulting, and (v) relative orientation, timing and magnitude of later deformational events.

Detailed analysis of fault rocks from core indicates cementation is the most effective fault sealing mechanism in the Jupiter Fields. Volumetrically significant cements include salt, anhydrite and quartz. Cataclasis and deformation induced mixing of authigenic clay with fragments of framework grains also contribute to the sealing potential of some faults. Permeabilities in cemented and cataclastic fault rocks are reduced by two or more orders of magnitude compared to undeformed sandstones.

3D seismic mapping indicates NNE-SSW-trending fault zones have the highest along-strike continuity, followed by NW-SE- and E-W-trending fault zones. The NNE-SSW-trending faults also appear to have had the simplest deformational history, with NW-SE- and E-W-trending faults exhibiting evidence of movement during multiple deformational events. Static reservoir data indicate that some NNE-SSW- and NW-SE-trending faults seal over geological time, and it is expected other faults will act as seals or baffles during reservoir depletion.
Diagenetic controls on reservoir quality in Permian Rotliegendes sandstones, Jupiter Fields area, southern North Sea
Authors: Leveille Gregory P. , Primmer Tim J. , Dudley Graham , Ellis David , Allinson Gareth J.
Published: April 2008

Reservoir quality in Lower Permian Rotliegendes Group sandstones in the Jupiter Fields varies considerably between fault blocks due to differing degrees of diagenetic alteration. Average porosities in individual fault blocks range from 12 to 21%, and geometric mean permeabilities vary between 2 and 200 md. Rotliegendes stratigraphy and sedimentology varies little across the area, and therefore does not strongly influence reservoir quality.

The two most important diagenetic processes were the formation of authigenic illite and burial compaction. Illite growth mainly occurred during the Middle Jurassic to Early Cretaceous, coincident with maximum burial of the Rotliegendes. Fault blocks with good reservoir quality generally contain (1) relatively low illite abundances, (2) low-potassium illite, (3) increasing illite abundances with depth, (4) illite ages that decrease with depth and (5) comparatively low amounts of burial compaction. Fault blocks with poor reservoir quality all exhibit (1) high illite abundances, (2) high-potassium illite, (3) no consistent trend in illite abundances or age with depth and (4) high amounts of burial compaction. These observations are believed to indicate that reservoir quality was preferentially preserved in fault blocks that were structurally high during the main phase of illite growth. Factors contributing to the preservation of reservoir quality in structurally high fault blocks included differences in pore fluid chemistry, less burial compaction, and, in places, early hydrocarbon charging. Reservoir quality in undrilled fault blocks can be predicted by reconstructing the structural geometries present during the Mid-Jurassic to Early Cretaceous.
Probing the lower limits of a fairway: further pre-Permian potential in the southern North Sea
Authors: Cameron Nick , Ziegler Tom
Published: April 2008

Although the southern North Sea has become a major centre of hydrocarbon production, the lower limit of the fairway has not been established. We show, using a review of the pre-Permian source-rock potential of the southern North Sea, that the regional geology will permit exploration below the present base of the fairway. Seismic mapping indicates that this portion of the stratigraphic column is associated with multiple objectives. Two very different examples demonstrate the range of opportunities. The first example is a conventional structural trap located on the northeast flank of the London-Brabant Ridge in Quadrant 53. Reservoirs are the Westphalian to Devonian succession. Source-rocks are lacustrine horizons within the local Westphalian succession and the Carboniferous to Devonian section to the northeast of the South Hewett Fault. The second example presents a new objective, a stratigraphic trap to the ESE of a high located in Quadrants 42 and 43 and identified for the first time by this study. The anticipated reservoir is Dinantian carbonate progradational wedge derived from the adjacent high. Namurian and Dinantian source-rocks are predicted. Until opportunities of these types are evaluated, the lower limit of the Southern North Sea fairway will remain undefined and ultimate reserves estimates will continue to be poorly constrained.
The structure of the Westphalian in the northern part of the southern North Sea
Authors: Quirk David G. , Aitken John F.
Published: April 2008

A clear understanding of the tectonic framework of the Westphalian in the northern part of the southern North Sea has improved confidence during seismic interpretation and offers the possibility of finding new exploration targets within structures that have already been drilled. Two aspects of the tectonic framework are crucial. Firstly, Westphalian strata were deposited within a major foreland basin; consequently, thickness variations on a local scale are minimal. Secondly, the area was affected by a phase of rifting, known as the Saalian event, during the early Permian. This rifting event led to the formation of major E-W and NW-SE normal faults that tilt and offset Westphalian strata. The Upper Rotliegend, which lies unconformably on top of the Westphalian, was deposited during thermal sag after rifting ceased. Identifying where Westphalian reservoirs are present within structure requires careful mapping of both intra-Westphalian and base Rotliegend levels.
Sequence stratigraphy of the Westphalian in the northern part of the Southern North Sea
Authors: Quirk D. G.
Published: April 2008

A series of stacked fluvio-lacustrine sequences in the Westphalian of the northern part of the Southern North Sea can be correlated over areas of greater than 2500 km
2
. Each sequence is similar in terms of thickness (100–300 m) and the internal arrangement of lithofacies but they differ in colour and in the amount of sandstone and coal that they contain. A typical sequence consists of a sand-rich lower unit, a mud-dominated middle unit which fines upwards towards its top and a mud-dominated upper unit which generally coarsens upwards. The main reservoir-prone intervals are confined to the lower-middle parts of sand-rich units and consist of coarse-grained braided or low-sinuousity channel deposits. These fluvial sandstones are laterally extensive and are neither typical of incised valley fills (in terms of stratal geometries) nor of progradational systems tracts (in terms of facies distribution). Instead they appear to have been deposited during periods of widespread fluvial aggradation caused by transgression as a result of relative lake-level rise. Each lower sand-rich unit is overlain by a dark mudstone with a high gamma ray expression which is interpreted as an initial (lake) flooding surface marking the onset of predominantly lacustrine and mire sedimentation associated with the development of the fining-upwards mud-dominated unit. The top of each fining-upwards unit is marked by a maximum gamma ray peak interpreted as a maximum flooding surface which defines the end of lake transgression. Above the maximum flooding surface, each coarsening-upwards mud-dominated unit shows increasing deltaic influence upwards associated with a slowing in the rate of relative lake level rise. The tops of some of these units are eroded suggesting that in some case deltaic progradation was followed by a relative fall in lake level; in other cases the boundary with the overlying transgressive sand-rich unit in the next sequence is wholly conformable. Coal mires developed in coastal areas, particularly during transgression when coarse-grained sediment was trapped up-dip on the coeval alluvial plain. Relative changes in lake level had a periodicity of 1.5 Ma or less indicating that they may be related to third order eustatic cycles.
Lower crustal structure of the East Irish Sea from deep seismic reflection data
Authors: England R. W. , Soper N. J.
Published: April 2008

Deep near-normal incidence reflection profiles across the East Irish Sea show that the middle and lower crust are dominated by dipping reflectors with a NE-SW strike. The northward dipping Iapetus suture can be traced and contoured beneath the Solway Firth where it projects upward beneath the Peel and Solway Firth basins. South of the suture there are both northward and southward dipping reflectors. These are considered to be related to Early Devonian (Acadian) deformation. Although the Carboniferous was deposited in basins with a broadly NE-SW trend there is no clear evidence of reactivation of earlier structures during either Carboniferous sedimentation or Variscan inversion. The faults that controlled Permian and Mesozoic basin development in the East Irish Sea are at a high angle to Caledonian and Acadian trends and are considered to be juvenile structures which developed in the late Westphalian.
The geology and hydrocarbon prospectivity of the North Channel Basin
Authors: Maddox Steven J. , Blow Richard A. , O’Brien Sean R.
Published: April 2008

The geology and hydrocarbon prospectivity of the offshore North Channel has been evaluated, integrating data from a number of onshore wells with seismic, gravity, magnetic and onshore outcrop studies. Interpretation of these data suggest that the North Channel can be divided into two sub-basins, separated by the offshore extension of the Southern Uplands Fault Zone (SUFZ). The narrow, southern, Portpatrick sub-basin has a NNW-SSE trend and consists of a series of simple tilted fault-blocks which dip east, towards the basin-bounding Portpatrick Fault. The northern sub-basin widens considerably into the Larne-Firth of Clyde basin complex, which has a predominantly Caledonide (NE-SW) orientation and is an extension of the Scottish Midland Valley. This sub-basin is characterised by westerly dipping fault blocks, the reversal in basin polarity apparently accommodated along the SUFZ.

The primary reservoir interval is expected to occur in the Lower Triassic Sherwood Sandstone Group, although secondary targets may exist in the Permian and Carboniferous. Shallow coring and seismic facies analysis suggests that the Mercia Mudstone Group subcrops Quaternary-Recent deposits at sea bed and overlies the Sherwood Sandstone. Halites and shales within the Mercia Mudstone Group should provide an effective regional top-seal, except in areas where the Sherwood Sandstone is close to the surface. Large tilted-fault block and rollover anticline traps have been identified on seismic data, although the Carboniferous source rock potential and burial history are poorly understood and exploration risk is high. Regional outcrop patterns and the compaction state of the Mesozoic strata, together with vitrinite measurements suggest the basin was uplifted in the early Tertiary. In common with the East Irish Sea, maturity was probably reached prior to the end of the Cretaceous. This implies that source rocks within the basin will not currently be generating hydrocarbons, having effectively been ‘switched’ off by Tertiary uplift. Charge mechanics are uncertain but must involve early pre-uplift migration or remigration.
Structural evolution of the Isle of Man and central part of the Irish Sea
Authors: Quirk D. G. , Kimbell G. S.
Published: April 2008

Gravity, aeromagnetic, seismic, borehole and outcrop data from the Isle of Man area have been used to study the structural framework and tectonic evolution of the central part of the Irish Sea since the Ordovician. The area has been affected by two major compressional events (Caledonian and Variscan), three rifting events (early Carboniferous, early Permian and ?late Jurassic) and a period of thermal uplift (early Tertiary). A large part of the Isle of Man consists of early Ordovician turbidites (‘basement’) interpreted to have been deposited in a back arc or fore arc basin that was inverted during the Caledonian orogeny. Major NE-SW and subsidiary NW-SE strike-slip faults were initiated at this time, some of which were later reactivated to form important basin controlling faults in the Irish Sea. Post-Caledonian basin subsidence was initiated in the early Carboniferous with a period of NW-SE directed extension followed by thermal sag which ceased at the end of the Carboniferous as a result of Variscan compression. E-W extension in the early Permian led to the development of new extensional faults which have influenced the thickness of the Collyhurst Sandstone in the offshore. Post-rift thermal sag continued throughout the late Permian and the Triassic. A late Jurassic period of extension has been proposed in order to explain post-Triassic offset across major normal faults east of the Isle of Man although direct evidence of syn-rift or post-rift strata has been removed by erosion during uplift in the early Tertiary. This uplift was due to thermal doming of the crust, an event which was associated with the intrusion of a large number of dolerite dykes. The structural evolution of the Isle of Man has also been influenced by a major NW-SE trending basement fracture known as the ‘Central Valley Lineament’ which extends into the offshore to the SE and NW of the island. The lineament appears to be important in defining areas of different hydrocarbon prospectivity in the Irish Sea.
The occurrence and correlation of oils and Namurian source rocks in the Liverpool Bay-North Wales area
Authors: Armstrong James P. , Smith Janet , D’Elia Victor A. A. , Trueblood Stephen P.
Published: April 2008

Along the northeast coast of Wales, the Holywell Shale is a significant lithological unit of about 150 m thickness. In the field, the Holywell Shale appears to be lithologically fairly uniform. Geochemical analysis of field samples has demonstrated highly variable features within the Holywell Shale. These pertain to organic richness and hydrocarbon source potential. Some samples exhibit good to rich potential for oil and gas, with extractable hydrocarbons akin to those of a light or medium gravity crude oil. Richer examples also exhibit higher hydrogen indices. These data point to oil-prone sources which have realised some of their potential. By contrast, the other samples taken from the section, whilst not poor in organic carbon, have low S
1
and S
2
and HI signatures. It is anticipated, from the data collected that cyclicity is present within the Holywell Shale sediments.

The isotope geochemical data also highlights another, more gradual variation. Sources towards the base of the Holywell Shale formation have generated hydrocarbons which are isotopically lighter than those from the middle and upper sections of the formation. This is attributed to middle/upper sections being more proximal to land and consequently, having higher proportions of terrestrially derived organic matter.

Two oils (110/13–10 and 110/15–6) from the Douglas and Lennox fields discovered within the Liverpool Bay area have been analysed. Although the two oils are isotopically similar, chromatography analyses reveal that one oil comprises two hydrocarbon phases whereas the other oil has three envelopes. Extracts taken from the Lower Holywell Shale sources and Holywell bitumen are isotopically similar to both oils. Organically rich sources from higher up in the Holywell Shale formation yield more condensate-like hydrocarbons upon extraction and are isotopically heavier than the oils.
Challenging the ‘sheetflood’ myth: the role of water-table-controlled sabkha deposits in redefining the depositional model for the Ormskirk Sandstone Formation (Lower Triassic), East Irish Sea Basin
Authors: Herries Robert D. , Cowan Greig
Published: April 2008

Two distinct units can be recognized in the Lower Triassic Ormskirk Sandstone Formation in the East Irish Sea Basin. Perennial fluvial channel, lacustrine and minor aeolian sandstones dominate the upper part, but the lower is characterized by thick (tens of metres) enigmatic wavy bedded deposits interbedded with aeolian and minor fluvial channel sandstones. Previous interpretations that invoked an overbank ‘sheetflood’ or ‘sandflat’ origin for the wavy bedding are difficult to reconcile with the sedimentary structures, which are more consistent with algal and evaporitic processes in modern sabkhas. These deposits contain widespread (km) ‘drying upward’ patterns 2–10 m thick, reflecting a sabkha to more aeolian dominated setting. Such thicknesses are consistent with an origin related to 23 000 year Milankovitch cyclicity.

The lower, wavy bedded portion of the Ormskirk Sandstone Formation is regionally truncated by fluvial channel-belt sandstones. Their extent reflects a combination of high sediment supply, uniform subsidence and low basinal relief. Lacustrine units near the top of the formation can be correlated regionally, with one passing southward into a major aeolian unit that thickens to 60 m in the south of the basin. This transition demonstrates the diachroneity of the Mercia Mudstone Group transgression. The key to correlating the Ormskirk Sandstone Formation lies in identifying intervals dominated by fluvial, lacustrine or sabkha-aeolian deposits. Correlation of water-table-controlled ‘drying upward’ patterns within sabkha-aeolian deposits allows finer scale subdivision, and provides an estimate for the degree of fluvial truncation at the top of the unit.
Early Dinantian evaporites of the Easton-1 well, Solway Basin, onshore, Cumbria, England
Authors: Ward Jim
Published: April 2008

An early Viséan, anhydrite-rich, carbonate-clastic succession, of vertical thickness 3784 feet (no base) was found in 1990 at the Easton-1 well in the Solway Basin, onshore Cumbria. The succession is stratigraphically located in the Lower Border Group where only traces of evaporites had been found at outcrop. It is proposed to name the succession the ‘Easton Anhydrite Facies of the Lower Border Group’, abbreviated to ‘EA Beds’.

The EA Beds are divided into three units. Unit 1 at the top, about 400 feet thick, contains two sequences of upwardly thickening anhydrite beds within mixed lithologies. Unit 2, about 2100 feet thick, consists of nine cyclic sequences of limestones, shales and sandstones with numerous interbeds of anhydrite. Overall similarity of several of the sequences suggests similar origins. Unit 2 sequences are grouped into three megacycles, two of approximately 750 feet and one 590 feet thick. Deposition is interpreted to have taken place in arid or partly arid climatic conditions, within a shallow and rapidly, but uniformly subsiding basin with glacio-eustatically controlled rise and fall of sea level. Many of the Unit 2 anhydrite beds are interpreted to be of subaqueous origin. Unit 3, about 1500 feet thick, displays complex patterns of cyclicity with sedimentation apparently responding directly to solar insolation under orbitally induced control within Milankovitch periodicities of 100 000 and 400 000 years. Seismic interpretation indicates that the regional extent of the EA Beds is greater than 1000 km
2
.
Faulting and porosity modification in the Sherwood Sandstone at Alderley Edge, northeastern Cheshire: an exhumed example of fault-related diagenesis
Authors: Rowe John , Burley Stuart D.
Published: April 2008

The Alderley Horst is an exhumed, titled structure close to the eastern margin of the Cheshire Basin, broadly analogous to the titled fault blocks in the East Irish Sea Basin. Sediments of the Lower and Middle Triassic Sherwood Sandstone Group are exposed at the crest of the horst whilst its flanks are capped by sediments of the Mercia Mudstone Group. Extensive diagenesis and porosity modification have taken place in the Sherwood Sandstone across the Alderley Horst.

Diagenetic modification includes reduction of hematite grain coatings and quartz cementation, together with Cu-Pb-Zn-Fe sulphide and barite mineralization. The distribution of this cementation is spatially related to faults that cross the horst and its style and extent varies between individual faults and between fault sets of different orientations. Different spatial distributions are observed for quartz cements, barite, sulphides, ferroan calcite, reduction of hematite grain coatings and secondary ore concentrations. Sandstone units close to the base of the Mercia Mudstone Group are more intensely altered than lower units showing that hematite reduction and mineralization are concentrated at the crest of the horst.

Fault-related mineralization and porosity modification post-dates all of the fault movement as brecciation and deformation of barite and sulphide cements are not observed. The intensity of mineralization decreases at structurally lower levels on the WNW-ESE oriented faults, so precluding them as conduits for the vertical migration of mineralizing fluids. However, the horst-bounding Kirkleyditch Fault was probably an important migration pathway that enabled valving of fluids from dowthrown sources in the Mercia Mudstone Group, Manchester Marls and Carboniferous shales, although the possibility of fluid migration up-dip from the south cannot be completely discounted. The mineralizing fluids were ponded at the crest of the horst where they were baffled by pre-existing structural barriers.
Calder Field appraisal well 110/7a-8, East Irish Sea Basin
Authors: Blow R. A. , Hardman M.
Published: April 2008

The Calder Field, Block 110/7a, is located approximately 5 km southwest of the South Morecambe Field in 100 feet of water. The field was discovered by well 110/7a-3 in 1982; this was the first well in the East Irish Sea Basin (EISB) to encounter sour gas (H
2
S 4500 ppm) and live oil. Well 110/7a-4 was drilled to appraise the discovery in 1983; this well produced sour gas at a combined flow rate in excess of 25 MMSCFD from the Sherwood Sandstone Group reservoir. Whilst the two wells proved the presence of gas within the Sherwood Sandstone Group they also indicated a significant velocity variation within the Mercia Mudstone Group overburden. This resulted in uncertainty in depth conversion to top reservoir and also in reserve estimates based upon the depth maps. In an attempt to narrow the reserve uncertainty an integrated geological and geophysical re-evaluation of the field was carried out. This involved detailed subdivision of the Mercia Mudstone Group based on mudstone/halite stratigraphy together with intra-Mercia Mudstone Group seismic interpretation. This approach generated a velocity and depth model successfully tested by appraisal well 110/7a-8 which was drilled during 1994. Implicit in the field model are the occurrences on seismic section of a dipping ‘flat spot’ associated with the gas/oil contact and also pseudo-faulting at top reservoir level, both generated by lateral velocity variations in the near-surface section.
The Czech Republic energy policy: conception and implementation in a market economy
Authors: Doruška Josef
Published: April 2008

In 1992 the government of the Czech Republic approved the ‘Energy Policy of the Czech Republic’. It was directed to the legislative and ecological respects which are compatible with European Union countries.
Coal production and usage in the Czech Republic
Authors: Pešek J. , Dopita M.
Published: April 2008

Coal mining in the industrialized countries of Europe including the Czech Republic is witnessing a prolonged recession in the production of bituminous coal and lignite in particular due to reduced demands. Recession in numerous fields of industry has resulted apparently in lower production of metallurgical coke as well as in power generation. In addition, some countries have substituted the burning of solid fossil fuels with petroleum or natural gas or with other energy sources such as nuclear power, hydroenergy or geothermal energy. The Czech Republic is facing similar problems.
The origin and properties of a coal seam associated with continental thin micritic limestones, Selimoglu-Divrigi, Turkey
Authors: Karayigit A. I. , Whateley M. K. G.
Published: April 2008

The Selimoglu coalfield is situated at the southeastern part of Divrigi, which is geographically distinct from the major coalfields of Turkey. A number of thin and lenticular coal seams and sedimentary rocks occur in the Selimoglu unit of the Ogulbey Formation of Upper Miocene age. Only one seam, which is produced by an underground method, is associated with continental thin micritic limestones that have a total thickness of about 150 cm. It has a macroscopically bright appearance and a working thickness of 50–90 cm (70 cm average). A total of 32 channel samples were collected from the mined seam for proximate, mineralogical and petrographic analyses. The results of proximate analyses on an air-dried basis show that the coal is characterized by low moisture content (1.68% average), high ash yield (24.04% average), high total sulphur content (up to 8.92%) and high calorific value (5606 kcal kg
−1
average). The coals average 65.5% vitrinite, 4.5% liptinite, 2.5% inertinite and 27.4% mineral matter. Desmocollinite is the dominant maceral in the vitrinite group and calcites in the whole-coal minerals. Carbonate minerals with irregular shapes are in general early-diagenetic, and occur in desmocollinites in all the samples. The micritic texture of the limestone shows both diagenetic and authigenic origin in subaquatic conditions with high pH, but organic debris is allochthonous in origin. The reflectance values of telocollinite (0.77% Rr) show a high volatile bituminous coal rank. The random reflectance of telocollinite and spectral maxima (625–661 nm) of sporinites, and proximate analyses reveal that the thermal history may have been affected by volcanic activity that occurred in the coal field.
The main coal facies and lithotypes of the Pliocene coal basin, Oltenia, Romania
Authors: Ţicleanu Nicolae , Diaconiţǎ Dorina
Published: April 2008

This paper presents the results of palaeobotanical studies correlated with coal petrography research carried out by the authors in the western part of the Dacic Basin (Oltenia) coal deposits. Of the seven coal facies that have been distinguished so far in the lignites of Oltenia, the present paper deals with the five main facies generated by: swamp deciduous forest, Carex ssp. grassy marsh, swamp with Glyptostrobus, reed swamp and aquatic macrophyte prairie. The palaeoecological and palaeophytocoenoical studies have led to the reconstruction of the factors that characterize the major coal facies.
Coal petrology and facies associations of the South Yakutian Coal Basin, Siberia
Authors: Stukalova I. E.
Published: April 2008

The South Yakutian Coal Basin consists of isolated depressions in the south of the Yakutian region of Eastern Siberia in Russia, which are filled with Jurassic and Cretaceous coal-bearing sediments. The basin contains considerable resources of high-quality bituminous coals, with a caking index (
y
) of 6–21 mm. The coal-bearing formation contains coal seams of various thickness, from 0.5–2.5 m up to 15.0 m and above. Some of them are near the surface and can be mined by opencut methods. Genetic types and facies of the Mesozoic coal-bearing strata have been recognised as proluvial, alluvial, delta, lacustrine-swamp and peat bogs sediments. The petrographic composition of the sandstones identified four terrigenous-mineral associations, which are represented by true arkoses, greywacke arkoses, feldspar-quartz and quartz-feldspar greywackes. Humic coals consists of vitrinite (70–90%), interinite (10–20%) and liptinite (0–10%) maceral groups. In the vitrinite maceral group there is a high percentage of telinite macerals, up to 60–65%. The basin is characterized by a high alteration of Mesozoic sediments and organic matter. Coals are of middle and high rank (0.65–2.15%
R
0
). There are high concentrations of bitumen in chloroform extracts of organic matter from the coals, from 0.0938% to 3.6466%. The mineral matter of terrigenous rocks is altered to the catagenetic stage and the metagenetic stage. The South Yakutian coals are of high quality because of their rank and composition.
Coal rank variations with depth related to major thrust detachments in the South Wales coalfield: implications for fluid flow and mineralization
Authors: Gayer Rod , Fowler Richard , Davies Gareth
Published: April 2008

Coal maturity data in the form of volatile matter (daf and dmmf) and random vitrinite reflectance have been analysed for the South Wales coalfield. They show that in general coals increase in rank with depth, obeying Hilt’s law, and increase in rank laterally from high volatile bituminous coals in the south and east of the coalfield to anthracite in the northwest of the coalfield. The lateral increase in rank does not coincide with the basin depocentre which was located to the southwest of the coal basin during Westphalian times. The rank pattern with depth in the Westphalian A-Lower Westphalian C Coal Measures of the eastern half of the coalfield suggests a palaeogeothermal gradient of approx. 310°C km
−1
, equivalent to a basal heatflow of 295 m Wm
−2
. Investigation of vitrinite reflectance in a coal sequence repeated by intense Variscan thrusting indicates that coal rank was acquired both pre- and syn-thrusting. Detailed analysis of the volatile matter data reveals the presence of excursions from Hilt’s law present in one or more coal seams close to the boundary between Westphalian A & B. Of the 154 data sets analysed from the coalfield, 94 (61%) show one or more excursion. It is shown that the excursions correlate with thrust detachments within the coal seams, and it is argued that the excursions represent an increase in maturity temperature caused by fluids carrying heat into the coal seam along the seismically active thrusts. The fluids may also have been responsible for the carbonate, oxide and sulphide mineralization of the coalfield. Preliminary comparisons with the Ruhr coal basin in Germany suggest that future studies involving computer generated thermal models are required to understand the thermal evolution of both basins.
Deep borehole evidence for a southward extension of the Early Namurian deposits near Němčičky, S. Moravia, Czech Republic: implication for rapid coalification
Authors: Dvořák J. , Honěk J. , Pešek J. , Valterová P.
Published: April 2008

Unexpected Early Namurian (Namurian A) sediments were identified in several boreholes in the vicinity of Němčičky (the Němčičky basin), south Moravia. Coal fragments were recovered from the boreholes Něm 1, 2, 5 and 6. These fragments come partly from
in situ
coal seams, partly from eroded coal seams and partly from coalified logs. Although these fragments were recovered from depths of 2690.9 m (Něm 5) to 4803 m (Něm 1), their mean reflectance (
R
0
) is 0.57% up to 0.9% which corresponds to subbituminous to high volatile bituminous coal. The very low rank of the coal at these depths argues for very fast coalification of the coal fragments most likely during the Carboniferous. The rank of the coal is believed not to have been affected by later burial beneath Jurassic sediments or by tectonic burial under Carpathian nappes.
Comparison of solid state
13
C NMR of algal coals/anthracite and charcoal-like fusinites: further evidence for graphitic domains
Authors: Premović P. I. , Nikolić R. S. , Premović M. P.
Published: April 2008

Carbon distribution in coals and coal macerals was studied by
13
C NMR cross-polarization (CP)/ magic angle spinning (MAS) spectrometry. We examined two charcoal-like fusinites from Serbia: the Jerma (Jerma mine) and Miroč (mine ‘Aliksar’) seams. This examination revealed that atomic H/C ratios calculated (on the basis of the CP/MAS parameters) for fusinites studied are higher by 68% (Jerma) and by 64% (Miroč) than the H/C values which are determined by elemental analysis. Calculated H/C values infer that either more carbon or less hydrogen is required for the fusinite structures than is contained in the samples. We conclude that the differences in the estimation of H/C for bituminous charcoal-like fusinites between solid state
13
C NMR and elemental analysis can be explained by graphitic domains within the maceral ‘invisible’ in the CP/MAS experiment.
Composition and properties of North Bohemian coals
Authors: Sýkorová Ivana , Černý Jaroslav , Pavlíková Helena , Weishauptová Zuzana
Published: April 2008

This work presents the mean chemical, micropetrographic, surface and other characteristics of coal seams from western, central, and eastern parts of the North Bohemian brown coal basin. Attention was especially paid to the elemental composition, ash content, content and forms of sulphur, occurrence of syngenetic and epigenetic sulphides, maceral composition, and degree of gelification and decomposition of components in the huminite maceral group. Some other coal characteristics were also assessed, such as pore texture, extractability and solvent swelling of the coals.

The coals examined were huminitic with a variable xylite and detrite content. Huminite reflectance varied between 0.33 and 0.39%. Substantial differences in pore texture of the coals were found in the range of meso- and macropores. These differences largely affected the extractability of the North Bohemian coals. The coals also exhibited extremely high swelling ratios in basic solvents, such as pyridine.
Floristic characters of the upper coal-bearing formation in the Transcarpathians
Authors: Syabryaj Svetilana
Published: April 2008

The results of palynological studies of samples from outcrops, boreholes and mines in the Transcarpathians are presented. Megafloral remains from the Ilnitsa suite show the age of the upper coal-bearing formation to be Romanian. The palynological analysis allows the reconstruction of changes in the plant cover during the Romanian, and the determination of the climatic and palaeogeographic conditions.
Sulphur distribution in a multi-bed seam
Authors: Cavender Paul F. , Alan Spears D.
Published: April 2008

The Parkgate Seam (Langsettian) is an important seam for the coal industry in the UK. It extends over a considerable part of the East Pennine Coalfield and a large database of information on the seam has been complied by (the former) British Coal for the Nottinghamshire area from many sampling locations. The seam has been subdivided into a series of mappable units termed plies. This paper demonstrates how sulphur concentrations may vary considerably on a vertical scale and that spatial distributions within individual plies may be markedly different to other plies within the seam. Often seam sulphur maps for industrial use are produced for a composite of the whole thickness of the seam, typically as the whole seam-less-dirt. The neglect of the vertical variation in seam sulphur content may lead to the production of maps which are of limited industrial use. Variations in sulphur distributions also has implications for the origin of the sulphur in the coal. Distribution maps have allowed the controls on sulphur in the Parkgate Seam to be investigated, and these are dominated by complex depositional processes.
Values of δ
34
S in iron disulphides of the North Bohemian Lignite Basin, Czech Republic
Authors: Bouška Vladimír , Pešek Jiří , Žák Karel
Published: April 2008

Three main, genetically different, types of iron disulphides occur in lignite of the North Bohemian Basin — synsedimentary, diagenetic and epigenetic. Among them the synsedimentary disulphide appears to be the most abundant. It forms fine dispersed microscopic framboids or veinlets mostly parallel with the coal bedding. This disulphide is mostly represented by pyrite. The other types are much less abundant. The epigenetic variety consists of large macroscopic clusters of crystals of marcasite twins or crystalline filling of fractures.

The shift in sulphur isotopic composition between the original sulphate and the derived sulphides, which originated through bacterial reduction, may vary considerably depending on conditions, particularly on the open or closed nature of the system with respect to sulphate. The largest shifts in the isotopic composition between sulphate and sulphide sulphur are typical for an open system. Dissolved sulphate which supplied the North Bohemian Basin during the Miocene is likely to have been derived from weathered sulphides of the Krušné hory crystalline complex. This unit has isotopic compositions of sulphide sulphur varying between −1 and +5‰ and assuming no significant shifts in sulphur isotope compositions, the sulphate supplying the basin should exhibit a slightly positive δ
34
S value. Organic sulphur is thought to have played a much less important role.

Synsedimentary pyrites, which form microframboids or veinlets in coal, show δ
34
S values close to 0‰. These values when compared with those of sulphur dioxide in gases exhaled by power stations burning lignite of the North Bohemian Basin indicate that they correspond to mean values for synsedimentary pyrite. This also implies that no considerable shifts in isotopic composition take place during thermal oxidation in power plants.
Origin of vanadium in coals: parts of the Western Kentucky (USA) No. 9 coal rich in vanadium
Authors: Premović P. I. , Nikolić N. D. , Pavlović M. S. , Jovanović LJ. S. , Premović M. P.
Published: April 2008

The existence of vanadyl (VO
2+
)-non-porphyrins (P) in a thin band (enriched with vanadium) of the Western (W.) Kentucky (KY) No. 9 coal seam was shown by electron spin resonance (ESR). The ESR analysis indicates that VO
2+
-non-P are associated with the coal organic insoluble fraction. ESR parameters show that VO
2+
ion is in an environment with approximately axial symmetry and chelated possibly by carboxylic/phenolic oxygen ligand donor atoms. These parameters are compared with those of VO
2+
-fulvic acid complexes and the model complexes with salicylic/phthalic acids reported by others. It is concluded that the vanadylation of W. KY No. 9 thin coal band occurred during its diagenetic (peat-forming) stage in the Pennsylvanian swamp. The extraordinary V enrichment of the top 15 cm, relative to the lower parts of the W. KY No. 9 coalbed is interpreted by a high V concentration of the past swamp water attained through a sudden and exceptional external supply. The predominant source of the metal was probably volcanic ash on the land that was weathered/leached of its vanadium. The association of V/Cr (together with their enrichment in the top of the seam) and Ni implies that the volcanic ash was derived from basalts. Abundant organic (humic) materials (with the high V enrichment factor) and low rate of deposition were the primary factors responsible for the high vanadium content of the coal. From the chemistry of VO
2+
, FeS
2
and CrOH
2+
it is deduced that the oxidation potential Eh and pH of the ancient peat interstitial water were approximately −0.2 to −0.3 V and 5–6, respectively.
Environmental impact of minerals in UK coals
Authors: Spears D. A.
Published: April 2008

Both detrital and diagenetic minerals are quantitatively important in UK coals. The detrital minerals include quartz, and the clay minerals illite, mixed-layer illite-smectite, kaolinite and chlorite. The diagenetic minerals are dominated by pyrite/marcasite, carbonates, mainly ankerite and calcite, and kaolinite. Pyrite makes an important contribution to the S contents of the coals and is largely responsible for the variation in total S. The S content of coals delivered to power stations could be reduced by selective extraction during mining and improved physical coal-cleaning. Pyrite is a major location for trace elements of environmental concern and the elimination of pyrite would reduce both SO
2
and trace element emissions. Pyrite is also important in the weathering environment due to its instability. Its breakdown in coal stocks and colliery discard heaps may lead to spontaneous combustion. In discard heaps, pyrite breakdown is also responsible for acid porewaters and toxic elements in solution which inhibit colonization by vegetation and thus hinder reclamation of derelict land. If carbonates are sufficiently abundant, acid conditions may be eliminated. Acid porewaters are one facet of the general problem of acid mine drainage, which has a major impact on water quality, particularly in streams and rivers. In the UK acid mine drainage is a problem of growing concern due to reduction of deep-mine pumping following closure of collieries. Although pyrite breakdown in colliery spoil has an important influence on porewater compositions, it does not greatly influence the engineering stability because the major component, the mudrocks, contain very little pyrite. Upon exposure, the mudrocks break down relatively rapidly due to sedimentary structures to form an aggregate. Loss of interparticle bonding is a much slower process but there are a few mudrocks associated with low rank bituminous coals with both a high mixed-layer clay content and porosity which disintegrate rapidly during cycles of wetting and drying. There are also regional variations in the relative proportions of the clay minerals which influence the engineering properties. Kaolinite is dominant in the northern coalfields. This is also detected in the composition of fly ash produced by coal-fired power stations. Fly ash is enriched in those trace elements which have an environmental impact. The volatile elements, many of which were sulphide-associated in the coal, are enriched on the surface of the ash particles where they are accessible to leaching in the weathering environment, resulting in the contamination of natural waters.
A logging correlation scheme for the Main coal seam of the North Bohemian brown coal basin, and the implications for the palaeogeographical development of the basin
Authors: Mach Karel
Published: April 2008

A method for correlating the Main coal seam in the North Bohemian brown coal basin by interpreting borehole logs is described. The most important well log was the gamma-gamma density log, but in some boreholes it was also necessary to use the natural radioactivity and electric resistance logs or technological sampling of the core. All these methods, at various levels of sensitivity, reflect changes in the amount of organic matter in the borehole profile. Vertical changes of coal matter content characterize variations of sedimentation conditions. In close boreholes gamma-gamma density logs are easily correlatable so that changes of sedimentation can be correlated over great distances. The method has been used to correlate the main seam along the axis of the basin. The main result of this correlation is that coal-bearing sedimentation occurred uninterruptedly along the main axis of the basin, with the development of swamp and lake conditions. During the swamp conditions peat accumulated over the majority of the present basin area, whilst during the shallow lake conditions the region of clastic sedimentation was controlled by the distance from the inflowing sediment source. The coal-bearing sedimentation cycle started by a levelling of the palaeorelief by infilling the depressions, and was followed an extension of the sedimentation area. Compaction of the previously deposited layers affected the ensuing strata. No significant variations in stratal thickness were found along the length of the main borehole line nor in any of the auxiliary lines whole, indicating that tectonic controls in basin subsidence were unimportant. Thus changes of sedimentation conditions dominantly of climatic conditions caused water levels in the basin area to fluctuate. For many reasons it is concluded that the correlatable boundaries are isochronal. The correlation scheme represents the first really objective correlation of the main coal seam over the area of the whole North Bohemian basin.
Seismic monitoring for rockburst prevention in the Ostrava-Karviná Coalfield, Czech Republic
Authors: Holub Karel
Published: April 2008

Seismic activity in the Ostrava-Karviná Coalfield is continuously monitored by networks of seismographic stations located both underground and on the surface. Software has been implemented for statistical analysis and various types of data display to aid interpretation. Practical experience obtained in long-term seismic monitoring has proved that it is an indispensable part of the rockburst prevention scheme applied in underground mines in this region. Continuous seismic monitoring enables us to delimit seismically active areas, observe the trends of seismic activity in time and space so that we can make more accurate estimates of local rockburst hazard, and check the effectiveness of the rockburst prevention methods used.
An analysis of mining induced seismicity and its relationship to fault zones
Authors: Kaláb Zdeněk
Published: April 2008

Intense induced seismicity has resulted from long-standing mining activity in the Karviná part of the Ostrava-Karviná Coal District, Upper Silesian coal basin. Interpretation of mining induced seismic events in combination with other knowledge (geological, tectonic, geomechanical, technological) aids the understanding of failure processes in the rock mass. Seismological observations over a three-year period were analysed. Four sets of mining-induced seismic events have been tested to evaluate the seismicity of important fault zones. It follows from the analysis that the seismic activity on important fault zones occurs only as a consequence of mining activities. Accumulations of mining induced seismic events occur on stress concentrators, which may be geological and/or anthropogenic structures.