impact of thermal maturation on nano scale elastic properties of organic matter in shales abstract the properties of organic matter change during diagenesis and catagenesis potentially altering the way shales deform and fracture although kerogen in mudrocks is thought to become stiffer during thermal maturation few studies have been able to confirm this by direct measurement as standard mechanical testing techniques cannot easily be used to measure the micrometer sized organic components in shales here we use a new non destructive atomic force microscopy technique to map the elastic modulus of organic and inorganic components at the nanometer scale in shales containing type ii kerogen from three different levels of thermal maturation we found that when vitrinite reflectance increases from 0 40 to 0 82 the average young modulus of kerogen increases from 6 1 gpa to 16 0 gpa however as ro increases further from 0 82 to 1 25 the modulus values for kerogen do not change significantly a high degree of variance is registered in the elastic moduli particularly at higher levels of thermal maturation probably reflecting the inherent heterogeneity in the depositional organic matter present in the shales the mean modulus for bitumen in the same samples identified as void filling organic matter that was present only at intermediate and higher levels of maturation was relatively constant with mean values of 7 5 gpa and 8 5 gpa respectively in the samples that experienced catagenesis the modulus maps reveal that individual kerogen macerals possess soft regions interpreted as exuded bitumen which act to soften the overall structure of the kerogen as well as providing high resolution mechanical data this technique could be used to track the way bitumen and other compounds are generated from kerogen during catagenesis

polylithionite from the rare metal deposits of the blachford lake alkaline complex n w t canada extensive deposits of rare lithophile elements are located within albitized and greisenized peralkaline granitb and syenite at thor lake in the blachford lake complex east of yellowknife northwest territories in canada five structural zones affected by metasomatic alteration and locally also brecciation host zoned assemblages with be nb ta ree y zr and ga mineralization polylithionite is a major phase in several units of the mineralized zones its abundance amounts to tens of thousands of tons the chemistry physical properties and structural characteristics of two polylithionite samples from widely separated locations are almost identical and are close to the typical properties of the end member lm polylithionite ti nb mg rb cs and fe3 fe2 are much higher whereas rb and cs are remarkably lower than their ranges in lepidolites from orogenic to post orogenic peraluminous granitic pegmatites however the compositional field of lm polylithionites is apparently transitional into that of lm lepidolites which partly overlaps with 2mt and 2m polytype ranges

petroleum geology of the puguang sour gas field in the sichuan basin sw china abstract the puguang sour gas field in northeastern sichuan basin is the largest gas discovery in the paleozoic marine strata in china with at least 9 trillion cubic feet tcf of proven gas reserves it is one of the many anticlinal structures formed during the indo sinian orogeny with gas being trapped in a composite structure lithology pool the presence of the upper permian coal measures lower silurian and lower cambrian marine shales provided excellent hydrocarbon source rocks the lower triassic and upper permian oolitic dolomites serve as high quality reservoir rocks with 10 25 porosity and 1 1000 md permeability largely due to diagenetically produced secondary porosity the lower and middle triassic evaporate beds have acted as the direct top seal for the large lower triassic upper permian gas accumulation the thick upper triassic and jurassic mudstone beds regionally cap the underlying marine carbonate strata the deep seated basement faults acted as vertical hydrocarbon migration conduits during faulting and became effective flow barriers when the faulting ceased the deep burial of a paleo oil accumulation in reservoirs rich in sulfate resulted in extensive thermochemical sulfate reduction tsr this together with the new gas injection and structural reconfiguration transformed a paleo oil pool to a large sour gas pool

high pressure water pyrolysis of coal to evaluate the role of pressure on hydrocarbon generation and source rock maturation at high maturities under geological conditions this study investigates the effect of water pressure on hydrocarbon generation and source rock maturation at high maturities for a perhydrous tertiary arctic coal svalbard using a 25 ml hastalloy vessel the coal was pyrolysed under low water pressure 230 300 bar and high water pressure 500 700 and 900 bar conditions between 380 c and 420 c for 24 h at 380 c and 420 c gas yields were not affected by pressure up to 700 bar but were reduced slightly at 900 bar at 380 c the expelled oil yield was highest at 230 bar but reduced significantly at 900 bar at 420 c cracking of expelled oil to gas was retarded at 700 and 900 bar as well as direct cracking of the coal the main source of gas generation at high pressure at both 380 c and 420 c is from bitumen trapped in the coal indicating that this is a key mechanism in high pressure geological basins vitrinite reflectance vr was reduced by 0 16 ro at 380 c and by 0 27 ro at 420 c at 900 bar compared to the low pressure runs indicating that source rock maturation will be more retarded at higher maturities in high pressure geological basins

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

the importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs abstract the effect of shale composition and fabric upon pore structure and ch 4 sorption is investigated for potential shale gas reservoirs in the western canadian sedimentary basin wcsb devonian mississippian d m and jurassic shales have complex heterogeneous pore volume distributions as identified by low pressure co 2 and n 2 sorption and high pressure hg porosimetry thermally mature d m shales 1 6 2 5 vro have dubinin radushkevich d r co 2 micropore volumes ranging between 0 3 and 1 2 cc 100 g and n 2 bet surface areas of 5 31 m 2 g jurassic shales which are invariably of lower thermal maturity ranging from 0 9 to 1 3 vro than d m shales have smaller d r co 2 micropore volumes and n 2 bet surface areas typically in the range of 0 23 0 63 cc 100 g co 2 and 1 9 m 2 g n 2 high pressure ch 4 isotherms on dried and moisture equilibrated shales show a general increase of gas sorption with total organic carbon toc content methane sorption in d m shales increases with increasing toc and micropore volume indicating that microporosity associated with the organic fraction is a primary control upon ch 4 sorption sorption capacities for jurassic shales however can be in part unrelated to micropore volume the large sorbed gas capacities of organic rich jurassic shales independent of surface area imply a portion of ch 4 is stored by solution in matrix bituminite solute ch 4 is not an important contributor to gas storage in d m shales structural transformation of d m organic matter has occurred during thermal diagenesis creating and or opening up microporosity onto which gas can sorb as such d m shales sorb more ch 4 per weight percent wt toc than jurassic shales inorganic material influences modal pore size total porosity and sorption characteristics of shales clay minerals are capable of sorbing gas to their internal structure the amount of which is dependent on clay type illite and montmorillonite have co 2 micropore volumes of 0 78 and 0 79 cc 100 g n 2 bet surface areas of 25 and 30 m 2 g and sorb 2 9 and 2 1 cc g of ch 4 respectively dry basis a reflection of microporosity between irregular surfaces of clay platelets and possibly related to the size of the clay crystals themselves mercury porosimetry analyses show that total porosities are larger in clay rich shales compared to silica rich shales due to open porosity associated with the aluminosilicate fraction clay rich sediments low si al ratios have unimodal pore size distributions

petrogenetic relationships between pegmatite and granite based on geochemistry of muscovite in pegmatite wall zones black hills south dakota usa abstract the compositions of large samples of granitic pegmatite wall zones have been determined for a suite of ten pegmatites of diverse geochemical character and degree of compositional evolution in the keystone area of the black hills whole rock compositions are strongly peraluminous and they deviate substantially from the granite minimum composition in quartz albite orthoclase normalized components showing considerably more scatter than harney peak granite whole rocks wall zone minerals are commonly coarsely segregated leading to large modal variability among whole rocks these features make whole rock samples of wall zones unsuitable for the determination of initial pegmatite bulk compositions trace and minor element compositions of muscovite separates from the wall zones were thus determined to eliminate the effects of modal variability on trace element concentrations so that geochemical differences between pegmatites could be modeled estimates of initial pegmatite melt trace element concentrations range from 800 4000 ppm rb 100 1000 ppm cs 200 2000 ppm li and 1 50 ppm ba trace element concentrations of muscovite from a given pegmatite generally cluster together although several show considerable intra pegmatite scatter and there are large overlaps among different pegmatites the geochemical characteristics of samples from the etta pegmatite indicate mixing with and assimilation of country rocks exceptionally low rb cs ratios of muscovite from the etta pegmatite are similar to those of muscovite from k feldspar rich assemblages of other pegmatites where the rb concentration of melt may have been buffered by crystallizing assemblages that had bulk rb distribution coefficients close to 1 the large degree of scatter of geochemical parameters among these pegmatites precludes derivation of the entire suite by either single stage crystallization or partial melting processes nor can the pegmatites be satisfactorily related by any fractionation trajectory from a single starting composition fractional crystallization is difficult to model due to an apparent geochemical decoupling that exists among several of these elements in different pegmatites e g rb from cs or li from rb cs and nonsystematic variation of ba concentrations however the magnitude of observed rare element enrichments could be achieved by 75 90 fractional crystallization of melts that crystallized harney peak granite in nearby exposures the inter pegmatite scatter and apparent geochemical decoupling that characterize the suite indicate an origin by partial melting of a heterogeneous source rock or rock sequence followed by an intermediate episode of fractional crystallization prior to final emplacement of the pegmatite melts additional compositional variations among samples from the wall zones of individual pegmatites were caused by processes during or after emplacement including local interaction with host metamorphic rocks and fractionation during internal evolution of the pegmatites as they crystallized

extreme fractionation in a granite pegmatite system documented by quartz chemistry the case study of tres arroyos central iberian zone spain abstract the tres arroyos granite pegmatite system is located in the sw margin of the nisa alburquerque variscan batholith two granitic facies monzogranite and marginal leucogranite and three types of aplite pegmatite dykes barren intermediate and highly evolved li rich have been distinguished in the area with a zoned distribution from the granite southwards trace elements in quartz from the five facies have been analysed by la icp ms in order to obtain information about the petrogenetic links among the different lithologies of this system as well as to better understand the regional and individual fractionation processes that led to the distinct rocks aluminium ti li and ge show continuous trends from the monzogranite through the marginal granitic facies the barren and intermediate aplite pegmatites up to the most evolved li rich dykes titanium and ge contents respectively decrease and increase gradually with fractionation in contrast al and li show a more complex trend with an initial descending trend to the marginal granitic facies and then showing the highest al and li contents in the quartz from the most fractionated li rich aplite pegmatites this suggests the influence of different competing factors controlling the incorporation of these trace elements in quartz such as the chemical composition of the melt the p and t conditions and the rate of crystallization based on the good correlation between al and li the substitution si4 al3 li seems to be the dominant mechanism of li incorporation into quartz the negligible amount of other trace elements suggests that the remaining al was mainly compensated with h ions via the si4 al3 h substitution a continuous fractionation trend from the monzogranite up to the most fractionated aplite pegmatites is inferred from geochemical modelling by applying the rayleigh equation for fractional crystallization fractionation rates over 50 are needed to obtain the marginal granite and the barren aplite pegmatites compositions and over 99 for the most evolved dykes no pattern in the chemical variation of the trace elements in quartz from different layers in the layered aplite pegmatites has been found suggesting the lack of internal fractionation processes most probably due to the rapid crystallization of the pegmatitic melt intruded into a colder country rock

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

crystal structure refinement of a rubidian cesian phlogopite the crystal structure of a rubidian cesian phlogopite 1 m from pegmatite exocontacts at red cross lake manitoba monoclinic a 5 343 1 b 9 247 2 c 10 397 3 a 100 04 2 v 505 8 2 a 3 has been refined to an r index of 4 5 based on 519 observed reflections measured with graphite monochromated moka x radiation on an automated four circle diffractometer the crystal used in the collection of the x ray intensity data was also analyzed by electron microprobe giving the unit formula k0 46rb0 28cs0 23 mg1 20fe1 00al0 38li0 34mn0 04ti0 04 si2 91al1 09 o10 oh 1 55f0 45 the interlayer site x contains large amounts of rb and cs and cell dimensions and the distance are in accord with data from synthetic rb and cs phlogopites and plutonic phlogopites the interlayer coordination is much more regular in rubidian cesian phologopite than in other trioctahedral micas defining a trend of increasing regularity with increasing interlayer cation size

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

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

transmission electron microscopy of muscovite alteration of tourmaline partially sericitized tourmaline from a pegmatite was investigated using high resolution transmission electron microscopy hrtem fine grained muscovite crystals form extensive narrow veinlets preferentially developed along the 110 and 100 cleavages of tourmaline indicating that a cleavage controlled alteration mechanism was dominant hrtem images show that tourmaline muscovite interfaces parallel well defined 110 and 100 of tourmaline in general 001 of muscovite parallels the c axis of tourmaline but otherwise tourmaline and replacing muscovite lack crystallographically oriented relation

strontium isotope composition of runoff from a glaciated carbonate terrain abstract the relationship between subglacial chemical weathering processes and the sr isotope composition of runoff from robertson glacier alberta canada is investigated this glacier rests on predominantly carbonate bedrock of upper devonian age but silicate minerals are also present the provenance of solute in meltwaters is found to vary systematically with solute concentration and by inference subglacial water residence time in dilute waters the principal process of solute acquisition is calcite dissolution fueled by protons derived from the dissolution of co 2 and subsequent dissociation of carbonic acid at higher solute concentrations dolomite dissolution coupled to sulfide oxidation is more important sr concentration is found to increase with total solute concentration in two separate meltwater streams draining from the glacier but 87 sr 86 sr only increases in the eastern melt stream carbonate and k feldspar sources are shown to dominate the sr content of the western stream irrespective of concentration they also dominate the sr content of the eastern stream at low and intermediate concentrations but at higher concentrations muscovite with high 87 sr 86 sr is also an important sr source this reflects the outcrop of muscovite bearing lithologies in the catchment of the eastern stream and an increase in the rate of weathering of k silicates relative to that of carbonates as more concentrated solutions approach saturation with respect to carbonates nonstoichiometric release of 87 sr 86 sr and preferential release of sr over k from freshly ground k silicate surfaces may also occur this may help to explain the radiogenic nature of runoff from distributed subglacial drainage systems which are characterized by long water rock contact times and water flow through environments in which crushing and grinding of bedrock are active processes although the exchangeable sr in tills has higher 87 sr 86 sr than local carbonate bedrock only the more concentrated meltwaters from the eastern stream display similarly high values the most dilute waters which probably transport the bulk of the dissolved sr flux from the glacier have 87 sr 86 sr characteristic of local carbonate bedrock thus the results suggest that although enhanced weathering of silicate minerals containing radiogenic sr such as muscovite does occur in glaciated carbonate terrains it is unlikely to contribute to any enhanced flux of radiogenic sr from glaciated continental surfaces to the oceans

the effect of oil expulsion or retention on further thermal degradation of kerogen at the high maturity stage a pyrolysis study of type ii kerogen from pingliang shale china high maturity oil and gas are usually generated after primary oil expulsion from source rocks especially from oil prone type i ii kerogen however the detailed impacts of oil expulsion or retention in source rock on further thermal degradation of kerogen at the high maturity stage remain unknown in the present study we collected an ordovician pingliang shale sample containing type ii kerogen the kerogens which had previously generated and expelled oil and those which had not were prepared and pyrolyzed in a closed system to observe oil expulsion or oil retention effects on later oil and gas generation from kerogen the results show that oil expulsion and retention strongly impacts on further oil and gas generation in terms of both the amount and composition in the high maturity stage gas production will be reduced by 50 when the expulsion coefficient reaches 58 and gas from oil expelled kerogen less oil retained is much drier than that from fresh kerogen the oil expulsion also causes n alkanes and gas compounds to have heavier carbon isotopic compositions at high maturity stages the enrichment of 13c in n alkanes and gas hydrocarbons are 1 and 4 6 respectively compared to fresh kerogen oil expulsion may act as open system opposite to the oil retention that influences the data pattern in crossplots of 13c2 13c3 versus c2 c3 13c2 13c3 versus 13c1 and 13c1 13c2 versus ln c1 c2 which are widely used for identification of gas from kerogen cracking or oil cracking these results suggest that the reserve estimation and gas source correlation in deep burial basins should consider the proportion of oil retention to oil expulsion the source rocks have experienced

rare metal pegmatites of wamba central nigeria their formation in relationship to late pan african granites he sn nb ta mineralization of the wamba field central nigeria occurs in muscovite quartz microcline pegmatites which are related to the late orogenic pan african f 550 ma older granites the emplacement of granites and pegmatites was controlled by late pan african shear tectonics the granitoid magmatism was multiphase and has produced peraluminous biotite granite biotite muscovite granite and muscovite granite plutons sodic metasomatism has altered highly evolved granite cupolas and many of the pegmatite dikes the pegmatitic mineralization of predominantly cassiterite is closely associated with albitization chemical data of granites and granitic and pegmatitic muscovites show that rb cs sn nb and ta are enriched during both magmatic and postmagmatic evolution with highest contents of these elements in early muscovites of the albitized and mineralized pegmatites trace element chemistry of the pegmatitic muscovites reveals a chemical zonation of the pegmatite field related to the late orogenic shear system

deleterious reactions of aggregate with alkalis in concrete concrete in the built environment the word concrete is derived from the latin concretus compact condensed representing a conjunction of con together and the past participle of cresco to grow compare crescendo thus concrete could be liberally translated as grown solid together alluding to the consolidation of a particulate aggregate material with a cement binder of some sort concrete containing aggregate has been used in construction by the ancient greek and romans possibly as a further development of clay initially used by the assyrians and babylonians as a binder later superseded by burnt lime and gypsum by the egyptians as a construction material concrete allows architects and engineers to design a structure with only minimal constraints to its form a complicated shape requiring great effort to chisel out from a piece of stone can simply be poured in a mold and reproduced as often as desired also ex situ both the invention of ordinary portland cement opc first patented by british bricklayer joseph aspdin in 1824 and of reinforced concrete first patented by parisian gardener joseph monier in 1867 for making durable flower pots contributed to the development of mechanically stronger concrete allowing yet slimmer and taller structures to be built today concrete is the most popular building and construction material with an annual production volume exceeding 7 5 km3 or about 20 billion tonne concrete is the prime ingredient in the world s largest and most prominent structures and landmark edifices including hydropower dams e g three gorges dam yichang cn also see charlwood and solymar 1995 coastal defense works e g delta works nl telecommunication e g cn tower toronto ca office skyscrapers e g burj khalifa dubai uae theatres e g opera house sydney au hotels and casinos e g marina bay area singapore sg nuclear power plants oil and gas drilling and productions rigs e g sakhalin ru sea ports and harbors e g

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

trace element geochemistry by laser ablation icp ms of micas associated with ta mineralization in the tanco pegmatite manitoba canada in the tanco pegmatite one of the world s major ta deposits tantalum mineralization shows a complexity that reflects the complex petrogenesis of its host pegmatite micas are common in most of the pegmatite units and are intimately associated with the successive stages of ta mineralization from the wall zone to the central zones where micaceous replacement is pervasive different generations of micas both primary and secondary associated with ta oxides were selected for electron microprobe and laser ablation icp ms investigation their chemical trends are used to constrain the magmatic versus hydrothermal processes that played a role in their crystallization and their associated ta mineralization micas range from dioctahedral muscovite to trioctahedral lepidolite through al li substitution unexpectedly the most evolved compositions low k rb ratios and high li contents occur in the wall zone they are interpreted to reflect nonequilibrium crystallization from an undercooled melt with or without boundary layer effects in the central zones the fine grained mica quartz assemblage hosts some coarser grained li muscovite which has the highest ta contents up to 400 ppm these li f a rich micas are interpreted to originate from a magmatic metasomatic event which was also at the origin of the mqm style ta mineralization at tanco however the li ta poor muscovite end member compositions of fine grained alteration micas suggest crystallization from an aqueous fluid during a metasomatic hydrothermal event involving late pegmatitic fluids the low ta concentrations around 50 ppm of this fine grained muscovite suggest that this fluid transported at least small amounts of ta

internal differentiation of rare element pegmatites effects of boron phosphorus and fluorine lithium rich rare element pegmatites are characterized by high concentrations of b p and f the interactions of these components with h2o and rare alkalis lower liquidas and solidus temperatures enhance silicate liquid h2o miscibility and control partitioning and concentration of group i elements and higher field strength cations boron f and perhaps p may form peralkaline na and li species that promote early saturation in mica quartz activities of f p and especially b are largely unbuffered throughout crystallization concentration of these components through fractional crystallization involving muscovite generates a peralkaline na aluminosilicate rich melt or vapor from which albitites rich in tourmaline phosphates f rich micas beryl zircon and nb ta sn oxides crystallize phase equilibrium experiments with peraluminous b p f rich rhyolite obsidian macusanite simulate many features of rare element pegmatites especially at h2o undersaturated conditions

bib sem characterization of pore space morphology and distribution in postmature to overmature samples from the haynesville and bossier shales abstract four haynesville shale and four bossier shale samples were investigated using a combination of scanning electron microscopy sem and broad ion beam bib polishing this approach enables the microstructure and porosity to be studied down to the mesopore size r in the haynesville shale to 1 79 2 26 vr r in the bossier shale this variety within the samples enabled us to study controls on the porosity distribution in these shales visible pores exist as intraparticle pores mainly in carbonate grains and pyrite framboids and as interparticle pores mainly in the clay rich matrix pores in organic matter show a characteristic porosity with respect to the type of organic matter which mainly consists of mixtures of amorphous organic matter and minerals organic laminae and discrete macerals a clear positive trend of organic matter porosity with maturity was found pore sizes are power law distributed in the range of 4 4 m to at least 36 nm in equivalent diameter the differences in power law exponents suggest that a more grain supported coarse grained matrix may prevent pores from mechanical compaction porosities measured in the bib cross sections were significantly lower in comparison to porosities obtained by mercury intrusion porosimetry mip this difference is mainly attributed to the different resolution achieved with bib sem and mip and type of pore network extrapolation of pore size distributions psds enables the bib sem porosity to be estimated down to the resolution of the mip and thus to upscale microstructural observation at the confined space of the bib sem method to bulk porosity measurement these inferred porosities are in good agreement with the mip determined porosities which underpins the assumption that pores segmented in bib sem mosaics are representative of the mip methodology

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

expression of seasonal and enso forcing in climatic variability at lower than enso frequencies evidence from pleistocene marine varves off california abstract upper pleistocene marine sediments along the upper continental slope off northern and central california contain alternations of varved and bioturbated sediments and associated changes in biota and sediment composition these alternations can be related to conditions that accompany el nino and anti el nino enso circulation anti el nino conditions are characterized by increased upwelling and productivity and by low concentrations of dissolved oxygen in the oxygen minimum zone that resulted in varve preservation el nino conditions are characterized by little or no upwelling low productivity and higher concentrations of dissolved oxygen that resulted in zones of bioturbation alternations of varves and zones of bioturbation that range from decades to millennia occur through the upper pleistocene section the inferred long term alternations in el nino and anti el nino conditions appear to be a re expression of enso s primary 3 7 year cycle decadal to millennial cycles of productivity associated with el nino and anti el nino conditions may have served as a carbon pump and transferred atmospheric co 2 to the marine reservoir changes in sediment composition and organisms associated with el nino or anti el nino conditions can be related to both seasonal and enso phenomena expression of these changes at lower than enso frequencies may be partly explained by adding the effects of seasonal variability to effects produced by a self oscillating enso system however deterministic mechanisms including solar modulation of enso may also contribute to long term alternations of el nino and anti el nino conditions

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

geological setting and timing of the world class sn nb ta and li mineralization of manono kitotolo katanga democratic republic of congo the central african mesoproterozoic kibara belt in katanga drcongo forms a metallogenic province that hosts a variety of granite related mineralization rich in cassiterite columbite tantalite wolframite ferberite spodumene and beryl this mineralization is mainly present in pegmatites and quartz veins that are thought to be associated with the youngest granite generation in the kibara belt i e so called e group granite generation manono kitotolo is one of the world s largest sn nb ta and li mineralized pegmatites with a large resource of spodumene columbite tantalite and cassiterite still remaining mineralized pegmatites have intruded along the foliation in the mesoproterozoic metasedimentary rocks and dolerites of the manono kitotolo area the pegmatites have been emplaced very late during the climax of the kibaran orogeny probably during the transition from orogenic collapse to extensional tectonics based on their structural position the emplacement of the pegmatites resulted in an intense alteration of the doleritic and metasedimentary host rocks resulting in muscovitization tourmalinization and silicification a mineralogical and geochemical zonation typical for granitic pegmatites has been identified that was affected by metasomatic hydrothermal alteration mainly albitization and greisenization the latter alteration is associated with the main phase of cassiterite mineralization a first stage with nb ta li and minor sn however already formed pre alteration directly associated with pegmatite crystallization 40ar 39ar muscovite dating of unaltered pegmatites resulted in ages of 938 8 5 1 ma and 934 0 5 9 ma these ages are overlapping with the u pb age of the nb ta mineralization 940 5 1 ma also giving new temporal constraints on the fertile e group granite generation in the kib the 40ar 39ar muscovite age of a mineralized greisen is 923 3 8 3 ma which is younger but still partly within error of the 40ar 39ar ages of the unaltered pegmatites based on the partial overlap in age but also on field and paragenetic relationships and the stable isotope composition of the fluids this greisenization and associated cassiterite mineralization can still be linked to the pegmatite crystallization

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

the organic matter distribution and methane capacity of the lower cretaceous strata of northeastern british columbia canada abstract the methane sorption capacity of a succession of sandstone siltstone shale and coal from the lower cretaceous fort st john group of northeastern british columbia was investigated average organic matter om content for all formations is 2 3 wt with a minimum of 0 6 wt and maximum of 10 1 wt the methane sorption capacity ranges between 0 19 and 2 74 cm3 g at 6 mpa and at 30 c total gas capacity free and sorbed gas ranges between 2 2 and 16 6 cm3 g at 6 mpa micropore volumes range between 0 43 and 1 69 cm3 100 g a positive correlation exists between the om content micropore volume and the methane capacity of shales shales with high methane capacities have either high contents of inertodetrinite or vitrinite moisture content shows a positive relationship with om content micropore volume and methane capacity the negative relationship between moisture and surface area derived from n2 adsorption suggests the moisture is located within the microporosity of the om and also explains the positive relationship between methane capacity and moisture the high inertodetrinite and vitrinite contents correlate with sea level regressions that delivered terrestrial om from coastal plains located south of the study area into the basin

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

effects of oil expulsion and pressure on nanopore development in highly mature shale evidence from a pyrolysis study of the eocene maoming oil shale south china abstract the influence of oil expulsion efficiency on nanopore development in highly mature shale was investigated by using anhydrous pyrolysis 425 600 c on solvent extracted and non extracted shales at a pressure of 50 mpa additional pyrolysis studies were conducted using non extracted shales at pressures of 25 and 80 mpa to further characterize the impact of pressure on pore evolution at high maturity the pore structures of the original shale and relevant artificially matured samples after pyrolysis were characterized by using low pressure nitrogen and carbon dioxide adsorption techniques and gas yields during pyrolysis were measured the results show that oil expulsion efficiency can strongly influence gas generation and nanopore development in highly mature shales as bitumen remained in shales with low oil expulsion efficiency significantly promotes gaseous hydrocarbon generation and nanopore diameter 10 nm remains flat at high maturation in addition high pressure can promote the development of micropores and fine mesopores in highly mature shales

climatically induced lake level changes at lake van turkey during the pleistocene holocene transition sediment core k10 from lake van eastern turkey provides a continuous varve record back to 14 570 calendar years b p before present 1950 the longest unbroken and non floating lake varve sequence yet described the underlying sediment is unvarved and hard changes in the aragonite calcite ratio the presence of protodolomite and magnesite in certain profile sections the annual record of the sedimentation rate the water content of the sediment the concentrations of organic carbon and opal and the texture of the sediments from this core provide a record of the lake level history the new chronology enabled us to redate the old pollen profile van zeist and woldring 1978a b and to establish an accurate timescale for the reconstructed lake level change carbon 14 dates show that the highest lake terrace corresponds to high lake level at around 19 000 years b p during the last glacial 70 m above its present level before 15 000 years b p the lake must have been completely dry marking a reduction of lake level by 500 m in maximum 4000 years beginning at 14 600 years b p and ending at 12 040 years b p the lake level recovered by 250 m to fall again during the next 1400 years by 10 600 years b p the lake began to rise and reached following another regression between 9000 and 8100 years b p the holocene highstand by about 7500 years b p dropping to today s level at about 3000 years b p

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

experimental study of fluid transport processes in the matrix system of the european organic rich shales ii posidonia shale lower toarcian northern germany abstract a laboratory study has been conducted to investigate the transport of gases he ar ch 4 and water in the matrix of lower toarcian posidonia shale samples from three shallow boreholes in northern germany the maturity of the organic matter of the shale samples ranged between 0 53 and 1 45 vitrinite reflectance vr r the measurements were performed at effective stresses ranging between 6 and 37 mpa and a temperature of 45 c the effects of different controlling factors including permeating fluid maturity anisotropy moisture content and effective stress on the fluid conductivity were analyzed and discussed permeability coefficients measured perpendicular and parallel to bedding 3 10 22 to 9 7 10 17 m 2 were within the range previously reported for other shales and mudstones they exhibited a strong dependence on permeating fluid maturity anisotropy moisture content and effective stress the permeability coefficients measured with helium as permeate were consistently higher up to two times than those measured with argon and methane permeability coefficients measured with water were up to three orders of magnitude lower than klinkenberg corrected gas permeability coefficients measured with helium and methane under similar experimental conditions among the samples studied the lowest porosity and permeability coefficients were measured on samples of intermediate thermal maturity 0 88 vr r oil window permeability coefficients he ch 4 measured parallel to bedding were up to more than one order of magnitude higher than those measured perpendicular to bedding permeability coefficients measured with he and ch 4 on a dry sample were up to two times higher than those measured on a sample with the as received moisture content all samples showed a nonlinear reduction in permeability parallel to bedding with increasing effective stress 6 37 mpa the permeability anisotropy and stress dependence of permeability were controlled by the mineralogy

mechanisms of shale gas storage implications for shale gas exploration in china this article reviews the mechanisms of shale gas storage and discusses the major risks or uncertainties for shale gas exploration in china at a given temperature and pressure the gas sorption capacities of organic rich shales are primarily controlled by the organic matter richness but may be significantly influenced by the type and maturity of the organic matter mineral composition especially clay content moisture content pore volume and structure resulting in different ratios of gas sorption capacity gsc to total organic carbon content for different shales in laboratory experiments the gsc of organic rich shales increases with increasing pressure and decreases with increasing temperature under geologic conditions assuming hydrostatic pressure gradient and constant thermal gradient the gsc increases initially with depth due to the predominating effect of pressure passes through a maximum and then decreases because of the influence of increasing temperature at greater depth this pattern of variation is quite similar to that observed for coals and is of great significance for understanding the changes in gsc of organic rich shales over geologic time as a function of burial history at an elevated temperature and pressure and with the presence of moisture the gas sorption capacities of organic rich shales are quite low as a result adsorption alone cannot protect sufficient gas for high maturity organic rich shales to be commercial gas reservoirs two models are proposed to predict the variation of gsc and total gas content over geologic time as a function of burial history high contents of free gas in organic rich shales can be preserved in relatively closed systems loss of free gas during postgeneration uplift and erosion may result in undersaturation the total gas contents lower than the sorption capacity and is the major risk for gas exploration in marine organic rich shales in china

mediterranean vegetation lake levels and palaeoclimate at the last glacial maximum the apparent conflict between pollen evidence for widespread artemisia steppe1 6 implying semi arid conditions and geomorphological evidence for high lake levels4 7 11 has produced controversy about the ice age palaeoclimate of the mediterranean region here we use a water balance model12 to predict catchment runoff and a biome model13 to predict vegetation type to reconstruct the palaeoenvironment around lake loannina a type locality for the northern mediterranean region we show that both sets of evidence are compatible with a summer dry winter wet regime with seasonal temperature anomalies similar to those predicted by atmospheric model simulations of the last glacial maximum14 18 the drying effect of the cold north atlantic ocean may have been counteracted in winter by increased storm frequency under a southward shifted jet stream as shown by several atmospheric models16 18

evolution of porosity and pore types in organic rich calcareous lower toarcian posidonia shale low and high resolution petrographic studies have been combined with mineralogical toc rockeval and porosity data to investigate controls on the evolution of porosity in stratigraphically equivalent immature oil window and gas window samples from the lower toarcian posidonia shale formation a series of 26 samples from three boreholes wickensen harderode and haddessen in the hils syncline was investigated the main primary components of the shales are microfossiferous calcite 30 50 clay minerals 20 30 and type ii organic matter toc 7 15 hi 630 720 mg gc in immature samples characteristic sub centimetric light and dark lamination reflects rapid changes in the relative supply of these components total porosities decrease from 10 to 14 at ro 0 5 to 3 5 at ro 0 9 and then increase to 9 12 at ro 1 45 these maturity related porosity changes can be explained by a the primary composition of the shales b carbonate diagenesis c compaction and d the maturation micro migration local trapping and gasification of heterogeneous organic phases calcite undergoes dissolution and reprecipitation reactions throughout the maturation sequence pores quantifiable in sem ca 50 nm account for 14 25 of total porosity at ro 0 5 sem visible macropores1 are associated mainly with biogenic calcite at this maturity clays and organic matter are not visibly porous but nevertheless hold most of the shale porosity porosity loss into the oil window reflects a compaction b carbonate cementation and c perhaps the swelling of kerogen by retained oil in addition porosity is occluded by a range of bituminous phases especially in microfossil macropores and microfractures in the gas window mineral hosted porosity is still the primary form of macroporosity most commonly observed at the organic inorganic interface increasing porosity into the gas window also coincides with the formation of isolated spongy and complex meso and macropores within organic particles related to thermal cracking and gas generation this intraorganic porosity is highly heterogeneous point counted macroporosity of individual organic particles ranges from 0 to 40 with 65 of organic particles containing no macropores we suggest that this reflects the physicochemical heterogeneity of the organic phases plus the variable mechanical protection afforded by the mineral matrix to allow macroporosity to be retained the development of organic macroporosity cannot alone account for the porosity increase observed from oil to gas window major contributions also come from the increased volume of organic micro and meso porosity and perhaps by kerogen shrinkage

holocene sedimentology of hypersaline lake urmia northwestern iran abstract a limnogeological expedition examined the sedimentary record of lake urmia one of the world s largest saline lakes located in a tectonically active arid intermontane plateau in northwestern iran near the cradle of western civilization lake urmia resembles the great salt lake u s a in many respects of morphology water chemistry and sediments the present lake area is about 5000 km 2 shallow 8 12 m and a perennial sodium chloride sulfate system 22 salts high resolution 3 5 khz seismic profiles show morphological relicts from a desiccation playa phase buried below only a few meters of sediments from lacustral phases in places around the deeper areas the lake floor is not smooth but covered with mounds aligned in prevailing current directions these are erosional relicts rather than bioherms sediments comprise aragonite chemical precipitates fecal pellet sands detrital clayey muds thin aragonite crusts oolites various gypsum types and occurrences of dolomite in peripheral areas organic matter characteristic of the present shorelines is not preserved at depth in basinal areas piston cores up to 6 m long penetrated a holocene sequence of hypersaline facies with laminated aragonite fecal pellet muds and bottomed in a playa mudflat facies with central gypsiferous muds and marginal terrigenous to dolomitic muds preliminary radiocarbon and pollen analyses suggest a playa stage prior to 9000 yr b p with saline lake deposition in a cool arid climate from 9000 to 7500 yr b p higher energy facies prevailed in a shallow saline lake and since then present day saline environments have persisted with evidence of numerous second order water level fluctuations the preliminary results suggest a lake system out of phase with north african and some other middle eastern lakes

characterization of gas shale pore systems by porosimetry pycnometry surface area and field emission scanning electron microscopy transmission electron microscopy image analyses examples from the barnett woodford haynesville marcellus and doig units the nanometer scaled pore systems of gas shale reservoirs were investigated from the barnett marcellus woodford and haynesville gas shales in the united states and the doig formation of northeastern british columbia canada the purpose of this article is to provide awareness of the nature and variability in pore structures within gas shales and not to provide a representative evaluation on the previously mentioned north american reservoirs to understand the pore system of these rocks the total porosity pore size distribution surface area organic geochemistry mineralogy and image analyses by electron microscopy were performed total porosity from helium pycnometry ranges between 2 5 and 6 6 total organic carbon content ranges between 0 7 and 6 8 wt and vitrinite reflectance measured between 1 45 and 2 37 the gas shales in the united states are clay and quartz rich with the doig formation samples being quartz and carbonate rich and clay poor higher porosity samples have higher values because of a greater abundance of mesopores compared with lower porosity samples with decreasing total porosity micropore volumes relatively increase whereas the sum of mesopores and macropore volumes decrease focused ion beam milling field emission scanning electron microscopy and transmission electron microscopy provide high resolution 5 nm images of pore distribution and geometries image analysis provides a visual appreciation of pore systems in gas shale reservoirs but is not a statistically valid method to evaluate gas shale reservoirs macropores and mesopores are observed as either intergranular porosity or are confined to kerogen rich aggregates and show no preferred orientation or align parallel with the laminae of the shale networks of mesopores are observed to connect with the larger macropores within the kerogen rich aggregates

experimental investigation of oil generation retention and expulsion within type ii kerogen dominated marine shales insights from gold tube nonhydrous pyrolysis of barnett and woodford shales using miniature core plugs abstract although oil retention has recently emerged as a key topic of unconventional shale resource assessment oil retention and expulsion controls in organic rich shales during thermal maturation remain poorly constrained this study presents an experimental comparison of oil generation retention and expulsion in two immature type ii kerogen dominated marine shales the mississippian barnett shale and the upper devonian lower mississippian woodford shale mainly with respect to the combined effects of the organic macerals and rock fabric involved in both cases miniature core plugs drilled from the given samples were isothermally pyrolyzed at 130 to 425 c for 72 h under a confining pressure of 68 mpa during gold tube nonhydrous pyrolysis corresponding to the thermally immature early stage of the oil window the main stage of the oil window the late stage of the oil window the main stage of oil cracking to wet gas and the late stage of oil cracking yields of generated oil retained oil and expelled oil for the two studied samples were systematically quantified on the basis of mass balance calculation of measured oil and gas yields as well as rock eval analyses on pyrolyzed subsamples through the six stages of petroleum formation investigated the principal difference in oil generation was observed in the two studied samples with approximately 38 to 68 greater yields of generated oil equivalent to 130 mg oil g toco for the woodford shale when it evolved into the main and late stages of the oil window these elevated yields of generated oil for the woodford shale were compensated for by additional oil generation resulting from conversion of abundant type i kerogen like algae such as tasmanites and leiosphaeridia which lag in onset and have a shorter period of petroleum generation upon maturation as a response to the difference in oil generation oil retention was found to be significantly enhanced for the woodford shale at equivalent stages with 0 2 to 1 7 times more free oil equivalent to 24 105 mg oil g toco and 0 7 to 3 9 times more sorbed oil equivalent to 58 76 mg oil g toco being retained than that of the barnett shale although this effect was not pronounced for oil expulsion in contrast to the barnett shale relatively low expelled oil yields and expulsion efficiencies both indicate highly limited oil expulsion in the woodford shale implying that the woodford shale whose mineral composition and lithofacies are similar to those of the barnett shale may have a relatively low permeability rock fabric to prevent oil from being expelled furthermore not only significantly higher oil saturation index osi values but also a wider range of maturity at which the oil crossover effect osi 100 mg g toc occurs is expected for the woodford shale when extrapolation to a geological setting occurs these data suggest that the presence of abundant type i kerogen like algae and relatively low permeability rock fabric in the woodford shale are critical to significant oil retention during oil generation and expulsion which jointly raise the possibility of potential commercial shale oil within type ii kerogen dominated marine shales

pore structure characteristics of lower silurian shales in the southern sichuan basin china insights to pore development and gas storage mechanism abstract silurian shale in sichuan basin is currently the most important target zone for shale gas exploration and development in china pore structure characteristics of lower silurian longmaxi shales from southern sichuan basin were investigated the combination of field emission scanning electron microscope fe sem and argon ion beam milling was utilized to describe the nanometer to micrometer scale 1 2 nm pore systems the shales were characterized by organic geochemical and mineralogical analyses total porosity pore size distribution psd specific surface area and gas content were determined controls of organic matter richness thermal maturity and mineralogy on porosity were examined the contribution of individual mineral components to total porosity was analyzed quantitatively total gas contents of the shales determined from canister desorption data were compared with theoretical sorptive and volumetric gas storage capacities the total organic carbon toc content of the shale samples ranges between 0 1 and 8 0 wt and helium porosity varies between 0 7 and 5 7 maturity in terms of equivalent vitrinite reflectance of bitumen reqv ranges from 1 8 to 3 2 toc content is a strong control for the pore system of these shales and shows a positive correlation with porosity porosity increases with increasing thermal maturity when reqv is less than 2 5 but decreases for higher thermal maturity samples fe sem reveals four pore types related to the rock matrix that are classified as follows organic matter om hosted pores pores in clay minerals pores of framework minerals and intragranular pores in microfossils pores in clay minerals are always associated with the framework of clay flakes and develop around rigid mineral grains because the pressure shadows of mineral grains prevent pores from collapsing pores of framework minerals are probably related to dissolution by acidic fluids and the dissolution related pores promote porosity of shales a unimodal psd exists in the micropore range of toc rich samples while the psd of carbonate rich samples are bimodal a psd maximum in the micropore range is attributed by om and another maximum in the range of mesopore macropores is probably caused by the dissolution of carbonate minerals quantitative evaluation of the contribution of individual mineral components to porosity shows that the organic matter contributes approximately 62 to the total porosity framework minerals quartz feldspar and carbonates et al and clay minerals contribute 25 and 13 respectively the total gas content of these shales ranges from 0 4 to 6 2 m3 t and the total gas contents of selected samples determined from canister desorption tests agree with the theoretically estimated original gas in place ogip om hosted pores are the main space for gas storage and accounted for about 78 55 adsorbed gas plus 23 free gas of the ogip while pores in the inorganic matter accommodate 22 free gas of the ogip

pore characterization of organic rich lower cambrian shales in qiannan depression of guizhou province southwestern china abstract nine organic rich shale samples of lower cambrian black shales were collected from a recently drilled well in the qiannan depression guizhou province where they are widely distributed with shallower burial depth than in sichuan basin and their geochemistry and pore characterization were investigated the results show that the lower cambrian shales in qiannan depression are organic rich with toc content ranging from 2 81 to 12 9 thermally overmature with equivalent vitrinite reflectance values in the range of 2 92 3 25 and clay contents are high and range from 32 4 to 53 2 the samples have a total helium porosity ranging from 2 46 to 4 13 and total surface area in the range of 9 08 37 19 m2 g the estimated porosity in organic matters defined as the ratio of organic pores to the volume of total organic matters based on the plot of toc vs helium porosity is about 10 for the lower cambrian shales in qiannan depression and is far lower than that of the lower silurian shales 36 in and around sichan basin this indicates that either the organic pores in the lower cambrian shale samples have been more severely compacted than or they did not develop organic pores as abundantly as the lower silurian shales our studies also reveal that the micropore volumes determined by dubinin radushkevich dr equation is usually overestimated and this overestimation is closely related to the non micropore surface area of shales i e the surface area of meso and macro pores however the modified bet equation can remove this overestimation and be conveniently used to evaluate the micropore volumes surface area and the non micropore surface areas of micropore rich shales

experimental investigation of thermal maturation on shale reservoir properties from hydrous pyrolysis of chang 7 shale ordos basin abstract thermal maturity has a significant impact on hydrocarbon generation and the storage capacity within shales but explicit and quantitative characterization of that impact on continental shales is scarce to better understand how thermal maturation affects the organic and inorganic changes of the continental shale reservoirs hydrous pyrolysis was performed to simulate the maturation process toc rock eval and adsorption isotherms tests were used to obtain various geochemical parameters of the shale solid residues the results indicate that with pyrolysis temperature increasing from ambient temperature to 550 c the vitrinite reflectance increases from 0 5 to 2 5 ro and the toc total organic carbon loss weight reaches 25 regarding porosity the fraction of micro to meso pores in the shale increases with an increase in the pyrolysis temperature whereas the macro pores do not change significantly the total amount of gas adsorption does not necessarily increase as the toc is consumed but the gas adsorption capacity per unit of toc increases with increasing thermal maturity our finding provides theoretical modelling for identifying shale gas development prospective zones according to thermal maturity mapping and for predicting quantitatively the geochemical and inorganic changes that occur with thermal evolution

effect of thermal maturation on chemical structure and nanomechanical properties of solid bitumen abstract an abundance of organic matter is present as solid bitumen in highly mature shales changes in chemical structure of solid bitumen during catagenesis could alter the way its mechanical properties evolve this study considers a series of solid bitumen samples artificially produced from the pyrolysis at 420 618 c of soluble organic matter which originated from maoming shale to examine alternations in their chemical structure nano morphological and mechanical properties during maturation solid state 13c nuclear magnetic resonance spectroscopy and elemental analysis were employed to characterize the structural changes young s modulus and microstructures were determined by atomic force microscopy the results show that both structural including c h atomic ratio and carbon aromaticity and mechanical young s modulus variations in solid bitumen exhibit two staged evolutions i e wet gas stage and dry gas stage during maturation in the wet gas stage easyro 1 85 2 64 the c h ratio and carbon aromaticity increase substantially with maturation and the solid bitumen is relatively compliant with an average young s modulus varying from 2 7 0 6 to 3 0 0 6 gpa when maturity reaches to dry gas stage easyro 2 64 4 59 structural parameters do not change greatly whereas solid bitumen becomes much stiffer with modulus rising sharply to 7 2 1 1 gpa at easyro 3 49 and further gently to 8 8 1 4 gpa at easyro 4 59 concomitantly great variations are observed on surface morphology and the degree of heterogeneity in solid bitumen is recorded to be increasingly high along thermal simulation given the strong correlation between structural parameters and young s modulus we suggest that the stiffening of solid bitumen is extensively affected by its structural condensation due to the loss of aliphatic carbons and the increase of aromaticity

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