comment on geologic evidence for chaotic behavior of the planets and its constraints on the third order eustatic sequences at the end of the late paleozoic ice age by fang q wu h hinnov l a jing x wang x jiang q palaeogeography palaeoclimatology palaeoecology volume 440 15 december 2015 848 859 2015 abstract fang et al 2015 geologic evidence for chaotic behavior of the planets and its constraints on the third order eustatic sequences at the end of the late paleozoic ice age claim to have identified a comprehensive suite of orbital periodicities milankovitch cycles in a permian succession in southern china through the use of spectral analysis we refute their claim on the grounds that their spectral analytic method specifically the estimation of significance thresholds greatly overestimates the significance of the periodicities we show that the same method implemented in the same software package yields significant cycle periods in purely random synthesised data in an earlier paper we warned that the cyclostratigraphic community is generating large numbers of similarly false claims of orbital periodicities in stratigraphic data by making the same mistakes as fang et al we urge greater awareness of this problem among editors reviewers readers and users of the cyclostratigraphic literature further all cyclostratigraphic conclusions dependent on the results of this kind of spectral analysis including but not restricted to astrochronological timescale calibrations should be regarded with suspicion unless confirmed by more rigorous methods

on the role of phyllosilicates on fault lubrication insight from micro and nanostructural investigations on talc friction experiments 1 exposures of mature faults at the earth s surface show that in the shallow crust some of co seismic slip occurs within a narrow phyllosilicate rich gouge material mechanical behavior of phyllosilicates sheared at seismic slip velocities remains a complex issue as suggested by the experimental and theoretical studies reported so far talc represents a simple case for common phyllosilicates in natural faults and therefore we chose talc as an analogue to better understand the mechanical behavior of clay rich mature crustal faults we present a series of high velocity friction experiments conducted on talc at 1 31 m s 1 and normal stresses of 0 3 1 8 mpa for wet and dry conditions at 1 mpa normal stress both wet and dry experiments show a slip weakening behavior however with a higher decreasing rate in wet conditions dynamic shear stress evolves from a peak value of 0 24 0 52 mpa down to a residual state value of 0 08 0 18 mpa in wet conditions and from a peak value of 0 46 1 17 mpa down to a residual state value of 0 12 0 62 mpa in dry conditions based on a detailed microstructural analysis down to the nanoscale we propose thermal pressurization as a possible slip weakening mechanism for wet conditions on the contrary in dry conditions the long lasting weakening is interpreted to be due to a combination of i progressive disappearance of geometrical incompatibilities ii solid lubrication of talc lamellae and iii powder lubrication by nanometric aggregates we conclude that initial gouge humid conditions and inherited fabric from past sliding may have large influence on the slip weakening for subsequent slip

experimental mechanical compaction of reconstituted shale and mudstone aggregates investigation of petrophysical and acoustic properties of sw barents sea cap rock sequences abstract this study investigates petrophysical and acoustic properties of experimentally compacted reconstituted samples of seal sequences from the southwestern barents sea the aggregates were collected from drill cuttings of mudstone and shale formations of two exploration wells 7220 10 1 salina discovery and 7122 7 3 goliat field the washed and freeze dried samples were characterized for grain size distributions geochemical analyses and mineralogical compositions a total of 25 compaction tests 12 dry and 13 brine saturated were performed with a maximum effective vertical stress of 50 mpa the laboratory measurements demonstrated that petrophysical and acoustic properties of argillaceous sediments can change within a sedimentary basin and even within a given formation the results show that the collected aggregates from goliat field are compacted more compared to salina discovery the maximum and minimum compaction are measured in samples collected from snadd and fuglen formations respectively the final porosity of brine saturated specimens varies between 5 and 22 the ultrasonic velocity measurements depict that samples with the same porosity values can have a broad range of velocity values the resulting compaction trends in this study were compared to published compaction curves for synthetic mixtures of quartz and clay all compaction trends show higher porosity reduction than the silt fraction with 100 quartz comparison of experimental compaction result of each mudstone and shale aggregate with its corresponding acquired well log data helps to delineate the burial history and exhumation in the study area a net exhumation of 950 m and 800 m is estimated at salina and goliat wells respectively the outcomes of this study can provide insights for hydrocarbon prospect discovery in a pre mature sedimentary basin in terms of exploration and production and also for geological co2 storage sites the experimental results may provide information for well log and seismic interpretation basin modeling and seal integrity of investigated horizons

porosity reduction by pressure solution a theoretical model for quartz arenites pressure solution and the subsequent precipitation of the dissolved material may play an important role in the lithification of sandstones and limestones this paper presents a one dimensional model for a well sorted quartz arenite sequence undergoing diagenesis the sedimentary sequence is treated as a saturated porous medium in which pressure solution occurs at individual grain contacts quartz dissolved at grain contacts precipitates on free surfaces of adjacent grains this solution and precipitation process reduces porosity and forces the migration of pore fluid permeability decreases with porosity hindering fluid migration and excess fluid pressures are generated distributions of porosity pore pressure and fluid flow rates are given for several sedimentation rates and thermal gradients complete reduction of the primary intergranular porosity was accomplished in all cases examined by a depth of 3 5 km

compaction behavior of argillaceous sediments as function of diagenesis the paper presents the results of laboratory compaction tests on samples of kimmeridge clay taken from two different locations in the uk the main objective of the laboratory tests is to determine how diagenesis affects the hydro mechanical properties and compaction behavior of argillaceous sediments the two kimmeridge clays used in the tests are essentially from the same parent material but have undergone different degrees of mechanical and chemical diagenesis the laboratory tests are designed to determine the effects of mechanical loading and chemical processes on changes in porosity permeability compressibility strength and effective horizontal stress in argillaceous materials another objective of the study is to investigate the adequacy of soil mechanical constitutive models in predicting the response of argillaceous materials to conditions corresponding to burial depths in sedimentary basins the tests on kimmeridge clay are carried out to as high as 150 mpa effective vertical stress corresponding to about 9 km in burial the results indicate that mechanical compaction and burial depth cannot explain the differences in the hydro mechanical behavior of the tested materials the differences in hydro mechanical response are attributed to chemical diagenesis by precipitation of minerals in the pores of the sediment other observed effects of chemical diagenesis on hydro mechanical behavior of lithified sediments are 1 increase in apparent pre consolidation stress 2 decrease in compressibility 3 decrease in permeability and 4 decrease in effective horizontal stress implications of the results to fluid flow and overpressure development in sedimentary basins are discussed

the thermal influence on the consolidation state of underthrust sediments from the nankai margin and its implications for excess pore pressure abstract the nankai trough convergent margin has been the focus of many multi methodological surveys including half a dozen scientific deep sea drilling expeditions the boreholes focused on the smectite dominated area off cape ashizuri and the thermally altered illite dominated region off cape muroto on the basis of these surveys a number of studies addressed to the stress state of the underthrust sediments and its implications for the plate boundary thrust although the basement temperature has been found to be up to 110 c none of these studies drew close attention to temperature effects on the consolidation state of the sediments to overcome this shortcoming we selected end member sediment lithologies from the incoming oceanic plate in the shikoku basin and subjected them to elevated stresses and temperatures we here present results from a series of heated 20 c 100 c 150 c uniaxial consolidation experiments up to effective normal stresses of ca 70 mpa the main finding is a positive correlation between temperature and pore space reduction based on in situ temperature information from earlier scientific drilling our study suggests that temperature has an influence on the consolidation state of underthrust sediments along the nankai margin together with secondary consolidation thermal consolidation serves to explain steep log linear consolidation curves of the incoming lower shikoku basin sediments the onset of diagenesis in this realm led to the transition of smectite to illite and to a different consolidation behaviour estimated in situ pore pressures based on in situ temperature data result in up to 1 mpa smaller overpressures than those previously estimated from drilling data alone those values which imply underconsolidation at drill sites near the frontal nankai accretionary complex are further believed to facilitate frictional sliding along the subduction thrust

mechanical behaviour of fine grained sediments experimental compaction and three dimensional constitutive model abstract the usual undimensional description of deformations of sediments based on a phenomenological relationship between porosity and the vertical effective stress does not give information about the horizontal stress and moreover is irrelevant for sedimentary structures in which deformation process is not only vertical modelling three dimensional deformation processes in sedimentary basins requires a three dimensional mechanical constitutive model for sediments a special dometric cell was conceived in g 3s this cell allows the measurement of the lateral stress during dometric compaction and so enables us to elaborate a three dimensional model of mechanical behaviour four varieties of fine grained sediments were studied by this cell in a large scale of strain and stresses the modified cam clay model was used for fitting the experimental data and it was shown that this model can reproduce the mechanical compaction of sediments up to 50 mpa of vertical effective stress about 3 km burial depth if its parameters are deduced from dometric zero lateral strain data

the measurement of soil stiffness in the triaxial apparatus this paper describes a simple technique for accurately measuring the mean local axial strains of triaxial samples over a central gauge length the technique makes use of an axial displacement gauge which is a development of one devised by burland symes 1982 which makes use of electrolytic levels the device can resolve to less than 1 m over a range of 15 mm is simple to mount on the specimen and is not damaged when the sample is taken to failure the results of undrained triaxial tests are presented for a wide spectrum of soil types ranging from sands through intact reconstituted and remoulded low plasticity till undisturbed london clay to intact unweathered chalk the test results show that conventional external measurements of displacement contain errors which are frequently so large that their use in the determination of soil stiffness at working levels of stress is invalid the errors mainly result from tilting of the sample bedding at the end platens and the effects of compliance in the app

compaction of quartz kaolinite mixtures the influence of the pore fluid composition on the development of their microstructure and elastic anisotropy abstract shales play important roles in sedimentary basins acting as both seals and reservoir rocks and knowledge of their anisotropic velocity trends is of practical importance for correct seismic image processing and inversion and for seismic to well tie whereas velocity depth trends are extensively studied for conventional reservoirs and critical factors that control their compaction are well understood little work has been done on shales compaction trends of shaly formations are controlled by a number of parameters such as clay mineralogy silt fraction and depositional environment this large number of parameters which are difficult if not impossible to control in naturally deposited shales make the study of shale compaction a statistically complex multivariate and non unique problem in such a situation laboratory experiments that allow precise planning of mixture mineralogy and chemical compositions of pore fluids as well as an accurate control of microstructural changes seems to be an attractive alternative in this work we have conducted two sets of compaction experiments on quartz kaolinite mixtures with 100 75 and 60 of kaolinite powders dry weight in the first set the use of a kcl brine solution to saturate the mixtures has led to the aggregation of the existing clay particles with each other and with silt particles in the other set the mixtures have been treated with a dispersant to separate existing clay aggregates into individual platelets the mixtures have been further compacted in an oedometric cell at uniaxial stresses up to 30 mpa compressional in vertical and horizontal directions and shear in vertical direction ultrasonic wave velocities have been measured during these compaction experiments and the p wave anisotropy has been estimated the effect of the chemical composition of the pore fluid on shale microstructure has been studied using the micro ct and sem image analysis neutron diffraction experiments have been conducted to understand the orientation of clay platelets at the final stage of the compaction our research shows that the chemical composition of pore fluid significantly affects the microstructure of the clay component and via this the elastic properties of the artificial shales the samples with the dispersed clay microstructure dcm have shown larger elastic anisotropies at the same porosity and significantly larger anisotropies at the same stress the dispersed clay platelets have orientated preferably parallel to bedding plane while the clay platelets in the samples with the aggregated clay microstructure acm show a wider angle distribution in the absence of quartz particles 100 kaolinite samples in the case of 40 of quartz fraction though the clay particles are more aligned in the acm sample than in the dcm one

some laboratory measurements of permeability of bothkennar clay in relation to soil fabric laboratory measurements of the vertical and horizontal permeability of samples of bothkennar clay have been made in controlled flow tests and values have been estimated from interpretation of consolidation tests the permeability anisotropy that has been observed can be linked with different clay facies that have been identified in parallel engineering geological studies la mesure de la permeabilite verticale et horizontale d echantillons d argile de bothkennar a ete faite dans des essais d ecoulement d eau controles et des valeurs ont ete estimees a partir de l interpretation d essais de consolidation l aniso tropie de la permeabilite qui a ete observee peut etre reliee avec differents facies argileux qui ont ete identifies dans des etudes de geologie appliquee menees en parallele

importance of mechanochemical effects on fault slip behavior during earthquakes 1 recent analyses of natural faults and laboratory rock friction experiments have revealed that physical transformations and chemical reactions of minerals and fluids occur in faults during earthquakes however exactly how these physicochemical processes affect fault weakening and earthquake energetics is not well understood we present quantitative experimental evidence of mechanochemical changes in a clay mineral illite during frictional slip and evaluate the effect of those changes on slip behavior friction distorts the crystal structure of illite and dramatically decreases the activation energy ea of the dehydroxylation reaction numerical modeling shows that the lower ea allows the dehydroxylation to occur at relatively low temperatures 200 300 c which in turn drastically reduces fault strength by pressurization of released water from the mineral thus dynamic thermo chemo mechanical processes can strongly affect earthquake instability especially along clay rich faults such as those in the shallow part of subduction zone plate boundaries

factors controlling the thermo mechanical deformation of oil shales implications for compaction of mudstones and exploitation abstract six permian to miocene organic matter rich mudstones were subjected to unconfined compression tests under three thermo mechanical regimes the aims of this study were to assess the role of factors that control deformation and highlight implications for mudstone compaction and oil shale exploitation axial strain ranged from 1 9 to 23 at 25 c 5 3 70 mpa 12 79 at 25 310 c 31 42 mpa and 1 38 40 at 25 350 c 0 8 mpa the axial strain data showed that the principal factor controlling mudstone compaction is temperature with a secondary role for effective stress during high temperature tests dehydration of smectite in the 94 150 c interval resulted in a distinct axial strain effect decomposition of organic matter and other minerals caused visible strain only above 280 c tests up to 350 c resulted in mass loss of 4 54 43 8 wt with 1 1 8 wt due to organic matter a strong positive correlation was found between the petroleum generation indices 4 6 55 8 and expulsion efficiencies 38 6 96 2 while compaction 0 68 51 4 correlated with axial strain 1 38 40 solid volume loss 2 55 12 15 due to petroleum generation from kerogen resulted in an increase in porosity 1 56 6 36 low rate heating and low retorting temperature are necessary to optimise yield from oil shale exploitation

microfabric and rock properties of experimentally compressed silt clay mixtures abstract oedometric mechanical compaction tests were performed on brine saturated synthetic samples consisting of silt clay mixtures to study changes in microfabric and rock properties as a function of effective stress the silt consisted of crushed quartz 100 with grain size range between 4 and 40 m whereas the clay consisted of 81 kaolinite 14 mica illite and 5 microcline of grain size between 0 4 and 30 m five sample pairs ranging in composition from pure silt to pure clay were compacted to 5 and 50 mpa effective stress respectively sem studies were carried out to investigate microfabric changes in the mechanically compacted silt clay mixtures the degree of alignment of the different minerals present quartz mica illite and kaolinite were computed by using an image analysis software experimental compaction have measured the changes in the rock properties such as porosity and velocity as a function of effective stress for different mixtures of clay and silt clay rich samples showed a higher degree of mineral orientation and lower porosity compared to silt dominated samples as a function of effective stress pure clay sample had 11 porosity at 50 mpa effective stress whereas the pure silt sample retained about 29 porosity at the same effective stress the experiments showed that low porosity down to 11 is possible by mechanical compaction only a systematic increase in strain was observed in the silt clay mixtures with increasing clay content but the porosity values found for the 50 50 silt clay mixture were lower than that of 25 75 silt clay mixture no preferential mineral orientation is expected before compaction owing to the high initial porosity suggesting that the final fabric is a direct result of the effective stress both p and s wave velocities increased in all silt clay mixtures with increasing effective stress the maximum p and s wave velocities were observed in the 25 75 silt clay mixture whereas the minimum vp and vs were recorded in the pure silt mixture at 50 mpa effective stress p wave velocities as high as 3 km s resulted from experimental mechanical compaction alone the results show that fine grained sediment porosity and velocity are dependent on microfabric which in turn is a function of grain size distribution particle shape sediment composition and stress at 5 mpa effective stress quartz orientation increased as a function of the amount of clay indicating that clay facilitate rotation of angular quartz grains adding clay from 25 to 75 in the silt clay mixtures at 50 mpa effective stress decreased the quartz alignment the clay mineral orientation increased by increasing both the amount of clay and the effective stress the mica illite fabric alignment being systematically higher than that of kaolinite even small amount of silt 25 added to pure clay reduced the degree of clay alignment significantly this study demonstrates that experimental compaction of well characterized synthetic mudstones can be a useful tool to understand microfabric and rock properties of shallow natural mudstones where mechanical compaction is the dominant process

1 d modelling rock compaction in sedimentary basins using a visco elastic rheology abstract recent experimental studies on unlithified sediments suggest that the compaction is in part viscous at the basin scale and on a geological time scale processes such as pressure solution can be approached by creep deformation subjected to a viscous rheology in the present work we have studied porosity reduction and fluid pressure development resulting from the visco elastic compaction of a sedimentary basin during its formation model equations include continuity equations darcy s law and a visco elastic rheology law which relates the strain rate to the effective stress and to the rate of change of this effective stress under the assumption that permeability is a power law function of porosity the equations become essentially non linear model results illustrate how the decrease of porosity starts at the base of the basin and spreads upward with increasing time in a wide range of input parameter values calculations indicate a zone of almost linear increasing of pore pressure just below the basin surface a transition zone of rapidly increasing fluid pressure with a large pressure gradient and a zone of lithostatic fluid pressure below this is consistent with the general features of zoning of fluid pressure distribution in overpressured areas but zones with high pressure also correspond to low porosity at depth the relative thickness of the zones depends on time subsidence velocity and the physical parameters of sediments which can be combined in order to define a characteristic compaction length and a characteristic compaction time in the upper zone the decrease of porosity results in a boundary layer within this layer the porosity decreases from its initial value down to its minimum value the deeper zone appears when the time of formation of the given depth basin exceeds the characteristic compaction time and the thickness of the basin is in order of compaction length zones of fluid overpressure may also develop due to the spatial variations of the physical properties of the sediments

evolution of microstructures and of macroscopic properties of some clays during experimental compaction abstract in order to understand the evolution of clay sediments during their burial to three or four kilometers depth remoulded and non remoulded clay samples were oedometrically consolidated under loads ranging from 0 1 50 mpa and their microstructural mechanical and transport properties were studied for this study four clays were selected on mineralogical grounds a kaolinite st austell clay two illitic clays la bouzule clay and salins 14 clay and an illite smectite mixed clay marais poitevin clay among those materials two are almost pure clays st austell clay and salins 14 clay and were compacted in a remoulded state the other two have a clay fraction about 60 and were studied in non remoulded state for marais poitevin clay and both remoulded and non remoulded for la bouzule clay the oedometric tests have been performed in classical oedometers and in a new oedometric cell specially designed to measure lateral stresses and to perform hydraulic conductivity measurements under compaction load the two pure clays show an evolution of their void ratio differing from what is expected considering their liquid limits the behaviour seems to be governed by the size of the clay particles around 1 m for st austell clay and around 0 1 m for salins 14 clay marais poitevin clay very slightly compacted in its natural state and remoulded la bouzule clay have consolidation coefficients cc and void ratios consistent with their liquid limits a relationship reported in soil mechanics literature skempton 1944 burland 1990 nagaraj et al 1994 the natural la bouzule clay shows very low void ratios and cc due to overconsolidation the microstructure observed by tem showed that clay particles are platy and made of aggregates of individual crystals except for salins 14 clay where individual crystals do not aggregate the evolution of the microstructure with applied stress shows no change in the particles structure but a progressive reorientation of the particles perpendicular to the load axis these microstructural observations explain the transport properties measured and their evolution the thermal conductivity of kaolinite measured in the axial and radial direction reflects the evolution of anisotropy with compaction observed on particles orientation the different hydraulic conductivities observed on the various samples are compared to those obtained with the kozeny carman formula using two types of specific surface determination this comparison emphasizes the importance of inter and intraparticule pore size and of their intimate organisation

compressibility of deep clay in east china subjected to a wide range of consolidation stresses the oedometer tests of remoulded deep clay in east china subjected to consolidation stresses ranging from 0 2 to 15 0 mpa were carried out both the measured compression curves and the curves of logarithmic permeability versus void ratio consist of two linear segments among which the bilinear shape of the compression curves is less noticeable the consolidation stress and void ratio at the intersection of two lines are around 2 mpa and 0 565 0 015 respectively and the corresponding saturated water content is very close to the reported saturated adsorbed water content lastly but most importantly the calculated microscopic pore size corresponding to the intersection point agrees well with the transitional range of the distance between two clay surfaces within which water molecules transform from bulk liquid like water into confined water this is confirmed by experimental results available in the literature

clay compaction modelling by homogenization theory the modelling of hydromechanical behavior of clayey sediments by homogenization theory is described the rheological model of clays buried in depth requires a three dimensional approach and laboratory experiments to quantify the model parameters an iterative process which can be coupled to any homogenization method is used to model the porous media behavior hydromechanical compaction results from oedometric experiments are simulated with the proposed model

elastoplastic deformation of porous media applied to the modelling of compaction at basin scale abstract for simulation and modelling of coupled phenomena occurring during basin evolution the mechanical aspects of rock deformation are generally restricted to vertical compaction characterized by a simple relation between the effective vertical stress and the rock porosity elasto plasticity leads to a more general formulation which in principle allows for the calculation of horizontal deformation and stress field various aspects of this application of continuum mechanics to the compaction of sedimentary rocks at basin scale are presented firstly the problems of mechanical deformation and of fluid flow or pressure evolution are shown to be intimately coupled through the effective stress concept the elasto plastic cam clay rheology is recalled as a satisfactory approach of the stress strain relationship for fine grained sediments this gives the complete bases for numerical modelling of the hydro mechanical problems related to sedimentary basin evolution secondly two numerical codes which are of standard use in civil engineering problems are tentatively applied to basin modelling the first code cesar is a finite element one which fully takes into account the hydro mechanical couplings the slow sedimentation process whereby the geological structure is progressively built can be accounted for by incremental deposition of layers in practice the computation is so time consuming that only restricted simulation on existing sedimentary structure can be seriously considered a second computer code flac based on finite difference method is then applied some special development makes it possible to account for the geometrical evolution build up of a basin and some cases studies are presented to show the importance of lateral deformation during the development of a margin type basin however these possibilities were obtained at the expense of a fixed fluid pressure field and we did not succeed in coupling the hydraulical and mechanical computations thirdly a simple incremental mechanical model is proposed for completely solving the coupled hydro mechanical problem in the case of progressive sedimentation a numerical solution is obtained in the 1 d case and gives results which are consistent with some published ones since it is 1 d this solution offers only a few advantageous features at present however generalization to several dimensions can be imagined

geological perspectives on consolidation of clay rich marine sediments 1 experimental consolidation of uncemented clay rich marine sediments provides information concerning their stress history a main finding is that some of the well known behavior of soft sediment deformation in geotechnical applications cannot validly be extrapolated to sediments that have been subjected to higher stresses and longer times of geologic conditions this study confirms that the yield stress of the uncemented sediment accurately reflects its previous maximum consolidation state furthermore we have identified a new phase of post yield strain that is associated with higher values of the modified compression index the slope of the porosity versus the logarithm of effective vertical stress than that of elastic deformation but with much lower values than that for primary consolidation this post yield behavior is a linear non elastic deformation and is termed tertiary consolidation yield stress appears independent of creep time or strain rate whereas the tertiary primary consolidation transition is sensitive to these parameters during post yield creep secondary consolidation the slope of the porosity versus the logarithm of time curve or the secondary consolidation index is generally assumed constant however this is not valid for claystones at effective vertical stresses above about 1 mpa where the secondary consolidation index increases with stress at a given effective vertical stress the secondary consolidation index also increases with creep times greater than about 105 s 28 h

influence of particle shape on the frictional strength of sediments a numerical case study abstract numerous direct and ring shear tests supply that composition and texture of sediments are crucial for shear and frictional strength we simulate particle interactions on a micro scale level during shearing with a numerical shear box using the discrete element method dem based on the granular model approach detailed information about slip localisation and rates forces at particle contacts as well as particle rotation can be quantified as function of particle shape stress conditions and shear rate our numerical experiments show that the deformation behaviour of clay is largely controlled by their particle shape two key factors sphericity and roughness could be identified as relevant for frictional strength shear zone development and particle rotation with sphericity dominating over roughness decreasing sphericity leads to complex initial microfabrics whose breakdown with increasing strain is caused by particle rotation preferred particle orientation favours low friction decreasing volume strain and the evolution of particle domains of similar orientation decreasing roughness results in particle interlocking of different degrees which obstructs slip and rotation to preferred orientations so that friction is high and volume strain positive spatial and temporal shear zone development depends on the roughness of particles increasing roughness precludes shear zone development and particle domain evolution shear zone localisation depends on particle sphericity increasing sphericity leads to more localised but vertically dilated deformation

some measurements of the permeability of kaolin this paper reports an experimental investigation of the vertical and horizontal permeabilities of speswhite kaolin clay the permeabilities were measured using falling head permeability tests a mo

experimental mechanical compaction of clay mineral aggregates changes in physical properties of mudstones during burial dry and brine saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory experiments were conducted by increasing vertical effective stress up to 50 mpa to study the changes in physical properties of mudstones during burial the results suggest that the physical properties porosity density acoustic velocity etc of mudstones vary greatly with increasing effective stress clay mineralogy and fluid content kaolinite aggregates are much more compressible than those composed of smectite brine saturated clay mixtures are much more compressible than dry clay mixtures brine may soften and lubricate the clay matrix compared to dry clays resulting in higher compressibility in the brine saturated state the lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays the extremely fine grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse grained kaolinite at 20 mpa effective stress corresponding to about 2 km burial depth with hydrostatic pore pressure brine saturated pure kaolinite compacted to 20 porosity while pure smectite retained 41 porosity brinesaturated clay mixtures show higher vp and lower vs than dry clay mixtures a pronounced difference in vs was observed among the brinesaturated clay mixtures the lowest vs as a function of vertical effective stress was found for pure smectite for a given porosity value smectitic clays have higher velocities and elastic moduli than the kaolinitic clays the vp vs ratio is significantly higher in smectite than in kaolinite aggregates treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties which are strongly affected by the clay mineralogy grain size the amount of other minerals present and fluid content our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth o 2k m 801c above depths where significant chemical compaction takes place r 2007 elsevier ltd all rights reserved

facies controls on the distribution of diagenesis and compaction in fluvial deltaic deposits abstract the upper triassic lower jurassic are formation comprising the deeper reservoir in the heidrun field offshore mid norway consists of fluvial channel sandstones fch floodplain fines ff and sandy and muddy bay fill sediments sbf mbf deposited in an overall transgressive fluvial to lower delta plain regime the formation has been investigated to examine possible sedimentary facies controls on the distribution of cementation and compaction based on petrography and sem micro probe analyses of core samples related to facies associations and key stratigraphic surfaces the most significant authigenic minerals are kaolinite calcite and siderite kaolinite and secondary porosity from dissolution of feldspar and biotite are in particular abundant in the fluvial sandstones the carbonate minerals show complex compositional and micro structural variation of pure siderite sid i mg siderite sid ii fe dolomite ankerite and calcite displaying decreasing fe from early to late diagenetic carbonate cements an early diagenetic origin for siderite and kaolinite is inferred from micro structural relations whereas pore filling calcite and ankerite formed during later diagenesis the fe dolomite probably related to mixing zone dolomitization from increasing marine influences and a regional correlatable calcite cemented layer has been related to a flooding event porosity values in non cemented sandstone samples are generally high in both fch and sbf facies associations averaging 27 differential compaction between sandstone and mudstone has a ratio of up to 1 2 and with lower values for mbf we emphasize the role of eogenetic siderite cementation in reducing compactability in the fine grained coal bearing sediments most prominent in mbf facies this has implications for modeling of differential compaction between sandstone and mudstones deposited in fluvial deltaic environments

evolution of petrophysical properties of oil shales during high temperature compaction tests implications for petroleum expulsion abstract the transport properties of permian to miocene oil shales torbanite posidonia messel himmetoglu and condor were studied using petrophysical and geochemical techniques the aims of this study were to assess permeability of oil shales evaluate the evolution of porosity specific surface area and intergranular permeability during high temperature compaction tests and to verify the suitability of intergranular permeability for petroleum expulsion measured permeability coefficients for two samples were 0 72 10 21 m for the eocene messel shale and 2 63 10 21 m for the lower jurassic posidonia shale from s germany respectively bet specific surface areas of the original samples ranged from 0 7 to 10 6 m g and decreased after compaction to values from 0 3 to 3 7 m g initial porosity values ranged from 7 6 to 20 1 for pre deformation and from 9 99 to 20 7 for post deformation samples porosity increased during the high temperature compaction experiments due to petroleum generation and expulsion permeability coefficients estimated using the kozeny carman equation varied from 6 97 10 24 m to 5 22 10 21 m for pre deformation and from 0 2 10 21 m to 4 8 10 21 m for post deformation samples reflecting the evolution of their porosity and bet specific surface areas measured and calculated permeability were similar for the messel shale whereas calculated permeability was two orders of magnitude lower for the posidonia shale from s germany petroleum expulsion efficiencies under the experimental conditions ranged from 38 6 for the torbanite to 96 2 for the posidonia shale from s germany they showed strong positive correlation with the petroleum generation index r 0 91 and poor correlations with porosity r 0 46 average pore throat diameters r 0 22 and compaction r 0 02 estimated minimum pore system saturations for petroleum expulsion during the experiments were 12 for the torbanite and 30 for the posidonia shale from n germany pore system saturation determines whether expulsion occurs mainly through matrix or fracture permeability for samples with saturation levels above 20 fracture permeability dominated during the experiments evidence based on the measured permeability coefficients expulsion flow rates consideration of capillary displacement during generation related pore invasion and the existence of transport porosity suggests that fracture permeability is the principal avenue of petroleum expulsion from source rocks this conclusion is supported by microscopic observations

on the hydro mechanical behaviour of remoulded and natural opalinus clay shale the geo energy sector makes use of advanced technologies such as shale gas extraction co2 sequestration and nuclear waste geological disposal that rely on the exploitation of shale formations due to the great depths involved in these applications and the difficulties in retrieving intact samples remoulded shale specimens are often adopted for hydro mechanical testing remoulded and intact shales may substantially differ in their hydro mechanical behaviour due to the particular structure of the natural material which is the result of diagenesis and burial history this paper presents an experimental campaign aimed at i characterizing the role of diagenesis and depth for opalinus clay shale and their impact on the hydro mechanical behaviour of the material and ii understanding how representative the behaviour of the remoulded material is with respect to that of the natural shale in this paper the hydro mechanical behaviour of remoulded and intact specimens from the opalinus clay shale formation is investigated by means of a comprehensive oedometric testing campaign the effects of depth and diagenesis on the material behaviour are analysed by testing intact specimens that come from two different sites and depths of the considered shale formation the results highlight a considerably greater stiffness for the natural opalinus clay with respect to the remoulded specimens when the same vertical effective stress is considered together with a significantly lower porosity for the former which is shown to be the result of diagenetic processes rather than solely mechanical compaction a lower swelling sensitivity is also manifested by the natural material with respect to the remoulded specimens as a result of the formation of bonding on the other hand the diagenetic processes do not seem to have a strong impact on the permeability of the material finally creep effects are reduced when diagenesis occurs while they become more relevant when the material is disturbed or remoulded the obtained results provide significant insight into the roles of depth diagenesis and structural disturbance on the hydro mechanical behaviour of the opalinus clay shale

stress state permeability relations for overconsolidated clays analysis of experimental data of soils in both the normally consolidated and overconsolidated states reveal that the proposed relationships are tenable preconsolidation stress level influences the level of permeability