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

specific surface area and pore size distribution in clays and shales one of the biggest challenges in estimating the elastic transport and storage properties of shales has been a lack of understanding of their complete pore structure the shale matrix is predominantly composed of micropores pores less than 2 nm diameter and mesopores pores with 2 50 nm diameter these small pores in the shale matrix are mainly associated with clay minerals and organic matter and comprehending the controls of these clays and organic matter on the pore size distribution is critical to understand the shale pore network historically mercury intrusion techniques are used for pore size analysis of conventional reservoirs however for unconventional shale reservoirs very high pressures 414 mpa 60 000 psi would be required for mercury to access the full pore structure which has potential pitfalls current instrumental limitations do not allow reliable measurement of significant portions of the total pore volume in shales nitrogen gas adsorption techniques can be used to characterize materials dominated by micro and mesopores 2 50 nm a limitation of this technique is that it fails to measure large pores diameter 200 nm we use a nitrogen gas adsorption technique to study the micro and mesopores in shales and clays and compare the results from conventional mercury porosimetry techniques our results on pure clay minerals and natural shales show that i they have a multiscale pore structure at different dimensions ii fine mesopores with a characteristic 3 nm pore size obtained with n2 gas adsorption are associated with an illite smectite group of clays but not with kaolinite iii compaction results in a decrease of pore volume and a reduction of pore size in the inter aggregate macropores of the illitesmectite clays while the fine intra tachoid mesopores are shielded from compaction iv for natural shales mineralogy controls the pore size distributions for shales and the presence of micropores and fine mesopores in natural shales can be correlated with the dominance of the illite smectite type of clays in the rock our assessment of incompressible 3 nm sized pores associated with illite smectite clays provides an important building block for their mineral modulus

influential factors and model of shale pore evolution a case study of a continental shale from the ordos basin abstract pore characteristics have a significant influence on the occurrence and enrichment of shale gas therefore these characteristics are key parameters in shale reservoir evaluation and have important research significance taking a continental shale sample from the ordos basin china as an example this research used low pressure co2 n2 adsorption high pressure mercury intrusion porosimetry mip vitrinite reflectance ro analysis hydrocarbon generation measurements x ray diffraction analysis and argon ion polishing field emission scanning electron microscopy aip fesem in conjunction with a thermal simulation experiment to study pore characteristics through the above analyses this study achieved a whole aperture dynamic characterization of the shale pores and discussed the characteristics of the shale pore distribution and evolution through geological history then the factors influencing pore evolution were analysed and a pore evolution model was established the results showed that the micropores and mesopores provided the majority of the surface area in the sample while the mesopores and macropores provided the majority of the pore volume in the sample during the thermal simulation experiment pore evolution was dominated by the hydrocarbon generation by organic matter the transformation of minerals and compaction according to the pore evolution characteristics and the main influential factors during the thermal simulation experiment the pore evolution model can be divided into four stages the characteristics of the micropores mesopores macropores and the influential factors differ in each stage

formation of nanoporous pyrobitumen residues during maturation of the barnett shale fort worth basin abstract hydrocarbon generation reactions occur within organic rich shales as a response to thermal maturation here we report observations on samples from the organic rich mississippian barnett shale gas system fort worth basin texas usa at varying stages of thermal maturation a multiscale characterization was achieved using a combination of compositional organic geochemistry and spectromicroscopy techniques including synchrotron based scanning transmission x ray microscopy stxm and transmission electron microscopy tem we document the chemical evolution of the macromolecular structure of barnett shale kerogen with increasing maturity from an immature kerogen containing a significant aliphatic component and an important concentration of oxygen and sulfur containing functional groups to an overmature kerogen dominated by poorly condensed aromatic structures in addition to the presence of bitumen in samples of oil window maturity very likely genetically derived from thermally degraded kerogen the formation of nanoporous pyrobitumen has been inferred for samples of gas window maturity likely resulting from the formation of gaseous hydrocarbons by secondary cracking of bitumen compounds

evolution of water content in organic rich shales with increasing maturity and its controlling factors implications from a pyrolysis experiment on a water saturated shale core sample abstract in the present study a pyrolysis experiment was performed on an immature water saturated shale core sample and a set of artificially matured subsamples maturity with equivalent vitrinite reflectance values of 0 67 3 20 i e eqvro values with initial water phases was obtained the water content of these shale samples and its influencing factors were investigated the results show that the water content significantly varies with maturity and is closely related to the hydrocarbon generation and expulsion clay mineral transformation and pore structure evolution of shales according to the changes of water content with maturity and the main influencing factors the evolution of the water content in shales is approximately divided into three stages at the low maturity stage 0 67 1 36 with increasing maturity the water content remarkably decreases at the wet gas window 1 36 1 90 which is mainly controlled by the displacement drainage of gaseous hydrocarbons in addition the pore structure evolution of shale which changes its water storage capacity also has an influence on the water content evolution

the campanian ignimbrite southern italy geochemical zoning insight on the generation of a super eruption from catastrophic differentiation and fast withdrawal more than ca 100 km3 of nearly homogeneous crystal poor phonolite and ca 100 km3 of slightly zoned trachyte were erupted 39 ka during the campanian ignimbrite super eruption the most powerful in the neapolitan area partition coefficient calculations equilibrium mineral assemblages glass compositions and texture were used to reconstruct compositional thermal and pressure gradients in the pre eruptive reservoir as well as timing and mechanisms of evolution towards magma chamber overpressure and eruption our petrologic data indicate that a wide sill like trachytic magma chamber was active under the campanian plain at 2 5 kbar before ci eruption thermal exchange between high liquidus 1199 c trachytic sill and cool country rocks caused intense undercooling driving a catastrophic and fast 102 years in situ fractional crystallization and crustal assimilation that produced a water oversaturated phonolitic cap and an overpressure in the chamber that triggered the super eruption this process culminated in an abrupt reservoir opening and in a fast single step high decompression sanidine phenocrysts crystal size distributions reveal high differentiation rate thus suggesting that such a sill like magmatic system is capable of evolving in a very short time and erupting suddenly with only short term warning

geochemical constraints on the origin and volume of gas in the new albany shale devonian mississippian eastern illinois basin this study involved analyses of kerogen petrography gas desorption geochemistry microporosity and mesoporosity of the new albany shale devonian mississippian in the eastern part of the illinois basin specifically detailed core analysis from two locations one in owen county indiana and one in pike county indiana has been conducted the gas content in the locations studied was primarily dependent on total organic carbon content and the micropore volume of the shales gas origin was assessed using stable isotope geochemistry measured and modeled vitrinite reflectance values were compared depth of burial and formation water salinity dictated different dominant origins of the gas in place in the two locations studied in detail the shallower owen county location 415 433 m 1362 1421 ft deep contained significant additions of microbial methane whereas the pike county location 832 860 m 2730 2822 ft deep was characterized exclusively by thermogenic gas despite differences in the gas origin the total gas in both locations was similar reaching up to 2 1 cm3 g 66 scf ton lower thermogenic gas content in the shallower location lower maturity and higher loss of gas related to uplift and leakage via relaxed fractures was compensated for by the additional generation of microbial methane which was stimulated by an influx of glacial melt water inducing brine dilution and microbial inoculation the characteristics of the shale of the maquoketa group ordovician in the pike county location are briefly discussed to provide a comparison to the new albany shale

mineral composition and seal condition implicated in pore structure development of organic rich longmaxi shales sichuan basin china abstract shale pore structure morphology type size distribution and porosity is important in controlling the storage and movement of oil and gas characterization of pore structure is one of the main research foci for unconventional resources however factors influencing its heterogeneity are poorly understood with total organic carbon ranging at 0 52 4 23 23 core samples from three wells jy2 wy1 and yz1 in different tectonic units of the longmaxi shale in sichuan basin were studied using a combination of petrographic geochemical and pore structure characterization techniques the shale porosity shows positive relationships with quartz and total organic carbon contents in jy2 and wy1 but not in yz1 because of its different pore structure pore structure differences are primarily attributed to the different contributions of organic matter om hosted nanopores which are controlled by preservation conditions due to the differences in the duration and intensity of tectonic activities the jy2 and wy1 areas are characterized by over pressured conditions with respective pressure coefficients of about 1 5 and 1 4 conversely the yz1 area has a normal pressure condition with a pressure coefficient of about 1 0 indicating a poor seal condition under good seal conditions generated hydrocarbons cannot escape easily thus the accumulation and expansion of shale gas trapped within organic pores increase the pore pressure to abnormally high levels which in turn protect the shale reservoir from compaction and support om hosted pore development the om pore evolution of the longmaxi shale in the sichuan basin during burial was generally uniform thus the differences in pore structure reflect subsequent tectonic uplift the siliceous shales of yz1 did not develop many om hosted pores because of the lack of seal conditions during the high maturity stage before uplift most of the pores shrink or close due to an escape of hydrocarbons mineral composition thermal maturity and seal conditions are identified to influence pore development and preservation in fine grained sedimentary rocks

fabric anisotropy induced by primary depositional variations in the silt clay ratio in two fine grained slope fan complexes texas gulf coast and northern north sea article i nfo high resolution x ray texture goniometry hrxtg has been used to quantify the alignment anisotropy of phyllosilicate minerals in a series of diagenetically altered mudstone samples from the deep subsurface of the texas gulf coast and the northern north sea the sampled formations have undergone a simple burial history with no overprint of tectonic deformation that may have influenced the phyllosilicate orientation observations have been made in two constrained temperature windows 148 150 c north sea data and 169 210 c texas gulf coast wherein less than 20 smectite remains in the mixed layer phase illite smectite quantitative x ray powder diffraction xrpd shows quartz which is dominantly detrital and phyllosilicate content having an inverse relationship quantified illite smectite fabric intensity phyllosi licate alignments ranges from low alignment values of 2 42 m r d multiples of a random distribution to high alignment values 6 75 m r d and chlorite kaolinite ranges from 1 80 to 6 46 m r d we propose that the broad range of phyllosilicate fabric intensity observed reflects the range of quartz phyllosilicate ratios that are the imprint of depositional setting bedform truncation and initial grain size detrital quartz acts to disrupt fabric intensity by being non platy producing areas sheltered from effective stress pressure shadows and acting as a matrix support there is no evidence that bioturbation is a significant control on phyllosilicate alignment in these quartz phyllosilicate mixtures these findings have important implications for the role of grain scale alignment on seismic anisotropy in mudstone systems fabric intensity in post diagenetic samples can be predicted from 1 quartz content and 2 total clay content where

the age of the neapolitan yellow tuff caldera forming eruption campi flegrei caldera italy assessed by 40ar 39ar dating method abstract the neapolitan yellow tuff nyt is the product of the largest known trachytic phreatoplinian eruption it covered an area larger than 1000 km2 with an estimated volume of about 40 km3 of erupted magma during the course of the eruption a caldera collapsed within the previously formed campanian ignimbrite caldera the resulting nested structure strongly influenced the following volcanic activity in the campi flegrei caldera as previous dating of the nyt does not converge toward a unique result a new set of 40ar 39ar age determinations has been carried out to better constrain the age of the eruption two variants of the 40ar 39ar dating method were applied to determine the age of the nyt eruption 1 single crystal total fusion sctf on an individual phenocryst of feldspar and 2 laser incremental heating lih on bulk aliquots of feldspar phenocrysts the results of the sctf analyses show that the overall sample weighted mean age derived from the conventional age calculation is 15 6 0 8 ka a weighted mean of the isochron age is 15 3 1 2 ka 2 and has been assumed as the best indicator of age to be derived from the sctf analyses the lih analyses results show that plateau ages vary from 15 4 0 5 to 14 5 0 5 ka the overall weighted mean age of the isochron results is 14 9 0 4 ka 2 this result has been assumed as the reference age for the nyt eruption and agrees with the sctf age the new age obtained for the nyt deposits is of great relevance for the understanding of the evolution and the present state of the campi flegrei caldera and collocates the nyt in a crucial stratigraphical position to date the climatic oscillations that occurred between the late glacial and the holocene

manganese in the s w pacific a brief review abstract manganese occurs as relatively small scale terrestrial deposits throughout the s w pacific and has been mined in vanuatu fiji new caledonia new zealand and papua new guinea listed in order of importance as producers in each case mining has now ceased to be economically profitable present information on s w pacific terrestrial manganese deposits is limited and dated and little work is being carried out no modern synthesis of these deposits or their mode of genesis exists data on the manganese distribution in soils are sparse in the marine environment substantial work has been carried out this review indicates the need for a comprehensive study of manganese ore deposits and manganese in soils in the s w pacific with a particular emphasis on comparison of results from different localities and settings

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

oil retention and porosity evolution in organic rich shales petroleum is retained in shales either in a sorbed state or in a free form within pores and fractures in shales with oil resource potential organic matter properties i e richness quality and thermal maturity control oil retention in general in gas shales organic pores govern gas occurrence although some pores may originate via secondary cracking reactions it is still largely unclear as to how these pores originate here we present case histories mainly for two classic shales the mississippian barnett shale texas and the toarcian posidonia shale lower saxony germany in both cases shale intervals enriched in free oil or bitumen are not necessarily associated with the layers richest in organic matter but are instead associated with porous biogenic matrices however for the vast bulk of the shale hydrocarbon retention and porosity evolution are strongly related to changes in kerogen density brought about by swelling and shrinkage as a function of thermal maturation secondary organic pores can form only after the maximum kerogen retention swelling ability is exceeded at tmax the temperature at maximum rate of petroleum generation by rock eval pyrolysis around 445 c 833 f approximately 0 8 vitrinite reflectance shrinkage of kerogen itself leads to the formation of organic nanopores and associated porosity increase in the gas window

geological controls on matrix permeability of devonian gas shales in the horn river and liard basins northeastern british columbia canada abstract controls of matrix permeability are investigated for devonian gas shales from the horn river and liard basins in northeastern british columbia canada mineralogy is varied with high carbonate high quartz and moderate quartz carbonate and clay rich strata quartz content varies between 2 and 73 carbonate varies between 1 and 93 and clay varies between 3 and 33 the toc content ranges between 0 3 and 6 wt and porosity varies between about 1 and 7 for horn river basin samples quartz is mainly biogenic in origin derived from radiolarians toc content increases with the quartz content suggesting the toc and quartz both are derived from siliceous phytoplankton a positive relationship between porosity and quartz content is due to the positive relationship between quartz and toc matrix permeability parallel to bedding varies between 7 5e 02 and 7 1e 07 md at an effective stress of 15 mpa variation in permeability is due to a complex combination of factors that includes origin and distribution of minerals pore size distribution and fabric mercury intrusion capillary curves indicate that the higher matrix permeability values 2e 03 md occurs in samples that contain interconnected pore apertures greater than 16 m even when these samples may contain less macropores than low permeability samples the fabric of high permeability samples can be either isotropic or anisotropic however permeability of anisotropic samples is more sensitive to changes in effective stress than isotropic samples more highly anisotropic samples contain moderate amounts of quartz carbonate and in some clay high permeability samples that contain a more balanced ratio between micro meso and macroporosity would not only have faster flow rates but also greater access to sorbed gas within the microporosity compared to samples that lack mesopores several muskwa samples compared to evie and besa river samples contain higher quartz moderate clay and high toc content coupled with high permeability less sensitivity to effective stress and balanced ratios between micro meso and macroporosity would be a lower exploration risk due a greater propensity to fracture the ability to produce and store hydrocarbons due to higher toc contents and greater communication between macropores and micropores in the organic and clay fractions

the pore structural evolution of the marcellus and mahantango shales appalachian basin abstract the generation and primary migration of hydrocarbons in organic rich shale leaves void space in organic matter which is the porosity associated with organic matter commonly observed under scanning electron microscope sem in this study middle devonian black shale core samples were collected from three wells penetrating the organic rich marcellus shale and the organic lean mahantango formation in pennsylvania and west virginia pyrolysis ion milled sem and low pressure nitrogen adsorption analysis were conducted to investigate the organic richness and the properties of the pore system vitrinite reflectance ro values in the range of 1 36 2 89 represent a maturity spectrum covering the wet gas to post mature zones in general the pore system is composed of organic matter hosted pores and mineral hosted pores however the dominant pore types and pore sizes vary stratigraphically across lithology and abundance of organic matter all the organic matter observed in this study shows an amorphous occurrence pore space between mineral grains both silt size and clay size can be filled by organic matter which contains secondary porosity generated by thermal cracking of kerogen mineral hosted pores are concentrated in organic lean samples in which secondary organic matter could not fill most of the primary pore space the destruction of primary mineral hosted pores and the generation of secondary organic matter hosted pores were observed toc values show positive correlations with the porosity specific surface area and the abundance of micropores increasing thermal maturity correlates with a significant decrease of pore volume and surface area primarily through diminishing or vanishing of micropores the richness and thermal maturity of organic matter in organic rich devonian shale can be effective parameters for evaluation of reservoir quality and upscaling the appraisal

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

cenozoic evolution of continental humidity and paleoenvironment deduced from the kaolinite content of oceanic sediments abstract the distribution of detrital kaolinite in cenozoic sediments of the atlantic and west pacific oceans has been used to reconstruct the variations of the continental humidity and associated paleoenvironmental factors five stages have been recognized 1 1 during the late oligocene chattian c 30 m y p21 and np24 increased kaolinite content at every site marked an increase of global humidity 2 2 during the early miocene aquitanian c 20 m y n5 n6 and nn2 nn3 increasing continental aridity is deduced from low kaolinite contents in the atlantic ocean and philippine sea 3 3 during the middle miocene langhian c 14 m y n10 n12 and nn5 nn6 increased kaolinite contents at most of the sites marked a further increase of global humidity which was especially important at low latitudes in africa 4 4 during the late miocene tortonian c 10 m y n16 and nn10 nn11 kaolinite content and inferred continental humidity increased toward high latitudes but decreased toward low latitudes especially off tropical africa where it marked the development of arid conditions 5 5 during the late pliocene piacenzian c 3 m y nn15 nn16 kaolinite content and humidity increased again toward high latitudes while these conditions decreased again toward low latitudes emphasizing the latitudinal climatic zonation periods of increasing humidity show good correlation with the development of polar ice locally volcanism tectonic activity oceanic circulation and migration of lithospheric obliterated the climatic significance of clay mineral associations which therefore express complementary aspects of the continental and marine paleoenvironments

evidences for disruption of a crystallizing front in a magma chamber during caldera collapse an example from the breccia museo unit campanian ignimbrite eruption italy abstract this work is focused on juvenile components and some cognate xenoliths of the breccia museo bm unit the bm is a coarse grained proximal unit of the caldera forming phase of the ignimbrite campana ic eruption southern italy the bm products show some peculiar characteristics that distinguish them from the other ic deposits in particular different types of pumice fragments constitute the juvenile fraction and their crystal contents are remarkably higher than the other ic units slightly porphyritic and highly porphyritic trachytic to phonolitic pumices were distinguished in each sample and investigated separately for mineralogy matrix glass composition melt and fluid inclusion studies most feldspar crystals may have formed at the margins of the magma chamber and the crystal content of both types of pumice fragments can be ascribed to variable entrainment of these crystals from the solidification front by the melt variably porphyritic

shale gas play risk of the lower cambrian on the yangtze platform south china this paper describes the establishment of shale gas play risk workflow and discusses the major geologic risks for the lower cambrian shale gas play on the yangtze platform the shale gas play risk is assessed by considering the probability of occurrence po of hydrocarbon charge reservoir and retention hcrr of a shale gas play the po of each of these three factors is determined according to geological understanding and data availability the risk of these factors is categorized into high risk po 0 3 relatively high risk 0 3 3 5 and poor hydrocarbon retention are the key geologic risks of the lower cambrian shale gas play uncertainty is inherent in the play risk assessment owing to sparse well data coverage understanding the play risks and uncertainties warrants further study of the impact of extremely high thermal maturities and burial history and how it facilitates decision making for exploration investment

oxygen isotope geochemistry of pyroclastic clinopyroxene monitors carbonate contributions to roman type ultrapotassic magmas the oxygen isotope geochemistry and chemical composition of clinopyroxene crystals from alban hills pyroclastic deposits constrain the petrological evolution of ultrapotassic roman type rocks volcanic eruptions in the 560 35 ka time interval produced thick pyroclastic deposits bearing clinopyroxene phenocrysts with recurrent chemical characteristics clinopyroxenes vary from si mg rich to al fe rich with no compositional break indicating that they were derived from a continuous process of crystal fractionation based on the 18o and trace element data no primitive samples were recovered monomineralic clinopyroxene cumulates set the oxygen isotope composition of primary magmas in the range of uncontaminated mantle rocks 5 5 but their ree composition resulted from extensive crystal fractionation departing from these mantle like 18ocpx values the effects of crustal contamination of clinopyroxene o isotope composition were identified and used to monitor chemical variations in the parental magma 18o values in si mg rich clinopyroxene are slightly higher than typical mantle values 5 9 6 2 and the low ree contents are representative of early stages of magmatic differentiation 18o values as high as 8 2 are associated with al fe3 rich clinopyroxene showing high ree contents these 18o values are characteristic of crystals formed during the late magmatic stages of each main eruptive phase geochemical modelling of 18o values vs trace element contents indicates that these ultrapotassic magmas were derived from fractional crystallization plus assimilation of limited amounts of carbonate wall rocks starting from a primary melt and from interaction with co2 derived from country rocks during crystal fractionation

continental and marine paleoenvironments reflected by west pacific clay sedimentation various stratigraphic and paleoenvironmental results arise from mineralogical geochemical and micromorpho logical investigations on late cretaceous and cenozoic sediments recovered by the deep sea drilling project in the west pacific stratigraphic correlations the deep pelagic red clays deposited on either side of the shatsky rise contain a variety of clay minerals which point to the importance of eolian detrital supply and allow rough stratigraphic correlations climate and paleocirculation neogene sediments of the lord howe rise area reflect closely the relationship between the evolution of the antarctic ice sheet and related aridification stages and the atmospheric and oceanic circulation pattern since 14 my regional and global tectonics the post eocene deposits around new zealand express a sequence of tectonic events and of relaxation stages associated with changes in the circulation regime along the inner wall of the japan trench clay mineral successions document the existence of an outer continental landmass until the late oligocene its collapse associated with volcanism close to the paleogene neogene boundary and an increased detrital influence from japan since the early middle miocene volcanism diagenesis and detrital supply the aptian to maastrichtian sediments in the mariana basin document a complex sequence of geochemical and geodynamical events proximal volcanism and local supply from subaerial archipelagoes early marine diagenesis during lithospheric subsidence and plate migration and finally the occurrence and evolution of terrigenous input from distant sources distributed by marine currents

foraminiferal and nannofossil paleoecology and paleoceanography of the cenomanian turonian eagle ford shale of southern texas article i nfo the uppercretaceous of central texas isdominated by a broad shallow carbonate platformcalled thecomanche platform that occupies an important gateway between the epeiric western interior seaway wis of north america to the open marine gulf of mexico tethys we investigated the cenomanian turonian eagle ford shale on and adjacent to the comanche platform to determine whether the eagle ford shale has an affinity with the western interior and if so determine where the transition from western interior to open ocean is located we were also interested in the relationship if any between the organic rich facies of the eagle ford and oceanic anoxic event 2 oae2 our work is based on quantitative foraminiferal population counts and associated sedimentary particles including inoceramid prisms sand glauconite and pyrite grains calcareous nannofossil assemblages carbon isotopes and total organic carbon toc from three sites across a range of paleowater depths an outcrop in lozier canyon in terrell county west of langtry tx an outcrop at bouldin creek outside of austin tx and swift energy s fasken a 1h core in webb county tx the highest toc intheeagle ford occurs beforethe onset of oae2 6 at loziercanyon 7 atboth bouldincreek and the fasken core and then declines steadily through the rest of the section except for a small increase at the end of oae2 at lozier and a fairly large post oae2 increase at bouldin creek nannofossil paleoproductivity indicators zeugrhabdotusand biscutum track tocatbouldincreekandinthefaskencoreanddisplaysimilar trends to those observed inthe western interior seawayto the north benthic foraminiferalabundances increase astoc decreasesand the lithology shifts from laminatedblack shale to bioturbatedlight gray shale low oxygen tolerant infaunal neobulimina spp appear first and gradually increase in abundance epifaunal benthics appear soon after this oxygenation trend continues through the oae2 interval and the upper eagle ford contains a diverse epi and infaunal benthic foraminiferal assemblage and macrofossil assemblage this trend of decreasing toc and nannofossil paleoproductivity indicators coupled with increasing benthic foraminiferal abundance and diversity and seafloor oxygenation corresponds to rising sea level based on foraminiferal and nannofossil events toc trends and changes in lithology both platform sites have a strong affinity with the western interior with lozier canyon being the most similar the fasken core bears all the characteristics of an open ocean site except for the fact that peak toc occurs before oae2 this suggests that the oceanographic boundary between wis and tethys can be placed on the edge of the comanche platform productivity was likely driven by bathymetry induced upwelling caused by restriction between the wisand tethys during times of low sea level as sea level rose upwelling diminished and productivity decreased this explains why the fasken core adjacent to the platform margin and in the center of this upwelling zone displays the same toc trends as the platform sites organic carbon content in the seaway was controlled by stratification and enhanced preservation but this was also reduced by rising sea level which is why the two areas show parallel trends

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

distribution and origin of clay minerals in surficial shelf sediments western north island new zealand abstract western shelf surficial sediments are mainly terrigenous muds and variably muddy fine and very fine sands of mixed modern relict heritage overall their clay fraction is dominated by illite and smectite lesser amounts of chlorite and mixed layer clays and some kaolinite the close similarity of shelf clay mineral assemblages with those in adjacent river and harbour sediments demonstrates that offshore north south regional trends in clay mineralogy parallel regional changes in onshore geology involving both western north island and more distant northwestern south island sources the same detrital clay mineral patterns on the shelf have persisted during the sea level rise following the last glaciation and are complicated only by local concentrations of authigenic smectite from volcanogenic material on the basis of the distribution and origin of the major clay minerals five north south clay petrologic zones occur on the shelf 1 hamilton shelf abundant smectite and common poorly crystalline illite primarily detrital from oligocene mudstones some smectite authigenic from quaternary volcanogenic material 2 north taranaki shelf abundant crystalline illite and common mixed layer clays and crystalline chlorite primarily detrital from miocene mudstones 3 central taranaki shelf abundant crystalline illite and common smectite and chlorite smectite is authigenic from egmont derived andesitic material contemporaneous with deposition of detrital illite and some chlorite derived from northwestern south island via the westland current and from adjacent shelf zones 4 south taranaki shelf abundant crystalline illite and chlorite detrital via the westland current from northwestern south island rivers that drain an actively eroding granitic schistose provenance and 5 north cook strait basin abundant crystalline illite and common mixed layer clays and crystalline chlorite detrital from pliocene quaternary mudstones of the south taranaki wanganui region as well as from northwestern south island sources via the d urville current

clinopyroxene liquid trace element partitioning in natural trachyte trachyphonolite systems insights from campi flegrei southern italy trace element partition coefficients between clinopyroxenes and associated glassy matrix cpx l d have been determined for 13 ree hfse4 5 u th sr pb sc and v from combined la icp ms emp analyses in selected trachytes and trachyphonolites from campi flegrei composition of clinopyroxene and glass is pretty homogeneous in the trachyphonolites pointing to an overall attainment of the equilibrium conditions in trachytes conversely phases show some compositional heterogeneity due to the presence of clinopyroxene xenocrysts that requested a more careful petrographic and geochemical inspection of the samples to assess the equilibrium clinopyroxene composition in the trachyte clinopyroxenes ree are compatible from nd to lu cpx l d up to 2 9 like y ti sc and v the cpx l d for eu is lower than those of the adjacent ree highlighting eu2 contribution high d values are also shown by u th pb zr hf nb and ta relatively to basaltic and andesitic systems whereas the d sr is roughly similar to that found for less evolved magmas trachyphonolites are characterized by an overall decrease of the cpx l d for highly charged cations with the exception of v and by a slight increase of d sr ree are still compatible from nd to lu cpx l d up to 2 1 like ti y sc and v this variation is also predicted for ree and y by models based on the elastic strain theory being consistent with the slightly lower polymerization degree estimated for the trachyphonolites however the observed cpx l d ree y are matched by the modelled ones only considering very low t 825 c which are believed unlikely this mismatch cannot be attributed to effects induced by the water rich composition of the trachyte trachyphonolite suite since they would lower the observed cpx l d ree y moreover the anomalous inflections of measured cpx l d for hree suggests some crystal chemical control such as the entrance of these elements in a site distinct from m2 it is concluded that the large cpx l d determined for trachytes and trachyphonolites are likely induced by hitherto unconstrained changes of the z3 activities related to the composition of melt and or solid all these considerations strongly highlight the importance of a direct characterization of trace element partitioning in natural samples from magmatic systems poorly characterized by experimental studies

grain assemblages and strong diagenetic overprinting in siliceous mudrocks barnett shale mississippian fort worth basin texas porosity permeability and total organic carbon toc in a heterogeneous suite of 21 high maturity samples vitrinite reflectance 1 52 2 15 from the barnett shale in the eastern fort worth basin display few correlations with parameters of rock texture fabric and composition these factors being mostly obscured by the effects of a protracted history of diagenesis diagenesis in these rocks includes mechanical and chemical modifications that occurred across a wide range of burial conditions compaction and cementation have mostly destroyed primary intergranular porosity the porosity average 5 vol by gas research institute helium porosimetry and pore size 8 nm median pore throat diameter are reduced to a degree such that pores are difficult to detect even by imaging ar ion milled surfaces with a field emission scanning electron microscope the existing porosity that can be imaged is mostly secondary and is localized dominantly within organic particulate debris and solid bitumen the grain assemblage is highly modified by replacement a weak pattern of correlation survives between bulk rock properties and the ratio of extrabasinal to intrabasinal sources of siliciclastic debris higher porosity permeability and toc are observed in samples representing the extreme end members of mixing between extrabasinal siliciclastic sediment and intrabasinal derived biosiliceous debris reservoir quality in these rocks is neither more strongly nor more simply related to variations in primary texture and composition because the interrelationships between texture and composition are complex and importantly the diagenetic overprint is too strong

application of proton microprobe data to trace element partitioning in volcanic rocks abstract in situ proton microprobe analyses are used to calculate partition coefficients d for mn fe cu zr ga rb sr y zr ba and pb and more restricted data for ni ge nb and as in pyroxenes olivines biotites hornblendes feldspars and fe ti oxides from 32 volcanic rocks all with glassy matrices these range from leucitite and picritic basalt to high silica and peralkaline rhyolites data for pigeonite aenigmatite allanite and leucite are included where these occur as additional phases coefficients have also been rayleigh fractionation corrected this correction being significant for those elements with high coefficients in specific mineral phases and where pronounced crystallisation has occurred partition coefficients are presented as plots vs nbo t ratios of coexisting glasses melts negative correlations are observed based on log transformed data for mn zn fe and y pyroxenes mn zn and fe olivines mn and zn fe ti oxides nb y sr and zr hornblendes sr plagioclase and ba cu zn and fe feldspars these element partition coefficients are not correlated with bulk mineral compositions zr and ga are not correlated with either glass or mineral compositions except zr in hornblende the correlations support the role of melt polymerisation in controlling element partitioning at least for those elements listed although possible effects of temperature cannot be uniquely isolated in the present data set the coefficients presented here are generally consistent with published values for equivalent rock compositions one difference being that some of the higher published coefficients e g sr in plagioclase are not matched in the present data set from a practical viewpoint the relative regularity of the coefficient data presented does facilitate choice of relevant coefficient values that are required for petrogenetic modelling procedures

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

geochemical controls on shale microstructure the uptick in hydrocarbon production from shale in the united states has generated interest in metrics of unconventional reservoir quality like permeability we use conventional gas sorption to characterize shale microstructure which provides insight on the features that govern mass transport the gas sorption data are analyzed to determine the surface area a s m2 g and pore volume v p cm3 g of 30 samples from basins across north america with this information we quantify the effect of composition and thermal maturity on shale microstructure in particular we find that the specific surface area of the organic component evolves from 50 m2 g total organic carbon toc in immature shale to 500 m2 g toc for regions that produce dry gas the increase in a s is accompanied by an increase in v p and concomitant decline in average pore size e g r h 4 v p a s we contend that the latter is due to the development of nanometer sized pores in kerogen as it is converted to mobile hydrocarbon which is ultimately expelled this hypothesis is supported by similar measurements on companion samples after bitumen extraction or combustion which underscore the intimate spatial association of petroleum and kerogen coupled with information on accessibility to the porosity garnered by varying the particle size these results establish a clear link between organic matter thermal maturity and reservoir quality in unconventional shale systems

a 2400 yr record of natural events and anthropogenic impacts in intercorrelated terrestrial and marine sediment cores waipaoa sedimentary system new zealand the waipaoa sedimentary system spans 100 km from terrestrial upland to continental rise alluvial buffering has little effect on sediment flux at the outlet of this mesoscale dispersal system and hinterland to margin transport is accomplished rapidly because of this synergy the floodplain and shelf depocenters are sensitive to changes in sediment production in the hinterland and natural and anthropogenically forced changes in sediment source dynamics that occur at several temporal and spatial scales leave distinctive signals in the stratigraphic record manifested as variations in sediment properties these signals appear in intercorrelated sediment cores from a headwater riparian storage area and the major terrestrial and marine repositories for sediment discharged during the past 2 4 k y the signals represent the landscape response to vegetation and land use change short term fluctuations in climate that affect surface properties and processes and extreme storms and subduction thrust earthquakes extreme storms are the minimum geomorphologically effective event preserved in the sediment records lower magnitude storms that are integral components of the prevailing hydrometeorological regime create high frequency fluctuations in sediment properties and collectively contribute to event sequences of 100 yr duration events and event sequences comprise a hierarchy of temporally sensitive phenomena the impacts of which are conditioned by frequency and magnitude by contrast vegetation disturbance is a spatially sensitive phenomenon that directly impacts sediment source areas and lowers the threshold of landscape sensitivity to erosion for this reason the taupo eruption of 1 718 ka and the piecemeal vegetation changes that occurred after the arrival of polynesian settlers also generated strong depositional signals after european colonization deforestation of the hinterland altered landscape sensitivity and precipitated the transition to an erosional regime that impacted sediment production and dispersal across the entire magnitude frequency spectrum of events regulating sediment delivery to and transport in stream channels no other perturbation had such a profound impact on the late holocene depositional record

characterizing the shale gas resource potential of devonian mississippian strata in the western canada sedimentary basin application of an integrated formation evaluation devonian mississippian strata in the northwestern region of the western canada sedimentary basin wcsb were investigated for shale gas potential in the subsurface thermally mature strata of the besa river horn river muskwa and fort simpson formations attain thicknesses of more than 1 km 0 6 mi encompassing an area of approximately 125 000 km2 48 300 mi2 and represent an enormous potential gas resource total gas capacity estimates range between 60 and 600 bcf section of particular exploration interest are shales and mudrocks of the horn river formation including the laterally equivalent lower besa river mudrocks muskwa formation and upper besa river formation which yield total organic carbon toc contents of up to 5 7 wt fort simpson shales seldom have toc contents above 1 wt horn river and muskwa formations have excellent shale gas potential in a region between longitudes 122w and 123w and latitudes 59n and 60n national topographic system nts 94o08 to 94o15 in this area which covers an areal extent of 6250 km2 2404 mi2 average toc contents are higher 3 wt as determined by wire line log calibrations and have a stratal thickness of more than 200 m 656 ft gas capacities are estimated to be between 100 and 240 bcf section and possibly greater than 400 tcf gas in place a substantial percentage of the gas capacity is free gas caused by high reservoir temperatures and pressures muskwa shales have adsorbed gas capacities ranging between 0 3 and 0 5 cm3 g 9 6 16 scf t at reservoir temperatures of 60 80c 140 176f whereas besa river mudrocks and shales have low adsorbed gas capacities of less than 0 01 cm3 g 0 32 scf t liard basin region because reservoir temperatures exceed 130c 266f potential free gas capacities range from 1 2 to 9 5 cm3 g 38 4 to 304 scf t when total pore volumes 0 4 6 9 are saturated with gas the mineralogy has a major influence on total gas capacity carbonate rich samples indicative of adjacent carbonate platform and embayment successions commonly have lower organic carbon content and porosity and corresponding lower gas capacity 1 toc and 1 porosity seaward of the carbonate slave point edge muskwa and lower besa river mudrocks can be both silica and toc rich up to 92 quartz and 5 wt toc and most favorable for shale gas reservoir exploration because of possible fracture enhancement of the brittle organic and siliceous rich facies however an inverse relation between silica and porosity in some regions implies that zones with the best propensity for fracture completion may not provide optimal gas capacity and a balance between favorable reservoir characteristics needs to be sought

the nature of porosity in organic rich mudstones of the upper jurassic kimmeridge clay formation north sea offshore united kingdom abstract analyses of organic rich mudstones from wells that penetrated the upper jurassic kimmeridge clay formation offshore united kingdom were performed to evaluate the nature of both organic and inorganic rock constituents and their relation to porosity in this world class source rock the formation is at varying levels of thermal maturity ranging from immature in the shallowest core samples to mature in the deepest core samples the intent of this study was to evaluate porosity as a function of both organic macerals and thermal maturity at least four distinct types of organic macerals were observed in petrographic and sem analyses and they all were present across the study area the macerals include in decreasing abundance 1 bituminite admixed with clays 2 elongate lamellar masses alginite or bituminite with small quartz feldspar and clay entrained within it 3 terrestrial vitrinite fusinite semifusinite grains and 4 tasmanites microfossils although pores in all maceral types were observed on ion milled surfaces of all samples the pores largely nanopores with some micropores vary as a function of maceral type importantly pores in the macerals do not vary systematically as a function of thermal maturity insofar as organic pores are of similar size and shape in both the immature and mature kimmeridge rocks if any organic pores developed during the generation of hydrocarbons they were apparently not preserved possibly because of the highly ductile nature of much of the rock constituents of kimmeridge mudstones clays and organic material inorganic pores largely micropores with some nanopores have been observed in all kimmeridge mudstones these pores particularly interparticle i e between clay platelets and intraparticle i e in framboidal pyrite in partially dissolved detrital k feldspar and in both detrital and authigenic dolomite are noteworthy because they compose much of the observable porosity in the shales in both immature and mature samples the absence of a systematic increase in organic porosity as a function of either maceral type or thermal maturity indicates that such porosity was probably unrelated to hydrocarbon generation instead much of the porosity within mudstones of the kimmeridge appears to be largely intraparticle and interparticle adjacent to inorganic constituents so the petroleum storage potential in these organic rich mudstones largely resides in inorganic pores

late quaternary sediment pathways through the deep ocean east of new zealand late quaternary sediment pathways through the deep ocean east of new zealand were determined using sand sized mica tracers in conjunction with physical oceanographic seismic and stratigraphic data results indicate that in glacial times micaceous sediment derived mainly from low grade metamorphic rocks of the eastern south island was delivered by rivers directly to bounty trough here turbidity currents transferred the sediment 1000 km eastward to the bounty fan on the 4500 m deep southwest pacific basin a western boundary current wbc flowing over the fan redirected the sediment 1000 km to the north and northwest where it eventually accumulated as a drift deposit near hikurangi trough the drift also received mica that had been transported 700 km along hikurangi trough from mainly plutonic sources on the northwestern south island interglacial episodes witnessed a major change in transport paths river borne sediment was diverted away from bounty trough which became a site of predominantly calcareous pelagic sedimentation denied the lateral injection of terrigenous sediment the wbc nevertheless continued to supply small quantities of mica to the drift through erosion of existing glacial deposits on the bounty fan the paucity of interglacial mica on the drift indicates it is also receiving little terrigenous sediment by way of hikurangi trough

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

distinct evolution trends of nanometer scale pores displayed by the pyrolysis of organic matter rich lacustrine shales implications for the pore development mechanisms abstract organic matter om compositions greatly affect hydrocarbon generation and expulsion processes which are critical for the organic porosity development in shale lacustrine shale samples of low thermal maturity were pyrolyzed using two pyrolysis systems closed and semi closed systems pore development was measured by low pressure gas adsorption and field emission scanning electron microscopy fe sem and bulk porosity was modeled utilizing organic geochemical data the gas adsorption analysis indicated that shale samples of different om compositions differed in pore volume evolution with thermal maturity mainly related to the different amounts of hydrocarbon generated and expelled residual bitumen significantly reduced the pore volume of om rich oil generative shale samples and restricted the micro meso and macro pore volumes to different extents calculations and experiments both showed that om rich and oil generative shale experienced a greater increase in pore volume after the oil peak in addition it was observed that variations in the main pore types were associated both with shale compositions and with exerted overburden pressure increase in overburden pressure were found to greatly facilitate the development of nanometer size spongy and complex om pores in shales containing type kerogens possibly as a result of the expulsion of gaseous hydrocarbons by contrast the shale with abundant type kerogen tended mainly to develop relatively large pores following oil expulsion regardless of overburden pressure the modeled organic porosity of pyrolyzed samples of type iii om was similar to the porosity of geological shale but the porosity of om rich oil generative shale samples with high expulsion efficiency at the oil generation stage was two to three times the measured porosity of the geological shale in some cases the higher modeled shale porosity might be related to the higher expulsion efficiency for geological shales of expulsion efficiency comparable to the pyrolyzed samples geological processes e g compaction and cementation may have greatly reduced the om associated pore volume

the crystallization of shoshonitic to peralkaline trachyphonolitic magmas in a h2o cl f rich environment at ischia italy with implications for the feeder system of the campania plain volcanoes abstract bulk rock and mineralogical characterization of massive samples lava flows lava domes scoria spatter chosen to be representative of different activity periods and of the whole known compositional range of ischia island roman magmatic province campanian district is reported in this paper the rocks vary in composition from shoshonites to peralkaline trachyphonolites crystallization started with al rich chromite inclusions and their host magnesian olivine in shoshonites and latites and ended with lavenite rinkite kochite hiortdahlite hainite mn aenigmatite britholite and ti zr rich aegirine in the groundmass of the peralkaline trachyphonolites removal of feldspar bearing assemblages with calcic to sodic plagioclase in shoshonites and latites sodic sanidine and anorthoclase in trachytes and trachyphonolites is established throughout the compositional range and is accompanied by interaction between variably evolved magmas with their differing phenocryst assemblage mostly in mafic and intermediate compositions this led to enrichment in mn alkalis zr nb ree rb th u cl and f and depletion in mg fe v ca ba sr and eu in the most evolved magmas the ischian rocks have a tendency to sodic affinity and by peculiar mineral compositions and compositional trends which do not indicate extremely oxidizing conditions the ischian rocks thus differ from the phlegrean fields analogues and the ultrapotassic more silica undersaturated rocks of somma vesuvius overall variations in the chemical compositions of the rocks and their trends imply unrelated feeding systems and thus are inconsistent with the hypothesis of a common magma reservoir beneath the main volcanic areas of the campanian plain

provenance of the detrital component of deep sea sediments from the sw pacific ocean based on mineralogy geochemistry and sr isotopic composition abstract clay mineralogy and chemical and strontium isotope compositions have been used to determine the detrital components of deep sea sediments from the sw pacific ocean continental detritus derived mainly from the new zealand landmass is characterised by high illite and chlorite contents and 87 sr 86 sr ratios close to 0 7110 this material eroded from the eastern margin of both islands is transported into deeper water by turbidity currents and hemipelagic processes and is carried northwards by the strong western boundary current as far north as the samoan basin due to the great distance from source and unfavourable prevailing winds the contribution of aeolian dust from the australian deserts to the sediment appears to be relatively small particularly in the northernmost part of the region in the vicinity of the oceanic volcanic islands of tonga samoa and the cook islands volcaniclastic material including heavy minerals pyroxene and magnetite pumice glass shards proximally and smectite clays distally is dispersed into the sediments by turbidity currents and airfall in areas of very low sedimentation distant from landmasses the sediments contain significant amounts of authigenic material rsos characterised by high concentrations of transition metals and rare earth elements strontium isotopes together with trace element compositions have proved particularly useful in determining the relative proportions of the detrital types the contrasting 87 sr 86 sr ratios and sr contents of the various source rocks permit the use of binary mixing relationships whch indicate that sediments less than 35 km from the cook islands contain 80 volcanic detritus and those more than 1200 km away contain up to 20 volcanic detritus

insights into pore scale controls on mudstone permeability through resedimentation experiments at a given porosity mudstone permeability increases by an order of magnitude for clay contents ranging from 57 to 36 2 m this increase in vertical permeability results from a dual porosity system that develops through three mechanisms 1 silt bridging preserves large pore throats 2 stress bridges inhibit clay particle alignment and 3 local clay particle compression within stress bridges alters pore throat size distribution uniaxial consolidation experiments on resedimented clay silt mixtures illuminate how permeability varies as a function of clay fraction during burial backscattered electron microscope images show that silty mixtures have larger pore throats and fewer aligned clay particles than do more clay rich mixtures we describe the permeability of clay silt mixtures with a geometric mean model our method provides a promising framework for modeling of mudstone permeability as a function of clay fraction and porosity how permeability and consolidation evolve during burial affects the ability of mudstones to seal co2 and hydrocarbons in the subsurface how mudstones behave as gas reservoirs and under what conditions mudstones will be overpressured dual porosity systems have fundamentally different transient flow and solute transport behaviors

an efficient consistent and trackable method to quantify organic matter hosted porosity from ion milled scanning electron microscope images of mudrock gas reservoirs to precisely quantify pore space and organic matter om from two dimensional scanning electron microscope sem images an efficient and consistent workflow using adaptive local thresholding otsu thresholding and image calculator are presented it can offer an automated segmentation of pore space and om then differentiates the porosity hosted by om and minerals the workflow is demonstrated on a widely distributed set of core samples from mahantango and marcellus shale units of the appalachian basin the vitrinite reflectance of these samples ranges from 1 36 to 2 89 covering a spectrum of thermal maturity organic matter abundance and mineralogy also vary significantly the results are compared with routine rock property tests such as helium porosimeter gas research institute method and total om the proposed workflow improves quantitative determination of porosity above a certain pore size and om in shale samples advantages of this workflow include improved consistency and speed of analysis of sem images of shale samples at the nanoscale

geochemical evolution of organic rich shales with increasing maturity a stxm and tem study of the posidonia shale lower toarcian northern germany hydrocarbon generation and retention processes occurring within gas shales as a response to increases in thermal maturation are still poorly constrained while efforts have been directed at unravelling the resource potential composition and textures of these economically important unconventional systems their spatial variability in chemistry and structure is still poorly documented at the sub micrometer scale here we have characterized samples of the lower toarcian posidonia shale samples from northern germany at varying stages of thermal maturation using a combination of compositional organic geochemistry and spectromicroscopy techniques including synchrotron based scanning transmission x ray microscopy stxm we document geochemical and mineralogical heterogeneities down to the nanometer scale within the investigated samples as a function of their level of thermal maturity in particular authigenic albite crystals containing nanometric halite inclusions have been documented within the investigated mature and overmature samples the presence of such tracers of palaeobrine carbonate interactions supports a maturation scenario for the lower toarcian posidonia shale intimately related to ascending brine fluids rather than a maturation scenario solely resulting from high heat flows in addition various types of asphaltene and nso rich bitumen have been detected within the same samples very likely genetically derived from thermally degraded organic precursors furthermore the formation of nanoporous pyrobitumen has been inferred for samples of gas window maturity likely resulting from the formation of gaseous hydrocarbons by providing in situ insights into the fate of bitumen and pyrobitumen as a response to the thermal evolution of the macromolecular structure of kerogen the results reported here constitute an important step towards better constraining hydrocarbon generation processes during natural shale gas maturation

constraining the recent plumbing system of vulcano aeolian arc italy by textural petrological and fractal analysis the 1739 a d pietre cotte lava flow 1 the 1739 a d pietre cotte lava flow is part of a sequence of low explosive to weak effusion events occurred at la fossa cone the active vent on vulcano island aeolian arc italy this lava is rhyolitic texturally heterogeneous and contains lati trachytic enclaves these compositions are recurrent in the la fossa volcanic products and are representative of the recent vulcano plumbing system the host lava is vesicular relatively phenocryst free and locally contains microlites and millimeter sized spherulites the enclaves are up to 10 cm in size display angular to spherical shapes and can form the core of spherulites enclaves mostly consist of plagioclase and augitic phenocrysts set in a weakly vesicular groundmass characterized by variable abundance of glass and feldspar microlites field textural and fractal data allow us to constrain the rheological features of the rhyolitic and lati trachytic magmas in situ major trace and volatile element analyses provide evidence for heterogeneities in the glassy matrix and zoning of phenocrysts processes of magma evolution have been quantitatively constrained by using the apparent distribution ratios of trace elements measured between mineral phases and glassy matrices the collected data in combination with petrological and fluid inclusion data from the literature provides evidence for 1 a genetic relationship between the two magmas through assimilation fractional crystallization process 2 a mingling mechanism between an uprising rhyolitic magma and a shallower partly crystallized lati trachytic magma plug 3 the desegregation enclaves at variable scales of the lati trachyte within the rhyolite and 4 the possible eruptive scenarios consequent to a future magmatic unrest

marine magnetic signature of the last glacial maximum and last deglaciation from the southern hemisphere mid latitudes abstract an environmental magnetic record is presented from piston core tan0712 23 collected on the southern flank of challenger plateau at a water depth of 2817 m magnetic grain size and concentration variations during the last glacial maximum lgm are interpreted to reflect variations in terrestrial influx corresponding to glacial advance and stagnation events on millennial time scales the lgm signal between 25 and 23 ka demonstrates an antiphase relationship with northern hemisphere records implying that the bipolar seesaw was active during that period the number and timing of features in tan0712 23 suggest that lgm millennial scale climate fluctuations are strongly realized in the mid latitudes possibly due to amplification by regional forcing mechanisms the onset of the deglacial magnetic signal defined by a low concentration of magnetic minerals is constrained at 18 6 cal ka bp by the radiocarbon age model and corresponds to southward migration of the southern hemisphere westerly wind system and subtropical front

pore scale modeling of electrical resistivity and permeability in fib sem images of organic mudrock abstractwe have developed a new pore scale method to quantify petrophysical properties of hydrocarbon hc bearing shale recent studies indicate that slip flow knudsen diffusion langmuir desorption and diffusion in kerogen contribute to the unconventional production properties of shale gas formations conventional petrophysical interpretation methods do not account for the aforementioned phenomena and are often inconclusive when estimating petrophysical properties in shale formations we constructed a pore scale representation of the lower eagle ford shale based on focused ion beam scanning electron microscope fib sem images permeability is calculated via previously developed finite difference methods for the cases with and without slip flow and knudsen diffusion the method also calculates streamlines to describe sample pore connectivity weighted throat size distributions are defined based on streamlines to represent the most resistive paths for fluid flow in the fib sem image subsequently perm

volatile element zonation in campanian ignimbrite magmas phlegrean fields italy evidence from the study of glass inclusions and matrix glasses the distribution of h2o f cl and s in the campanian ignimbrite ci magma chamber was investigated through study of primary glass inclusions and matrix glasses from pumices of the plinian fall deposit the eruption fed by trachytic to phono trachytic magmas mainly produced a trachytic non welded to partially welded tuff underlain by a minor cogenetic fallout deposit the entire chemical variability of the eruptive products is well represented in the pumices of the plinian fall deposit which we divide into a basal lower fall unit lfu and an overlying upper fall unit ufu primary glass inclusions were only found in clinopyroxenes associated with the lfu pumice and contain a mean of 1 60 0 32 wt h2o analysed by ftir 0 11 0 08 wt f 0 37 0 03 wt cl and 0 08 0 04 wt so3 emp analysis co2 concentrations were below the ftir detection limit 10 20 ppm the coexisting matrix glasses contain similar amounts of halogens and sulfur but less water 0 60 wt partially degassed matrix glasses from ufu pumices contain a mean of 0 30 0 02 h2o 0 28 0 10 f 0 04 0 02 so3 and 0 80 0 04 wt cl to reconstruct the total amount of volatiles dissolved in the most evolved trachytes we have used experimental solubility data and mass balance calculations concerning the amount of crystal fractionation required to produce the most evolved trachyte from the least evolved trachyte these yield an estimated pre eruptive magma volatile content h2o cl f of 5 5 wt for the most evolved magmas on the basis of new determinations of cl solubility limits in hydrous trachytic melts coexisting with an aqueous fluid phase hydrosaline melt brine we suggest that the upper part of the magma chamber which fed the ci eruption was fluid s saturated and at a minimum depth of 2 km variations in eruptive style plinian fallout pyroclastic flows do not appear to be related to significant variations in pre eruptive volatile contents

timing of magma extraction during the campanian ignimbrite eruption campi flegrei caldera a core drilled within the northern part of the city of napoli has offered the unique opportunity to observe in one single sequence the superposition of the four pyroclastic flow units emplaced during the campanian ignimbrite ci eruption such a stratigraphic succession has never been encountered before in natural or in man made exposures therefore the ci sequence was reconstructed only on the basis of stratigraphic correlations and compositional data in literature the occurrence of four superposed ci flows together with all the data available in literature allowed us to better constrain the chemical stratigraphy of the deposit and the compositional structure of the ci magma chamber the ci magma chamber includes two cogenetic magma layers separated by a compositional gap the upper magma layer was contaminated by interaction with radiogenic fluids the two magma layers were extruded either individually or simultaneously during the course of the eruption in the latter case they produced a hybrid magma but no evidence of input of new geochemically and isotopically distinct magma batches just prior or during the eruption has been found comparison with the exposed ci deposits has permitted reconstruction of variable eruption phases and related magma withdrawal and caldera collapse episodes the eruption was likely to have began with phreatomagmatic explosions followed by the formation of a sustained plinian eruption column fed by the simultaneous extraction from both magma layers towards the end of this phase the upward migration of the fragmentation surface and the decrease in magma eruption rate and or activation of fractures formed an unstable pulsating column that was fed only by the most evolved magma layer this plinian phase was followed by the collapse of the eruption column and the beginning of caldera formation at this stage expanded pyroclastic flows fed by the upper magma layer in the chamber generated during the following major caldera collapse episode the maximum mass discharge rate was reached and both magma layers were tapped generating expanded pyroclastic flows towards the end of the eruption only the deeper and less differentiated magma layer was tapped producing more concentrated pyroclastic flows that traveled short distances

porosity of devonian and mississippian new albany shale across a maturation gradient insights from organic petrology gas adsorption and mercury intrusion the evolution of porosity in shales with increasing maturity was examined in a suite of five new albany shale samples spanning a maturity range from immature vitrinite reflectance ro 0 35 to postmature ro 1 41 devonian to lower mississippian new albany shale samples from the illinois basin used in this study contain marine type ii kerogen having total organic carbon contents from 1 2 to 13 0 wt organic petrology co2 and n2 low pressure adsorption and mercury intrusion capillary pressure techniques were used to quantify pore volumes pore sizes and pore size distributions increasing maturity of the new albany shale is paralleled by many changes in the characteristics of porosity the total porosity of 9 1 vol in immature new albany shale decreases to 1 5 vol in the late mature sample whereas total pore volumes decrease from 0 0365 to 0 0059 cm3 g in the same sequence reversing the trend at even higher maturity the postmature new albany shale exhibits higher porosity and larger total pore volumes compared to the late mature sample with increasing maturity changes in total porosity and total pore volumes are accompanied by changes in pore size distributions and relative proportions of micropores mesopores and macropores porosity related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition but maturity exerts the dominant control upon these characteristics we conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences

a dual porosity model for evaluating petroleum resource potential in unconventional tight shale plays with application to utica shale quebec canada unconventional tight to shale reservoirs vary from tight sandstone siltstone to organic rich mudstone shale commonly with mixed lithologies in such reservoir systems matrix pores and organic pores with different origins and distinct physical and chemical properties co exist for hydrocarbon storage traditional resource assessment methods designed for conventional reservoirs cannot handle the two pore systems properly this study proposes a dual porosity model to respond to the need for a new method in assessing hydrocarbon resource potential in such reservoir systems the dual porosity model treats the two types of pores separately and derives the resource estimates from different sources of data thus better characterizing unconventional reservoirs with complicated pore systems the new method also has the flexibility of assessing resource potential for the entire spectrum of mixed lithologies ranging from a complete tight to a pure source rock organic rich shale mudstone reservoir the proposed method is illustrated through the assessment of the in place petroleum resource potential in the upper ordovician utica shale of southern quebec canada the results of the application suggest that the proposed approach effectively handles the two pore systems in tight shale reservoirs effectively and provides a useful tool for estimating resource potential in unconventional plays

organic rich marcellus shale lithofacies modeling and distribution pattern analysis in the appalachian basin the marcellus shale is considered to be the largest unconventional shale gas resource in the united states two critical factors for unconventional shale reservoirs are the response of a unit to hydraulic fracture stimulation and gas content the fracture attributes reflect the geomechanical properties of the rocks which are partly related to rock mineralogy the natural gas content of a shale reservoir rock is strongly linked to organic matter content measured by total organic carbon toc a mudstone lithofacies is a vertically and laterally continuous zone with similar mineral composition rock geomechanical properties and toc content core log and seismic data were used to build a three dimensional 3 d mudrock lithofacies model from core to wells and finally to regional scale an artificial neural network was used for lithofacies prediction eight petrophysical parameters derived from conventional logs were determined as critical inputs advanced logs such as pulsed neutron spectroscopy with log determined mineral composition and toc data were used to improve and confirm the quantitative relationship between conventional logs and lithofacies sequential indicator simulation performed well for 3 d modeling of marcellus shale lithofacies the interplay of dilution by terrigenous detritus organic matter productivity and organic matter preservation and decomposition affected the distribution of marcellus shale lithofacies distribution which may be attributed to water depth and the distance to shoreline the trend of normalized average gas production rate from horizontal wells supported our approach to modeling marcellus shale lithofacies the proposed 3 d modeling approach may be helpful for optimizing the design of horizontal well trajectories and hydraulic fracture stimulation strategies

high resolution stratigraphy and facies architecture of the upper cretaceous cenomanian turonian eagle ford group central texas rock based studies of the eagle ford group of central texas demonstrate that mudrock deposition is more complicated than previously supposed x ray diffraction x ray fluorescence total organic carbon toc and log data collected from eight cores and two outcrops demonstrate that bottom current reworking and planktonic productivity are primary depositional controls acting independently from eustatic forcing central texas eagle ford facies include 1 massive argillaceous mudrock 2 massive foraminiferal calcareous mudrock 3 laminated calcareous foraminiferal lime mudstone 4 laminated foraminiferal wackestone 5 cross laminated foraminiferal packstone grainstone 6 massive bentonitic claystone and 7 nodular foraminiferal packstone grainstone high degrees of lateral facies variability characterized by pinching and swelling of units lateral facies changes truncations and locally restricted units are observed even at small lateral scales 50 ft 15 m at 10 mi 16 km and greater lateral spacings core and geochemical data significantly underestimate intraformational facies variability approximately 73 of units can be successfully correlated across a distance of 500 ft 152 m 35 are traceable across 1 mi 1 6 km and only 16 of beds are correlative across 10 mi 16 km geochemical proxies enrichment in molybdenum and other trace elements indicate that maximum anoxia occurred within the bouldin member despite being composed of the most calcareous and high energy facies comparison of total gamma ray gr logs to computed gr logs is requisite because gr alone may provide misleading determination of facies toc content depositional environment and sequence stratigraphic implications

pore characteristics of lacustrine shale within the oil window in the upper triassic yanchang formation southeastern ordos basin china abstract organic matter om rich shale in the yanchang formation is recognized as a promising hybrid shale oil shale gas system in lacustrine strata in china being mainly in the oil window both the type and distribution of the pores in the shale have been affected by several factors including petroleum expulsion and retention mineral and organic composition and compaction to obtain a better understanding of the factors controlling om pore development 10 core samples were selected with various om content from the chang 7 and chang 9 members of the yanchang formation for pore characterization the investigation combined microscopic observation both of thin sections and ion milled surfaces of samples with low pressure carbon dioxide and nitrogen adsorption and bulk porosity measurements with the main emphasis being on om associated pores the selected samples generally have relatively low total porosity with the pores being poorly connected most pore types found in marine shales were present the size of porous om is usually small mostly measuring several hundreds of nanometers to a few micrometers which suggest a general compaction effect on pore development the pore development is related to different petroleum expulsion processes shale with very porous om was a very important feature the om coexisting with fluorescent lipitinites was present in a cross linked nanofiber structure possibly related to altered extracellular polymeric substances eps by compaction and maturation various om types that varied in both size and shape did not contain any visible pores e g woody relics migrated solid bitumen and om laminae in close association with clay minerals unusually low meso and macropore volume in the sample with the highest total organic carbon toc content was confirmed by the predominance of om laminae without visible pores however abundant micropores were indicated by co 2 adsorption analysis meso and macropores in this sample had probably not developed due to a significant compaction effect due to the small numbers of studied samples these om pore characteristics need to be viewed with caution

on the effects of petrographic composition on coalbed methane sorption abstract the effect of petrographic composition on the methane sorption capacity has been determined for a suite of coals and organic rich shales subbituminous and bituminous coals were separated into bright and dull lithotypes by hand picking the methane sorption capacities range between 0 5 and 23 9 cm 3 g at a pressure of 6 mpa the low volatile bituminous canmore coal and the anthracite sample have the highest capacities with the natural coke having the lowest for low rank coals there is no significant difference between bright and dull samples except for one coal with the dull sample having a greater sorption capacity than its bright equivalent for higher rank coals the bright samples have a greater methane capacity than the dull samples and the difference between sample pairs increases with rank the boghead coal samples have the highest sorption capacities in the liptinite rich coals suite and are higher than subbituminous to medium volatile bituminous samples pore size distribution indicates that methane is held as solution gas in liptinite rich coals and by physical sorption in micropores in liptinite poor coals these contrasting processes illustrate that liptinite rich samples need to be independently assessed the positive relationship between reactive inertinite content and methane sorption capacity occurs within the subbituminous to medium volatile bituminous coals because the reactive inertinite is structurally similar to vitrinite and have a higher microporosity than non reactive inertinite reactivity of inertinite should be assessed in cbm studies of dull coals to provide a better understanding of petrographic composition effects on methane capacity

pore structure characteristics of coal bearing shale using fluid invasion methods a case study in the huainan huaibei coalfield in china abstract organic shale in coal bearing strata which was deposited in marine continental transitional and lacustrine environments is well developed in china and contains a large amount of shale gas however the present research concerning shale predominantly focuses on marine shale in this research the pore structure characteristics of coal bearing shale in the huainan huaibei coalfield in southeastern north china block were analyzed using fluid invasion methods including helium including helium pycnometry mercury intrusion porosimetry and n 2 physisorption the methodology is to determine the porosity using helium pycnometry the pore size distribution psd of pores between 0 1 m and 200 m using mercury intrusion and the psd of pores between 1 nm and 100 nm using n 2 physisorption it is worth noting that the accuracy decreases for pores less than 1 5 nm the specific surface area ssa and pore volume pv for pores between 1 nm and 200 m are calculated from interpreted psd data in addition the brunauer emmett teller bet model was used to calculate the ssa of shale pores the results indicated that 1 silt shaped pores are dominant followed by cylindrical and spherical pores 2 coal bearing shale pv is primarily from mesopores 2 50 nm and macropores 50 nm 5 m and the ssa is mainly from mesopores and micropores 2 physisorption the psd ssa and pv of pores between 1 nm and 200 m can be determined for shale which is critical to understand the shale pore structure and its effects on gas storage and flow mechanisms

trace element partitioning in pantellerites and trachytes abstract in order to investigate the effect of increasing melt peralkalinity on partitioning partition coefficients have been determined using neutron activation analyses of coexisting phenocrysts and glass of five samples from pantelleria spanning the range trachyte to pantellerite alkali feldspar partition coefficients for fe rb ba sr and eu vary with melt peralkalinity due to changes in melt polymerization and to the systematic increase in xor and decrease in xan of the feldspar in going from trachyte to pantellerite fe partition coefficients increase from 0 04 to 0 10 presumably because fe 3 increasingly substitutes in the feldspar tetrahedral site as melt activity of al declines and fe concentrations increase partition coefficients for trivalent light rees decrease and the partitioning pattern becomes flatter the most evolved samples having some of the lowest published values for feldspar the hundredfold decline in eu partition coefficients 2 5 to 0 024 and the decrease in the size of the positive partitioning anomaly are attributed to increasing eu3 eu2 in the melt as it becomes more peralkaline as well as to concomitant decrease in the ca content of feldspar as a result the behavior of eu during fractional crystallization of peralkaline suites is fundamentally different from that in metaluminous suites absolute abundances rise and the size of the negative eu anomaly changes little with fractionation beyond pantelleritic trachyte barium and strontium do not decline to extremely low concentrations in pantellerites as they do in highly evolved metaluminous rhyolites because the feldspar partition coefficients drop precipitously with peralkalinity similarly rb contents do not get large because the partition coefficient increases slightly 0 11 to 0 25 with peralkalinity and is sufficient to make rb only weakly incompatible in the feldspar dominated assemblage partition coefficients calculated for sr and ba from natural phenocryst matrix pairs can be gross over estimates in these feldspar rich felsic rocks if phenocrysts are zoned this effect is severe for assemblages with bulk distribution coefficients d greater than 4 even at very small crystal contents and for 4 d 2 it is significant if crystal contents exceed about 25 some of the very high values and much of the variability reported in the literature for ba and sr feldspar partition coefficients may be a result of this effect in contrast to feldspar partition coefficients for apatite and mafic phases change little with peralkalinity partition coefficients for rees and the compatible elements sc co and cr are all less than half those in fe rich clinopyroxene and olivine of similar composition in high silica rhyolite although absolute levels of partition coefficients are a function of melt polymerization the shapes of the ree partitioning patterns appear to be related to the composition of the clinopyroxene scandium is most strongly concentrated in clinopyroxene partition coefficient 27 60 having larger values in more fe rich compositions apatite shows a wide range in composition within the suite the concentrations of si fe rees and y increasing and mg ca and p decreasing in more evolved samples these trends however parallel those in coexisting glasses so that partition coefficients are essentially constant in peralkaline suites cs is the most incompatible of commonly analyzed elements but its great mobility during alteration and weathering limits its use as a differentiation index next in order of incompatibility are th u hf zr and ta which have small but finite values of d due to the partitioning of th and u into apatite 2 the accommodation of zr and hf by clinopyroxene 0 4 and titanomagnetite 0 2 and relatively high concentrations of ta in cossyrite and fe ti oxides the next most incompatible are the lightest and the heaviest rees and finally the middle trivalent rees and rb plots of pairs of relatively incompatible elements form straight line trends over large compositional ranges in peralkaline suites because the replacement of olivine titanomagnetite by cossyrite as the melt becomes more peralkaline causes little change in d the ree patterns of titanomagnetite and cossyrite are both approximately flat at values less than 0 1 and the relatively high titanomagnetite partition coefficients for ta 2 zr and hf when combined with the very low partition coefficients for these elements for olivine approximate the moderate partition coefficients for cossyrite

input of river derived sediment to the new zealand continental shelf i mass abstract the input of river borne sediments to the new zealand continental shelf has been calculated for all the major rivers and basins in new zealand south island yields 284 40 106 tonnes per year of sediment from a land area of 152 977 km2 and north island yields 105 9 4 106 tonnes per year from a land area of 114 621 km2 particularly high discharges are noted off the west coast of south island and east coast of north island and result in higher offshore sedimentation there the data are compatible with measured sedimentation rates on the new zealand continental shelf the specific sediment yield from south island is amongst the highest previously recorded

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

input of river derived sediment to the new zealand continental shelf ii mineralogy and composition abstract clay mineralogies and elemental compositions of river borne sediments from new zealand were examined as indicators of likely sources of the lithogenous component of sediments on the continental shelf relative occurrences of kaolin and smectite enabled the rivers to be fitted into three main groups these correspond closely with geography as follows 1 most of the rivers from north island 2 all the rivers from the north east coast of south island 3 most of the rivers from the remainder of south island elemental analyses of their sediments also led to a geographical grouping of rivers six main groups resulted from a q mode cluster analysis of elemental compositions these were the northernmost river wairoa river the east coast of north island the west coast of north island the east coast of south island the south east and west coasts of south island the west coast of south island there is substantial overlap between the groupings by clay mineralogy and by composition the results can be interpreted mainly in terms of the geologies of source areas exceptions to regional trends reflect either an unusual geology in the source areas or low sediment loads where soils contribute significantly to the sediments the terrigenous component of offshore sediments and new zealand riverine sediments have similar compositions suggesting that the former are derived in a relatively unmodified form from riverine sediments

experimental determination of ree partition coefficients between amphibole and basaltic to andesitic liquids at high pressure abstract amphibole liquid partition coefficients for the ree damph liqree obtained from natural rocks increase systematically with bulk rock compositional change from basalt to rhyolite and are higher for the middle to heavy ree five new experimentally determined sets of dree la sm eu2 ho lu and 4 published sets are similar to these data and provide values for use in geochemical modelling of magmatic processes involving amphibole over a range of temperature pressure and oxygen fugacity the partition coefficients increase significantly with decreasing temperature and increase slightly with increasing oxygen fugacity pressure does not appear to have a major effect although one data set suggests increased pressure lowers damph liqree in a basaltic composition

time dependent geochemistry of clinopyroxene from the alban hills central italy clues to the source and evolution of ultrapotassic magmas abstract we investigated chemical and isotopic compositions of clinopyroxene crystals from well age constrained juvenile scoria clasts lava flows and hypoabyssal magmatic ejecta representative of the whole eruptive history of the alban hills volcanic district the alban hills is a quaternary ultra potassic district that was emplaced into thick limestone units along the tyrrhenian margin of italy alban hills volcanic products even the most differentiated are characterised by low sio2 content we suggest that the low silica activity in evolving magmas can be ultimately due to a decarbonation process occurring at the magma limestone interface according to the liquid line of descent we propose the differentiation process is driven by crystallisation of clinopyroxene leucite apatite magnetite coupled with assimilation of a small amount of calcite and or with interaction with crustal co2 by combining age chemical data strontium and oxygen isotopic compositions and ree content of clinopyroxene we give insights into the evolution of primitive ultrapotassic magmas of the alban hills volcanic district over an elapsed period of about 600 kyr geochemical features of clinopyroxene crystals consistent with data coming from other italian ultrapotassic magmas indicate that alban hills primary magmas were generated from a metasomatized lithospheric mantle source in addition our study shows that the 87sr 86sr and lree hree of alban hills magmas continuously diminished during the 600 35 ka time interval of the alban hills eruptive history possibly reflecting the progressive depletion of the metasomatized mantle source of magmas

crystal mush reactivation by magma recharge evidence from the campanian ignimbrite activity campi flegrei volcanic field italy abstract processes of crystal mush remobilization by mafic magma recharges are often related to the outpouring of large volumes of silicic melt during caldera forming eruptions this occurred for the campanian ignimbrite ci eruption campi flegrei italy which produced a voluminous trachy phonolitic ignimbrite in southern central italy about 40 ka ago we focussed on the proximal ci deposits at san martino that are composed of a main sequence of early erupted crystal poor units and a late erupted post caldera collapse crystal rich upper pumice flow unit upfu detailed micro analytical geochemical data were performed on glasses and crystals of pyroclasts from these deposits and coupled with sr nd isotopic measurements on glasses results show that the ci eruption was fed by two distinct melts for the early erupted units and the late upfu respectively the glasses of the early erupted units have negative eu anomalies and show more evolved compositions and higher nd isotope ratios than those of the upfu which have positive eu eu the magmas of the early units formed the main volume of eruptible melt of the ci reservoir and are interpreted as having been extracted from cumulate crystal mush without a vertical geochemical gradient within the magma reservoir the data indicate that the generation of the distinctive upfu melts involved the injection of a new batch of mafic magma into the base of the ci reservoir the mafic magma allowed heating and reactivation of the ci crystal mush by melting of low or sanidines low an plagioclases leaving high an plagioclases and high mg clinopyroxenes as residual phases and a crystal mush melt made of 20 of the initial mush interstitial melt with a composition similar to the early erupted units and 80 of sanidine melt when the mush crystallinity was sufficiently reduced the mafic magma was able to penetrate into the reactivated crystal mush mixing with variable proportions of crystal mush melt and generating cooler hybrid melts which underwent further crystallization of high or sanidine at variable degrees 10 25 finally possibly a short time before the eruption the upfu magmas were able to mix and mingle with the crystal poor eruptible melts still persisting in the ci reservoir at the time of upfu emission we suggest that the complex mechanisms described for the magma evolution feeding the ci eruption may occur whenever a crystal mush is reactivated by new mafic magma inputs

a chemostratigraphic study of the campanian ignimbrite eruption campi flegrei italy insights on magma chamber withdrawal and deposit accumulation as revealed by compositionally zoned stratigraphic and facies framework abstract petrochemical analyses of juvenile samples from twenty stratigraphic sections of the campanian ignimbrite medial deposits located from 30 to 79 km from the vent are presented here sampling has accurately followed a well defined stratigraphic framework and the new component facies scheme the campanian ignimbrite succession is formed by a basal plinian pumice fall deposit overlain by a complex architecture of pyroclastic density current deposits emplaced from a single sustained pyroclastic density current through a mechanism of vertical and lateral accretion the deposit is broadly zoned from more evolved trachyte at its base to less evolved trachyte at its top and is similarly less evolved with increasing distance from the area of emission irregular chemical trends are locally observed and interpreted to represent only a limited patchy record of the entire vertical geochemical trend the petrochemical variation observed horizontally was ascribed to changes in the flow dynamics and interaction between the advancing flow and the underlying topography the results of this study were used to propose a unified volcanological petrological model for the campanian ignimbrite eruption taking into account the emplacement of both the proximal i e the breccia museo formation and medial deposits

petrogenesis and tectonic setting of the roman volcanic province italy abstract the volcanism in the roman province of italy can be modelled by the partial melting of heterogeneously enriched mantle sources the heterogeneity was created by materials derived from a subducted slab which can still be traced geophysically beneath the central apennines new petrographical and chemical data are presented for the high k calc alkaline and the shoshonitic volcanics of the campania region primary magmas are present only locally the existence of spatial zonation in the volcanism of campania is documented for the first time the shoshonitic leucite basanitic and leucititic volcanics of the phlegraean fields procida ischia and the somma vesuvius areas are at similar degrees of evolution about two times richer in nb and ba than those of northwestern campania and the latium part of the roman province accordingly distinct north western and south eastern subprovinces can be defined the evaluation of enrichment factors that is the abundance ratio between the average contents of each element in the relatively primitive lavas of the low k and the high k suites shows that the mantle sources prior to k metasomatism were different in the two sub provinces of the roman province in the north western one they resembled the sources of ocean island tholeiites and moderately enriched mor basalts in the south east they were similar to those of ocean island alkaline lavas and enriched morb s modelling based on k p ce sr rb ba th sm eu gd y nb and 87 sr 86 sr was carried out it indicates that the range of mantle sources of the volcanics in northwestern campania and latium can be modelled by the addition of 3 to 20 of materials derived by partial melting of carbonaceous pelites to a sr enriched mantle wedge comparable to the honolulu mantle source least enriched in nb the production of sr enriched mantle wedge requires either the action of fluids produced by dehydration of subducted oceanic crust or a small amount of metasomatism caused by the presence of carbonatite melts the near absence of ti ta nb yb and the highly fractionated ree in the metasomatizing component requires the presence of residual garnet and accessory ti rich minerals during the partial melting of the subducted sediments the writers propose that the mantle wedge overlying the subducted slab was hybridized by melts produced by partial fusion of subducted material derived from the continental crust probably sediments this process played a dominant role in the generation of the mantle sources from which the high k calc alkaline shoshonitic leucite basanitic and leucititic magmas of the roman province were derived

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

evidence of crystallization in residual cl f rich agpaitic trachyphonolitic magmas and primitive mg rich basalt trachyphonolite interaction in the lava domes of the phlegrean fields italy the lava domes in the northwestern cuma northern punta marmolite and central accademia parts of the phlegrean fields are the subject of this study the cuma and punta marmolite trachyphonolitic lava domes are among the oldest phlegrean products cropping out the cuma rocks have an agpaitic groundmass with early alkali feldspar fe rich clinopyroxene fe edenite and sodalite and late rosenbuschite fluorite baddeleyite pyrochlore britholite monazite aegirine often zr rich and exceptionally fe mn rich olivine the bulk rock compositions at cuma have some of the highest concentrations of zn mn zr nb th u and lanthanides among the phlegrean fields rocks and some of the lowest mgo p 2 o 5 sr eu and ba the punta marmolite dome is chemically less evolved and lacks characteristic agpaitic minerals but features alkali feldspar sodalite nepheline and relatively na poor fe rich hedenbergite with rare ca rich plagioclase xenocryst cores the accademia dome belonging to the recent activity is latitic to trachytic in composition has highly forsteritic olivine with chromiferous spinel inclusions calcic plagioclase and mg rich diopside phlogopite xenocrysts in an evolved host rock with phenocrysts and microlites of alkali feldspar fe rich clinopyroxene fe rich amphibole magnetite fe rich olivine and accessory baddeleyite zirconolite and fluorite there is clear evidence of open system magma crystallization in the form of interaction between a crystallizing primitive shoshonitic basalt in a reservoir already filled by rather evolved trachytic magma the magmatic evolution towards the evolved compositions is dominated by crystallization of more and more na rich alkali feldspar in a cl f rich and relatively h 2 o poor environment input of mafic magma is evident in many trachytic eruptions of the phlegrean fields and even in the products of the campanian ignimbrite but eruptions having mineral assemblages rich in xenocryst phases as well as eruptions virtually free of mafic magma input are also frequently observed throughout the history this suggests a variable pattern of open and closed system crystallization which may or may not be linked to explosive activity and that can be caused by intermittent supply of basaltic magma from depth

comment on formation of nanoporous pyrobitumen residues during maturation of the barnett shale fort worth basin by bernard et al 2012 abstract in their 2012 paper discussing the character of pores and organic matter in the mississippian barnett shale bernard et al 2012 identified only nonporous kerogen and nonporous solid bitumen in oil window maturity samples but nanoporous pyrobitumen in gas window maturity samples our examination of samples from the same wells shows that pores are also present in organic matter from oil window maturity samples we also argue that some of the pores we identified in gas window maturity samples are developed in organic matter that is unlikely to be pyrobitumen

a method for estimating microporosity of fine grained sediments and sedimentary rocks via scanning electron microscope image analysis this study presents a method of two dimensional scanning electron microscope image analysis that directly quantifies microporosity abundance in clay rich fine grained sediments the method is novel in that it is specifically designed to circumvent the challenge to porosity quantification posed by mineral surface charging and topographical artifacts created during ar ion cross section polishing it utilizes the finding that differences in circularity values can be used to distinguish micropores from blemishes in a thresholded image this method is powerful because it is fast and provides a direct microporosity estimation technique to augment or replace experimental data the pore size range to which the method is applicable is clear and can be selected depending on the application of the analysis when used appropriately the method can be implemented on microporous sediments and sedimentary rock in general the method is developed using marine muds of pliocene and miocene ages from the nankai margin burial depths from approximately 200 to 1100 m the close match between imaging derived microporosity and bulk n2 microporosity measurements shows that porosity in these young and relatively shallowly buried sediments is dominated by pores of sizes that can be imaged by scanning electron microscopy in kumano forearc basin sediments of the nankai trough results of this method show a significant increase in microporosity with burial depth probably due to microporosity preservation during compaction and possibly early volcanic ash diagenesis

the breccia museo formation campi flegrei southern italy geochronology chemostratigraphy and relationship with the campanian ignimbrite eruption the breccia museo is one of the most debated volcanic formations of the campi flegrei volcanic district the deposit made up of six distinctive stratigraphic units has been interpreted by some as the proximal facies of the major caldera forming campanian ignimbrite eruption and by others as the product of several more recent independent and localized events new geochemical and chemostratigraphical data and ar ar age determinations for several units of the breccia museo deposits 39 ka correlate well with the campanian ignimbrite forming eruption the chemical zoning of the breccia museo deposits is interpreted here to be a consequence of a three stage event that tapped a vertically zoned trachytic magma chamber

nano scale pore structure and fractal dimension of organic rich wufeng longmaxi shale from jiaoshiba area sichuan basin investigations using fe sem gas adsorption and helium pycnometry abstract much attention have been recently paid to the upper ordovician wufeng shale o3w and lower silurian longmaxi shale s1l in the jiaoshiba area of sichuan basin which is now the largest producing shale gas field in china field emission scanning electron microscopy fe sem low pressure gas n2 and co2 adsorption helium pycnometry x ray diffraction and geochemical analyses were performed to investigate the pore structure and fractal dimension of the pores in o3w s1l shale formation in the jiaoshiba area fe sem images show that organic matter om pores are dominant in the organic rich samples and these pores are often irregular bubble like elliptical and faveolate in shape while in organic poor samples limited and isolated interparticle interp intraparticle intrap and om pores are observed reversed s shaped isotherms obtained from nitrogen adsorption are type and hysteresis loops indicate that the shape of micropore in the samples is slit or plate like bet surface areas and total pore volume vary from 12 2 to 27 1 m2 g and from 1 8 10 2 to 2 9 10 2 cm3 g with an average of 19 5 m2 g and 2 3 10 2 cm3 g respectively adsorption volume from both n2 and co2 adsorption increases with respect to toc contents porosities obtained from helium porosimetry are comparable with these from gas co2 and n2 adsorption in o3w s1l shale however porosity determined by quantitative fe sem analysis is much smaller which is mainly related to limited resolution and the small areas of investigation based on the frenkel halsey hill fhh model of low pressure n2 adsorption fractal dimensions of the pores varied from 2 737 to 2 823 relationships between pore structure parameters and toc content mineral composition and fractal dimension reveal that the fractal dimension is mainly associated with micropores samples with higher toc content higher quartz content and lower clay content tend to contain more heterogeneous micropores resulting in higher fractal dimensions and more complicated pore structure in shales therefore fractal dimension is an effective parameter to reflect the complexity of pore structure and the degree of micropore development in o3w s1l shale

thickness trends and sequence stratigraphy of the middle devonian marcellus formation appalachian basin implications for acadian foreland basin evolution analysis of more than 900 wireline logs indicates that the middle devonian marcellus formation encompasses two third order transgressive regressive t r sequences mss1 and mss2 in ascending order compositional elements of the marcellus formation crucial to the successful development of this emerging shale gas play including quartz clay carbonate pyrite and organic carbon vary predictably within the proposed sequence stratigraphic framework thickness trends of marcellus t r sequences and lithostratigraphic units reflect the interplay of acadian thrust load induced subsidence short term base level fluctuations and recurrent basement structures rapid thickening of both t r sequences especially mss2 toward the northeastern region of the basin preserves a record of greater accommodation space and proximity to clastic sources early in the acadian orogeny however local variations in t r sequence thickness in the western more distal area of the basin may reflect the reactivation of inherited eocambrian basement structures including the rome trough and northwest striking cross structural discontinuities induced by acadian plate convergence episodes of block displacement locally warped the basin into northeast southwest trending regions of starved sedimentation and or erosion adjacent to depocenters in which regressive systems tract deposits were ponded block movement appears to have initiated in late early devonian time resulting first in thinning and local erosion of the oriskany sandstone in northwest pennsylvania this study in addition to providing the basis for a predictive sequence stratigraphic model that can be used to further marcellus exploration tells of a foreland basin more tectonically complex than accounted for by simple flexural models

algal blooms and marine snow mechanisms that enhance preservation of organic carbon in ancient fine grained sediments abstract combined petrographic and geochemical methods are used to investigate the microfabrics present in thin sections prepared from representative organic carbon rich mudstones collected from three successions the kimmeridge clay formation the jet rock member of the whitby mudstone formation and the pebble shale and hue shale this study was initiated to determine how organic carbon rich materials were being delivered to the sediment water interface and what happened to them after deposition prior to deep burial analyses of the fabrics present shows that they exhibit many common attributes in particular they are all 1 highly heterogeneous on the scale of a thin section 2 organized into thin beds the organomineralic aggregates present in these mudstones are interpreted to be ancient examples of marine snow this marine snow likely formed in the water column particularly during phytoplankton blooms and was then transported rapidly to the seafloor the existence of the thin beds with homogenized tops and an in situ infauna indicates that between blooms there was sufficient oxygen and time for a mixed layer to develop as a result of sediment colonization by diminutive organisms using either aerobic or dysaerobic metabolic pathways these textures suggest that the constituents of these mudstones were delivered neither as a continuous rain of sediment nor were the bottom waters persistently anoxic in addition the presence of thin lags and sharp based beds suggests that the seafloor was being episodically reworked during deposition these fabrics indicate that conditions in the water columns and at the seafloors while these rocks were being deposited were very dynamic and episodic fluxes of high concentrations of organic carbon to the seafloor during phytoplankton blooms likely enhanced preservation of organic carbon

microstructural investigation of gas shales in two and three dimensions using nanometer scale resolution imaging the microstructure of gas shale samples from nine different formations has been investigated using a combination of focused ion beam fib milling and scanning electron microscopy sem backscattered electron bse images of fib cross sectioned shale surfaces show a complex microstructure with variations observed among the formations energy dispersive spectroscopy of the shale cross sections indicates that clay carbonate quartz pyrite and kerogen are the most prevalent components in the bse images areas of kerogen are observed interspersed with the inorganic grains pores are observed in both the kerogen and inorganic matrix with the size shape and number of pores varying among the shale samples by using fib milling and sem imaging sequentially and repetitively three dimensional 3 d data sets of sem images have been generated for each of the shale samples three dimensional volumes of the shales are reconstructed from these images by setting thresholds on the gray scale the kerogen and pore networks are segmented out and visualized in the reconstructed shale volumes estimates of kerogen and pore volume percentages of the reconstructed shale volumes have been made and range from 0 to 90 0 for the kerogen and 0 2 to 2 3 for pores estimates of pore size distributions suggest that although pores with radii of approximately 3 nm dominate in number they do not necessarily dominate in total volumetric contribution scanning electron microscopy images and 3 d reconstructions reinforce the facts that shales are quite different and that their microstructures are highly variable and complex

bulk and position specific isotope geochemistry of natural gases from the late cretaceous eagle ford shale south texas abstract a dataset of bulk and position specific isotope compositions of shale gases from the late cretaceous eagle ford shale south texas is reported the chemical and bulk isotopic compositions of the seven samples in this study and those available from the literature show that across the play produced natural gas from the eagle ford shale preserves a wide range of gas compositions wetness 5 to 90 and 13c values of c1 c3 the depth profiles of the isotopic compositions suggest that the western region of the eagle ford shale deposit had experienced as much as 700 800 m of uplift erosion or gas migration the timing of and lost gas fractions by gas expulsion events very likely affected their gas compositions and bulk isotope compositions some deep 3000 3500 m matured ro 1 5 gases with heavy 13c c1 c3 values indicate significant loss 50 of the early stage gases for the position specific isotope deviations of propane the c2 1 values of the five samples show small decrease with well depths while the h2 1 values have a general increasing trend although some samples fall very close to the equilibrium model trajectories with reasonable calculated temperatures 138 148 c the position specific isotope compositions of propane from the eagle ford shale gases are likely results of thermal cracking of various organic molecules within the source rocks which have different activation energy for cracking and non statistical distributions of c h isotope within them