pore structure gas storage and matrix transport characteristics of lacustrine newark shale abstract shale gas production in the u s fuelled research activities in unconventional reservoir rock characterization most studies focused on organic rich shales of marine origin while disregarding lacustrine sequences in this study thirteen lacustrine shale samples from the newark basin nj usa are comprehensively characterised in terms of pore structure gas storage and matrix transport characteristics these thermally overmature vrr 1 4 2 7 shales have a na rich heterogeneous mineralogy with toc contents of up to 3 6 methane sorption capacity and pore structure parameters as identified with low pressure n2 physisorption microporosity bet surface area are neither interrelated with each other nor with any shale components e g clay content toc in contrast porosity shows a positive correlation with toc content which is also typical for many thermally overmature marine shale sequences correspondingly porosity and toc positively correlate to bedding parallel matrix permeability coefficients between 2 and 80 nd at 40 mpa effective stress in contrast permeability coefficients perpendicular to bedding are two to three orders of magnitude lower compared to previous studies on marine lithotypes newark shales have rather poor gas storage properties with average he porosities of 2 3 and average methane sorption capacities of 0 047 mmol g 1

reflectance of dispersed vitrinite in palaeozoic rocks with and without cleavage implications for burial and thermal history modeling in the devonian of rursee area northern rhenish massif germany abstract vitrinite reflectance is used as coalification parameter in coals and as maturity and palaeotemperature indicator in sedimentary rocks in high grade diagenetic rocks i e rocks at the boundary between diagenesis and metamorphism vitrinites become increasingly anisotropic therefore it has been suggested to study maximum minimum reflectance instead of mean reflectance for rocks which reached this stage in the present study vitrinite reflectance data from a folded sequence of the northern rhenish massif germany are combined with microtectonic study of thin sections in samples in which both bedding and cleavage are present we show that vitrinites in different microtectonic domains cleavage domains and microlithons show significant differences in both maximum vitrinite reflectance and vitrinite reflectance anisotropy this behaviour is due to a strong partitioning of deformation in cleavage domains as compared to microlithons so that vitrinite reflectance is controlled by the thermal and deformation history accordingly estimation of maximum palaeotemperatures during burial should be based on vitrinite reflectance measurements in microlithons unaffected by deformation after maximum burial based on this finding burial and temperature history of the rursee area in the eastern rhenish massif is reconstructed numerical simulations indicate a maximum burial at the siegen ems boundary of about 5000 m and a maximum burial temperature of about 220 c

the composition and its impact on the methane sorption of lacustrine shales from the upper triassic yanchang formation ordos basin china abstract the organic geochemistry mineralogy and methane sorption of lacustrine shales of the upper triassic yanchang formation collected from the south eastern ordos basin were investigated to characterize them and clarify the effects of shale composition on their sorbed gas capacity these yanchang shales have recently been selected as a target area for shale gas exploration in typical terrestrial strata in china the two main sections of these shales containing type ii organic matters chang 7 and chang 9 have relatively high total organic carbon content toc of 2 10 the two shales also have similar mineralogies mainly comprising quartz clay minerals and feldspars both the chang 7 and chang 9 shales are generally in the oil window chang 9 is slightly more mature than chang 7 higher methane sorption capacity was observed for chang 9 than for chang 7 shales determined on a dried basis at 50 c methane sorption measurements were further performed on three samples from which the residual bitumen had been extracted and their corresponding kerogen fractions to gain insight into the effects of shale composition on methane sorption this was significantly higher in solvent extracted samples than in raw samples indicating that residual bitumen largely restricts methane sorption on such shales a positive correlation between the amount of clay minerals and methane sorption capacity of bulk rocks was evident suggesting that clay mineral content is relevant to methane sorption this result was also supported by the much higher methane sorption capacity of solvent extracted shales compared to the extracted kerogen from those shales when measured sorption data was normalized to toc values the effects of both residual bitumen and clay mineral on the methane sorption of bulk rocks have complicated the evaluation of methane sorption on organic matter in these mature shales

experimental study of fluid transport processes in the matrix system of the european organic rich shales i scandinavian alum shale abstract this contribution presents results from a laboratory study investigating the fluid gas water transport properties in the matrix system of the scandinavian alum shale the maturity of the organic matter of the shale samples ranged between 0 5 and 2 4 vitrinite reflectance vr r gas he ar ch 4 and water flow properties were determined at effective stresses ranging between 5 and 30 mpa and a temperature of 45 c the effects of different controlling factors parameters on the fluid conductivity including permeating fluid moisture content anisotropy heterogeneity effective stress pore pressure and load cycling were analyzed and discussed pore volume measurements by helium expansion were conducted under controlled in situ effective stress conditions on a limited number of plugs drilled parallel and perpendicular to bedding for alum shale the intrinsic permeability coefficients measured parallel and perpendicular to bedding 6 10 22 8 10 18 m 2 were within the range previously reported for other shales and mudstones permeability coefficients were strongly dependent on permeating fluid moisture content anisotropy effective stress and other sample to sample variations the intrinsic absolute permeabilities measured with helium were consistently higher up to five times than those measured with argon and methane permeability coefficients he ch 4 measured on a dry sample were up to six times higher than those measured on an as received sample depending on effective stress the effect of moisture on measured permeability coefficients became more significant as effective stress increased 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 parallel to bedding all samples showed a nonlinear reduction in permeability with increasing effective stress 5 30 mpa the stress dependence of permeability could be well described by an exponential relationship

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

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

petrology geochemistry and na metasomatism of triassic jurassic non marine clastic sediments in the newark hartford and deerfield rift basins northeastern usa many sandstones and associated siltstones and shales of the triassic jurassic newark supergroup in the newark hartford and deerfield rift basins are immature feldspathic alluvial and lacustrine closed basin deposits they were derived from felsic igneous and metamorphic continental blocks on the flanks of their depositional basins the provenance was dominantly calc alkaline basement rocks similar to the sierra nevada of california the physical and chemical environments of erosion and deposition were probably similar to those in moist pleistocene holocene alluvial basins and playas in the great basin of california and nevada new petrographic and geochemical data for 113 samples indicate that albite rich sandstones and shales of the stockton lockatong and passaic formations in the newark basin and in the portland and east berlin formations of the hartford basin and analcime rich shales up to 52 normative analcime of the lockatong formation have unusually high na2o contents 4 7 textural evidence indicates both sodium replacement in feldspars and formation of authigenic albite and analcime in these rocks by comparison with modem sediments derived from similar provenance using mixing models it is estimated that up to 4 na2o was diagenetically added to the detrital clastics trace metals co cr cu ni zn abundances were apparently enhanced by deposition from brines in the lockatong formation analcime deposition occurred in shales with al2o3 na2o sio2 0 46 this ratio is found only in sediments to which na has been added from salts brines source rocks and the weathering products derived from them may be considered as a closed system in which sodium was retained partly in solids as feldspar and part went into solution during weathering the dilute solution migrated into the depositional basin where evaporation yielded concentrated brine during semi arid to arid climate in the drier parts of 21 000 yr milankovitch cycles reaction of brine during diagenesis at near surface and or shallow depths 2 km with ca plagioclase k feldspar and layer silicates at estimated temperatures 50 c to 100 c and ph 7 9 yielded thermodynamically stable authigenic albite and analcime in the sodium metasomatised clastic sediments low activity of k precluded development of authigenic k feldspar however k from solution incorporated into muds and silts as smectites were transformed to illite some lockatong beds contain anomalously high p2o5 ce la y th and u in authigenic apatite or monazite suggestive of mobilization of these elements in diagenesis

high pressure methane and carbon dioxide sorption on coal and shale samples from the parana basin brazil abstract an experimental study has been conducted to assess the potential for coalbed methane production and carbon dioxide storage in coals carbonaceous shales and source rocks in the parana basin in brazil high pressure sorption tests with methane and carbon dioxide were performed on coal and carbonaceous shales from the santa terezinha coalfield and samples from two principal petroleum source rocks measured excess sorption capacities ranged from 0 03 to 0 47 mmol g for methane and 0 14 to 0 81 mmol g for carbon dioxide showing a decrease with decreasing organic matter content linear regression lines for methane sorption capacity vs toc extrapolated to approximately zero whereas for carbon dioxide the intercept of the regression line indicated a residual sorption capacity of 0 2 mmol g on the mineral matter present day gas contents of coals collected from the first cbm well in the santa terezinha coalfield correspond to 13 38 of the measured maximum sorption capacities carbon dioxide sorption capacities exceed methane sorption capacities by a factor of 1 9 to 6 9 for these coals free sorption capacities of the under saturated coals in combination with preferential sorption of carbon dioxide could favour co 2 enhanced methane recovery and co 2 storage in coals and shales of the study area based upon the calculated coal reserves gas contents and measured sorption capacities a total storage potential of 15 4 gt co 2 was estimated for an area of 20 40 km 2 in the santa terezinha coal field assuming a combined co 2 enhanced coalbed methane ecbm production and co 2 storage operation to fully evaluate the potential for carbon dioxide storage and coalbed methane production further studies are required to assess producibility of methane and efficiency of long term co 2 storage in the study area

improving sub salt imaging using 3d basin model derived velocities abstract the quality of depth imaging is directly related to the accuracy of the underlying velocity model in most sub salt settings lack of angular illumination severely degrades the resolution and accuracy of velocity information derived from the seismic data itself a standard approach for building a starting velocity model uses more reliable velocity information outboard of salt which is subsequently extrapolated to populate the sub salt regions the shortcoming of this method lies in the assumption that the effective stress observed outboard of salt can be extrapolated beneath salt solely as a function of depth below mudline velocities derived from basin model effective stress data show excellent large scale agreement to seismic velocities 3d basin modeling represents the most rigorous approach for determining sub salt effective stresses because it accounts for depositional history sand distribution and connectivity variable shale properties timing of salt emplacement all of which influence the magnitude and distribution of abnormal pore pressure in the presented study a calibrated present day effective stress cube from a 3d basin model was used to calculate sub salt velocities for an exploration well in the central gulf of mexico the comparison between basin modeling derived velocities and the original velocity field showed remarkable differences particularly in that the former indicated a far more complex sub salt velocity distribution than the latter utilizing basin model sediment velocities to re migrate the seismic data set resulted in a more detailed image as well as changed source rock geometries where the original image showed a deep de focus at the source rock level the new geometry would focus hydrocarbons into the identified trap based on the results of the subsequently drilled exploration well it has to be assumed that the re migrated data aided by basin modeling derived velocities provide a more accurate image of the sub salt geology

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

stratigraphic record of the early mesozoic breakup of pangea in the laurasia gondwana rift system rift basins of the central atlantic margins cam of north america and morocco preserve largely continental sequences of sedimentary strata and less important minor basalt flows spanning much of the early mesozoic the best known is the newark basin of new jersey new york and pennsylvania where an astronomically calibrated magnetic polarity time scale is developed lacustrine cycles of milankovitch origin are commonly present in cam basins with the period changing from 10 ky paleoequator with coals to 20 ky 4 10n to perhaps 40 ky northward with evaporites cycles of100 ky 413 ky and2 my are also important four mostly unconformity bounded tectonostratigraphic sequences are present the anisian ts i is fluvial and eolian ts ii ts iv late triassic to early jurassic consist of tripartite lacustrine sequences caused by extension pulses the newark basin accumulation rate history allows comparison with quantitative rift basin models the north american plate s slow northward drift resulted in a relative shift of climate although the rapid humidification during the latest triassic and early jurassic is associated with a sea level rise the triassic jurassic mass extinction is of independent origin plausibly impact related

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

porosity of coal and shale insights from gas adsorption and sans usans techniques two pennsylvanian coal samples spr326 and spr879 in1 and two upper devonian mississippian shale samples mm1 and mm3 from the illinois basin were studied with regard to their porosity and pore accessibility shale samples are early mature stage as indicated by vitrinite reflectance ro values of 0 55 for mm1 and 0 62 for mm3 the coal samples studied are of comparable maturity to the shale samples having vitrinite reflectance of 0 52 spr326 and 0 62 spr879 in1 gas n2 and co2 adsorption and small angle and ultrasmall angle neutron scattering techniques sans usans were used to understand differences in the porosity characteristics of the samples the results demonstrate that there is a major difference in mesopore 2 50 nm size distribution between the coal and shale samples while there was a close similarity in micropore 2 nm size distribution micropore and mesopore volumes correlate with organic matter content in the samples accessibility of pores in coal is pore size specific and

fractal characteristics of upper cretaceous lacustrine shale from the songliao basin ne china abstract to improve our understanding of the characteristics of nanopores and their influence on liquid hydrocarbon occurrences in lacustrine shale we carried out fractal analysis on 21 lacustrine shale cores from the upper cretaceous qingshankou formation k2qn in the songliao basin ne northeast china using toc total organic carbon and rock eval analysis xrd x ray diffraction low pressure nitrogen adsorption experiments and the fhh frenkel halsey hill method the relationships between composition of lacustrine shale toc minerals oil content the pore structure parameters bet surface area pore volume pore average diameter and the fractal dimensions were investigated two fractal dimensions d1 and d2 at relative pressures of 0 5 1 and 0 0 5 respectively were obtained with d1 ranging from 2 5055 to 2 8888 and d2 between 2 1026 and 2 733 d1 is greater than d2 indicating that small pores are more homogeneous than larger pores both d1 and d2 increase with increasing bet surface areas and total pore volumes and increase with decreasing average pore diameters the fractal dimensions of lacustrine shale are negatively correlated with the clay content but show no obvious relationship with the quartz content the relationship between fractal dimensions both d1 and d2 and toc content is a u shaped curve with minimum d values at 2 5 3 wt toc fractal dimension d1 can be used to characterize the shale oil content and lacustrine shale samples with a lower fractal dimension have greater free oil therefore considering the influence of toc content on fractal dimension and the relationship between oil content and fractal dimension we conclude that lacustrine shale in the oil generation stage with 2 5 3 0 wt toc is probably the preferred shale oil exploration target in the songliao basin the results indicate that fractal analysis leads to a better understanding of the pore structure and oil storage capacity of lacustrine shale

feldspar dissolution enhanced porosity in paleoproterozoic shale reservoir facies from the barney creek formation mcarthur basin australia the paleoproterozoic barney creek formation bcf mcarthur basin australia is one of the oldest active hydrocarbon systems on earth with oil and gas shows present within organic rich intervals up to 7 wt total organic carbon we combine bulk geochemical analyses pore space characterization and high resolution electron imaging techniques to characterize the evolution of the bcf pore system with maturity a thermal gradient from the pre oil window 0 48 calc to gas window 1 01 calc shows a progressive change in pore networks with the loss of organic hosted pores dominant in thermally immature samples to porosity increasingly associated with the mineral matrix with thermal maturity precipitation of fine grained high surface area cements reduced porosity within the oil window whereas feldspar and dolomite dissolution and creation of secondary pores increased porosity within the gas window the abundance of feldspar grains up to 50 provided a significant potential for secondary pore formation as well as a source of silica and clay cement this study identifies a first order linkage between the chemically reactive sediments that are key to the reservoir properties in the bcf and a provenance and or weathering intensity conducive to supplying fine grained mineralogically immature sediments during deposition these findings likely apply more broadly to other chemically immature mudrocks typical of precambrian age sediments or phanerozoic settings subject to limited chemical weathering

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

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

geological evaluation of halfway doig montney hybrid gas shale tight gas reservoir northeastern british columbia abstract evaluation of the reservoir quality of the triassic halfway montney doig hybrid gas shale tight gas reservoir in the groundbirch field in northeastern british colombia requires an integration of unconventional and conventional methodologies reservoir evaluation includes reservoir thickness and structure total porosity toc content organic maturity pore size distribution micro to macro pore size fractions surface area mineralogy and pulse decay permeability quartz 10 74 carbonate 13 73 and feldspar 0 42 dominate the mineralogy of all formations with illite 0 32 being locally important the t max values range between 443 and 478 c placing the reservoirs beyond the oil window pore size distribution by low pressure gas adsorption analysis identifies a large variation between the contributions from the micro meso and macro pore size fractions matrix permeabilities range between 1 0e 3 and 6 5e 7 md at an effective stress between 2400 and 3300 psi 16 5 22 8 mpa changes in depositional environments and diagenetic processes manifest as differences in lithology and mineralogy within the montney and doig reservoirs which subsequently affect the fabric texture and pore size distribution fabric texture and pore size distribution contribute to the variation in the permeability and the proportions of free to sorbed gas within the reservoir quartz rich coarser grained intervals upper portions of doig c b and halfway formation have lower surface area greater porosities and a higher volume of macropores compared to the carbonate and clay rich finer grained intervals doig a permeabilities do not vary according to lithology with higher permeabilities found within both fine grained doig a and coarser grained halfway formation units permeability is controlled by pore size distribution higher permeability samples contain a balanced ratio between micro meso and macro porosity the finer grained intervals have higher sorbed gas capacity due to higher surface areas because of the higher volumes of finer mesopores and micropores than the coarser grained units however porosity and permeability are low in some parts of the doig a and fracture stimulation is necessary to achieve economic flow rates

investigations on the methane sorption capacity of marine shales from sichuan basin china abstract high pressure methane sorption isotherms measured at 30 50 and 80 c and pressure up to 20 mpa were measured on lower silurian marine shales from sichuan basin of china the effect of total organic carbon content temperature thermal maturity mineral composition and pore structure on methane sorption capacity has been investigated a linear combination approach has been developed to predict the langmuir sorption capacity of shales based on the mass fractions of their organic and inorganic components this information can be used to estimate the in situ sorption capacity of shale layers as a function of burial depth formation pressure and temperature and composition methane sorption capacity of the dry shales shows a positive relationship with toc and specific surface area the langmuir pressure decreases with increasing maturity but the toc normalized langmuir sorption capacity of over mature shales also decreases with increasing thermal maturity this may be related to the carbonization of highly over mature organic matter for the samples investigated approximately 16 3 46 7 average 28 6 of the methane sorption can be attributed to clay minerals and 46 5 81 5 to average 67 6 organic matter in these shales respectively using the linear combination approach the calculated langmuir sorption capacity function matches the measured values reasonably methane sorption capacity computed as a function of depth for a mean hydrostatic pressure gradient of 0 01 mpa m and a geothermal gradient of 0 03 c m shows a rapid increase and reaches a maximum between 900 and 1800 m followed by a slow decrease with increasing depth at shallow burial depths 900 1800 m sorption capacity is controlled by the geothermal gradient higher geothermal gradients result in a steeper decline of sorption capacity

the role of the residual bitumen in the gas storage capacity of mature lacustrine shale a case study of the triassic yanchang shale ordos basin china abstract the role of the residual bitumen in the shale gas storage capacity is investigated for potential terrestrial shale gas reservoirs in the yanchang area southern ordos basin china the upper triassic organic rich yanchang shales comprise of thermally mature chang 7 shale average toc 5 12 wt type i ii1 kerogen tmax 443 458 c ro 0 83 1 02 and relatively mature chang 9 shale average toc 4 40 wt type i ii1 kerogen tmax 443 476 c ro 0 88 1 10 the mineralogy of yanchang shales is dominated by clay minerals average 48 85 and quarts average 31 7 a series of low pressure nitrogen adsorption desorption and high pressure methane sorption experiments were conducted on pretreated fresh drilling cores including three groups of core samples one original group one group extracted by dichloromethane and the other group extracted by trichloromethane selected from yanchang shales to demonstrate the role of the residual bitumen in the shale gas potential low pressure nitrogen sorption method was used to elucidate the effect of the residual bitumen on the pore structure of yanchang shales the results show that the specific surface area and pore volume and pore surface area of shale samples after the extraction greatly increase and their growth was closely related with pores of 30 nm and

geochemical geochronological and sr nd hf isotopic constraints on the petrogenesis of the qicun intrusive complex from the handan xingtai district implications for the mechanism of lithospheric thinning of the north china craton abstract the qicun intrusive complex is one of the major ore related intrusions in the handan xingtai district eastern north china craton it consists of four intrusive bodies dominated by monzonite quartz monzonitic diorite quartz monzonite and biotite diorite respectively the biotite diorite has a la icp ms zircon u pb age of 128 9 0 93 ma indicating its emplacement in the early cretaceous when the north china craton was extensively reactivated rocks of the qicun complex have high mgo 1 69 9 50 wt high la n yb n 5 32 17 59 and sr y 18 05 101 10 ratios with low y 8 17 20 43 ppm and yb 0 86 1 85 ppm contents they are enriched in light rare earth elements lree but depleted in heavy rare earth elements hree and high field strength elements hfse with weak or no positive eu anomalies features assembling adakites in addition whole rock samples have initial 87 sr 86 sr ratios ranging from 0 70663 to 0 70767 and e nd t 130 ma between 16 5 and 14 3 which are consistent with zircon 176 hf 177 hf ratios of 0 281739 to 0 282083 and e hf t values of 33 8 to 21 7 the isotopic signatures when combined with existing geological and geochemical data indicate that the qicun complex and by inference other contemporaneous intrusions in the handan xingtai district formed by mixing of mantle derived magmas with partial melts of delaminated lower continental crust under a lithospheric extensional setting related to the destruction of the north china craton widespread presence of inherited zircon grains of ca 2 5 2 4 ga in the intrusions is consistent with a contribution of delaminated lower crust in the formation of the qicun complex

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

lacustrine basin unconventional resource plays key differences abstract there has been a revival in hydrocarbon source rock characterization and development associated with growing interest in unconventional resources where these fine grained organic rich rocks act as both source and reservoir to date the exploration focus on shale reservoirs has been largely on marine systems lacustrine source rocks for conventional resources are geographically important dominating regions such as china indonesia and brazil s resource base however they have been generally untested for unconventional resources there are a number of key differences in the nature of these hydrocarbon systems that should be considered when assessing whether lacustrine systems may represent future unconventional opportunities in areas where the conventional resource base is dominated by lacustrine sourced oil among the key differences between these depositional systems is the greater sensitivity to high frequency climatic variability within lacustrine systems lacustrine systems are highly sensitive to changes in the balance between precipitation and evaporation which may lead to rapid changes in lake level potentially exceeding 600 m these changes in depositional conditions are geologically rapid and may occur over periods of thousands of years such changes can reduce the areal extent of potentially thick source rock intervals to only those portions of a basin where a permanent deep lake was present thus the core unconventional target area may be geographically limited compared with their marine counterpart although potentially areally limited a review of many lacustrine source rocks suggests that their thicknesses are often significantly greater than marine source rocks an examination of the more distal portions of lacustrine systems where better source rock potential is present reveals that there is generally limited connectivity between source and conventional reservoir in these settings such as the wind river basin waltman shale the hydrocarbons remain trapped within the shales potentially leading to over pressured hydrocarbon charged systems such conditions suggest that although areally limited viable unconventional targets may exist if suitable reservoir conditions are present finally the character of the oils produced is different in these settings with lacustrine oils being waxy and displaying different hydrocarbon generation and cracking kinetics high wax oils display distinct flow characteristics being more viscous and may offer different production challenges than their non waxy marine equivalents additionally differences in their cracking kinetics may indicate that the timing of gas generation for shale gas plays may differ significantly from marine systems

late cretaceous late turonian coniacian and santonian petroleum source rocks as part of an oae tarfaya basin morocco abstract late turonian coniacian and santonian source rock samples from a recently drilled well tafaya sondage no 2 2010 in the tarfaya basin were analyzed for quantity quality maturity and depositional environment of the organic matter om to our knowledge such a thick sequence of organic matter rich turonian to santonian source rocks was investigated in that great detail for the first time organic geochemical and organic petrological investigations were carried out on a large sample set from the 200 m thick sequence in total 195 core samples were analyzed for total organic carbon corg total inorganic carbon contents and total sulfur ts contents rock eval pyrolysis and vitrinite reflectance measurements were performed on 28 samples chosen on the basis of their corg content non aromatic hydrocarbons were analyzed on selected samples by way of gas chromatography flame ionization detection gc fid and gc mass spectrometry gc ms the organic matter rich carbonates revealed a high source rock potential representing type i kerogen and a good preservation of the organic matter which is mainly of marine phytoplankton origin hi values are high 400 900 mg g corg and in a similar range as those described for more recent upwelling sediments along the continental slope of north africa ts corg ratios as well as pristane over phytane ratios indicate variable oxygen content during sediment deposition all samples are clearly immature with respect to petroleum generation which is supported by maturity parameters such as vitrinite reflectance 0 3 0 4 tmax values 401 423 c production indices s1 s1 s2 0 1 as well as maturity parameters based on ratios of specific steranes and hopanes

geological controls and estimation algorithms of lacustrine shale gas adsorption capacity a case study of the triassic strata in the southeastern ordos basin china abstract high pressure methane adsorption experiments on a series of triassic lacustrine shale moisture equilibrated samples from the southeastern ordos basin china were conducted at pressure up to 20 mpa two of which were measured at 30 c 40 c 50 c 60 c and 70 c and seven were performed under reservoir temperature from 48 c to 62 c to investigate the effect of organic matter content maturity mineralogical compositions and reservoir conditions temperature and pressure on the methane sorption capacity the total organic carbon contents tocs range from 0 91 wt to 6 11 wt the thermal maturities as inferred from rock eval analysis range from low mature to high mature the minerals of the shale samples are dominated by clays 36 57 wt and quartz 19 44 wt for the entire shale samples the dominant clay minerals are mixed layer illite smectite with some illite and no smectite exists corresponding to a stage of late diagenesis the studied samples have n2 bet surface areas ranging between 1 47 and 9 21 m2 g and pore volumes of 0 013 0 034 cm3 g the methane sorption capacities of moisture equilibrated shale samples show a positive correlation with toc contents and bet surface areas no relationship was observed between the clay contents and methane sorption capacities indicating that clay minerals do not significantly contribute to methane sorption capacity in these organic shales the langmuir pressure pl increases exponentially with temperature and the langmuir volume vl decreases linearly with temperature a computational scheme has been developed to calculate the methane sorption capacity of shales as a function of toc content temperature and pressure based on langmuir sorption isotherm function using this algorithm methane sorption capacity of organic shales as function of depth can be obtained due to the predominating effect of pressure the methane sorption capacity increases with depth initially through a maximum and then decreases due to the influence of increasing temperature at a greater depth the maximum gas sorption capacity typically occurs at a depth range between 400 and 900 m with toc content increasing the maximum methane sorption capacities of organic shales and the corresponding depths increase

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

characterizing the pore structure in the silurian and permian shales of the sichuan basin china abstract nitrogen sorption and mercury intrusion methods were applied to characterize the pore structure of the lower silurian shales of the long ma xi formation and upper permian shales of the da long formation in the sichuan basin the results indicate that the specific surface areas and porosities of the silurian shales are in the range of 17 83 29 49 m 2 g and 3 65 18 26 respectively the silurian shales show a bimodal pore size distribution and consist of both micropores and nanopores ranging from 30 to 60 m and 1 7 20 nm respectively a strong positive linear correlation between the surface areas and total organic carbon content toc suggests that the organic matter contributes mostly to the amount of specific surface area of the silurian shales whereas the contribution of clay minerals appears to be negligible the organic matter also accounts for 50 70 of the porosity in the silurian shales soluble organic matter in the form of bitumen however has a negative impact on the surface area and porosity of the silurian shales and reduce the amount of surface area and porosity in these shales for the permian shales their surface area and porosity are lower than those of the silurian shales and are in the ranges of 2 20 3 52 m 2 g and of 1 30 4 15 respectively the pore size distribution of the permian shales shows a unimodal pattern of micropores in a size range of 30 60 m their toc and clay mineral contents display poor correlation with the surface areas and suggest that both the organic matter and clay minerals have very low surface areas a clear negative correlation between the porosity and toc in the permian shales indicates that organic matter contributes little or insignificantly to the porosity due to poorly developed organic pores in kerogen because the permian shales are much lower in thermal maturity than the silurian shales furthermore there is a consistent negative linear correlations between the bitumen content and the porosity for both the permian shales and silurian shales and indicate that the bitumen may significantly reduce the porosity of the shales by occupying the pore spaces in the mineral and organic matrix finally it is clear that the lower silurian shales have a greater shale gas potential than the upper permian shales do based on their surface area and porosity

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

a preliminary study on the characterization and controlling factors of porosity and pore structure of the permian shales in lower yangtze region eastern china abstract permian organic rich shales occur throughout the lower yangtze region in eastern china and are potentially a future target for shale gas exploration due to the lack of data the gas potential of these permian shales is difficult to evaluate in this study a total of 22 permian shale samples were collected from two wells and their geochemical and rock property porosity characteristics were investigated the results show that the samples have a total organic carbon toc content of 0 6 17 4 wt derived from mainly gas prone kerogen with a vitrinite reflectance ro value ranging from 2 3 to 2 7 total porosity of the samples ranges between 1 and 5 5 the micropore and mesopore surface areas range between 5 41 35 69 m2 g and 3 59 11 23 m2 g respectively micropore and mesopore volumes range between 0 22 1 44 cm3 100 g and 0 67 1 76 cm3 100 g respectively total porosity and pore structure data of these samples show a correlation with toc for samples with toc 12 wt negative correlation relationships were observed toc content strongly impacts gas storage capacity of the permian shales in the lower yangtze region and the preliminary results of the present study have important implications for the shale gas play evaluation in this area

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

a preliminary study on the pore characterization of lower silurian black shales in the chuandong thrust fold belt southwestern china using low pressure n2 adsorption and fe sem methods although lower silurian black shales within and around the sichuan basin have received renewed attention during the past few years because of their potential prospectivity for shale gas studies associated with shale gas reservoir evaluation are still rare in this study eight black shale core samples were collected from a well drilled recently in the chuandong thrust fold belt southwestern china and their geochemistry and pore structures were investigated using low pressure n2 adsorption analysis and field emission scanning electron microscopy fe sem observations the results show that the black shales have total organic carbon toc values ranging from 1 01 to 3 98 and their equivalent vitrinite reflectance values are in the range of 2 84 3 05 both mineral matrix and organic matter pores are well developed with pore sizes ranging from several to several hundred nanometers the total porosity for the eight samples ranges from 2 60 to 4 74 and the percentages of organic matter pores are estimated to be in the range of 31 62 the total surface area ranges from 5 06 m2 g to 19 32 m2 g and the micropore 2 nm surface area estimated by the t plot method ranges from 3 13 m2 g to 9 27 m2 g the toc values have positive relationships with the total porosity total surface area and the micropore 2 nm volume and surface area indicating toc may be an effective parameter for shale gas reservoir evaluation in the studied area

the effect of analytical particle size on gas adsorption porosimetry of shale abstract gas storage capacity and gas producibility of shale gas reservoirs are critically limited by shale porosity in spite of its importance porosimetric characterization of shale remains challenging due to highly heterogeneous structures small average pore sizes and wide pore size distributions this study utilizes low pressure n 2 and co 2 gas adsorption porosimetry to investigate the evolution of micro and mesopores in a suite of 11 new albany shale samples across a wide range of thermal maturity corresponding to vitrinite reflection r o values from 0 35 to 1 41 mesopore volumes follow a nonlinear evolutionary path starting with a maximum in immature shale sample 472 1 subsequent intermittent minima in mesopore volumes during early and late maturity are consistent with the transformation of kerogen during the early mature stage sample 554 2 and secondary cracking of bitumen oil at the late mature stage sample il2 respectively micropore volumes display a varying trend throughout thermal maturation and are significantly controlled by total organic carbon contents both meso and micropore volumes are positively correlated with clay content and tend to decrease with an increase in feldspar content a reduction in grain size of shale samples for gas adsorption porosimetry prominently enhances mesopore volumes whereas the effects on micropore volumes are variable these findings may be associated with the fact that smaller particles are able to attain complete adsorption equilibrium quickly which in turn reduces experimental artefacts during gas adsorption porosimetry crushing of shale not only alters the shape of gas adsorption hysteresis loops but also tends to tighten the openings of hysteresis loops by enhancing the connectivity of pores and reducing the likelihood of gas being trapped during desorption

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

bib sem study of the pore space morphology in early mature posidonia shale from the hils area germany abstract this contribution reports on the study of the pore space morphology in two early mature vr r 0 59 and 0 61 samples of posidonia shale from the hils syncline in germany using broad ion beam bib polishing and high resolution scanning electron microscopy sem this allows imaging pores with resolution down to 10 nm in equivalent diameter d eq and quantitative estimation of porosity using a combination of bse and se detectors and semi automatic segmentation of the gigapixel images the representative elementary area of the samples on the scale of a few mm is inferred to be about 140 140 m 2 pore morphologies and pore sizes are clearly related to the mineral fabric with large differences very large typically several microns pores with internal faceted crystal morphology in recrystallized calcite clasts and smaller pores d eq cf schizosphaerella nanofossils typically 200 nm pores are less common in organic material and in pyrite aggregates pore characteristics are very similar for both samples and porosity resolvable by bib sem is 2 75 and 2 74 pore size distribution can be described by a power law with an exponent about 2 0 and 2 2 respectively for the pore population excluding the fossils pores in the carbonate fossils show dual power law distribution with power law exponents of about 1 and 3 by extrapolating the power law distribution for each sample total porosity is estimated to be 4 8 0 9 1 7 and 6 5 2 7 7 2 respectively this estimate can be compared with 3 4 3 7 and 3 3 3 6 as measured by mercury injection porosimetry we interpret this difference to reflect the unconnected for mercury part of the porosity comparison of imaged pores and mercury injection porosimetry suggest a very high pore body to pore throat ratio this results in a pore model where large pores represented mainly by pores in fossils and calcite grains are connected via a low porous and low permeable clay rich matrix with pore throats below 10 nm in both samples