mechano chemical interactions in sedimentary rocks in the context of co2 storage weak acid weak effects abstract due to the corrosive nature of dissolved co2 the potential short or long term alteration of rock properties represents a major issue in several sites where natural co2 circulation is observed as well as in reservoirs targeted for storage of anthropogenic co2 to date this has been primarily studied from a transport chemical perspective with laboratory evidence of microstructural modifications together with the consequences for flow properties compared to the transport chemical aspects the mechanical chemical aspects have been less investigated though it is to be expected that mechanical properties e g elastic properties failure parameters and time dependent mechanical behaviour could potentially be affected in a similar manner to hydraulic parameters yet since co2 is a weak acid the ph drop is expected to be moderate with a likely lower limit close to 4 0 the buffering of ph by calcite minerals present in most reservoirs targeted for storage may further limit the ph drop as well as confining it to a localized rock volume around the injection well this leads to the question of the magnitude and time spatial scales of chemically mediated mechanical processes during co2 sequestration the authors propose to address this issue by reviewing recent laboratory based studies restricted to sedimentary rocks namely reservoir rocks carbonate or sandstone intact or fractured caprocks and fault rocks key findings include the following 1 the short term impact on the elastic and inelastic behaviour of intact caprocks remains limited 2 shear strength weakening is likely to be respectively low and low to moderate for shale clay rich and anhydrite rich faults but without modifying slip stability in either case 3 the largest impact is located within carbonate reservoirs but with a broad range of reported responses depending on hydrodynamic conditions closed or open and on dissolution regime uniform or channelling and 4 creep experiments confirm that co2 induced dissolution may enhance long term compaction of carbonate reservoirs but the magnitude of acceleration varying from non significant to 50 times depends to a large extent on site specific conditions grain size ph temperature effective stress state etc which renders any direct extrapolation from laboratory to reservoir scale difficult finally some directions for future research studies are discussed

wave attenuation in partially saturated porous rocks new observations and interpretations across scales abstract seismic waves propagating in porous rocks saturated with two immiscible fluids can be strongly attenuated predicting saturation effects on seismic responses requires a sound understanding of attenuation and velocity dependencies on the fluid distribution decoding these effects involves interpreting laboratory experiments analyzing well log data and performing numerical simulations despite striking differences among scales flow regimes and frequency bands some aspects of wave attenuation can be explained with a single mechanism wave induced pressure diffusion different facets of wave induced pressure diffusion can be revealed across scales

ultrasonic velocity and attenuation during co2 injection into water saturated porous sandstone measurements using difference seismic tomography we undertook laboratory based seismic measurements with dense sensor array at ultrasonic frequencies during the injection of co2 into a water saturated sandstone specimen the resulting high quality seismic data enabled detailed determination of the relative velocity and attenuation coefficient of the compressional wave using difference seismic tomography which directly inverses time lapse changes in rock properties from time lapse changes in observed data co2 migration and water displacement were clearly mapped using tomographic images of relative velocity and the attenuation coefficient the final and largely stabilised volume fraction of co2 in the pore space of the sample is about 30 40 on average the p velocity fell by 7 5 12 and 14 5 and the attenuation coefficient q 1 increased by factors of 3 3 2 7 and 3 7 as a result of the replacement of water with co2 during the injection of gaseous liquid and supercritical co2 respectively as a function of gas saturation both the velocity and attenuation data are in good agreement with results obtained using the white and dutta ode model for partial saturation indicating that viscous losses due to fluid diffusion are of significant importance for compressional waves travelling at ultrasonic frequencies in porous rocks

continuous porosity characterization metric scale intervals in heterogeneous sedimentary rocks using medical ct scanner abstract although computed tomography ct scanning has been regularly applied to core analyses in petroleum geology there is still a need to improve our ways to document porosity and porosity distribution in the entire pore scale spectrum from the tens of nanometer to the meter scale porosity imaging is particularly crucial for complex and heterogeneous rocks such as hydrothermally altered and fractured carbonates the present work proposes an improved method using medical ct to reliably estimate reservoir porosity an in house core flooding setup allowed to analyse several individual core samples scanned simultaneously dry and saturated as well as continuous core sections up to 1 5 m long without any prior knowledge of samples three dimensional alignment and subtraction of the two data sets dry and saturated states results in the generation of 3d porosity matrices the methodology tested on a large set of reference core material shows a strong correlation between conventional gas porosimetry techniques and porosity from ct scan the added value of the porosity measurements by ct scan is first of all the generation of 3d images of pore network allowing to assess spatial attributes of macropores their distribution and connectivity secondly the ct scan method also provides continuous porosity profile at the millimetric scale both developments are crucial for the understanding of reservoir rock properties

microbially induced sedimentary structures from the 1 64 ga chuanlinggou formation jixian north china abstract the present study documents abundant exceptionally preserved microbially induced sedimentary structures miss from the 1 64 ga chuanlinggou formation of the jixian area north china craton the chuanlinggou formation is dominated by black silty shale mudstone with fine sandstone of the lower part and was likely deposited in a relatively restricted shallow marine environment varying from fair weather wave action zone to below storm wave action zone both wrinkle structures and sand veins are very abundant in the lower and middle parts of the formation wrinkled layers are dark colored densely laminated and contain floating quartz grains and abundant mica grains both of which are aligned parallel to bedding plane such an arrangement pattern is attributed to the microbe s binding and trapping of miss sem imaging also shows that sticky networks interwoven by filamentous extracellular polymer substances eps and biofilms with distinct pores are very pronounced in clay matrix of wrinkled layers providing direct evidence of microbial activities during the formation of wrinkle structures in addition the circularly arranged quartz grains forming hollow cavities and vertical channels of quartz grains beneath the laminated layers are unique to the wrinkle structures showing initial forming stage of the sand veins sand veins similar to fills of sand cracks are usually preserved in silty shales and occasionally occur beneath the winkled surfaces they were formed due to methane degassing of decay of microbial mats and biofilms abundant nano particles of various epss isolated nanoglobules paired nanoglobules dumbbell shaped nanoglobules and polyhedron aggregates are detected in clay matrix close to sand veins indicating microbial participation in the formation of sand veins wide spatial distribution broadened environmental inhabitation and extremely high abundance and bed surface density of the misss indicate proliferation of miss forming microbial mats in mesoproterozoic times

approaching raw material functionality in the upper magdalenian of coimbre cave asturias spain through geometric morphometrics abstract coimbre cave penamellera alta asturias is an upper palaeolithic site in northern spain spanning an occupation sequence from the gravettian to the magdalenian periods the upper layers layer i and ii corresponding to the upper magdalenian register the highest intensity of human activity in this paper we analyse raw material functionality at the site through the study of cut marks found on bone remains at coimbre we have documented mainly quartzite followed by flint other raw materials are found in very low frequencies there are several types of local quartzite that appear mainly as flaking debitage and stone tools such as burins and scrappers on the other hand flint is mainly knapped to elaborate blades and bladelets as well as specialised implements such as different types of side scrappers retouched flakes on flint are relatively more abundant than those made on quartzite in this paper we employ the use of photogrammetry geometric morphometrics and statistics to analyse the cut marks from the upper magdalenian assemblage of coimbre cave our aim is to determine the lithic raw material preferentially used for carcass processing at the site

now a bone then calcite abstract critical transformation and degradation of skeletal tissues most frequently affect their organic components while the mineral component of bones and fossils comprises one of the most stable mineral groups on earth the apatites the case we present here relates to fossil bones from palaeolake shores whose shapes are preserved within the sediment itself but which disintegrate into a chalky disaggregated substance at the slightest touch or breath the rarity of bone apatite transformation into calcite is due to the extreme insolubility and stability of bone mineral which is highly tolerant of ionic substitutions and inclusions without changing its basic mineral nature and composition observation of this chalky substance under high magnifications reveals a delicate structure of microcrystals these crystals enclose microtunnels and grooves identical in shape and size to the characteristic bone bioerosion caused by aquatic microorganisms this microtunnelling preservation allows us to confirm that disaggregate calcite crystals replaced areas where once there had been bone furthermore the bone chalky material transformation had to occur when microorganisms were still in the interior of these tunnels otherwise the delicate empty microtunnels observed today would have collapsed two calcareous palaeo lakeshore sites show identical phenomenon detailed taphonomic environmental and chemical studies indicate that the transformation process was initiated by microorganisms arising from a combination of their metabolism and the alkaline environment they inhabited that caused a local and sudden increase in local acidity this chalky material is referred to as biogenic in contrast to environmental calcite deposits geodes and calcite infilling bone fissures that formed in the lake conditions the calcium carbonate phase of both biological and environmental origin in these two palaeolakes is aragonite which forms under restricted situations of aridity and warming and may provide a precise indication of environmental conditions when these sites formed similar situations may occur today in arid areas

saturation path dependency of p wave velocity and attenuation in sandstone saturated with co2 and brine revealed by simultaneous measurements of waveforms and x ray computed tomography images abstractwe performed a laboratory experiment to measure compressional p wave velocity and its attenuation in low permeability striped sandstone at ultrasonic frequency during drainage co2 injection and imbibition brine injection x ray computed tomography ct images of the rock sample were simultaneously recorded during the injections on the basis of the ct images we calculated the co2 saturation inside a prolate spheroid shaped volume the first fresnel zone that enclosed the wave propagation path the relationship of p wave velocity and that of attenuation to the co2 fraction were then obtained both relationships showed nonuniqueness with remarkable hysteresis in a drainage imbibition cycle to explain the nonunique relationship of p wave velocity to the co2 fraction we investigated the continuous random patchy saturation model by using exponent type autocorrelation the nonunique relationship of velocity to the co2 fraction was explained by the model with a correlation length from an order

direct laboratory observation of patchy saturation and its effects on ultrasonic velocities maximizing the recovery of known hydrocarbon reserves is one of the biggest challenges facing the petroleum industry today optimal production strategies require accurate monitoring of production induced changes of reservoir saturation and pressure over the life of the field time lapse seismic technology is increasingly used to map these changes in space and time however until now interpretation of time lapse seismic data has been mostly qualitative in order to allow accurate estimation of the saturation it is necessary to know the quantitative relationship between fluid saturation and seismic characteristics elastic moduli velocity dispersion and attenuation the problem of calculating acoustic properties of rocks saturated with a mixture of two fluids has attracted considerable interest gist 1994 mavko and nolen hoeksema 1994 knight et al 1998 for a comprehensive review of theoretical and experimental studies of the patchy saturation problem see toms et al 2006

algal mats load structures and synsedimentary sulfides in revett quartzites of montana and idaho carbonate rich patches in quartzites of the revett formation are due to algal mats in marine arenites of about a 1 3 b y age some occur in growth positions on bedding planes some on slumped foresets but mostly they were disrupted by faster currents depositing heavy minerals as lag sediments discovery of stromatolites in the revett formation confirms the algal growths algal debris provided the food source for anaerobes which produced h 2 s for sulfide precipitation of copper silver lead zinc and iron in the zonal sequence typical of stratiform syngenetic sulfides at the troy mine these sulfide zones cross the strata sulfides vary in grain size and aggregation and are classified into original fine disseminations reworked aggregates formed during dewatering and infilling of fractures and vein openings by lateral secretion the relationship of fine sulfide disseminations to heavy minerals and to algal carbonate indicates deposition of minute sulfide grains with the sediment a quartzite pillow which contained 24 sagged and folded layers each layer with three sublayers of first heavy minerals and then clean quartzite both overlain by sulfide rich quartzite was examined and revealed the previously poorly understood mechanism of pillow growth contemporaneous with sedimentation and in this example also with sulfide precipitation better mineralization in arenites is ascribed not to permeability but to stronger currents depositing sand and causing increased mixing of the upper metal bearing waters with the lower anoxic water in which hydrogen sulfide precipitates selectively first copper and silver as minute sulfide grains the sulfides are incorporated into the suspended sediment which is then sorted by waxing and waning currents according to grain size and specific gravity into the varying proportions especially observed in the tripartite laminae of the 24 layers of the quartzite pillow described in detail

effect of sub core scale heterogeneities on acoustic and electrical properties of a reservoir rock a co2 flooding experiment of brine saturated sandstone in a computed tomography scanner the effect of sub core scale heterogeneity on fluid distribution pattern and the electrical and acoustic properties of a typical reservoir rock was studied by performing drainage and imbibition flooding tests with co2 and brine in a laboratory moderately layered rothbach sandstone was used as a test specimen two core samples were drilled one perpendicular and the other parallel to the layering to allow injection of fluids along and normal to the bedding plane during the test 3d images of fluid distribution and saturation levels were mapped by an industrial x ray ct scanner together with simultaneous measurement of electrical resistivity ultrasonic velocities as well as amplitudes the results showed how the layering and the flooding direction influenced the fluid distribution pattern and the saturation level of the fluids for a given fluid saturation level the measured changes in the acoustic and electrical parameters were affected by both the fluid distribution pattern and the layering orientation relative to the measurement direction the p wave amplitude and the electrical resistivity were more sensitive to small changes in the fluid distribution patterns than the pwave velocity the change in amplitude was the most affected by the orientation of the layering and the resulting fluid distribution patterns in some instances the change due to the fluid distribution pattern was higher than the variation caused by the change in co2 saturation as a result the gassmann relation based on uniform or patchy saturation pattern was not suitable to predict the p wave velocity variation overall the results demonstrate the importance of core imaging to improve our understanding of fluid distribution patterns and the associated effects on measured rock physics properties

surface modification on bone trampling versus butchery abstract previous researchers have reported difficulties in distinguishing between surface marks on bone formed by sedimentary abrasion and those inflicted while butchering trampling by large ungulates and humans has been credited with producing pseudocut marks natural alterations to the bone that mimic cultural ones the purposes of this research are 1 to re examine trampling as a taphonomic process and 2 to suggest criteria useful for distinguishing sedimentary abrasion including trampling from butchery macroscopic and microscopic comparison of experimentally trampled bones and those which have had soft tissue removed with a flint tool demonstrate significant differences between the surface modifications produced by the two processes

micro photogrammetric characterization of cut marks on bones in the last few years the study of cut marks on bone surfaces has become fundamental for the interpretation of archaeological sites and prehistoric butchery practices due to the difficulties in the correct identification of cut marks many criteria for their description and classifications were suggested this article presents an innovative methodology which supplements the microscopic study of cut marks despite the benefits of using scanning electron microscopy sem for the two dimensional identification of these marks it has a number of drawbacks such as the high costs and consequently the limited sample studied in this article a low cost technique for the analysis of cut mark micromorphology from a tri dimensional perspective is introduced it provides a high resolution approach to cut mark characterisation such as morphology depth width and angle estimation as well as section determination measured directly on the marks on bones macro photogrammetry records quantitative and qualitative information which can be statistically processed with standard multivariate and geometric morphometric tools

characterization of recent marks produced on fossil bone surface during sullegic and trephic processes and their influence on taphonomic studies abstract different taphonomic processes throughout the history of a fossil assemblage may preserve modify or destroy particular palaeobiological traits but these processes always increase taphonomic information of the past similarly fossils are affected during later stages of taphonomic history i e excavation preparation study and storage of fossils known as sullegic and trephic phases tools used during excavation and preparation of fossils can damage them and produce marks on their surface some of these recent marks highly mimic taphonomic marks produced before excavation both modern and fossil marks lead to misinterpretations and erroneous conclusions when similarities are not clearly detected in order to distinguish recent from ancient marks several diagnostic criteria resulting from experimental work are described in this paper

siliciclastic stromatolites and other microbially induced sedimentary structures in an early devonian barrier island environment muth formation nw himalayas microbially induced sedimentary structures including spectacular siliciclastic domal stromatolites up to 80 cm wide and 30 cm high have been found in coastal quartzites of the lower devonian muth formation pin valley nw himalayas the microbial struc tures occur in intervals of the formation associated with physical sed imentary structures that indicate at least temporally emergent con ditions these observations support the interpretation of a peritidal setting for the microbial structures within the wave dominated bar rier island depositional environment of the muth formation the sil iciclastic domal stromatolites probably formed in a shallow subtidal to intertidal environment with high hydraulic energy where periods of high sedimentation rates are interrupted by periods of low or zero sedimentation microbial gas pits and microbial gas domes were pro duced by ascending gas from degrading buried organic material in a lower supratidal zone influenced by tidal flushing multidirected ripple marks document a series of erosion events interfering with microbial stabilization in lower supratidal settings polygonal shrinkage cracks from supratidal environments indicate a semiarid paleoclimate the replacement textures of the microquartz matrix in the stromatolites indicates the former existence of syngenetic carbonate cements which may explain the preservation of the domal stromatolites in the high energy siliciclastic environments of the muth formation the muth stromatolites commonly containing more than 60 vol siliciclastic grains prove the existence of microbial activity in environments of higher sedimentary stress than generally thought and extend our knowledge of the capability of benthic microbial organisms to settle in siliciclastic shallow marine environments

a laboratory study of the dependence of elastic wave velocities on pore scale fluid distribution laboratory data have been collected during a continuous imbibition drainage experiment that show a clear dependence of elastic wave velocities on the details of the pore scale distribution of water and air in a sandstone compressional wave velocity vp was measured at a frequency of 1 mhz shear wave velocity vs was measured at a frequency of 600 khz during the experiment vp showed little variation with the level of water saturation sw during increasing sw through imbibition until sw 0 80 at which point vp increased dramatically when sw was decreased pronounced saturation induced hysteresis was observed in the region 03 0 4 as a simple model we consider the imbibition process as producing a partially saturated state in all pores i e all pores contain both air and water the drainage process in contrast favors the existence of either air filled or water filled pores as elastic wave velocities are very sensitive to the saturation state in the smaller crack like pores these variations in fluid distribution cause related variations in velocities

fluid distribution effect on sonic attenuation in partially saturated limestones extensional and torsional wave attenuation measurements are obtained at a sonic frequency around 1 khz on partially saturated limestones using large resonant bars 1 m long to study the influence of the fluid distribution we use two different saturation methods drying and depressurization when water saturation sw is higher than 70 the extensional wave attenuation is found to depend on whether the resonant bar is jacketed this can be interpreted as the biot gardner white effect the experimental results obtained on jacketed samples show that during a drying experiment extensional wave attenuation is influenced strongly by the fluid content when sw is between approximately 60 and 100 this sensitivity to fluid saturation vanishes when saturation is obtained through depressurization using a computer assisted tomographic ct scan we found that during depressurization the fluid distribution is homogeneous at the millimetric scale at all saturations in contrast during drying heterogeneous s

possible indicators of microbial mat deposits in shales and sandstones examples from the mid proterozoic belt supergroup montana u s a abstract it has been suspected for some time that microbial mats probably colonized sediment surfaces in many terrigenous clastic sedimentary environments during the proterozoic however domination of mat morphology by depositional processes post depositional compaction and poor potential for cellular preservation of mat building organisms make their positive identification a formidable challenge within terrigenous clastics of the mid proterozoic belt supergroup a variety of sedimentary structures and textural features have been observed that can be interpreted as the result of microbial colonization of sediment surfaces among these are a domal buildups resembling stromatolites in carbonates b cohesive behaviour of laminae during soft sediment deformation erosion and transport c wavy crinkly character of laminae d bed surfaces with pustular wrinkled appearance e rippled patches on otherwise smooth surfaces f laminae with mica enrichment and or randomly oriented micas g irregular curved wrinkled impressions on bedding planes h uparched laminae near mud cracks resembling growth ridges of polygonal stromatolites and i lamina specific distribution of certain early diagenetic minerals dolomite ferroan carbonates pyrite although in none of the described examples can it irrefutably be proven that they are microbial mat deposits the observed features are consistent with such an interpretation and should be considered indicators of possible microbial mat presence in other proterozoic sequences

characterisation and multifaceted anisotropy assessment of corvio sandstone for geological co2 storage studies we present a comprehensive characterisation of the physical mineralogical geomechanical geophysical and hydrodynamic properties of corvio sandstone this information together with a detailed assessment of anisotropy is needed to establish corvio sandstone as a useful laboratory rock testing standard for well constrained studies of thermo hydro mechanical chemical coupled phenomena associated with co2 storage practices and for geological reservoir studies in general more than 200 core plugs of corvio sandstone 38 1 and 50 mm diameters 2 1 length to diameter ratio were used in this characterisation study with a rock porosity of 21 7 1 2 dry density 2036 32 kg m 3 and unconfined compressive and tensile strengths of 41 3 28 and 2 3 0 14 mpa respectively geomechanical tests show that the rock behaves elastically between 10 and 18 mpa under unconfined conditions with associated young s modulus and poisson s ratio of 11 8 2 8 gpa and 0 34 0 01 gpa respectively permeability abruptly decreases with confining pressure up to 10 mpa and then stabilises at 1 md ultrasonic p and s wave velocities vary from about 2 8 3 8 km s 1 and 1 5 2 4 km s 1 respectively over confining and differential pressures between 0 1 and 35 mpa allowing derivation of associated dynamic elastic moduli anisotropy was investigated using oriented core plugs for electrical resistivity elastic wave velocity and attenuation permeability and tracer injection tests corvio sandstone shows weak transverse isotropy symmetry axis normal to bedding of 10 for velocity and 20 for attenuation

velocity saturation relation in partially saturated rocks modelling the effect of injection rate changes the relationship between p wave velocity and fluid saturation in a porous medium is of importance for reservoir rock characterization forced imbibition experiments in the laboratory reveal rather complicated velocity saturation relations including rollover like patterns induced by injection rate changes poroelasticity theory based patchy saturation models using a constant fluid patch size are not able to describe these velocity saturation relations therefore we incorporate a saturation dependent patch size function into two models for patchy saturation this recipe allows us to model observed velocity saturation relations obtained for different and variable injection rates the results reveal an increase in patch size with fluid saturation and show a reduction in the patch size for decreasing injection rate this indicates that there can exist a distinct relation between patch size and injection rate we assess the relative importance of capillarity on velocity saturation relations and find that capillarity stiffening impairs the impact of patch size changes capillarity stiffening appears to be a plausible explanation when a decrease in the injection rate is expected to boost the importance of capillarity

the origin and economic potential of sandstone hosted disseminated pb zn mineralization in pyritic shale horizons of the mid proterozoic newland formation montana usa pyritic shale horizons of the newland formation belt series mid proterozoic show striking similarities to proterozoic pyritic shales elsewhere that are host to major lead zinc deposits such as mt isa and mcarthur river however in contrast to these deposits the pyritic shales of the newland formation contain only minute quantities of lead and zinc elevated concentrations of lead and zinc are only found in pore spaces of intercalated sandstone beds petrographic and geochemical data indicate that pyritic shale deposition and elevated lead zinc concentrations in sandstone beds are unrelated that base metal mineralization is controlled by initial porosity and that iron and base metals were derived from different sources

an experimental study of acoustic responses on the injection of supercritical co2 into sandstones from the otway basin quantitative knowledge of the acoustic response of rock from an injection site on supercritical co2 scco2 saturation is crucial for understanding the feasibility of time lapse seismic monitoring of co2 plume migration a suite of shaley sandstones from the injection interval of the crc 2 well otway basin australia is tested to reveal the effects of supercritical co2 injection on acoustic responses co2 is first injected into dry samples flushed out with brine and then injected again into brine saturated samples such a suite of experiments allows us to obtain acoustic velocities of the samples for a wide range of co2 brine saturations from 0 to 100 on injection of scco2 into brine saturated samples the rocks exhibit a decrease of compressional velocities by about 7 with the increase of co2 saturation from 0 to a maximum of about 50 anisotropy of the shaley sandstones from the otway basin must be taken into account as the difference in the velocities normal and parallel to bedding is comparable with the perturbation due to co2 injection and the samples of different orientations exhibit transition from gassmann hill to gassmann wood bound at different scco2 saturations changes of the dry samples before and after the co2 injection if any are not traceable by acoustic methods

a sulfur isotope study of pyrite genesis the mid proterozoic newland formation belt supergroup montana abstract different generations of sedimentary pyrite from the mid proterozoic newland formation usa have been analysed for their sulfur isotopic compositions the results indicate bacterial sulfate reduction as the pyrite forming process the 34 s values for early diagenetic pyrite around 14 are in contrast to dominantly more positive values for many other middle proterozoic units a progressive reduction of sulfate availability during diagenesis can be recognized by an increase in 34 s content rayleigh distillation as well as through detailed petrographic observations contemporaneous seawater had a sulfur isotopic ratio between 14 and 18 as measured from sedimentary barite within the unit

simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell a feasibility study adaptations of existing triaxial cells for ultrasonic p and s wave measurements are well documented this paper proposes further modification of such a cell so that also resistivity measurements can be carried out simultaneously at reservoir conditions by employing the top cap and the pedestal of the cell as electrodes axial resistivity measurements are now feasible in order to minimize the polarization effect of this two electrode arrangement careful analyses have been carried out to optimize the choice of electrode coating and measurement frequency band radial resistivity measurements are also included in the system by introducing a strap electrode system in a reservoir under production changes in both saturations temperature if steam injection and stresses can take place therefore the modified triaxial system should be able to measure the integrated effects on the acoustic parameters and electric responses caused by variations in each of these parameters the feasibility of the system to obtain such reliable information is demonstrated employing a small selection of core samples in the future such combined measurements on reservoir core samples can be used to link both seismic and electromagnetic observations to the actual earth model and constrain both modelling and inversion

saturation scale effect on time lapse seismic signatures quantitative interpretation of time lapse seismic signatures aims at assisting reservoir engineering and management operations time lapse signatures are thought to be primarily induced by saturation and pressure changes core flooding and reservoir flow simulations indicate that a change of the driving forces during dynamic fluid injection gives rise to a varying saturation scale this saturation scale is yet another variable controlling the time lapse seismic signal in this work we investigate the saturation scale effect on time lapse seismic signatures by analysing simple modelling scenarios we consider three characteristic saturation scales ranging from few millimetres to metres which may form during gas injection in an unconsolidated water saturated reservoir using the random patchy saturation model we compare the corresponding acoustic signatures i e attenuation reflectivity and seismic gather associated with each saturation scale the results show that the millimetre saturation scale produces minimum attenuation and the same seismic signatures with those obtained from the elastic modelling the centimetre saturation scale produces maximum attenuation whereas the metre saturation scale causes highest velocity dispersion the analyses of the time shift and amplitude change indicate that ignoring a time dependent saturation scale can result in biased estimation discrimination of the saturation and the fluid pressure in particular the 4d signal can be strongly affected by the saturationscale change when the reservoir gas saturation is low and the effective pressure is high in the presence of an increasing decreasing saturation scale during injection interpreting an observed time shift and amplitude change using the gassmann model will lead to underestimation overestimation of the change in gas saturation and fluid pressure we show that including the effects of capillarity and residual saturation into the rock physics modelling can potentially reduce the interpretation uncertainty due to the saturation scale change

compressive marks from gravel substrate on vertebrate remains a preliminary experimental study abstract lakeshore sites such as cerro de la garita miocene of teruel spain and seneze pliocene of haute loire france yielded fossils with distinct puncture marks these marks were described as punctures surrounded by plastically deformed bone and were proposed to have been caused by compression or trampling on bones against coarse sediment grain when deposited in damp environments a series of experiments was performed to test this hypothesis cow red deer and fallow deer metapodials were compressed by applying a mechanical load on them against a gravel substrate under dry damp environments results confirm that these characteristic puncture marks are associated with compression efforts on bones in wet environments

microbial mat structures in profile the neoproterozoic sonia sandstone rajasthan india abstract ubiquitous microorganisms especially cyanobacteria preferably grow on the sediment surface thereby producing microbial mats in the absence of grazers and bioturbators microbial mat is a unique feature of the proterozoic most of the papers so far published described a wide variety of bed surface microbial mat structures with rare illustrations from sections perpendicular to bedding nonetheless bed surface exposures are relatively rare in rock records this limitation of bed surface exposures in rock records suggest that a study of microbial mats in bed across sections is needed the 60 m thick coastal marine interval of the sonia sandstone formation is bounded between two terrestrial intervals a transgressive lag at the base and an unconformity at the top and has been chosen for exploration of microbial mat structures in bed across sections a wide variety of microbial mat induced structures in bed across sections are preserved within the coastal interval of the sonia sandstone though many of these structures are similar in some aspects with bed surface structures some of those presented here are new the palaeogeographic range of these microbial structures extends from supralittoral to neritic diagenetic alterations of microbial mats produce pyrite and those zones are suitable for the preservation of microbial remains sem and edax analyses show fossil preservation of filamentous microbial remains that confirm the presence of microbial mats within the coastal interval of the sonia sandstone effects of proliferation of microbial mats in the siliciclastic depositional setting are numerous the mat cover on sediment surfaces hinders reworking and or erosion of the sediments thereby increases the net sedimentation rate successive deposition and preservation of thick microbial mat layer under reducing environments should have a great potential for hydrocarbon production and preservation and therefore these proterozoic formations could be a target for exploration

mineralogical footprints of microbial life earth s geosphere is intimately tied to its biosphere a major link between the two lies in the microbial realm microorganisms grow in and upon rocks and minerals often relying on their substratum for critical compounds needed in order to produce cellular energy the presence of a metabolizing cell on a mineral substrate has a significant effect on the mineral texture and on the geochemistry of the surrounding microenvironment in nature microorganisms exist in microbial commu nities as mats or biofilms growing upon a solid substrate as such they cover a vast surface area both within and below the surface of earth s land and sea the following review will provide a glimpse into the latest findings in the field of geomicrobiology and is intended to convey a sense of the profound influence microorganisms can have upon the geological environment they inhabit

proliferation of miss related microbial mats following the end permian mass extinction in terrestrial ecosystems evidence from the lower triassic of the yiyang area henan province north china microbially induced sedimentary structures misss are commonly present in siliciclastic shallow marine settings following the end permian mass extinction but have been rarely reported in the post extinction terrestrial ecosystems here we present six types of well preserved misss from the upper sunjiagou formation and lower liujiagou formation of induan early triassic age in the yiyang area henan province north china these misss include polygonal sand cracks worm like structures wrinkle structures sponge pore fabrics gas domes and leveled ripple marks microanalysis shows that these misss are characterized by thin clayey laminae and filamentous mica grains arranged parallel to bedding plane as well as oriented matrix supported quartz grains which are indicative of biogenic origin facies analysis suggests that the miss hosting sediments were deposited in a fluvial sedimentary system during the early triassic including lake delta riverbeds point bars and flood plain paleoenvironments abundant misss from yiyang indicate that microbes also proliferated in terrestrial ecosystems in the aftermath of the permian triassic p tr biocrisis like they behaved in marine ecosystems microbial blooms together with dramatic loss of metazoans may reflect environmental stress and degradation of terrestrial ecosystems or arid climate immediately after the severe permian triassic ecologic crisis

seismic wave attenuation and dispersion resulting from wave induced flow in porous rocks a review one major cause of elastic wave attenuation in heterogeneous porous media is wave induced flow of the pore fluid between heterogeneities of various scales it is believed that for frequencies below 1 khz the most important cause is the wave induced flow between mesoscopic inhomogeneities which are large compared with the typical individual pore size but small compared to the wavelength various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter scale mesoscopic heterogeneities laboratory and field measurements of seismic attenuation in fluid saturated rocks provide indications of the role of the wave induced flow signatures of wave induced flow include the frequency and saturation dependence of p wave attenuation and its associated velocity dispersion frequency dependent shear wave splitting and attenuation anisotropy during the last four decades numerous models for attenuation and velocity dispersion from wave induced flow have been developed with varying degrees of rigor and complexity these models can be categorized roughly into three groups according to their underlying theoretical framework the first group of models is based on biot s theory of poroelasticity the second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation another group of models is derived using the theory of viscoelasticity though all models predict attenuation and velocity dispersion typical for a relaxation process there exist differences that can be related to the type of disorder periodic random space dimension and to the way the local flow is incorporated the differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies in recent years some theoretical models of wave induced fluid flow have been validated numerically using finite difference finite element and reflectivity algorithms applied to biot s equations of poroelasticity application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data

effect of brine co2 fracture flow on velocity and electrical resistivity of naturally fractured tight sandstones abstractfracture networks inside geologic co2 storage reservoirs can serve as the primary fluid flow conduit particularly in low permeability formations although some experiments focus on the geophysical properties of brine and co2 saturated rocks during matrix flow geophysical monitoring of fracture flow when co2 displaces brine inside the fracture seems to be overlooked we have conducted laboratory geophysical monitoring of fluid flow in a naturally fractured tight sandstone during brine and liquid co2 injection for the experiment the low porosity low permeability naturally fractured core sample from the triassic de geerdalen formation was acquired from the longyearbyen co2 storage pilot at svalbard norway stress dependence hysteresis and the influence of fluid rock interactions on fracture permeability were investigated the results suggest that in addition to stress level and pore pressure mobility and fluid type can affect fracture permeability during loading and unloading cycles moreo

improved understanding of velocity saturation relationships using 4d computer tomography acoustic measurements a recently developed laboratory method allows for simultaneous imaging of fluid distribution and measurements of acoustic wave velocities during flooding experiments using a specially developed acoustic sample holder that combines high pressure capacity with good transparency for x rays it becomes possible to investigate relationships between velocity and fluid saturation at reservoir stress levels high resolution 3d images can be constructed from thin slices of cross sectional computer tomography scans ct scans covering the entire rock core volume and from imaging the distribution of fluid at different saturation levels the x ray imaging clearly adds a new dimension to rock physics measurements it can be used in the explanation of variations in measured velocities from core scale heterogeneities computer tomography gives a detailed visualization of density regimes in reservoir rocks within a core this allows an examination of the interior of core samples revealing inhomogeneities porosity and fluid distribution this mapping will not only lead to an explanation of acoustic velocity measurements it may also contribute to an increased understanding of the fluid flow process and gas liquid mixing mechanisms in rock immiscible and miscible flow in core plugs can be mapped simultaneously with acoustic measurements the effects of core heterogeneity and experimentally introduced effects can be separated to clarify the validity of measured velocity relationships

velocity and attenuation in partially saturated rocks poroelastic numerical experiments we use a poroelastic modelling algorithm to compute numerical experiments on wave propagation in a rock sample with partial saturation using realistic fluid distribution patterns from tomography scans frequencies are in the range 10 to 500 khz the rock is a homogeneous isotropic sandstone partially filled with gas and water which are defined by their characteristic values of viscosity compressibility and density we assume no mixing and that the two different pore fills occupy different macroscopic regions the von karman self similar correlation function is used employing different fractal parameters to model uniform and patchy fluid distributions respectively where effective saturation is varied in steps from full gas to full water saturation without resorting to additional matrix fluid interaction mechanisms we are able to reproduce the main features of the variation in wave velocity and attenuation with effective saturation and frequency as those of published laboratory experiments furthermore the behaviour of the attenuation peaks versus water saturation and frequency is similar to that of white s model the conversion of primary p wave energy into dissipating slow waves at the heterogeneities is shown to be the main mechanism for attenuating the primary wavefield fluid gas patches are shown to affect attenuation more than equivalent patches in the permeability or solid grain properties

geomechanical and geochemical effects on sandstones caused by the reaction with supercritical co2 an experimental approach to in situ conditions in deep geological reservoirs the geochemical and geomechanical behaviour of reservoir rocks from deep saline aquifers during the injection and geological storage of co2 is studied in laboratory experiments a combination of geochemical and geomechanical studies was carried out on various sandstones from the north german basin after the mineralogical geochemical and petrophysical characterization a set of sandstone samples was exposed to supercritical sc co2 and brine for 2 4 weeks in an autoclave system one sample was mineralogically and geochemically characterised and then loaded in a triaxial cell under in situ pressure and temperature conditions to study the changes of the geomechanical rock properties after treatment in the autoclaves geochemical alterations mainly in the carbonate but also in the sheet silicate cements as well as in single minerals of the sandstones were observed affecting the rocks granular structure in addition to partial solution effects during the geochemical experiments small grains of secondary carbonate and other mineral precipitations were observed within the pore space of the treated sandstones results of additional geomechanical experiments with untreated samples show that the rock strength is influenced by the saturation degree the confining pressure the pore fluid pressure and temperature the exposure to pure scco2 in the autoclave system induces reduced strength parameters modified elastic deformation behaviour and changes of the effective porosity in comparison to untreated sandstone samples experimental results show that the volume of pore fluid fluxing into the pore space of the sandstones clearly depends on the saturation level of the sample

stromatolites in the late ordovician eureka quartzite implications for microbial growth and preservation in siliciclastic settings well preserved siliciclastic domal stromatolites up to 2 m wide and 1ae 5m high are found in a 10 to 15 m thick interval within the late ordovician eureka quartzite of southern nevada and eastern california usa these stromatolites appear as either isolated features or patchy clusters that contain more than 70 by volume quartz grains their association with planar trough and herringbone cross bedding suggests that they were formed in an upper shoreface environment with high hydraulic energy in this environment sand bars or dunes may have provided localized shelter for initial microbial mat colonization biostabilization and early lithification of microbial mats effectively prevented erosion during tidal flushing and storm surges and the prevalence of translucent quartz sand grains permitted light penetration into the sediment leading to thick microbial mat accretion and the formation of domal stromatolites decimetre scale to metre scale stromatolite domes may have served as localized shelter and nucleation sites for further microbial mat colonization forming patchy stromatolite clusters enrichment of iron minerals including pyrite and hematite within dark internal laminae of the stromatolites indicates anaerobic mineralization of microbial mats the occurrence of stromatolites in the eureka quartzite provides an example of microbial growth in highly stressed siliciclastic sedimentary environments in which microbial communities may have been able to create microenvironments promoting early cementation lithification essential for the growth and preservation of siliciclastic stromatolites

integrated geophysical and hydromechanical assessment for co2 storage shallow low permeable reservoir sandstones geological reservoirs can be structurally complex and can respond to co2 injection both geochemically and geomechanically hence predicting reservoir formation behaviour in response to co2 injection and assessing the resulting hazards are important prerequisites for safe geological co2 storage this requires a detailed study of thermal hydro mechanical chemical coupled phenomena that can be triggered in the reservoir formation most readily achieved through laboratory simulations of co2 injection into typical reservoir formations here we present the first results from a new experimental apparatus of a steady state drainage flooding test conducted through a synthetic sandstone sample simulating real co2 storage reservoir conditions in a shallow 1 km low permeability 1md 26 porosity sandstone formation the injected pore fluid comprised brine with co2 saturation increasing in steps of 20 brine co2 partial flow rates up to 100 co2 flow at each pore fluid stage an unload loading cycle of effective pressure was imposed to study the response of the rock under different geomechanical scenarios the monitoring included axial strains and relative permeability in a continuous mode hydromechanical assessment and related geophysical signatures ultrasonic p wave and s wave velocities vp and vs and attenuations qp 1 and qs 1 respectively and electrical resistivity on average the results showed vp and vs dropped 7 and 4 respectively during the test whereas qp 1 increased 55 and qs 1 decreased by 25 from the electrical resistivity data we estimated a maximum co2 saturation of 0 5 whereas relative permeability curves were adjusted for both fluids comparing the experimental results to theoretical predictions we found that gassmann s equations explain vp at high and very low co2 saturations whereas bulk modulus yields results consistent with white and dutta ode model predictions this is interpreted as a heterogeneous distribution of the two pore fluid phases corroborated by electrical resistivity tomography images the integration of laboratory geophysical and hydromechanical observations on representative shallow low permeable sandstone reservoir allowed us to distinguish between pure geomechanical responses and those associated with the pore fluid distribution this is a key aspect in understanding co2 injection effects in deep geological reservoirs associated with carbon capture and storage practices

proliferation of miss related microbial mats following the end permian mass extinction in the northern paleo tethys evidence from southern qilianshan region western china as a consequence of the end permian mass extinction microbes proliferated in the post extinction shallow marine ecosystems in which they grew as various microbially induced sedimentary structures misss in siliciclastic settings this paper reports for the first time the discovery of abundant misss from the lowest triassic sandstones of shallow water margin origin in the zhihema sections of the southern qilianshan region west china the sandstones are characterized by well developed cross beddings and ripple marks and a claraia dominated bivalve assemblage of middle late griesbachian age these sedimentary structures together with the bivalves suggest a high energy peritidal zone of a shoreface setting in a clastic shallow sea environment seven types of misss are recognized and described here pictograph like sand cracks crack fills polygonal sand crack fills erosional remnants multidirectional linear grooves sinuous crack fills fusiform sand cracks crack fills and leveled ripple marks most of the newly found misss are morphologically comparable with their ancient and modern counterparts detailed optical microscope and scanning electron microscope sem analyses reveal that thin clayey laminae and filamentous mica grains are aligned parallel to bedding plane and that the matrix supported quartz grains overall are oriented both of which are interpreted to indicate biogenic origin the biogenic origin of these misss is reinforced by the presence of copious putative nanoglobules and filamentous biofilm like organic objects in the interspaces of clay minerals in laminated layers these nanometer scale objects are interpreted as bacterial bodies or remains that have been replaced with inorganic minerals upon fossilization the presence of misss on the northern margins of paleo tethys indicates that the post extinction microbial mats had expanded their distributions from low latitude to moderate high latitude regions moreover unlike some previously reported microbial mats that contain very rare body and trace fossils the southern qilianshan misss were found in association with abundant vertical burrows and bivalves suggesting that the miss forming microbial mats may have served as oases for trace making organisms and opportunistic bivalves to flourish in shallow marine habitats immediately after the end permian mass extinction