predicting the elastic response of organic rich shale using nanoscale measurements and homogenisation methods determination of the mechanical response of shales through experimental procedures is a practical challenge due to their heterogeneity and the practical difficulties of retrieving good quality core samples here we investigate the possibility of using multiscale homogenisation techniques to predict the macroscopic mechanical response of shales based on quantitative mineralogical descriptions we use the novel peakforce quantitative nanomechanical mapping technique to generate high resolution mechanical images of shales allowing the response of porous clay organic matter and mineral inclusions to be measured at the nanoscale these observations support some of the assumptions previously made in the use of homogenisation methods to estimate the elastic properties of shale and also earlier estimates of the mechanical properties of organic matter we evaluate the applicability of homogenisation techniques against measured elastic responses of organic rich shales partly from published data and also from new indentation tests carried out in this work comparison of experimental values of the elastic constants of shale samples with those predicted by homogenisation methods showed that almost all predictions were within the standard deviation of experimental data this suggests that the homogenisation approach is a useful way of estimating the elastic and mechanical properties of shales in situations where conventional rock mechanics test data cannot be measured

the front speed of intrusions into a continuously stratified medium this paper examines intrusive boussinesq gravity currents propagating into a continuously stratified fluid we develop a model based on energy arguments to predict the front speed of such an intrusive gravity current from a lock release we find that the depth at which the intrusion occurs which corresponds to the level of neutral buoyancy i e the depth where the intrusion density equals the stratified fluid density affects the front speed the maximum speeds occur when the intrusion travels along the top and bottom boundaries and the minimum speed occurs at mid depth experiments and numerical simulations were conducted to compare to the theoretically predicted values and good agreement was found

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

impact of thermal maturation on nano scale elastic properties of organic matter in shales abstract the properties of organic matter change during diagenesis and catagenesis potentially altering the way shales deform and fracture although kerogen in mudrocks is thought to become stiffer during thermal maturation few studies have been able to confirm this by direct measurement as standard mechanical testing techniques cannot easily be used to measure the micrometer sized organic components in shales here we use a new non destructive atomic force microscopy technique to map the elastic modulus of organic and inorganic components at the nanometer scale in shales containing type ii kerogen from three different levels of thermal maturation we found that when vitrinite reflectance increases from 0 40 to 0 82 the average young modulus of kerogen increases from 6 1 gpa to 16 0 gpa however as ro increases further from 0 82 to 1 25 the modulus values for kerogen do not change significantly a high degree of variance is registered in the elastic moduli particularly at higher levels of thermal maturation probably reflecting the inherent heterogeneity in the depositional organic matter present in the shales the mean modulus for bitumen in the same samples identified as void filling organic matter that was present only at intermediate and higher levels of maturation was relatively constant with mean values of 7 5 gpa and 8 5 gpa respectively in the samples that experienced catagenesis the modulus maps reveal that individual kerogen macerals possess soft regions interpreted as exuded bitumen which act to soften the overall structure of the kerogen as well as providing high resolution mechanical data this technique could be used to track the way bitumen and other compounds are generated from kerogen during catagenesis

the effect of thermal maturity on geomechanical properties in shale reservoirs an example from the upper devonian duvernay formation western canada sedimentary basin abstract shale reservoirs are characterized by low matrix permeability and therefore require effective models of geomechanical properties to optimize drilling and hydraulic fracturing strategies both initial rock composition and thermal maturity are potentially critical controls on geomechanical properties we investigate the upper devonian duvernay formation western canada sedimentary basin a major shale gas target that spans a wide range in rock compositions and thermal maturity to identify relationships between these parameters and geomechanical properties core hardness measurements and dipole sonic and density log data were used to characterize the geomechanical properties major element chemical analysis x ray diffraction analysis and leco combustion were used to determine mineralogy bulk rock chemistry and total organic carbon toc content and to distinguish biogenic from detrital silica scanning electron microscopy sem images with complementary energy dispersive spectroscopy eds maps were obtained for representative samples to document the rock fabric and distribution of organic matter and minerals hardness and al2o3 concentrations are strongly negatively correlated in all cores regardless of thermal maturity suggesting that clay minerals are the most significant factor controlling geomechanical properties biogenic silica is positively correlated to hardness detrital silica is negatively correlated to hardness an artifact of the positive correlation between detrital clay minerals and detrital quartz the positive correlations between cao content and hardness in all cores suggest the brittle behavior of carbonate minerals increased thermal maturity from immature to oil window results in greater hardness for rocks of similar geochemical compositions we propose that this results from 1 enhanced mechanical compaction 2 carbonate cementation 3 increased stiffness of kerogen and 4 partial conversion of kerogen into expelled hydrocarbons that reduces the load bearing function of the organic matter at maturities greater than oil window thermal maturity does not exert a major control on the rock strength thus there are no significant changes in hardness between samples from oil window and dry gas window geomechanical properties can be related to mineralogy which exerts a major impact on the geomechanical properties quartz cements sourced from biogenic silica rather than smectite to illite transition are the primary contributor to the rock strength in the duvernay formation however it is noteworthy that thermal maturity should also be considered as an important factor when predicting geomechanical properties from mineralogy

intrusive gravity currents between two stably stratified fluids we present an experimental and numerical study of one stratified fluid propagating into another the two fluids are initially at rest in a horizontal channel and are separated by a vertical gate which is removed to start the flow we consider the case in which the two fluids have the same mean densities but have different constant non zero buoyancy frequencies in this case the fluid with the smaller buoyancy frequency flows into the other fluid along the mid depth of the channel in the form of an intrusion and two counter flowing gravity currents of the fluid with the larger buoyancy frequency flow along the top and bottom boundaries of the channel working from the available potential energy of the system and measurements of the intrusion thickness we develop an energy model to describe the speed of the intrusion in terms of the ratio of the two buoyancy frequencies we examine the role of the stratification within the intrusion and the two gravity currents and show that this stratification plays an important role in the internal structure of the flow but has only a secondary effect on the speeds of the exchange flows

development of organic porosity in the woodford shale with increasing thermal maturity abstract using a combination of focused ion beam milling and scanning electron microscopy we describe the evolution of secondary organic porosity in eight woodford shale late devonian early mississippian samples with mean random vitrinite reflectance values ranging from 0 51 ro to 6 36 ro organic porosity was observed to be absent in samples with vitrinite reflectance values of up to 0 90 ro with the first appearance of secondary pores starting with the 1 23 ro sample porosity in the organic matter was unexpectedly absent in a sample with a vitrinite reflectance of 2 00 ro however organic pores were again found in samples with higher thermal maturities porosity when present did not appear to be uniformly distributed among the organic matter that was within less than a micron of each other suggesting important differences in composition of the organic matter thin regions of organic matter were observed between grains raising the possibility that small amounts of the deposited organic matter were compacted between grains to form thin layers and or the structures are part of the secondary organic matter interpreted to be post oil bitumen which was left behind as a residue during oil migration through the shale some regions of porous organic matter appeared to be grain protected whereas others did not which indicates that these non protected porous organic regions may be stress supporting with porosity intact under in situ reservoir conditions these observations suggest that thermal maturity alone is insufficient to predict porosity development in organic shales and other factors such as organic matter composition complicate porosity development

nanomechanical characterization of organic matter in the bakken formation by microscopy based method abstract organic rich shales are highly heterogeneous due to the presence of a variety of constituent components among them organic matter is poorly known in terms of mechanical properties due to the lack of high resolution analytical equipment to isolate organic matter in situ for mechanical testing in this study we proposed a new method to link morphology and geochemical properties of organic matter to its mechanical characteristics at the nanoscale kerogen type and thermal maturity along with mineralogy were evaluated by rock eval 6 pyrolysis total organic carbon toc analysis and x ray diffraction xrd analysis then the atomic force microscopy peakforce quantitative nano mechanical mapping afm peakforce qnm mode was employed and coupled with optical and electron microscopy to first visualize and then quantify the elastic properties of organic components in three different samples from the bakken formation hebamorphinite matrix bituminite and solid bitumen were identified as the main organic constituent along with oil prone marine kerogen type ii alginite and acritarch and also a bacterial derived granular micrinite like maceral based on tmax and vitrinite ro values or vro eq from bitumen ro thermal maturity of the samples ranged from immature to mature past peak oil window the average value of young s modulus for organic matter was measured in the range of 2 91 11 77 gpa it was also found that organic matter becomes stiffer with increased thermal maturity this study exhibits a great potential as a novel method for in situ analysis of mechanical properties of organic matter in shale reservoirs at a fine scale

effective elastic properties of solid clays clay minerals are perhaps the most abundant materials in the earth s upper crust as such their elastic properties are extremely important in seismic exploration seismic reservoir characterization and sonic log interpretation because little exists in the literature on elastic properties of clays we have designed a method of measuring effective elastic properties of solid clays clays without pores in this method clay minerals are mixed with a material with known elastic properties to make composite samples elastic properties of these clay minerals are then inverted from the measured elastic properties of the composite samples using the weighted hashin shtrikman average using this method we have measured 66 samples of 16 types of clays in this paper we present a comprehensive data set of elastic properties of solid clays that commonly occur in or are related to petroleum reservoirs although uncertainties up to 10 exist the data set reported here is by far the most comprehensive set of e

microfracturing and microporosity in shales shales are ubiquitous rocks in sedimentary basins where their low permeability makes them efficient seals for conventional oil and gas reservoirs and underground waste storage repositories waste waters co2 nuclear fuels moreover when they contain organic matter they form source rocks for hydrocarbons that may escape towards a more porous reservoir during burial a process referred to as primary migration and when the hydrocarbons cannot escape these rocks can be exploited as oil or shale gas reservoirs while the presence of fractures at the outcrop scale has been described the existence of fractures at smaller scales their link with microporosity the mechanisms that created them their persistence over geological times and their effect on the petrophysical properties of shales represent scientific challenges for which drillings in various sedimentary basins over the past decades may hold timely key data here we review and synthetize the current knowledge on how microfractures and micropores in shales can be imaged and characterized and how they control their anisotropic mechanical properties and permeability one question is whether such microfractures when observed in outcrops or in drilled core samples extracted from boreholes are related to decompaction and do not exist at depth another question is whether veins observed in shales represent microfractures that were open long enough to have acted as flow paths across the formation the mechanisms of microfracture development are described some have an internal origin fracturing by maturation of organic matter dehydration of clays while others are caused by external factors tectonic loading importantly the amount of microfracturing in shales is shown to depend strongly on the content in 1 organic matter and 2 strong minerals the nucleation of microfractures depends on the existence of mechanical heterogeneities down to the nanometer scale their propagation and linkage to create a percolating network will depend on the presence of heterogeneities at the meso to macro scales such percolating microfracture networks could control both the long term sealing capabilities of cap rocks and the further propagation of hydraulic fracturing cracks finally possible areas of research for describing the mechanism of microfracture formation in greater detail and how this impacts the transport and mechanical properties of shales are also discussed

the effect of thermal transfer on the zeroing of the luminescence of quartz from recent glaciofluvial sediments abstract the natural optically stimulated luminescence osl response of quartz grains extracted from a range of recent glaciofluvial and other glaciogenic sediments from western greenland is presented all samples were deposited within the last 10 years many only days or hours before collection consequently we would expect to measure zero or very small d e values had optical resetting of the osl signal been complete in the case of most samples d e values in the range 0 5 10 gy are observed while higher values are observed for a handful of samples however the regenerated osl growth curves constructed after daylight exposure of at least several hours also show large apparent d e values negative x axis intercepts corresponding samples from four different locations in the indian himalaya display similar osl characteristics the measurement of several regenerated osl growth curves omitting the preheat procedure which normally precedes osl measurement confirms that a significant degree of thermal transfer is occurring during the preheating it is this thermal transfer of charge during the preheat which is responsible for a significant contribution to the large apparent d e values observed for the regenerated osl growth in this paper we describe combined osl and tl measurements which have been used to monitor the charge transfer in detail for one sample an attempt is made to describe the charge transfer behaviour and we discuss methods appropriate to eliminating the unwanted effects of this phenomenon during osl dating preliminary results from the application of these techniques are presented and the implications of these observations for the osl dating of glaciogenic sediments are discussed

assessing the depth resolution of tomographic models of upper mantle structure beneath iceland 1 earlier inversions of body wave delay time data recorded during the icemelt portable broadband experiment imaged a cylindrical plume like low velocity anomaly extending to at least 400 km depth beneath iceland but the depth extent of the anomaly resolvable by tomography has recently been called into question we have performed several additional resolution tests to evaluate the depth resolution of tomographic models of the icelandic upper mantle the distribution of paths of body waves recorded by icemelt can distinguish among three different types of models a a wide and shallow anomaly b a narrow and deep anomaly and c a narrow and shallow anomaly while tomographic models contain an element of nonuniqueness these tests illustrate that the depth resolution of passive seismic experiments spanning subaerial iceland is adequate for distinguishing among alternative geodynamic models

silica diagenesis in the lower paleozoic wufeng and longmaxi formations in the sichuan basin south china implications for reservoir properties and paleoproductivity abstract silica diagenesis is one of the most important aspects of black shale diagenesis and critically controls the reservoirs properties of black shales three stratigraphic sections of the wufeng and longmaxi formations in the sichuan basin along a proximal to distal transect were investigated to study quartz types and their silica sources as well as their influences on reservoirs properties including rock mechanical properties and porosity preservation six types of quartz including detrital quartz recrystallized radiolaria siliceous fossil fragments microcrystalline quartz quartz overgrowth and hydrothermal quartz veins were identified based on their occurrences and morphologies under the petrographic microscope and scanning electron microscope and cathodoluminescence color and intensity original biogenic silica now exists as recrystallized radiolaria and microcrystalline silica in the mudstone matrix and follows systematic distribution patterns both laterally and stratigraphically the biological origin of this silica component is supported by the presence of recrystallized radiolaria with preserved spines preservation of ghosts of the central capsule serrated edges reflecting the spherical lattices of the outer shell and in addition preserved sponge spicules a further source of silica for microcrystalline quartz formation was silica released in the course of clay mineral smectite to illite transformation the different types of quartz make different contributions to the reservoir properties of shales with microcrystalline quartz having the most important impact microcrystalline quartz enhances the rock mechanical properties of shales and protects initial porosity from mechanical compaction through a rigid framework of interconnected diagenetic silica grains pores between microcrystalline quartz grains are shielded from complete mechanical compaction and provide space for accumulation of bitumen and oil later in burial history subsequently these pore filling organic matter develop secondary organic nanopores at higher thermal maturity although biogenic silica content has been used as a paleoproductivity proxy the method used to calculate it is based on questionable assumptions and model parameters need to be fine tuned for a given shale succession on the basis of petrographic observations in addition the commonly observed positive correlation between total organic carbon toc and biogenic silica is invalid for very low sedimentation rates and extremely high concentrations of biogenic silica from low to extremely high biogenic silica content in organic rich sediments a parabolic relationship between toc and biogenic silica should be common

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores

modelling intrusions through quiescent and moving ambients volcanic eruptions commonly produce buoyant ash laden plumes that rise through the stratified atmosphere on reaching their level of neutral buoyancy these plumes cease rising and transition to horizontally spreading intrusions such intrusions occur widely in density stratified fluid environments and in this paper we develop a shallow layer model that governs their motion we couple this dynamical model to a model for particle transport and sedimentation to predict both the time dependent distribution of ash within volcanic intrusions and the flux of ash that falls towards the ground in an otherwise quiescent atmosphere the intrusions spread axisymmetrically we find that the buoyancy inertial scalings previously identified for continuously supplied axisymmetric intrusions are not realised by solutions of the governing equations by calculating asymptotic solutions to our model we show that the flow is not self similar but is instead time dependent only in a narrow region at the front of the intrusion this non self similar behaviour results in the radius of the intrusion growing with time t as t3 4 rather than t2 3 as suggested previously we also identify a transition to drag dominated flow which is described by a similarity solution with radial growth now proportional to t5 9 in the presence of an ambient wind intrusions are not axisymmetric instead they are predominantly advected downstream while at the same time spreading laterally and thinning vertically due to persistent buoyancy forces we show that close to the source this lateral spreading is in a buoyancy inertial regime whereas far downwind the horizontal buoyancy forces that drive the spreading are balanced by drag our results emphasise the important role of buoyancy driven spreading even at large distances from the source in the formation of the flowing thin horizontally extensive layers of ash that form in the atmosphere as a result of volcanic eruptions

influence of geochemical features on the mechanical properties of organic matter in shale organic matter is an important constituent in organic rich shale which influences the hydrocarbon generation as well as the mechanical behavior of shale reservoirs the physical chemical and m

effect of thermal maturity on elastic properties of kerogen abstractwe have performed spatially continuous nanodynamic mechanical analysis on four organic rich shale samples with different thermal maturities to extract the elastic modulus of the kerogen particles aliquots were rigorously prepared and three scans were acquired from each aliquot subcritical nitrogen adsorption pore characterization was performed to determine the abundance of kerogen hosted porosity to fully characterize the pore system of samples from the oil window toluene and then chloroform extraction were performed to remove the pore filling hydrocarbons prior to nitrogen adsorption the statistical distribution of the measured modulus values was analyzed to extract the properties of the shale particles in mature samples from the peak oil generation or gas window the kerogen porosity was the dominant pore morphology we found that significant lowering of the kerogen particle modulus resulted from intraparticle kerogen porosity the kerogen particle modulus in mature samples was measured a

geomechanical and ultrasonic characterization of a norwegian sea shale anisotropy of velocity in shaly overburden is known to cause significant problems for geophysical interpretation including depth conversion and fluid identification in addition mechanical and dynamic elastic shale behavior is not well understood because few tests have been performed on well preserved samples multiple stage triaxial tests were performed upon horizontal core plugs of a shale from the norwegian sea with a view to evaluating rock strength and the evolution of ultrasonic response during rock deformation in addition standard rock physical properties were characterized as well as composition the shale microfabric is seen to be strongly laminated with alternating thick clay rich laminae and thin silt rich laminae occasional microfractures are also noted parallel to these laminations the shale has low friction coefficient and cohesive strength and shows anisotropy of these parameters when the maximum principal stress is oriented parallel to and at 45 to the microfabric the orientation of the maximum principal stress parallel to the intrinsic fabric and microcracks was seen to significantly impact on velocity normal to the fabric as stress parallel to the fabric increased s wave anisotropy was significantly affected by the increasing stress anisotropy stress orientation with respect to fabric orientation was therefore found to be an important control on the degree of anisotropy of dynamic elastic properties in this shale

the impact of rock composition on geomechanical properties of a shale formation middle and upper devonian horn river group shale northeast british columbia canada the geomechanical properties of a shale reservoir are essential both to the development of natural fractures and to the formation s response to hydraulic fracture stimulation we evaluate the rock mechanical properties in the middle and upper devonian horn river group shale including the evie and otter park members and the muskwa formation applying core hardness measurements and log derived young s modulus poisson s ratio and brittleness and relate these to shale composition and texture clay content is the most significant factor controlling the brittleness of shale rocks the effect of quartz content on rock mechanical properties depends on the type of quartz present in the rock authigenic quartz is positively correlated with brittleness but detrital quartz has little or no effect factor analysis indicates that carbonate increases brittleness while no obvious correlation between toc content and brittleness was observed depositional facies are related to geomechanical properties because each facies has a distinctive composition massive mudstone and pyritic mudstone are relatively brittle because of abundant authigenic quartz cement laminated mudstone and bioturbated mudstone are relatively ductile because most detrital carbonate and quartz grains are set in a matrix of clay minerals brittleness in the horn river group shale shows both geographic and stratigraphic variability increasing brittleness in the northwest part of the basin largely results from greater distance from the clastic sediment source the otter park member represents a period of major relative sea level fall and is relatively ductile because of its high clay content whereas the underlying evie member and the overlying muskwa formation are relatively brittle because of high carbonate and biogenic silica content respectively

influence of tectonic exhumation on porosity of wufeng longmaxi shale in the fuling gas field of the eastern sichuan basin china thermal cracking of organic matter om can enhance gas shale porosity however thermally matured shales are generally characterized by low porosity with high om content in tectonic exhumation settings the wufeng longmaxi shale in the fuling gas field china was investigated via bulk analysis and scanning electron microscopy to reveal the influence of tectonic exhumation on the porosity of om rich shale thermal maturity and organic and mineralogical compositions are regionally homogeneous in the fuling gas field shale porosity is positively correlated with total organic carbon toc and clay mineral content in the gentle and open anticlines respectively the om hosted pores were preserved with spherical morphologies because of overpressure associated overburden stress unloading in the gentle anticlines whereas om hosted pores in the open anticlines are characterized by high aspect ratios and are regularly aligned perpendicular to lateral compression stress a simple simulation confirmed that tectonic folding and compaction during exhumation caused the loss of porosity in the inner arcs of the open anticlines only pressure shadows formed by assemblages of clay mineral platelets and mechanically competent grains inhibited tectonic compaction of some om hosted pores in the open anticlines tectonic compaction of porosity generally increased the mean value of water saturation in the open anticlines the extremely high water saturation 60 in the high toc interval 2 wt was generally associated with natural fractures suggesting the occurrence of gas leakage

intrusive gravity currents in a stratified ambient shallow water theory and numerical results the intrusion of a fixed volume of fluid which is released from rest and then propagates horizontally at the neutral buoyancy level in a vertically stratified ambient fluid is investigated the density change is linear in a restricted layer or over the full depth of the container and locks of both rectangular and cylindrical shapes are considered a closed one layer shallow water inviscid formulation is used to obtain solutions of the initial value problem similarity solutions for the large time developed motion and an approximate box model are also presented the results are corroborated by numerical solutions of the full two dimensional navier stokes equations and comparisons with previously published experiments

organic maturity elastic properties and textural characteristics of self resourcing reservoirs abstractorganic rich rocks have long been recognized as source rocks for clastic reservoirs but more recently they have gained importance as reservoirs however the processes of kerogen maturation and hydrocarbon transport and storage are still poorly understood some empirical relations have been developed to relate the increase in elastic modulus with increasing maturity a systematic study of the cause for this increase in elastic modulus is still lacking and information about seismic and mechanical properties of kerogen and its alteration products is scarce consequently any rock models must rely on anecdotal or extrapolated data about various types of kerogen our experiments address this paucity of data by grain scale modulus measurements coupled with careful field emission scanning electron microscopy fesem microstructural assessments on organic rich bakken formation shale samples with a range of maturities carefully acquired and detailed fesem images help to understand the microstructural c

optical dating of tsunami laid sands abstract the ages of some tsunami deposits can be determined by optical dating a key requirement being that the deposits are derived from sediment that was reworked and exposed to daylight by tidal currents waves wind or bioturbation during the last years before the tsunami measurements have been made using 1 4 ev infrared excitation of k feldspar grains separated from samples of prehistoric tsunami sand sheets and modern analogs of tsunami source sediments at four sites in washington state and british columbia source sands gave equivalent doses indicative of recent exposure to daylight tsunami sand at cultus bay washington yielded an optical age of 1285 95 yr calendric years before a d 1995 1 at 2 this age overlaps the range of from 1030 to 1100 yr determined through a combination of high precision radiocarbon dating and stratigraphic correlation tsunami sands at three sites near tofino and port alberni on vancouver island british columbia have optical ages of 260 20 325 25 and 335 45 yr historical records and radiocarbon dating show that the sand at each of the three sites is between 150 and 400 yr old these optical ages support the hypothesis that the vancouver island sands were deposited by a tsunami generated by a large earthquake on the cascadia subduction zone about 300 yr ago

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

effects of crystallographic anisotropy on fracture development and acoustic emission in quartz 1 transgranular microcracking is fundamental for the initiation and propagation of all fractures in rocks the geometry of these microcracks is primarily controlled by the interaction of the imposed stress field with the mineral elastic properties however the effects of anisotropic elastic properties of minerals on brittle fracture are not well understood this study examines the effects of elastic anisotropy of quartz on the geometry of brittle fracture and related acoustic emissions ae developed during indentation experiments on single crystals at ambient pressure and temperature a hertzian cone crack developed during blunt indentation of a single crystal of flawless brazilian quartz parallel to the c axis shows geometric deviation away from predictions based on the isotropic case consistent with trigonal symmetry the visible cone crack penetration depth varies from 3 to 5 mm and apical angle from 53 to 40 electron backscatter diffraction ebsd mapping of the crack tip shows that fracturing initiates along a 40 m wide process zone comprising damage along overlapping en echelon high index crystallographic planes shown by discrete bands of reduced electron backscatter pattern ebsp quality band contrast coalescence of these surfaces results in a stepped fracture morphology monitoring of ae during indentation reveals that the elastic anisotropy of quartz has a significant effect on ae location and focal mechanisms ninety four ae events were recorded during indentation and show an increasing frequency with increasing load they correspond to the development of subsidiary concentric cracks peripheral to the main cone crack the strong and complex anisotropy in seismic velocity 28 vp 43 vs with trigonal symmetry resulted in inaccurate and high uncertainty in ae locations using geiger location routine with an isotropic velocity model this problem was overcome by using a relative master event location algorithm that only requires a priori knowledge of the velocity structure within the source volume the ae location results correlate reasonably well to the extent of the observed cone crack decomposition of ae source mechanisms of the geiger relocated events shows dominantly end member behavior between tensile and compressive vector dipole events with some double couple dominated events and no purely tensile or compressive events the same events located by the master event algorithm yield greater percentage of vector dipole components and no double couple events indicating that ae source mechanism solutions can depend on ae location accuracy and therefore relocation routine that is utilized calculations show that the crystallographic anisotropy of quartz causes apparent deviation of the moment tensors away from double couple and pure tensile compressive sources consistent with the observations preliminary modeling of calcite anisotropy shows a response distinct from quartz indicating that the effects of anisotropy on interpreting ae are complex and require detailed further study

intrusive gravity currents from finite length locks in a uniformly stratified fluid gravity currents intruding into a uniformly stratified ambient are examined in a series of finite volume full depth lock release laboratory experiments and in numerical simulations previous studies have focused on gravity currents which are denser than fluid at the bottom of the ambient or on symmetric cases in which the intrusion is the average of the ambient density here we vary the density of the intrusion between these two extremes after an initial adjustment the intrusions and the internal waves they generate travel at a constant speed for small departures from symmetry the intrusion speed depends weakly upon density relative to the ambient fluid density however the internal wave speed approximately doubles as the waves change from having a mode 2 structure when generated by symmetric intrusions to having a mode 1 structure when generated by intrusions propagating near the bottom in the latter circumstance the interactions between the intrusion and internal waves reflected from the lock end of the tank are sufficiently strong and so the intrusion stops propagating before reaching the end of the tank these observations are corroborated by the analysis of two dimensional numerical simulations of the experimental conditions these reveal a significant transfer of available potential energy to the ambient in asymmetric circumstances

geomorphological effects of tsunami run up and backwash abstract geomorphological processes associated with tsunami run up and backwash are highly complex to date most studies have considered the sedimentology of palaeo tsunamis while almost no detailed studies have been undertaken in areas known to have been affected by tsunamis in recent times research on contemporary tsunamis show that coastal landscapes may be greatly altered not only by direct tsunami run up orthogonal to the shoreline but also by episodes of vigorous backwash and by water flow sub parallel to the coastline the combined effect of these processes produces hitherto unrecognised coastal landforms that are dominated by the effects of high magnitude erosion and deposition deposition of large boulders is also associated with severe tsunamis while in adjacent areas run up processes often result in the deposition of continuous and discontinuous sediment sheets in many instances the upper limit of sediment deposition lies well below the upper limit of wave run up which is frequently marked by a well defined zone of stripped vegetation and soil the processes described have considerable implications for models of coastal evolution it may even be the case that the evolution of particular stretches of coastline are dominated by such high magnitude low frequency events

mechanical properties of organic matter in shales mapped at the nanometer scale abstract the mechanical properties of organic matter strongly affect the way shales deform and fracture however the way organic matter responds to mechanical stresses is poorly understood representing a critical obstacle to assessing oil and gas production in shale formations little is known about the mechanical properties of organic matter in fine grained rocks primarily because it often occupies tiny nanometer scale voids between the mineral grains which cannot be accessed using standard mechanical testing techniques here we use a new atomic force microscopy technique peakforce qnm to map the mechanical properties of organic and inorganic components at the nanometer scale we find that the method is able to distinguish between different phases such as pyrite quartz clays and organic matter moreover within the organic component young s modulus values ranged from 0 to 25 gpa in 3 different samples all of which come from thermally mature type ii iii source rocks in the dry gas window a modal value of 15 16 gpa was measured with additional peaks measured at 10 gpa in addition the maps suggest that some porous organic macerals possess a soft core surrounded by a harder outer shell 50 100 nm thick thus our results demonstrate that the method represents a powerful new petrographic tool with which to characterize the mechanical properties of organic rich sedimentary rocks

relationship between pore type and pore size of marine shale an example from the sinian cambrian formation upper yangtze region south china abstract to clarify the size distribution of different types of shale pores nine sinian cambrian shale samples from south china were examined using ion milling fe sem nitrogen adsorption and mercury intrusion image based point counting data indicated that nanopores are predominant whereas pores larger than 1 m are absent organic matter hosted pores dominate below 130 nm whereas intraparticle pores within carbonate probably caused by dissolution constitute most pores larger than 400 nm the small amount of residual intraparticle and interparticle pores associated with rigid minerals mostly range from 50 nm to 250 nm a positive relationship was found between the toc and total pore volume measured by nitrogen and mercury the mercury volume of pores larger than 300 nm increased with increasing dolomite and decreasing clay mineral content the statistics from image analysis and the relationship between pore volume and shale components were in good agreement indicating that different types of pores have their own relative restricted size range generally intrap pores are larger than pores associated with rigid minerals whereas the om pores and interp pores associated with om or clay are the smallest through a comparison with other less matured shale formations the highly matured equivalent vitrinite reflectance above 3 sinian cambrian shale in south china was characterized in this study as those with smaller interp pores which is probably due to a stronger compacting effect

an investigation on the effect of thermal maturity and rock composition on the mechanical behavior of carbonaceous shale formations abstract an accurate assessment of the geomechanical behavior of shale reservoirs is extremely significant in screening the potential intervals for hydraulic stimulation and sweet spot mapping while most of the studies were carried out on siliciclastic shales we here examine the mechanical behavior of a carbonaceous organic rich shale in the lurestan basin iran and the factors controlling them direct laboratory measurements at reservoir stress conditions static method and well logging interpretations dynamic approach were employed to assess the main geomechanical properties besides various experimental techniques have been employed to evaluate the dominant shale mineralogy geochemical properties and rock fabric it is observed that young s modulus and poisson s ratio obtained from either static or dynamic approaches are capable of reflecting rock brittleness conducted sensitivity analyses also reveal that abundances of organic matter clay and carbonate minerals are the most significant factors controlling rock brittleness an increase in the brittleness is envisioned by increasing the carbonate content and inversely by decreasing the concentrations of clay minerals and organic matter moreover week or no clear relationship regarding the possible effects of thermal maturity and quartz content could be distinguished incorporating the distinguished controlling factors into a compositional index a similar relative brittleness sequence with the elasticity based approach was detected this indicates that both independent methods are suitable for the identification of brittle layers inspected shale samples illustrate notably higher strengths in comparison with well characterized organic rich shales in the world translated as a direct contribution of firm carbonate textures to the rock framework taking these textures together with the main mineral contents into account the reservoir can be subdivided into three lithofacies including limestone argillaceous limestone and micritic limestone micritic limestones show relatively higher strength and brittleness whereas limestone and argillaceous limestone facies in spite of high variability reflect in average lower strength and brittle characteristics

scilly isles uk optical dating of a possible tsunami deposit from the 1755 lisbon earthquake abstract we present the results of optical dating of quartz from marine and aeolian deposits on st agnes island scilly isles uk the single aliquot regenerative dose protocol was used to estimate the equivalent dose in these samples proposed tsunami laid deposits at big pool provided ages of 230 40 and 380 60 years both are consistent with an expected age of 244 years an osl age of 6 3 years was obtained on a modern sub aqueous beach deposit these results suggest that the osl signal in the tsunami laid quartz was completely reset before deposition and that these sediments can be dated accurately by optical dating techniques sand dunes at bergecooth 250 m south of big pool were also dated using osl these ages indicate phases of aeolian activity at 300 a and 1000 a in the scilly isles

time varying underflow into a continuous stratification with bottom slope results are presented from a laboratory investigation of a continuous discharge gravity current moving down an inclined plane into a linearly stratified fluid the density of the inflow decreasing linearly with time initially larger and finally smaller than the bottom ambient density the inflowing water was observed to follow both underflowing and intrusive flow regimes hence during the time in which the inflow was denser than the water in the stratified reservoir an underflow was observed to descend down the sloping bottom with a speed that was consistent with that given by the theory for a buoyancy conserving gravity current on gentle slopes however the continuous decrease of the density at the source shortly lead to an unstable density distribution within the initial underflow which then collapsed into an intrusion that traveled as a horizontal gravity intrusion scaling arguments were used to identify both the position and time to the breakup of the underflow to the end of the experiment multiple intrusions were established successively at different depths in between the initial underflow and the surface buoyant plume

relationships between compressional wave and shear wave velocities in clastic silicate rocks new velocity data in addition to literature data derived from sonic log seismic and laboratory measurements are analyzed for clastic silicate rocks these data demonstrate simple systematic relationships between compressional and shear wave velocities for water saturated clastic silicate rocks shear wave veloci ty is approximately linearly related to compressional wave velocity and the compressional to shear velocity ratio decreases with increasing compressional velocity laboratory data for dry sandstones indicate a nearly constant compressional to shear velocity ratio with rigidity approximately equal to bulk modulus ideal models for regular packings of spheres and cracked solids exhibit behavior similar to the observed water saturated and dry trends for dry rigidity equal to dry bulk modulus gassmann s equations predict velocities in close agreement with data from the water saturated

optical dating using inclusions within quartz grains a sequence of stranded beach dunes in the southeast of south australia which resulted from the advance and retreat of the sea over a tectonically rising land surface during the past 800 ka has been securely dated by geological means and successfully used to test thermoluminescence dating based on quartz we have now obtained a series of promising results from the same sequence with a test of optical dating on inclusions within the quartz grains the innovative aspect of the measurements is the use of infrared irradiation to stimulate emission from the inclusions rather than conventional stimulation of the quartz itself by light of shorter wavelength satisfactory ages were found for seven dunes covering the time span 0 400 ka

effect of thermal maturation on chemical structure and nanomechanical properties of solid bitumen abstract an abundance of organic matter is present as solid bitumen in highly mature shales changes in chemical structure of solid bitumen during catagenesis could alter the way its mechanical properties evolve this study considers a series of solid bitumen samples artificially produced from the pyrolysis at 420 618 c of soluble organic matter which originated from maoming shale to examine alternations in their chemical structure nano morphological and mechanical properties during maturation solid state 13c nuclear magnetic resonance spectroscopy and elemental analysis were employed to characterize the structural changes young s modulus and microstructures were determined by atomic force microscopy the results show that both structural including c h atomic ratio and carbon aromaticity and mechanical young s modulus variations in solid bitumen exhibit two staged evolutions i e wet gas stage and dry gas stage during maturation in the wet gas stage easyro 1 85 2 64 the c h ratio and carbon aromaticity increase substantially with maturation and the solid bitumen is relatively compliant with an average young s modulus varying from 2 7 0 6 to 3 0 0 6 gpa when maturity reaches to dry gas stage easyro 2 64 4 59 structural parameters do not change greatly whereas solid bitumen becomes much stiffer with modulus rising sharply to 7 2 1 1 gpa at easyro 3 49 and further gently to 8 8 1 4 gpa at easyro 4 59 concomitantly great variations are observed on surface morphology and the degree of heterogeneity in solid bitumen is recorded to be increasingly high along thermal simulation given the strong correlation between structural parameters and young s modulus we suggest that the stiffening of solid bitumen is extensively affected by its structural condensation due to the loss of aliphatic carbons and the increase of aromaticity

characterization of electrical properties of organic rich shales at nano micro scales abstract a new experimental protocol is explored to characterize electrical properties of hydrocarbon bearing mudrocks at nano micro scales two current flow regimes of peak force tunneling atomic force microscopy pf tuna have been used 1 the vertical out of plane current regime with hundred micrometer diameter top electrodes obtains homogenized conductivity quantitatively 2 the horizontal in plane current regime was shown powerful to visualize the conductive paths related to connectivity and tortuosity for heterogeneous and anisotropic shales results show that the approach works well with one to two layers of adsorbed water 25 55 relative humidity under low frequency 0 5 20 hz for shale rocks current maps with sub nanometer resolution emphasize the dominant role of hydrated ions associated with the hydrophilic clay minerals in driving the dielectric response of shales while conductivity of pyrite and kerogen cannot be neglected for mature organic rich shale conductive network the acquired i v curves at microscale provide a reliable mean to evaluate homogenized conductivity of such multiscale multi component heterogeneous material under controlled environmental conditions the procedure discussed herein serves as a complement for fine grained rocks and minerals of ionic electronic hybrid conductive mechanism under partially water saturation these results can be used to develop accurate electrical models specifically for shale rocks with heterogeneous and sophisticated microstructure the methodology can be also extended to other micro or meso porous geomaterials such as cementitious and bituminous nanoporous media

variability of rock mechanical properties in the sequence stratigraphic context of the upper devonian new albany shale illinois basin abstract rock mechanical properties of tight shale reservoirs are important parameters in the exploration and development of unconventional shale oil and gas understanding the stratigraphic variability of rock mechanical properties in black shale successions is important for identifying promising intervals for hydraulic stimulation high resolution hardness tests 6 cm spacing with an equotip bambino 2 hardness tester were conducted on a new albany shale core to study the stratigraphic variability of rock mechanical properties combined with high resolution geochemical analyses 8 cm spacing acquired with a portable x ray fluorescence spectrometer it is possible to relate hardness variability to shale composition the results of our study suggest an average quartz content of about 28 for the entire succession approximately half of that amount 13 is interpreted to be of biogenic origin biogenic quartz mainly derived from dissolution of radiolaria occurs as authigenic quartz precipitated in tasmanites cysts and as microcrystalline quartz precipitated in the shale matrix petrographic observations indicate that the hardness of the new albany shale is critically controlled by biogenic quartz content not by total quartz content as suggested in multiple prior studies biogenic quartz forms an interconnected stiff framework which increases the hardness of shales in contrast dispersed hard grains e g detrital quartz feldspar and dolomite do not contribute to brittle behavior when examined under a scanning electron microscope hard shales are rich in biogenic quartz and contrast visibly with soft shales that are characterized by high contents of clay minerals negative correlation between hardness and al2o3 content as well as differential compaction of clay minerals around hard grains indicate that clay minerals are an important ductile component in the new albany shale although the general softness of kerogen suggests that there should be an influence of organic matter on hardness this effect is counteracted by biogenic quartz cementation which has a comparable stratigraphic distribution pattern we propose a new mineral composition based brittleness index on the basis of biogenic quartz content to characterize the brittleness of tight shale reservoirs within a sequence stratigraphic context the hardness of the new albany shale increases in transgressive systems tracts reaches a maximum at maximum flooding surfaces and decreases in highstand systems tracts with the exception of the blocher member maximum flooding surface intervals have the highest potential to develop brittle fractures and should be potential targets for hydraulic stimulation

imaging pores in sedimentary rocks foundation of porosity prediction abstract this review examines the history and current practice of technologies for imaging of pores in sedimentary rocks pores are that portion of the rock volume occupied by components of relative mobility such as water of various salinities microbial life petroleum liquids gases and supercritical fluids through a rock s history the contained pores evolve as the primary detrital assemblage responds chemically and mechanically to changing conditions in the subsurface description and classification of pores based upon their paragenesis depends upon inspection by imaging that allows the pores to be seen and interpreted in the context of historical processes responsible for formation of the pore walls since the late 1960s sample preparation and imaging methodologies that clarified our understanding of pores in their correct historical context have been at the root of important advances in prediction of porosity and related bulk properties in the subsurface these older approaches are now joined by new technologies that serve current efforts to extend predictive capabilities to nm scale pores in the fine grained low permeability rocks that dominate in the deeper parts of sedimentary basins and indeed in the sedimentary record as a whole placing the smallest pores into their proper paragenetic context presents a challenge in the quest to develop predictive models for porosity evolution in fine grained rocks

overall properties of heterogeneous material summary small scale heterogeneity in crustal structure can be very complex and difficult to describe in detail and yet at the same time can be very important for the description of for instance tectonic stress and porosity statistical properties of such heterogeneity can be derived from the properties of waves of relatively large wavelength as they propagate through the crust the differences between measured wavelengths and attenuation coefficients and those of compact rock and the variations of these quantities in space and time provide in principle a means of determining quantities like the density and orientations of microfractures and the nature of crack infill material the theoretical basis for inferences of this kind is the concept of the effective or equivalent material based on an averaging process taken over the microstructure a number of methods have been used to calculate the properties of the effective medium several of which are described here

shales at all scales exploring coupled processes in mudrocks abstract fine grained sedimentary rocks namely mudrocks including their laminated fissile variety shales make up about two thirds of all sedimentary rocks in the earth s crust and a quarter of the continental land mass organic rich shales and mudstones are the source rocks and reservoirs for conventional and unconventional hydrocarbon resources mudrocks are relied upon as natural barriers for geological carbon storage and nuclear waste disposal consideration of mudrock multi scale physics and multi scale spatial and temporal behavior is vital to address emergent phenomena in shale formations perturbed by engineering activities unique physical characteristics of shales arise as a result of their layered and highly heterogeneous and anisotropic nature low permeability fabric compositional complexity and nano scale confined chemical environments barriers of lexicon among geoscientists and engineers impede the development and use of conceptual models for the coupled thermal hydraulic mechanical chemical biological thmcb processes in mudrock formations this manuscript reviews the thmcb process couplings resulting emergent behavior and key modeling approaches we identify future research priorities in particular fundamental knowledge gaps in understanding the phase behavior under nano scale confinement coupled chemo mechanical effects on fractures the interplay between physical and chemical processes and their rates and issues of non linearity and heterogeneity we develop recommendations for future research and integrating multi disciplinary conceptual models for the coupled multi scale multi physics behavior of mudrocks consistent conceptual models across disciplines are essential for predicting emergent processes in the subsurface such as self focusing of flow time dependent deformation creep fracture network development and wellbore stability