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

late glacial stage and holocene tropical ice core records from huascaran peru two ice cores from the col of huascaran in the north central andes of peru contain a paleoclimatic history extending well into the wisconsinan wurm glacial stage and include evidence of the younger dryas cool phase glacial stage conditions at high elevations in the tropics appear to have been as much as 8 to 12 c cooler than today the atmosphere contained about 200 times as much dust and the amazon basin forest cover may have been much less extensive differences in both the oxygen isotope ratio 18o 8 per mil and the deuterium excess 4 5 per mil from the late glacial stage to the holocene are comparable with polar ice core records these data imply that the tropical atlantic was possibly 5 to 6 c cooler during the late glacial stage that the climate was warmest from 8400 to 5200 years before present and that it cooled gradually culminating with the little ice age 200 to 500 years before present a strong warming has dominated the last two centuries

present day south american climate abstract this paper documents the main features of the climate and climate variability over south america on the basis of instrumental observations gathered during the 20th century it should provide a modern reference framework for paleoclimate research in south america targeting high resolution proxies over the past few centuries several datasets suitable for present day climate research are first described highlighting their advantages as well as their limitations we then provide a basic physical understanding of the mean annual cycle of the precipitation and atmospheric circulation over the continent and the adjacent oceans in particular the diversity of precipitation temperature and wind patterns is interpreted in terms of the long meridional extent of the continent and the disruption of the large scale circulation caused by the andes cordillera the contrasting oceanic boundary conditions and the landmass distribution similarly the intensity and timing of the interannual and interdecadal climatic fluctuations exhibit considerable geographical dependence as some regions are more influenced by large scale phenomena rooted in the tropical oceans while others are more influenced by high latitude phenomena the impact of these large scale phenomena over south america is documented by a regression analysis between selected atmospheric indices and the precipitation and temperature fields we have included a discussion on the seasonality and long term stability of such impacts and complemented our general description by an updated review of the literature on climate variability over specific regions

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

role of pore structure in the percolation and storage capacities of deeply buried sandstone reservoirs a case study of the junggar basin china abstract deeply buried sandstone reservoirs are characterized by their wide pore throat distributions and varied storage and percolation capacities an integrated analysis comprising casting thin section scanning electron microscopy x ray computed tomography micro ct high pressure mercury intrusion hpmi and constant rate mercury intrusion crmi is performed on thirteen samples from the jurassic sangonghe formation in the junggar basin to investigate the pore structures and their influence on the storage and percolation capacities hpmi crmi and micro ct are combined to determine the full range pore size distributions fpsds which have multimodal distributions between 2 77 nm and 500 m with three broad peaks the right peak ranging from 100 to 500 m is associated with residual and dissolution intergranular pores the middle peak is mainly composed of dissolution intergranular and intragranular pores with radii between 10 and 100 m the left peak exhibited fluctuations and is characterized by dissolution intragranular and intercrystalline pores with radii of 37 nm 10 m according to the pore types sizes and proportions in the fpsd the pores are classified as intercrystalline nanopores 100 m a storage capacity evaluation combining the classifications and fpsd indicates that the macropores and nanopores primarily contribute to porosity albeit with contrasting influences on the storage capacity the contents of macropores determine the storage capacity of a deeply buried sandstone reservoir while the negative effects of nanopores become predominant with decreasing porosity a percolation capacity evaluation on the basis of crmi results suggests that the permeability contribution is dominated by nanopores in tight sandstone controlled by micro small pores in low permeability sandstone and dominated by mesopores in conventional sandstone mesopores always play a favorable role in percolation however the negative impacts of nanopores should be considered in low permeability and tight sandstone micro small pores have a negative influence on the permeability of conventional sandstone but are favorable for the fluid percolation of most low permeability and tight sandstone reservoirs a new empirical equation indicates that r10 of the fpsd is the suitable as the proper pore throat radius for the permeability estimation of deeply buried sandstone reservoirs

glacier recession on cerro charquini 16 s bolivia since the maximum of the little ice age 17th century cerro charquini bolivia cordillera real 5392 m a s l was selected as a site to reconstruct glacier recession since the maximum of the little ice age lia in the central andes five glaciers located on differently exposed slopes present comprehensive and well preserved morainic systems attributed to former centuries the moraines were dated by lichenometry and show a consistent organization on the different slopes the past geometry of the glaciers was reconstructed using ground topography and aerophotogrammetry lichenometric dating shows that the lia maximum occurred in the second half of the 17th century after which the glaciers have receded nearly continuously over the last decades of the 20th century 1983 97 recession rates increased by a factor of four on the northern and western slopes glaciers receded more than on the southern and eastern slopes by 78 and 65 of their lia maximum area respectively the mean equilibrium line altitude ela rose by about 160 m between the lia maximum and 1997 recession rates were analysed in terms of climatic signal suggesting that glacier recession since the lia maximum was mainly due to a change in precipitation and that the 19th century may have been drier for the 20th century a temperature rise of about 0 68c appears to be the main cause of glacier recession recent climatic conditions from 1983 to 1997 correspond to a mass deficit of about 1 36 m w e a 1 if such conditions persist the small glaciers below 5300 m a s l in the cordillera real should disappear completely in the near future

how does the pore throat size control the reservoir quality and oiliness of tight sandstones the case of the lower cretaceous quantou formation in the southern songliao basin china abstract pore throat size is a very crucial factor controlling the reservoir quality and oiliness of tight sandstones which primarily affects rock properties such as permeability and drainage capillary pressure however the wide range of size makes it difficult to understand their distribution characteristics as well as the specific controls on reservoir quality and oiliness in order to better understand about pore throat size distribution petrographic scanning electron microscopy sem pressure controlled mercury injection pmi rate controlled mercury injection rmi quantitative grain fluorescence qgf and environmental scanning electron microscopy esem investigations under laboratory pressure conditions were performed on a suite of tight reservoir from the fourth member of the lower cretaceous quantou formation k 1 q 4 in the southern songliao basin china the sandstones in this study showed different types of pore structures intergranular pores dissolution pores pores within clay aggregates and even some pores related to micro fractures the pore throat sizes vary from nano to micro scale the pmi technique views the pore throat size ranging from 0 001 m to 63 m and revealed that the pore throats with radius larger than 1 0 m are rare and the pore throat size distribution curves show evident fluctuations rmi measurements indicated that the pore size distribution characteristics of the samples with different porosity and permeability values look similar the throat size and pore throat radius ratio distribution curves had however significant differences the overall pore throat size distribution of the k 1 q 4 tight sandstones was obtained with the combination of the pmi and rmi methods the permeability is mainly contributed by a small part of larger pore throats less than 30 and the ratio of the smaller pore throats in the samples increases with decreasing permeability although smaller pore throats have negligible contribution on reservoir flow potential they are very significant for the reservoir storage capacity the pore throats with average radius larger than 1 0 m mainly exist in reservoirs with permeability higher than 0 1md when the permeability is lower than 0 1md the sandstones are mainly dominated by pore throats with average radius from 0 1 m to 1 0 m the ratio of different sized pore throats controls the permeability of the tight sandstone reservoirs in different ways we suggest that splitting or organizing key parameters defining permeability systematically into different classes or functions can enhance the ability of formulating predictive models about permeability in tight sandstone reservoirs the pmi combined with qgf analyses indicate that oil emplacement mainly occurred in the pore throats with radius larger than about 0 25 0 3 m this result is supported by the remnant oil micro occurrence evidence observed by sem and esem

ice core palaeoclimate records in tropical south america since the last glacial maximum ice core records spanning the last 25 000 yr from the tropical andes of south america are reviewed these records from quelccaya huascaran and sajama present a high temporal resolution picture of both the late glacial stage lgs and the holocene climatic and environmental conditions in the south american andes late glacial stage conditions at high elevations appear to have been cooler than today although the magnitude of the inferred cooling differs with the particular proxy used e g snowline depression pollen ice cores insoluble dust and anion concentrations in the ice cores reveal that lgs hydrological conditions in the tropics 9 s were much drier than today whereas in the subtropics 18 s lgs conditions were much wetter this probably reflects the migration of the tropical hadley cell in response to a different meridional temperature gradient low nitrate concentrations in the lgs ice from both huascaran and sajama suggest that the amazon basin forest cover may have been much less extensive discussed is the conundrum surrounding the use of d 18 o as a palaeothermometer in the tropics where temperatures exhibit little seasonal variation yet the ice core records suggest that d 18 o records temperature variations on decadal to millennial time scales finally evidence is presented for a strong twentieth century warming copyright 2000 john wiley sons ltd

enso signals of the twentieth century in an ice core from nevado illimani bolivia 1 an ice core from nevado illimani in the eastern bolivian altiplano was used to establish proxy data for past climate conditions for this purpose a principal component analysis pca was performed on the records of ionic species of the upper 59 2 m time period 1887 6 to 1999 a d the first principal component pc1 shows high loadings of mainly dust related ions this signal is inversely correlated on a monthly basis with precipitation on the bolivian altiplano maxima in the pc1 time series correspond to the dry season on the altiplano during the austral winter whereas minima occur during the wet season from november to march interannual variability of pc1 reveals correlations with indices of the el nino southern oscillation enso showing elevated reduced dust values at the nevado illimani site during warm cold phases this relationship may be explained by below above average december february precipitation in the bolivian altiplano during el nino la nina episodes persistent el nino events such as those in the years 1915 1942 and 1993 a d seem to imprint very strong dust signals in the illimani ice core out of the six pcs extracted only the pc1 time series is correlated with the tropical southern atlantic index thus we suggest that the major climate variability on the bolivian altiplano as recorded in the nevado illimani ice core is more closely related to conditions in the pacific even though the moisture source at this site is ultimately the atlantic ocean

a new andean deep ice core from nevado illimani 6350 m bolivia abstract a new ice core record from the nevado illimani 16 s bolivia covers approximately the last 18 000 years bp a comparison with two published ice records from sajama 18 s bolivia thompson et al science 282 1998 1858 1864 and huascaran 9 s peru thompson et al science 269 1996 46 50 documents a regionally coherent transition from glacial to modern climate conditions in south america north of 20 s the strong resemblance between the illimani and huascaran water isotope records and their differences from the sajama record in particular during the period from 9000 years bp to 14 000 years bp suggest that local water recycling or local circulation changes played a major role for sajama we interpret the common illimani huascaran water isotope history in terms of a common change from wetter cooler conditions during glacial times to drier warmer conditions in the early holocene

characterization of pore systems in seal rocks using nitrogen gas adsorption combined with mercury injection capillary pressure techniques abstract porous microstructure parameters of seal rock samples originating from different depths within brazilian geological formations were correlated to empirical models which predict the intrinsic permeability mercury injection capillary pressure micp and nitrogen gas adsorption n 2 ga were applied in combination as complementary techniques micp to obtain the porosity values and the size distribution of meso and macropores and n 2 ga associated with the brunauer emmett and teller bet theory to determine the specific surface area s o the barret joyner and hallenda bjh theory was applied to find the size distribution of the micro and mesopores the combination of the micp and n 2 ga curves showed that the samples analyzed present a polymodal pore size distribution psd and a total porosity ranging from 0 33 to 10 44 the s o values measured by n 2 ga were higher than those calculated by micp due to the majority of the samples having a mean pore size of 20 1000 a the intrinsic permeability could also be predicted applying the measured parameters s o psd curves and total porosity in the carman kozeny and series parallel models the ranges of permeability values obtained were 4 09 10 24 4 96 10 21 m 2 and 9 48 10 27 9 14 10 22 m 2 respectively these results were compared with values reported in the related literature and those obtained for four samples submitted to pressure pulse decay permeability pdp tests

el nino southern oscillation events recorded in the stratigraphy of the tropical quelccaya ice cap peru snow accumulation measured during 1982 1983 on the quelccaya ice cap peru was 70 percent of the average from 1975 through 1983 inspection of 19 years 1964 through 1983 of accumulation measured near the summit of quelccaya reveals a substantial decrease 30 percent in association with the last five el nino southern oscillation enso occurrences in the equatorial pacific the enso phenomenon is now recognized as a global event arising from large scale interactions between the ocean and the atmosphere understanding this extreme event with the goal of prediction requires a record of past occurrences the quelccaya ice cap which contains 1500 years of annually accumulated ice layers may provide a long and detailed record of the most extreme enso events

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

evaluation of pore structures in volcanic reservoirs a case study of the lower cretaceous yingcheng formation in the southern songliao basin ne china different pore types and variable pore structures can determine reservoir potentials of volcanic rocks therefore it is of great importance to understand the pore structures of volcanic reservoirs with the lower cretaceous yingcheng volcanic rocks this study attempts to investigate and evaluate the micro pore structures of a volcanic reservoir through 1 measuring porosity and permeability of core samples 2 identifying pore types within thin sections 3 characterizing pore structures with pressure controlled mercury injection the lower cretaceous yingcheng volcanic rocks exhibits low porosities on average 7 39 and very low permeability on average 0 283 10 6 m2 three major pore types were identified from the lower cretaceous yingcheng volcanic reservoir including primary pores secondary pores and fractures additionally the pore structures of the lower cretaceous yingcheng volcanic reservoir can be classified into three types type i pore structure primarily occurs in the volcanic breccia crystal tuff and tuffites the corresponding pore system is dominated by primary intergranular pores intragranular dissolved pores and devitrified micropores with porosity and permeability higher than 5 4 and 0 05 10 6 m2 respectively corresponding mercury intrusion curves are characterized by low displacement pressure high maximum mercury saturation and mercury withdrawal efficiency type ii pore structure is commonly observed in the tuff and tuffites while primary intergranular pores and secondary micropores dominate pore system with porosity of 2 5 5 4 and permeability of 0 012 0 05 10 6 m2 the mercury intrusion curves are similar to the type i type iii pore structure is also pervasively developed in the crystal tuff and tuffites intragranular dissolved micropores are most important ones with porosity and permeability less than 2 5 and 0 01 10 6 m2 respectively different from type i and ii pore structure the mercury intrusion curves of the type iii have high displacement pressure low maximum mercury saturation and mercury withdrawal efficiency indicating poor reservoir quality

microscopic pore structures of tight sandstone reservoirs and their diagenetic controls a case study of the upper triassic xujiahe formation of the western sichuan depression china abstract the study of microscopic pore structures is of central significance to the evaluation of the reservoir quality and well productivity of tight gas sandstone the second and fourth members abbreviated as t3x2 and t3x4 respectively of the upper triassic xujiahe formation of the western sichuan depression were used as cases to analyze microscopic pore structures and diagenetic controls in consideration of the disparities in reservoir quality and well productivity optical microscopy of thin sections micro ct scanning scanning electron microscopy sem high pressure mercury injection hpmi and apex methods based on the hpmi results were used to determine the pore and throat geometries and the types and pore size distributions in terms of the quantity and levels of pore connectivity tight sandstone reservoirs of the study area are characterized by poor physical properties with the t3x2 reservoirs presenting relatively higher levels of permeability and lower porosity levels than those of the t3x4 reservoirs the pore spacing configurations sizes and distributions and throat geometries reveal significant disparities primary pores and micro fractures were found to be more developed in the t3x2 reservoirs with bending and narrow pore throats measured as smaller than 0 5 m compared to those of the t3x2 reservoirs secondary pores including moldic and intracrystalline pores were more developed in the t3x4 reservoirs with relatively larger straighter and wider throats of 0 5 1 0 m an evaluation of the pore connectivity levels shows that only 26 86 and 28 90 pores are closely connected to the whole for t3x2 and t3x4 reservoirs respectively four major diagenetic processes were found to control reservoir quality and the microscopic pore structure mechanical compaction is the primary cause of the densification of reservoirs in the study area compared to that observed in the t3x4 reservoirs more intensive mechanical compaction was observed in the t3x2 reservoirs changing the configuration of the throats present reducing the pore throat radii and ultimately lowering the porosity of t3x2 reservoirs as a whole quartz overgrowth and late period carbonate cements were observed in partly filled pore spaces narrowing throats and reducing pore connectivity but eogenetic cementation and chlorite cements can increase the pressure resistance of sandstone and inhibit compaction quartz overgrowth thus t3x4 reservoirs are relatively more porous as a result of eogenetic calcite cementation and primary pores are more developed in t3x2 reservoirs with chlorite cements dissolution is a major factor that improves the tight sandstone reservoir quality because it generates a large volume of secondary pores the more intensive levels of dissolution in t3x4 reservoirs not only creates more intergranular intragranular moldic and intracrystalline pores but also further increases the porosity of t3x4 reservoirs fracturing effects have developed in the study area to improve pore connectivity levels and thus the permeability of tight sandstone reservoirs potentially explaining the pore connectivity and permeability of certain t3x2 reservoirs this work may be able to be used as a useful reference for the reservoir quality evaluation and exploration of tight gas sandstone reservoirs for similar oil fields worldwide

diagenetic alteration pore throat network and reservoir quality of tight gas sandstone reservoirs a case study of the upper paleozoic sequence in the northern tianhuan depression in the ordos basin china the sulige gas field in the ordos basin is the largest gas field in china the studied area the northern tianhuan depression is located west of the gas field and is considered as a potential gas producing area the complex diagenetic alteration history and its effects on the pore throat network and reservoir quality of the tight gas sandstones are explained the upper paleozoic first member of the shanxi formation and eighth member of the shihezi formation tight gas reservoir rocks are composed of coarse to medium grained sandstones and are dominated by sublitharenites the most important diagenetic factor for porosity reduction was compaction followed by cementation diagenetic mineral phases include quartz overgrowth calcite cement and replacement and kaolinite cement and replacement with minor heulandite and chlorite pressure dissolution of quartz grains and quartzite fragments is the main source of silica for the early and late quartz overgrowth cementation formed mainly from 120 c to 140 c the hydrolysis and alteration of volcanic material and mica flakes released some silicon calcium and aluminum ions calcium and carbon in calcite cements could be derived from surrounding mudstones calcite replaced the quartz overgrowths the formation of kaolinite as cement and replacements was controlled by the interactions of silica aluminum ph and temperature 140 c because of deformation of detrital components mica flakes and ductile rock fragments and diagenetic replacement clear negative correlations between reservoir quality and contents of the diagenetic minerals are lacking a complex and isolated pore throat network was created by strong diagenetic transformation based on analysis of thin sections three dimensional x ray micro computed tomography and constant rate mercury injection data the samples with relatively good reservoir quality porosity 10 and permeability 0 5 md are characterized by dissolution pores and primary intergranular pores and commonly contain more and larger pore throats both in volume counts 1800 and size 0 02 per unit volume and diameter 1 20 m than the samples with poor reservoir quality the intercrystalline pores of kaolinite are very widespread and considered favorable for oil and gas accumulation because some asphalt was found within these pores this study may be used by analogy to better understand diagenetic factors controlling the formation of tight gas sandstone reservoirs and predict the development of pore throat systems

innovative methods for flow unit and pore structure analyses in a tight siltstone and shale gas reservoir tight gas reservoirs are notoriously difficult to characterize routine methods developed for conventional reservoirs are not appropriate for tight gas reservoirs in this article we investigate the use of nonroutine methods to characterize permeability heterogeneity and pore structure of a tight gas reservoir for use in flow unit identification profile permeability is used to characterize fine scale 1 in 2 5 cm vertical heterogeneity in a tight gas core more than 500 measurements were made profile permeability although useful for characterizing heterogeneity will not provide in situ estimates of permeability furthermore the scale of measurement is much smaller than log scale pulse decay permeability measurements collected on core plugs under confining pressure were used to correct the profile permeability measurements to in situ stress conditions and 13 point averages of profile permeability were used to relate to log derived porosity measurements finally n2 adsorption a new method for tight gas was used to estimate the pore size distribution of several tight gas samples a unimodal or bimodal distribution was observed for the samples with the larger peak corresponding to the dominant pore throat size as confirmed by independent methods furthermore the adsorption desorption hysteresis loop shape was used to interpret the dominant pore shape as slot shaped pores which is typical of many tight gas reservoirs the n2 adsorption method provides rapid analysis and does not suffer from some of the same limitations of hg injection in the future we hope that the n2 adsorption method may prove useful for flow unit characterization based on dominant pore size of fine grained siltstone shale tight gas reservoirs

pore structure characteristics of an ultradeep carbonate gas reservoir and their effects on gas storage and percolation capacities in the deng iv member gaoshiti moxi area sichuan basin sw china abstract evaluating reservoir storage and percolation capacities which are closely associated with pore morphology and connectivity is significant for the exploration and exploitation of oil and gas fields however ultradeep carbonate gas reservoirs have extremely high heterogeneity and complexity compared to other relatively shallow reservoirs therefore investigations into all aspects of ultradeep carbonate face enormous challenges to the best of our knowledge no systematic study on the pore structure characteristics of ultradeep carbonate gas reservoirs has been conducted to date in this paper the pore structure characteristics and their effects on the gas storage and percolation capacities of the deng iv member gas reservoir were investigated using conventional petrophysical measurements casting thin section analysis scanning electron microscopy sem high pressure mercury intrusion hpmi tests and multiscale ct scanning analysis the results show that the lithology of the deng iv member reservoir is dominated by algal clotted dolomite algal stromatolite dolomite and algal doloarenite the conventional petrophysical measurements indicate that the average porosity and permeability are 3 91 and 1 02 md respectively however the high porosity 8 4 and high permeability 10 10 000 md intervals are developed locally the casting thin sections sem and two dimensional ct analyses identify six main types of reservoir spaces in the deng iv member interparticle dissolution pores intercrystal dissolution pores fenestriform cavities dissolution cavities structural fractures and dissolution fractures furthermore three types of throats that is necking tubular and lamellar were also detected four types of reservoirs namely matrix type pore type cavity type and fracture cavity type were classified according to the comprehensive analysis of hpmi data and curves three dimensional pore throat network topologies were reconstructed for four types of representative core samples based on the multiscale ct scanning data and maximum ball method the distribution characteristics of pore throat radii volumes and coordination numbers reveal the following the reservoir space of fracture cavity type is dominated by cavities and multiscale pore throats with the best pore throat connectivity the reservoir space of cavity type is primarily controlled by cavities and large scale pore throats with moderate connectivity the reservoir space of pore type comprises multiscale pore throats with moderate connectivity and most areas of matrix type reservoir are occupied by rock matrix and the pore throat connectivity is the worst in conclusion the development of fractures and bedding cavities considerably improves the reservoir percolation capacity and the development of cavities is an important supplement to the reservoir storage capacity the reasonable combination of cavities and fractures is the basis for the efficient development of ultradeep carbonate gas reservoirs

pore throat sizes in sandstones tight sandstones and shales pore throat sizes in siliciclastic rocks form a continuum from the submillimeter to the nanometer scale that continuum is documented in this article using previously published data on the pore and pore throat sizes of conventional reservoir rocks tight gas sandstones and shales for measures of central tendency mean mode median pore throatsizes diameters are generally greater than2 mm in conventionalreservoir rocks range from about 2 to 0 03 mm in tight gas sandstones and rangefrom0 1to0 005 mminshales hydrocarbonmolecules asphaltenes ring structures paraffins and methane form another continuum ranging from 100 a 0 01 mm for asphaltenes to 3 8 a 0 00038 mm for methane the pore throat size continuum provides a useful perspective for considering 1 the emplacement of petroleum in consolidated siliciclastics and 2 fluid flow through fine grained source rocks now being exploited as reservoirs

the little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap the analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent annual variations in visible dust layers oxygen isotopes microparticle concentrations conductivity and identification of the historical a d 1600 huaynaputina ash permit accurate dating and time scale verification the fact that the little ice age about a d 1500 to 1900 stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event

impacts of sedimentology and diagenesis on pore structure and reservoir quality in tight oil sandstone reservoirs implications for macroscopic and microscopic heterogeneities abstract integrated analysis of reservoir quality pore structure depositional and petrologic characteristics and types and degree of diagenetic alterations was done in this study by employing petrophysical evaluation thin section observation stable isotope analysis scanning electron microscopy combined with eds x ray computed tomography and high pressure mercury intrusion the purpose was to investigate the macroscopic and microscopic heterogeneities and the effects of depositional factors and diagenetic alterations responsible for them the results indicate that the chang 8 tight oil sandstone of the longdong area in the ordos basin can be divided into three categories namely the type i reservoir with porosity greater than 10 and permeability greater than 1 0 md having sparse lenticular distributions in the mouth bar of the braided delta front the type ii reservoir with porosity of 6 10 and permeability of 0 1 1 0 md mainly distributing in the distributary channel and the type iii reservoir with porosity less than 6 and permeability less than 0 1 md having a reticular distribution in the distributary bay the type i reservoir has an intergranular pore inter p dominant pore system with a greater pore throat radius 1 10 m a larger pore volume and better connectivity the type ii reservoir has a mixed system consisting of intragranular pores intra p and inter p with a pore throat radius of 0 1 1 m smaller pore volume and worse connectivity the type iii reservoir is characterized by an intra p dominated system with a radius between 10 and 500 nm smallest pore volume and worst connectivity the wide range of porosity permeability and pore structure parameters can be attributed to the frequent variations in depositional facies and diagenetic alterations larger grain size higher content of quartz and feldspar and moderate grain coating chlorite content less than 8 are favorable for the preservation of intergranular pores and dominate the formation of the type i reservoir the mesogenetic calcite and ferrocalcite cementation and pore filling kaolinite precipitation obstruct the intergranular space and are the predominant factors tightening the reservoirs in the distributary channel and distributary bay leading to multi scale heterogeneities secondary porosity from dissolution plays a much more important role in contributing to the porosity and permeability of the type ii and iii reservoirs than of the type i reservoir the study provide a comprehensive understanding for the multi scale heterogeneities and can be used to predict the potential high quality zones in tight oil sandstone reservoirs

recording of el nino in ice core δ18o records from nevado huascaran peru the 68 year monthly resolved time series of 18 o from ice cores retrieved from the glaciated col of nevado huascaran peru 9 s 77 w 6050 m reflects climate variability over amazonia and the western tropical atlantic over the 25 year period 1968 1993 of midtroposphere observations the interannual variations in huascaran 18 o relate closely with the zonal wind variations over tropical south america at the 500 hpa level additionally there is some evidence that the spatial distribution of temperature anomalies in the western tropical atlantic has influence on the 500 hpa circulation and hence the isotopic fractionation of moisture advected across amazonia during el nino warming the moisture convergence axis over the atlantic ocean is commonly diverted northward leading to unusual warm and dry conditions over northeast brazil and 18 o enriched snowfall at huascaran this enrichment phase is enhanced when the peak pacific warming occurs during the first half of the calendar year coincident with the wet season over amazonia approximately 12 months later the el nino demise is affiliated with a reprisal of strong trade wind circulation and the resultant cool pluvial environment over amazonia triggers a reversal to strongly depleted isotope anomalies

comparison of recent probabilistic seismic hazard maps for southern california abstract probabilistic seismic hazard psh maps for southern california produced from the models of ward 1994 the working group on california earthquake probabilities 1995 and the u s geological survey and california division of mines and geology frankel et al 1996 petersen et al 1996 show the peak ground accelerations predicted with each model to occur at 10 probability in 50 years and the probability that 0 2 g will occur in 30 years for rock site conditions differences among the maps range up to 0 4 g and 50 respectively we examine the locations and magnitudes of the differences as a basis to define the issues and avenues of research that may lead to more confident estimates of psh in the future our analysis shows that three major factors contribute to the observed differences between the maps they are the size of maximum magnitude assigned to a given fault the proportion of predicted earthquakes that are distributed off the major faults and the use of geodetic strain data to predict earthquake rates

dating of two nearby ice cores from the illimani bolivia 1 in order to establish a chronology of two nearby ice cores from a glacier at illimani 6438 m bolivia a broad dating approach is presented here which in particular makes use of the fast simple and nearly nondestructive electrical conductivity method ecm that provides a highly resolved record thus ecm is suited for counting annual layers in the ice especially for ice cores extracted from high mountain glaciers with a fast layer thinning furthermore ecm can be used for detecting volcanic signals annual signals in the ecm record of the illimani ice core were identified using the 1964 a d tritium reference horizon and were counted along 125 m or 90 of the core representing the time period from 1200 240 a d estimated accumulated error to 1999 a d the resulting age depth relationship was supported by counting annual peaks in the microparticle record as well as by nuclear dating using the decay of 210pb the identification of volcanic signals originating from eruptions such as pinatubo 1991 a d el chichon 1982 a d agung 1963 a d krakatoa 1883 a d tambora 1815 a d and the unknown 1258 a d significantly reduced the uncertainty of annual layer counting alc to 2 years in the vicinity of these events

a first shallow firn core record from glaciar la ollada cerro mercedario central argentine andes in january 2003 shallow firn cores were recovered from glaciar esmeralda on cerro del plomo 33814 0 s 70813 0 w 5300 m a s l central chile and from glaciar la ollada on cerro mercedario 31858 0 s 70807 0 w 6070 m a s l argentina in order to find a suitable archive for paleoclimate reconstruction in a region strongly influenced by the el nino southern oscillation in the area between 288 s and 358 s the amount of winter precipitation is significantly correlated to the southern oscillation index with higher values during el nino years glaciochemical analysis indicates that the paleo record at glaciar la ollada is well preserved whereas at glaciar esmeralda the record is strongly influenced by meltwater formation and percolation a preliminary dating of the mercedario core by annual layer counting results in a time span of 17 years 1986 2002 yielding an average annual net accumulation of 0 45 m w e

insights into the pore structure and implications for fluid flow capacity of tight gas sandstone a case study in the upper paleozoic of the ordos basin abstract tight gas sandstone is characterized by varied pore structures controlling the fluid flow and influencing the gas productivity a combination of casting thin section scanning electron microscopy pressure controlled porosimetry x ray computed tomography nuclear magnetic resonance x ray diffraction and grain size analysis is conducted on the permian aged tight gas sandstone in the daniudi area of the ordos basin to investigate the overall pore structure its controlling factors and its influences on the fluid mobility pores of tight gas sandstone are in a wide size range 65 nm 100 m dominated by gaussian and bimodal distribution patterns and can be divided into intergranular and intragranular pores according to the fractal features varied pore structures are attributed to the differences in compaction and cementation high framework grain content and large grain size benefit the intergranular porosity preservation resulting in larger pore volumes greater pore radii and better connectivity calcite and clay cements dominate the tightening of tight gas sandstone according to the connection between pore structure and its main geological controlling factors the grain supported intergranular pore model with high rigid grain content large grain size and dominant intergranular porosity compaction intergranular pore model with relative low rigid grain content smaller grain size medium cement content and mixed intergranular and intragranular porosities and cementation intragranular pore model with small grain size high cement content and dominant intragranular porosity are defined correlation analyses indicate that the reservoir quality and fluid mobility are controlled by pore structures the porosity exhibits a strong positive dependence on the average pore volume while permeability is determined by median pore radius coordination number and intergranular pore proportion movable fluids occur in a wide pore range between 96 nm and 98 m with their minimum and upper bound radii positively correlated with permeability movable porosity can serve as a direct indicator for fluid flow capacity which is determined by the movable porosity contribution of intergranular pores the increasing negative influence of intragranular pores on fluid flow should be taken into account with decreasing permeability and increasing clay content the grain supported pore model is deduced to be characterized by the highest fluid mobility indicating a great tight gas production potential

high net accumulation rates at campo de hielo patago nico sur south america revealed by analysis of a 45 97 m long ice core a45 97mlongicecorewasrecoveredintheaccumulationareaof glaciar tyndall 50 59 05 s 73 31 12 w 1756ma s l campo de hielo patagonico sur southern patagoniaicefield during december1999 thefirncorewassubjectedtovisualstratigraphic observationandbulkdensitymeasurementsinthefield andlatertoanalysesofwaterisotopes d 18 o dd major dissolved ions and snow algalbiomass the drillhole remained dry down to about 43m depth where a water soaked layer appeared seasonal cycles were found for d 18 o dd and the d excess although the amplitudes of the cycles decreased with depth major dissolved ions na k mg 2 ca 2 cl so4 2 and algal biomass exhibit rapid decreases in the upper 3m probably due to meltwater elution annual increments defined by the d 18 o and d excess peaks suggest that the minimum net accumulation rates at this locationwere17 8ma 1 in1997 98 1998 99 and 411 0ma 1 in1998 99 1999 2000 theseare much higher valuesthanthose previously obtained frompast ice core studies in patagonia but are of the same order of magnitude as those predicted from various observations in ablation areas of patagonian glaciers

low latitude ice cores record pacific sea surface temperatures matic records suggested that a more conventional temperature interpretation might be more appropriate with lower isotopic values during the presumed to be cooler little ice age and increasingly enriched precipitation during the 20th century warming phase thompson 2001 3 both of these conflicting interpretations suffer from inadequate calibration of the observed isotopic record in relation to climatic conditions during periods of snow accumulation on the ice caps here we use the results of on site meteorological measurements to determine the seasonality of the ice core record and then assess how the isotopic records relate to temperature precipitation and the larger scale circulation associated with snowfall at these high elevation sites we then extend the analysis to ice core records from the asian monsoon region this empirical approach to the interpretation of the isotopic record in low latitude ice cores complements theoretical studies by broecker 1997 and pierrehumbert 1999

a 25 000 year tropical climate history from bolivian ice cores ice cores that were recovered from the summit of sajama mountain in bolivia provide carbon 14 dated tropical records and extend to the late glacial stage lgs oxygen isotopic ratios of the ice decreased 5 4 per mil between the early holocene and the last glacial maximum which is consistent with values from other ice cores the abrupt onset and termination of a younger dryas type event suggest atmospheric processes as the probable drivers regional accumulation increased during the lgs during deglaciation and over the past 3000 years which is concurrent with higher water levels in regional paleolakes unlike polar cores sajama glacial ice contains eight times less dust than the holocene ice which reflects wetter conditions and extensive snow cover

pore structure characteristics of tight sandstones in the northern songliao basin china abstract understanding the pore structure characteristics of tight gas sandstones is the primary purpose of reservoir evaluation and efforts to characterize tight gas transport and storage mechanisms and their controls due to the various pore types and multi scale pore sizes in tight reservoirs it is essential to combine several techniques to characterize pore structure scanning electron microscopy sem nitrogen gas adsorption n2ga mercury intrusion porosimetry mip and nuclear magnetic resonance nmr were conducted on tight sandstones from the lower cretaceous shahezi formation in the northern songliao basin to investigate pore structure characteristics systematically e g type and size distribution of pores and to establish how significant porosity and permeability are for different pore types the studied tight sandstones are composed of intergranular pores dissolution pores and intercrystalline pores the integration of n2ga and nmr can be used as an efficient method to uncover full pore size distribution psd of tight sandstones with pore sizes ranging from 2 nm to dozens of microns the full psds indicate that the pore sizes of tight sandstones are primarily distributed within 1 0 m with an increase in porosity and permeability pores with larger sizes contribute more to porosity intercrystalline pores and intergranular dissolution pores can be clearly distinguished on the basis of mercury intrusion and surface fractal the relative contribution of intercrystalline pores to porosity ranges from 58 43 to 91 74 with an average of 79 74 the intercrystalline pores are the primary contributor to pore space whereas intergranular dissolution pores make a considerably greater contribution to permeability a specific quantity of intergranular dissolution pores is the key to producing high porosity and permeability in tight sandstone reservoirs the new two permeability estimation models show an applicable estimation of permeability with r2 values of 0 955 and 0 962 for models using dmax pore diameter corresponding to displacement pressure and df pore diameter at inflection point respectively these results indicate that both dmax and df are key factors in determining permeability

pore throat structure characteristics and its effect on flow behavior in gaotaizi tight siltstone reservoir northern songliao basin abstract the features of pore and throat structure of an unconventional reservoir are very complex due to multiscale pore throat size and various pore types and thus hard to characterize in this study thin sections field emission scanning electron microscope fe sem x ray diffraction xrd granulometry analysis physical properties measurements mercury intrusion capillary pressure micp and nitrogen gas adsorption analysis n2ga were combined to investigate the pore throat structures of the gaotaizi tight siltstone reservoir in the northern songliao basin the results of observation suggest that the pores are composed of intergranular pores dissolution pores intercrystalline pores within clay minerals and micro fractures the content of calcite cement has some negative effect on porosity the content and types of clay minerals have some negative influence on petrophysical properties of reservoir as well micp and n2ga are combined to get the full range of pore throat size distribution based on previous studies and the actual situation of the gaotaizi reservoir a new classification for pore throat size has been proposed including micropore 100 nm mesopore 100 nm 0 625 m and macropore 0 625 m on this basis the contents of pore throat in different scales have been calculated the gaotaizi tight siltstone reservoir has been divided into three types based on the pore throat structure there are big differences among the three types of reservoir with respect to the grain size the content of matrix the types of diagenetic minerals the dominant pore types the pore throat size distribution and the percentage of pore throats in different scales accordingly a pore structure model has been constructed for each type of reservoir in addtion it has been found that the pore throat structure has an important effect on the percolation capacity of the tight siltstone reservoir porosity and pore throat radius have a positive correlation with the permeability pore throats in different scales have different impact on the flow characteristics of tight reservoir the mesopores and macropores make a great contribution to the flow in the reservoir while the micropores and transition pores do not contribute and even have an inhibitional effect in general the permeability or the flow characteristics of the tight siltstone reservoir are mostly controlled by the pore throats larger than 0 1 m

insight into pore throat size distribution and the controls on oil saturation of tight sandstone reservoirs using nuclear magnetic resonance parameters a case study of the lower cretaceous quantou formation in the southern songliao basin china pore throat structure characterization is crucial in tight oil sandstone reservoir studies to better understand pore throat size distribution and the effects on reservoir oil saturation petrographic scanning electron microscopy quantitative grain fluorescence qgf nuclear magnetic resonance nmr and pressure controlled mercury injection investigations were performed on a suite of tight sandstones from the fourth member of the lower cretaceous quantou formation k1q4 in the southern songliao basin china the tight sandstone samples showed similar compositional and textural maturity but different reservoir qualities at different depth intervals two oily indicators qgf index and qgf on extract spectra intensity varied significantly with respect to burial depth suggesting the existence of strong oil heterogeneities in the k1q4 tight sandstones oil emplacement occurred mainly in the primary pores associated with the absence of pore filling authigenic minerals pore throat size distributions had wider ranges in the oil rich layers than in the samples lacking oil emplacement the nmr pore throat radii ranged from 0 01 to 10 m in oil lacking samples but ranged from 0 01 to 100 m in oil rich layers oil signals were mainly detected in the pore throats with radii ranging from approximately 0 1 to 1 0 m in oil rich layers the nmr porosity can be divided into three parts based on transverse relaxation time t2 spectrum 1 immovable fluid 2 porosity of effective movable fluid pemf and 3 porosity of bound fluid bivariate plots of the ratios of various porosity types have significant effects in deciphering the oil saturation of tight sandstone reservoirs the pemf reflected well the reservoir qgf index among others therefore it can be considered as an effective nmr parameter to characterize pore size distribution and helpful in oil reservoir prediction a good relationship exists between pemf and geometric mean of the t2 distribution t2gm indicating that t2gm could also reflect reservoir oil saturation the pemf is mainly contributed by large pore throats and the poorly sorted pore throat distribution is better for effective movable fluids occurrence in tight sandstones the approach employed in this study provides a more comprehensive and accurate pore throat structure characterization in tight sandstone oil reservoirs generating effective parameters and convenient ways to evaluate reservoir oil saturation importantly it could be applicable for improving tight sandstone oil exploration and development efficiencies

clarifying pore diameter pore width and their relationship through pressure measurements a critical study abstract understanding geometrical and topological properties of the pore space in permeable media is of paramount importance particularly in oil and gas production pore space characteristics such as pore sizes and their probability distributions as well as pore s connectivity are main factors in the modeling of fluid flow and chemical transport in soils and rocks a common method to determine the pore size is to convert an implemented pressure via either the young laplace or kelvin equation by assuming a specific pore shape simple geometries such as cylindrical and slit shaped have been frequently used in the literature particularly to represent pores and to derive theoretical models estimating permeability from pore throat size distribution in this study we clarify the relationship between pore diameter d and pore width w two terms interchangeably used in the literature the former corresponds to a cylindrical pore while the latter to a slit shaped one we emphasize that d 2w in contrast to previously published studies claiming that the diameter of a cylindrical pore is equal to the distance between sides of a slit shaped pore i e d w in addition we discuss that comparing combining pore size distribution derived from mercury intrusion porosimetry and that determined from nitrogen adsorption isotherm is not supported unless the effect of hysteresis is trivial as most probably the former represents pore throat while the latter pore body size distributions

effect of pore structure on the producibility of tight gas sandstones the estimated ultimate recovery eur is one of the most significant properties of tight gas sandstone reservoirs but it remains difficult to predict estimated ultimate recovery is dependent on the success of stimulation by hydraulic fracturing the existence and connectivity of natural fractures and as illustrated in this article the pore structure of the matrix here we analyze the lab measurements that are indicative of the pore structure and then we predict the effect of pore structure on producibility we develop a relationship between the eur of tight gas sandstones and their petrophysical properties measured by drainage and imbibition tests mercury intrusion withdrawal and porous plate and by resistivity analyses we use the ratio of residual mercury saturation after mercury withdrawal s gr to initial mercury saturation s gi which is the saturation at the start of withdrawal as a measure of gas likely to be trapped in the matrix during production and hence a proxy for eur a multitype pore space model is required to explain mercury intrusion capillary pressures in these rocks implications of this model are supported by other available laboratory measurements the model comprises a conventional network model and a treelike pore structure an acyclic network that mimic the intergranular and intragranular void spaces respectively the notion of the treelike pore structure is introduced here for the first time in the context of tight gas sandstones applying the multitype model to porous plate data we classify the pore spaces of rocks into intergranular dominant intermediate and intragranular dominant this pore space classification is topological and is not based on scale or size these classes have progressively less drainage and imbibition hysteresis which leads to the prediction that significantly more hydrocarbon is recoverable from intragranular porosity than intergranular porosity available field data production logs corroborate the higher producibility of intervals with intragranular porosity although the data are not sufficient to eliminate the possible contribution of other factors such as size and shape of the volume contacted by hydraulic fractures or the presence and attributes of natural fractures the superior recovery of hydrocarbon from intragranular dominant pore structures is despite its inferior initial production rate

recalibration of the yellow rhizocarpon growth curve in the cordillera blanca peru and implications for lia chronology abstract a new lichen dating method and new moraine observations enabled us to improve the chronology of glacier advances in the cordillera blanca peru during the little ice age lia our results reveal that an early lia glacial advance occurred around ad 1330 29 however a second major glacial advance at the beginning of the 17th century overlapped the earlier stage for most glaciers hence this second glacial stage dated from ad 1630 27 is considered as the lia maximum glacial advance in the cordillera blanca during the 17th 18th centuries at least three glacial advances were recorded synchronously for the different glaciers ad 1670 24 1730 21 and 1760 19 the moraines corresponding to the two first stages are close to the one in 1630 suggesting a slow recession of about 18 in the total length of the glacier from the lia maximum extent to the beginning of the 20th century the 24 glaciers have retreated a distance of about 1000 m corresponding to a reduction of 30 in their length this rate is comparable to that observed during the 20th century estimates of palaeo equilibrium line altitudes show an increase in altitude of about 100 m from the lia maximum glacial extension at the beginning of the 17th century to the beginning of the 20th century because long time series are not available for precipitation and temperature this glacial retreat is difficult to explain by past climate changes however there is a fair correspondence between changes in glacier length and the 18 o recorded in the quelccaya ice core at a century timescale our current knowledge of tropical glaciers and isotope variations leads us to suggest that this common tropical signal reflects a change from a wet lia to the drier conditions of today finally a remarkable synchronicity is observed with glacial variations in bolivia suggesting a common regional climatic pattern during the lia

climate variability during the last 1000 years inferred from andean ice cores a review of methodology and recent results abstract andean ice core investigations began approximately 30 years ago today 10 drilling sites from 0 to 52 s have been explored for paleoclimate reconstructions most of the ice cores reaching the bedrock cover the last 20 000 years with seasonal resolution over the last few centuries to the last 1000 years for the quelccaya site we discuss both the potential and the limitations of tropical ice cores as climate archives with regard to the collaborative effort to reconstruct past climate variations in south america over the last 1000 years we point out the uniqueness of south american ice cores due to their location at high altitude and also their two main limitations which are related to i the interpretation of certain proxies in terms of climate and ii the relatively poor dating when seasonal cycles are no longer resolved in addition we present an overview of the proxies that have been used so far to analyze tropical climate dynamics finally we discuss records of enso the little ice age and the 20th century decadal variability including the anthropogenic period which are all preserved in ice cores

global surface temperatures over the past two millennia 1 we present reconstructions of northern and southern hemisphere mean surface temperature over the past two millennia based on high resolution proxy temperature data which retain millennial scale variability these reconstructions indicate that late 20th century warmth is unprecedented for at least roughly the past two millennia for the northern hemisphere conclusions for the southern hemisphere and global mean temperature are limited by the sparseness of available proxy data in the southern hemisphere at present

magnitude of isotope temperature scaling for interpretation of central antarctic ice cores 1 the conventional interpretation of ice core deuterium and oxygen 18 isotope profiles based on the use of present day observations spatial slope underestimates glacialinterglacial surface temperature changes in central greenland by up to a factor of two this likely results from changes in the seasonality of the precipitation due to the particular location of the greenland ice sheet next to the highly variable northern polar front in this regard the situation is much simpler for central antarctica and this should be reflected in the temperature interpretation of ice core isotopic records with this in mind we closely examine all relevant information focusing on the east antarctic plateau where both model and empirical isotope temperature estimates are available we point to the fact that correctly accounting for the influence of ocean isotopic change is important when interpreting deuterium profiles from ice cores in this region the evidence presently available indicates that unlike for greenland the present day spatial slope can probably be taken as a surrogate of the temporal slope to interpret glacial interglacial isotopic changes at sites such as vostok and epica dome c corresponding temperature changes are within 10 to 30 of those obtained from the conventional interpretation based on the use of the spatial slope index terms 1040 geochemistry isotopic composition chemistry 1827 hydrology glaciology 1863 3344 meteorology and atmospheric dynamics paleoclimatology 9310 information related to geographic region antarctica keywords water isotopes temperature estimate antarctica deuterium oxygen 18

fluctuations of glaciers in the tropical andes over the last millennium and palaeoclimatic implications a review abstract the aim of this paper is to document the evolution of glaciers in the tropical andes between 10 n and 16 s for the last millennium based on moraines dated by lichenometry and radiocarbon lake sediment records and historical documents viewed collectively several glacial advances occurred synchronously the first advance is dated around ad 1200 1350 the maximum glacial extent mge defined as the furthest down valley extent recorded synchronously by the majority of glaciers occurred around 1630 1680 in bolivia and peru the outer tropics and around ad 1730 in ecuador colombia and venezuela the inner tropics subsequently during the 18th and 19th centuries glaciers retreated continuously with only minor synchronous readvances in the outer tropics minor glacial advances occurred around 1730 1760 1800 1850 and 1870 in the inner tropics synchronous minor advances occurred around 1760 1820 and 1880 between the mge and the early 20th century glaciers lost about 30 of their total length the retreat was slow between the 17th and 18th centuries but then became more marked use of the accumulation area ratio aar method or historical observations in the different cordilleras revealed an increase in the equilibrium line altitude ela of about 300 m from the mge onward palaeoclimatic hypotheses based on glaciological models run in different countries suggest a cool and humid period in the 16 18th centuries followed by a colder and drier period in the 19th century the reduction of glaciers observed from the middle of the 19th century is due to increasingly warmer conditions than before here quantitative estimates are proposed to explain the evolution of the glaciers in venezuela results indicate for the period 1250 1820 that mean air temperatures were 3 2 1 4 c cooler and precipitation was about 22 higher than at present in ecuador temperatures of between 0 8 and 1 1 c lower than today and between 25 and 35 higher accumulation than today appear to have occurred in the 18th century followed by a short drier but colder period at the beginning of the 19th century in bolivia the mge could be a consequence of a decrease in temperature of 1 1 to 1 2 c and a 20 to 30 increase in accumulation or an increase in cloudiness of about 1 2 10 we discuss not only external climatic forcing but also the coincidence between glacier expansion and a decrease in solar irradiance dating uncertainties however have made the role of volcanism in glacier fluctuations impossible to determine finally we discuss the relationships between enso and glacier fluctuations in recent centuries which do not match directly with current knowledge of modern teleconnections between tropical pacific ssts and variations in glacier mass balance

a potential high elevation ice core site at hielo patagonico sur the patagonia icefields constitute a unique location in the southern hemisphere for obtaining non polar paleo records from ice cores south of 458 s nevertheless no ice core record with meaningful paleoclimate information has yet been obtained from patagonia this deficiency is due to extremely harsh field conditions and to the fact that the main plateaus of both hielo patagonico norte hpn northern patagonia icefield and hielo patagonico sur hps southern patagonia icefield are strongly affected by meltwater percolation in order to explore the suitability of high elevation glacier sites at hps as paleoclimate archives three shallow firn cores were retrieved covering the altitude range 1543 2300 m a s l the glaciochemical records from the two lower sites confirm the presence of superimposed ice a clear sign of meltwater formation and percolation in the core from 2300 m the glaciochemical signature appears to be preserved indicating that no significant melting occurred although there might be problems associated with wind erosion and extreme melt events there is good potential for well preserved paleo records within glaciers in the patagonia icefields located higher than 2300 m

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

what are the climate controls on δd in precipitation in the zongo valley bolivia implications for the illimani ice core interpretation abstract controversy has surrounded the interpretation of the water isotopic composition d or 18o in tropical and subtropical ice cores in south america although recent modeling studies using agcm have provided useful constraints at interannual time scales no direct calibration based on modern observations has been achieved in the context of the recent ice core drilling at nevado illimani 16 39 s 67 47 w in bolivia we examine the climatic controls on the modern isotopic composition of precipitation in the zongo valley located on the northeast side of the cordillera real at about 55 km from nevado illimani monthly precipitation samples were collected from september 1999 to august 2004 at various altitudes along this valley first we examine the local and regional controls on the common d signal measured along this valley we show that 1 local temperature has definitely no control on d variations and 2 local rainout is a poor factor to explain d variations we thus seek regional controls upstream the valley potentially affecting air masses distillation based on backtrajectory calculations and using satellite data trmm precipitation noaa olr and direct observations of precipitation iaea gnip we show that moisture transport history and the degree of rainout upstream are more important factors explaining seasonal d variations analysis of a 92 yr simulation from the echam 4 model t30 version implemented with water stable isotopes confirms our observations at seasonal time scale and emphasize the role of air masses distillation upstream as a prominent factor controlling interannual d variations lastly we focus on the isotopic depletion along the valley when air masses are lifted up our results suggest that if the temperature gradient between the base and the top of the andes was higher by a few degrees during the last glacial maximum lgm less than 10 of the glacial to interglacial isotopic variation recorded in the illimani ice core could be accounted for by this temperature change it implies that the rest of the variation would originate from wetter conditions along air masses trajectory during lgm

pore development of the lower longmaxi shale in the southeastern sichuan basin and its adjacent areas insights from lithofacies identification and organic matter abstract x ray diffraction xrd field emission focusing ion beam scanning electron microscopy fe fib sem nitrogen gas adsorption n2ga and geochemical analyses were performed on the lower longmaxi shale in the southeastern sichuan basin and its adjacent areas to reveal the controls of shale lithofacies and organic matter om on pore development the results showed that the lower longmaxi shale primarily comprises three types of lithofacies based on shale compositions and sedimentary environment om rich siliceous shale orss om moderate mixed shale omms and om lean argillaceous shale olas orss comprises high contents of om and siliceous minerals quartz and feldspar deposited in a deep water shelf and early semi deep water shelf environment while olas consists of high clay mineral and low om contents primarily formed in a shallow water shelf environment omms witness a transition from orss to olas in sedimentary environment and shale components om hosts a higher volume of pores per unit weight compared to inorganic minerals corresponding to 0 1878 ml g and 0 00396 ml g respectively om hosted pores are dominant in orss constituting 72 whereas olas mainly consists of mineral hosted pores comprising 63 2 om hosted and mineral hosted pores in omms exist in similar proportions namely 56 4 and 43 6 respectively differentiated diagenetic paths resulting from sedimentary environment are responsible for the differences in pore development under various shale lithofacies the thermal maturity macerals and abundance of om all play a significant role in the morphology and development of om hosted pores om hosted pores are primarily founded in migrated om mainly sapropelic type instead of structured om mainly humic type in the form of secondary pores that are derived from dry gas generation stage furthermore om hosted pore development in shale gas reservoirs is slowed or even reduced because of the weakening of shale s resistance to compaction resulting from excessively high om content

potential for climate variability reconstruction from andean glaciochemical records inorder to selectglacier sites suitableforthe reconstruction of short term climate variability chemical constituents of shallow cores from chimborazo ecuador illimani bolivia and cerrotapado chile were analyzed to determine if they represent theclimateandatmosphericconditionsoftheparticulararea pronouncedvariationswere observed inthe chimborazo core whichwere attributedtothe seasonal occurrence of wet anddry periods using chemicaltracers thepacificandtheamazonbasinwereidentified asthe two principal sourcesof atmospheric moisture inthe illimani record seasonality is obvious but is less regular than in the chimborazo core chemical tracers point to the amazonbasinasa moisture source post depositional sublimation masksapossibleatmos pheric signal in the glaciochemical records from cerrotapado the arid conditions and a prevailing highcondensation levelalso cause little variability inthe stable isotopecontent irregular more negative d 18 o values occur during the humid phases of el nin o events despite alterations due to sublimation chemical tracers indicate the pacific ocean as a main moisture source for precipitation preserved on glaciar cerrotapado

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

clay mineral content type and their effects on pore throat structure and reservoir properties insight from the permian tight sandstones in the hangjinqi area north ordos basin china abstract clay mineral content and pore throat structure including type morphology size distribution and porosity and permeability are very important in factors that control gas storage in tight sandstone reservoirs in this study integrated thin section and field emission scanning electron microscope fe sem observation x ray diffraction xrd nuclear magnetic resonance nmr and rate controlled mercury porosimetry rcp analysis were used to investigate pore throat structure and the effects of clay minerals on pore throat connectivity size distribution and reservoir properties of tight sandstones in the middle permian successions of the hangjinqi area north ordos basin china results show that the tight sandstones have very low porosity and permeability averaged 9 76 and 0 968 md with diverse clay mineral compositions and grain sizes the main pore types are intergranular and intragranular dissolution pores intercrystalline and interstitial micropores most pores and throats are infilled with authigenic clay minerals such as acicular chlorite booklet kaolin and scaly and filamentous illite with minor silica and calcareous cements the pore and throat sizes in tight sandstones exhibit large variation with 147 648 m and 1 051 m in sandy conglomerates 160 998 m and 1 285 m in pebbly coarse grained sandstones 155 016 m and 0 868 m in coarse grained sandstones 158 134 m and 1 178 m in medium grained sandstones and 154 m and 0 379 m in fine grained sandstones respectively the results indicate that clay minerals affected the pore throat connectivity size distribution and reservoir properties of different lithofacies the properties of tight sandstone reservoirs are heavily influenced by illite content and throat size played a more important role influencing porosity and permeability this study helps to clarify the relationship of clay minerals pore throat structure and reservoir properties of the permian tight sandstones in the hangjinqi area and can guide associated work on tight sandstone reservoirs in the ordos basin and other basins worldwide