stable carbon isotopes of coal derived gases sourced from the mesozoic coal measures in china coal derived large scale gas fields derived from the mesozoic coal measures in china are mainly distributed in the middle lower jurassic coal measures in the tarim junggar and turpan hami basins in northwest china and the upper triassic xujiahe formation coal measure in sichuan basin central china in 2011 the annual production was 21 6 109 m3 and the proved geological reserves were 2485 109 m3 accounting for 21 and 30 of the total in china respectively based on analyses of gas composition and stable carbon isotopes ratios of 203 samples and stable carbon isotopes of 102 co2 samples the following conclusions were made a based on diagnostic plots using the stable carbon isotopic and molecular composition of gas samples alkane gas from the mesozoic coal measures in china is shown to be coal derived b according to the 13c2 vs c2h6 plot of a great number of oil derived and coal derived gases in china it is concluded that gases with 13c2 28 5 are coal derived and those with 13c2 28 5 are oil derived in most cases c among the natural gases from the mesozoic coal measures in china primary coal derived gases with normal carbon isotopic distribution pattern among the c1 c4 alkanes i e 13c1 13c2 13c3 13c4 are dominant d carbon isotopic pattern reversal mainly results from the mixing of coal derived gases having different maturities but the same source and secondly from microbial oxidation of propane e g mu 3 and mu 4 wells in the gumudi gas field junggar basin e co2 in the coal derived gases from the mesozoic coal measures in china has both biogenic and abiogenic origins the biogenic origin is dominant and the abiogenic co2 is mainly found in the kuqa depression in the tarim basin and western sichuan basin f isotopic differences between heavy hydrocarbon gases and methane become less with increasing maturity

correlation of reservoired gases using the carbon isotopic compositions of wet gas components the carbon isotopic compositions of the wet gas components particularly propane isobutane and normal butane have been found to be particularly valuable for correlating one reservoired gas with another the usefulness of these components for correlation results from their carbon isotopic compositions reflecting both the nature of their source and their maturity this source control is strongest for gases derived from the more highly structured types of kerogen i e woody coaly type iii although the wet gas components carbon isotopic compositions of most gases are at least partly controlled by their source for levels of maturity below the point at which thermal destruction of the wet components occurs as a result the wet gas components are found to provide more ositive correlations than is methane alone three exploration examples illustrate the use of the carbon isotopic compositions of the wet gas components for correlation the leduc reef trend of alberta canada the sleipner area in the north sea and the lena field offshore louisiana united states the three examples also illustrate the need to integrate geochemical interpretations with regional geology to obtain a good understanding of the hydrocarbon source

modelling coseismic displacements during the 1997 umbria marche earthquake central italy summary we propose a dislocation model for the two normal faulting earthquakes that struckthe central apennines umbria marche italy on 1997 september 26 at 00 33 mw 5 7 and 09 40 gmt mw 6 0 we t coseismic horizontal and vertical displacements resulting from gps measurements at several monuments of the igmi istituto geogra co militare italiano by means of a dislocation model in an elastic homogeneous isotropic half space our best tting model consists of two normal faults whose mechanisms and seismic moments have been taken from cmt solutions it is consistent with other seismological and geophysical observations the rst fault which is 6 km long and 7 km wide ruptured during the 00 33 event with a unilateral rupture towards the se and an average slip of 27 cm the second fault is 12 km long and 10 km wide and ruptured during the 09 40 event with a nearly unilateral rupture towards the nw slip distribution on this second fault is non uniform and is concentrated in its se portion maximum slip is 65 cm where rupture initiated the 00 33 fault is deeper than the 09 40 one the top of the rst rupture is deeper than 1 7 km the top of the second is 0 6 km deep in order to interpret the observed epicentral subsidence we have also considered the contributions of two further moderate magnitude earthquakes that occurred on 1997 october 3 mw 5 2 and 6 mw 5 4 immediately before the gps survey and were located very close to the 09 40 event of september 26 we compare the pattern of vertical displacements resulting from our forward modelling of gps data with that derived from sar interferograms the t to sar data is very good con rming the reliability of the proposed dislocation model

late and deep fermentative methanogenesis as reflected in the h c o s isotopy of the methane water system in deep aquifers of the pannonian basin se hungary abstract h and o isotope ratios and h and c isotope ratios of methane as well as the abundances of some major and minor dissolved components were measured in 26 subsurface waters from se hungary produced from late neogene aquifers within the upper two kilometres in depth mixing with meteoric water of glacial age is of importance the hydrocarbon gas hc gas content of the great majority of the waters is dominated by isotopically light bacterial methane the depth of the onset of thermal gas generation varies from 0 7 to 1 2 km but the amount of thermogenic methane leaving the kerogen was not sufficient to overprint the light isotopic signature of the methane in the waters about two thirds of the waters group i samples are characterised by low sulfate content 20 and methane d values less negative than 260 they also show a direct relationship between the h isotope ratio of the methane and that of the water these waters experienced exhaustive bacterial sulfate reduction followed by a relatively shallow bacterial methanogenesis in a third of the waters group ii samples the methane d values are more negative than 278 the group ii samples which are not affected by an admixture of glacial age meteoric waters contain a relatively high amount of sulfate 35 45 mg l and do not show a direct relationship between the h isotope ratio of the methane and that of the water in group ii waters bacterial sulfate reduction was not exhaustive and the residual sulfate inhibited shallow bacterial methanogenesis as a result of continuing burial the aquifers were heated up to 40 60 c thereby allowing a relatively intensive bacterial acetogenesis followed by acetate fermentation to methane our results show that deep acetate fermentation and early thermal gas generation can occur closely in space and time even partly overlapping with each other

geodetic strain in peninsular italy between 1875 and 2001 1 we determine geodetic strain in peninsular italy by the gps reoccupation of the first order triangulation network of italy installed from 1860 the uncertainties in the original measurements about 3 ppm and the time span between the two observations imply that tectonic signals larger than about 0 03 ppm yr are resolvable along the apenninic belt where the largest earthquakes are concentrated the geodetic deformation has a clear and consistent strain pattern between adjacent regions well above the uncertainties and shows a pervasive ne sw extension along the tyrrhenian and adriatic coasts the geodetic signal is not homogeneous and is comparable with the uncertainty in the original measurements seismic deformation calculated over the same time interval agrees well with estimated extensional direction but the magnitudes of geodetic and seismic strain differ suggesting that in part of the apennines significant strain accumulation over the past 130 years may not have been released in earthquakes

impacts of hydrothermal dolomitization and thermochemical sulfate reduction on secondary porosity creation in deeply buried carbonates a case study from the lower saxony basin northwest germany the role of deep burial dissolution in the creation of porosity in carbonates has been discussed controversially in the recent past we present a case study from the upper permian zechstein 2 carbonate reservoirs of the lower saxony basin in northwest germany these reservoirs are locally characterized by high amounts of carbon dioxide co2 and variable amounts of hydrogen sulfide h2s which are derived from thermochemical sulfate reduction tsr and inorganic sources to study the contribution of these effects on porosity development we combine petrography stable isotope and rare earth and yttrium rey analyses of fracture cements with raman spectroscopy and 13c analyses of fluid inclusions it is shown that fluid migration along deep fault zones created and redistributed porosity fluid inclusion analyses of vein cements demonstrate that hydrothermal fluids transported inorganic co2 into the reservoir where it mixed with minor amounts of tsr derived organic co2 the likely source of inorganic co2 is the thermal decomposition of deeply buried devonian carbonates the rey distribution patterns support a hydrothermal origin of ascending iron and co2 rich fluids causing dolomitization of calcite and increasing porosity by 10 16 along fractures this porosity increase results from hydrothermal dolomitization and dissolution by acids generated from the reaction of fe2 with h2s to precipitate pyrite in contrast hydrothermal dolomite cements reduced early diagenetic porosity in dolomitic intervals by approximately 17 however the carbonate dissolution in the predominantly calcitic host rock results in a net increase in porosity and permeability in the vicinity of the fracture walls which has to be considered for modeling reservoir properties and fluid migration pathways

modes of fault reactivation from analogue modeling experiments implications for the seismotectonics of the southern adriatic foreland italy abstract the active tectonics at the front of the southern apennines and in the adriatic foreland is characterized by e w striking right lateral seismogenic faults interpreted as reactivated inherited discontinuities the best studied among these is the molise gondola shear zone mgsz the interaction of these shear zones with the apennines chain is not yet clear to address this open question we developed a set of scaled analogue experiments aimed at analyzing 1 how dextral strike slip motion along a pre existing zone of weakness within the foreland propagates toward the surface and affects the orogenic wedge 2 the propagation of deformation as a function of increasing displacement 3 any insights on the active tectonics of southern italy our results stress the primary role played by these inherited structures when reactivated and confirm that regional e w dextral shear zones are a plausible way of explaining the seismotectonic setting of the external areas of the southern apennines

carbon isotope geochemistry of natural gases from the green tuff basin japan carbon isotopic analyses of c1 c4 hydrocarbons were carried out to investigate the origin and formation mechanism of natural gases commercially produced from volcanic rocks as well as sedimentary rocks in the green tuff basin of northeast japan whose high 3he 4he ratios have suggested a possible magmatic origin 13c pdb values of methane ethane propane and n butane range from 54 4 to 33 3 from 32 5 to 20 9v from 27 7 to 20 6 and from 25 3 to 20 5 respectively all of which fall within the ranges of published data of worldwide gases of biogenie origin most samples show the isotope distribution pattern wherein the 13c values become less negative with increasing molecular weight of the hydrocarbons suggesting that the c2 hydrocarbons were not derived by methane polymerization the 13c values of c2 c4 hydrocarbons are explained by thermogenic breakdown of organic matter whereas the 13c values of methane are more or less lower than those expected from the same origin these results indicate that the gases from the green tuff basin consist of thermogenic hydrocarbons plus variable amounts of isotopically lighter microbial methane significant contributions of abiogenic methane which would be isotopically heavier than the thermogenic methane are not plausible for the gases

origin of oil and gas occurrences in the pliocene sediments of the pannonian basin hungary abstract considerable volumes of oil and gas in the pannonian basin have been discovered in pliocene sediments having good reservoir characteristics the pliocene sediments belonging to delta facies contain quantitatively very good but immature source rocks at depths of 0 5 2 km the origin of the oil and gas accumulations in the pliocene reservoirs is very different due to diverse conditions of hydrocarbon generation and secondary migration the aim of this paper is to establish the origin of oil and gas trapped in pliocene reservoirs in order to have a picture of the migration and accumulation systems different cases examined by means of the geochemical characteristics of oil and gases indicate that the pliocene reservoirs contain indigenous dry gases generated by bacterial and early catagenetic processes and vertically migrated hydrocarbon rich wet gases associated with oil and carbon dioxide rich gases derived from high temperature zones of the earth crust or from volcanic bodies

some observations on the origins of large volumes of carbon dioxide accumulations in sedimentary basins large volumes of carbon dioxide i e up to 90 v v have been encountered in sedimentary basins from various geological settings but their origins remain enigmatic evidence from carbon and noble gas isotope analyses indicate a variety of interpretations for the origins of the co2 including mantle degassing metamorphic reactions or magmatic processes the formation of large accumulations of large volumes of co2 in sedimentary basins is discussed with specific reference to published data from the pannonian basin hungary the cooper eromanga basin australia and the south viking graben north sea these basins have occurrences of large volumes i e over 15 v v of isotopically heavy carbon dioxide thought to be of inorganic origin and although they differ somewhat in terms of sedimentary fill all have major structural features close to the gas accumulations the available geochemical data are currently neither sufficient to confirm the specific origin s of the co2 e g mantle derived carbonate metamorphism nor unscramble co2 mixed from two or more sources ongoing studies especially those involving noble gas analyses should provide fuller answers

do strike slip faults of molise central southern italy really release a high stress the 31 october and 1 november 2002 molise earthquakes both m w 5 7 were caused by right lateral slip between 12 and 20 km depth these earthquakes are the result of large scale reactivation of preexisting left lateral regionally extended east west structures of mesozoic age although recorded ground motions were generally smaller than expected for typical italian earthquakes a recent paper attributes a stress drop as high as 180 bars to the molise earthquakes we remark that a high stress drop is in contrast both with the relatively long source duration inferred in previous investigations and with geodetic evidence for a significantly smaller fault slip compared with other apennine earthquakes having similarly large rupture area e g 1997 umbria marche earthquakes we analyzed both ground acceleration spectra of the mainshocks and single station spectral ratios of broadband seismograms in an extended magnitude range 2 7 m w 5 7 our results show that neither the spectral amplitudes of recorded ground motions nor the spectral ratios can be fit by a high stress drop source instead we find that the observations are consistent with a low stress drop our best estimates ranging between 6 and 25 bars in agreement with the relatively long source duration and small coseismic slip we interpret the low stress of the 2002 molise earthquakes in terms of lower energy release mechanisms due to the reutilization of faults reactivated opposite to their original sense of slip

petroleum geochemistry of the deep part of the drava depression croatia the drava depression is located in the southwestern margin of the pannonian basin the northern zone of the depression is called the deep drava geochemical data imply that in the northwestern part of deep drava the mudstones carbonate fossiliferous mudstones compact marls and siltites of lower miocene to badenian age at the depths of more than 3000 m are petroleum source rocks the organic matter is mostly of terrigeneous origin with local occurrences of hydrogen rich terrigeneous components the source rocks have reached a high level of thermal alteration in the condensate gas window between 3150 and 3800 m hydrocarbons in accumulations are interpreted to be migrated thermogenic condensate associated gases and their compositions are consistent with the facies type and maturity of the source rocks mineralogical composition of reservoir rocks and specific thermodynamic conditions control the formation of co2 and h2s the high co2 concentrations mainly result from the thermal breakdown of carbonates while h2s is the product of thermochemical sulphate reduction from anhydrite in the presence of hydrocarbons

an electrical resistivity crustal section from the alps to the baltic sea central segment of the egt abstract electrical resistivity models derived from magnetotelluric and magnetovariational measurements in the past 10 years have been compiled along the central segment of the european geotraverse along the profile low resistivity structures exist particularly in the middle and upper crust and probably mask deeper low resistivity zones these structures can be related to different tectonic units along the profile the prominent features are the two dimensional low resistivity structures at the transition from the moldanubian to the saxothuringian and from the saxothuringian to the rhenohercynian unit of the variscan belt the depth correlation of the low resistivity horizon in the rhenish massif with a seismic low reflectivity band the very high conductance of an upper to middle crustal layer in the north german lowlands and its cessation at the river elbe towards the baltic sea the reduction in the resistivity of these zones is very likely due to graphite at mid crustal depths it is obvious that there exists a general increase of electrical conductance in the upper half of the crust from south to north of the central segment which may be due to increasing accumulation of graphite and successive tectonically controlled ordering processes this phenomenon may by relating it to the growing crustal age from south to north be the indicator of a maturing continental crust

temperature dependent viscoelastic compaction and compartmentalization in sedimentary basins the near surface compaction regime of most sedimentary basins is characterized by hydrostatic fluid pressures and is therefore determined entirely by sediment matrix rheology within this regime compaction is initially well described by a pseudoelastic rheological model with increasing depth precipitation dissolution processes lead to thermally activated viscous deformation the steady state porosity profile of the viscous regime is a function of two length scales the viscous e fold length related to the compaction activation energy and a scale determined by the remaining parameters of the sedimentary process overpressure development is weakly dependent on the second scale for activation energies 20 kj mol application of the steady state model to pannonian basin shales and sandstones indicates a dominant role for viscous compaction in these lithologies at porosities below 10 and 25 respectively activation energies and shear viscosities derived from the profiles are 20 40 kj mol and 1020 1021 pa s at 3 km depth the analytical formulation of the compaction model provides a simple method of predicting both the depth at which permeability limits compaction resulting in top seal formation and the amount of fluid trapped beneath the top seal fluid flow during hydraulically limited compaction is unstable such that sedimentation rate perturbations or devolatilization cause nucleation of porosity waves on the viscous e fold length scale 0 5 1 5 km the porosity waves are characterized by fluid overpressure with a hydrostatic fluid pressure gradient and propagate through creation of secondary porosity in response to the mean stress gradient the waves are a mechanism of episodic fluid expulsion that can be significantly more eycient than uniform darcyian fluid flow but upward wave propagation is constrained by the compaction front so that the waves evolve into essentially static domains of high porosity following cessation of sedimentation yielding mechanisms do not appreciably alter the time and length scale of episodic fluid flow because fluid expulsion is ultimately controlled by compaction the flow instabilities inherent in viscous compaction are similar to and a possible explanation for fluid compartments 2000 elsevier science b v all rights reserved

do co2 charged fluids contribute to secondary porosity creation in deeply buried carbonates abstract carbonate dissolution by acidic co2 charged fluids is one possible mechanism leading to the creation of burial porosity the late permian carbonates of the lower saxony basin nw germany are a suitable target to study the influence of such co2 charged fluids on porosity evolution the so called zechstein 2 carbonates ca2 consist of alternating dolomitic and calcitic intervals and contain locally very high amounts of co2 80 and variable amounts of h2s in reservoir gas and vein cement hosted fluid inclusions composition and isotope data from fluid inclusions suggest that the co2 is sourced from the thermal decomposition of underlying devonian carbonates far reaching fault systems connect the devonian co2 source with the permian ca2 reservoir while thick rock salt deposits above the zechstein 2 carbonates prohibit an influence of surface derived meteoric fluids the aim of the study is to evaluate the contribution of co2 on carbonate dissolution seven wells were preferentially sampled along mineral veins which are interpreted as the preferred migration pathways for the present gas classic petrography methods such as transmitted light microscopy and cathodoluminescence were combined with fluid inclusion analysis and porosity data petrographic analysis reveals no great impact of the massive co2 presence on porosity creation as fluids get quickly saturated with respect to ca2 minor vuggy porosity is associated with fractures in only one of the studied wells but the dominant porosity types are early diagenetic fabric selective oomoldic and intercrystal porosity to evaluate whether the porosity values are higher than usual a comparison with a global porosity dataset is included which however shows no increase in average porosities compared to global values the results of this case study suggest that the contribution of co2 alone on carbonate dissolution and therefore reservoir quality is negligible as long as other processes such as late dolomitization or pyrite formation by thermochemical sulphate reduction derived h2s are absent

carbon isotope geochemistry of petroleum associated gases in krishna godavari basin india abstract this paper presents the results of a comprehensive study of the compositional and stable carbon isotopic characteristics of 23 natural gases from 13 structural areas from different tectonic blocks of the krishna godavari basin the 13 c ethane and 13 c propane values of reservoired associated gases have been used in furthering an understanding of origin and occurrence of these hydrocarbons three aspects have been discussed 1 genetic correlation of gases 2 evaluation of maturity level of the source of these gases by james method and 3 delineation of major hydrocarbon generation centres for reservoired petroleum the isotopic data reveal a multiplicity of hydrocarbon generation centres in terms of inter basinal and inter structural within a basin variations in maturation and organic facies the study illustrates the use of gas isotopic data for predicting the source of petroleum and for developing a model of source accumulation relationships across the basin in the west godavari basin oil has been generated at a maturity of 1 0 vr o which corresponds to sources in the vicinity of these accumulations in the east godavari basin hydrocarbons have been generated at maturities of 0 55 1 4 vr o which correspond to sources adjacent to reservoirs in the godavari offshore basin oil has been generated at 0 78 vr o which corresponds to a deeper source and medium distance upward migration the validity of the methodology of isotopic gas to gas and gas to source correlation for modelling the origin and migration of petroleum is confirmed by the hydrocarbon occurrence pattern in the krishna godavari basin

isotope techniques for tracing migration of gases in sedimentary basins the isotopic composition of methane is primarily dependent on the stage of maturation of organic matter present in the hydrocarbon source rocks and is not changed during migration the isotopic composition of in situ methane can be estimated from the maturity of the source organic matter migrated methane from deeper more mature sources is recognized by its relative 13 c enrichment compared to indigenous methane examples are presented in this paper to evaluate the migration pattern of gases in sedimentary basins

thermogenic and secondary biogenic gases san juan basin colorado and new mexico implications for coalbed gas producibility the san juan basin is the most prolific coalbed gas basin in the world with 1992 production exceeding 440 gcf footnote 12 4 billion m3 resources of approximately 50 tcf 1 4 trillion m3 and proved reserves of over 6 tcf 170 billion m3 coalbed gas wells with the highest production initial potential greater than 10 mcf day or 0 28 million m3 day occur in the overpressured north central part of the basin hydrologic analysis indicates that overpressure in the fruitland formation is artesian in origin and represents repressuring that developed during the middle pliocene highly permeable laterally continuous coal beds override abandoned shoreline pictured cliffs sandstones and extend to the elevated recharge area in he northern basin to form a dynamic regionally interconnected aquifer system coal rank and basin hydrodynamics control the composition of fruitland coalbed gases which varies significantly across the basin chemically dry gases in the north central part of the basin coincide with meteoric recharge and regional overpressure the consistency of methane dgr13c values across the basin the presence of isotopically heavy carbon dioxide in coalbed gases and bicarbonate in formation waters and biodegraded n alkane distributions of some coal extracts indicate that coalbed gases in the north central basin are a mixture of thermogenic 25 50 secondary biogenic 15 30 and migrated thermogenic 12 60 gases migrated conventionally and hydrodynamically trapped gases in situ generated secondary biogenic gases and solution gases result in gas content that plot on or above the coal sorption isotherm bacteria transported basinward in groundwater flowing from the elevated northern basin margins metabolized wet gas components n alkanes and organic compounds in the coal and generated secondary biogenic methane and carbon dioxide subsequent to coalification uplift erosion and cooling these gases may be limited to basin margins where shallow depths and structural deformation result in higher permeability or may extend more than 35 mi 56 km basinward from the recharge zone the presence of appreciable secondary biogenic gas indicates an active dynamic flow system with overall permeability sufficient for high productivity basin hydrogeology reservoir heterogeneity location of permeability barriers no flow boundaries and the timing of biogenic gas generation and trap devel pment are critical for exploration and development of unconventional gas resources in organic rich rocks

insights into present day crustal motion in the central mediterranean area from gps surveys summary in this paper we present observations of crustal motion related to a large gps network located in the central western mediterranean area velocities are obtained by the analysis of more than 30 observing sites at which at least three different gps campaigns were carried out in the time span 1991 1999 the results are presented both in the itrf96 reference frame and with respect to a eurasian fixed reference frame the sites located along the northern african margin in sicily and southern italy show prevalent northeastward movements with a mean velocity of roughly 0 7 cm yr 1 the relatively dense network available in the southern apennines led us to try a tentative estimate of the average strain rate in this zone resulting in a maximum extension of 0 021 0 006 10 6 yr 1 normal to the chain in ionian greece the two sites located south of the kephallinia discontinuity lefkas and kastro ilias consistently indicate a south to southwestward motion at an average rate of roughly 15 mm yr 1

active stress map of italy we present a new map of the present day stress field in italy obtained from all the available data the map reports 200 horizontal stress directions inferred from 109 borehole breakout data 44 centroid moment tensor solutions 34 other focal mechanisms most of which are from polarity distributions seven stress inversions of microearthquake data two averages of t and p axes of earthquake focal mechanisms in zones of diffuse seismic activity and four fault slip data the integration of breakout data which yield horizontal stress directions with fault plane solutions which reflect the stress regime allows us to obtain an improved map of the present day stress in italy this stress field map can be used for a better comprehension of active tectonic processes for seismic hazard assessment and to foresee the behavior of faults recognized with other methods stress directions obtained from different data although relative to different depth intervals e g 0 7 km for breakouts and 0 20 km for most of the earthquakes and to different tectonic units are consistent since many regions in italy are characterized by an extensional stress regime we report the minimum horizontal stress shmin orientations the map shows that an extensional regime affects most of the apenninic belt conversely a compressional or transpressional regime characterizes the eastern alps the eastern side of the northern apennines and the southern tyrrhenian to northern sicily zone an abrupt change in stress directions marks the transition between northern and southern apennines suggesting that the two arcs are characterized by a different tectonic setting and recent evolution in this paper we report all the data analyzed to date with their geographic coordinates and average stress directions and we describe the main stress provinces in italy in the framework of the tectonic evolution of the region

co seismic displacements associated to the molise southern italy earthquake sequence of october november 2002 inferred from gps measurements abstract the 2002 earthquake sequence of october 31 and november 1 main shocks mw 5 7 struck an area of the molise region in southern italy in this paper we analyzed the co seismic deformation related to the molise seismic sequence inferred from gps data collected before and after the earthquake that ruptured a rather deep portion of crust releasing a moderate amount of seismic energy with no surface rupture the gps data have been reduced using two different processing strategies and softwares bernese and gipsy to have an increased control over the result accuracy since the expected surface displacements induced by the molise earthquake are in the order of the gps reliability the surface deformations obtained from the two approaches are statistically equivalent and show a displacement field consistent with the expected deformation mechanism and with no rupture at the surface in order to relate this observation with the seismic source an elastic modeling of fault dislocation rupture has been performed using seismological parameters as constraints to the model input and comparing calculated surface displacements with the observed ones the sum of the seismic moments 8 9 1017 nm of the two main events have been used as a constraint for the size and amount of slip on the model fault while its geometry has been constrained using the focal mechanisms and aftershocks locations since the two main shocks exhibit the same fault parameters strike of the plane dip and co seismic slip we modelled a single square fault size of 15 km 15 km assumed to accommodate the whole rupture of both events of the seismic sequence a vertical e w trending fault strike 266 has been modeled with a horizontal slip of 120 mm sensitivity tests have been performed to infer the slip distribution at depth the comparison between gps observations and displacement vectors predicted by the dislocation model is consistent with a source fault placed between 5 and 20 km of depth with a constant pure right lateral strike slip in agreement with fault slip distribution analyses using seismological information the gps strain field obtained doesn t require a geodetic moment release larger than the one inferred from the seismological information ruling out significant post seismic deformation or geodetic deformation released at frequencies not detectable by seismic instruments the molise sequence has a critical seismotectonic significance because it occurred in an area where no historical seismicity or seismogenic faults are reported the focal location of the sequence and the strike slip kinematics of main shocks allow to distinguish it from the shallower and extensional seismicity of the southern apennines being more likely related to the decoupling of the southern adriatic block from the northern one

origin and accumulation of co2 and its natural displacement of oils in the continental margin basins northern south china sea many rich up to 97 by volume natural gas pools have been found in the continental margin basins of the northern south china sea by combining the geochemical data from 53 samples with their geologic backgrounds this study investigated the origins and accumulation mechanism of and discussed the role of in driving oil as it charged the reservoirs the results reveal that the gases in the yinggehai basin originate mainly from the thermal decomposition of both miocene calcareous shales and paleozoic carbonates and that from mantle degassing is only a minor contributor the accumulations in the yinggehai basin are mainly controlled by diapiric faults and episodic thermal fluid movements the gases in the eastern qiongdongnan and western pearl river mouth basins are mainly related to magmatic or mantle degassing and the volatiles from magmatic degassing during the igneous intrusion stage are the most likely major source of in these reservoirs with basement faults providing pathways for upward migration of rich mantle fluids natural displacements of oil by appear to be common in the eastern qiongdongnan and western pearl river mouth basins the flooded oil or gas reservoirs have two common features that the present gas pools or oil bearing structures have residual oils representing prior charge and are close to the basement faults that provide pathways along which the mantle derived rich gas was migrated the oils from prior hydrocarbon reservoirs have been naturally driven out by to form secondary oil reservoirs in the eastern qiongdongnan and western pearl river mouth basins therefore a full understanding of the origin and distribution of cannot just be used to trace hydrocarbon migration pathways but also provide useful information for risk assessment prior to drilling

neural network analyses of stress induced overpressures in the pannonian basin summary artificial neural networks can learn relationships between sediment characteristics burial depth composition coordinates and thickness of overlying quaternary deposits and overpressures from well data after which they can interpolate and extrapolate to areas and depths not covered by wells we analyse data from the south eastern part of the pannonian basin we use a neural network for analysing fluid overpressures because of the complex interaction of the key variables making it difficult to derive the functional relationships required for a statistical analysis the optimal topology of the network number of hidden layers and neurons is found by minimizing the network s training and testing errors the optimal design of the network resembles the interactions scheme of the key variables the pannonian basin originally formed in an extensional regime has been in a compressive state of stress since late pliocene causing anomalous subsidence patterns numerical forward modelling of compaction driven fluid overpressures shows that due to an increase in the level of compressive interplate stress the fluid overpressures in the deep subbasins have increased substantially since late pliocene giving rise to a very high overpressure up to 45mpa at present the neural network analyses provide an independent estimate of the current amount of overpressuring in this basin complementing the numerical forward modelling results the overpressure profiles obtained by the two modelling approaches are in excellent agreement showing the same magnitude of overpressures a reversal of the overpressure in the deepest parts of the subbasins and a general decrease of the overpressure from sw to ne

characterization of coal derived hydrocarbons and source rock potential of coal beds san juan basin new mexico and colorado u s a coal beds are considered to be a major source of nonassociated gas in the rocky mountain basins of the united states in the san juan basin of northwestern new mexico and southwestern colorado significant quantities of natural gas are being produced from coal beds of the upper cretaceous fruitland formation and from adjacent sandstone reservoirs analysis of gas samples from the various gas producing intervals provided a means of determining their origin and of evaluating coal beds as source rocks the rank of coal beds in the fruitland formation in the central part of the san juan basin where major gas production occurs increases to the northeast and ranges from high volatile b bituminous coal to medium volatile bituminous coal rm values range from 0 70 to 1 45 on the basis of chemical isotopic and coal rank data the gases are interpreted to be thermogenic gases from the coal beds show little isotopic variation 13c1 values range 43 6 to 40 5 ppt are chemically dry c1 c1 5 values are 0 99 and contain significant amounts of co2 as much as 6 these gases are interpreted to have resulted from devolatilization of the humic type bituminous coal that is composed mainly of vitrinite the primary products of this process are ch4 co2 and h2o the coal generated methane rich gas is usually contained in the coal beds of the fruitland formation and has not been expelled and has not migrated into the adjacent sandstone reservoirs in addition the coal bed reservoirs produce a distinctive bicarbonate type connate water and have higher reservoir pressures than adjacent sandstones the combination of these factors indicates that coal beds are a closed reservoir system created by the gases waters and associated pressures in the micropore coal structure in contrast gases produced from overlying sandstones in the fruitland formation and underlying pictured cliffs sandstone have a wider range of isotopic values 13c1 values range from 43 5 to 38 5 ppt are chemically wetter c1 c1 5 values range from 0 85 to 0 95 and contain less co2 2 these gases are interpreted to have been derived from type iii kerogen dispersed in marine shales of the underlying lewis shale and nonmarine shales of the fruitland formation in the underlying upper cretaceous dakota sandstone and tocito sandstone lentil of the mancos shale another gas type is produced this gas is associated with oil at intermediate stages of thermal maturity and is isotopically lighter and chemically wetter at the intermediate stage of thermal maturity as compared with gases derived from dispersed type iii kerogen and coal this gas type is interpreted to have been generated from type ii kerogen organic matter contained in coal beds and carbonaceous shales of the fruitland formation has hydrogen indexes from rock eval pyrolysis between 100 and 350 and atomic h c ratios between 0 8 and 1 2 oxygen indexes and atomic o c values are less than 24 and 0 3 respectively extractable hydrocarbon yields are as high as 7 000 ppm these values indicate that the coal beds and carbonaceous shales have good potential for the generation of liquid hydrocarbons voids in the coal filled with a fluorescent material that is probably bitumen is evidence that liquid hydrocarbon generation has taken place preliminary oil source rock correlations based on gas chromatography and stable carbon isotope ratios of c15 hydrocarbons indicate that the coals and or carbonaceous shales in the fruitland formation may be the source of minor amounts of condensate produced from the coal beds at relatively low levelsof thermal maturity rm 0 7

occurrence and origin of carbon dioxide in the fushan depression beibuwan basin south china sea abstract natural gases produced from the fushan depression beibuwan basin south china sea are generally rich in carbon dioxide the 13 c values of methane in these gases are within the range of 41 18 to 47 00 this together with the linearity of the 13 c values of methane to butane in the natural gas plots indicates that the hydrocarbon gases are of organic origin the 13 c co 2 values of these gases are in the range of 5 1 to 7 5 suggesting an inorganic origin a dominant mantle source for the co 2 in these gases was determined on the basis of a simple binary mixing model using the 13 c co 2 values and 3 he 4 he ratios of associated helium in these gases the primary geological controls on the occurrence of co 2 rich gas accumulations in the fushan depression are discussed following a comparison with other sedimentary basins in the region

in reservoir mixing of mantle derived co2 and metasedimentary ch4 n2 fluids noble gas and stable isotope study of two multistacked fields pannonian basin system w hungary abstract several multistacked gas fields located in very different parts of hungary display a large variation in their gas composition the shallow position of the mantle beneath the basement of the pbs is responsible for the high heat flux it facilitates that the co 2 intensely released from the ascending upper mantle derived melts could reach the basin system in this work the results of a geochemical study of the main components and noble gases of the multistacked repcelak co 2 hc n 2 and mihalyi co 2 fields are presented and discussed the vertical variations of gas composition in the repcelak and mihalyi fields fit well with in reservoir mixing of two end members a mantle related magmatic co 2 fluid and a n 2 rich hc gas fluid of crustal origin however it is very likely that other processes modified to some extent the gas composition of the two fields carbon isotopic composition of the co 2 of the samples studied agrees with both the carbonate decomposition and mantle degassing origins it is very likely that the marked difference in helium isotopic composition between the neighbouring repcelak and mihalyi fields also reflects this heterogeneity

the fate of mantle derived carbon in a continental sedimentary basin integration of c he relationships and stable isotope signatures abstract the isotopic composition and abundances of the rare gases he ne and ar and active gases co2 ch4 have been determined in a series of commercial gas reservoirs in the pannonian and vienna basins of hungary and austria respectively in these zones of continental extension significant components of mantle derived 4he up to 39 8 and 21ne up to 58 are identified the results of this study indicate a major component of mantle derived carbon in these systems as well ranging in composition from close to 100 co2 to ch4 dominated reservoirs with trace concentrations ppm of co2 these gas reservoirs provide a unique opportunity to examine the relationship of the conservative rare gases to the active gas components and to examine the sources and sinks for mantle and crustal derived carbon phases with the exception of kismarja gas field which shows evidence of addition of 3he depleted crustal co2 all gas fields exhibit a trend whereby the most co2 rich samples approach co 2 3 he mntl values similar to morb 2 109 to 7 109 while co2 depleted samples extend to co 2 3 he mntl values as low as 105 the lack of any correlation of co 2 3 he mntl ratios with r ra values indicates the observed trends are not a function of mixing between crustal and mantle derived endmembers but instead reflect progressive loss of the mantle derived co2 carrier phase during volatile transport and emplacement in the continental crust based on stable isotopic signatures from the kismarja field a crustal co2 endmember with an isotopic composition of 6 8 and a mantle co2 endmember with an isotopic composition no more depleted in 13c than 5 0 can be identified one of the few instances where the isotopic signatures of mantle and crustal derived co2 can be reliably distinguished in a continental setting covariation in 13cco2 and 13cch4 values in the gas fields is used to place constraints on two alternative models whereby the trends in percent co2 and co 2 3 he mntl ratios can be accounted for by 1 loss of the mantle derived co2 carrier phase 2 addition of crustal derived co2 3 addition of crustal derived thermogenic ch4 and potentially 4 conversion of the co2mntl carrier phase to mantle derived ch4 based on an estimated total mantle 4he flux for the pannonian basin of 4 2 108 atoms m 2 s 1 mantle carbon flux estimates for this basin alone range from 3 108 g c yr to 1 109 g c yr which over the lifetime of the basin is only 4 5 orders of magnitude less than flux estimates based on the total area of the spreading ridges clearly the addition of mantle derived carbon to the crust in areas of continental extension is significant and may have been previously underestimated we demonstrate here that integration of 13c data with rare gas isotopic tracers provides an important tool in constraining models of mantle carbon sources and sinks in continental settings

the 2002 molise earthquake sequence what can we learn about the tectonics of southern italy abstract on october 31 2002 a m l 5 4 earthquake occurred in southern italy at the margin between the apenninic thrust belt to the west and the adriatic plate to the east in this area neither historical event nor seismogenic fault is reported in the literature in spite of its moderate magnitude the earthquake caused severe damage in cities close to the epicenter and 27 people out of a total of 29 casualties were killed by the collapse of a primary school in s giuliano di puglia by inverting broadband regional waveforms we computed moment tensor solutions for 15 events as small as m l 3 5 m w 3 7 the obtained focal mechanisms show pure strike slip geometry mainly with focal planes oriented to ns sinistral and ew dextral in several solutions focal planes are rotated counterclockwise in particular for later events occurring west of the mainshock from the relocated aftershock distribution we found that the mainshock ruptured along an ew plane and the fault mechanisms of some aftershocks were not consistent with the mainshock fault plane the observed stress field resulting from the stress tensor inversion shows a maximum principal stress axis with an east west trend n83 w whereas the minimum stress direction is almost n s considering both the aftershock distribution and moment tensor solutions it appears that several pre existing faults were activated rather than a single planar fault associated with the mainshock the finite fault analysis shows a very simple slip distribution with a slow rupture velocity of 1 1 km s that could explain the occurrence of a second mainshock about 30 h after finally we attempt to interpret how the molise sequence is related to the normal faulting system to the west along the apennines and the dextral strike slip mattinata fault to the east

time and temperature in petroleum formation application of lopatin s method to petroleum exploration n v lopatin in the soviet union has developed a method for taking both time and temperature into account as factors in thermal maturation of kerogen lopatin s time temperature index of maturity tti values correlate with the thermal regimes corresponding to generation and preservation of hydrocarbons because such information is potentially of great interest for oil exploration a calibration and evaluation have been made of lopatin s method within the limitations of the data presently available the following statements can be made 1 the rate of the chemical reactions involved in thermal maturation of organic material appears to double with every 10 c 18 f rise in temperature 2 threshold values of lopatin s time temperature index of maturity tti are 15 onset of oil generation 75 peak oil generation 160 end oil generation 500 40 oil preservation deadline 1 000 50 oil preservation deadline 1 500 wet gas preservation deadline 65 000 dry gas preservation deadline 3 tti values calculated from lopatin reconstructions consistently agree with other maturation parameters commonly used by petroleum geochemists potential applications of lopatin s method for oil exploration include timing of oil generation calculation of volume of hydrocarbons generated within a basin and determination of economic deadlines

mixing of thermogenic natural gases in northern appalachian basin stable isotopic studies were undertaken to investigate the origin of 20 oil associated and non associated gases from western and central new york state in the northern appalachian basin gas wetness c2 c5 c1 c5 methane dgr13c and methane dgrd values range from 0 8 to 26 9 47 9 to 30 7 pmil and 305 to 143 pmil respectively corresponding ethane and propane dgr13c values range from 40 9 to 32 0 pmil and 34 9 to 27 9 pmil these data are interpreted to indicate a thermogenic origin with source rock maturities ranging from early mature equivalent vitrinite reflectance ro approximately 0 5 to post mature equivalent ro 2 0 inferred gas maturities generally in rease with increasing reservoir age from late to middle devonian marcellus and overlying rocks middle devonian to latest silurian oriskany onondaga akron silurian lockport herkimer medina to ordovician queenston and black river oil and gas in many late to middle devonian reservoirs may have migrated from interbedded organic rich shales in other reservoirs particularly those of ordovician and silurian age unusual isotopic reversals methane dgr13c ethane dgr13c suggest that gas generated locally from equivalent age rocks within the oil window mixed with post mature gas migrated from deeply buried sources to the south and southeast the post mature gas was probably sourced from middle to late ordovician shales regional migration of middle ordovician gas may have occurred along the middle ordovician knox unconformity gas was presumably channeled into overlying silurian and devonian reservoirs along faults and fractures

the october november 2002 molise seismic sequence southern italy an expression of adria intraplate deformation a new seismotectonic model for the outer central southern apennines including the epicentral area of the 2002 molise seismic sequence and adjacent foreland is proposed the seismic sequence is related to foreland deformation affecting the adriatic lithosphere such deformation is characterized by active nw se compression resulting in the reactivation mainly as dextral strike slip faults of pre existing east west oriented structures both offshore and onshore one of these structures is interpreted to extend westward and to reach the epicentral area of the recent earthquakes nw se compression ultimately related with africa europe plate convergence and uplift would essentially control the active tectonics of the analysed region

composition and origin of coalbed gases in the lower silesian basin southwest poland abstract coalbed gases in the lower silesian coal basin lscb of poland are highly variable in both their molecular and stable isotope compositions geochemical indices and stable isotope ratios vary within the following ranges hydrocarbon chc index chc ch4 c2h6 c3h8 from 1 1 to 5825 wet gas c2 index c2 c2h6 c3h8 c4h10 c5h12 ch4 c2h6 c3h8 c4h10 c5h12 100 from 0 0 to 48 3 co2 ch4 cdmi index cdmi co2 co2 ch4 100 from 0 1 to 99 9 13c ch4 from 66 1 to 24 6 d ch4 from 266 to 117 13c c2h6 from 27 8 to 22 8 and 13c co2 from 26 6 to 16 8 isotopic studies reveal the presence of 3 genetic types of natural gases thermogenic ch4 higher gaseous hydrocarbons and co2 endogenic co2 and microbial ch4 and co2 thermogenic gases resulted from coalification processes which were probably completed by late carboniferous and early permian time endogenic co2 migrated along the deep seated faults from upper mantle and or magma chambers minor volumes of microbial ch4 and co2 occur at shallow depths close to the abandoned mine workings late stage microbial processes have commenced in the upper cretaceous and are probably active at present however depth related isotopic fractionation which has resulted from physical and physicochemical e g diffusion and adsorption desorption processes during gas migration cannot be neglected the strongest rock and gas outbursts occur only in those parts of coal deposits of the lscb which are dominated by large amounts of endogenic co2

the telluric field in northern germany induced by tidal motion in the north sea summary by faraday s law of induction tidal currents of the north sea induce electric currents which to a certain extent spread out far inland their influence on the telluric field in northern germany was investigated time variations of the telluric field at six field sites in northern germany were recorded continuously for at least 2 months during 1984 together with variations of the magnetic field at gottingen transfer functions between the telluric and magnetic fields were calculated from the dst and d continuum from 0 5 to 8cpd cycles per day they are presented as continuous functions of frequency by orthogonal polynomials this serves a to estimate the local telluric dc distortion matrix by comparing the transfer function values of the sq harmonics at 1 2 3 4cpd with undistorted impedances obtained by schmucker s sq analysis b to eliminate that part of the induced telluric field which is correlated with magnetic field variations in the uncorrelated part of the spectra a significant peak appears at the lunar frequency m2 24 12 4206 cpd the chapman miller method yields amplitude and phase of the mzvariation in the uncorrelated telluric fields local influences are eliminated using the inverse of the distortion matrices mentioned above the amplitudes then vary between 0 3 and 0 6 mv km the direction and phase of the uncorrelated telluric field at five field sites reflect well the pattern of the tidal current in the north sea along the coast and coincide with the assumed motion induced electric currents

accuracy of modern global earthquake catalogs we compare several modem 1977 present worldwide earthquake catalogs to infer their completeness earthquake origin time and hypocenter location accuracy magnitude scalar seismic moment errors and difference between individual focal mechanism moment tensor solutions the harvard centroid moment tensor cmt us geological survey usgs mt usgs first motion fm focal mechanism pde and isc catalogs have been analyzed and compared the catalogs completeness and accuracy vary in time and depend on earthquake depth and tectonic environment we propose a new statistical method for evaluating catalog completeness and show the results for the cmt dataset a difference in frequency range of seismic waves used in earthquake processing leads to varying degrees of catalog completeness for foreshocks and aftershocks close in time earthquake origin time versus centroid time as well as hypocenter location versus centroid location can be explained well by earthquake scaling relations comparing moment magnitudes and regular earthquake magnitudes yields estimated magnitude uncertainties and shows that latter magnitudes poorly estimate earthquake size for large events moment errors reported in the cmt solutions are well correlated with the cmt gs mt magnitude difference and hence indicate magnitude uncertainty well a normalized seismic moment tensor has 4 d f and its accuracy can be represented as the non double couple non dc component value the 3 d angle phi of dc source rotation and a position of the rotation pole our results suggest that a routinely determined non dc component is in most cases only an artifact the distribution of the phi value varies over catalog time earthquake depth focal mechanism and magnitude the seismic moment errors and the value of the non dc component are indicative of the phi value for the best solutions the 3 d angle in the cmt catalog is on the order of 5 7degrees the cmt catalog is obviously the best dataset in completeness and accuracy of its detailed solutions our results specifying uncertainties and completeness of global earthquake catalogs can be used in studies of geodynamic processes tectonic deformation associated with earthquakes earthquake stress analysis and in many other applications of earthquake catalog data seismogram interpretation techniques can be reviewed and possibly revised in light of these results c 2002 elsevier science b v all rights reserved

identifying and quantifying natural co2 sequestration processes over geological timescales the jackson dome co2 deposit usa co2 sources sinks and migration mechanisms in natural co2 gas fields provide critical analogues for developing the safe application of anthropogenic co2 sequestration technologies here we use noble gas and carbon isotopes together with other gases to identify and quantify the origin transport and trapping mechanisms of co2 in the late cretaceous jackson dome co2 gas deposit 98 75 to 99 38 co2 located in central mississippi usa and producing from 5000 m it is one of the deepest commercial co2 gas fields in the world 10 gas samples from producing wells were determined for their noble gas chemical and stable carbon isotope composition he 3 he 4 ratios range between 4 27r a and 5 01r a where r a is the atmospheric value of 1 4 x 10 6 indicating a strong mantle signature similar to co2 deposits worldwide co2 he 3 decreases with increasing groundwater derived ne 20 and he 4 we model several different processes that could account for the jackson dome data and conclude that similar to other co2 dominated deposits a groundwater gas stripping and re dissolution ggs r process best accounts for observed ne 20 ar 36 kr 84 ar 36 co2 he 3 delta c 13 co2 he 4 ne 20 and ar 36 in this context crustal and magmatic co2 components contribute 57 and 43 respectively changes in co2 he 3 across the field show that groundwater contact is responsible for up to 75 loss of original emplaced co2 delta c 13 co2 variance limits the degree of precipitation to be less than 27 with the remaining co2 loss being accounted for by dissolution only a higher degree of dissolution gas loss and evidence for water contact at the reservoir crest compared to the reservoir flanks is used to argue that co2 in this system has not undergone subsequent loss to either dissolution or precipitation since shortly after reservoir filling at over 60 ma c 2012 elsevier ltd all rights reserved

recent advances in petroleum isotope geochemistry abstract organic matter is isotopically heterogeneous lipids tend to be depleted in the heavy carbon and hydrogen isotopes as compared to carbohydrates and lignite the c and h isotopic composition of kerogens is determined by many factors such as environmental conditions during formation and deposition and variability of sources of organic matter stable isotope concentrations in mature kerogens are not significantly altered during maturation and hence reflect the variability of the organic matter during deposition isotope variations in kerogens therefore reflect to some extent the paleogeographic situation and can be used for paleoreconstruction a basin facies with anoxia and a marginal facies with detrital input can be differentiated isotopically in the toarcian of central europe coals are isotopically heterogeneous due to different isotopic composition of macerals inertinite and vitrinite tends to be enriched in deuterium as compared to exinite also boghead coals tend to be depleted in dueterium which possibly reflects various lipid contents of respective precursor materials petroleums can be genetically classified through the patterns of covariance of their compound classes carbonate and shale sourced petroleums may be additionally differentiated through their deuterium content the general world wide applicability of such genetic differentiations needs still to be proved carbon and hydrogen isotope variations in methane are genetically controlled bacterial methane in freshwater environments is characteristically depleted in deuterium even complex origins of natural gases can be unraveled using compositional and isotopic variations new analytical developments led to the application of carbon isotope analyses of gaseous hydrocarbons desorbed from sediments for geochemical surface exploration a discussion reveals that processes such as isotope effects during degassing and bacterial oxidation as well as indigenous formation of hydrocarbons may completely obscure the results

quantification of co2 generation in sedimentary basins through carbonate clays reactions with uncertain thermodynamic parameters abstract we develop a methodological framework and mathematical formulation which yields estimates of the uncertainty associated with the amounts of co 2 generated by carbonate clays reactions ccr in large scale subsurface systems to assist characterization of the main features of this geochemical process our approach couples a one dimensional compaction model providing the dynamics of the evolution of porosity temperature and pressure along the vertical direction with a chemical model able to quantify the partial pressure of co 2 resulting from minerals and pore water interaction the modeling framework we propose allows i estimating the depth at which the source of gases is located and ii quantifying the amount of co 2 generated based on the mineralogy of the sediments involved in the basin formation process a distinctive objective of the study is the quantification of the way the uncertainty affecting chemical equilibrium constants propagates to model outputs i e the flux of co 2 these parameters are considered as key sources of uncertainty in our modeling approach because temperature and pressure distributions associated with deep burial depths typically fall outside the range of validity of commonly employed geochemical databases and typically used geochemical software we also analyze the impact of the relative abundancy of primary phases in the sediments on the activation of ccr processes as a test bed we consider a computational study where pressure and temperature conditions are representative of those observed in real sedimentary formation our results are conducive to the probabilistic assessment of i the characteristic pressure and temperature at which ccr leads to generation of co 2 in sedimentary systems ii the order of magnitude of the co 2 generation rate that can be associated with ccr processes

the origin and formation of co2 gas pools in the coal seam of the yaojie coalfield in china abstract high concentrations of co 2 have been observed in the no 2 coal seam in the yaojie coalfield a number of instantaneous co 2 outbursts occurred during coal mining the co 2 concentration range in the eastern coalfield is 18 79 to 96 6 the 13 c co 2 values are mainly in the range of 5 0 to 1 0 pdb suggesting an inorganic origin of co 2 the 3 he 4 he ratios are 0 6 25 9 10 8 and the r ra is 0 0042 0 185 which is a characteristic of crust derived co 2 gas the dynamic thermal metamorphism of the f19 ductile brittle shear zone is believed to result in the release of co 2 from basement marble formations which show an inorganic source of co 2 in the yaojie coalfield the regional geological evolution and multi periodical f19 fault movement control the formation migration and accumulation of the co 2 in addition to the development of co 2 gas pools in the yaojie coalfield the f19 fault played multiple roles in the generation transport and sequestration of gas during the co 2 formation the displacement of ch 4 carbonate generation and pore structure transformation of coal due to a series of physical and chemical effects occurred after co 2 flux into the coal seams

geochemical characteristics and origins of natural gas in the zhu iii sub basin pearl river mouth basin china abstract the zhu iii sub basin is an important petroliferous region in the south china sea where hydrocarbon distribution shows strong heterogeneity with oil primary produced from the wenchang b depression and gases from the wenchang a depression however a mixture of oil and gases are produced from the surrounding qionghai and shenhu uplifts the origin generation history and migration pathway of oil have been intensively studied but no study have been done directly on the gas which restricts future petroleum exploration in this study natural gas molecular compositions were measured on 46 samples stable carbon isotopic composition were measured on 39 samples and light hydrocarbon composition were measured on 30 samples results indicate that natural gases in the zhu iii sub basin are mainly composed of hydrocarbon gases with abundant co2 and n2 the hydrocarbon gases are all thermogenic gases which are mainly derived from the oligocene enping formation e3e 35 30 ma the contribution of the eocene wenchang formation e2w 56 35 ma to natural gases increases from the wenchang a depression to the south boundary fault sbf and surrounding uplifts this is caused by the early generated natural gases with more contribution from the e2w and dissolved in oils that migrated to the surrounding qionghai and shenhu uplifts natural gases and oil in the surrounding uplifts and near the sbf therefore avoided secondary cracking due to the high gas migration rate through the sbf and lateral sandstone carrier beds whereas natural gases in the wenchang a depression mainly originated from the secondary cracking of oil the equivalent vitrinite reflectance values of source rocks when the natural gases were generated varied from 0 6 to 1 5 based on carbon isotope differences between hydrocarbons indicating mature to high mature stage co2 with abundance less than 10 mainly originated from organic matter decomposition co2 with abundance more than 15 was sourced from the deep mantle and crust and mainly concentrated in the deep layers near the sbf which cuts into the basement n2 is probably the product of in situ reservoir alteration such as biodegradation in shallower layers our study on the geochemical characteristics and origins of the natural gas will enable a better understanding of petroleum system in the zhu iii sub basin and provide theoretical basis for optimizing future petroleum exploration strategy detailed study on shallow layers in the qionghai and shenhu uplifts and deep layers near the sbf are needed because exploration risks are relatively high in these plays

origin and migration of hydrocarbon gases and carbon dioxide bekes basin southeastern hungary the bekes basin is a sub basin within the pannonian basin containing about 7000 m of post cretaceous sedimentary rocks natural gases are produced from reservoirs precambrian to tertiary in age located on structural highs around the margins of the basin gas composition and stable carbon isotopic data indicate that most of the flammable gases were derived from humic kerogen contained in source rocks located in the deep basin the depth of gas generation and vertical migration distances were estimated using quantitative source rock maturity carbon isotope relationships for methane compared to known neogene source rock maturity depth relationships in the basin these calculations indicate that as much as 3500 m of vertical migration has occured in some cases isotopically heavy 7 0 co2 is the predominant species present in some shallow reservoirs located on basin margin structural highs and has probably been derived via long distance vertical and lateral migration from thermal decompositon of carbonate minerals in mesozoic and older rocks in the deepest parts of the basin a few shallow reservoirs 2000m contain isotopically light 50 to 60 0 methane with only minor amounts of c2 homologs 3 v v this methane is probably mostly microbial in origin above normal pressures occuring at depths greater than 1800 m are believed to be the principal driving force for lateral and vertical gas migration these pressures are caused in part by active hydrocarbon generation undercompaction and thermal decomposition of carbonates

deep burial dissolution in an oligocene miocene giant carbonate reservoir perla limestone gulf of venezuela basin implications on microporosity development abstract sedimentary rocks tend to progressively lose porosity with depth due to mechanical and chemical compaction in carbonates this trend is hard to predict since many factors can create porosity in the burial setting the oligocene miocene perla limestone a giant gas reservoir located in the gulf of venezuela basin shows a complex porosity system marked by a strong diagenetic control despite exhaustive depositional facies modelling carried out in the carbonate reservoir inconsistencies remained when distributing petrophysical properties with depositional facies these inconsistencies become more important in areas strongly affected by intense diagenetic processes after the initial investigation burial dissolution was identified as the main diagenetic process affecting porosity in this succession to understand the origin of the burial dissolution process and its distribution along the reservoir detailed petrographic mineralogical and isotopic studies were carried out on recovered cores from different exploration wells results show a series of diagenetic features which were associated with the evolution of the strata including burial dissolution dolomitization and compaction as the main processes after testing several hypotheses the results support an inorganic co2 model as responsible for the burial dissolution process in the perla limestone according to this model deep burial dissolution created pervasive microporosity with subordinated moldic and vuggy pores that enhanced the reservoir quality in localized areas of the carbonate succession these features are located where the ascent of hydrothermal co2 rich fluids funneled by discontinuity surfaces faults fractures stylolites etc reached the perla limestone

relation of natural gas composition to thermal maturity and source rock type in san juan basin northwestern new mexico and southwestern colorado san juan basin is a roughly circular asymmetric structural depression located in northwestern new mexico and southwestern colorado ultimate recoverable reserves of predominantly nonassociated gas 23 tcf 0 65 1012 m3 are present in the structurally low part of the central basin the major producing intervals are low permeability sandstone reservoirs in the upper cretaceous dakota sandstone mesaverde group and pictured cliffs sandstone lesser amounts of oil and or gas are produced from pennsylvanian jurassic and cretaceous rocks along the southern and western flanks of the basin the gases display a trend of becoming isotopically heavier dgr13c1 values range from 48 7 to 31 4 pmil and chemically drier c1 c1 5 values range from 0 75 to 0 99 with increasing depth these changes are assumed to be the result of thermal cracking processes and the gases are interpreted to have been generated during the mature and post mature stages of hydrocarbon generation however there is considerable scatter in the data which is interpreted to result from a difference in source rock type gases generated from nonmarine humic source rocks are isotopically heavier and chemically drier than those generated from marine sapropelic source rocks at equivalent levels of maturity the gases also become isotopically heavier and chemically drier to the northeast following the trend of increasing maturity of all units in that direction the increase in maturity is attributed to a combination of greater burial depth and a higher geothermal gradient resulting from batholiths to the north in the san juan mountains area maximum burial and heat flow occurred during the oligocene which probably coincided with peak hydrocarbon generation lack of oil in the central basin is believed to be the result of two factors first gas in reservoirs such as the dakota sandstone may have resulted from thermal cracking of oil generated from marine source rocks during late mature wet gas condensate and post mature dry gas stages of hydrocarbon generation second gas in reservoirs such as mesaverde group and pictured cliffs sandstone is nonassociated and probably was generated from nonmarine coaly organic matter during the mature and post mature stages minor amounts of condensate instead of oil may have been generated from nonmarine source rocks during the mature stage

active crustal extension in the central apennines italy inferred from gps measurements in the interval 1994 1999 we present the first gps estimate of crustal extension in the central apennines italy through the analysis of the deformation of a sub network of the national gps geodetic network igm95 in the interval 1994 1999 the selected sub network spans the entire active deformation belt perpendicularly to its axis and allows the evaluation of 1 the total extension rate absorbed in this sector of the apennines and 2 the seismogenic potential of the normal faults active in the late pleistocene holocene interval within the network results of this reoccupation are consistent with an extensional strain rate of 0 18 10 6 yr 1 concentrated in an area of about 35 km width giving an average extension rate of 6 2 mm yr across the central apennines the pattern of active deformation suggests active elastic strain accumulation on the westernmost of the two fault systems active in the late pleistocene holocene interval and may also suggest the presence of another active fault system not recognized so far

source analysis of the 2002 molise southern italy twin earthquakes 10 31 and 11 01 1 on october 31 2002 a moderate size earthquake mw 5 8 occurred in molise region southern italy causing loss of young human lives in a school collapse and destructions in several villages the day after a slightly smaller earthquake happened a few kilometers westward from the first one without making strong damage we use a complete set of seismological data global regional and local including both body and surface waves to better understand the source process of these two events we show that the two earthquakes are similar in terms of hypocentral depth focal mechanism and source kinematics moreover the imaged slip zones are almost contiguous which makes the time delay between the two shocks 29 hours an open question the identified updip rupture propagation has amplified the radiation usually created by such mw 5 8 earthquakes at 15 20 km depth we model a maximum acceleration zone in agreement with location of damaged villages

3 d modelling the electric field due to ocean tidal flow and comparison with observations 1 the tidal motion of the ocean water through the ambient magnetic field generates secondary electric field this motionally induced electric field can be detected in the sea or inland and has a potential for electrical soundings of the earth a first goal of the paper is to gain an understanding of the global distribution of the electric signal due to tidal ocean flow we simulate the electric signals for two tidal constituents lunar semidiurnal m2 and diurnal o1 tides we assume a realistic earth s conductivity model with a surface thin shell and 1 d mantle underneath simulations demonstrate that in some coastal regions the amplitudes of the electric field can reach 100 mv km and 10 mv km for m2 and o1 tides respectively the changes of lithosphere resistance produce detectable changes in the tidal electric signals we show that our predictions are in a good agreement with observations

dongfang 1 1 gas field in the mud diapir belt of the yinggehai basin south china sea abstract the dongfang 1 1 df1 1 mud diapir field is the largest gas field discovered in the yinggehai basin up to now with a proven gas reserve of 99 68 10 9 m 3 the gas pay zones are within the pliocene fine sandstones and siltstones of the littoral and sand bar facies with normal pressure regimes the gases include variable amounts of co 2 and n 2 in addition to hydrocarbon gases the hydrocarbon gases with the exception of biogenic methane and nitrogen originated from the marine source rocks within the overpressured lower to middle miocene strata while co 2 is most likely the product of thermal decomposition of the tertiary calcareous mudstones and pre tertiary carbonates through relatively long distance vertical migration the field has received at least four phases of natural gas charging occurring relatively late most likely during the post pliocene himalayan orogeny diapiric faults act as the main conduit for upward movement of fluids released from the deep high pressure system with abnormally high pressures providing the significant driving force for gas migration because of the episodic nature of the deep high pressured fluid release and the diapir fault activity this shallow diapir gas field is characterized by multiple gas sources and episodic fluid accumulation

occurrence and geochemistry of natural gases piceance basin northwest colorado the piceance basin is a hydrocarbon rich province that has natural gas production from reservoirs ranging in age from late jurassic to eocene and large undeveloped resources of natural gas in coal beds and tight sandstone reservoirs of cretaceous age gases from all producing intervals are of predominantly thermal origin and become isotopically heavier delta isotope 13 c 1 51 3 to 29 1 o oo and chemically drier c 1 c 1 5 0 26 to 1 00 with increasing thermal maturity of reservoirs r o 0 45 to 2 40 over a depth range of 1100 to 11 702 ft 335 3567 m scatter in trend is attributed to source rock differences and considerable vertical and lateral migration based on chemical and isotopic composition three major types of gases can be distinguished those generated from mixed type ii and iii kerogens those from dispersed type iii kerogen and those from coal gases generated from mixed type ii and iii kerogens are produced from the upper jurassic morrison formation the lower cretaceous cedar mountain formation the upper cretaceous dakota sandstone the upper cretaceous mancos b producing interval and marginal marine sandstones of the upper cretaceous iles producing interval these gases are associated with minor amounts of oil and probably were generated from kerogen in the marine mancos shale gases generated from dispersed type iii kerogen are produced from nonmarine sandstones of the upper cretaceous williams fork producing inter al and from thermally immature reservoirs in the overlying paleocene and eocene fort union and wasatch formations these nonassociated gases contain large amounts of co 2 and probably were generated from carbonaceous shales in the williams fork producing interval their presence in immature fort union and wasatch reservoirs implies considerable vertical migration the third type of gas is methane rich is produced by devolatilization of humic coal and is generally in coal beds of the cameo fairfield zone of the williams fork producing interval these gases are not the major source for adjacent sandstone reservoirs a fourth distinct type of isotopically light thermogenic gas occurs in immature reservoirs of the eocene green river formation this gas is inferred to have migrated from u identified deeper more mature source rocks

tectonic evidence for the ongoing africa eurasia convergence in central mediterranean foreland areas a journey among long lived shear zones large earthquakes and elusive fault motions an edited version of this paper was published by agu copyright 2010 american geophysical union

helium and neon isotope systematics in carbon dioxide rich and hydrocarbon rich gas reservoirs the isotopic compositions and elemental abundances of helium and neon were measured in three natural gas reservoirs in the pannonian sedimentary basin of hungary kismarja a co2 rich reservoir and szeghalom south and szeghalom north both ch4 dominated reservoirs are located on topographic basement highs close to the derecske sub basin in eastern hungary mantle derived neon has been identified in mixed ch4 co2 reservoirs in the vienna basin austria this study establishes that mantle derived neon and helium are a characteristic feature of gas reservoirs throughout the neogene extensional basins of hungary and austria regardless of the dominant active gas composition 3he4he ratios within these samples are attributable to a two component mixing between mantlederived and crustal radiogenic helium the percent contribution of mantle derived 4he varies from 2 3 to 17 in contrast neon isotopic ratios indicate that the gases contain a significant component of atmosphere derived neon in addition to the mantle and crustal derived components 20ne 21ne and 22ne abundances can be corrected for this atmospheric contribution calculated contributions of mantle and crustal derived 21ne are between 3 6 21 and 1 37 respectively 20ne22nec and 21ne22nec ratios derived for these atmosphere corrected components correlate with measured r ra values and plot along a single two component mixing line between crustal and mantle isotopic endmembers this is consistent with a model in which simple mixing occurs between crustal and mantle endmembers with fixed he ne ratios the mixing line is defined by a hyperbolic constant k where k 4he22ne rad 4 he22ne mntl with a mean value of 67 3 11 8 based on estimated values of 0 47 for 21ne22nerad and 1 62 0 03 107 for 4he21ne rad kennedy et al 1990 values of 7 61 106 for he22ne rad and 11 3 104 for 4he22ne mntl can be calculated for the pannonian basin gases this 4he22ne mntl value is indistinguishable within error from the value of 8 04 104 calculated for rare gases in natural gases from the vienna basin these results clearly establish that the continental expression of mantle derived rare gases in continental extensional systems in austria and hungary is distinct and consistently different from that of gases discharging at the spreading ridges where best estimates of 4he22ne mntl are 8 1 11 3 times higher 9 10 105 staudacher et al 1989 given the remarkable agreement in the continental expression of mantle derived gases throughout the pannonian and vienna basins it is difficult to attribute the observed neon enrichment helium depletion with respect to morb gases to fractionation related to lithospheric transport processes kinetic fraction ation processes involved in transport through the crust might be expected to produce a much wider variation in the observed he ne elemental ratios the consistent order of magnitude neon enrichment observed throughout these gas fields instead implies that mantle derived fluids in these continental extensional systems may be sourced in a region of the mantle distinct from that supplying the mid ocean spreading ridges

origins of co2 in permian carbonate reservoir rocks zechstein ca2 of the nw german basin lower saxony permian carbonate reservoir rocks stassfurt carbonate of the co2 province lower saxony basin nw germany are locally characterised by high amounts of co2 leading to serious problems on exploration in order to receive information on the major co2 sources and co2 migration and accumulation processes mineralogical geochemical and stable isotope analyses c 13 o 18 were carried out on authigenic precipitations within the stassfurt carbonate rocks ca2 these rocks contain early diagenetic e g formed in soft sediment carbonate minerals calcite dolomite and anhydrite in concretions and small cracks in addition large up to 2 cm wide carbonate cemented fractures formed in solid ca2 rocks semi quantitative estimates of the diagenetic mineral content showed variations between the investigated rock cores nine out of 12 ca2 rock cores are derived from wells situated in the area of modem ch4 rich reservoirs and have distinct fracture systems developed in contrast the other three rock cores are from wells characterised by co4 rich reservoirs and lack fractures of similar thickness the assumed relationship between tectonically induced fractures and the gas content of the ca2 reservoir rocks implies co2 degassing of the ca2 rocks at approximately 102 degrees c to similar to 150 degrees c assumed delta 18o pore water variation from 0 parts per thousand to 4 parts per thousand smow ree distribution indicates at least three types of fracture and crack filling carbonates two carbonate generations formed from evolving diagenetic pore waters whereas one type reflects carbonate formation under hydrothermal influence the ages of these cementations derived from rb sr and u pb isotope analyses indicate their fort nation during late stage of or after the inversion of the lower saxony basin in late cretaceous times the stable carbon isotope composition of the authigenic carbonate minerals reflects at least two carbon source endmembers available during diagenesis whereas many early formed carbonates are related to the permian c 13 rich carbon source those carbonates which precipitated or recrystallised during early to late stage diagenesis and or were induced by local tectonic events incorporated c 12 enriched co from organic degradation processes the stable oxygen isotope values of authigenic carbonates probably still reflect low temperatures of mineral formation from permian sea water as it is assumed for non recrystallised carbonates or late stage high temperature up to similar to 150 degrees c precipitation ftoin sea water derived pore waters which may have been locally influenced by o 18 enriched fluids however most of the carbonate samples investigated are recrystallised crystal enlargement of concretionary and fracture carbonate is observed and hence these carbonates are at least partly re equilibrated original o 18 content reduced with surrounding pore waters at elevated temperature similar to the authigenic carbonate at least two sources may explain the concentration carbon isotope relationship of modem co present in the ca 2 reservoir rocks an organic derived co2 endmember source delta c 13 near 20 parts per thousand is present in relatively low concentrations whereas large co concentrations derived from an endmember source with all isotope value near 0 parts per thousand although the latter source is unknown such heavy co sources are most likely attributed to carbonate decomposition processes c 2005 elsevier b v all rights reserved

crustal velocity and strain rate fields in italy and surrounding regions new results from the analysis of permanent and non permanent gps networks summary we present a new geodetic velocity solution for italy and the surrounding areas obtained from an analysis of continuous and survey mode global positioning system observations collected between 1991 and 2002 we have combined local regional and global networks into a common reference frame velocity solution providing a new detailed picture of the regional scale deformation field in the central mediterranean our velocity estimates are computed with respect to a new stable eurasian reference frame constraining the kinematics of the greater african eurasian plate boundary system in the study area we provide strain rate values for the main seismotectonic districts which are in good agreement with the seismic deformation inferred from earthquake focal mechanisms the southern tyrrhenian area calabria the apennines the southeastern alps the southern dinarides and the albanides display deformation rates at the order of 20 30 nanostrain yr 1 the corsica sardinia block moves according to eurasian plate motions and there is no indication that the opening of the tyrrhenian is still active the pelagian and sicilian domains are separated by a northwest southeast discontinuity the sicily channel rifted area and marginally significant relative motion between the pelagian plateau and the african plate is also observed the southern tyrrhenian is affected by north south compression and accommodates up to 50 per cent of the africa eurasia relative plate motion whereas the calabrian arc exhibits 2 mm yr 1 northwest southeast extension the observed deformation pattern suggests the presence of a major approximately north south tectonic discontinuity separating the sicilian and calabrian domains an extensional boundary observed along peninsular italy coincides with the distribution of seismogenic faults along the axis of the apennines this boundary separates a tyrrhenian and an adriatic domain with diverging velocities orientated north nnw ward and northeastward respectively the apennines are extending perpendicularly to the chain axis at rates of less than 3 mm yr 1 and only in the outer northern apennines indications of active shortening are observed insignificant deformation is observed in the western po plain and the western alps while the central and eastern alps display north south shortening the eastern adriatic domain is shortening perpendicular to the dinaric front with strain rates increasing from north to south the locus of collision between the aegean balkan system and the adriatic and ionian domains is marked by the kephalonia fault system which accommodates up to 20 1 mm yr 1 of right lateral motion the deformation pattern observed in the peri adriatic domain is well described by a counter clockwise rotation of the adriatic microplate around a pole located in the western alps

fluorescent spectral types of selected colorado bituminous coals abstract fluorescent spectral types determined from quantitative spectral analysis provided detailed characterization of the liptinite macerals in selected upper cretaceous lower tertiary coals from colorado the spectral type concept identifies submacerals of each individual liptinite maceral without significantly increasing existing maceral nomenclature upon comparison of rank sensitive fluorescent properties the colorado coals display the same changes with increasing rank as in older carboniferous coals but at lower vitrinite reflectances spectral analysis failed to reveal significant differences in the peak wavelengths of liptinite fluorescence between these two groups of coals this comparison suggests that the colorado and carboniferous coals have responded differently to coalification

geochemistry and episodic accumulation of natural gases from the ledong gas field in the yinggehai basin offshore south china sea abstract the ledong gas field consisting of three gas pools in a shale diapir structure zone is the largest gas discovery in the yinggehai basin the gases produced from the pliocene and quaternary marine sandstone reservoirs show a considerable variation in chemical composition with 5 4 88 ch 4 0 93 co 2 and 1 23 7 n 2 the co 2 enriched gases often display heavier methane 13 c values than those with low co 2 contents the 15 n values of the gases range from 8 to 2 and the n 2 content correlates negatively with the co 2 content the high geothermal gradient associated with a relatively great burial depth in this area has led to the generation of hydrocarbon and nitrogen gases from the lower middle miocene source rocks and the formation of abundant co 2 from the tertiary calcareous shales and pre tertiary carbonates the compositional heterogeneities and stable carbon isotope data of the produced gases indicate that the formation of the ld221 gas field is attributed to three phases of gas migration initially biogenic gas followed by thermogenic hydrocarbon gas and then co 2 rich gas the filling processes occurred within a short period approximately from 1 2 to 0 1 ma based on the results of the kinetics modeling geophysical and geochemical data show that the diapiric faults that cut through miocene sediments act as the main pathways for upward gas migration from the deep overpressured system into the shallow normal pressure reservoirs and that the deep overpressure is the main driving force for vertical and lateral migration of the gases this gas migration pattern implies that the transitional pressure zone around the shale diapir structures was on the pathway of upward migrating gases and is also a favorable place for gas accumulation the proposed multiple sources and multiple phases of gas migration and accumulation model for the ledong gas field potentially provide useful information for the future exploration efforts in this area

organic matter variations in transgressive and regressive shales abstract organic matter in the upper cretaceous mancos shale adjacent to the tocito sandstone in the san juan basin of new mexico was characterized using organic petrology and organic geochemistry differences in the organic matter found in these regressive and transgressive offshore marine sediments have been documented and assessed within a sequence stratigraphic framework the regressive lower mancos shale below the tocito sandstone contains abundant well preserved phytoclasts and correspondingly low hydrogen indices total organic carbon values for the regressive shale are low sediments from the transgressive systems tract tocito sandstone and overlying upper mancos shale contain less terrestrially derived organic matter more amorphous non structured protistoclasts higher hydrogen indices and more total organic carbon advanced stages of degradation are characteristic of the phytoclasts found in the transgressive shale amorphous material in the transgressive shale fluoresces strongly while that found in the regressive shale is typically non fluorescent data from pyrolysis gas chromatography confirm these observations these differences are apparently related to the contrasting depositional styles that were active on the shelf during regression and subsequent transgression it is suggested that data from organic petrology and organic geochemistry provide greater resolution in sedimentologic and stratigraphic interpretations particularly when working with basinward fine grained sediments petroleum source potential for the regressive lower mancos shale below the tocito sandstone is poor based on abundant fluorescent amorphous material high hydrogen indices and high total organic carbon the transgressive upper mancos shale above the tocito sandstone possesses excellent source potential this suggests that appreciable source potential can be found in offshore fine grained sediments of the transgressive systems tract below the condensed section and associated downlap surface organic petrology can be used to accurately predict petroleum source potential the addition of simple fluorescence microscopy greatly enhances this predictive ability because non generative amorphous material is generally non fluorescent organic petrology must also be used to properly evaluate the utility of t max from programmed pyrolysis as a thermal maturity indicator organic matter dominated by autochthonous amorphous protistoclasts exhibits lower t max values than that which is composed of mostly phytoclasts

hydrocarbon generation as a mechanism for overpressuring in rocky mountain region overpressured reservoirs are present in the deeper parts of most basins in the rocky mountain region a variety of conditions can cause overpressuring however most high pressures in the region are caused by present day or recently active oil and gas generation or generation in the last few million years in low permeability rock successions that still contain organic matter capable of yielding thermally generated hydrocarbons rocks with above normal pressure range from devonian to tertiary and commonly are associated with low permeability tight reservoirs most of the overpressuring occurs in cretaceous and tertiary rocks overpressuring in rocks older than cretaceous is rare and where present only occurs in strata with very rich hydrocarbon source beds such as the d vonian mississippian bakken formation most organically lean pre cretaceous source beds are no longer capable of yielding enough hydrocarbons to maintain abnormal pressure nearly all overpressured reservoirs and source rocks have temperatures of approximately 200 f 93 c or higher in addition available data indicate that hydrocarbon related overpressuring does not generally occur if vitrinite reflectance ro values are less than 0 6 in oil prone strata or less than 0 7 in gas prone strata overpressured gas bearing strata generally have ro values of 0 8 or higher maximum reservoir pressures are about equal to the fracture gradient pressure in the reservoir rocks some vertical fractures in reservoir rocks are probably caused by rapid expulsion of hydrocarbons from the source beds high pressures in the rocky mountain region means that the rock succession is gas or oil saturated and discrete hydrocarbon water contacts are generally not present classical concepts of hydrodynamics do not appear to be applicable to these overpressured successions the optimum depths for exploration are generally the upper 1 000 2 000 ft 305 610 m of the overpressured succession

geochemistry of coalbed gas a review coals are both sources and reservoirs of large amounts of gas that has received increasing attention in recent years as a largely untapped potential energy resource coal mining operations such as ventilation of coalbed gas from underground mines release coalbed ch4 into the atmosphere an important greenhouse gas whose concentration in the atmosphere is increasing because of these energy and environmental issues increased research attention has been focused on the geochemistry of coalbed gas in recent years this paper presents a summary review of the main aspects of coalbed gas geochemistry and current research advances

rates of geodetic deformation across active faults in southern italy abstract active deformation in southern italy is accommodated by a distributed number of faults with low moderate slip rates outcropping extensional faults and mostly blind transcurrent faults are mapped within a western or axial and an eastern domain respectively we use a combination of continuous 2001 00 2011 84 and episodic 1995 68 2010 79 gnss observations to firstly estimate the geodetic deformation rate on 32 faults geodetic results were successively compared with geological displacement estimates in agreement with seismological and geological information a net spatial segregation emerges between the extensional axial belt and the eastern domain where strike slip faults are geodetically active although uncertainties are at times large average displacement rates show broadly consistent patterns within both domains a longitudinal gradient in extension rate is observed for the axial fault array with two sectors of higher magnitude 0 8 1 7 mm yr for individual faults this result is consistent with geological observations and supports the notion that extension occurs in discrete patches faults of the eastern domain have lower few 0 1 to 1 2 mm yr strike slip rates and an eastward decreasing extensional component but significant geodetic displacement is detected in areas lacking clear evidence of activity few faults with 1 2 mm yr extension rate are locally found in the eastern domain but based on their limited length and on inconsistency with seismology and geology they are considered as due to deep seated gravitational spreading for crustal faults although geodetic slip and moment rates are larger than geological rates the broad trend of long to short term rates is similar indicating the feasibility of geodetic analysis to contribute estimating fault slip rate and testing tectonic models in the region whereas the western domain extension is thought to be controlled by potential energy related to the tyrrhenian moho uplift beneath the apennines strike slip in the east is related to shear on inherited faults within the adriatic crust

fault charged mantle fluid contamination of united kingdom north sea oils insights from re os isotopes 187 os 188 os as expected from a kimmer idge clay formation source however oils from the viking graben with which the brent fi eld is associated and main east shetland basin display unradiogenic 187 os 188 os in this study we seek to demonstrate that these anomalous results are due to interaction with a mantle like fl uid that propagated through the main fault zone of the viking graben and east shetland basin this study enhances our understanding of the re os oil systematics and supports cur rent ideas regarding fault architecture crustal thinning and associated fl uid fl ow and interac tion in the north sea oil system abstract united kingdom north sea oils sourced from the kimmeridge clay formation contain unradiogenic 0 17 to 0 48 and radiogenic 1 04 to 3 34 187 os 188 os values the unra diogenic 187 os 188 os values are spatially associated with the main basin bounding faults of the viking graben and east shetland basin in contrast the radiogenic 187 os 188 os values are associated with north sea basins located farther away from the basin boundary faults we suggest that crustal thinning and strain localization within the viking graben and east shetland basin are suffi cient to have allowed basin bounding faults to propagate to suffi cient depth to act as conduits for mantle derived fl uids to interact with oil this hypothesis is sup ported by previous geochemical data for north sea oil fi elds furthermore we demonstrate the use of os isotopes as an important tracker of crustal scale fl uid dynamics and petroleum migration pathways in extensional basins

carbon isotopes of hydrocarbons and carbon dioxide in natural gases in china abstract 130 natural gases in the continent of china were determined for the abundance and carbon isotopes of hydrocarbons and carbon dioxide the 13c pdb values of methane range from 68 to 24 4 and the largest isotopic variability for hydrocarbons is of 13c1 there is no direct evidence for the presence of abiogenic hydrocarbon in natural gases in china one sample from songliao basin shows a heavier 13c1 24 and reverse isotopic distribution pattern 13c1 13c2 13c3 concerning the occurrence of mantle derived he ne ar and xe in the south songliao basin we propose that the methane mantle derived and heavy hydrocarbons ethane propane butane etc formed from polymerization of the mantle derived methane the 13c values for carbon dioxide range from 13 9 to 13 5 suggesting the multiple origins gases with co2 concentrations greater than 10 have a narrow range of 13c values from 8 to 2 and show higher 1he 4he ratios 0 1 times the atmospheric value suggesting that a mantle derived component is diluted by co2 derived from carbonate and or organic matter positive 13c values 4 14 indicate co2 reduction to ch2 co2 with trace concentration in ch4 rich gases can be attributed to microbial decomposition of organic matter in sedimentary rocks

exploration for oil accumulations in entrada sandstone san juan basin new mexico recent exploration activity in the san juan basin of northwestern new mexico has resulted in the discovery of new oil fields in the entrada sandstone of jurassic age the major trapping element is provided by topographic relief in excess of 100 ft 30 m on top of the entrada preliminary analyses indicate that the topographic relief was created by preserved eolian sand dunes which were formed in a topographic basin which then became the sight of a large lake in which limestones and anhydrites of the todilto formation were deposited over the entrada sands the organic rich limestones of the todilto provide the most likely source for the oil found in the underlying entrada analysis of stratigraphy oil shows source rock potential and porosity distribution led to the selection of an initial exploration area located along the southeastern flank of the san juan basin seismic model studies confirmed by an experimental seismic program indicated that the topographic relief on top of the entrada could be mapped seismically an extensive seismic and drilling program has resulted in the discovery of six new oil pools in addition to the topographic relief on top of the entrada other factors which control the oil accumulations include local structural conditions hydrodynamics source rock and oil migration history and porosity permeability relations in the entrada the knowledge gained from this exploration program should aid in future exploration for entrada oil fields in the san juan basin and encourage exploration for similar stratigraphic traps in other basins

evaluation of dissolved light hydrocarbons in different geological settings in romania abstract the paper presents the first systematic geochemical study on the content of natural gas methane heavier alkanes co2 and isotopic composition of methane dissolved in natural springs in romania from various tectonic and geological settings the dissolved methane concentrations in the investigated areas range between 0 08 and 16 359 g l based on isotopic analyses the origin of methane in the gas mixture released by the investigated springs has been inferred the highest concentrations of methane have been measured in the transylvanian basin and carpathian foredeep ethane in relatively high concentrations has been detected in herculane and calimanesti caciulata areas very high concentrations of dissolved co2 were determined in the eastern carpathians volcanic chain area lower amounts of dissolved co2 were detected in the carpathian foredeep southern carpathians transylvanian basin and pannonian basin the measured values of 13c ch4 range between 67 and 4 the methane from the investigated areas is biotic microbial in the transylvanian basin pannonian basin and moldavian platform and thermogenic in the carpathian foredeep we report for the first time the presence of a presumably abiotic methane component in romania from geothermal sources in the areas of ciomadul volcano and herculane area

current strain regime in the western alps from continuous global positioning system measurements 1996 2001 four to six years of continuous measurements at 10 permanent global positioning system sites in the western alps show horizontal residual velocities of 2 mm yr with respect to stable europe uncertainties range from 0 3 to 1 4 mm yr these velocities and the associated strain rate field indicate that the central part of the range is currently dominated by east west extension whereas the southern part shows north south to northwest southeast compression the geodetic and seismotectonic data are consistent with a model where strain is essentially controlled by the counterclockwise rotation of the adriatic microplate with respect to eurasia this rotation together with the arcuate shape of the contact between the adriatic microplate and the alps induces dextral shear kinematic boundary conditions across the western alps with an additional divergence component in their central part and in switzerland and a convergence component in their southern part

genesis of authigene carbonate minerals in the upper cretaceous reservoir honggang anticline songliao basin a natural analog for mineral trapping of natural co2 storage abstract dawsonite naalco 3 oh 2 as a trace mineral of co 2 is abundant in the upper cretaceous reservoir of the honggang anticline southern songliao basin petrologic and isotopic geochemical characteristics have been investigated by a polarizing microscope a scanning electron microscope sem x ray diffraction xrd cathode luminescence cl fluid inclusions and carbon oxygen isotopic analysis the diagenetic sequence indicated that dawsonite late generation microcrystalline quartz late generation kaolinite late generation calcite and ankerite was formed after co 2 flooding meanwhile as a function of analysis on carbon oxygen isotope the mantle magmatic co 2 provided a carbon source for the precipitation of dawsonite late generation calcite and ankerite the three kinds of carbonate minerals mentioned earlier grew in a progressively evolved condition using a basic thermodynamic fraction equation the total quantity of natural co 2 captured by dawsonite bearing sandstones per cubic meter was calculated to be 99 51 kg

disruptive earthquakes revealed by faulted archaeological relics in samnium molise southern italy 1 archaeoseismic and paleoseismic analyses carried out along the northern slope of the matese massif samnium southern apennines revealed cumulative offsets affecting the walls of the hercules s sanctuary of campochiaro 4th cent bc 5th cent ad and its foundation deposits on the basis of the archaeological data a first faulting event unknown in historical sources and seismic catalogues occurred during the 3rd cent bc followed by other displacements which are consistent with the catastrophic 1456 and 1805 earthquakes the sanctuary is located close to one of the e w strands of the northern matese fault system nw se trending to which we relate the observed deformation our data suggest that the activity of this fault system is characterized by high slip rates 0 9 mm yr if compared to other known active faults in the apennines and irregular return time for earthquakes with m 6 5

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

stable carbon isotope geochemistry of adsorbed alkane gases in near surface soils of the saurashtra basin india abstract the stable carbon isotopic compositions of light hydrocarbon gases adsorbed in near surface soil and sediments from the saurashtra basin were characterized for their origin and maturity saurashtra is considered geologically prospective for oil and gas reserves however a major part of the basin is covered by the deccan traps hindering the exploration of mesozoic hydrocarbon targets surface geochemical prospecting based on micro seepage of hydrocarbons from subsurface accumulations could be advantageous in such areas in light of this 150 soil samples were collected from the northwestern part of saurashtra around the jamnagar area where a thick sedimentary sequence of about 2 3 km exists under 1 1 5 km of deccan basalt the concentration of acid desorbed alkane gases from soil samples was found to vary in ppb as methane c 1 3 518 ethane c 2 0 430 propane c 3 0 331 i butane ic 4 0 297 n butane nc 4 2 116 i pentane ic 5 0 31 and n pentane nc 5 0 23 respectively fifteen samples with high concentrations of alkane gases were measured for their 13 c 1 13 c 2 and 13 c 3 compositions using gas chromatography combustion isotope ratio mass spectrometry gc c irms the values for methane varied from 27 to 45 4 ethane from 20 9 to 27 6 and propane from 20 4 to 29 1 versus the vienna peedee belemnite vpdb the carbon isotope ratio distribution pattern represents isotopic characteristics pertaining to hydrocarbon gases derived from thermogenic sources comparisons of carbon isotopic signatures and compositional variations with the standard carbon isotopic models suggest that hydrocarbon gases found in the shallow depths of the study area are not of bacterial origin but are formed thermally from deeply buried organic matter likely to be mainly a terrestrial source rock with a partial contribution from a marine source these gases may have migrated to the near surface environment where they represent an admixture of thermally generated hydrocarbon gases from mixed sources and maturity the maturity scale 13 c versus log ro applied to the surface sediment samples of the jamnagar area indicated the source material to be capable of generating oil and gas the detection of thermogenic alkane gases in near surface sediments offers the possibility of hydrocarbons at depth in saurashtra

generation accumulation and resource potential of biogenic gas biogenic gas is generated at low temperatures by decomposition of organic matter by anaerobic microorganisms more than 20 of the world s discovered gas reserves are of biogenic origin a higher percentage of gases of predominantly biogenic origin will be discovered in the future biogenic gas is an important target for exploration because it occurs in geologically predictable circumstances and in areally widespread large quantities at shallow depths in rapidly accumulating marine sediments a succession of microbial ecosystems leads to the generation of biogenic gas after oxygen is consumed by aerobic respiration sulfate reduction becomes the dominant form of respiration methane generation and accumulation become dominant only after sulfate in sediment pore water is depleted the most important mechanism of methane generation in marine sediments is the reduction of co2 by hydrogen electrons produced by the anaerobic oxidation of organic matter co2 is the product of either metabolic decarboxylation or chemical decarboxylation at slightly higher temperatures the factors that control the level of methane production after sediment burial are anoxic environment sulfate deficient environment low temperatu e availability of organic matter and sufficient space the timing of these factors is such that most biogenic gas is generated prior to burial depths of 1 000 m in marine sediments most of the biogenic gas formed can be retained in solution in the interstitial pore waters because of higher methane solubility at the higher hydrostatic pressures due to the weight of the overlying water column under certain conditions of high pressures and or low temperatures biogenic methane combines with water to form gas hydrates biogenic gas usually can be distinguished from thermogenic gas by chemical and isotopic analyses the hydrocarbon fraction of biogenic gas consists predominantly of methane the presence of as much as 2 of heavier hydrocarbons can be attributed to admixture of minor thermogenic gas due to low temperature degradation of organic matter the amounts of hydrocarbon components other than methane generally are proportional to temperature age and organic matter content of the sediments biogenic methane is enriched in the light isotope 12c dgr13c1 lighter than 55 ppt owing to kinetic isotope fractionation by methanogens the variations in isotopic composition of biogenic methane are controlled primarily by dgr13c of the original co2 substrate which reflects the net isotopic effect of both addition and removal of co2 the methane isotopic composition also can be affected by mixing of isotopically heavier thermogenic gas the possible complicating factors require that geologic chemical and isotopic evidence be considered in attempts to interpret the origin of gas accumulations accumulations of biogenic gas have been discovered in canada germany italy japan trinidad the united states and ussr in cretaceous and younger rocks at less than 3 350 m of burial and in marine and nonmarine rocks other gas accumulations of biogenic origin have undoubtedly been discovered however data that permit their recognition are not available

predicting co2 occurrence on a regional scale southeast asia example abstract prediction of co 2 occurrence in natural gases is difficult owing to the interplay among basinal sources e g volcanic emanations carbonate hydrolysis and metamorphism organic diagenesis and maturation reservoir processes e g mineralogical transformations and poorly understood physicochemical phenomena e g differential solubility of gas components carbonate buffering phase segregation published approaches to assessing co 2 risk are based either on circumstantial evidence of basinal influences or statistical analysis of reservoir attributes the present study presents the results of empirical statistical and neural network analysis of co 2 abundance in natural gas and discusses potentially influential basinal and reservoir attributes to quantify risk factors for anomalous co 2 occurrences in southeast asia the results of this study indicate that tectonic setting including basement crustal age basement fault density reservoir temperature and reservoir pressure are key elements controlling co 2 abundance assignment of co 2 risk at the basin level can be roughly approximated using the results of this study more accurate assessments of co 2 risk at the basin play field and reservoir levels require more comprehensive geological and geochemical data as well as consideration of potentially influential physico chemical processes

present day kinematics of the plate boundary zone between africa and europe from the azores to the aegean anticlockwise rotation of africa relative to europe around an euler pole in the eastern atlantic causes plate convergence in the central mediterranean towards n20 w at rate considered a priori to be 5 10 mm yr 1 however previous summaries of the present day deformation sense in the central mediterranean are inconsistent with observations in southern italy recent investigations of italy and adjacent parts of north africa enable local deformation sense observed to be reconciled with sense predicted from relative plate motions suggested angular velocity of the african plate relative to europe is 0 07 myr 1 around a pole near 21 n 21 w this predicts 2 6 mm yr 1 maximum extension rate towards n64 e near the azores consistent with the minimum local accretion of new oceanic crust in the past few millions of years and 4 3 mm yr 1 plate convergence towards n20 w in the central mediterranean at 13 e further east the northern margin of the african plate can be regarded as the gargano seismic zone in the central adriatic sea the northern adriatic sea is a microplate rotating anticlockwise relative to europe at 0 3 myr 1 around a pole in northwestern italy causing northeastward shortening in yugoslavia and up to 4 mm yr 1 extension in central and northern italy the african plate is deforming internally in tunisia and northern libya extending obliquely in direction e10 s at rate up to 5 5 mm yr 1 the resultant velocity relative to europe in the ionian and southern adriatic seas 5 mm yr 1 towards n50 e explains the observed relative velocity across southern italy kinematic consistency requires present day shortening rate east of calabria associated with subduction on the tyrrhenian sea benioff zone and tyrrhenian sea extension rate to be both zero or equal to within 1 mm yr 1

on the combination of the magnetotelluric and the geomagnetic depthsounding method for resolving an electrical conductivity increase at 400 km depth the simultaneous use of two different passive electromagnetic em sounding techniques for resolving the upper mantle electrical conductivity structure is emphasized the geomagnetic gm method uses magnetic field variations at periods between 3 hours and 600 hours yielding penetration depths between 300 km and 1000 km the magnetotelluric mt method is applied to field variations at periods between a few seconds and 16 hours and yields penetration depths between a few km and 600 km this is an extension of both methods using additional d sub st data for mt and additional s sub q data for gm in application to field data from western europe the resulting overlap of the target depths includes an electrical conductivity increase from 10 sup minus 2 s m at 300 km to 1 s m at 700 km depth while a single conductivity jump at either 400 500 or 700 km cannot explain the broadband data although the olivine to spinel transition is a possible explanation of the conductivity enhancement at 400 km depth another mineralogy could also occur this conductivity increase has not been resolved in other sub continental profiles and lateral heterogeneity is probable in this depth range 27 refs 3 figs 2 tabs

dawsonite and ankerite formation in the ldx 1 structure yinggehai basin south china sea an analogy for carbon mineralization in subsurface sandstone aquifers abstract the geochemistry and petrology of the ldx 1 structure of the yinggehai basin a natural analog of a sedimentary carbon storage site was investigated to understand the consequences of the charging of co2 gas in this system the rocks in this structure are dominated by subarkose and sublitharenite sandstones the authigenic minerals formed after co2 injection are dawsonite microcrystalline quartz kaolinite and ankerite dawsonite and ankerite are formed just beneath a co2 bearing anticlinal structure due to the reactions between silicate minerals feldspars and clay minerals and the fluid phase carbon and oxygen isotopic analyses indicate that the main carbon source for dawsonite and ankerite formation was mantle magmatic co2 the aqueous activities of sodium and calcium the partial pressure of co2 ph and temperature are the key factors influencing the stability of the dawsonite and ankerite the presence of the anticlinal structure maintaining a locally high co2 partial pressure in the waters beneath this structure is likely responsible for the observed long term persistence of dawsonite and ankerite in this system

middle pleistocene to holocene activity of the gondola fault zone southern adriatic foreland deformation of a regional shear zone and seismotectonic implications abstract recent seismicity in and around the gargano promontory an uplifted portion of the southern adriatic foreland domain indicates active e w strike slip faulting in a region that has also been struck by large historical earthquakes particularly along the mattinata fault seismic profiles published in the past two decades show that the pattern of tectonic deformation along the e w trending segment of the gondola fault zone the offshore counterpart of the mattinata fault is strikingly similar to that observed onshore during the eocene pliocene interval based on the lack of instrumental seismicity in the south adriatic offshore however and on standard seismic reflection data showing an undisturbed quaternary succession above the gondola fault zone this fault zone has been interpreted as essentially inactive since the pliocene nevertheless many investigators emphasised the genetic relationships and physical continuity between the mattinata fault a positively active tectonic feature and the gondola fault zone the seismotectonic potential of the system formed by these two faults has never been investigated in detail recent investigations of quaternary sedimentary successions on the adriatic shelf by means of very high resolution seismic stratigraphic data have led to the identification of fold growth and fault propagation in middle upper pleistocene and holocene units the inferred pattern of gentle folding and shallow faulting indicates that sediments deposited during the past ca 450 ka were recurrently deformed along the e w branch of the gondola fault zone we performed a detailed reconstruction and kinematic interpretation of the most recent deformation observed along the gondola fault zone and interpret it in the broader context of the seismotectonic setting of the southern apennines foreland region we hypothesise that the entire 180 km long molise gondola shear zone is presently active and speculate that also its offshore portion the gondola fault zone has a seismogenic behaviour