petrological and organic geochemical investigation of recent peats with known environments of deposition abstract a series of recent peat samples from tropical sub tropical and temperate locations were investigated using coal petrographical and organic geochemical techniques maceral and biomarker compositions were examined to see if they correlated or diverged from the known environment of deposition of the peats the proportion of humotelinite was related to the water depth and the frequency of dry periods the ph and trophic level have a modifying influence on the preservation of tissues furthermore the proportions of sclerotinite in the peats seem to reflected the oxygen status in the mire which was also mirrored in the abundance of humic and fulvic acids a facies diagram was calculated for the peat samples to see how maceral indices would fare in interpreting their known environments of deposition the results proved to be generally unsuccessful as the herbaceous and woody peats did not always give the predicted high humodetrinite and humotelinite compositions respectively the aliphatic hydrocarbon fraction from the extracts of the peat samples show that mainly odd numbered n alkanes are present diterpenoids triterpenoids and hopanoids were found in most samples and were mainly unsaturated in nature the relative proportion of hopanoids in pears appears to be related to bacterial activity in acidic environments de a triterpenoids were also detected in the peat stage of diagenesis in an angiosperm dominated peat type mariscus polycyclic aromatic triterpenoids were present in the aromatic fraction of the extract their occurrence and proportion appears to be related to the degree of humification in a taxodium peat mono di and triaromatic diterpenoids were detected the presence of these aromatic biomarkers indicate the rapid formation of these compounds in the peat stage mainly mediated by microbial activity

utility of coal petrology for sequence stratigraphic analysis abstract sequence stratigraphy seeks to predict the depositional architecture of sediments based on the principle that their superposition and lateral arrangement are largely determined by the rate at which accommodation is made below depositional base level relative to the supply rate of sediments depositional base level is generally correlated with sea level which in paralic peat coal deposits controls the position of the groundwater table above which oxidation ablation and erosion would occur the current late quaternary sequence is used to discuss some of the constraints on coal formation that stem from the interaction of short and long period modulations on sequence forming eustatic cycles the results show that the mid transgressive systems tract is unlikely to produce significant coal deposits which is supported by a survey of the relevant literature from eight different countries it reveals a bimodal distribution of coal deposits with the strongest mode being situated in the early transgressive systems tract while a broader secondary mode occurs in the early and mid highstand position this concentration contrasts with the complete absence of any significant coal deposits in the early and mid lowstand systems tract and only a low occupancy of the late highstand systems tracts the reasons for this distribution are briefly discussed and attention is drawn to the possible over stating of the coal forming potential of the late lowstand systems tract following a brief discussion of the sequence stratigraphic interpretation of coal measures emphasis is put on the application of sequence stratigraphy to the study of coal seams and their composition at various levels of petrographic detail while in low rank coals botanical affinities contribute much to the lithotype based analysis a genetic assessment of bituminous coal seams relies primarily on physical and chemical palaeo environmental signatures simple properties such as maximum coal thickness low detrital mineral content and maximum preservation of vitrinite particularly of telovitrinite define a good balance between the former rates of accommodation versus peat accumulation iso metamorphic variations in telovitrinite reflectance and its dispersion measured by the coefficient of variation have also contributed to the palaeo environmental interpretation this paper confirms the identification within coal seams of most of the sequence stratigraphically significant surfaces e g sequence and parasequence boundaries transgressive flooding and maximum flooding surfaces it also gives examples of some new ones referred to as accommodation reversal non marine flooding give up transgressive terrestrialisation and paludification surfaces some of these are specific to coal measures but the give up transgressive and accommodation reversal surfaces may have wider significance

brittle ductile transition shear failure and leakage in shales and mudrocks abstract this paper presents an experimental study on brittle ductile transition shear behaviour the formation of shear fractures in shales and mudrocks and the hydraulic properties of shales and mudrocks with shear induced fractures the experimental study is based on triaxial tests on different mudrocks and shales from north sea reservoirs and adjacent areas sheared at different effective confining stresses it is shown that during burial mudrocks behave as normally consolidated materials and exhibit ductile response to increased load however several processes like uplift chemical diagenesis and overpressure build up turn mudrocks into overconsolidated materials which exhibit brittle behaviour during loading triaxial tests with different loading conditions have been performed to establish the brittle to ductile transition of various mudrocks based on the results of the tests it is shown that the brittle to ductile transition can be related to the overconsolidation ratio a relationship between normalized undrained shear strength and overconsolidation ratio is established in combination with this relationship a correlation between compressional wave velocity and apparent pre consolidation stress which accounts for both mechanical and chemical diagenesis may be used as a tool to evaluate possible leakage of hydrocarbon seals

sequence stratigraphy and coal petrography applied to the candiota coal field rio grande do sul brazil a depositional model abstract the sedimentary rocks of the candiota coal field which belong to the rio bonito formation guata group tubarao supergroup in the parana basin eopermian were studied on the basis of sequence stratigraphy six fourth order parasequences designated a the oldest to f and a third order sequence sequence were identified in outcrops drill cores and well logs the rocks were deposited in an incised valley superimposed on the rocks of the itarare group tubarao supergroup up to 23 coal seams have been observed however they do not extend through the entire coal field the gelification and the tissue preservation indexes based on maceral analysis diessel 1986 were used to infer the depositional environments of the coal seams

a model for seismic velocity and attenuation in petroleum source rocks petroleum source rock is modeled as a viscoelastic transversely isotropic medium composed of illite smectite and organic matter the wave velocities and attenuation of petroleum source rocks are obtained as a function of excess pore pressure initial kerogen content and water saturation the model generalizes a previous approach based on a pure elastic formulation of backus averaging and introduces the pressure effect and the presence of fluids oil and water the model allows the simulation of different maturation levels induced by pore pressure changes caused by the conversion of kerogen to oil the higher the oil saturation the higher the maturation level assuming that the source rock has a very low permeability the excess pore pressure can be calculated as a function of the conversion factor then the bulk modulus and density of the kerogen oil mixture are obtained with the kuster and toks oz model assuming that oil is the inclusion in a kerogen matrix finally backus averaging of this mixture with the illite smectite layers gives the complex stiffnesses of the transversely isotropic and anelastic medium computed p and s velocities and quality factors parallel to bedding are higher than those normal to bedding with attenuation anisotropy higher than stiffness anisotropy in particular for the north sea kimmeridge shale and at maximum anisotropy p and s parallel velocities are approximately 0 7 km s higher than the corresponding p and s normal velocities the maximum attenuation and stiffness anisotropies are obtained for 18 and 30 volumetric kerogen content respectively both velocities and quality factors decrease with increasing kerogen content at a given pore pressure the decrease in wave velocity is 2 km s for p waves and 1 km s for s waves when kerogen increases from zero to 100 moreover anisotropy increases and velocities decrease with increasing pore pressure i e with higher kerogento oil conversion finally the presence of water affects the normal bedding velocity i e higher water saturation implies lower velocities

observations on the nature and origin of fusain abstract evidence for a wildfire origin of fusain is examined charcoal produced by natural fires and artificial charring resembles fossil fusain both in physical size and shape and in optical reflectance artificially charred leaves and naturally burnt wood are illustrated using the sem reflectance studies on modern charcoals suggest that much semifusinite may be produced by pyrolysis the ecological implications of a wildfire origin of fusain are discussed and it is concluded that fires have been a feature of terrestrial ecosystems from at least the late devonian

freshening of the ross sea during the late 20th century ocean measurements in the ross sea over the past four decades one of the longest records near antarctica reveal marked decreases in shelf water salinity and the surface salinity within the ross gyre these changes have been accompanied by atmospheric warming on ross island ocean warming at depths of 300 meters north of the continental shelf a more negative southern oscillation index and thinning of southeast pacific ice shelves the freshening appears to have resulted from a combination of factors including increased precipitation reduced sea ice production and increased melting of the west antarctic ice sheet

organic rich shale caprock properties of potential co2 storage sites in the northern north sea offshore norway abstract assessment of the geomechanical properties of organic rich shale caprocks is critical for a successful co2 storage into a saline aquifer in this study we investigated the geochemical properties of the organic rich shale caprocks of the draupne and heather formations overlying the potential sandstone reservoirs of sognefjord fensfjord and krossfjord formations in the northern north sea offshore norway the caprock s depositional variations within the sub basins are established by analyzing the gamma ray shape and stacking patterns the effect due to differences in depositional environments on the caprock compaction behavior is investigated by integrating petrographical analysis of core and cutting samples from 3 wells and by rock physical analysis of wireline log data from 27 exploration wells three rock physics templates are used where the wireline log data are interpreted using the published background trends the effect of kerogen type maturation level and deposition environment on caprock properties within the study area are also evaluated moreover the caprock property such as brittleness is estimated by using four mineralogy and elastic property based empirical relations which is a quantitative measure of caprock property with respect to changes in stress state finally the seismic inversion method is assessed for the possibility of extracting caprock properties from surface seismic data regardless of compaction processes the results indicate that the heather formation is mechanically stronger than the draupne formation however both formations appear to be ductile in nature the depositional environments control the mineralogical composition and fabric of the draupne and heather formations which influence the caprock properties significantly results also show that the effect of toc on caprock properties is insignificant in the study area the brittleness of the organic rich shale caprocks in the study area follows a different trend compared to the published trends we also observed an excellent correlation between the log derived elastic properties and geomechanical parameters still it is difficult to assess the caprock elastic properties from seismic due to the overlap of data clusters the evaluation of caprock geomechanical behaviors is challenging as these properties are site specific and also influenced by other factors such as exhumation in situ stress conditions the existence of natural fractures and their orientations

the application of famm fluorescence alteration of multiple macerals analyses for evaluating rank of parana basin coals brazil abstract combining vitrinite reflectance vr and fluorescence alteration of multiple macerals famm analyses provide insights into the chemical nature of vitrinites i e perhydrous vs orthohydrous vs subhydrous compositions in permian gondwana coals of the parana basin brazil the famm derived equivalent vr eqvr values and relationships with vr can be determined according to calibration curves based largely on permian gondwana coals of eastern australia the analytical results indicate that vitrinites in the parana basin coals studied generally range from orthohydrous to perhydrous with interpreted vr suppression ranging up to 0 2 absolute for the most perhydrous case the eqvr values of the santa catarina coals which range from about 0 85 to 0 95 differ from vr values by about 0 10 0 15 absolute potentially having significant implications on coal utilization the causes of vitrinite reflectance suppression in the parana basin coals are as yet poorly understood but are likely to be related to a combination of factors

petrological and geochemical characterization of candiota coal seams brazil implication for coal facies interpretations and coal rank abstract seven coal seams from cores of the borehole m iv c 101 candiota coalfield located in rio grande do sul state southern part of the parana basin were analyzed by coal petrographical and organic geochemical methods the seams occur in the rio bonito formation guata group tubarao supergroup of the parana basin and are of permian artinskian kungurian age the composition rank coal facies and depositional environment characterization were made based on lithotype maceral and microlithotype analyses the data were then used in the definition of different types of facies critical petrographical indices and were displayed in diagrams of coal facies in addition coal seams samples from candiota mine were analyzed by proximate total moisture and gross calorific values and were classified using the united nations economic commission for europe un ece classification in addition rock eval pyrolysis liquid chromatography gc and gc ms analyses were made to obtain independent parameters on coal rank and organic matter composition and environment of deposition the results suggest deposition in open mires with elevated contents of detrital macerals and clay minerals and also limno telmatic coal facies coal bearing sequence of coal seams represent a back barrier setting according to the international classification un ece candiota coals are in the subbituminous or low rank coal a stage results from geochemical analyses showed that terrestrial organic matter is predominant as indicated by hydrogen and oxygen indices carbon preference indices and the sterane distribution geochemical maturity parameters such as the 20 s 20 s 20 r and ratios for c 29 regular steranes support the low level of rank maturity as indicated by the vitrinite reflectance measurements 0 41 0 45 and gross calorific values

comparison of geomechanical deformation induced by megatonne scale co2 storage at sleipner weyburn and in salah geological storage of co2 that has been captured at large point source emitters represents a key potential method for reduction of anthropogenic greenhouse gas emissions however this technology will only be viable if it can be guaranteed that injected co2 will remain trapped in the subsurface for thousands of years or more a significant issue for storage security is the geomechanical response of the reservoir concerns have been raised that geomechanical deformation induced by co2 injection will create or reactivate fracture networks in the sealing caprocks providing a pathway for co2 leakage in this paper we examine three large scale sites where co2 is injected at rates of 1 megatonne y or more sleipner weyburn and in salah we compare and contrast the observed geomechanical behavior of each site with particular focus on the risks to storage security posed by geomechanical deformation at sleipner the large high permeability storage aquifer has experienced little pore pressure increase over 15 y of injection implying little possibility of geomechanical deformation at weyburn 45 y of oil production has depleted pore pressures before increases associated with co2 injection the long history of the field has led to complicated sometimes nonintuitive geomechanical deformation at in salah injection into the water leg of a gas reservoir has increased pore pressures leading to uplift and substantial microseismic activity the differences in the geomechanical responses of these sites emphasize the need for systematic geomechanical appraisal before injection in any potential storage site

a sequence stratigraphic investigation of a miocene formation supported by coal seam quality parameters central paratethys n hungary abstract a stratigraphic investigation of the coal bearing miocene siliciclastic succession in structurally dissected basins of northern hungary was performed based on log correlations and is supported by coal petrology and sulphur data the succession represents the karpatian lower order global eustatic cycle of the paratethys and was dissected into six higher order sedimentary sequences sq 1 sq 6 the coal bearing strata in the nograd basin sq 1 sq3 represent a lowstand systems tract lst prior to the karpatian relative sea level rise the transgressive systems tract tst starts with the oncophora beds sq 4 accumulated above a regional unconformity and containing coal beds in the borsod basin the tst is superimposed by tectonically forced higher order lowstand systems tracts sq 5 sq 6 containing coal beds only in the relatively elevated east borsod basin to support the sequence stratigraphic model the average maceral and sulphur content of coal seams was also interpreted the low sulphur 0 47 content in sq 1 reflects the lowstand environment determined by continental derived freshwater input transitional sulphur contents 0 66 1 02 in the late lowstand sq 2 and sq 3 indicate occasional saline invasions related to relative sea level rises high 2 3 2 6 sulphur contents in the tst sq 4 were caused by regular seawater inundations into the lagoon while decreasing sulphur contents in sq 5 and sq 6 2 28 2 09 reflect the increasing rate of freshwater income in association with the stepwise basinward shifts of the shoreline and the lagoonal facies within the lower to middle miocene salgotarjan lignite formation the analysis of coal seams contributed to the interpretation of relative sea level changes and the sequence stratigraphic context facilitated both the interpretation of sulphur content in coals and the reliable correlation of coal seams

petrology and chemistry of permian coals from the parana basin 1 santa terezinha leao butia and candiota coalfields rio grande do sul brazil the current paper presents results on petrological and geochemical coal seam characterization in permian coal bearing strata from the parana basin southern brazil sequence stratigraphic analysis shows that peat accumulation in permian time was closely linked to transgressive regressive cycles with peat accumulation occurring in a predominantly back barrier lagoonal setting coal petrographic analysis indicates subbituminous coals at candiota and leao butia and high volatile bituminous coals at santa terezinha where locally the coal seams are thermally altered by volcanic intrusions petrographic composition is highly variable with seams at candiota and santa terezinha frequently enriched in inertinite chemical analyses indicate that all coals are mineral matter rich mean 49 09 wt with sio2 and al2o3 dominating as determined by icp aes quartz is also the predominant mineral detected by x ray diffraction where it is associated with feldspar kaolinite and hematite and iron rich carbonates the results from scanning electron microscopy are broadly consistent with the bulk chemical and mineralogical analysis quartz and clays are common in all samples analyzed other minerals observed were amongst others carbonates calcite siderite ankerite pyrite monazite kaolinite barite sphalerite rutile and quartz of volcanic origin the distribution of trace elements is well within the range typical for coal basins of other areas despite the fact that the parana basin coals are very high in ash yields the average concentrations for elements of environmental concern as b be cd co cr cu hg li mn mo ni pb sb se tl u v zn are similar to or less than the mean values for u s coal however considered on an equal energy basis parana basin coals will produce in combustion 5 to 10 times the amount of most elements compared to an equal weight us coal concentrations of major and trace elements such as fe b and s appear to be controlled by depositional setting with increasing values in coal seams overlain by brackish marine strata hierarchical cluster analysis identified three groups of major minerals and seven groups of trace elements based on similarity levels on a regional scale the coalfields can be separated by the differences in rank candiota and leao butia versus santa terezinha and by applying discriminant analysis based on 4 trace elements li as sr sb highest rb and sr values occur at candiota and are linked to syngenetic volcanism of the area whereas high y and sr values at santa terezinha can be related to the frequent diabase intrusions in that area

formation of immature asphalt from organic rich carbonate rocks i geochemical correlation abstract the formation of low maturity asphaltic oils immature asphalts from carbonate source rocks was investigated the senonian bituminous rocks sbr in israel are organic rich carbonate rocks that were deposited in a high productivity environment and they are part of a sedimentary sequence that also contains cherts and phosphorites the sbr were studied in different basins and the samples are from outcrops and three deep drillholes the bitumen contents of the rocks are exceptionally high up to 700 mg g c org and immature asphalts are found to be associated with them geochemical analysis indicates that the bitumens are indigenous to the host sbr and the associated asphalts are bitumens that have migrated a short distance with negligible chemical fractionation the high heteroatom content of the kerogens up to 30 in the sbr is suggested as a possible cause of the generation of asphaltic oils in an early stage of maturation

accommodation based coal cycles and significant surface correlation of low accommodation lower cretaceous coal seams lloydminster heavy oil field alberta canada implications for coal quality distribution sequence stratigraphy and coal cycles based on accommodation trends were investigated in the coal bearing lower cretaceous mannville group in the lloydminster heavy oil field eastern alberta the study area is in a low accommodation setting on the cratonic margin of the western canada sedimentary basin geophysical log correlation of coal seams shoreface facies and the identification of incised valleys has produced a sequence stratigraphic framework for petrographic data from 3 cored and 115 geophysical logged wells maceral analysis telovitrinite reflectance and fluorescence measurements were taken from a total of 206 samples three terrestrial depositional environments were interpreted from the petrographic data ombrotrophic mire coal limnotelmatic mire coal and carbonaceous shale horizons accommodation based coal wetting and drying upward cycles represent trends in depositional environment shifts and these cycles were used to investigate the development and preservation of the coal seams across the study area the low accommodation strata are characterized by a high frequency occurrence of significant surfaces coal seam splitting paleosol and incised valley development three sequence boundary unconformities are identified in only 20 m 66 ft of strata coal cycle correlations illustrate that each coal seam in this study area was not produced by a single peat accumulation episode but as an amalgamation of a series of depositional events complex relations between the cummings and lloydminster coal seams are caused by the lateral fragmentation of strata resulting from the removal of sediment by subaerial erosion or periods of nondeposition syndepositional faulting of the underlying basement rock changed local accommodation space and increased the complexity of the coal cycle development this study represents a low accommodation example from a spectrum of stratigraphic studies that have been used to establish a terrestrial sequence stratigraphic model the frequency of changes in coal seam quality is an important control on methane distribution within coalbed methane reservoirs and resource calculations in coal mining a depositional model based on the coal cycle correlations as shown by this study can provide coal quality prediction for coalbed methane exploration reservoir completions and coal mining

burial and exhumation history controls on shale compaction and thermal maturity along the norwegian north sea basin margin areas abstract the north sea area has been subjected to significant erosion and subsequent deposition of sediments in the basin margin and deeper basin areas respectively during the late neogene a large amount of cretaceous early quaternary sediments have been removed below the angular unconformity along the west and southwest coast of norway and deposited in the huge north sea fan at the mouth of the norwegian channel at the same time a considerable thickness of early quaternary paleocene sediments was also eroded towards the east in the central north sea and subsequently deposited in the deeper basin areas to the west this study seeks to estimate exhumation from compaction and thermal maturity based techniques by using sonic velocities of shales carbonates and vitrinite reflectance data in a large number of boreholes in the central eastern and northern north sea the results indicate no or minor exhumation in the central graben and flanking high areas whereas more than 1 km sediments are eroded in the basin margin areas towards the norwegian coast more than 500 m sediments are eroded in the egersund basin and stord basin areas a similarity of exhumation estimates from the early cretaceous early miocene shales and late cretaceous early paleocene carbonates indicates maximum burial sometime after the early miocene in most of the central and northern north sea areas however the maximum burial throughout the north sea basin may be diachronous seismostratigraphic analysis indicates maximum burial sometime during the oligocene in the sorgenfrei tornquist zone area in the eastern north sea maximum burial in the norwegian danish basin varies from miocene pliocene in eastern parts to early pleistocene in western parts whereas sediments are currently at their maximum burial in the central graben and southern viking graben areas restoration of surface elevations to their original position before the onset of erosion indicated large subaerially exposed areas in the norwegian danish basin and along the southwest coast of norway this is also supported by predominantly coastal and or deltaic environments in the norwegian danish basin area during the late neogene these subaerially exposed areas may be linked to the regional tilting and erosion of the basin margin areas to the east and progressive basinward migration of deposition centres to the west since the oligocene the exhumation had significant effects on the petroleum system in the basin margin areas by cooling down the source rock however the deeper burial of sediments may also have changed the rheological properties of sediments from more ductile to brittle due to compaction and diagenetic processes which makes them more failure prone during exhumation leading to hydrocarbon leakage or seal failure in case of co2 injection

physical properties of cenozoic mudstones from the northern north sea impact of clay mineralogy on compaction trends vertical and lateral changes in physical properties in cenozoic mudstones from the northern north sea basin reflect differences in the primary mineralogical composition and burial history which provides information about sedimentary facies and provenance integration of well log data with mineralogical information shows the effect of varying clay mineralogy on compaction curves in mudstones the main controlling factor for the compaction of eocene to early miocene mudstones within the north sea is the smectite content which is derived from volcanic sources located northwest of the north sea mudstones with high smectite content are characterized by low p wave velocities and bulk densities compared to mudstones with other clay mineral assemblages at the same burial depths smectitic clays are important during mechanical compaction because they are less compressible than other types of clay minerals a comparison between well log data and experimental work also shows that smectite may be a controlling factor for overpressure generation in the smectite rich eocene and oligocene sediments at greater burial depths and temperatures 70 80c the dissolution of smectite and precipitation of illite and quartz significantly increases velocities and densities miocene and younger mudstones from the northern north sea have generally low smectite contents and as a result have higher velocities and densities than eocene and oligocene mudstones lateral differences in the compaction trends between the north and south for these sediments also exist which may be related to two different source areas in the pliocene the log derived petrophysical data from the northern north sea basin show that mudstone lithologies have very different compaction trends depending on the primary composition simplified compaction curves may therefore affect the outcomes from basin modeling the amplitude versus offset response of hydrocarbon sands and the seismic signature on seismic sections are also dependent on the petrophysical properties of mudstones and will vary depending on the mineralogical composition

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

comparing maceral ratios from tropical peatlands with assumptions from coal studies do classic coal petrographic interpretation methods have to be discarded petrographic investigations of tropical peat deposits from the tasek bera basin malaysia show that petrographic methods can contribute valuable information about paleoecological settings of mire deposits comparing modern peat forming environments and the pre maceral composition of peat samples allows the reconstruction of paleoecological conditions such as floral composition fires microbial activity etc and gives insight into paleodepositional environments in the past maceral ratios of coals have been used to interpret paleodepositional settings of coal deposits such a procedure assumes that coal texture and coal maceral composition are dictated solely by the depositional environment and thus different depositional environments should be clearly discriminated based on maceral ratios in the modern peat deposits of tasek bera divergent petrographic results occur in similar depositional environments hence poor correlation occurs between the petrography the degree of decomposition and the depositional environment furthermore from the time of peat deposition peat is subject to considerable alteration during subsequent diagenesis preservation of structured and strongly altered material such as inertinite gelified material or funginite is favoured and results in biased coal maceral compositions because maceral indexes in modern peat studies are of little utility in the reconstruction of paleoenvironmental settings it follows that coal maceral indexes should not be utilized in the future to interpret paleodepositional environments of coals

investigations of fusain transition fossils from the lower carboniferous comparisons with modern partially charred wood plant fossils showing vitrinite semifusinite fusinite transitions and permineralised semifusinite transitions were collected from lower carboniferous locations within the british isles several were obtained from east kirkton quarry bathgate scotland and one fusinite semifusinite vitrinite semifusinite fusinite transition fossil was collected at muckros head county donegal ireland the muckros head fossil was found in a limestone sea cliff face where it had been weathered proud of the rock matrix thus enabling a detailed examination and interpretation of the macroscopic appearance of the specimen the distinctive sandwich like cross section of the fossil is interpreted as being caused by the burial and coalification of a partially charred plant stem with recent exposure and weathering resulting in the loss of its shattered edges under s e m and reflected light microscopy non permineralised transition fossils are seen to grade from structureless vitrinite into compressed and bogen structured semifusinite and occasionally continue through to structured uncompressed fusinite with corresponding increases in reflectance these gradations parallel the reflectances seen in modern partially charred stems stable carbon isotopic analysis of the transition fossils c13 17 19 0 to 19 26 0 22 46 0 to 24 54 0 24 47 0 24 47 0 to 26 20 0 show a significant difference between the vitrinite and semifusinite fusinite with the semifusinite fusinite isotopically heavier the various techniques employed to investigate these transition fossils all indicate that they represent coalified partially charred stems correlation of the properties and characteristics of the semifusinite fusinite in transition fossils with the properties and characteristics of isolated semifusinite and fusinite fragments collected from rocks of the lower carboniferous through to the tertiary supports the view that most of these isolated fragments also represent fossil charred wood and charcoal

source rock evaluation by well log analysis lower toarcian hils syncline abstract the feasibility of conducting petroleum source rock evaluations from well log data was examined using three continuously cored sections immature mature and postmature stages of the lower toarcian posidonia shale northern germany logs depicting natural gamma emission k u th bulk density sonic travel time and resistivity were utilised as was the borehole televiewer for fracture control selected data from these logs were correlated with parameters of source richness hydrocarbon content and maturity the resulting three dimensional cross plot shows at a glance well by well comparison of facies maturity and hydrocarbon content a simple correlation between organic geochemical and petrophysical parameters is of course not perfect since log response is complex and affected by mineralogical and pore fluid properties of the rock as well as by organics however source rock characterization by wireline logging is still a fast and therefore economical method relative quick look comparisons from well to well are possible without calibration to core data and can easily be performed at once at the drill site the present application is limited to clastic source rocks in basins with simple geologic histories

velocity depth trends in mesozoic and cenozoic sediments from the norwegian shelf sonic velocity density and resistivity log data from 60 wells on the norwegian shelf have been used to investigate velocity depth trends in sedimentary rocks as a function of sediment composition porosity pore pressure burial history and compaction processes a first order linear velocity depth trend line has been estimated from published velocity data the data analyzed in this study however show significant variations from this trend line indicating that no general velocity depth function can be used when performing more accurate analyses like depth conversion of seismic data pore pressure prediction or basin modeling lower tertiary smectitic sediments from the northern north sea and haltenbanken are characterized by relatively low velocities compared to the overlying pliocene and pleistocene sediments causing a distinct velocity inversion a significant velocity increase at a burial depth corresponding to 70 100c was found and may reflect the alteration of smectite to illite and the initial precipitation of quartz cement in both sandstones and shales overpressured jurassic sediments from haltenbanken have lower velocities than equivalent hydrostatically pressured sequences but no significant porosity difference the reduced velocities may be a direct response to lower effective stresses and thus reduced elastic compaction low velocities in source rocks are mainly attributed to the relatively soft kerogen and resulting velocity anisotropy the high velocity depth ratio of barents sea sediments after correcting for tertiary exhumation is explained by the burial history of the area the subsequent thermal exposure of the sediments over time and thus the amount of quartz cementation

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

rock physics templates for clay rich source rocks shale source rocks are composed of various minerals mainly smectite and illite depending on the burial depth and they can be described as transversely isotropic media the pore space may contain kerogen water oil and gas determined by the in situ conditions a petroelastic description is based on the following smectite illite transformation as a function of depth is described by a fifth order kinetic reaction backus averaging to mix isotropic smectite and anisotropic illite is then used to obtain the elasticity constants of the mineral composing the frame porosity is obtained from density and water is part of the mineral whose elasticity constants are obtained from gassmann equations oil and gas generated from kerogen are assumed to saturate the kerogen phase the bulk modulus of the oil gas mixture is calculated by a mesoscopic loss model and the stiffnesses of the kerogen fluid mixture are obtained with the kuster and toksoz model assuming that the fluid is included in a kerogen matrix two models are considered to obtain the seismic velocities of the shale namely backus averaging and the gassmann equation generalized to the anisotropic case with a solid pore infill we built rock physics templates rpts containing only kerogen immature and kerogen plus hydrocarbons mature pore pressure effects were modeled and used as templates we considered the kimmeridge shale at different depths to model kerogen oil and oil gas conversions we assumed a basin evolution model with a constant sedimentation rate geothermal gradient and a first order kinetic arrhenius reaction the detection of the hydrocarbons was investigated from rpts built with wave velocities impedances lame constants density poisson ratio young modulus and anisotropy parameters for varying kerogen content fluid saturations and pore pressure moreover the amplitude variation with offset intercept and gradients were computed corresponding to the seismic response of a source rock layer for varying kerogen content and fluid saturation

sequence stratigraphic distribution of coaly rocks fundamental controls and paralic examples significant volumes of terrigenous organic matter can be preserved to form coals only when and where the overall increase in accommodation approximately equals the production rate of peat accommodation is a function of subsidence and base level for mires base level is very specifically the groundwater table in paralic settings the groundwater table is strongly controlled by sea level and the precipitation evaporation ratio peat accumulates over a range of rates but always with a definite maximum rate set by original organic productivity and space available below depositional base level groundwater table below a threshold accommodation rate nonzero no continuous peats accumulate due to falling or low groundwater table sedimentary bypass and extensive erosion by fluvial channels this is typical of upper highstand lowstand fan and basal lowstand wedge systems tracts higher accommodation rates provide relatively stable conditions with rising groundwater tables mires initiate and copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received september 7 1995 revised manuscript received november 25 1996 final acceptance may 5 1997 2exxon production research company 3120 buffalo speedway houston texas 77096 3exxon production research company 3120 buffalo speedway houston texas 77096 present address conoco inc p o box 2197 houston texas 77252 we benefited from the input and assistance of many people of special assistance were the teams involved in collaborative studies with esso australia and esso malaysia p moore m sloan j emmett b burns a partridge s creaney hanif hussein r hill r lovell and m feeley we also thank the rock springs team r beauboeuf p mclaughlin w devlin a carroll y y chen g grabowski jr k miskell gerhardt m farley r webster and j schwalbach group members d curry and j yeakel were always helpful we also enjoyed and profited from many discussions of these concepts with our colleagues outside exxon c diessel r boyd k shanley b zaitlin p mccabe m hendricks a cohen and m kirschbaum we thank the reviewers of company reports whose careful comments on several generations of this work improved it s creaney m feeley j van wagoner f wehr j yeakel and a young f weber and j zullig provided extensive management support k linke translated our sketches into the fine figures herein we value all the help

elastic anisotropy of source rocks implications for hydrocarbon generation and primary migration we combined acoustic velocities and anisotropy measurements with x ray diffraction mineralogy rock eval organic geochemical analyses vitrinite reflectance and scanning electron microscope observations on 69 cores of hydrocarbon source rocks collected from eight sedimentary basins the velocity data indicate the lamellar distribution of solid organic matter kerogen in compacted black shales and show a strong correlation between their elastic anisotropy and organic richness the experimental results are consistent with the two component anisotropic model of black shales with a continuous kerogen network in both bedding parallel and bedding normal directions beginning from relatively low toc values the strong elastic anisotropy of tight thermally mature source rocks i further enhanced by overpressure induced bedding subparallel microcrack development during the main stage of hydrocarbon hc generation and primary migration at r0 greater than 0 75 in agreement with published petrographic observations these microcracks significantly aid primary hc migration particularly horizontally elastic anisotropy of medium to high porosity illite smectite shales is weaker than in lower porosity predominantly illite shales however the overall positive trend of elastic anisotropy with kerogen content remains unchanged

using borehole geophysical data as soft information in indicator kriging for coal quality estimation abstract mineral resources estimation comprises basically two stages i data collection analysis and validation and ii the estimate of the grades and tonnes of the deposit the most often applied method for obtaining geological data during mineral exploration is rotary drilling with total core recovery high drilling costs make borehole geophysical logging attractive to obtain the maximum possible information from each borehole helping to understand ore intersections grades variability and extension of the deposit and its continuity in this paper borehole geophysical logging was used to enhance the sampling survey and to derive grades indirectly without lab analysis with a certain amount of uncertainty soft indicator kriging ik was selected to estimate coal quality by combining hard data from drill holes and soft data from geophysical logging correlation the method showed to be adequate to incorporate the uncertainty associated with the geophysical derived grade values the results were compared to the conventional procedures using grades determined via core analysis and ordinary kriging borehole geophysical logging proved to be essential to define the features of ore deposit and soft ik provided results with acceptable precision and accuracy if compared to the model provided by ordinary kriging and hard data

determination of organic matter content of appalachian devonian shales from gamma ray logs the organic matter content of the devonian shale of the appalachian basin is important for assessing the natural gas resources of these rocks and patterns of organic matter distribution convey information on sedimentary processes and depositional environment in most of the western part of the appalachian basin the organic matter content of the devonian shale can be estimated from gamma ray wire line logs using the equation phgro ggrb ggr 1 378a where phgro is the organic matter content of the shale fractional volume ggr the gamma ray intensity api units ggrb the gamma ray intensity if no organic matter is present api units and a the slope of the crossplot of gamma ray intensity and formation density api units g cm3 the quantities a and ggrb vary regionally and are mapped using data from gamma ray and formation density wire line logs organic matter contents estimated using this equation are compared with organic matter contents determined from direct laboratory analyses of organic carbon for 74 intervals of varying thickness from 12 widely separated wells the organic matter content of these intervals ranges from near zero to about 20 by volume excluding the cleveland member of the ohio shale and the lower part of the olentangy shale the distribution of the differences between volume percent organic matter content determined from core samples and estimated from gamma ray logs has a mean of 0 44 and a standard deviation of 1 98 which indicates that the accuracy of the gamma ray method is adequate for most geologic applications the gamma ray intensity of the cleveland member of the ohio shale and the lower pa t of the olentangy shale is anomalously low compared to other devonian shales of similar richness so that organic matter content computed for each of these units from gamma ray logs is likely to be too low wire line methods for estimating organic matter content have the advantages of economy readily available sources of data and continuous sampling of the vertically heterogenous shale section the gamma ray log in particular is commonly run in the devonian shale its response characteristics are well known and the cumulative pool of gamma ray logs forms a large and geographically broad data base the quantitative computation of organic matter content from gamma ray logs should be of practical value in studies of the appalachian devonian shale the general approach described here may also be applicable to other formations with physical and geochemical characteristics similar to the appalachian devonian shale

natural fractures in the barnett shale and their importance for hydraulic fracture treatments gas production from the barnett shale relies on hydraulic fracture stimulation natural opening mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone knowledge of both the present day maximum horizontal stress which controls the direction of hydraulic fracture propagation and the geometry of the natural fracture system which we discuss here is therefore necessary for effective hydraulic fracture treatment design we characterized natural fractures in four barnett shale cores in terms of orientation size and sealing properties we measured a mechanical rock property the subcritical crack index which governs fracture pattern development natural fractures are common narrow 0 05 mm 0 002 in sealed with calcite and present in en echelon arrays individual fractures have high length width aspect ratios 1000 1 they are steep 75 and the dominant trend is west northwest other sets trend north south the narrow fractures are sealed and cannot contribute to reservoir storage or enhance permeability but the population may follow a power law size distribution where the largest fractures are open the subcritical crack index for the barnett shale is high indicating fracture clustering and we suggest that large open fractures exist in clusters spaced several hundred feet apart these fracture clusters may enhance permeability locally but they may be problematic for hydraulic fracture treatments the smaller sealed fractures act as planes of weakness and reactivate during hydraulic fracture treatments because the maximum horizontal stress trends northeast southwest and is nearly normal to the dominant natural fractures reactivation widens the treatment zone along multiple strands

stratigraphic distribution of macerals and biomarkers in the donets basin implications for paleoecology paleoclimatology and eustacy abstract more than one hundred and thirty coal seams and coaly layers occur in the donets basin donbas twenty eight 52 samples of them ranging in age from serpukhovian late mississipian to gzhelian late pennsylvanian 33 clastics and three limestones were studied in terms of maceral composition sulphur contents and biomarker distribution diterpanes are used to estimate the contribution of different groups of plants and the height of the water table in the swamp hopanes are a measure of bacterial activity in the peat and steranes indicate the relative input of wood and algae stratigraphic trends in these parameters are discussed in relation to paleoenvironment climatic changes and eustacy a tropical climate prevailed in the donbas from serpukhovian to kasimovian times nevertheless periods with drier and wetter conditions can be distinguished based on maceral and biomarker data relatively dry conditions are observed during serpukhovian and vereian times whereas wetter climates with a maximum of coal deposition occurred during the late bashkirian most of the moscovian and the earliest kasimovian no economic coal seams are hosted in upper kasimovian and gzhelian deposits a result of a change to an arid climate our data also suggest climatic changes during sequences of different order for the second order third order and fourth order sequences relatively dry or wet conditions occurred during coal deposition in the lowstand systems tract an intermediate climate during the transgressive systems tract and the maximum flooding and a wet climate during the highstand systems tract the results for high frequency sequences support the cecil s paleoclimatic model an intermediate paleoclimate during lst sandstone and levee siltstone a wet climate during early tst coal and a dry climate during late tst limestone mfs claystone and hst deltaic siltstone coals deposited during maximum flooding periods are more enriched in c27 steranes derived from algae and contain lower proportions of c29 steranes derived from the wood of higher plants

cenozoic sequence stratigraphy of the central and northern north sea basin tectonic development sediment distribution and provenance areas the cenozoic succession in the central and northern north sea has been investigated to establish a regional sequence stratigraphic framework changes in sediment distribution indicate a complex pattern of regional vertical movements along older palaeozoic and mesozoic structures in cenozoic times these vertical movements mainly related to tectonic processes along the continental margin to the north and north west were responsible for the generation and removal of provenance areas for sediments delivered to the north sea basin through cenozoic time during the early through middle palaeogene sediments were mainly sourced from areas in the west and from the atlantic margin in the north uplift in the northern north sea in the late eocene was in the earliest oligocene followed by marked basin subsidence and tectonic uplift of southern norway a similar pattern of tectonic movements resulted in subaerial exposure of the northern north sea in the early miocene followed by significant tectonic subsidence in the basin and along the atlantic margin in late miocene pliocene times at the same time southern norway was uplifted and became a major sediment source after the miocene pliocene subsidence uplift events glacial processes in southern norway and fluvial processes in a large drainage area east and south east of the north sea were responsible for the main sediment influx to the north sea the cenozoic depositional sequences in the north sea developed in close interaction with regional tectonic movements and changes in provenance areas tectonic movements in north west europe overprinted global sea level changes so that the generation of depositional sequences and sequence boundaries apparently occurred independently of the rate of eustatic sea level change

occurrence and distribution of sulfur in peat forming environments of southern florida abstract cores and surface samples of peats from the everglades mangrove region of southern florida were analyzed for total sulfur and pyritic sulfur these values were compared with the petrographic botanical components of the peats as determined from point counts of oriented microtome sections pyrite occurs as individual euhedral crystals loosely packed framboids and lenses or crusts of minute crystals framboids and minute crystals are often associated with organic matter and sometimes with bacteria and fungi pyrite tends to selectively occur in void spaces in or between peat tissues in samples containing very small amounts of pyrite framboidal pyrite is the prevalent form marine to brackish peats contain the highest pyrite and total sulfur contents with brackish peats generally containing more pyrite than marine peats pyrite tends to be lower in all peats within 30 cm of the surface whether marine or brackish burial of freshwater peats beneath marine or brackish peats tends to increase the total sulfur and pyritic sulfur in the underlying peats burial beneath brackish water clay rich deposits such as splays tends to increase total sulfur and pyritic sulfur in the underlying deposits more than burial beneath less clay rich deposits

relation between source rock properties and wireline log parameters an example from lower jurassic posidonia shale nw germany abstract the relationships between source rock quality and wireline log parameters were established for the lower jurassic posidonia shale the most prolific petroleum source rock of central europe wireline logs used are the gamma ray spectrometry density sonic and various resistivity logs the organic geochemical parameters considered include the organic carbon content hydrogen index and the hydrocarbon potential expressed by pyrolysis yield the case history presented is based on a continuous core through the entire posidonia shale interval from a location where this source rock is immature care was taken to detect and to avoid samples and log values influenced by bore hole roughness and fractures fair correlations were observed only between uranium content from gamma ray spectrometry log and organic carbon content no correlation was recognized between uranium content and kerogen type as defined by hydrogen indices for various reasons density sonic and resistivity logs did not provide useful data in this study three rock units with irregular high and low uranium contents could be differentiated possible causes for this tripartition are different environments during deposition and postdepositional redistribution of uranium during early diagenesis and in association with fractures

coal petrology and the origin of coal macerals a way ahead the development of coal petrology and the establishment of a nomenclatural system have proved of major use both for the industrial utilization of coal and for the development of a broad understanding of coal formation and diagenesis the development over the past 30 years however of nomenclature that includes aspects of plant origin and process is a retrograde step e g pyrofusinite degradofusinite and funginite equally problematic is the use of prescriptive formulae to indicate coal origins this paper reviews some of the problems involved with coal petrology as it is usually practiced in addition new advances in organic geochemical techniques have led to a fuller understanding of the relationship of plants and coal macerals recent research on the origin of coal macerals is presented and there is a discussion of the problems and challenges facing coal petrologists a holistic approach to studies of the origin of coal and coal macerals which includes not only petrographic but also chemical and biological studies is advocated d 2002 elsevier science b v all rights reserved

on balanced and unbalanced accommodation peat accumulation ratios in the cretaceous coals from gates formation western canada and their sequence stratigraphic significance coal composition was investigated by means of photometric and maceral analyses on closely spaced lithotype based strip samples over the full thickness of several paralic coal seams from the cretaceous gates formation of the western canadian sedimentary basin the aim of this investigation was to test various methods of identifying accommodation trends in coal and use them to refine sequence stratigraphic interpretation of continental sediments conventional sequence stratigraphy derives its subdivisions and significant surfaces from the records left by relative sea level oscillations these records either do not project into the continental realm or are difficult to recognise in clastic non marine sediments paralic coal seams have been selected to study this problem because they are not entirely removed from marine influence and compared with most inorganic deposits coal has stored a greater wealth of information that can be analysed at a higher level of resolution the study has led to the identification of five new surfaces with chronostratigraphic potential in the sequence stratigraphic analysis of non marine sediments two of these surfaces called paludification surface pas and terrestrialisation surface tes occur at the bases of the investigated coal seams while two other surfaces referred to as non marine flooding surface nfs and give up transgressive surface guts form the tops of the coal the fifth and probably most important new surface called the accommodation reversal surface ars is independent of any particular facies and may either coincide with some of the other surfaces or occur separately the proportion of detrital minerals has been used as the chief discriminator between different mire types and accommodation trends other useful indicators of mire type and peat dispersal have been the proportions of sporinite and inertodetrinite as well as some derived maceral and or mineral ratios e g the groundwater influence index and the tissue preservation index isometamorphic variations of telovitrinite reflectance and fluorescence as well as their coefficients of variation were also found to contribute to the identification of cyclic shifts between balanced and unbalanced accommodation peat accumulation ratios some of these cycles which are backed up by clastic stratigraphy appear to correspond to the development of shallowing upward and deepening upward parasequences superimposed high frequency low amplitude perturbations in the coal cycles relate to smaller scale accommodation cycles of sub parasequence level not always recognised in non marine strata these sub parasequence coal cycles do not always continue the shallowing upward trend typical of conventional parasequences several coals were found to contain stacks of small scale cycles with upward increasing accommodation signatures either in their lower or upper halves or over the whole seam section

high resolution sequence stratigraphic correlation between shallow marine and terrestrial strata examples from the sunnyside member of the cretaceous blackhawk formation book cliffs eastern utah the sunnyside member of the upper cretaceous blackhawk formation in the book cliffs of eastern utah provides an ideal opportunity to investigate high resolution sequence stratigraphic correlation between shallow marine and terrestrial strata in an area of outstanding outcrop exposure the thick laterally extensive coal seam that caps the sunnyside member is critical for correlating between its shallow marine and terrestrial components petrographic analysis of 281 samples obtained from 7 vertical sections spanning more than 30 km 18 mi of depositional dip enabled us to recognize a series of transgressive regressive coal facies trends in the seam on this basis we were able to identify a high resolution record of accommodation change throughout the deposition of the coal as well as a series of key sequence stratigraphic surfaces the stratigraphic relationships between the coal and the siliciclastic components of the sunnyside member enable us to correlate this record with that identified in the time equivalent shallow marine strata and to demonstrate that the coal spans the formation of two marine parasequences and two high frequency fourth order sequence boundaries this study has important implications for improving the understanding of sequence stratigraphic expression in terrestrial strata and for correlating between marine and terrestrial records of base level change it may also have implications for improving the predictability of vertical and lateral variations in coal composition for mining and coalbed methane projects

the hardangerfjord shear zone in sw norway and the north sea a large scale low angle shear zone in the caledonian crust the hardangerfjord shear zone is a more than 600 km long low angle extensional structure that affects the south norway and north sea caledonides the ductile shear zone which shows total maximum onshore displacement of the order of 10 15 km is primarily a basement structure with an associated passive monoclinal fold structure of the overlying caledonian nappes deep seismic data indicate that the shear zone continues down to the lower crust 20 25 km at a dip of 22 23 where it appears to flatten and merge with the general lower crustal deformation fabric onshore the hardangerfjord shear zone consists of a system of hard linked ductile shear zone segments brittle faults the l rdal gjende fault system occur in the folded caledonian allochthons in the ne part of the hardangerfjord shear zone and reappear in the north sea these may represent a high level brittle response to the devonian development of the hardangerfjord shear zone but were reactivated during permo triassic and late jurassic extensional events a c 5 km thick package of seismic reflectors along the hardangerfjord shear zone is presumed to represent a mylonite zone which is too thick to be formed entirely by 10 15 km of devonian displacement hence the hardangerfjord shear zone is likely to be a proterozoic shear zone reactivated during devonian extension

effect of mineral matrix and seam thickness on reflectance of vitrinite in high to low volatile bituminous coals an enigma abstract the variation of vitrinite reflectance with respect to mineral matrix lithology the thickness of coal seams and coal lenses and the type of organic matter was studied from two cores in a 550 m sedimentary succession from the upper jurassic to lower cretaceous kootenay group the data obtained indicate that reflectance in high to low volatile bituminous coals ro max 0 8 1 35 with depth of burial is affected by the percentage of organic matter in the samples a positive correlation between the vitrinite reflectance and the percentage of organic matter and a negative correlation with the percentage of mineral matter exist and the thicker the coal interval the higher the vitrinite reflectance thick coal seams 1 m with a mineral content 20 vitrinite dispersed in sandstone and to a lesser extent siltstone and carbonaceous shale has the lowest reflectance variations in vitrinite reflectance may be attributed to chemical differences in the organic matter possibly induced by degradation and diagenesis syn or post depositionally and to the effect of some clay minerals present in the sediments which may act as catalysts differences in the thermal conductivity of the strata have demonstratably not accounted for the observed variations in reflectance with lithology the differences in the vitrinite reflectance of organic matter between lithotypes is substantial and is thus an important consideration in resolving the time temperature history and generation of hydrocarbons from a sedimentary succession

rock physics of organic shales several publications over the last 20 years have established that black organic shales are generally characterized by strong velocity anisotropy low velocity in the bedding normal direction and relatively low density and porosity e g vernik and nur 1992 vernik and liu 1997 these rock properties are of interest in seismic attribute studies but even more so in geomechanical applications related to reservoir characterization and hydraulic fracture stimulation organic shales typically but not necessarily express strong vertical transverse isotropy vti with axis of symmetry perpendicular to the bedding parallel lamination and clay particle preferred orientation high resolution sem imaging figure 1 immediately reveals all these textural features in addition to silt grains and the lenticular distribution of the solid organic matter kerogen which in turn is characterized by significant intraparticle porosity in mature shales any ti medium is described by the five independent elastic consta

the eo permian coal seams of the parana basin in southernmost brazil an analysis of the depositional conditions using sequence stratigraphy concepts the eo permian of the parana basin is studied using sequence stratigraphy the study was based on data acquired from 92 entirely cored and geophysically logged boreholes the study is an applicability test of the conceptual and methodological framework of sequence stratigraphy in the examination of the coal seams of the eo permian rio bonito formation the coal seams were predominantly deposited in a lagoon barrier system linked with a third order transgressive systems tract subdivided into four parasequence sets each set represents a major transgressive pulse in the sedimentary history of the basin

a practical model for organic richness from porosity and resistivity logs a practical method the delta log r technique for identifying and calculating total organic carbon in organic rich rocks has been developed using well logs the method employs the overlaying of a properly scaled porosity log generally the sonic transit time curve on a resistivity curve preferably from a deep reading tool in water saturated organic lean rocks the two curves parallel each other and can be overlain since both curves respond to variations in formation porosity however in either hydrocarbon reservoir rocks or organic rich non reservoir rocks a separation between the curves occurs using the gamma ray curve reservoir intervals can be identified and eliminated from the analysis the separation in organic rich intervals results from two effects the orosity curve responds to the presence of low density low velocity kerogen and the resistivity curve responds to the formation fluid in an immature organic rich rock where no hydrocarbons have been generated the observed curve separation is due solely to the porosity curve response in mature source rocks in addition to the porosity curve response the resistivity increases because of the presence of generated hydrocarbons the magnitude of the curve separation in non reservoirs is calibrated to total organic carbon and maturity and allows for depth profiling of organic richness in the absence of sample data this method allows organic richness to be accurately assessed in a wide variety of lithologies and maturities using common well logs

latest caledonian to present tectonomorphological development of southern norway abstract the regional resultant stress field of the northeastern north atlantic has shifted significantly throughout the phanerozoic in fennoscandian parts of the caledonian orogen mountain building which was characterized by nw se contraction reference to present north was followed by a collapse with transport both parallel and transverse to the mountain chain the late palaeozoic mesozoic saw several stages of e w to nw se extension varying in time and position local episodes of inversion are traceable in some cases particularly in connection with deep seated and long lived zones of weakness the cenozoic has to a larger degree been affected by compression including folding and basin inversion again some of the more pronounced effects of local inversion are related to pre existing fault systems neogene uplift of the western mountainous area in scandinavia can be unravelled by potential field study aft data and reflection seismic sections assuming that the region is close to isostatic equilibrium the uplifted areas must be supported at depth by substantial volumes of low density material within the crust or the mantle close to the crust mantle interface or close to the lithosphere asthenosphere interfaces a series of nw se oriented cross sections representing successive stages of development from the late caledonian to present were prepared and used to analyse the tectonomorphological development as related to the shifting stress configurations three stages are inferred stage 1 devonian late permian denudation of the caledonian mountain chain during the latest stage of closing of the iapetus ocean in early to mid devonian times the caledonian mountain chain reached its maximum elevation of perhaps as much as 8 9 km including the foreland basins to the east the average topographic gradient of the eastern flank may have been in the order of 1 3 the denudation of the caledonian mountains continued into the permian and by the end of the permian the mountain system was more or less obliterated with a gradient of the eastern flank probably continued to fall to less than 0 1 stage 2 triassic late cretaceous tectono thermal uplift of central south norway uplift of central south norway was rejuvenated in triassic times and continued throughout the jurassic and early cretaceous the gradient of the eastern flank increased to a maximum of approximately 0 15 and master structural elements like the laerdal gjende olestol fault complex again played important roles in the development stage 3 tertiary present renewed tectono thermal activity and post glacial rebound a second phase of post caledonian tectono thermal uplift of south central norway started in oligocene time again increasing the gradient of the eastern flank of south norway around 0 2

mineralogy and leaching characteristics of beneficiated coal products from santa catarina brazil abstract petrographic mineralogical and geochemical studies have been carried out on beneficiated coal products from mines and preparation plants in the santa catarina basin southern brazil to investigate the range of characteristics exhibited by the materials and the potential impact of their stockpiling and storage on the environment the coals contain varying proportions of vitrinite and inertinite macerals and have vitrinite reflectance values ranging from 0 44 to 1 38 with the exception of one material blended with peat from an external source they have relatively high percentages of ash 30 58 and mineral matter 36 66 the mineral matter consists mainly of clay minerals kaolinite illite and illite smectite together with 15 25 quartz up to 10 feldspar up to 5 calcite and or dolomite and up to 5 pyrite and around 1 anatase and or rutile bassanite is also present in low temperature ash derived from the coals mainly derived from interaction of ca and s associated with the organic matter jarosite is formed by pyrite oxidation in coals that have been exposed in stockpiles for extended periods most of the trace elements in most of the coals have higher concentrations than average values for world coals generally probably due to the relatively high mineral matter content a lower ash product representing a blend of coal and peat has similar to lower concentrations of most elements but higher concentrations of b ba be cd ge and mn which may be associated with the peat component interaction of relatively fresh coals with water in laboratory tests produces leachates with near neutral to mildly acid ph values but leaching of oxidized jarosite bearing coal produces a strongly acid leachate with higher concentrations of cd co cu ni and zn leachates derived from coals in which the pyrite has been oxidized during storage would thus be expected to have a more adverse environmental impact than leachates derived from coals in which such oxidation has not had an opportunity to develop

organic carbon in bakken formation united states portion of williston basin the upper and lower members of the mississippian and devonian bakken formation in the united states portion of the williston basin are black shales that are extremely rich in organic matter and are the source of much of the oil found in the basin organic carbon values are calculated from formation density logs using the equation toc 154 497 rgr 57 261 where toc is organic carbon content wt and rgr is formation density g cm3 test calculations comparing this equation to laboratory organic carbon analyses from 39 wells in north dakota show an average absolute difference of 1 1 in organic carbon content organic carbon content calculated at 159 locations in north dakota and 107 in montana averages 12 1 for the upper member of the bakken formation and 11 5 for the lower member there is a regional depletion of organic carbon paralleling present day isotherms that reflects the conversion of organic matter to oil and subsequent expulsion of the oil from the formation the mass of organic carbon in the bakken formation is approximately evenly divided between the upper and lower members and it totals about 126 1012 kg in the study area of which 102 1012 kg are in the thermally mature region the assumption that 167 mg hc g toc have migrated out of the mature bakken shales leads to a tentative estimate that hydrocarbons equivalent to 132 billion bbl of 43 api gravity oil have been expelled from the united states portion of the upper and lower members of the bakken formation

interaction of permo triassic and jurassic extensional fault blocks during the development of the northern north sea the main structural elements resulting from late permian early triassic extension have been resolved across the total width of the northern north sea the northern segment of the basin north of 61 n bounded to the west by the hutton fault and to the east by the norwegian mainland was occupied by four westerly tilted half grabens 25 35 km in width prior to jurassic extension the central segment of the basin 60 20 61 n exhibits a full graben beneath the jurassic horda platform flanked by half grabens tilted towards the basin margins the change in permo triassic fault block configuration defining structural domains is largely constrained by a basement discontinuity which runs diagonally ne sw across the basin maximum jurassic extension is represented by several centres of subsidence aligned nne ssw across a n s oriented and broader permo triassic basin jurassic extension was concentrated within the viking graben proper south of 60 n which in this area is represented by single westerly tilted en echelon half graben segments 20 25 km wide the area affected by jurassic extension becomes progressively wider to the north again governed by the basement discontinuity eventually encompassing the total width of the basin c 200 km north of 61 n the central segment of the northern north sea displays the greatest contrast in permo triassic and jurassic structural styles and basin geometry jurassic stretching and faulting was negligible to the east horda platform precisely the area which had been the site of maximum permo triassic stretching and fault activity it has generally been assumed that jurassic fault configuration along the eastern margin of the central segment of the viking graben to a large extent reflects the reactivation of major permo triassic faults this study demonstrates the interference of permo triassic and jurassic basin geometries in this area due to major faults of the two generations dipping in opposite directions as a consequence the e tilted oseberg fault block of jurassic origin and c 20km in width is underlain by a wider c 35 km and w tilted permo triassic fault block

experimental mechanical compaction of clay mineral aggregates changes in physical properties of mudstones during burial dry and brine saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory experiments were conducted by increasing vertical effective stress up to 50 mpa to study the changes in physical properties of mudstones during burial the results suggest that the physical properties porosity density acoustic velocity etc of mudstones vary greatly with increasing effective stress clay mineralogy and fluid content kaolinite aggregates are much more compressible than those composed of smectite brine saturated clay mixtures are much more compressible than dry clay mixtures brine may soften and lubricate the clay matrix compared to dry clays resulting in higher compressibility in the brine saturated state the lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays the extremely fine grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse grained kaolinite at 20 mpa effective stress corresponding to about 2 km burial depth with hydrostatic pore pressure brine saturated pure kaolinite compacted to 20 porosity while pure smectite retained 41 porosity brinesaturated clay mixtures show higher vp and lower vs than dry clay mixtures a pronounced difference in vs was observed among the brinesaturated clay mixtures the lowest vs as a function of vertical effective stress was found for pure smectite for a given porosity value smectitic clays have higher velocities and elastic moduli than the kaolinitic clays the vp vs ratio is significantly higher in smectite than in kaolinite aggregates treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties which are strongly affected by the clay mineralogy grain size the amount of other minerals present and fluid content our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth o 2k m 801c above depths where significant chemical compaction takes place r 2007 elsevier ltd all rights reserved

identification of source rocks on wireline logs by density resistivity and sonic transit time resistivity crossplots source rock formations generally show a lower density a lower sonic transit time and a higher resistivity than other sediments of equal compaction and comparable mineralogy this phenomenon can be used to identify source rocks on wireline logs provided the source rocks have a minimum thickness within the resolution of the sondes used and are sufficiently rich in organic matter classification rules have been established to assist in the recognition of source rocks on a combination of logs because of the low density contrast between water and organic matter the method becomes inaccurate at high water saturations i e low compaction within limits the amount of organic matter contained in a sediment can be estimated from log anomalies when source rocks become mature free oil is present in addition to kerogen and the resistivity increases by a factor of 10 or more

merging sequence stratigraphy and geomechanics for unconventional gas shales the recent revelation of vast global quantities of potentially gas and oil productive shales has paved the way for rapid advancements in understanding their geological properties many of which affect their geomechanical properties and ultimately reservoir operations and performance because of shale s unique and very intricate geological physical and mechanical properties at all scales from nano to macro scale abousleiman et al 2010 compared with sandstones and carbonates the ad jective unconventional has often been applied to their characterization although many shale characteristics are different than those of sandstones and carbonates and require new technologies to measure them other characteristics mentioned below are similar as such customized conventional methodologies and concepts can be applied to exploration and production of shale gas and oil

the nature and influence of fire in carboniferous ecosystems fusain occurs widely in carboniferous coals and sediments it is now recognised to represent charcoal and be the product of wildfire the occurrence of fire is partly constrained by atmospheric oxygen levels availability and nature of fuel and by aspects of climate rainfall and seasonability in particular the majority of fires in the carboniferous were probably started by lightning strikes or by volcanic activity experiments on the charring of modern plants has shown that the reflectance of charcoal and hence fusain is directly related to temperature of formation different fire types may yield fusain assemblages of differing reflectance spectrums but it may be significant that many modern charcoal assemblages yield only semifusinites as seen by reflectance microscopy the significance of these findings is assessed in relation to the use of fusinites and semifusinites as depositional indicators as interpreted from coal petrology fires may have a dramatic effect on ecosystems not only causing changes in vegetational succession but also severe erosion can occur following a major fire which can be traced in depositional systems in this paper we document three major carboniferous sedimentary systems affected by fire clastic sedimentary systems using extensive fusain deposits in mid lower carboniferous near shore sediments in donegal ireland volcanic systems using late early carboniferous volcaniclastic sequences in the midland valley of scotland and coal and coal bearing sequences in the upper carboniferous westphalian b of the pennine basin england in the later settings the influence of fire in peat formation and succession is assessed in addition data on the vegetational composition of charcoal assemblages is considered it is concluded that fire plays a major role in many carboniferous ecosystems

the lower and upper coal seams of the candiota coalfield brazil geological setting petrological and chemical characterization and studies on reactivity and beneficiation related to their combustion potential abstract in the candiota coalfield rs brazil the candiota superior and inferior coal seams are at current time being mined for power generation the current study characterizes the other seams of the deposit which include the upper s2 s9 seams the banco louco bl seam and the lower i1 i5 seams which up to date have not been considered for power generation the analytical techniques applied in this study include sequence stratigraphic analysis of the coal bearing interval petrographical and chemical analyses of the coal seams reactivity tests based on thermobalance experiments and studies on beneficiation sequence stratigraphic analyses sedimentological analyses identified four depositional systems in the study area alluvial fan fluvial lagoon barrier and shallow marine with coal seams developed in transgressive systems tract highstand systems tract and lowstand systems tract petrographical and chemical analyses the petrographical analyses showed that the most abundant maceral in the coals is vitrinite followed by inertinite and liptinite the average vitrinite reflectance is indicative of subbituminous rank 0 41 rr the values for ash yield range from 29 0 to 74 2 wt average 49 1 wt and for volatile matter contents vary from 13 5 to 29 5 wt average 19 9 wt sulfur contents range from 0 4 to 8 1 wt average 1 9 wt the gross calorific values as received basis range from 841 to 3727 cal g average 2632 cal g based on x ray diffraction analysis the most abundant minerals in the coal seams are quartz kaolinite illite and k feldspar reactivity studies thermogravimetric analyses carried out on fourteen seam channel samples showed differences in the combustion behavior of the seams in particular for the inertinite rich seams s8 and banco louco the i2 seam analyzed from four of the eight exploration wells indicated very similar combustion properties based on the thermogravimetric analyses beneficiation tests from the sink float tests and proximate and ultimate analyses washability curves were prepared for all upper lower and bl seams 20 cm thick these curves were plotted showing ash distribution and total sulfur content for a grain size between 25 4 mm and 2 0 mm fraction a 25 4 2 0 mm and for a grain size between 2 0 mm and 0 1 mm fraction b 2 0 0 1 mm these curves provided important information to a possible gravimetric beneficiation for both size fractions however the performance of such beneficiation mainly depends on both the near gravity material ngm value and separation density of each seam which are the main parameters analyzed in addition these curves showed low values of total sulfur content in any separation density however the densest fractions were not taken into consideration conclusion the results of the chemical and petrological analyses as well as the studies on combustion and beneficiation characteristics suggest that the seams investigated in this study s1 s9 bl i1 i5 do have the potential for being used in power generation

rapid wastage of alaska glaciers and their contribution to rising sea level we have used airborne laser altimetry to estimate volume changes of 67 glaciers in alaska from the mid 1950s to the mid 1990s the average rate of thickness change of these glaciers was 0 52 m year extrapolation to all glaciers in alaska yields an estimated total annual volume change of 52 15 km 3 year water equivalent equivalent to a rise in sea level sle of 0 14 0 04 mm year repeat measurements of 28 glaciers from the mid 1990s to 2000 2001 suggest an increased average rate of thinning 1 8 m year this leads to an extrapolated annual volume loss from alaska glaciers equal to 96 35 km 3 year or 0 27 0 10 mm year sle during the past decade these recent losses are nearly double the estimated annual loss from the entire greenland ice sheet during the same time period and are much higher than previously published loss estimates for alaska glaciers they form the largest glaciological contribution to rising sea level yet measured

concentration of elements in lacustrine coals from zone a hat creek deposit no 1 british columbia canada abstract coal samples from the 170 m thick a zone of the hat creek coal deposit no 1 in central british columbia were examined for major minor and trace element distribution the coal is lignite subbituminous in rank and of eocene age this study shows 1 as b br cl and s are the only elements organically associated in these samples 2 concentration of certain elements such as fe mn and co can be related to the presence or absence of carbonate and or sulphide minerals 3 distribution of certain elements i e al b br cl cr fe th u and zn follow similar patterns of concentration or depletion across the vertical thickness of zone a and suggest three depositional cycles 4 concentration of boron versus chromium sodium sulphur and uranium for these coals clearly placed them in a freshwater environment 5 rates of sedimentation using the na k ratio also suggest three depositional cycles 6 in resinite samples hand picked from these coals the concentrations of all elements except as and se were lower than their concentrations in the whole coals

sequence stratigraphy organic petrology and chemistry applied to the upper and lower coal seams in the candiota coalfield parana basin rs brazil abstract the permian age coal seams in the candiota coalfield represent the largest coal deposit of the country currently two seams are mined called camada candiota superior and camada candiota inferior the other coal seams of the coalfield seams s1 s9 upper seams and i1 i5 lower seams have as yet not been exploited the objective of this paper is to perform a detailed sequence stratigraphic petrologic and chemical study of the upper and lower coal seams thereby generating data for assisting in the development and better use of the coal bearing interval the methodology includes application of the concepts of sequence stratigraphy which includes the lithological interpretation of the core to establish the depositional environments and genetic correlation between facies associations to define parasequences and bounding surfaces coal petrology analysis of the reflectance of vitrinite determination of the petrographic composition of the coals by maceral analyses and chemical analyses such as sulphur determination proximate analyses ash moisture volatile matter and fixed carbon and elemental analyses three main depositional systems were so far identified alluvial fan fluvial system lagoonal estuary system this study shows that coal development was controlled by accommodation accumulation rates with coal seams with greater thickness and lateral continuity being formed within the transgressive systems tract lagoonal depositional system of parasequence 2 ps2 indicating that the accumulation rates of the peat and distribution of the coal seams were controlled by stratigraphic setting vitrinite reflectances for the upper and lower coal seams are indicative of subbituminous rank rrandom 0 36 0 47 with evidence that anomalously low reflectance values are related to high mineral matter contents maceral composition is highly variable with some coal seams being extremely rich in inertinite up to 65 vol the upper and lower coal seams are ash rich ranging from 22 4 to 62 3 wt with the majority being classified as carbonaceous rocks very low grade coal sulphur contents in the upper and lower seams range from 0 41 to 8 08 wt with the majority below 1 wt the high amounts of sulphur 3 wt in some of the coal seams may indicate coastal flooding during the lifetime of the mire or shortly after

palaeotopography related plant succession stages in a coal forming deltaic succession in early jurassic in hungary abstract an integrated palaeoecological study was performed regarding the early jurassic coal bearing succession mecsek coal formation of the mecsek basin s hungary focusing on boreholes from maza south and rucker areas representing the periphery and the central part of the coastal plain of a delta respectively comparative investigations were based on a previous palaeobotanical ecogroup model and on the integrated interpretation of sedimentological and palaeobotanical data from maza south sedimentary isopach and coal seam ash content data were applied to reconstruct palaeotopography and coal seam thickness data to detect plant growing intensity at maza south 10 km2 plant fossils identified from the corresponding strata were used as sources for the identification of four topography related plant succession stages determined by sequential facies changes channel banks and small islands are characterised by underdeveloped associations composed of colonist elements exposed slopes or levees or local elevations in overbank conditions are covered with assemblages of small herbaceous plants crevasse splay complexes are characterised by more developed plant cover and swamps in floodplain depressions are characterised by typical swampy successions based on these succession stages plant remains from rucker were also interpreted however mainly swampy and elevated overbank habitats alternated at rucker reflecting continuous floods according to the results maza south was a small area located very close to the bayline between the alluvial plain and the coastal plain of a delta less favourable for intensive plant growing where dry land was restricted to levees and crevasse splays this resulted in more dynamic plant changes typical for deltaic peripheral territories in contrast rucker represents the central part of the delta plain environment dominated by woody forms of large growth in the uppermost sequence plant composition at maza south became similar to that of rucker indicating that with transgression the central delta plain environment permanent at rucker advanced towards the peripheral zone represented by maza south