early differentiation of the earth and the problem of mantle siderophile elements a new approach the long standing problem of the excess abundances of siderophile elements in the mantle can be resolved by considering an equilibrium core mantle differentiation in the earth at 3000 to 3500 kelvin this high temperature differentiation results in mantle siderophile element abundances that closely match the observed values some lithophile light elements could enter the core in this process as is necessary to account for its low density the abundances of siderophile elements in the mantle are consistent with the conclusion derived from the recent physical models that the earth was molten during accretion

metal silicate thermochemistry at high temperature magma oceans and the excess siderophile element problem of the earth s upper mantle recent theoretical considerations indicate that earth should have been at least partly molten at the end of accretion and perhaps sufficiently to produce a magma ocean metal silicate partition coefficients applicable to a magma ocean 3000 k 4000 k and up to 130 gpa would be valuable to test such models against well known mantle siderophile element abundances but they have not been measured however an extrapolation of existing low temperature data to these extreme conditions has recently been attempted murthy 1991 murthy s results seem to account for many apparent excesses of siderophile elements in the mantle we examined his extrapolation method and found it to be inconsistent with published temperature dependencies for metal silicate partition coefficients we also attempted an extrapolation to magma ocean temperatures based on known chemical behavior for several elements and using published metal silicate partition coefficients if the chemistry quantified by the low temperature data is applicable at high temperature an important assumption then our results indicate that high temperature alone will not help ameliorate the excess siderophile element problem of the upper mantle in contrast to the conclusions of murthy 1991 for most elements a modest increase in siderophile behavior is predicted with rising temperature if an iron wustite redox buffer is paralleled but long range extrapolation of experimental data containing even modest experimental errors is hazardous extrapolated high temperature partition coefficients can differ by orders of magnitude for a given element even though the input from independent studies is consistent within quoted errors direct experimental measurements for at least some of the siderophile elements will be necessary to accurately assess siderophile element behavior in a magma ocean the excess siderophile element problem of the earth s upper mantle remains unsolved

microseismic and precursor analysis of high stress hazards in tunnels a case comparison of rockburst and fall of ground abstract in rock engineering microseismic monitoring technology has been extensively applied for the interpretation and forecast of rockburst hazards however highly stressed hard rocks could suffer dynamic geological hazards rockburst and gravity driven geological hazards fall of ground both of which have distinct developmental processes and precursory features that await comprehensive exploration hence in this study we adopted microseismic monitoring and an advanced method based on the source parameters of seismic energy seismic moment and apparent stress the ems method the source parameter space was constructed to ascertain microseismic events as stress adjusting deformation driven or energy releasing type the evolution of the event type and the microseismic path precisely revealed the characteristics of the hazard development in a case study of a deeply buried tunnel we analyzed the process by which high stress hazards occur using the proposed method and distinguished between the respective microseismic characteristics of the rockburst and fall of ground in the development and occurrence stages finally we proposed the key precursory of rockburst and fall of ground in high stress rock masses while deformation driven events increase notably in rockburst stress adjusting events are dominant in fall of ground overall this study could facilitate precise interpretation and warning about different high stress hazards and provide effective measures to curb the development of hazards

evolution of methane sorption capacity of coal seams as a function of burial history a case study from the campine basin ne belgium based on extensive data sets of high pressure sorption isotherms and canister desorption data from two central european coal basins campine and ruhr basins a computational scheme has been developed to calculate the maximum coal bed methane cbm sorption capacity of coal seams as a function of pressure temperature and coal rank in addition the effects of in situ moisture content and maceral composition have been tentatively implemented using this algorithm it is possible to explicitly take into account variations in sorption capacity of the coal seams in sedimentary basins over geologic time as a function of burial history and thermal evolution the procedure has been applied to model the evolution and the present day coal bed methane content of the campine basin ne belgium it is demonstrated how the present day gas content of the campine basin is controlled by the burial history of the coal layers throughout geologic time the maximum gas sorption capacity typically occurs at a depth range between 500 and 1000 m during periods of uplift and erosion 250 and 90 ma before present the uppermost coal layers have lost methane due to a reduction of gas storage capacity while their storage capacity has increased during periods of burial 300 and 180 ma ago and present additionally the present day gas content is controlled by the gas generation history coal layers which have lost storage capacity during geologic time will stay undersaturated if not replenished by late stage e g microbial gas the gas content profile of test well kb206 in the ne campine basin established from canister desorption tests can be reproduced by assuming that undersaturation of the coals is due to erosion and re burial and that no significant gas generation e g microbial gas has taken place after the time of maximal burial isotopic data d 178 13c 59 indicate the presence of a small portion of microbial gas the absolute gas contents in this well are lower than the calculated maximum present day sorption capacity this may be due to an underestimation of the effect of water content on sorption capacity or result from degassing via nearby faults enforced by fluid circulation

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

pre himalayan tectono magmatic imprints in the darjeeling sikkim himalaya dsh constrained by 40 ar 39 ar dating of muscovite abstract the lower lesser himalayan sequence l lhs in darjeeling sikkim himalaya dsh displays intensely deformed low grade meta sedimentary rocks frequently intervened by granite intrusives of varied scales the principal motivation of our present study is to constrain the timing of this granitic event using 40ar 39ar geochronology we dated muscovite from pegmatites emplaced along the earliest fabric in the low grade daling phyllite and obtained 1850 ma ar ar muscovite cooling age which is broadly coeval with crystallization ages of lingtse granite protolith e g 1800 1850 ma u pb zircon ages reported from the l lhs we present here field observations to show the imprints tectonic fabrics of multiple ductile deformation episodes in the lhs terrain the earliest penetrative fabric axial planar to n s trending reclined folds suggest a regional tectonic event in the dsh prior to the active phase of indo asia collision based on the age of granitic bodies and their structural correlation with the earliest fabric we propose that the l lhs as a distinct convergent tectono magmatic belt delineating the northern margin of indian craton in the framework of the 1850 ma columbia supercontinent assembly

a strain based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets numerical modelling of impact cratering has reached a high degree of sophistication however the treatment of porous materials still poses a large problem in hydrocode calculations we present a novel approach for dealing with porous compaction in numerical modelling of impact crater formation in contrast to previous attempts e g p alpha model snowplow model our model accounts for the collapse of pore space by assuming that the compaction function depends upon volumetric strain rather than pressure our new e alpha model requires only four input parameters and each has a physical meaning the model is simple and intuitive and shows good agreement with a wide variety of experimental data ranging from static compaction tests to highly dynamic impact experiments our major objective in developing the model is to investigate the effect of porosity and internal friction on transient crater formation we present preliminary numerical model results that suggest that both porosity and internal friction play an important role in limiting crater growth over a large range in gravity scaled source size

post oil solid bitumen network in the woodford shale usa a potential primary migration pathway abstract an important if not predominant component of porosity in many gas shales has been identified in organic matter an organic network in shales has been described in the literature as organic matter generalized term kerogen primary or bitumen secondary recognition of the type and origin of an organic network in shales has relevance in establishing the origin and timing of porosity and fracture development the pervasive nature of the organic network adopting the shape of pores in type ii kerogen rich woodford shale suggests it is the residue of primary oil migration we use the term post oil solid bitumen to distinguish this bitumen occurrence from pre oil solid bitumen defined as a precursor of oil three forms of this post oil solid bitumen network are recognized in reflected white light at 500 magnification and confirmed in backscattered scanning electron microscope images at 2500 magnification namely speckled 1 2 m wispy 2 5 m and connected 5 m the post oil solid bitumen network demonstrates the prior occurrence of oil generation and migration within this hydrocarbon source rock provides porosity for hydrocarbon storage sites and forms hydrocarbon migration pathways

evolution of water content in organic rich shales with increasing maturity and its controlling factors implications from a pyrolysis experiment on a water saturated shale core sample abstract in the present study a pyrolysis experiment was performed on an immature water saturated shale core sample and a set of artificially matured subsamples maturity with equivalent vitrinite reflectance values of 0 67 3 20 i e eqvro values with initial water phases was obtained the water content of these shale samples and its influencing factors were investigated the results show that the water content significantly varies with maturity and is closely related to the hydrocarbon generation and expulsion clay mineral transformation and pore structure evolution of shales according to the changes of water content with maturity and the main influencing factors the evolution of the water content in shales is approximately divided into three stages at the low maturity stage 0 67 1 36 with increasing maturity the water content remarkably decreases at the wet gas window 1 36 1 90 which is mainly controlled by the displacement drainage of gaseous hydrocarbons in addition the pore structure evolution of shale which changes its water storage capacity also has an influence on the water content evolution

reconstructing the late accretion history of the moon the importance of highly siderophile elements hses namely gold iridium osmium palladium platinum rhenium rhodium and ruthenium in tracking the late accretion stages of planetary formation has long been recognized however the precise nature of the moon s accretional history remains enigmatic there is a substantial mismatch in the hse budgets of the earth and the moon with the earth seeming to have accreted disproportionally more hses than the moon1 several scenarios have been proposed to explain this conundrum including the delivery of hses to the earth by a few big impactors1 the accretion of pebble sized objects on dynamically cold orbits that enhanced the earth s gravitational focusing factor2 and the sawtooth impact model with its much reduced impact flux before about 4 10 billion years ago3 however most of these models assume a high impactor retention ratio the fraction of impactor mass retained on the target for the moon here we perform a series of impact simulations to quantify the impactor retention ratio followed by a monte carlo procedure considering a monotonically decaying impact flux4 to compute the impactor mass accreted into the lunar crust and mantle over their histories we find that the average impactor retention ratio for the moon s entire impact history is about three times lower than previously estimated1 3 our results indicate that to match the hse budgets of the lunar crust and mantle5 6 the retention of hses should have started 4 35 billion years ago when most of the lunar magma ocean was solidified7 8 mass accreted before this time must have lost its hses to the lunar core presumably during lunar mantle crystallization9 the combination of a low impactor retention ratio and a late retention of hses in the lunar mantle provides a realistic explanation for the apparent deficit of the moon s late accreted mass relative to that of the earth lunar impact simulations find an impactor retention ratio three times lower than previously thought and indicate that highly siderophile element retention began 4 35 billion years ago resolving accretion mass discrepancies between earth and the moon

the importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs abstract the effect of shale composition and fabric upon pore structure and ch 4 sorption is investigated for potential shale gas reservoirs in the western canadian sedimentary basin wcsb devonian mississippian d m and jurassic shales have complex heterogeneous pore volume distributions as identified by low pressure co 2 and n 2 sorption and high pressure hg porosimetry thermally mature d m shales 1 6 2 5 vro have dubinin radushkevich d r co 2 micropore volumes ranging between 0 3 and 1 2 cc 100 g and n 2 bet surface areas of 5 31 m 2 g jurassic shales which are invariably of lower thermal maturity ranging from 0 9 to 1 3 vro than d m shales have smaller d r co 2 micropore volumes and n 2 bet surface areas typically in the range of 0 23 0 63 cc 100 g co 2 and 1 9 m 2 g n 2 high pressure ch 4 isotherms on dried and moisture equilibrated shales show a general increase of gas sorption with total organic carbon toc content methane sorption in d m shales increases with increasing toc and micropore volume indicating that microporosity associated with the organic fraction is a primary control upon ch 4 sorption sorption capacities for jurassic shales however can be in part unrelated to micropore volume the large sorbed gas capacities of organic rich jurassic shales independent of surface area imply a portion of ch 4 is stored by solution in matrix bituminite solute ch 4 is not an important contributor to gas storage in d m shales structural transformation of d m organic matter has occurred during thermal diagenesis creating and or opening up microporosity onto which gas can sorb as such d m shales sorb more ch 4 per weight percent wt toc than jurassic shales inorganic material influences modal pore size total porosity and sorption characteristics of shales clay minerals are capable of sorbing gas to their internal structure the amount of which is dependent on clay type illite and montmorillonite have co 2 micropore volumes of 0 78 and 0 79 cc 100 g n 2 bet surface areas of 25 and 30 m 2 g and sorb 2 9 and 2 1 cc g of ch 4 respectively dry basis a reflection of microporosity between irregular surfaces of clay platelets and possibly related to the size of the clay crystals themselves mercury porosimetry analyses show that total porosities are larger in clay rich shales compared to silica rich shales due to open porosity associated with the aluminosilicate fraction clay rich sediments low si al ratios have unimodal pore size distributions

seismotectonic model of the sikkim himalaya constraint from microearthquake surveys the seismotectonic model in the sikkim himalaya does not fit well with the proposed steady state or evolutionary models the main boundary thrust mbt is seismogenic and is a mantle reaching fault the earthquakes are not confined to shallower depths 25 km above the plane of detachment as proposed in the models the seismic activity continues from surface to the lower crust 0 45 km to the north of mbt and earthquakes are produced by a thrust mechanism the earthquakes to the east of sikkim in the bhutan himalaya on the other hand are produced along a 200 km long northwest southeast trending lineament by transverse tectonics the seismogenic lineament cuts across the himalayan major thrusts and extends to the goalpara wedge in the southeast the earthquakes occur by strike slip mechanism in the midcrust at a depth range of 10 25 km along this long active lineament

dynamical effects of multiple impacts large impacts on a mars like planet abstract the earliest stage of the evolution of a fully assembled planet is profoundly affected by a number of basin forming impacts large enough to change the dynamics of its deeper interior these impacts are in some cases quite closely spaced and follow one another in short time intervals so that their effects interact and result in behavior that may differ from a simple sum of the effects of two individual and isolated impacts we use two dimensional models of mantle convection in a mars like planet and a simple parameterized representation of the principal effects of impacts to study some of the dynamical effects and interactions of multiple large impacts in models of only two impacts we confirm that the dynamical effects of the impacts reinforce each other the closer they are in space and time but that the effects do not always correspond to straightforward superpositions of those of single isolated impacts in models with multiple 4 8 impacts with variable sizes distances and frequencies the global response of the mantle is as variable as the impact sequences in the short term but in the long term the different evolutionary paths converge for several indicator variables such as the mean flow velocity temperature or heat flow nonetheless beyond a certain impact frequency and energy lithospheric instabilities triggered by large impacts occur on a global scale reinvigorate mantle dynamics for long time spans and entail a late stage of melt production in addition to the initial melting stage that is not observed in one or two impact models after one or several very large impacts some lithospheric material may founder and sink to the core mantle boundary and if enough of it accumulates there it enhances the heat flux out of the core for several hundred millions of years with possible effects on dynamo activity

organic matter clay mineral intergranular pores in the lower cambrian lujiaping shale in the north eastern part of the upper yangtze area china a possible microscopic mechanism for gas preservation abstract gas shales with a high gas content were encountered in the lower cambrian lujiaping formation in the northeast part of the upper yangtze area china in this area the tectonic condition is complex and the organic matter is over matured so conventional oil and gas exploration have not previously been considered during a recent shale gas exploration canister desorbed gas contents of more than 1 m 3 t were detected from 490 to 825 m depth with a maximum value of 3 18 m 3 t at 762 m hence to understand the mechanism of preservation of the gas is important the gas shales have a total organic carbon toc content of between 0 44 and 6 91 and vitrinite like macerals reflectance r o between 3 3 and 4 3 with type ii kerogen the porosity of 22 gas shale samples ranges between 0 4 and 2 29 and their permeability is between 6 9 10 5 and 3 8 10 1 md to investigate the shale s pore structure and its relation to gas storage behavior we studied the microscopic mechanism of gas preservation using a combination of pore characterization techniques including focused ion beam scanning electron microscope fib sem imaging and comparison of gas sorption and free gas storage capacity folding thrusting and subsequent rapid uplifting movements occurred after most of the dry gas had been originally generated and the present gas is a mixture originated from the cracking of liquid hydrocarbons at high maturity and kerogen pyrolysis in the early hydrocarbon generation phase sem observations combined with low temperature gas adsorption and mercury injection capillary pressure analyses show that pores within the organic matter or the mineral particles in the lujiaping shale are rare while the nanometer sized pores 1 4 nm between organic matter and clay mineral particles especially in cleavage domains are greatly developed thus the gas in these shales is mainly adsorbed gas due to the limited free gas storage space this is unlike most other shale gas reservoirs pores within the organic matter and pores between or within mineral particles are dominant moreover the desorbed gas content correlates well with toc content and the microporous and mesoporous specific surface area determined by low temperature co 2 and n 2 respectively suggesting that the nanometer sized pores associated with the organic matter make up the fundamental storage space for this shale the calculations based on fib sem observation showed that the nanometer sized intergranular pores have large specific surface areas with their small pore throat diameters resulting in high capillary pressure these characteristics have contributed to the preservation of shale gas in this complex tectonic area

seismic moment estimation based on fracture induced electromagnetic radiation abstract a new method to calculate the seismic moment based on electromagnetic radiation emitted during fracturing is presented results of this method for small fractures arising during the nucleation stages of an earthquake are shown to agree with former laboratory seismic measuring technique this method is quite easy to implement and can be used for measuring engineering failure intensity it can also be used to measure the seismic moment at the nucleation stages of an earthquake when seismic devices seismographs seismometers are not effective these measurements can then be used to calibrate the seismic devices for the estimation of the seismic moment during the catastrophic stages of earthquakes when these seismic devices are suitable and no electromagnetic radiation is present

calculation of electromagnetic radiation criterion for rockburst hazard forecast in coal mines intensive micro fracturing of rock close to mining operations accompanies an increase in the likelihood of rockbursting this fracturing causes an increase of the electromagnetic radiation emr level by up two orders of magnitude depending on the mining environment several examples of this enhanced emr are presented in this paper we first treat the emr theoretical criterion of rockburst hazard in coal mines and compare it with the empirical criterion of emr activity that was revealed on the basis of more than 400 different hazardous and non hazardous situations in underground coal mines only the following parameters are needed to estimate the emr criterion of rockburst hazard limiting value of gum volume mine working width coal seam thickness and coal elastic properties

extensional reactivation of an abandoned thrust a bound on shallowing in the brittle regime abstract shallow dip angles 45 suggested by field observations of continental extensional faults are not predicted by classical isotropic mohr coulomb anderson theory earthquake data indicate that normal faults exist in the upper crust with dip angles commonly as shallow as 30 some structural evidence suggests brittle normal faulting with dip angles as shallow as 10 one explanation of the apparent conflict between theory and structural seismic observations is that intrinsically weak shallow dipping pre existing faults are preferentially reactivated any reduction in frictional strength of the pre existing structure below that of surrounding rock increases the likelihood that such structures will be first breaking when extension is initiated enhanced fluid pore pressure on the pre existing fault reduces the effective strength and can further enhance shallow fault reactivation an analytical treatment clarifies the roles of geometry intact pre existing fault strengths and fluid pore pressures frictional strength ratios of 3 or greater could account for extremely shallow normal faults dips 10 20 without consideration of pore pressures in excess of the least principal stress or of principal stress systems rotated away from the gravity vector moderate reduction in friction 3 4 with respect to wall rock can reduce the dip to 30 and can account for shallow normal slip earthquakes

magma ocean formation due to giant impacts current understanding of the last stages of planetary accretion suggests that mass and energy accumulation are dominated by a few large impacts an important thermal consequence of such impacts is melting and formation of a large melt pond if the planet s isostatic adjustment time scale is short compared to the magma pond s cooling time scale the melt may be extruded onto the surface and form a magma ocean of approximately uniform depth although a giant impact striking at 10 15 km s 1 deposits enough energy to melt the entire planet the distribution of that energy is important in determining the thermal outcome of the collision we examine the thermal effects of giant impacts by estimating the melt volume generated by the initial shock wave and corresponding magma ocean depths additionally we examine the effects of the planet s initial temperature on the generated melt volume the hugoniot curve plotted in pressure entropy space is used to determine the shock pressure required to completely melt the material for room temperature dunite this pressure is about 150 gpa and the partial melt region is narrow for dunite initially at the solidus temperature this pressure is about 115 gpa the partial melt region extends throughout the planet once the melting pressure is known an impact melting model based on the second hugoniot equation the linear shock particle velocity relationship and the empirical particle velocity distance relationship is used to estimate the radial distance melting occurred from the impact site once the distance is found the melt region s geometry determines the associated melt volume partial melt volume is also estimated the melt fraction that is not excavated during crater formation is estimated and magma ocean depths resulting from both excavated and retained melt are calculated the model is also used to estimate the fraction of a planet melted by the initial shock wave nominal conditions of the moon forming giant impact projectile planet mass 0 14 impact speed 15 km s 1 generate melting of 30 65 of the planet depending on its initial temperature whole planet melting requires projectile planet mass ratios of 0 4 for a 15 km s 1 impact if the planet was near its solidus before the impact isostatic relaxation may generate a significant volume of additional melting

experimental investigation of changes in methane adsorption of bitumen free woodford shale with thermal maturation induced by hydrous pyrolysis this study quantifies the effects of organic matter om thermal maturity on methane ch4 sorption on the basis of five samples that were artificially matured through hydrous pyrolysis achieved by heating samples of immature woodford shale under five different time temperature conditions ch4 sorption isotherms at 35 degrees c 50 degrees c and 65 degrees c and pressures up to 14 mpa on dry solvent extracted samples of the artificially matured woodford shale were measured the results showed that ch4 sorption capacity normalized to toc varied with thermal maturity following1 the trend maximum oil 367 degrees c oil cracking 400 degrees c maximum bitumen early oil 333 degrees c early bitumen 300 degrees c immature stage 130 degrees c the langmuir constants for the samples at maximum oil and oil cracking stages are larger than the values for the bitumen forming stages the total pore volume determined by n 2 physisorption at 77 k increases with increased maturation mesopores 2 50 nm in width were created during the thermal conversion of organic matter and a dramatic increase in porosity appeared when maximum bitumen and maximum oil generation stages were reached a linear relationship between thermal maturity and brunauer emmett teller bet surface area suggests that the observed increase in ch4 sorption capacity may be the result of mesopores produced during om conversion no obvious difference is observed in pore size distribution and pore volume for samples with pores 2 0 nm with the increase of thermal maturity based on co2 physisorption at 273 k the isosteric heat of adsorption and the standard entropy for artificially matured samples ranged from 17 9 kj mol 1 to 21 9 kj mol 1 and from 85 4 j mol 1 k 1 to 101 8 j mol 1 k 1 respectively these values are similar to the values of immature woodford kerogen concentrate previously observed but are larger than naturally matured organic rich shales high temperature hydrous pyrolysis might have induced lewis acid sites on both organic and mineral surfaces resulting to some extent in chemical interactions between the adsorption site and the methane c h bonds the formation of abundant mesopores 2 50 nm within organic matter during organic matter thermal maturation makes a great contribution to the increase in both bet surface area and pore volume and a significant increase in 2 6 nm pores occurs at maximum oil generation and oil cracking to gas ultimately controlling the methane adsorption capacity therefore consideration of pore size effects and thermal maturity is very important for gas in place gip prediction in organic rich shales c 2014 elsevier ltd all rights reserved

polyphase thermal evolution in the infra cambrian ara group south oman salt basin as deduced by maturity of solid reservoir bitumen petrographic and organic geochemical analyses on solid reservoir bitumen from the late precambrian to early cambrian ara group indicate polyphase thermal evolution in the south oman salt basin sosb the ara group constitutes a complex petroleum system in the deep subsurface 3 5 km of interior oman salt diapirs encase isolated partly highly overpressured carbonate bodies intra salt stringers which represent a predominantly self charging hydrocarbon system a large number of stringer cores show that reservoir quality is decreased by the presence of solid reservoir bitumen by using different microscopy techniques this solid reservoir bitumen has been identified within pores pore throats and microfractures of the carbonates solid bitumen reflectance measurements brr were converted to vitrinite reflectance vrr using a new improved calibration vitrinite reflectance geothermometry shows that maximum paleo temperatures have a highly heterogeneous distribution paleo temperatures of 380 c were obtained from coke like solid reservoir bitumen which most likely formed from thermal cracking of oil in our model this process is related to hydrothermal fluids deriving from deeper pre salt strata of the sosb which entered the intra salt carbonate stringers during times of basement tectonic activity via hydrofractures this caused the formation of high maturities pyrobitumens in close vicinity to the fractures and precipitation of migrabitumens with increasing distance to the ht source which is supported by the geochemical composition of the solid reservoir bitumens the influx of these fluids into the carbonate stringers is considered to represent a major contribution to their strong overpressures 2007 elsevier ltd all rights reserved

turbulent mixing of metal and silicate during planet accretion and interpretation of the hf w chronometer in the current view of planet formation the final assembly of the earth involved giant collisions between proto planets 1000 km radius with the moon formed as a result of one such impact at this stage the colliding bodies had likely differentiated into a metallic core surrounded by a silicate mantle during the moon forming impact nearly all metal sank into the earth s core we investigate to what extent large self gravitating iron cores can mix with surrounding silicate and how this influences the short lived chronometer hf w used to infer the age of the moon we present fluid dynamical models of turbulent mixing in fully liquid systems attempting to place constraints on the degree of mixing erosion of sinking cores driven by rayleigh taylor instability does lead to intimate mixing and equilibration but large blobs 10 km diameter do not emulsify entirely emulsification is enhanced if most of the accreting metal cores deform into thin structures during descent through the earth s mantle yet only 1 20 of earth s core would equilibrate with silicate during earth s accretion the initial speed of the impactor is of little importance we proceed to evaluate the mixing potential for shear instabilities where silicate entrainment across vertical walls causes mixing the turbulent structure indicates that vortices remain at the largest scale and do not mix to centimeter length scale where diffusion operates and isotopes can equilibrate thus incomplete emulsification and equilibration of accreting iron cores is likely to occur the extent of metal silicate equilibration provides key information for interpretation of siderophile budgets and the timing of core formation using the hf w chronometer the time scale of core formation derived from the hf w chronometer is usually tied to the last major metal silicate re equilibration believed to coincide with time of the moon forming impact however we show that large cores have limited ability to reset the hf w system in the silicate earth excess 182 w in bulk silicate earth is more sensitive to early core formation processes than to radiogenic ingrowth after the last giant impact

underground measurements of electromagnetic radiation related to stress induced fractures in the odenwald mountains germany the regional stress field at wald michelbach odenwald mountains germany induces a secondary stress field around the space of the local railway tunnel resulting maximum shear stresses produce microfractures which emit electromagnetic radiation emr from emr measured along the cross section and the long axis of the tunnel the regional stress field is determined by a correlation of detected impulses per time with stresses calculated from the orientation of the tunnel its diameter and topographic load the major horizontal principal stress has an azimuth of 103 at times strongly alternating emr values are observed which indicate electromagnetic disturbances of unknown origin such disturbances are identified by repeated measurements and are not evaluated the repeated measurements which are not disturbed differ with median 112 impulses per 100 ms this difference corresponds to 0 037 mpa and indicates a good reproducibility of the results regional stress magnitudes and the wnw ese orientation of the major horizontal principal stress indicate a minor n s directed tensional force at the western shoulder of the upper rhine graben

fluid dynamics of local martian magma oceans the evolution of a melt region produced by a large impact during mars formation is addressed while some impact induced melt is redistributed during crater excavation sufficiently large impacts much larger than basin forming impacts generate an intact melt region which is retained beneath the excavation zone i e a local magma ocean local magma ocean evolution depends on the effective rheology controlling large scale deformation of the solid part of the planet mechanism of crystallization and melt region size within the uncertainties of various parameters two scenarios are possible for sufficiently weak rheology or large melt region size evolution is characterized by rapid extrusion and formation of a global magma ocean for sufficiently strong rheology or small melt region size in situ crystallization to a partially molten solid state occurs prior to isostatic adjustment subsequent to in situ crystallization local magma ocean evolution depends on melt region size and efficiency of lateral redistribution compared to bulk conductive cooling for large melt regions lateral spreading occurs via plastic deformation and results in an asymmetric global partial melt layer for small melt region size viscous spreading viscous can result in bulk cooling below the solidus prior to formation of a global layer a hypothesis for the origin of the hemispherical crustal dichotomy and tharsis rise is suggested the dichotomy is associated with a global partial melt layer produced by evolution of a large local magma ocean after dichotomy formation evolution of a second smaller local magma ocean is related to tharsis development

turbulent metal silicate mixing fragmentation and equilibration in magma oceans abstract much of the earth was built by high energy impacts of planetesimals and embryos many of these impactors already differentiated with metallic cores of their own geochemical data provide critical information on the timing of accretion and the prevailing physical conditions but their interpretation depends critically on the degree of metal silicate chemical equilibration during core mantle differentiation which is poorly constrained efficient equilibration requires that the large volumes of iron derived from impactor cores mix with molten silicates down to scales small enough to allow fast metal silicate mass transfer here we use fluid dynamics experiments to show that large metal blobs falling in a magma ocean mix with the molten silicate through turbulent entrainment with fragmentation into droplets eventually resulting from the entrainment process in our experiments fragmentation of the dense fluid occurs after falling a distance equal to 3 4 times its initial diameter at which point a sizable volume of ambient fluid has already been entrained and mixed with the dense falling fluid contrary to previous assumptions we demonstrate that fragmentation of the metallic phase into droplets may not be required for efficient equilibration turbulent mixing by drastically increasing the metal silicate interfacial area may result in fast equilibration even before fragmentation efficient re equilibration is predicted for impactors of size small compared to the magma ocean depth in contrast much less re equilibration is predicted for large impacts in situations where the impactor core diameter approaches the magma ocean thickness

laboratory experiments on the breakup of liquid metal diapirs the validity of the iron rain scenario i e the widely accepted model for the dynamics of iron sedimentation through a magma ocean during the latest stage of the earth s accretion is explored via a suite of laboratory experiments liquid gallium and mixtures of water and glycerol are used as analogs of the iron and the molten silicate respectively this allows us to investigate the effects of the viscosity ratio between iron and silicate and to reproduce the relevant effects of surface tension on the fragmentation dynamics while the classical iron rain scenario considers a population of purely spherical drops with a single characteristic radius that fall towards the bottom of the magma ocean at a unique velocity without any further change our experiments exhibit a variety of stable shapes for liquid metal drops a large distribution of sizes and velocities and an intense internal dynamics within the cloud with the superimposition of further fragmentations and merging events our results demonstrate that rich and complex dynamics occur in models of molten metal diapir physics further we hypothesize that the inclusion of such flows into state of the art thermochemical equilibration models will generate a similarly broad array of complex and likely novel behaviors

recent movements along the main boundary thrust of the himalayas normal faulting in an over critical thrust wedge abstract the main boundary thrust mbt is one of the major himalayan thrusts occurring during the cainozoic and it is presently incorporated within the himalayan thrust wedge lesser and outer himalayas displaced above the indian lithosphere nonetheless the mbt shows recent normal displacement along most of its length we suggest that the orientation of the major principal stress within the himalayan thrust wedge deviates significantly from the horizontal and when this deviation exceeds the dip of the vectors normal to back tilted thrusts the normal component of displacement may act along these faults steep north dipping segments of the mbt therefore show a normal component of displacement if a geometrical definition is used but they are faults in a compressional regime where the major principal stress axis has deviated from the horizontal micro structural data recorded along the surkhet ghorahi segment of the mbt are consistent with a strong deviation of the state of stress the presence of such peculiar normal faulting along the mbt is used to calibrate the mechanical characteristics of the belt considered as a coulomb wedge the following characteristics are suggested a very poor strength contrast between basal decollement and rocks in the wedge body b a high pore fluid pressure ratio probably close to 0 8 0 9 and a higher fluid pressure ratio close to 1 0 along the active normal faults if a high internal friction angle close to the byerlee value is considered the strong deviation in principal stress direction may have recently increased due to a taper of the himalayan wedge exceeding the stability boundary and may be controlled by erosion and isostatic uplift rebound of the himalayan range

experiments on fragmentation and thermo chemical exchanges during planetary core formation abstract the initial thermo chemical state of telluric planets was largely controlled by mixing following the collision of differentiated proto planets up to now most models of planet formation simply assume that the iron core of the impactors immediately broke up to form an iron rain within a large scale magma ocean leading to the rapid equilibration of the whole metal with the whole mantle only recent studies have focused on resolving the fluid mechanics of the problem with the aim to define more relevant diffusion advection models of thermal and chemical exchanges within and between the two fluids furthermore the influence of the viscosity ratio on this dynamical process is generally neglected whilst it is known to play a role in the breakup of the initial iron diapirs and in the shape of the resulting droplets here we report the results of analog laboratory experiments matching the dynamical regime of the geophysical configuration high speed video recording allows us to describe and characterize the fluid dynamics of the system and temperature measurements allow us to quantify the diffusive exchanges integrated during the fall of the liquid metal we find that the early representation of this flow as an iron rain is far from the experimental results the equilibration coefficient at a given depth depends both on the initial size of the metal diapir and on the viscosity of the ambient fluid whereas the falling speed is only controlled by the initial size various scalings for the diffusive exchanges coming from the literature are tested we find good agreement with the turbulent thermal model developed by deguen et al 2014

methane adsorption characteristics of overmature lower cambrian shales of deepwater shelf facies in southwest china abstract the lower cambrian shales of deepwater shelf facies comprise an important part of the marine black shales in southern china in this study twenty four lower cambrian shale samples from southwest china were subjected to analysis of geochemistry pore structure and methane adsorption capacity the samples have total organic carbon toc contents ranging from 0 25 to 11 3 and equivalent vitrinite reflectance eqvro values in the range of 2 51 4 23 specific surface areas determined from n2 adsorption at 77 4 k and specific micropore volumes from co2 adsorption at 273 15 k are in the range of 3 0 38 6 m2 g rock and 2 5 11 4 cm3 kg rock respectively and both of them have positive relationships with toc values the langmuir volumes of these samples at 60 c range from 0 47 cm3 g rock to 5 96 cm3 g rock and are positively correlated with toc values which on the one hand confirms the toc control on methane adsorption capacity and on the other hand also suggests a weak control of thermal maturity on methane adsorption capacity at overmature stages although both specific surface area and specific micropore volume are positively correlated with methane adsorption capacity the latter seems to have a stronger effect and the specific micropore volume determined from subcritical co2 adsorption may be considered as a proxy for the volume of adsorbed methane in dry shales for the extrapolation of measured methane excess adsorption isotherms to geological conditions the use of a constant or varying langmuir volume makes no significant difference with respect to the methane storage capacity of shales when the density of the adsorbed methane is allowed to change with temperature however the absolute methane adsorption quantity at subsurface is obviously dependent on the use of a constant or varying langmuir volume which subsequently affects the estimation of the relative percentages of adsorbed and free methane

simple kinetic models of petroleum formation part ii oil gas cracking kinetic schemes describing oil gas cracking are a required component of models which predict the masses compositions and phases of petroleum expelled from source rocks an additional application is in predicting the temperature zone over which reservoired oil deposits will be degraded to gas this simple first order kinetic model calibrated on closed system laboratory pyrolysis of 16 different source rock samples describes the bulk conversion of oil c6 molecular range to gas c1 5 molecular range cracking rates vary markedly between samples depending on the saturate to aromatic ratio of the generated oil the initial hydrogen index hl0 of the sample taken as an indirect measure of the saturate to aromatic ratio of the oil it generates correlates strongly with optimized rate constants for oil cracking in individual samples thus cracking rates are predictable using a simple routinely performed geochemical screening measurement source rocks with high hl0 tend to generate saturate rich oils with a high mean activation energy and a tight distribution of bond energies which crack relatively slowly over a high but relatively narrow temperature range source rocks with low hl0 generate aromatic rich oils with a low mean activation energy and a broad distribution of bond energies which crack relatively rapidly over a lower but relatively wide temperature range this is an important contributing factor in the observed gas proneness of type iii source rocks with low hl0 the projected cracking window defined limits at 10 90 of initial oil degraded reference heating rate 2 c ma 1 varies from 155 to 205 c in very high quality source rocks hl0 600 mg g c 1 to 115 205 c in very poor quality source rocks hl0 50 mg g c 1 an order of magnitude increase decrease in heating rate elevates depresses these temperature windows by ca 15 c the extrapolations to the geological subsurface are subject to a confidence limit no better than 7 c extrapolation to the reservoir environment requires caution because kerogen an important potential catalyst and hydrogen donor allowing 100 cracking efficiency in the source rock is absent furthermore fractionation during expulsion causes saturate enrichment of expelled ultimately reservoired oils thus in reservoir cracking should be at least as slow as cracking in good quality source rocks and coke or pyrobitumen formation is needed to conserve the hydrogen balance a case history based on deep petroleum pools of the uk central north sea confirms these projections demonstrating no positive evidence of significant in reservoir cracking at temperatures as least as high as 174 c and perhaps even 195 c previous studies have overestimated the importance of in reservoir cracking future studies aiming to predict petroleum composition in traps should concentrate on understanding the charge composition expelled from the kitchen

differentiated planetesimal impacts into a terrestrial magma ocean fate of the iron core abstract the abundance of moderately siderophile elements iron loving e g co ni in the earth s mantle is 10 to 100 times larger than predicted by chemical equilibrium between silicate melt and iron at low pressure but it does match expectation for equilibrium at high pressure and temperature recent studies of differentiated planetesimal impacts assume that planetesimal cores survive the impact intact as concentrated masses that passively settle from a zero initial velocity and undergo turbulent entrainment in a global magma ocean under these conditions cores greater than 10 km in diameter do not fully mix without a sufficiently deep magma ocean we have performed hydrocode simulations that revise this assumption and yield a clearer picture of the impact process for differentiated planetesimals possessing iron cores with radius 100 km that impact into magma oceans the impact process strips away the silicate mantle of the planetesimal and then stretches the iron core dispersing the liquid iron into a much larger volume of the underlying liquid silicate mantle lagrangian tracer particles track the initially intact iron core as the impact stretches and disperses the core the final displacement distance of initially closest tracer pairs gives a metric of core stretching the statistics of stretching imply mixing that separates the iron core into sheets ligaments and smaller fragments on a scale of 10 km or less the impact dispersed core fragments undergo further mixing through turbulent entrainment as the molten iron fragments rain through the magma ocean and settle deeper into the planet our results thus support the idea that iron in the cores of even large differentiated planetesimals can chemically equilibrate deep in a terrestrial magma ocean

investigation of pore structure and fractal characteristics of organic rich shale reservoirs a case study of lower cambrian qiongzhusi formation in malong block of eastern yunnan province south china abstract in order to study pore structure and fractal characteristics of the organic rich marine shale fourteen shale samples from lower cambrian qiongzhusi formation in malong block of eastern yunnan province were investigated by organic geochemical analysis total organic carbon content analysis and thermal maturity analysis x ray diffraction xrd analysis porosity and permeability tests field emission scanning electron microscopy fe sem low pressure nitrogen adsorption and methane adsorption experiments fractal dimensions d 1 and d 2 at relative pressure of 0 0 5 and 0 5 1 respectively were obtained from the nitrogen adsorption data using the fractal frenkel halsey hill fhh method not only have the relationships among pore structure parameters of shale the relationships between toc content mineral compositions pore structure parameters and fractal dimensions been discussed but also the significance of two fractal dimensions d 1 and d 2 and the impact of fractal dimensions on adsorption capacity have been investigated the results showed that fourteen shale samples have toc content ranging from 1 25 to 7 72 two fractal dimensions both increase with the increasing toc content and gradually come to a standstill the curves present the shape of parabola the major mineralogical compositions of shales are quartz and clay minerals the quartz contents are between 25 5 and 42 7 the clay contents are between 26 6 and 44 2 fractal dimension d 1 has a negative correlation with quartz contents and a positive correlation with clay minerals contents but fractal dimension d 2 has no apparent relationship with quartz and clay minerals contents the specific surface area is in the range of 4 98 m 2 g 19 66 m 2 g the total pore volume is between 0 00479 cm 3 g and 0 01765 cm 3 g and the average pore diameter is between 3 37 nm and 6 02 nm two fractal dimensions increase with the increasing surface area and pore volume and also increase with the decreasing average pore diameter because of the complicated pore surface and structure of small pores further investigation indicates that d 1 represents fractal characteristics from the irregular pore surface while d 2 represents fractal characteristics related to the complicated pore structure and shale samples with larger fractal dimensions have higher methane adsorption capacity therefore fractal analysis is helpful to have a better understanding of pore structure and adsorption capacity of marine shale

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

orogen transverse tectonic window in the eastern himalayan fold belt a superposed buckling model abstract the eastern lesser himalayan fold thrust belt is punctuated by a row of orogen transverse domal tectonic windows to evaluate their origin a variety of thrust stack models have been proposed assuming that the crustal shortening occurred dominantly by brittle deformations however the rangit window rw in the darjeeling sikkim himalaya dsh shows unequivocal structural imprints of ductile deformations of multiple episodes based on new structural maps coupled with outcrop scale field observations we recognize at least four major episodes of folding in the litho tectonic units of dsh the last episode has produced regionally orogen transverse upright folds f 4 the interference of which with the third generation f 3 orogen parallel folds has shaped the large scale structural patterns in dsh we propose a new genetic model for the rw invoking the mechanics of superposed buckling in the mechanically stratified litho tectonic systems we substantiate this superposed buckling model with results obtained from analogue experiments the model explains contrasting f 3 f 4 interferences in the lesser himalayan sequence lhs the lower order terrain scale folds have undergone superposed buckling in mode 1 producing large scale domes and basins whereas the rw occurs as a relatively higher order dome nested in the first order tista dome the gondwana and the proterozoic rocks within the rw underwent superposed buckling in modes 3 and 4 leading to type 2 fold interferences as evident from their structural patterns

experiments on turbulent metal silicate mixing in a magma ocean we compare the results of laboratory fluid dynamics experiments with theoretical models of turbulent entrainment in two phase buoyant plumes and thermals to estimate the amount of mixing between the iron core of a planetesimal or planetary embryo and the molten silicates in a magma pool formed by its impact with a growing planet during accretion we demonstrate experimentally that turbulent plumes in immiscible fluids fragment into droplets and that the envelope of the droplet distribution is indistinguishable from the envelope of a turbulent plume in a single phase fluid under the same dynamical conditions implying that turbulent entrainment concepts are applicable to immiscible fluids mixing a series of experiments are made on the time evolution of a two phase turbulent thermal representing a planetesimal core falling under its own negative buoyancy in a spherical fluid representing an impact produced magma pool two stages of mixing are observed in these experiments the first corresponding to turbulent entrainment during free fall of the thermal the second corresponding to entrainment in turbulent gravity currents that form after the thermal reaches the base of the magma pool we demonstrate that the amount of mixing between metals and silicate liquids in a magma pool depends on the rouse number of the metal fragments and increases rapidly with the radius of the proto planet we derive a similarity model for metal silicate mixing in a spherical magma pool assuming a constant entrainment coefficient for the turbulent liquid metal phase this model supports our experimental finding that a small metal core of an impactor will become diluted i e mix within a deep magma pool but a large impacting core will not fully dilute before reaching the base of the magma pool

geometry and timing of mesozoic deformation in the western part of the xuefeng tectonic belt south china implications for intra continental deformation abstract the xuefeng tectonic belt is an important intraplate structural system in the south china block its west margin is up to 1300 km away the present day continental margin and the mesozoic structural trends in this belt are perpendicular to and have no correlation with the triassic qinling dabie orogenic belt this belt provides important clues for understanding the mechanism of intraplate deformation and the tectonic history of south china we identified two generations of folding with different strike directions in the xuefeng tectonic belt based on the youngest folding involved strata and their overprinting relationship the early one is ne striking overprinted by the n s striking folds both during late jurassic and late cretaceous thrust faults in the xuefeng tectonic belt mainly show top to west thrust movement which is approximately coeval with the n s striking folding the thrust fault system can be divided into three zones the root zone with steep thrusts the middle zone characterized by imbricate thrusts and the frontal zone with a few shallow thrusts in addition two generations of strike slip faults with different structural trends have been identified e w striking strike slip faults showing dextral transpression and ne striking strike slip faults with sinistral offset and controlling the upper cretaceous basins according to regional geological relationship and structural overprinting we interpret that the e w trending strike slip faults formed in the first stage whereas the ne striking strike slip faults formed later during an e w oriented compressional event therefore the principal stress direction varies from nw se to e w

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

heterogeneous delivery of silicate and metal to the earth by large planetesimals after the moon s formation earth experienced a protracted bombardment by leftover planetesimals the mass delivered during this stage of late accretion has been estimated to be approximately 0 5 of earth s present mass based on highly siderophile element concentrations in the earth s mantle and the assumption that all highly siderophile elements delivered by impacts were retained in the mantle however late accretion may have involved mostly large 1 500 km in diameter and therefore differentiated projectiles in which highly siderophile elements were sequestered primarily in metallic cores here we present smoothed particle hydrodynamics impact simulations that show that substantial portions of a large planetesimal s core may descend to the earth s core or escape accretion entirely both outcomes reduce the delivery of highly siderophile elements to the earth s mantle and imply a late accretion mass that may be two to five times greater than previously thought further we demonstrate that projectile material can be concentrated within localized domains of earth s mantle producing both positive and negative 182w isotopic anomalies of the order of 10 to 100 ppm in this scenario some isotopic anomalies observed in terrestrial rocks can be explained as products of collisions after moon formation

characteristics of molecular nitrogen generation from overmature black shales in south china preliminary implications from pyrolysis experiments abstract high content of molecular nitrogen n2 is one of the natural gas exploration risks in petroliferous basins where black shales act as source rocks of either hydrocarbon gas or molecular nitrogen in this study two overmature and one low maturity shale samples and their kerogens were investigated to determine the generation characteristics of molecular nitrogen as well as methane and the differences in the release processes of inorganic nitrogen fixed in ammonium bearing minerals and organic nitrogen bound in kerogen the results illustrate that with increasing pyrolysis temperature the yield of methane first increases and then decreases with an inflection temperature of 650 c eqvro 3 4 whereas the yield of molecular nitrogen shows a continuous increase throughout the pyrolysis experiment the molecular nitrogen during the stage of methane generation i e eqvro 3 4 the results also reveal that at the experimental maxima of thermal maturity eqvro 4 9 the generation potential of inorganic molecular nitrogen mg g ninorg is much lower than that of organic molecular nitrogen mg g norg indicating that in our experiments the organic nitrogen in kerogen is more easily to be converted into molecular nitrogen than the inorganic nitrogen in ammonium bearing minerals all these results indicate that molecular nitrogen content in shale gas may change dramatically during thermal evolution and source rocks with exceptionally high maturity and high abundance of organic nitrogen likely lead to a high molecular nitrogen risk particularly in regions of poor preservation conditions of shale gas which may be the main reasons for the high molecular nitrogen content in the lower cambrian shale gas in south china

the methane sorption capacity of paleozoic shales from the sichuan basin china the methane sorption capacities of paleozoic shales from the sichuan basin were investigated the primary results show they have sorption capacities ranging between 0 94 and 4 29 cm3 grock at stp comparable to the sorption capacity 1 27 2 41 cm3 grock at stp of barnett shale however the sorption isotherms indicate that most of the sichuan basin shales would reach their approximate sorption equilibrium at 3 4 mpa in contrast to the continuously upward trend of north american shales a general positive relationship between toc content and methane sorption capacity indicates that toc content is the major controlling factor for the methane sorption of the sichuan shales a negative relationship between the clay mineral content and the sorption capacity of these shales may suggest that clay minerals play an insignificant role in the methane sorption of these paleozoic shales sorption capacities and variation ranges are generally ordered as to geological age viz cambrian silurian permian

geochemical characteristics of marine and terrestrial shale gas in china abstract although the annual production of shale gas in china was 13 10 8 m 3 in 2014 a systematic study on geochemical and isotopic characteristics of these unconventional gases has not been well addressed in the present study almost all shale gas samples available in china including marine shale gas from the wufeng longmaxi formation in the sichuan basin o 3 w s 1 l and terrestrial shale gas from chang 7 member t 3 y 7 in the ordos basin were collected and analyzed for their geochemical and isotopic compositions the shale gas from the wufeng longmaxi shale is dry gas with an average methane content of 98 38 and records a highest content of ch 4 in the world 99 59 which is consistent with the very high thermal maturity levels of the gas shales that have equivalent vitrinite reflectance eqvro values between 2 4 and 3 6 the 13 c 1 values are correspondingly heavy and record a heaviest 13 c 1 values 26 7 for the shale gases found in the world as well the average values of 13 c 1 13 c 2 and 13 c 3 for the wufeng longmaxi shale gas are 31 3 35 6 and 47 2 respectively displaying a complete carbon isotopic reversal i e 13 c 1 13 c 2 13 c 3 2 h ch4 and 2 h c2h6 has an average value of 148 and 173 respectively also yielding a hydrogen isotopic reversal i e 2 h ch4 2 h c2h6 the chang 7 shale has an average toc content of 13 81 with vitrinite reflectance vro values between 0 7 and 1 2 the chang 7 shale gas is wet gas with an average methane content of 84 90 and is rich in heavy gaseous hydrocarbons c 2 c 5 the respective values of 13 c 1 13 c 2 and 13 c 3 are 48 7 36 4 and 31 3 displaying a positive carbon isotopic distribution pattern i e 13 c 1 13 c 2 13 c 3 the average 2 h ch4 2 h c2h6 and 2 h c3h8 values are 256 244 and 188 respectively and are characterized by a positive distribution pattern i e 2 h ch4 2 h c2h6 2 h c3h8 the differences in gas wetness and carbon and hydrogen isotopic distribution patterns between the shale gases from the wufeng longmaxi and chang 7 shale are attributed to variations in thermal maturity levels co 2 is present in low content in both the wufeng longmaxi and chang 7 shale gases mostly less than 1 13 c values for the co 2 in the wufeng longmaxi formation are between 8 9 and 9 2 indicating an inorganic origin from the cracking of carbonate mineral in the shales under high temperatures in contrast 13 c values of the co 2 in the chang 7 shale gas range from 8 2 to 22 7 indicating an organic origin from the thermal degradation of organic matter helium in both the wufeng longmaxi and chang 7 shale gases is dominantly of curst origin in terms of their r ra ratios that vary from 0 01 to 0 08 positive carbon isotopic distribution pattern is typical of primitive thermogenic gas however it can be converted into complete or partial carbon isotopic reversal patterns due to secondary alteration the causes that yield carbon isotopic reversal include 1 mixing of gases with the same source but different thermal maturity levels 2 secondary cracking of oil or wet gas 3 formation water involved reactions 4 gas diffusion and 5 carbon isotope exchange between alkane gases at high temperature among them carbon isotopic exchange between alkane gases at high temperature is a key factor nine plots have been drawn based on the shale gases from china usa and canada among them the plot of 13 c 2 versus wetness demonstrates a lying s shape with two inflection points on the gas wetness axis the wetness value of 1 4 represents a critical point from pyrolytic gas primary cracking gas to cracking gas secondary cracking gas and whereas the wetness value of 6 marks the end of oil generation on the diagram of wetness versus 13 c shale gases with wetness values greater than 1 6 are characterized by positive carbon isotopic distribution pattern whereas a complete or partial carbon isotopic reversals are observed for shale gases with wetness values less than 1 6

quantification of principal horizontal stresses inside a tunnel an application of fracture induced electromagnetic radiation femr technique in the darjeeling sikkim himalayas abstract characterization of recent stresses delineation of the locations of active faults landslide prone slip planes and forecasting earthquakes are some of the emerging applications of the fracture induced electromagnetic radiation femr technique it is believed that such radiation is polarized along the direction of maximum compression and proportional to the maximum applied shear stress in this paper we have demonstrated the use of the femr technique to calculate the magnitude and directions of principal horizontal stresses inside a tunnel of 240 m length over a hilly road between jorethang and mayong near the village of miyong in sikkim india by taking 11 cross sectional measurements using a portable femr recording device called angel m although a reverse stress regime is obvious and established over the himalayas the results show a normal stress regime prevailing over this shallow near surface region of the tunnel and the direction of maximum shear stress changes along the tunnel length the results were explained with the aid of a simple clay analogue model where normal reactivation of a thrust plane with changing dips was simulated with this communication we hope to encourage scientists and engineers to deploy the femr technique which is lesser known but quicker non destructive cheaper and more accessible than conventional methods in evaluating tunnel safety by calculating shallow stresses locally modified inside a tunnel

the organic matter distribution and methane capacity of the lower cretaceous strata of northeastern british columbia canada abstract the methane sorption capacity of a succession of sandstone siltstone shale and coal from the lower cretaceous fort st john group of northeastern british columbia was investigated average organic matter om content for all formations is 2 3 wt with a minimum of 0 6 wt and maximum of 10 1 wt the methane sorption capacity ranges between 0 19 and 2 74 cm3 g at 6 mpa and at 30 c total gas capacity free and sorbed gas ranges between 2 2 and 16 6 cm3 g at 6 mpa micropore volumes range between 0 43 and 1 69 cm3 100 g a positive correlation exists between the om content micropore volume and the methane capacity of shales shales with high methane capacities have either high contents of inertodetrinite or vitrinite moisture content shows a positive relationship with om content micropore volume and methane capacity the negative relationship between moisture and surface area derived from n2 adsorption suggests the moisture is located within the microporosity of the om and also explains the positive relationship between methane capacity and moisture the high inertodetrinite and vitrinite contents correlate with sea level regressions that delivered terrestrial om from coastal plains located south of the study area into the basin

models of shale gas storage capacity during burial and uplift application to wufeng longmaxi shales in the fuling shale gas field abstract marine shales in south china such as the upper ordovician wufeng o3w and lower silurian longmaxi s1l shales have generally experienced a long term burial and rapid uplift process the variations of temperature and pressure caused by the complex tectonic movements have significant effects on the shale gas storage capacities based on the supercritical dubinin radushkevich sdr equation and high pressure methane ch4 adsorption experiments equations to calculate the shale gas storage capacities under geological conditions were established in this work using the derived equations the gas storage capacities in two basic geological processes were modeled namely the burial process which has an increased gas content and the uplift process which has a constant gas content the two basic models were applied to investigate the evolution of the shale gas content of the o3w s1l shales in the jy 1 well in the fuling shale gas field sichuan basin south china geological models of the gas storage capacities of the shales during burial show that the storage capacity of adsorbed gas scadsorbed gas initially rapidly increases and then slowly decreases with the increasing burial depth the storage capacities of free gas scfree gas and total gas sctotal gas increase with the increasing burial depth compared with scadsorbed gas scfree gas significantly increases as the pore pressure increases such an obvious difference implies that free gas is the predominant gas form in the initial stage of shale gas production during uplift the gas content remains unchanged resulting in a linear decrease in scfree gas and a linear increase in sctotal gas nonetheless scfree gas during uplift is still higher than scfree gas during burial at the same burial depth the modeling of the shale gas content evolution of the o3w s1l shales in the jy 1 shows that from the maximum burial depth of 6200 m to the present day burial depth of 2415 m the free gas content declines by 0 89 m3 t from 2 30 m3 t to 1 41 m3 t while the adsorbed gas content only increases by 0 58 m3 t from 0 47 m3 t to 1 05 m3 t this difference indicates that only a small amount 0 31 m3 t of shale gas was lost during the uplift and that most 0 58 m3 t of the reduced free gas was converted into adsorbed gas a unique aspect of this study is that we illustrate how adsorbed and free gas are converted when the total gas content remains constant moreover the two basic geological models established in this study can also be applied to other shale gas systems with complex tectonic movements

in situ stress amplification due to geological factors in tunnels the case of pajares tunnels spain geological and geomechanical anisotropies can significantly increase the magnitude of in situ stress in a rock mass excavated for tunnelling purposes four tunnels for the new high speed railway lines in pajares in the cantabrian mountains n spain were analysed and significant deformations was found to have occurred in forty specific zones of these tunnels during excavation requiring much more support than envisaged before construction local factors influencing in situ stress have been identified in these zones of the tunnels related to geological structures of high compressive tectonic stress regimes including thrust faults folds with steep flank dip orwith geomechanical anisotropies in contact zones between rock formations of different strengths amethodological procedurewas applied to four tunnels to assess the influence of the geological anisotropies on the insitu stress magnitudes this procedure is based on the analysis of tunnel deformations and the support pressure needed to stabilise the excavations affected by geological anisotropies the increase of in situ stress due to local factors is expressed by the stress amplification factor saf defined by the ratio between the k h v local value estimated in a particular rock mass tunnel zone and the mean k h v regional value representative of the whole rock mass tunnel kregional was estimated from hydrofracture tests and from the tsi index klocal was calculated from the back analysis of the support pressure required to stabilise the deformed tunnel zones saf values for the forty specific tunnel zones ranged from 1 1 to 2 5 this significant increase in the magnitude of in situ stress emphasises the influence of geological and geomechanical anisotropies in tunnel stability and support design the results provide a quantitative approach for assessing structural stresses in rock masses for tunnelling excavations

hf w evidence for rapid differentiation of iron meteorite parent bodies abstract new high precision w isotope data on iron meteorites are presented that provide important constraints on the timing of silicate metal segregation in planetesimals magmatic iron meteorites all have e 182 w within error or less radiogenic than initial e 182 w estimated by studies of chondritic meteorites at face value this implies that iron meteorites are as old and older than refractory calcium aluminium rich inclusions cai which are widely thought to be the oldest solar system objects moreover different meteorites from the same magmatic groups believed to be derived from the same planetissimal core display a range of e 182 w we suggest that the paradoxical e 182 w values more negative than initial solar system initial ssi are most readily explained as a result of secondary spallation reactions with cosmic rays during transit between parent body and the earth this is supported by the most negative e 182 w being found in meteorites with the oldest exposure ages and the magnitude of the effect is shown to be consistent with known nuclear reactions on the other hand it is also striking that none of the magmatic iron group meteorites have e 182 w analyses outside error more radiogenic than the estimated solar system initial ratio this suggests that core formation in parent bodies of magmatic iron meteorites occurred 1 5 myr after the formation age of cai y amelin a n krot i d hutcheon and a a ulyanov lead isotopic ages of chondrules and calcium aluminum inclusions science 297 1678 1683 2002 this extremely early metal silicate differentiation is coeval with the first chondrules m bizzarro j a baker and h haack mg isotope evidence for contemporaneous formation of chondrules and refractory inclusions nature 431 275 278 2004 a n krot y amelin p cassen and a meibom young chondrules in cb chondrites from a giant impact in the early solar system nature 436 989 992 2005 formation of later chondrules and hence the parent bodies of some chondritic meteorites must therefore have occurred in the presence of planetesimals large enough to possess iron cores we conclude that early planetary accretion and differentiation was sufficiently fast for 26 al decay to be an important heat source non magmatic iron meteorites however display more radiogenic and varied w isotope signatures this is in keeping with them being generated later by impact melting during which the metal partially re equilibrated with the then more radiogenic silicate fraction

porosity of devonian and mississippian new albany shale across a maturation gradient insights from organic petrology gas adsorption and mercury intrusion the evolution of porosity in shales with increasing maturity was examined in a suite of five new albany shale samples spanning a maturity range from immature vitrinite reflectance ro 0 35 to postmature ro 1 41 devonian to lower mississippian new albany shale samples from the illinois basin used in this study contain marine type ii kerogen having total organic carbon contents from 1 2 to 13 0 wt organic petrology co2 and n2 low pressure adsorption and mercury intrusion capillary pressure techniques were used to quantify pore volumes pore sizes and pore size distributions increasing maturity of the new albany shale is paralleled by many changes in the characteristics of porosity the total porosity of 9 1 vol in immature new albany shale decreases to 1 5 vol in the late mature sample whereas total pore volumes decrease from 0 0365 to 0 0059 cm3 g in the same sequence reversing the trend at even higher maturity the postmature new albany shale exhibits higher porosity and larger total pore volumes compared to the late mature sample with increasing maturity changes in total porosity and total pore volumes are accompanied by changes in pore size distributions and relative proportions of micropores mesopores and macropores porosity related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition but maturity exerts the dominant control upon these characteristics we conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences

pore structure of cambrian shales from the sichuan basin in china and implications to gas storage abstract the microstructure of black siliceous shale from the lower cambrian niutitang formation sichuan basin in china was investigated by the combination of field emission scanning electron microscope fe sem and argon ion beam milling the nanometer to micrometer scale pore systems of shales are an important control on gas storage and fluid migration in this paper the organic porosity in shale samples within oil and gas window has been investigated and the formation mechanism and diagenetic evolution of nanopores have been researched fe sem reveals five pore types that are classified as follows organic nanopores pores in clay minerals nanopores of framework minerals intragranular pores in microfossils and microfractures numerous organic nanopores are observed in shales in the gas window whereas microfractures can be seen within the organic matter of shales in the oil window microfractures in oil window shales could be attributed to pressure buildup in the organic matter when incompressible liquid hydrocarbon are generated and the orientation of microfractures is probably parallel to the bedding and strength anisotropy of the formation pores in clay minerals are always associated with the framework of clay flakes and develop around rigid mineral grains because the pressure shadows of mineral grains protect pores from collapse and the increasing of silt content would lead to an increase in pressure shadows and improve porosity nanopores of rock framework are probably related to dissolution by acidic fluids from hydrocarbon generation and the dissolution related pores promote permeability of shales porosity in the low toc low thermal maturity shales contrast greatly with those of high toc high thermal maturity shales while the high toc shales contain abundant organic microporosity the inorganic pores can contribute a lot to the porosity of the low toc shales

use of electromagnetic radiation for potential forecast of earthquakes a forecast of an earthquake should identify the first stages of earthquake development nucleation and stick slip we show that a forecast cannot be achieved by seismic measurements due to their high attenuation but can be obtained by judicial filtering of electromagnetic radiation results show that electromagnetic radiation emitted from fractures femr during the early stages of an earthquake is less attenuated than seismic measurements due to the high frequencies involved but could be cluttered by external noise based on our previous studies an analysis of femr constructed on a profile of individual pulses can remove part of the clatter

formation of a solid inner core during the accretion of earth the formation of an inner core during the accretion of earth is investigated using self gravitating and compressible earth models formed by accreting a total of 25 or 50 moon to mars size planetary embryos the impact of an embryo heats the proto earth s interior differentially more below the impact site than elsewhere the rotating core dynamically overturns and stratifies shortly after each impact creating a spherically symmetric and radially increasing temperature distribution relative to an adiabatic profile merging of an embryo to the proto earth increases the lithostatic pressure that results in compressional temperature increase while further enhances the melting temperature of the core causing solidification a total of 36 thermal evolution models of the growing proto earth s core are calculated to investigate effects of major physical parameters no solidification is considered in the first 21 models where modified two body escape velocities are used as the impact velocities of the embryos at the end of accretion temperatures in the upper part of the core are significantly different among these models whereas temperatures in the deeper parts are similar the core solidification considered in the remaining 15 models where impact velocities higher than the modified two body escape velocities are adopted drastically changes the temperature distribution in the deeper parts of the core all of the models produce partially solidified stiff inner cores 1000 2100 km in radius at the end of accretion where the solid fraction is larger than 50 the innermost of the stiff inner cores are completely solidified to radii 250 1500 km

mechanisms of shale gas storage implications for shale gas exploration in china this article reviews the mechanisms of shale gas storage and discusses the major risks or uncertainties for shale gas exploration in china at a given temperature and pressure the gas sorption capacities of organic rich shales are primarily controlled by the organic matter richness but may be significantly influenced by the type and maturity of the organic matter mineral composition especially clay content moisture content pore volume and structure resulting in different ratios of gas sorption capacity gsc to total organic carbon content for different shales in laboratory experiments the gsc of organic rich shales increases with increasing pressure and decreases with increasing temperature under geologic conditions assuming hydrostatic pressure gradient and constant thermal gradient the gsc increases initially with depth due to the predominating effect of pressure passes through a maximum and then decreases because of the influence of increasing temperature at greater depth this pattern of variation is quite similar to that observed for coals and is of great significance for understanding the changes in gsc of organic rich shales over geologic time as a function of burial history at an elevated temperature and pressure and with the presence of moisture the gas sorption capacities of organic rich shales are quite low as a result adsorption alone cannot protect sufficient gas for high maturity organic rich shales to be commercial gas reservoirs two models are proposed to predict the variation of gsc and total gas content over geologic time as a function of burial history high contents of free gas in organic rich shales can be preserved in relatively closed systems loss of free gas during postgeneration uplift and erosion may result in undersaturation the total gas contents lower than the sorption capacity and is the major risk for gas exploration in marine organic rich shales in china

characterization of methane adsorption on overmature lower silurian upper ordovician shales in sichuan basin southwest china experimental results and geological implications abstract a series of methane adsorption isotherms were measured at 35 4 c 50 6 c and 65 4 c at pressures up to 15 0 mpa for eight dried overmature lower silurian upper ordovician shale samples collected from the sichuan basin with toc values in the range of 1 87 5 74 the measured maxima of excess adsorption capacity of methane range from 1 25 to 2 50 cm 3 g rock at 65 4 c the maxima are slightly enhanced at 35 4 c but all are positively correlated with total organic carbon toc both the supercritical dubinin radushkevich sdr and langmuir based excess adsorption models were found to represent the experimental excess adsorption isotherms equally well within the experimental range the temperature dependent densities of adsorbed methane resulting from the parameter fit of the sdr based excess adsorption model are in the range of 297 415 mg cm 3 for the langmuir based excess adsorption model the adjusted densities range from 386 mg cm 3 to 1027 mg cm 3 and most of them are much larger than the liquid density of methane at its boiling point 424 mg cm 3 nevertheless the maxima of absolute methane adsorption capacity fitted by both models are not significantly different and are linearly correlated one of the contributors to the uncertainty of the gas in place estimation in geological conditions is the inconsistent utilization of experimental excess sorption data as absolute sorption values particularly at high pressures however the choice of adsorption model itself langmuir or sdr based and the fitting procedure assuming either constant or temperature dependent adsorbed phase density and maximum sorption capacity do not significantly affect the estimated gips for the geological system studied here with depths of less than 4000 m

the influence of pre existing thrust faults on normal fault geometry in nature and in experiments relations between normal faults and pre existing thrust faults are classically described in terms of three basic situations normal faults can cross cut thrust faults they can branch out from thrust faults at depth on a de collement level or they can entirely reactivate thrust planes the mechanical aspects of these types of interaction were studied by analogue modelling in which sand simulates the brittle rocks and silicone putty an interlayered de collement the models underwent compression producing thrust faults with variable dips followed by extension three possible ways of interaction are described here a no interaction occurs in the case of low dip thrust faults 32 1 and normal faults are developed independently displaying a listric geometry b branching at depth on the de collement level occurs when dip of the thrust faults reaches 32 1 in this case the dip of the normal faults whose geometry becomes planar decreases with increasing thrust dip we suggest that this change in dip of normal faults depends upon the rotation of stress tensor axes along the pre existing fault zone where a drop in the friction coefficient is likely to occur c reactivation occurs in brittle material when dip of the pre existing fault exceeds 41 1

extensional reactivation of thrust faults accompanied by coseismic surface rupture southwestern wyoming and north central utah extensional reactivation of thrust faults north of the uinta mountains in utah and wyoming is accompanied by quaternary surface faulting tilting and monoclinal folding the 40 km long bear river fault zone consists of down to the west right stepping en echelon scarps each about 3 0 to 3 5 km in length striking n20 w to n20 e scarp derived colluvial deposits record two holocene surface ruptures with net vertical tectonic displacements ranging from 5 m per event west 1989 in press radiocarbon ages indicate surface faulting events occurred at about 4 6 ka and 2 4 ka the length of surface rupture and net slip per event in the bear river fault zone imply a seismic potential comparable to the lost river fault hebgen lake fault and the wasatch fault zone a late quaternary normal scarp is also coincident with the leading edge of the absaroka thrust fault 7 2 km west of the bear river fault zone scarp derived colluvial deposits record one surface faulting event over a length of at least 5 0 km the age of surface rupture is coeval with the bear river fault zone 2 4 ka normal faults displacing pleistocene surfaces deposits and tectonic tilt indicate that the hogsback thrust east of the bear river fault zone was reactivated in a normal sense but now may be inactive due to subsequent development of the bear river fault zone cumulative normal throw of 200 m on the hogsback fault may be responsible for postulated tectonic separation of the bear river and green river drainage basins neotectonic deformation results from east west extension superposed on the hogsback and absaroka thrust plates extensional reactivation of thrust faults caused propagation of new normal faults over stress points particularly at the hogsback ramp to flat transition and at the thrust leading edges the ages of surface rupture and cumulative throws indicate normal reactivation of the hogsback and absaroka thrusts and propagation of the intervening bear river fault zone proceeded from east to west opposite initial development of the thrusts in late cretaceous to paleocene time normally reactivated thrust faults and propagation of listric normal faults accompanied by surface rupture have significant implications for the tectonic seismogenic development of the eastern basin and range transition zone

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

regional stress field as determined from electromagnetic radiation in a tunnel abstract the paper presents the results of electromagnetic radiation emr measurements in the feuerberg tunnel in southwest germany emr is associated with small scale fracturing processes the measured numbers of emr impulses are shown to be proportional to shear stresses from the correlation of emr and shear stresses along the long axis of the tunnel orientations and magnitudes of the horizontal principal stresses are determined the major horizontal principal stress is 3 6 0 3 mpa and has an azimuth of 143 6 the minor principal horizontal stress is 2 1 0 3 mpa zones in the tunnel are located where low shear stresses occur because vertical overburden and horizontal stresses are equal in these zones also minimum radiation was detected a possible stress accumulation close to a fault is suggested by higher emr values in a part of the tunnel orientations and magnitudes of the horizontal principal stresses which are derived from the measurements of emr correlate well with conventional stress measurements it is suggested that the cross section measuring method described in the study is used to determine regional stress fields as well as to investigate endangered zones with high stresses in underground facilities which may be critical with regard to stability

pore characterization of organic rich lower cambrian shales in qiannan depression of guizhou province southwestern china abstract nine organic rich shale samples of lower cambrian black shales were collected from a recently drilled well in the qiannan depression guizhou province where they are widely distributed with shallower burial depth than in sichuan basin and their geochemistry and pore characterization were investigated the results show that the lower cambrian shales in qiannan depression are organic rich with toc content ranging from 2 81 to 12 9 thermally overmature with equivalent vitrinite reflectance values in the range of 2 92 3 25 and clay contents are high and range from 32 4 to 53 2 the samples have a total helium porosity ranging from 2 46 to 4 13 and total surface area in the range of 9 08 37 19 m2 g the estimated porosity in organic matters defined as the ratio of organic pores to the volume of total organic matters based on the plot of toc vs helium porosity is about 10 for the lower cambrian shales in qiannan depression and is far lower than that of the lower silurian shales 36 in and around sichan basin this indicates that either the organic pores in the lower cambrian shale samples have been more severely compacted than or they did not develop organic pores as abundantly as the lower silurian shales our studies also reveal that the micropore volumes determined by dubinin radushkevich dr equation is usually overestimated and this overestimation is closely related to the non micropore surface area of shales i e the surface area of meso and macro pores however the modified bet equation can remove this overestimation and be conveniently used to evaluate the micropore volumes surface area and the non micropore surface areas of micropore rich shales

geohazards of tunnel excavation in interbedded layers under high in situ stress abstract in situ stress is one of the most important parameters that affect rock mass stability during tunnel excavation high in situ stress may induce a series of geohazards such as rockburst in strong rock and squeezing in weak rock this paper presents a case study of a tunnel excavated using a tunnel boring machine across interbedded strong and weak rock layers under high in situ stress in pakistan to estimate the induced geohazards during tunnel excavation in situ stress was measured and the stability of the tunnel was analyzed using the finite element method in situ stress measured in the strong rock layers shows that the maximum compressive stress is very high and its direction is almost perpendicular to the tunnel axis using a simple analytical method stress distribution in weak layers was determined and the results show that the magnitude of the maximum compressive stress in the weak layers is much less than that in strong layers and the direction is almost parallel with the tunnel axis the fem simulation reveals that the redistributed stress due to the tunnel excavation is more concentrated in strong layers and less concentrated in weak layers both the initial in situ stress distribution and the stress redistribution after tunnel excavation predict geohazard in strong layers rather than in weak layers this point is consistent with the field records which indicated that rockbursts were frequent in the strong rock layers and no squeezing occurred in the weak rock layers

fractured shale gas systems the first commercial united states natural gas production 1821 came from an organic rich devonian shale in the appalachian basin understanding the geological and geochemical nature of organic shale formations and improving their gas producibility have subsequently been the challenge of millions of dollars worth of research since the 1970s shale gas systems essentially are continuous type biogenic predominant thermogenic or combined biogenic thermogenic gas accumulations characterized by widespread gas saturation subtle trapping mechanisms seals of variable lithology and relatively short hydrocarbon migration distances shale gas may be stored as free gas in natural fractures and intergranular porosity as gas sorbed onto kerogen and clay particle surfaces or as gas dissolved in kerogen and bitumen five united states shale formations that presently produce gas commercially exhibit an unexpectedly wide variation in the values of five key parameters thermal maturity expressed as vitrinite reflectance sorbed gas fraction reservoir thickness total organic carbon content and volume of gas in place the degree of natural fracture development in an otherwise low matrix permeability shale reservoir is a controlling factor in gas producibility to date unstimulated commercial production has been achievable in only a small proportion of shale wells those that intercept natural fracture networks in most other cases a successful shale gas well requires hydraulic stimulation together the devonian antrim shale of the michigan basin and devonian ohio shale of the appalachian basin accounted for about 84 of the total 380 bcf of shale gas produced in 1999 however annual gas production is steadily increasing from three other major organic shale formations that subsequently have been explored and developed the devonian new albany shale in the illinois basin the mississippian barnett shale in the fort worth basin and the cretaceous lewis shale in the san juan basin in the basins for which estimates have been made shale gas resources are substantial with in place volumes of 497 783 tcf the estimated technically recoverable resource exclusive of the lewis shale ranges from 31 to 76 tcf in both cases the ohio shale accounts for the largest share

geochemical characterization and methane adsorption capacity of overmature organic rich lower cambrian shales in northeast guizhou region southwest china abstract the niutitang shale lower cambrian is another set of organic rich shale in addition to the lower silurian longmaxi shale in southwest china in this study methane adsorption capacities of both whole rock and organic matter were investigated based on adsorption isotherms measured at various temperatures 40 120 c and pressures up to 35 0 mpa for eleven niutitang shale samples collected from northeast guizhou province the investigated samples cover a wide range of toc contents varying from 1 8 to 11 3 with an average equivalent vitrinite reflectance eqvro value of approximately 4 0 their bet specific surface areas and micropore volumes range from 11 1 to 26 2 m2 g rock and between 4 3 and 11 2 cm3 kg rock respectively both of which are positively correlated to toc content model fitted methane maximum absolute adsorption capacities n range from 1 80 to 5 85 cm3 g rock at 60 c and are found to largely increase with increasing toc this suggests that the toc control on methane adsorption capacity obtained by other authors for other shales with relative low thermal maturity levels may be extended to a very high thermal maturity level e g eqvro 4 0 the methane adsorption capacity of organic matter om in our shale samples however is somehow reduced as compared to the lower silurian longmaxi shale and other shales that display eqvro values smaller than 3 0 indicating thermal maturity may adversely affect methane adsorption capacity of shales when it evolves to be eqvro 4 0 nevertheless this reduction in adsorption capacity may be compensated by the very enrichment of om in the niutitang shale in addition a higher thermal maturity level results in a lower langmuir pressure value which makes it more difficult for methane desorption at reservoirs conditions the temperature dependency of adsorption parameters was also investigated which could be used to predict the changes of methane adsorption with burial depth under geological conditions beyond experimental temperature and pressure ranges

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

a re evaluation of metal diapir breakup and equilibration in terrestrial magma oceans abstract due to mechanisms such as impact heating early atmospheric thermal blanketing and radioactive heating the presence of at least one global magma ocean stage in the early histories of terrestrial planets seems unavoidable in such a context a key question to constrain the early thermo chemical evolution of the earth is how much iron diapirs provided by differentiated impactors emulsified during their sinking towards the bottom of an early magma ocean in the past years several workers have focused on this question using however various approaches and making different assumptions while most studies favor rapid breakup and equilibration of iron bodies during their sinking through the magma ocean recent work suggests that iron bodies of size comparable or greater than a few tens of kilometers may preserve most of their initial volume as they reach the bottom of a magma ocean therefore leading to metal silicate disequilibrium to clarify the discrepancies and the differences among studies i have conducted a series of numerical simulations and theoretical calculations to derive the conditions and the timing for the breakup of metal diapirs of any size sinking through a silicate magma ocean with a large range of plausible viscosity values the obtained breakup criterion is used to derive stable diapir sizes and their ability to equilibrate with the surrounding silicates i show that for plausible magma ocean viscosities diapirs with initial radii smaller than the thickness of a magma ocean rapidly break up into stable diapir sizes smaller than 0 2 m at which metal silicate equilibration is rapidly achieved

stress orientations found in north east germany differ from the west european trend knowledge about the acting stresses is of crucial importance for understanding the tectonics of a region data about the stress field in north eastern germany used to be very rare in general it was assumed that the orientation of the larger horizontal principal stress sh is similar to that found for western germany and central west europe i e nw se to check this several borehole logs of the late 1980s were analysed for information on the principal horizontal stress orientations they include four arm dipmeter and borehole televiewer data from 15 boreholes the depth range of our stress results reaches from 1500 to 6700 m they were compared to a few other data especially from hydraulic fracturing and to recent findings on the stresses in the northwest german basin in contrast to expectation sh derived from breakout orientations below the salt layers displayed n to ne orientation the latter was found at 10 locations spread over the ne german basin from berlin to the baltic sea from the polish border to the former border between east and west germany moreover this stress rotation in the subsaline formations seems to be the continuation of a trend found in the nw german basin

numerical study of multi period palaeotectonic stress fields in lower cambrian shale reservoirs and the prediction of fractures distribution a case study of the niutitang formation in feng gang no 3 block south china abstract fractures not only control the distribution of oil and gas reservoirs but also are key points in the research of oil and gas reservoir development programmes the tectonic fractures in the lower cambrian shale reservoirs in the feng gang no 3 block are effective reservoir spaces for hydrocarbon accumulation and these fractures are controlled by palaeotectonic stress fields therefore quantitatively predicting the development and distribution of tectonic fractures in the lower cambrian shale reservoir is important for the exploration and exploitation of shale gas in the feng gang no 3 block in the present study a reasonable geological mechanical and mathematical model of the study area was established based on the faults systems interpreted from seismic data fracture characteristics from drilling data uniaxial and triaxial compression tests and experiments on the acoustic emissions ae of rocks then a three dimensional 3 d finite element method is applied to simulate the palaeotectonic stress field with the superposition of the yanshan and himalayan movements and used to predict the fracture distribution the simulation results indicate that the maximum principal stress value within the study area ranged from 269 97 mpa to 281 18 mpa the minimum principal stress ranged from 58 29 mpa to 79 64 mpa and the shear stress value ranged from 91 05 mpa to 106 21 mpa the palaeotectonic stress field is controlled by the fault zone locations the fracture development zones are mainly controlled by the tectonic stress fields and are located around the faults at the end of the fault zones at the inflection point and at the intersection of the fault zones

geological models of gas in place of the longmaxi shale in southeast chongqing south china abstract gas in place gip is one of the primary controlling factors in shale gas production but studies examining gip have been lacking for the lower silurian longmaxi shale in south china in the present study a suite of longmaxi shale samples was collected from an exploratory well in southeast chongqing south china and the adsorption parameters were fitted using a supercritical dubinin radushkevich sdr model based on the high pressure methane adsorption experiment data for the samples the results show that the adsorbed phase density and the adsorbed gas capacity of the samples have a positive correlation with the content of total organic carbon toc but a negative correlation with temperature combined with the geological characteristics of the longmaxi shale in southeast chongqing gip models were constructed under three different fluid pressure conditions the absolute adsorbed amount of the samples increases and later decreases with increasing depth with a maximum corresponding to depths between 800 and 1200 m the fluid pressure coefficient has no obvious effect on the absolute adsorbed amount when burial depth is over 2000 m but controls the free gas content overpressure primarily increases the free gas content and thus increases the total gas content the free gas content of the longmaxi shale in the pengshui block is reduced to 47 58 of that in the fuling block which is the main reason for its low gas production further exploration of the longmaxi formation should be expanded to deeper burial shales in the eastern area of southeast chongqing