impact of early dolomitization on multi scale petrophysical heterogeneities and fracture intensity of low porosity platform carbonates albian cenomanian southern apennines italy abstract petrographic petrophysical and fracture analyses were carried out on middle cretaceous platform carbonates of the southern apennines italy that represent an outcrop analogue of the val d agri and tempa rossa reservoirs of the basilicata region the studied outcrops which are made of interlayered limestones and dolomites of inner platform environment were selected to study the impact of dolomitization on reservoir properties and the control of dolomite texture on fracture development two types of dolomites both formed during very early diagenesis were found interlayered at a metre scale with micrite rich limestones mainly mudstones and wackestones dolomite a is fine to medium crystalline and makes non planar mosaics dolomite b is coarse crystalline and makes planar s and planar e mosaics the intercrystalline space of the planar e subtype of dolomite b is either open or filled by un replaced micrite or by late calcite or saddle dolomite cement dolomite a and dolomite b have similar average porosities of 3 7 and 3 1 respectively which are significantly higher than the average porosity of limestones 1 4 their poro perm relationships are similar with the notable exception of planar e type b dolomites which generally display higher permeability values the intensity of top bounded fractures is distinctly lower in coarse crystalline dolomites than in fine crystalline dolomites and limestones both at the macro and the micro scale on the other hand neither lithology i e limestone vs dolomite nor dolomite crystal size control the intensity of perfect bed bounded fractures which is strictly controlled by the fracture layer thickness our results provide information that could be used as guidance for the characterization and modelling of fractured carbonate reservoirs made of interlayered limestones and dolomites

investigation of a lower mantle shear wave triplication using a broadband array sh signals recorded by an array of four broadband benioff 1 90 instruments run by caltech are inspected for evidence of a lower mantle shear wave velocity discontinuity previously detected using wwssn data deep focus earthquakes beneath argentina span the distance range 78 to 82 from the array where the triplication in the travel time curve produced by the discontinuity is expected to result in an arrival between the direct shear wave s and the reflection off of the core mantle boundary scs the sh data for these events do show evidence of the arrival however the broadband signals also show significant receiver structure complexity empirical receiver functions are determined for each station by stacking observations for events in south america closer than 75 from the array incorporating these receiver functions into the synthetic modeling demonstrates that lower mantle shear velocity models with a discontinuity fit the observations better than models without one

reservoir heterogeneity and quality of khuff carbonates in outcrops of central saudi arabia abstract the khuff carbonates host several main gas reservoirs in the middle east these reservoirs are known for their heterogeneity both of sub seismic scale and beyond the interwell spacing to get a better insight in these reservoirs the heterogeneity of the upper khartam member placed in a high frequency sequence stratigraphic framework was studied with a lateral resolution between logged sections of 5 m the sedimentology and sequence stratigraphy of four outcrop localities were studied and approximately 600 samples were collected for petrographic porosity and permeability analyses seventeen lithofacies types were recognised and six major diagenetic processes could be differentiated in the studied outcrops dissolution is likely the result of intensive circulation of meteoric water undersaturated with respect to calcite significantly cementation has blocked most of the original intergranular porosity pore lining detrital clay severely impacted reservoir permeability and complicated the pore geometry dolomitization is associated with the upper khuff sudair boundary and is likely the result of influx of water highly saturated with mg 2 that developed during the deposition of the sudair evaporites finally stylolites are to a major extend controlled by lithofacies and geobody configuration ten porosity types could be namely intergranular intragranular shelter dissolution enlarged moldic vuggy micro porosity and porosity in relation to dolomite dedolomite dolomite leaching and fracture development overall intertidal creeks are characterized by a complex and heterogeneous pore geometry if compared to the intertidal channels and this can be attributed to the geobody architecture with intertidal creeks being composed of dense and small tidal bodies 1 m in length and 20 cm in thickness while intertidal channels are composed of thick amalgamations of intertidal channels 5 m by 50 cm most critically the horizontal reservoir quality was influenced differentially by diagenesis which resulted in a lateral segmentation of single bodies into different hydraulic units the differential mold filling calcite cements have significantly reduced porosity and permeability generally mineral content has little impact on the reservoir quality although clay minerals played a central role in lining the pore space and affecting permeability finally horizontal reservoir heterogeneity seems to have been controlled by fractures and stylolites which respectively acted as conduits to and barriers for vertical fluid flow and hence controlled the differential cementation and dissolution processes

impact of pore structure and fractal characteristics on the sealing capacity of ordovician carbonate cap rock in the tarim basin china abstract evaluating the heterogeneity and sealing capacity of carbonate cap rocks is of great significance for hydrocarbon production however the main controls on pore size distribution in carbonate cap rocks are not well constrained in this contribution we analyze drill core samples of carbonate cap rocks from the ordovician yingshan formation tarim basin to study their pore properties and investigate the controls of pore throat structure and fractal dimension on the sealing capacity of the cap rock results from petrography and a combination of mercury injection capillary pressure and nitrogen gas adsorption tests reveal that there are four lithological cap rock types with micrite being the most prevalent one followed by calcarenite six types of pore throat structures and fractal dimensions from d1 to d6 are classified based on the pore size distributions including macropore i macropore ii mesopore i mesopore ii transitional pore i and transitional pore ii the fractal dimensions show that there is a decreasing trend from d1 to d6 with decreasing pore size diameter suggesting that the macropore and mesopore types present more complex pore throat structures than the transitional type the total fractal dimension dtotal indicates that the pore throat structures are complex and heterogeneous the sealing heights of the gas column have a positive correlation with cement content in calcarenite and a negative correlation with microfracture density mesopore ii and transitional pore types make a significant contribution to enhancing the breakthrough pressure the fractal variations mainly result from macropores and mesopores while transitional pores and micropores weaken the impact of the whole pore system on the dtotal value the heterogeneity and anisotropy of macropores is the main control on the sealing capacity of the cap rock the increasing of d1 considerably contributes to the pore shape heterogeneity and enhances the capillary resistance force to hydrocarbon migration therefore the fractal dimension is an effective approach for investigating the pore throat structure and sealing capacity of carbonate cap rocks

impact of sedimentology and diagenesis on the petrophysical properties of a tight oolitic carbonate reservoir the case of the oolithe blanche formation bathonian paris basin france the oolithe blanche formation was studied in three quarries located at the south eastern edge of the paris basin france heterogeneities in reservoir properties were assessed through a sedimentological diagenetic and petrophysical study the relationships between depositional settings diagenesis and petrophysical properties were analysed using detailed petrographic studies image analysis nano ctscans and petrophysical measurements the carbonate reservoir pore network is mainly controlled by intraparticle microporosity which ensures the connectivity with interparticle meso and macroporosity early cementation vs early compaction processes mainly grain interpenetration may have considerable influence on fluid flow properties and parameters such as permeability acoustic velocities and tortuosity better reservoir properties are found when compaction processes begin before cementation from statistical analyses e g principal component analysis and linear discriminant analysis a sedimentological diagenetic and petrophysical model is proposed that is in a good agreement with the geological model developed from field work

heterogeneous nanoporosity of the silurian longmaxi formation shale gas reservoir in the sichuan basin using the qemscan fib sem and nano ct methods abstract nanoporosity of a shale gas reservoir provides essential information on the gas accumulation space and controls the gas reserves the characteristics of heterogeneous nanoporosity of four shale samples are analyzed by combining quantitative evaluation of minerals by scanning electronic microscopy qemscan focused ion beam scanning electron microscopy fib sem and nano ct the representative elementary area rea is proposed by qemscan to detect the imaging area that can represent the overall contents of minerals and organic matter combined with the statistics of pores in minerals and organic matter by fib sem the quantitative nanoporosity is obtained the nano ct is used to compare the total nanoporosity that was obtained by fib sem the results show that shale has distinct characteristics in nanoporosities due to the variation in organic matter and mineral content the major pore sizes of the organic matter and clay minerals are smaller than 400 nanometers nm and the pore sizes of feldspar and pyrite are mainly 200 600 nm the pore sizes for pores developed in quartz and carbonate minerals range from a few nanometers to 1000 nm furthermore pores smaller than 400 nm mainly provide the total nanoporosity the nanoporosities in the organic matter are approximately 17 21 since the organic matter content 0 54 6 98 is low the organic matter contributes approximately 5 33 of the total nanoporosity in shale conversely the nanoporosities in quartz and clay are generally lower than 3 since the mineral content 93 02 99 46 is obviously higher than the organic matter content the minerals contribute approximately 67 95 of the total nanoporosity in shale

fractal measurements of sandstones shales and carbonates measurements were made of the fractal properties of sandstones shales and carbonates using a statistical analysis of structural features on fracture surfaces fractal behavior is associated with power law behavior for the number of features as a function of the feature size on the pore rock interface only one sedimentary rock a novaculite was found not to have a fractal structure the fractal dimensions range from 2 27 to 2 89 and the long length limits to the fractal regime range from 2 m to over 50 m in all cases the fractal behavior extends to less than 0 2 m which is the measurement resolution the porosity associated with the fractal pore rock interface can be calculated from the fractal parameters some of the samples have additional porosity not associated with power law behavior photographs and other evidence are used to show that the fractal structures are the result of diagenesis fractal diagenetic structures include euhedral quartz overgrowths druse quartz calcite dolomite clays and chert

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

body wave amplitude patterns and upper mantle attenuation variations across north america summary a broad band amplitude study of p and sh waves from deep south american events recorded at wwssn stations in the united states provides constraints on upper mantle variations in attenuation the events were selected to minimize contamination due to source complexity radiation pattern and source structure the prevalent feature in the short and longperiod bands is that the sh amplitudes show the same regional variations as the p amplitudes with the regional variations of short periods being similar but enhanced relative to the variations at long periods the amplitudes show some systematic regional difference between the east coast and rocky mountain provinces and both short and long periods are enhanced at the gulf coast and midwestern stations probably due to thick sedimentary bed receiver structure since detailed receiver structures for individual stations are poorly known we used the working hypothesis that the regional amplitude patterns are caused by lateral variations in upper mantle attenuation both a constant q and a frequency dependent attenuation operator were considered with the relative amplitudes and waveforms in short and long period bands used to estimate the acceptable range of at in the constant q model or the acceptable range of the parameter r which describes the high frequency roll off of the absorption band in the frequency dependent model time domain modelling indicates that the short period p and sh amplitudes and waveforms in the 1 10s period range do not unambiguously demand frequency dependent attenuation allowing for the uncertainty in source frequency content and long period absorption band amplitude the short period p amplitudes can be fit with a range in at 0 5 s or a range in r from 0 001 to 0 25s with either single parameter variation consistent with the general short period sh amplitude behaviour a technique for determining the absolute value of t and possible r values appropriate for the 5 20s band was applied to selected data a value of t 0 8 s and small 7 were found for travel paths from the deep events to north america and lower t or large r values were found for paths to southern african stations longperiod amplitude variations cannot be explained by frequency dependent

discrimination of effective from ineffective porosity in heterogeneous cretaceous carbonates al ghubar field oman the natih e heavy oil reservoir 21 api at al ghubar field oman has produced less than 5 of the calculated oil in place porosity logs used to calculate reserves show high porosity throughout the reservoir but further analysis of the only continuous core taken from the field indicates that much of the porosity is ineffective there are four heavily oil stained high permeability skeletal pelletal grainstone units with interparticle porosity in the core that probably contributed most of the production the four permeable grainstone units occur at the top of small scale accommodation cycles that have wackestone and packstone bases these grainstones make up about 20 of the total thickness of the porous natih e reservoir the other 80 is composed of packstone and wackestone with ineffective microporosity interparticle porosity in burrows and isolated moldic and intraskeletal porosity the small scale reservoir bearing cycles can be correlated across the field using the separation between the medium and deep induction curves as a guide resistivity logs are the most reliable tool to distinguish effective from ineffective porosity most high permeability grainstone units have deep induction values more than 100 ohm m and separation of more than 10 ohm m between the medium and deep induction curves the ineffective intervals with microporosity burrow porosity and moldic porosity have lower resistivity and little separation between the medium and deep induction curves

origin of lower ordovician dolomites in eastern laurentia controls on porosity and implications from geochemistry the catoche formation of the st george group in eastern laurentia western newfoundland consists of early ordovician arenigian shallow marine platform carbonates 160 m thick which were extensively dolomitized during the course of their diagenetic history the dolomites occur as both replacement and pore filling cements and are a major control on porosity distribution in the formation the origin and diagenetic history of the catoche dolomites at daniel s harbour western newfoundland were analysed in comparison to equivalent successions at port au choix pac and port au port peninsula pap to assay the reservoir potential of these dolomites in eastern laurentia petrographic examination identified at least three generations of dolomites in the catoche formation which are 1 an early replacement sub to eu hedral micritic dolomite 4 m 30 m d1 2 eu to sub hedral dolomite 70 m 1 mm often with cloudy cores and clear rims d2 and 3 subhedral to anhedral saddle dolomite cement 200 m 3 mm d3 the micritic dolomite d1 exhibits a dull cathodoluminescence cl under cathodoluminoscope whereas dolomite d2 exhibits consistent concentric cl zonation some subhedral crystals of d3 appear zoned both in plane polarized light and cathodoluminoscope otherwise d3 exhibits a dull cl stoichiometric dolomite occurs in all three generations with d2 as the dominant dolomite by abundance the low strontium 47 25 ppm content coupled with depleted 18o value of dolomitizing fluids 10 to 11 2 vsmow and near micritic grain size suggests an early precipitation of dolomite d1 at low temperatures of near surface conditions from solutions likely formed by mixing of early ordovician sea and meteoric waters in contrast microthermometric measurements of primary two phase fluid inclusions in dolomite d2 homogenization temperatures of 102 168 c with a salinity range of 19 8 25 eq wt nacl and dolomite d3 homogenization temperatures of 158 190 c with a salinity range of 20 2 22 2 eq wt nacl suggest that both dolomite generations were generated in mid to deep burial settings from high salinity low temperature 200 c hydrothermal fluids likely under suboxic conditions this is consistent with the low sr concentrations for d2 36 4 8 ppm and d3 38 7 9 ppm 18o values of dolomitizing fluids for d2 2 1 to 8 1 vsmow and d3 6 to 8 1 vsmow coupled with fe contents of d2 1684 1096 ppm and d3 1783 7 618 ppm as well as the respective mn d2 131 2 50 and d3 197 5 55 ppm concentrations ree and shale normalized reesn values of catoche carbonates indicate enrichment in rare earth element ree composition of the earliest calcite c1 relative to those of arenig seawater whereas the reesn profiles of the dolomite generations mimic that of calcite c1 the ce ce ce sn and la la la pr pr sn anomalies of the catoche dolomites are consistent with precipitation in equilibrium with source fluids in slightly oxic to suboxic conditions whereas eu eu eu cn anomalies suggest similar source fluids for d2 and d3 results of fluid inclusion gas analysis are consistent with petrographic features and geochemical compositions and support the exclusion of magmatic fluids during dolomitization visual estimates of porosity from thin sections indicate four porous 4 12 horizons vugs and intercrystalline pores are two types of porosity associated with the dolomites with the latter being the dominant type and associated mainly with dolomite d2

carbonate rock characterization and modeling capillary pressure and permeability in multimodal rocks a look beyond sample specific heterogeneity carbonate rocks are known for their heterogeneity and petrophysical complexity this commonly leads to large uncertainties in reservoir models that are intended to predict fluid storage and fluid flow in this article focus is given to the characterization of pore systems at core plug scale to provide improved models for permeability and saturation prediction these methods fall under a wider rock typing workflow we examine the use of mercury air capillary pressure data for rock type definition and for predicting saturation and permeability we present new methods for modeling saturation in rocks with multimodal pore throat size distributions the methods bear similarity to those previously published but with some key differences mainly by relating the capillary pressure data to the pore systems representative for a rock type we also present a new method for relating permeability to pore throat sizes that is more versatile in that it can be employed for all types of pore throat size distributions unimodal or multimodal we demonstrate that a normalized pore throat radius parameter forms a straight line relationship with permeability over six orders of magnitude it appears to be a fundamental property for all pore systems so far examined the wider implication of the workflows presented is that they offer better integration between the methods used for saturation prediction and the methods used for permeability prediction something that is desirable for all subsurface studies

microfacies depositional environment and diagenetic evolution controls on the reservoir quality of the permian upper dalan formation kish gas field zagros basin abstract the upper permian upper dalan formation contains one of the largest gas reservoirs in the world the formation consists of carbonates with some evaporite intercalations that developed on a gently sloping homoclinal carbonate ramp facing the late permian paleo tethys ocean this study focuses on the kish gas field zagros offshore basin situated between iran and qatar and is based on a 222 m thick continuous core based on the integration of core and wireline log data coupled with petrographic analyses of 580 thin sections three major depositional environments facies belts with 11 carbonate microfacies are identified these include 1 sabkha to tidal flat laminated to massive anhydrite dolomudstone with anhydrite nodules dolomudstone and intraclastic dolowackestone 2 lagoon and leeward shoals bioclastic wackestone dolowackestone to packstone and peloid dolopackstone and peloid bioclastic dolopackstone and 3 mobile windward sand shoal ooid peloid dolograinstone ooid dolograinstone ooid intraclast dolograinstone ooid bioclast dolograinstone packstone and coarse bioclast intraclast dolograinstone diagenetic evolution of the upper dalan formation is associated with evaporative marine shallow water normal marine meteoric and burial diagenetic environments common diagenetic effects include dolomite and calcite cementation mechanical and chemical compaction dissolution dolomitization and evaporative anhydrite mineralization reservoir quality is strongly affected by variations in the original rock fabrics and subsequent diagenetic alterations the most common pore types include interparticle moldic and connected vug fracture and cavernous the interparticle porosity permeability relationship for the studied facies suggests that the reservoir quality is not affected by different crystal sizes and most samples plot in the low porosity and low to high permeability field or display lucia class 1 or 2 petrophysical relationships the study shows that the pervasive pore filling anhydrite mineralization lead to a significant decrease in porosity and permeability poikilotopic anhydrite cement reduced matrix porosity but the pore size was less affected

the structure of monohydrocalcite and the phase composition of the beachrock deposits of lake butler and lake fellmongery south australia samples of beachrock from lakes butler and fellmongery near robe south australia were examined by neutron and x ray powder diffraction considerable variation in phase composition was observed although all samples possessed monohydrocalcite calcite aragonite and magnesiancalcite the rietveld refinement of the structure of monohydrocalcite showed significant changes in the orientation of water molecules and a major change in the orientation of a carbonate group with respect to the currently accepted structure the current refinement shows that the hydrogen bonding structure consists of three distinct networks with each of the three carbonate groups being bonded to a single water molecule via one linear and one bifurcated hydrogen bond

the effects of burial diagenesis on multiscale porosity in the st peter sandstone an imaging small angle and ultra small angle neutron scattering analysis abstract to examine the effects of burial diagenesis on heirarchical pore structures in sandstone and compare those with the effects of overgrowth formation we obtained samples of st peter sandstone from drill cores recovered from the illinois and michigan basins the multiscale pore structure of rocks in sedimentary reservoirs and the mineralogy associated with those pores are critical factors for estimating reservoir properties including fluid mass in place permeability and capillary pressures as well as geochemical interactions between the rock and the fluid the combination of small and ultra small angle neutron scattering with backscattered electron imaging provided a means by which pore structures were quantified at scales ranging from approximately 1 nm to 1 cm seven orders of magnitude larger scale 10 m porosity showed the expected logarithmic decrease in porosity with depth although there was significant variation in each sample group however small and ultra small angle neutron scattering data showed that the proportion of small scale porosity increased with depth porosity distributions were not continuous but consisted of a series of log normal like distributions at several distinct scales within these rocks fractal dimensions at larger scales decreased surfaces smoothed with increasing depth and those at smaller scales increased surfaces roughened and pores become more isolated higher lacunarity data suggest that changes in pore size distributions are controlled by both physical compaction and chemical effects precipitation cementation dissolution

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

depositional environment and geochemical characteristics of the lower carboniferous source rocks in the marsel area chu sarysu basin southern kazakhstan abstract there are two sets of carbonate source rocks in the lower carboniferous layers in marsel the visean c1v and serpukhovian c1sr however their geochemical and geological characteristics have not been studied systematically to assess the source rocks and reveal the hydrocarbon generation potential the depositional paleoenvironment and distribution of c1v and c1sr source rocks were studied using total organic carbon toc content rock eval pyrolysis and vitrinite reflectance ro data stable carbon isotope data gas chromatography gc and gas chromatography mass spectrometry gc ms analysis data the data were then compared with well logging data to understand the distribution of high quality source rocks the data were also incorporated into basin models to reveal the burial and thermal histories and timing of hydrocarbon generation the results illustrated that the average residual toc contents of c1v and c1sr were 0 79 and 0 5 respectively which were higher than the threshold of effective carbonate source rocks dominated by type iii kerogen the c1v and c1sr source rocks tended to be gas bearing the two source rocks were generally mature to highly mature the average ro was 1 51 and 1 23 in c1v and c1sr respectively the source rocks were deposited in strongly reducing to weakly oxidizing marine terrigenous environments with most organic material originating from higher terrigenous plants and a few aquatic organisms during the permian the deep burial depth and high heat flow caused a quick and high maturation of the source rocks which were subsequently uplifted and eroded stopping the generation and expulsion of hydrocarbons in the c1v and c1sr source rocks the initial toc fitted by the logr method was recovered and it suggests that high quality source rocks toc 1 are mainly distributed in the northern and central local structural belt

new insight into the microtexture of chalks from nmr analysis an integrated petrographical and petrophysical study was carried out on a set of 35 outcrop chalk samples covering a wide range of lithologies and textures in this study various chalk rock types have been characterized in terms of microtextures and porous network by integrating both geological sediment petrological and petrophysical data including porosity permeability low field nmr nuclear magnetic resonance micp and specific surface area bet measurements the data allow an in depth understanding of the nmr signal of chalks with a focus on tight chalks including all low reservoir quality chalks independently of their sedimentological and or diagenetic history the study aims to develop an nmr based approach to characterize a broad range of chalk samples the provided laboratory low field nmr chalk classification can be used as a guide to interpret nmr logging data based on the petrographical and petrophysical analysis 6 groups of samples were identified each of them characterized by a unique nmr signature 1 micritic chalks 2 grainy chalks 3 cemented chalks 4 marl seam chalks 5 argillaceous chalks and 6 silicified chalk nmr t2 distributions were linked to pore body size and t2 logarithmic t2lm was calculated it is apparent that tight chalks whether their characteristics are sedimentological or diagenetic yield smaller pore body sizes t2lm 60 ms and pore throats average radius 290 nm and higher permeabilities up to 13 md the marl seam chalk samples yield bimodal t2 distributions with a first peak related to the micritic matrix pores and a second peak related to intraparticle pores within fossils for all samples permeability was inferred from nmr spectra using sdr schlumberger doll research model

electrical and fluid flow properties of carbonate microporosity types from multiscale digital image analysis and mercury injection electrical and fluid flow properties of porous media are directly related to the morphology of pores and the connectivity of the pore network both are closely linked to the amount and type of intrinsic microporosity in carbonate rocks which is not resolved by conventional techniques broad ion beam bib milling produces high quality true two dimensional cross sections for scanning electron microscopy sem and enables accurate quantification of carbonate microporosity for the first time the combination of bib sem mosaics with optical micrographs yields a multiscale digital image analysis msdia spanning six orders of magnitude in this paper the pore structures of 12 different carbonate rock samples from various rock types are quantified using msdia mercury injection capillary pressure measurements are used to assess pore throat properties the quantified pore structure parameters are correlated with plug measurements of electrical resistivity and permeability results indicate that petrophysical properties are closely linked to the type of microporosity which is distinctive for a certain rock type rock types with crystalline microporosity such as mudstone and dolomite generally show good connectivity in which the size of the pore network determines if the rock favors either hydraulic or electric flow rock types with intercement or micromoldic microporosity such as bindstone and travertine show variations in connectivity due to layering and moldic micropores of biological origin furthermore pore size distributions psd follow a power law in all samples despite their depositional and diagenetic differences the slope of the psd correlates with the electric properties in which samples with a steeper slope show lower cementation factors the linearity of the power law distribution enables predictions of pore populations outside the investigated length scales

continental carbonates as a hydrocarbon reservoir an analog case study from the travertine of saturnia italy the pleistocene saturnia travertine central italy represents a possible analog of the pre salt continental carbonate reservoirs discovered in the santos and other basins in the south atlantic margin of brazil two subhorizontal travertine tabular bodies several tens of meters thick and extending over an area of have been studied in two quarries facies variations and associated petrophysical properties were reconstructed applying a multidisciplinary approach the saturnia travertine formed from a warm water spring is composed of various stacked carbonate banks separated by subaerial erosive phases and paleosols the lacustrine tabular bodies terraces and sills are made of crystalline crust shrub pisoid paper thin raft coated bubble reed and lithoclast breccia facies the from 4 to 8 supports an interpreted volcanic mantle source whereas the from 9 to 5 is in agreement with warm meteoric waters the ratio isotopic signature indicates a carbonate from dissolution of deep seated carbonates the facies reservoir properties were studied via porosity and permeability analysis of plugs three dimensional x ray computer tomography as well as image analysis on microscale under thin section and macroscale on large rock slabs to define various porosity indices a strong heterogeneity of the petrophysical properties and variable connectivity were observed porosity from 4 to 30 and permeability up to hundreds of md but no compartmentalization of the carbonate bodies is present

contrasting diagenetic evolution patterns of platform margin limestones and dolostones in the lower triassic feixianguan formation sichuan basin china abstract deeply buried carbonate reservoirs from the lower triassic feixianguan formation in the sichuan basin of china host extensive natural gas resources these reservoirs are predominantly found in oolitic shoals with the reservoir quality of dolomitized zones being higher than that of undolomitized limestone counterparts here we present a combination of petrographic isotopic fluid inclusion and quantitative porosity data in order to understand and predict the diagenetic processes that have impacted the reservoir quality of dolostones and limestones the porosity of limestones has been reduced to 7 5 due to calcite cementation whereas the porosity in oolitic dolostones is not cemented with calcite and typically has 23 5 porosity dolomitization and concurrent early diagenetic gypsum growth played crucial roles on the development and preservation of high porosity in the oolitic dolostone first by stabilizing the rock fabric to inhibit loss of porosity during burial and secondly through the generation of new porosity by dissolution of carbonate and anhydrite a negative shift of 18 o and salinity values 13 c values 20 vpdb and 18 o 10 vpdb together with elevated calcite precipitation temperatures 110 c it is likely that tsr was responsible for the formation of enlarged dissolution vugs that increased porosity by 2 in dolostones due to i anhydrite dissolution ii production of significant amounts of water resulting in formation water undersaturated with respect to calcite and dolomite iii generation of h 2 s and co 2 and the consequent reaction of h 2 s with the siderite feco 3 component in calcite and dolomite this study demonstrates the importance of diagenesis in the formation of deeply buried high quality reservoirs in ooid dominated grainstones influenced by the presence of evaporites our results should be useful for guiding future exploration and reservoir developments in similar paleogeographic and diagenetic settings

the role of fe on the formation and diagenesis of interstratified glauconite smectite and illite smectite a case study of upper cretaceous shallow water carbonates abstract the widespread formation of interstratified glauconite smectite gl s and illite smectite i s in modern and ancient diagenetic settings records the physicochemical conditions prevailing during clay mineral authigenesis to date however significant gaps in our knowledge persist in respect to the influence of interstitial solution chemistry temperature and reaction kinetics on the evolution of composition mineralogy and microstructure of gl s and i s herein we present a study on the reaction mechanisms and the physicochemical conditions that led to the precipitation of early diagenetic gl s and late diagenetic i s on a stable carbonate platform during the cenomanian at langenstein in the northern german basin the texture and the k ar age 95 0 1 8 ma of the green glauconitized grains revealed that green clay authigenesis progressed in initially organic rich semi confined micromilieus i e in fecal pellets and in foraminifera close to the sediment seawater interface the composition of gl s varied in the range k 0 20 0 74 na 0 0 10 ca 2 0 0 05 0 28 0 75 fe 3 0 63 1 20 fe 2 0 08 0 24 al 3 0 19 0 97 mg 2 0 29 0 52 2 01 2 12 al 3 0 09 0 35 si 4 3 65 3 91 o 10 oh 2 and depended on the rate of aqueous fe 2 and k ion diffusion the micromilieu of glauconitization and on the bulk sedimentation rate the mineralogical microstructural and chemical changes of the ongoing gl s products revealed the following reaction for green clay authigenesis at langenstein fe iii smectite reacted with monosilicic acid goethite and aqueous k mg 2 and fe 2 to form glauconite and aqueous na ca 2 and h ions this process considers complex mineral transformations commonly associated with glauconitization such as early diagenetic oxidation of organic matter and microbial catalyzed dissolution of fe oxy hydroxides carbonates and detrital silicates in contrast the k ar age of i s 68 0 1 6 ma and its compositional variability k 0 29 0 45 na 0 0 10 ca 2 0 0 06 0 30 0 55 fe 3 0 16 0 29 fe 2 0 0 10 al 3 1 37 1 68 mg 2 0 18 0 43 2 00 2 12 al 3 0 17 0 39 si 4 3 61 3 83 o 10 oh 2 indicate a burial diagenetic origin for this mineral phase rather than transformation of illitic clays into i s during weathering under warm and humid climatic conditions the results from kinetic modelling support a diagenetic origin of i s 50 60 i layers and 50 40 s layers and imply its formation by the replacement of pre existing k feldspar at high pore fluid activity k na ratios and at low fe 2 concentrations we propose that the substitution of al 3 for fe 3 fe 2 and mg 2 in the octahedral sheet shifts the stability field of the kaolinite fe al mg smectite fe al mg illite or glauconite triple point to much lower monosilicic acid activities and stabilizes the i s or gl s structure this reaction supports the idea that the bio availability of fe is the rate limiting factor for glauconitization which is not the case for the diagenetic growth of i s whereby the pore water fe 2 concentration may be limited by the competing formation of fe oxy hydroxides and or fe sulfides

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

a lower mantle s wave triplication and the shear velocity structure of d summary a lower mantle s wave triplication detected with short and longperiod wwssn and csn recordings indicates a substantial shear velocity discontinuity near 280 km above the core mantle boundary the triplication can be observed in rotated sh seismograms from intermediate and deep focus events throughout the distance range from 70 to 95 three distinct source region receiver array combinations that have been investigated in detail demonstrate consistent travel time and relative amplitude behaviour of the triplication with slight systematic shifts in the triplication indicating up to 40km variations in the depth of the discontinuity modelling of the observations with synthetic seismograms produced with the cagniard de hoop and reflectivity methods constrains the shear velocity increase to be 2 75 k 0 25 per cent comparable to upper mantle discontinuities short period observations indicate that the velocity increase may be a sharp first order discontinuity or may extend over a transition zone no more than 50 km thick the shear velocity gradient below the discontinuity within the d layer is not well constrained by the sh data but slightly positive or near zero velocity gradients are consistent with the long period amplitude ratios of scsh sh

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

pore structure and fractal analysis of lower carboniferous carbonate reservoirs in the marsel area chu sarysu basin abstract evaluation of carbonate heterogeneity closely related to pore geometry and connectivity is important in oil and gas field production and reservoir prediction to profoundly understand the heterogeneity of lower carboniferous carbonate reservoirs in the marsel area including visean c1v and serpukhovian c1sr the pore structure and fractal characteristics are investigated using routine petrophysical measurements x ray diffraction xrd cast thin section analysis scanning electron microscopy sem and mercury injection capillary pressure micp tests the origin of potentially prolific reservoir the relationships between fractal dimension and reservoir physical properties mineral composition and pore structure are also discussed xrd results reveal that the mineral compositions are highly heterogeneous in c1v and c1sr routine petrophysical experiments indicate that c1v and c1sr are generally tight however some high porosity permeability zones exist in c1sr which is described as a potentially prolific reservoir the cast thin section and sem analyses identify three main pore types in the potentially prolific reservoir interparticle dissolution pores intercrystalline dissolution pores and moldic pores the micp data reflect that the pore throat radii in the prolific reservoir range from 0 29 to 4 6 m whereas those in tight section are typically

application of mercury injection capillary pressure to mudrocks conformance and compression corrections abstract mercury injection capillary pressure micp is a commonly used technique for measurements of porosity pore throat size distribution and injection pressure vs mercury saturation for many types of rocks the latter two are correlated to and can be used to estimate permeability problems for micp application in mudrocks are associated with two types of system errors conformance and compression effects these two sources of error are well recognized but no standard procedures to correct them exist in this study a new method for conformance and compression corrections was developed and the method applied to five eagle ford shale samples conformance correction is based on comparison of mercury injection volume vs pressure curves between epoxy coated and uncoated samples compression correction is based on calculation of compressions before and after mercury intrusion in micp experiment different types of compressions are quantified and compression corrections on porosity pore throat size distribution and injection pressure vs mercury saturation are performed porosity and permeability were calculated based on corrected micp data results show that both conformance and compression corrections are important for accurate micp porosity calculation whereas conformance correction is more important than compression correction in permeability calculation

high resolution imaging of lowermost mantle structure under the cocos plate 1 broadband seismic shear waves are analyzed to investigate the fine velocity structure in the lowermost mantle beneath the cocos plate a region where previous studies have indicated the presence of a shear velocity increase about 200 300 km above the core mantle boundary data from 14 south american earthquakes recorded at california broadband networks provide dense ray path sampling of the lowermost mantle in an approximately 700 km long north south corridor roughly 150 km wide application of a simplified seismic migration method that uses a homogeneous background velocity model suggests topography of the previously imaged positive impedance jump varying in depth from north to south by as much as 150 km with a weakly reflecting transition zone in between the migration approach enables examination of small scale spatial variations and out of plane scattering effects topography of the discontinuity may account for observed variations in the amplitude of reflected arrivals or there may be lateral variations in the velocity contrast across the boundary lateral variations of the shear velocity structure within the d layer may produce some apparent topography in the discontinuity image but any such volumetric structure is not yet well enough determined to incorporate in the migration a localized negative impedance contrast reflector or scatterer is imaged at depths about 100 km below the positive reflector in the northern portion of the study area several scenarios can explain these results including 1 a slab that reaches the lowermost mantle 2 the birth of an upwelling beneath a recumbent slab or 3 chemical layering in this region

meteoric calcite cementation diagenetic response to relative fall in sea level and effect on porosity and permeability las negras area southeastern spain abstract a dolomitized upper miocene carbonate system in southeast spain contains extensive upper and lower zones of calcite cementation that cut across the stratigraphy cement textures including isopachous and circumgranular which are consistent with phreatic zone cementation cements in the upper cemented zone are non luminescent whereas those in the lower cemented zone exhibit multiple bands of luminescent and non luminescent cements in the upper cemented zone isotopic data show two meteoric calcite lines mcl with mean 18 o at 5 1 and 5 8 vpdb whereas no clear mcl is defined in the lower cemented zone where mean 18 o for calcite cement is at 6 7 vpdb 13 c values in both cement zones are predominantly negative ranging from 10 to 2 vpdb suggestive of carbon from soil gas or decayed organics measurements of tm ice in primary fluid inclusions yield a mode of 0 0 c in both zones indicating calcite cementation from fresh water these two zones define the positions of two different paleo water tables that formed during a relative sea level fall and erosional downcutting during the plio pleistocene the upper cemented zone pre dated the lower cemented zone on the basis of known relative sea level history meteoric calcite cementation reduced porosity and permeability but measured values are inconsistent with simple filling of open pore space each texture boundstone grainstone packstone wackestone produces a different relationship between percent calcite cement and porosity permeability distribution of cements may be predictable on the basis of known sea level history and the effect of the cementation can be incorporated into subsurface geomodels by defining surfaces of rock boundaries that separate cemented zones from uncemented zones and applying texture specific relationships among cementation porosity and permeability

modelling the permeability evolution of carbonate rocks abstract diagenesis is a major control on the distribution of porosity and permeability in carbonate rocks and therefore impacts fluid flow in the subsurface while changes in porosity can be directly related to diagenetic petrographic characteristics such as cement distribution and dissolution features quantifying how these textures relate to attendant changes in permeability is more challenging here we demonstrate for the first time how pore scale models representing typical carbonate sediments and their diagenetic histories can be used to quantify the evolution of petrophysical properties in carbonate rocks we generate 3d pore architecture models i e the spatial distribution of solid and pores from 2d binarized images representing the typical textural changes of carbonate sediments following hypothetical diagenetic pathways for each 3d rock model we extract the pore system and convert this into a network representation that allows flow properties to be calculated the resulting porosity and permeability evolution scenarios display several diagenetic tipping points where the decrease in permeability is dramatically larger than expected for the associated decrease in porosity the effects of diagenesis also alter the capillary entry pressures and relative permeabilities of the synthetic cases providing trends that can be applied to real rocks indeed values of porosity and absolute permeability derived from these synthetic 3d rock models are within the range of values measured from nature such diagenetic pathway models can be used to provide constraints on predicted flow behaviour during burial and or uplift scenarios using diagenetic back stripping of real carbonate rocks

heterogeneities and diagenetic control on the spatial distribution of carbonate rocks acoustic properties at the outcrop scale abstract carbonate rocks are characterized by a high heterogeneity of their properties at the outcrop scale that results from complex interactions between sedimentary diagenetic and fracturing processes here we show acoustic p wave velocity measurements conducted step by step on three decameter scale outcrop surfaces in cretaceous carbonate rocks with contrasted heterogeneities two shallow water highly fractured cassis and low fractured calissanne carbonates and one basin highly compacted grignantes p wave measurements were compared to outcrop geology and with plug porosity p wave velocity laboratory measurements and a thin section study results show a strong scale dependence of p wave velocities which always are lower at the decimeter scale than at the plug scale vp in situ versus vp plug large discrepancies 2000 m s highlight the signature of large heterogeneities open fractures stylolithes and lower discrepancies in situ distribution follows the dip of the ripple foresets which are controlling grain sorting and porosity in calissanne outcrop the near isotropic vp are explained by an early intense fracturing and cementation in cassis outcrop and the strong horizontal anisotropy with a hole effect behavior on variograms highlights the late re opening of multiple intervals of compaction bands in grignantes these results illustrate that the early diagenesis coupled to fracture or stylolithe reactivation opening are two key processes that explain the outcrop scale p wave velocity distribution anisotropy in carbonates

fractal and multifractal analysis of carbonate pore scale digital images of petroleum reservoirs the petrophysical evaluation of the reservoir capacity is of great importance in predicting the reserves and productivity of petroleum fields which may directly affect petroleum exploration in the past such kind of evaluation was mainly based on the experimental measurements of the petrophysical porosity and permeability of reservoir rock samples assessing quantitatively the microstructures of carbonates including irregularities of pore shapes and frequency distributions of pore sizes is becoming one of the most challenging efforts in pore scale analysis based on the digital analyses of the two dimensional images from thin sections taken under the environmental scanning electron microscope esem at various magnification scales the current paper tries to quantify the pore spaces of carbonate samples by fractal and multifractal methods which have been demonstrated to be effective the study area is located in the western hubei and eastern sichuan china as many as 25 carbonate samples from various members in five formations of the permian triassic periods and 132 esem images were chosen in this study all individual pores had been recognized and their areas and perimeters had been calculated as well the box counting fractal dimensions and four major multifractal parameters associated with the multifractal spectra are used the results show that the values of the petrophysical porosity and permeability are closely related to the box counting dimensions and the multifractal parameters which demonstrates that the textural arrangements of the pores control the porosity and permeability to a certain extent there is also a link between the reservoiring capabilities of different formations and the fractal and multifractal parameters the reservoiring capability assessment result is in agreement with the field research analysis

pore structure evaluation of tight reservoirs in the mixed siliciclastic carbonate sediments using fractal analysis of nmr experiments and logs abstract the study on mixed depositional reservoirs is widely attended in recent years however the mixed depositional reservoirs are generally characterized by complex pore structure which is caused by strong heterogeneity complex mineral compositions and varying pore sizes presenting a major challenge to describe the difference in pore structure between different samples to address this challenge the pore structure of mixed depositional reservoirs was evaluated by the fractal dimensions and the influences of various mineral compositions on pore structure were analyzed the fractal dimensions derived from nmr measurements or nmr logging data can be divided into two segments at t 2cutoff values representing different fractal values and characteristics of pore structure for the e 3 2 formation in yingxi field the fractal dimension of movable fluid pores ranges from 2 628 to 2 917 average 2 765 whereas the bound fluid pore systems are not following the fractal theory meanwhile the fractal dimensions show a negative relationship with movable fluid porosity and permeability the effects of various mineral compositions on fractal laws of the pore networks are different fractal dimension increases with the increases of clay mineral contents and the decrease of dolomite content while the effect of calcite content on fractal laws of the pore system is uncertain and quartz from different genetic type represents different effect on fractal dimensions this study is contributed for petroleum exploitation in mixed depositional reservoirs and shows that the fractal dimension can comprehensively indicate the complexity of the pore structure in mixed depositional reservoirs

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

using the porosity exponent m and pore scale resistivity modelling to understand pore fabric types in coquinas barremian aptian of the morro do chaves formation ne brazil abstract the recent major discoveries of petroleum in pre salt carbonate reservoirs of mainly lacustrine origin offshore brazil has increased interest in studying these complex non marine reservoirs which present many production development challenges largely due to their heterogeneous nature some of the reservoir carbonate rock types present in brazil are limestones composed predominantly of bivalve shells which are known as coquinas the coquinas show a variety of pore types pore sizes pore shapes and pore connectivity which define their porosity and strongly influence the permeability and resulting electrical resistivity but this aspect of these relationships in these carbonates has been relatively poorly characterised particularly in a quantitative manner in the literature the petrophysical characterisation of the coquinas of the morro de chaves formation barremian aptian exposed in a quarry in ne brazil was carried out using the outcrop selected samples plugs and petrographic thin sections to investigate these aspects porosity permeability grain density and porosity exponent m measurements were carried out on the plugs x ray microtomography was performed to identify key characteristics of the pore system and for the basis of 3 d modelling significant variation in m was observed across the plug data set which is not unexpected in carbonates but it suggested that a range of fabrics and pore topology were present in these rocks which are described only as calcirudites modelling of the resistivity using 3d pore scale models was used to understand the role of disconnected macro pores and dissolution seams in controlling the more extreme variation in petrophysical properties observed in the coquinas this understanding of the controls on resistivity pathways in this outcrop coquina will help in understanding the pore types in the subsurface and the estimation of saturations in these complex rocks where they are found to be oil bearing

the fate of co2 derived from thermochemical sulfate reduction tsr and effect of tsr on carbonate porosity and permeability sichuan basin china abstract this article discusses the role of methane in thermochemical sulfate reduction tsr the fate of tsr derived co2 and the effect of tsr on reservoir porosity and permeability and the causes of the anomalously high porosity and permeability in the lower triassic soured carbonate gas reservoirs in the northeast sichuan basin southwest china the lower triassic carbonate reservoirs were buried to a depth of about 7000 m and experienced maximum temperatures up to 220 c before having been uplifted to the present day depths of 4800 to 5500 m but they still possess porosities up to 28 9 and permeabilities up to 3360 md the present day dry gas reservoirs evolved from a paleo oil accumulation and experienced varying degrees of tsr alteration as evidenced from the abundant sulfur rich solid bitumens and varying h2s and co2 concentrations tsr occurred mainly within the oil and condensate wet gas windows with liquid hydrocarbons and wet hydrocarbon gases acting as the dominant reducing agents responsible for sulfate reduction sulfur rich solid bitumen and h2s generation and calcite precipitation methane dominated tsr was a rather late event and had played a less significant role in altering the reservoirs intensive h2s and co2 generation during tsr resulted in calcite cementation rather than carbonate dissolution which implies that the amount of water generated during tsr was volumetrically insignificant 13c depleted co2 derived from hydrocarbon oxidation preferentially reacted with ca2 to form isotopically light calcite cements and the remaining co2 re equilibrated with the 13c enriched water rock systems with its 13c rapidly approaching the values for the host rocks which accounted for the observed heavy and relatively constant co2 13c values the carbonate reservoirs suffered from differential porosity loss by tsr involved solid bitumen generation and tsr induced calcite and pyrite precipitation intensive tsr significantly reduced the porosity and permeability of the intervals expected to have relatively high sulfate contents the evaporative platform dolostones and the platform margin shoal dolostones immediately underlying the evaporative facies early oil charge and limited intensity of tsr alteration together with very low phyllosilicate content and early dolomitization accounted for the preservation of anomalously high porosities in the reservoirs above the paleo oil water contact a closed system seems to have played a special role in preserving the high porosity in the gas zone reservoirs below the paleo oil water contact the closed system which is unfavorable for deep burial carbonate dissolution and secondary porosity generation was favorable for the preservation of early formed porosity in deeply buried carbonates especially sucrosic and vuggy dolostones have a high potential to preserve such porosity

micro nanoscale pore structure and fractal characteristics of tight gas sandstone a case study from the yuanba area northeast sichuan basin china abstract the pore size distribution psd and fractal dimension are two typical parameters that are used to evaluate the heterogeneous characteristics of unconventional reservoir pores the micro nanoscale psd and pore fractal dimension characteristics of tight gas sandstones from the upper triassic xujiahe formation in the yuanba area were investigated by using nuclear magnetic resonance nmr nuclear magnetic resonance cryoporometry nmrc mercury injection capillary pressure micp and scanning electronic microscopy sem techniques to date no other attempts have been made to use nmrc with octamethylcyclotetrasiloxane omcts as a probe material to describe the pore fractal characteristics of tight gas sandstones in this study the fractal dimensions of tight gas sandstones were estimated by processing raw nmrc data with a fractal theoretical model and the nmrc fractal results were compared to the calculated fractals from the micp tube model micp sphere model and nmr t2 spectrum the results consistently show that the pore fractal characteristics of tight sandstone samples from the yuanba area exhibit multiple fractal structures at different pore size ranges large pores in the samples are more complex with rougher surfaces and small pores correspond to smoother surfaces sandstones with greater porosity and pore space possess more heterogeneous structures the psd and fractal dimensions can be combined and used as an indicator for the presence of gas bearing and dry formations in the study area the tight sandstone samples from the dry formations have both lower porosities and smoother pore surfaces with smaller fractal dimensions these characteristics may not be beneficial for the preservation of hydrocarbon fluids in the target area

structure of the earth mantle and core the deep interior structure of the earth has been extensively analyzed using a wide variety of seismic phases and techniques during the last four years most studies have emphasized quantitative three dimensional mapping of the lateral velocity heterogeneity of the mantle and core these aspherical velocity variations are believed to be direct manifestations of thermal and compositional heterogeneity associated with convective processes a first generation of global models for the lateral velocity variations in the deep earth has been produced providing tantalizing images of large scale structures suggestive of a non steady state thermal convection system the upper 400 km of the mantle has the strongest lateral velocity variations of up to 10 for shear velocity surface wave analyses that do not require a priori regionalizations have demonstrated that there is a strong association between surface tectonic provinces and the uppermost mantle velocity variations thus the thermal and convective state of the upper 200 km of the mantle can be reliably interpreted in the context of plate tectonics the upper mantle models support the contention that continents have deep roots with differences in velocity structure from oceanic and active tectonic regions extending as deep as 400 km very long wavelength lateral velocity variations of a few percent have been detected in the transition zone at depths from 400 to 670 km as well as throughout the lower mantle these deep seated variations have little correspondence to surface tectonics and efforts to interpret their nature are just beginning the lowermost 200 km of the mantle d region has lateral velocity fluctuations comparable to those in the upper mantle and evidence has been presented for the presence of a sizable velocity discontinuity at the top of the d layer a combined thermal and compositional boundary layer roughly mirroring the lithosphere is a likely explanation for this anomalous zone the core mantle boundary appears to have significant 10 km long wavelength topography presumably sustained by dynamic stresses from deep mantle convection the inner core may have strong lateral heterogeneity or axially symmetric anisotropy suggesting a complex thermal and compositional state significant progress has been made in characterizing the frequency dependence of anelastic attenuation in the mantle in the short period body wave band models for teleseismic p wave attenuation operators have converged with t values of 0 7 1 0 s appropriate at 1 hz and t values of 0 4 0 6 s appropriate at 4 hz regional variations of attenuation are slowly being mapped out as well

modelling d structure beneath central america with broadband seismic data deep south american events recorded at distances between 70 and 96 are used to constrain the lower mantle structure beneath central america employing data from the terrascope bdsn iris and cnsn canadian national seismic network broadband arrays we obtain a 1 d shear model with a 200 km thick d layer with a 3 velocity jump at the top and a negative gradient within the layer from broadband waveform modelling of sh polarized s scs and scd the shear structure above d is similar to the preliminary reference earth model prem dziewonski and anderson 1981 preliminary reference earth model physics of earth planetary interiors 25 297 356 in terms of dt d and s sks differential times sv synthetics for this model assuming a prem core produce a satisfactory fit to the data except at the larger ranges to the north where the waveforms display rapid variation this feature is indicative of lateral variation of the type suggested by grand 1994 where the discontinuity becomes less well defined synthetics computed for a simplified 2 d cross section through this structure produce the scd phase and simple s at larger distances while scd is easily observed in the shear wave data there is little evidence of its counterpart in the p data by testing several models with different p velocity jumps at the same depth as the d jump in shear structure we conclude that the velocity jump must be less than 1 in fact prem provides an excellent fit both in timing and waveform shapes and therefore we conclude that lower mantle structure beneath central america shows clear evidence for a discontinuity in s velocity but not in p

fracture characterization in tight carbonates an example from the ozark plateau arkansas outcrop studies of fracture development used as analogs for subsurface fracture patterns are critical because of the importance of fractures as fluid flow pathways and the fact that most fracture networks exist at a smaller resolution than current seismic data can resolve fracture networks in carbonate units are typically controlled by the mechanical properties of the unit indicating that the mechanical stratigraphy as well as the fracture stratigraphy should be considered this study presents the results of a fracture analysis in the mississippian carbonates of the ozark plateau considering both mechanical and fracture network characteristics mechanical characteristics of the succession were defined using a combination of rebound values and thin section petrography fracture characteristics included orientation and intensity together with abutting relationships results indicate that fracture orientations show a distinct evolution throughout the measured succession including the appearance of early systematic sets followed by pervasive systematic fracture sets related to existing basement features fracture orientation changes do not correspond to changes in mechanical stratigraphy fracture intensity however is related to the thickness of the mechanical unit instead of the bed thickness and is greatest in less competent units mechanical control influences the fracture network on a smaller scale than that of regional tectonic stresses thus evaluations of carbonate reservoirs must account for both the large scale and the small scale investigations into fracture characteristic controls outcrop evaluations are of critical importance to properly assess characteristics that are challenging to recover from conventional subsurface data sets such as core and seismic reflection volumes