a detailed 2840 year record of explosive volcanism in a shallow ice core from dome a east antarctica a detailed history of volcanism covering the last 2840 years is reconstructed from the top 100 42 m of a 109 91 m ice core from dome a da2005 ice core east antarctica using two known volcanic stratigraphic markers the mean accumulation rate during the period ad 1260 1964 is found to be 23 2 mm w e a 1 consistent with the previously reported accumulation rate at dome a this mean accumulation rate is used to date the entire core volcanic eruptions in the period 840 bc ad 1998 are detected as outstanding sulphate events seventy eight eruptions are identified with a mean of 2 7 eruptions per century comparisons with previous antarctic ice core volcanic records are made to assess the quality of this new da2005 record in terms of dates for volcanic events the da2005 record is in good agreement with previous records in the second millennium ad ad 1000 1998 a series of volcanic signatures found in both the da2005 record and several other antarctic ice core records in the first millennium ad ad 1 1000 appear to validate the da2005 record during this time period for the older periods direct comparisons are difficult between the da2005 record and other antarctic ice core records due to the lack of well dated stratigraphic horizons

spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related mudrock pores matrix related pore networks in mudrocks are composed of nanometer to micrometer size pores in shale gas systems these pores along with natural fractures form the flow path permeability network that allows flow of gas from the mudrock to induced fractures during production a pore classification consisting of three major matrix related pore types is presented that can be used to quantify matrix related pores and relate them to pore networks two pore types are associated with the mineral matrix the third pore type is associated with organic matter om fracture pores are not controlled by individual matrix particles and are not part of this classification pores associated with mineral particles can be subdivided into interparticle interp pores that are found between particles and crystals and intraparticle intrap pores that are located within particles organic matter pores are intrap pores located within om interparticle mineral pores have a higher probability of being part of an effective pore network than intrap mineral pores because they are more likely to be interconnected although they are intrap om pores are also likely to be part of an interconnected network because of the interconnectivity of om particles in unlithifed near surface muds pores consist of interp and intrap pores and as the muds are buried they compact and lithify during the compaction process a large number of interp and intrap pores are destroyed especially in ductile grain rich muds compaction can decrease the pore volume up to 88 by several kilometers of burial at the onset of hydrocarbon thermal maturation om pores are created in kerogen at depth dissolution of chemically unstable particles can create additional moldic intrap pores

evidence for warmer interglacials in east antarctic ice cores reconstructions of temperature variations from antarctic ice cores rely on the assumption that the relationship between hydrogen and oxygen isotopic ratios and temperature are stable in space and time sime et al analyse three 340 000 year old ice cores from east antarctica and use an isotope enabled general circulation model to show that instead the relationship is nonlinear during warm periods the ratios are less sensitive to temperature so previous estimates of interglacial temperatures are likely to be about 3 c too low this is consistent with peak antarctic interglacial temperatures at least 6 c higher than today this work suggests that there are serious deficiencies in our understanding of climates that are warmer than today s reconstructions of temperature variations from antarctic ice cores rely on the assumption that the relationship between hydrogen and oxygen isotope ratios and temperature are stable in space and time three east antarctic ice core records are now analysed alongside input from general circulation models to reveal that during warmer interglacial periods the isotope ratios are less sensitive to temperature than during colder interglacials consequently previous estimates of interglacial temperatures are probably too cold stable isotope ratios of oxygen and hydrogen in the antarctic ice core record have revolutionized our understanding of pleistocene climate variations and have allowed reconstructions of antarctic temperature over the past 800 000 years 800 kyr refs 1 2 the relationship between the d h ratio of mean annual precipitation and mean annual surface air temperature is said to be uniform 10 over east antarctica3 and constant with time 20 refs 3 5 in the absence of strong independent temperature proxy evidence allowing us to calibrate individual ice cores prior general circulation model gcm studies have supported the assumption of constant uniform conversion for climates cooler than that of the present day3 5 here we analyse the three available 340 kyr east antarctic ice core records alongside input from gcm modelling we show that for warmer interglacial periods the relationship between temperature and the isotopic signature varies among ice core sites and that therefore the conversions must be nonlinear for at least some sites model results indicate that the isotopic composition of east antarctic ice is less sensitive to temperature changes during warmer climates we conclude that previous temperature estimates from interglacial climates are likely to be too low the available evidence is consistent with a peak antarctic interglacial temperature that was at least 6 k higher than that of the present day approximately double the widely quoted 3 1 5 k refs 5 6

effects of firn ventilation on isotopic exchange a new model of isotopic diffusion in the upper few meters of firn tracks the isotopic composition of both the ice matrix and the pore space vapor through time in two dimensions stable isotopes in the vapor phase move through the firn by diffusion along concentration gradients and by advection wind driven ventilation carries atmospheric water vapor into the firn where it mixes with existing pore space vapor unlike previous models our model allows disequilibrium between pore space vapor and the surrounding snow grains we also calculate the isotopic effects of ventilation driven sublimation and condensation in the firn model predictions of isotopic diffusion in firn compare favorably with existing diffusion models model results quantify what other investigators have suggested isotopic change in the upper few meters is more rapid than can be explained by the whillans and grootes 1985 model isotopic equilibration with atmospheric vapor is an important component of post depositional isotopic change and ventilation enhances isotopic exchange by creating regions of relatively rapid sublimation and condensation in the firn

pore types and pore network evolution in upper devonian lower mississippian woodford and mississippian barnett mudstones insights from laboratory thermal maturation and organic petrology abstract pore evolution models from immature organic matter om rich barnett 0 42 r o and woodford 0 49 r o mudstones were compared with models previously developed from low maturity om lean boquillas eagle ford equivalent mudstones to investigate whether 1 different mineralogy siliceous vs calcareous exerts different catalytic and sorption effects and influences om pore origin and evolution and 2 different types of macerals show different om pore evolution history laboratory gold tube pyrolysis scanning electron microscopy sem and thin section petrography organic petrography and geochemical characterization were used to investigate the role of bulk mineralogy maceral type and thermal maturation on om pore evolution results suggest that mineralogy has little impact on om pore development and evolution macerals identified using both sem platy om particulate om organic mineral admixtures tasmanites and organic petrology vitrinite inertinite amorphous organic matter aom bituminite telalginite leiosphaeridia tasmanites do affect the origin and evolution of om pores owing to differences in chemical compositions generation kinetics and activation energy distributions between tasmanites matrix bituminite and other types of macerals leiosphaeridia and tasmanites in woodford mudstone samples exhibit a delay in onset and a shorter period of petroleum generation and pore development compared to the matrix bituminite in the barnett and woodford mudstone samples pre oil solid bitumen was observed to have migrated into initial primary mineral pore networks at the bitumen generation stage in both barnett and woodford samples at higher levels of thermal maturation the volume of primary mineral pores decreases and the pore volume composed of modified mineral pores and om pores becomes greater pore evolution and pore type heterogeneity in these mudstones is a function of the initial mineral pore network types of kerogen and macerals and generation kinetics of individual macerals upon thermal maturation

development of organic porosity in the woodford shale with increasing thermal maturity abstract using a combination of focused ion beam milling and scanning electron microscopy we describe the evolution of secondary organic porosity in eight woodford shale late devonian early mississippian samples with mean random vitrinite reflectance values ranging from 0 51 ro to 6 36 ro organic porosity was observed to be absent in samples with vitrinite reflectance values of up to 0 90 ro with the first appearance of secondary pores starting with the 1 23 ro sample porosity in the organic matter was unexpectedly absent in a sample with a vitrinite reflectance of 2 00 ro however organic pores were again found in samples with higher thermal maturities porosity when present did not appear to be uniformly distributed among the organic matter that was within less than a micron of each other suggesting important differences in composition of the organic matter thin regions of organic matter were observed between grains raising the possibility that small amounts of the deposited organic matter were compacted between grains to form thin layers and or the structures are part of the secondary organic matter interpreted to be post oil bitumen which was left behind as a residue during oil migration through the shale some regions of porous organic matter appeared to be grain protected whereas others did not which indicates that these non protected porous organic regions may be stress supporting with porosity intact under in situ reservoir conditions these observations suggest that thermal maturity alone is insufficient to predict porosity development in organic shales and other factors such as organic matter composition complicate porosity development

a comprehensive study on geometric topological and fractal characterizations of pore systems in low permeability reservoirs based on sem micp nmr and x ray ct experiments abstract characterization of pore systems in subsurface systems is of great importance for predicting the properties of rocks and classifying the subsurface systems geometric features have been used widely for this aim but topological characteristics of the pore structures are not studied much in fact accurate characteristics of pore space should comprise both its geometric and topological properties in this paper the above vital characteristics are comprehensively studied based on direct experimental results besides previous studies aiming at linking fractal dimension analysis to pore space are often based on limited sources of information which are the mercury injection capillary pressure micp and nuclear magnetic resonance nmr in this paper the scanning electron microscope sem micp nmr and x ray computed tomography x ray ct experiments are all used to characterize the geometric and topological properties of pore space of several low permeability porous media based on our observations the advantages and disadvantages of the above techniques in characterizing the pore structure are also summarized moreover the differences of these three experiments are quantified using fractal dimension the results indicate that the nmr technique is a promising tool for characterizing geometric features of pore systems as it can cover more details than other techniques most of geometric topological fractal and transport properties of pore space can be obtained from x ray ct method which is unique among all the methods in addition the 3d fractal dimensions of pore systems obtained from nmr is smaller than that from micp which is due more ultra micropores captured by nmr that smooth the surface of the pore systems finally a novel method constrained by a new pore shape factor for calculating the pore size from 2d images is proposed by which the pore size distributions are compared more effectively

experimental investigation of matrix permeability of gas shales predicting long term production from gas shale reservoirs has been a major challenge for the petroleum industry to better understand how production profiles are likely to evolve with time we have conducted laboratory experiments examining the effects of confining stress and pore pressure on permeability experiments were conducted on intact core samples from the barnett eagle ford marcellus and montney shale reservoirs the methodology used to measure permeability allows us to separate the reduction of permeability with depletion because of the resultant increase in effective confining stress and the increase in permeability associated with knudsen diffusion and molecular slippage also known as klinkenberg effects at very low pore pressure by separating these effects we are able to estimate the relative contribution of both darcy and diffusive fluxes to total flow in depleted reservoirs our data show that the effective permeability of the rock is significantly enhanced at very low pore pressures because of the slippage effects we use the magnitude of the klinkenberg effect to estimate the effective aperture of the flow paths within the samples and compare these estimates to scanning electron microscopy image observations our results suggest effective flow paths to be on the order from tens of nanometers in most samples to 100 200 nm in a relatively high permeability eagle ford sample finally to gain insight on the scale dependence of permeability measurements the same core plugs were crushed and permeability was again measured at the particle scale using the so called gas research institute method the results show much lower permeability than the intact core samples with very little correlation to the measurements on the larger scale cores

organic matter hosted pore system marcellus formation devonian pennsylvania the marcellus formation of pennsylvania represents an outstanding example of an organic matter om hosted pore system most pores detectable by field emission scanning electron microscopy fe sem are associated with om instead of mineral matrix in the two wells studied here total organic carbon toc content is a stronger control on om hosted porosity than is thermal maturity the two study wells span a maturity from late wet gas vitrinite reflectance ro 1 0 to dry gas ro 2 1 samples with a toc less than 5 5 wt display a positive correlation between toc and porosity but samples with a toc greater than 5 5 wt display little or no increase in porosity with a further increasing toc in a subset of samples 14 across a range of toc 2 3 13 6 wt the pore volume detectable by fe sem is a small fraction of total porosity ranging from 2 to 32 of the helium porosity importantly the fe sem visible porosity in om decreases significantly with increasing toc diminishing from 30 of om volume to less than 1 of om volume across the range of toc the morphology and size of om hosted pores also vary systematically with toc the interpretation of this anticorrelation between om content and sem visible pores remains uncertain samples with the lowest om porosity higher toc may represent gas expulsion pore collapse that was more complete as a consequence of greater om connectivity and framework compaction whereas samples with higher om porosity lower toc correspond to rigid mineral frameworks that inhibited compactional expulsion of methane filled bubbles alternatively higher toc samples may contain om low initial hydrogen index relatively unreactive that is less prone to development of fe sem detectable pores in this interpretation om type controlled by sequence stratigraphic position is a factor in determining pore size distribution

pore types and pore size distributions across thermal maturity eagle ford formation southern texas pore types pore size and pore abundance vary systematically across thermal maturity in the eagle ford formation maverick basin southern texas scanning electron imaging of 20 samples from four wells is used to assess the complex response of pores to chemical and mechanical processes entailing both destruction of primary porosity and generation of secondary pores primary mineral associated pores are destroyed by compaction cementation and infill of secondary organic matter whereas secondary pores are generated within organic matter om destruction of primary pores during early burial to 0 5 occurs by compaction of ductile detrital om and clays and to a lesser degree as a result of cementation and infill of secondary om larger pores are associated with coccolith debris the dominant om is spatially isolated detrital om stringers porosity is volumetrically dominated average 6 2 by relatively large mostly interparticle mineral associated pores median size 51 6 nm 0 000002 in detection limit near 3 4 nm 0 00000012 0 00000015 in at low maturity porosity and pore size correlate directly with calcite abundance and inversely with om volumes at higher maturity further destruction of primary pores occurs through cementation secondary om infill and greater compaction mineral associated pores are present at high maturity 1 2 1 3 but are smaller median size 30 2 nm 0 0000011 in and less abundant average of 2 5 than at low maturity a large portion of om within high maturity samples is diagenetic in origin and has pervaded into primary pore space coating cement crystals and filling intraparticle pores substantial mineral associated porosity is locally present in samples where incursion of primary pore space by secondary om has not occurred abundant secondary porosity is generated as om matures into the wet gas window porosity in most high maturity samples is volumetrically dominated average of 1 3 by smaller om hosted pores median size 13 2 nm 0 00000051 in

process based and dynamic 2d modeling of shale samples considering the geology and pore system evolution abstract accurate characterization of shale samples is of great importance for predicting and evaluating their intrinsic properties as they undergo various geological processes as such constructing shale models not only entails accounting for the numerous components and pores but also requires considering the effects of thermal maturation on the evolutions of the pore systems and components in this study a new dynamic and process based modeling for considering the geological evolutions occurred in pore systems is developed which makes a significant improvement in reproducing the complex geological features in shale samples three types of pores including organic matter om interparticle interp and intraparticle intrap pores and several other components including kerogen pyrite clay minerals globigerinids calcite feldspar quartz and petroleum products are all considered in our process based modeling in order to demonstrate the performance of our process based method two dimensional 2d dynamic shale models of multiple cases with different geological processes are constructed then to characterize the constructed samples the occurrences and distributions of all components are studied using a two point correlation function aside from statistical comparisons the gas flow in these shale models is also simulated to exhibit the permeability variations produced in the process based models moreover the degree of cementation the fractions of interp intrap and om pores are varied to mimic new geological scenarios which aims to further evaluate the performance of the proposed technique the results indicate that our process based model presents an excellent performance furthermore the presented modeling technique can be extended to investigating the effects of various components and pores on the intrinsic properties of shales in the future

3d digital rock modeling of the fractal properties of pore structures abstract fractal parameters of porous media have been a focus of study in petroleum engineering and hydrogeology for several decades because they provide an effective way to describe the complexity of pore structure across a wide range of scales this paper combines 3d process driven digital rock modeling with fractal analysis in order to understand the effect of varying sorting compaction cementation and the fine grain fraction of binary models on the fractal parameters and specific surface area of porous media digital rock models drms were constructed to simulate sandstone using a process driven modeling technique which simulates sedimentation the fractal parameters of the resulting pore geometry were calculated using the box counting method on 2d and 3d representations of the drms our simulations indicate that increasing compaction or cementation lead to significant decreases in fractal dimension specific surface area ssp and porosity showing that these two diagenetic processes can affect the pore microstructure of the rock significantly while interface fractal dimension di and ssp both increase slightly with decreases in sorting grain size variety and porosity decreases slightly examining the behavior of binary models the porosity of our digital models shows a v shaped curve as fine grain fraction increases from 0 to 1 consistent with but higher than the theoretical values which we attribute to incomplete packing of the grains arising from the simplified packing algorithm and finite boundary of models the value of both ssp and di increase as the fine grain fraction increases however we must notice that the porosity may be underestimated and the fractal dimension may be overestimated when we use models consisting of very fine spherical grains due to the effect of image resolution

combined sem and reflected light petrography of organic matter in the new albany shale devonian mississippian in the illinois basin a perspective on organic pore development with thermal maturation abstract organic matter hosted pores are an important aspect of pore systems in unconventional gas shale reservoirs along with thermal maturity organic maceral type critically controls the development of secondary organic matter hosted pores three new albany shale samples devonian mississippian kerogen type ii sequence having thermal maturities ranging from a vitrinite reflectance ro of 0 55 to 1 42 were analyzed using a reflected light microscope and a field emission scanning electron microscope organic pores were examined in specific organic macerals and solid bitumen at different thermal maturities vitrinite and inertinite derived from terrestrial woody materials occur as discrete particles in this black shale within the resolution limits of the scanning electron microscope these two macerals do not appear to display enhanced secondary pores associated with increases in thermal maturity cellular pores 0 2 10 m in inertinite were observed throughout the entire maturity range and were typically filled with authigenic quartz or solid bitumen because of thermal degradation amorphous organic matter was not observed at maturities greater than ro 0 80 alginite derived from tasmanites cysts matures later than amorphous organic matter and is still present at ro 0 80 however it is in the process of transforming to pre oil bitumen and shows weak orange yellow fluorescence compared to strong greenish yellow fluorescence in lower maturity samples at a maturity of ro 1 42 alginite could no longer be observed as a distinct phase because of its complete transformation to hydrocarbons and bitumen alginite began to develop secondary pores when it was in the process of transforming to pre oil bitumen which indicates that some liquid and gaseous hydrocarbons left the alginite during this part of the maturation process solid bitumen developed along the original amorphous organic matter networks and now occupies interparticle space between quartz dolomite k feldspar clay and mica grains as well as the cellular pores in inertinite particles solid bitumen becomes smaller and more porous with thermal maturation and thus becomes increasingly unidentifiable with the optical microscope solid bitumen hosted pores 20 1000 nm are the main organic pore type documented in the studied samples and they are more common in shales within the gas window than those in the oil window secondary nanopores in the solid bitumen network play a significant role in hydrocarbon storage and migration

sem petrography of eastern mediterranean sapropels analogue data for assessing organic matter in oil and gas shales abstract examination of organic matter hosted pore systems in unconventional reservoir rocks has drawn attention to the appearance of sedimentary organic matter om as seen in high resolution sem images field emission sem imaging of eastern mediterranean sapropels pliocene pleistocene age from ocean drilling program drill sites was performed on samples prepared by ar ion cross section polishing the immaturity of marine kerogen in these rocks allows inspection of petrographic textures without overprints related to thermal maturation hydrocarbon generation kerogen in these samples includes discrete particles that in some cases contain primary intragranular pores the most abundant organic matter is in the form of microns thick flaky or stringy material largely nonporous and internally amorphous and lacking the well defined shapes of discrete particles this dominant om has behaved in a highly ductile manner in compaction and is now highly pervaded into intergranular spaces between silt and clay size grains a portion of the larger mineral hosted pores remain open unfilled by ductile om minor nanometer scale pores of uncertain origin occur in the dominant om silt and clay size mineral crystals are distributed in organic matter of most types and it is difficult to fully ascertain if the om mineral mixing has occurred during compaction versus during aggregation during gravity settling marine snow sedimentation or through sediment accumulation in om rich microbial mats results indicate that sediments rich in marine kerogen are subject to substantial compactional porosity loss in early burial these observations of marine detrital organic matter in its early diagenetic state provide a useful baseline for interpretation of petrographic features in more mature om rich mudrocks it is clear that petrographic discrimination of diagenetically generated organic matter bitumen and related om types from ductile dispersed amorphous detrital om kerogen using sem data will be challenging in the absence of compositional information

origin and characterization of eagle ford pore networks in the south texas upper cretaceous shelf abstract recent studies have shown that the loss of primary pores and the development of secondary pores in mudrocks are primarily controlled by burial diagenesis of the mineral matrix and thermal maturation of organic matter om however the lack of quantitative data on nanometer to micrometer scale rock properties has limited the ability to define and predict petrophysical properties and fluid flow in these fine grained rocks to upscale these rock properties quantitative data are needed at multiple scales representative eagle ford group samples were collected from continuous cores taken from two adjacent oil producing wells in karnes county texas to investigate small scale variations in mineralogy diagenesis and pore type point count and pore tracing methods were used to systematically quantify pore types and determine the size and shape of the identified pores the two cores from the eagle ford are dominated by modified mineral pores although secondary om pores in migrated petroleum bitumen are also important the mineral pore network includes 1 primary mineral pores originally saturated with formation water and 2 modified mineral pores containing migrated petroleum bitumen and or residual oil the om pore network includes 1 primary om pores and 2 secondary om pores including relatively large less abundant om bubble pores and relatively small more abundant om spongy pores the abundance of om spongy pores correlates positively with total organic carbon toc content and that of mineral pores weakly correlates with the volume of quartz plus feldspar studied samples have similar thermal maturities although samples from one deeper core are slightly more mature than the other except for thermal maturation the strong micrometer scale heterogeneity of rock components and properties texture fabric mineralogy and toc impacts the abundance distribution and type of pores this micrometer scale heterogeneity in porosity and pore networks would in turn significantly impact matrix permeability

three common source rock evaluation errors made by geologists during prospect or play appraisals geologists are frequently called on to evaluate the source rocks associated with their exploration prospects or plays the three most common questions asked and answered about the source rock during project reviews are what s the total organic carbon toc what kerogen type does rock eval indicate and what maturity level does the vitrinite reflectance data point to the answers to these seemingly innocuous questions may in fact be providing a false sense of security about the source rock in question understanding how this line of questioning can lead you astray and make you the victim of the toc myth if i have high toc i have a good source rock the rock eval fallacy the rock eval data tell me what kind of kerogen is in my source rock and the vitrinite reflectance deficiency vitrinite reflectance will tell me if my source rock is generating is important some of the solutions to these problems include fully integrating toc and rock eval data supplementing rock eval data with pyrolysis gas chromatography and using burial history diagrams to help interpret vitrinite reflectance harry dembicki jr is a senior geological advisor for geochemistry in the geological technology group at anadarko petroleum corporation where he provides technical support to both exploration and development teams he holds a b s degree 1973 in geology from the state university college of new york at new paltz and a ph d 1977 in geology with emphasis in organic geochemistry from indiana university he previously worked as an organic geochemist for conoco and marathon

pore and pore network evolution of upper cretaceous boquillas eagle ford equivalent mudrocks results from gold tube pyrolysis experiments low maturity boquillas formation eagle ford formation equivalent organic lean calcareous mudrock samples collected from outcrop were heated in gold tubes under confining pressure to investigate the evolution of organic matter om pores and mineral pores the majority of om in the boquillas samples was migrated petroleum bitumen based on evidence from geochemical analyses solvent extraction and scanning electron microscopy sem petrography the sem images showed several diagenetic events including framboidal pyrite precipitation and euhedral calcite quartz kaolinite and chlorite cementation that were all interpreted to have occurred prior to petroleum expulsion and pore scale to bed scale petroleum bitumen migration two major pore types were present prior to heating primary mineral pores and modified mineral pores with migrated relic om from heating experiments pores were found to be associated with stages of om maturation during the bitumen generation stage modified mineral pores were dominant and primary interparticle and intraparticle pores were present during the oil generation stage modified mineral pores with isopachous om rim were observed to be the most abundant pore type during the gas generation stage both modified mineral pores and nanometer sized spongy om pores were predominant we interpreted the occurrence of modified mineral pores to be the result of 1 oil and gas filled or partially filled voids that developed during petroleum migration and water expulsion 2 voids after removing of oil gas and water during sample preparation and 3 trapping of water molecules the formation of these nanopores was interpreted to be related to gas generation and structural rearrangement of om

pore types in the barnett and woodford gas shales contribution to understanding gas storage and migration pathways in fine grained rocks the identification of organoporosity microscale and nanoscale pores within organic matter in shales its importance to storage and perhaps transfer of gas molecules through shales and methods for gathering three dimensional images of the pores such as by argon ion milling and or field emission scanning electron microscopy have all been well documented and discussed for unconventional gas shales however other types of pores exist within shales that can be important to storage and migration of gas and oil and other technologies are available for their identification and imaging the different pore types found in the barnett and woodford shales are described and classified in this article scanning electron microscopy revealed the presence of porous floccules in both the barnett and woodford shales which appear similar to laboratory produced floccules and to those in other ancient shales published experimental and observational studies indicate that floccules are hydraulically equivalent to coarser grains and are transported by traction processes current induced microsedimentary structures and textures within the barnett and woodford shales as well as the preserved floccules suggest such processes were active during transport and deposition pore spaces between the floccules are open and can provide storage space as well as permeability pathways for gas molecules through the shales pores are also found within organic matter that occurs both as discrete particles and as adsorbed coatings around clay grains in the shale they are referred to here as organopores porous fecal pellets are also common in the barnett shale preserved fossil fragments such as organic walled spores and inorganic sponge spicules have hollow central chambers which may remain partially or completely open even after burial intraparticle pores occur between grains of various minerals e g pyrite framboids microchannels within shale matrix which may be the bounding surfaces of scours or microsedimentary structures may also provide permeability pathways for hydrocarbon migration mircrofractures are also common and their initiation might be related to mineral crystal structure when present in sufficient quantity these pore types offer potential gas and oil molecule storage spaces and permeability pathways through the shales

synchronicity of antarctic temperatures and local solar insolation on orbital timescales records of past temperatures derived from greenland and antarctic ice cores are important for the understanding of the global climate system on long timescales according to milankovitch theory glacial to interglacial climate variability as recorded in antarctic ice cores is governed by summer insolation the amount solar of radiation received at earth s surface at high northern latitudes thomas laepple and colleagues now show that accumulation of antarctic snow is biased towards austral winter and may be explained simply by variations in local insolation with no recourse to northern influences although the results do not constitute a complete negative proof they show that the antarctic ice core records do not in themselves provide sufficient support for milankovitch theory according to the milankovitch theory glacial to interglacial climate variability as recorded in antarctica ice cores is governed by summer insolation at high northern latitudes it is now shown that accumulation of antarctic snow is biased towards austral winter and may be explained simply by variations in local insolation with no recourse to northern influences although not constituting a complete negative proof the results show that the antarctic ice core records do not in themselves provide sufficient support for the milankovitch theory the milankovitch theory states that global climate variability on orbital timescales from tens to hundreds of thousands of years is dominated by the summer insolation at high northern latitudes1 2 the supporting evidence includes reconstructed air temperatures in antarctica that are nearly in phase with boreal summer insolation and out of phase with local summer insolation3 4 5 antarctic climate is therefore thought to be driven by northern summer insolation5 a clear mechanism that links the two hemispheres on orbital timescales is however missing we propose that key antarctic temperature records derived from ice cores are biased towards austral winter because of a seasonal cycle in snow accumulation using present day estimates of this bias in the recorder system here we show that the local insolation can explain the orbital component of the temperature record without having to invoke a link to the northern hemisphere therefore the antarctic ice core derived temperature record one of the best dated records of the late pleistocene temperature evolution cannot be used to support or contradict the milankovitch hypothesis that global climate changes are driven by northern hemisphere summer insolation variations

diagenetic history and reservoir quality of tight sandstones a case study from shiqianfeng sandstones in upper permian of dongpu depression bohai bay basin eastern china abstract the upper permian shiqianfeng sandstones located in the dongpu depression bohai bay basin china are fluvio lacustrine deposits and have high content of pore filling volcanic dust average 7 93 vol this study focuses on diagenetic processes and reservoir quality of the tight sandstones based on different lithofacies an integrated approach such as core observation x ray diffraction scanning electron microscopy cathode luminescence stable isotope analysis of carbon and oxygen compositions electron microprobe analysis and fluid inclusion analysis were utilized the tight sandstones consist of subarkose and lithic subarkose and have undergone significant diagenetic events including compaction quartz cementation carbonate cementation mainly calcite and ferrocalcite and formation of authigenic clay minerals i e chlorite rims kaolinite and mixed layer illite smectite the volcanic dust altered with increase of burial depth resulting in the production of abundant silicic materials and depletion of metallic ions i e fe 2 mg 2 ca 2 and mn 2 this process formed subhedral micro quartz pore filling authigenic quartz smectite and chlorite rims during the early diagenetic stage early phase carbonate cements calcite ferrocalcite occurred in several samples they were also influenced by volcanic dust alteration resulting in intrusive of fe 2 and high contents of mn 2 average 12 5 mol further alteration of volcanic dust at the mesogenetic stage can result in cementation of kaolinite and euhedral micro quartz quartz overgrowth developed because of smectite to illite reactions and the alteration of volcanic dust late phase carbonate cements dolomite and ankerite are rare the present low porosity average 6 17 vol and permeability average 0 198 md of the shiqianfeng sandstones mainly resulted from intense compaction diverse cementation and pore filling of volcanic dust as strong hydrodynamic conditions of pore water modification of reservoir quality in the conglomeratic sandstone and gritstone lithofacies mainly distribute in braided channel occurred by alteration of volcanic dust thick braided channel at the high structural position should be the focal point for the future exploration

snow accumulation and its moisture origin over dome argus antarctica the spatial and temporal variability of snow accumulation near dome argus antarctica is assessed using new snow pit and stake measurement data together with existing snow pit ice core and automatic weather station records snow accumulation rate shows large inter annual variations but stable multi decadal levels over the last seven centuries spatial variations in snow accumulation within the space of 50 km of dome argus are relatively small probably thanks to the smooth topography a comparison of theses accumulation observations with ecmwf reanalyses era 40 and era interim suggests ecmwf reanalysis captures the seasonal variations but underestimates the overall snow accumulation at dome argus by 50 the moisture sources for precipitation over dome argus are examined by means of a lagrangian moisture source diagnostic based on the tracing of specific humidity changes along air parcel trajectories for the period 2000 2004 using operational ecmwf analysis data dome argus mainly receives moisture from the mid latitude 46 4 s south indian ocean with a seasonal latitudinal shift of about 6 compared to other central east antarctic deep ice core sites such as dome f dome c vostok and epica dronning maud land dome argus has a more southerly moisture origin probably due to topographic influences on the moisture transport paths these results have important implications for the interpretation of future ice cores at dome argus

a comparison of experimental methods for describing shale pore features a case study in the bohai bay basin of eastern china abstract to compare experimental methods for describing shale pore features we performed a series of parallel experiments on typical continental shales from the bohai bay basin of eastern china including scanning electronic microscopy sem focused ion beam scanning field emission scanning electron microscopy fib fe sem low temperature nitrogen adsorption desorption ltna mercury intrusion porosimetry mip and nuclear magnetic resonance nmr techniques the results show that artificial peaks located at 3 to 5 nm affected by the tensile strength effect tse are clearly seen in the bjh pore size distributions psds calculated using the low temperature nitrogen desorption curve of shale with narrow neck pores e g ink bottle pores although the ltna technique cannot completely reveal large pores the adsorption desorption curve and the psd acquired from it can still indicate the relatively high or low extent of development of large pores in different shales shale within the oil window primarily contains inorganic pores as organic nanopores are generally formed during the high or over mature stage of organic matter during the mercury intrusion high pressures forcing liquid mercury to enter small pores less than 40 to 70 nm will cause pores in the samples to crack especially for shale with slit shaped and wedge shaped pores unlike ltna mip measures only pore throats and does not detect pore bodies therefore the effective pore size revealed by the ltna method may be up to 300 nm instead of only 50 nm when ltna is combined with mip to reveal the psd of shales with narrow necked pores nmr and ltan can be complemented by each other and the psd results revealed by them are anastomotic which suggests that the combination of nmr and ltan is an ideal method for revealing the psd of shale

a comparative study of representative 2d microstructures in shaly and sandy facies of opalinus clay mont terri switzerland inferred form bib sem and mip methods abstract a combination of broad ion beam bib polishing and scanning electron microscopy sem has been used to study qualitatively and quantitatively the microstructure of opalinus clay in 2d high quality 2d cross sections ca 1 mm 2 belonging to the shaly and sandy facies of opalinus clay were investigated down to the nanometre scale in addition mercury intrusion porosimetry mip and x ray powder diffraction experiments have been used to extend characterization of the microstructure to the mm cm scale on bulk volume sample material interestingly both end member samples of the opalinus clay show qualitatively similar mineralogy and pore characteristics as well as a comparable pore size distribution and pore morphology within the different mineral phases and mineral aggregates differences between the facies are mainly due to variations in mineral size and mineral amount present in the alternating layers of the different facies six different porous mineral phases have been identified and the pores have been subdivided into ten different pore types pores visible in the sem images are most abundant in the clay matrix and these seem to follow a power law distribution with a power law exponent of ca 2 25 independent of the sample location furthermore all common mineral grains show characteristic porosity pore shape and pore size distribution in 2d and are proposed to be considered as elementary building blocks for opalinus clay combined these homogeneous elementary building blocks make up the heterogeneous fabric of the different facies of opalinus clay based on extrapolation of the power law size distribution in the clay matrix below sem resolution results in a porosity of 10 25 for clay rich layers 60 90 of clay matrix whereas sand and carbonate layers show an extrapolated porosity of 6 14 these extrapolated porosities are in agreement with water loss and physical porosity measurements performed on bulk material of comparable samples

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores

pore characterization and methane sorption capacity of over mature organic rich wufeng and longmaxi shales in the southeast sichuan basin china abstract currently the upper ordovician wufeng o3w and lower silurian longmaxi s1l formations in southeast sichuan basin have been regarded as one of the most important target plays of shale gas in china in this work using a combination of low pressure gas adsorption n2 and co2 mercury injection porosimetry mip and high pressure ch4 adsorption we investigate the pore characteristics and methane sorption capacity of the over mature shales and discuss the main controlling factors for methane sorption capacity and distribution of methane gas in pore spaces low pressure co2 gas adsorption shows that micropore volumes are characterized by three volumetric maxima at about 0 35 0 5 and 0 85 nm the reversed s shaped n2 adsorption isotherms are type with hysteresis being noticeable in all the samples the shapes of hysteresis loop are similar to the h3 type indicating the pores are slit or plate like mesopore size distributions are unimodal and pores with diameters of 2 16 nm account for the majority of mesopore volume which is generally consistent with mip results the methane sorption capacities of o3w s1l shales are in a range of 1 63 3 66 m3 t at 30 c and 10 mpa methane sorption capacity increase with the toc content surface area and micropore volume suggesting organic matter might provide abundant adsorption site and enhance the strong methane sorption capacity samples with higher quartz content and lower clay content have larger sorption capacity our data confirmed that the effects of temperature and pressure on methane sorption capacity of shale formation are opposite to some extent suggesting that during the burial or uplift stage the gas sorption capacity of hydrocarbon reservoirs can be expressed as a function of burial depth based on the adsorption energy theory when the pore diameter is larger than 2 nm much methane molecular will be adsorbed in pores space with distance to pore wall less than 2 nm while free gas is mainly stored in the pore space with distance to pore wall larger than 2 nm distributions of adsorption space decrease with the increasing pore size while free gas volume increase gradually assuming the pore are cylindrical or sphere particularly when the pore size is larger than 30 nm the content of adsorbed gas space volume is very low and its contribution to the all gas content is negligible

stochastic shale permeability matching three dimensional characterization and modeling abstract the recently discovered promise of shale gas reservoirs necessitates their characterization as a first step two dimensional 2d scanning electron microscope sem imaging can provide excellent view of the complexity associated with such reservoirs and has been used in recent years to study organic materials clays minerals and the pores in shales other important information such as the connectivity of the pores in 3d and such macroscopic properties as the permeability are difficult to infer from 2d sem images newer techniques such as focused ion beam sem fib sem have been utilized to overcome the shortcomings the extremely small sample size and the costs associated with the fib sem technique limit however wide use of the fib sem in characterization of shale samples an alternative approach is to use the recently developed advanced algorithms for 3d reconstruction that use one or a few 2d samples such methods may not however be able to fully reproduce the shale permeability to accurately reproduce the permeability we propose a new method based on a combination of the metropolis hastings and the genetic algorithms the new method learns from its own previously generated realizations of the shale and produces models that match the existing permeability data the method is validated with the measured permeability for an actual 3d shale sample it generates an ensemble of stochastic realizations that honor the permeability data which may then be used for more accurate characterization of shale gas reservoir and analysis of their pore network