mechanical properties of shale gas reservoir rocks part 1 static and dynamic elastic properties and anisotropy abstractunderstanding the controls on the elastic properties of reservoir rocks is crucial for exploration and successful production from hydrocarbon reservoirs we studied the static and dynamic elastic properties of shale gas reservoir rocks from barnett haynesville eagle ford and fort st john shales through laboratory experiments the elastic properties of these rocks vary significantly between reservoirs and within a reservoir due to the wide variety of material composition and microstructures exhibited by these organic rich shales the static young s modulus and dynamic p and s wave moduli elastic parameters generally decrease monotonically with the clay plus kerogen content the variation of the elastic moduli can be explained in terms of the voigt and reuss limits predicted by end member components however the elastic properties of the shales are strongly anisotropic and the degree of anisotropy was found to correlate with the amount of clay and organic content as well as the shale fab

drained and undrained anisotropic elastic stiffness parameters equations that map drained to undrained elastic stiffness parameters in a cross anisotropic material are presented graphs of various anisotropic stiffness ratios are used to illustrate the important trends a new 2 d graph showing the elastic bound enables measured elastic parameters to be plotted which all lie well within it the 2 d graph enables uncoupled and incompressible materials to be shown plus materials with particular initial effective stress path slopes in an undrained triaxial test bounds more restrictive than the elastic one are also discussed and the likely ranges of various anisotropic stiffness ratios are presented in general undrained anisotropy is much less than drained that is closer to isotropic in undrained plane strain conditions vertical and horizontal moduli are found to be the same in drained plane strain conditions the ratios of the moduli are almost the same as the young s moduli

elastic anisotropy of tambo gneiss from promontogno switzerland a comparison of crystal orientation and microstructure based modelling and experimental measurements author s vasin rn kern h lokajicek t svitek t lehmann e mannes dc chaouche m wenk hr abstract the authors 2017 felsic and mafic gneisses constitute large proportions of the upper and lower continental crust gneisses often display high anisotropy of elastic properties associated with preferred orientations of sheet silicates here we study the elastic anisotropy of a sample of tambo gneiss from promontogno in the central alps we apply optical microscopy time of flight neutron diffraction neutron and x ray tomography to quantify mineral composition and microstructures and use them to construct self consistent models of elastic properties they are compared to results of ultrasonic measurements on a cube sample in a multi anvil apparatus and on a spherical sample in an apparatus that can measure velocities in multiple directions both methods provide similar results it is shown that models of microstructure derived elastic properties provide a good match with ultrasonic experiment results at pressures above 100 mpa at a pressure of 0 1 mpa the correspondence between the model and the experiment is worse this may be caused by an oversimplification of the model with respect to microfractures or uncertainties in the experimental determination of s wave velocities and elastic tensor inversion the study provides a basis to determine anisotropic elastic properties of rocks either by ultrasonic experiments or quantitative models based on microstructures this information can then be used for interpretation of seismic data of the crust

mechanical and petrophysical properties of north sea shales one of the problems when evaluating potential borehole stability problems in the drilling of hydrocarbon exploration and production wells is the lack of relevant data to describe the lithologies this relates in particular to the shales since these constitute most of the overburden and are also the most troublesome this paper presents a set of data from a variety of deeply cored shales from the north sea the shales have been extensively characterised and span a wide range of both petrophysical and mechanical properties depending on for example burial history and diagenesis special characteristics of shales have been tested and described including pore size distribution permeability anisotropy and temperature dependence appropriate procedures for sample handling testing and interpretation have been developed or modified from other related sciences

intrinsic elasticity of a textured transversely isotropic muscovite aggregate comparisons to the seismic anisotropy of schists and shales 1 the anisotropic properties of phyllosilicate rocks are investigated through the modeling of the pore free intrinsic elasticity of a textured muscovite aggregate the elastic constants were calculated for textures as defined using orientation distribution functions odfs ranging from perfectly aligned to completely random the odfs were described using a gaussian distribution the width of which is controlled by the standard deviation of the orientations of the crystal c axis with respect to the sample foliation plane under the assumption that the sample has hexagonal transversely isotropic symmetry the values were obtained using the widely used voigt reuss hill averaging techniques as well as the geometric mean average gma the gma is more physically meaningful in that it requires that the elastic constants determined in either the stiffness or the compliance domains be invertible comparisons between these different averages indicate that strictly the voigt and reuss values do not necessarily provide the limiting bounds as is expected for the isotropic case despite this some characteristics of the elastic wave p wave anisotropy are only weakly dependent on the averaging procedure employed the calculated elastic constants are converted to the anisotropic and parameters in order to allow for comparison to existing measurements in the literature however these intrinsic results are not intended to provide a measure of the properties of phyllites per se but to provide a reference against which more sophisticated models that incorporate porosity layering and composition may be constructed

ultrasonic velocity and anisotropy of hydrocarbon source rocks an experimental study of the physical properties of black kerogen rich shales also including maturation analysis scanning electron microscope sem observations and physical modeling revealed fairly peculiar petrophysical parameters specifically these rocks have very low porosity and density but most importantly both p and s ultrasonic velocities normal to bedding are extremely low whereas they are much higher parallel to bedding giving rise to a strong anisotropy even at high confining pressures we found that these parameters primarily reflect kerogen content microstructure and maturation level of these rocks we found also that microcracks inferred from ultrasonic velocity measurements occur only in mature shales these microcracks are parallel to the bedding plane and further enhance strong intrinsic anisotropy notably at low effective pressure our results show that on a small scale kerogen rich shales are transversely isotropic rocks and can be effectively modeled using the thin laye

fracture mechanical properties of carbonate and evaporite caprocks in sichuan basin china with implications for reservoir seal integrity abstract fracture development in reservoir rocks enhances the flow and transport properties of the petroleum system yet fracture in caprocks can significantly risk reservoir seal integrity over geological time scales the slow subcritical fracture propagation can contribute considerably to the fracture system development especially under reactive fluid environments during petroleum migration and accumulation using the double torsion technique we measure the subcritical fracture growth properties of carbonate and anhydrite caprock core samples in sichuan basin china under different environments of ambient air de ionized water and formation water experimental results show that the aqueous fluids significantly promote subcritical fracture growth 1 compared to ambient air the presence of aqueous fluids dramatically reduces both the fracture toughness kic and subcritical fracture growth index sci of the caprocks 2 the kic reduction is more prominent for the anhydrite 50 caprock than the carbonate 30 caprock which suggest that mineral solubility is responsible for the fluid weakening effect 3 a systematic change of sci with varying fluid conditions is observed sci is the largest in air smallest in formation water and intermediate in de ionized water microstructural analysis suggests a predominantly opening mode for both the natural fractures and induced fractures during fracture mechanical testing our results further demonstrate that subcritical fracture growth process is also strongly related to rock composition and stress conditions these observations provide insights into the mechanisms controlling fracture growth in carbonate and evaporite caprocks which could extend to brittle failure and fluid rock interactions occurring during the seismic cycle in the upper crust

crustal stress determination from boreholes and rock cores fundamental principles abstract obtaining quantitative information on the state of stress in the crust can only be accomplished by accessing the zone of interest by drilling the borehole cavity however disrupts the virgin stress state by concentrating stresses in predictable patterns with a number of consequences at sufficiently low stress magnitudes the concentrated stresses amplify the elastic anisotropy azimuthally around the borehole because the elastic properties of most rocks depend nonlinearly on stress at higher levels the stresses damage then fracture the rock near the wellbore wall or within a growing core stub indeed almost all of the borehole techniques indirectly measure stress through these manifestations of the concentrated stresses this contribution reviews at a fundamental level the concentration of stresses by the borehole the effects on the materials in the borehole s vicinity and how these are used to infer stress states stress concentrations applied to rocks which are generally nonlinear elastic materials induce both radial and azimuthal variations in elastic wave speeds near the borehole that can be used to infer stress directions from advanced acoustic logging methods hydraulic fractures initiate propagate and remain propped open by measured pressures that can be interpreted with knowledge of the stress concentrations to obtain quantitative stress magnitudes at higher stress levels the rock fails producing borehole breakouts or drilling induced tensile fractures both of which are indicative of stress directions and can be used to constrain stress magnitudes similarly the various styles of drilling induced core fractures indicate both stress directions and the faulting environment encountered unfortunately no method currently allows for complete determination of the stress tensor using a number of different but complementary techniques is necessary to best constrain in situ stress states

heat flow heat production and lithospheric thermal regime in the iberian peninsula abstract the first heat flow and heat production maps of the iberian peninsula and its margins using previously acquired data are presented the surface heat flow map includes 553 determinations carried out on water and mining exploration wells oil exploration wells and on the seafloor the surface heat flow varies noticeably from the iberian mainland 65 10 mw m 2 to the atlantic and the mediterranean margins where the heat flow reaches values of about 40 50 mw m 2 and 80 100 mw m 2 respectively the heat production map consists of 664 determinations carried out on rock samples from the variscan iberian massif and the betics the higher values are obtained for granitic rocks 2 5 3 5 w m 3 whereas metasediments and basic rocks reach values of 1 2 5 w m 3 and nearly zero respectively the lithospheric structure deduced for the iberian peninsula by combining heat flow heat production and elevation data indicates that most of the iberian mainland is characterized by a lithospheric thickness of 110 5 km this value is maintained across the west atlantic margin whereas towards the mediterranean margin the lithospheric thickness decreases down to 60 40 km this study also suggests that the heat production in the southern variscan iberian massif must be noticeably higher 3 7 0 5 w m 3 than in the rest of the areas in order to fit the measured heat flow crustal thickness and elevation data

estimation of elastic stiffness coefficients of an orthorhombic physical model using group velocity analysis on transmission data abstractwe acquired 3c ultrasonic transmission seismograms measured group velocities associated with the three quasi body wave types and determined density normalized stiffness coefficients aij cij over an orthorhombic physical laboratory model the estimation of aij is based on an approximate relationship between the nine orthorhombic aij and group velocities estimation of the anisotropic aij is usually done using phase velocities with well known formulas expressing their theoretical dependence on aij however on time domain seismograms arrivals are observed traveling with group velocities group velocity measurements are found to be straightforward reasonably accurate and independent of the size of the transducers used in contrast the accuracy of phase velocities derived from the p transform analysis was found to be very sensitive to small differences in picked arrival times and to transducer size theoretical phase and group velocities calculated in a forward manner from the aij est

radiogenic heat production in the variscan crust new determinations and distribution models in corsica northwestern mediterranean abstract new heat production values of variscan volcanic rocks cropping out in the southern part of the corsican batholith were determined in the laboratory by analysing uranium thorium and potassium concentrations with gamma ray spectrometry they vary from a minimum of 0 2 for basalts to a maximum of 4 2 w m 3 for calc alkaline granites the th u ratio in variscan granitoids is slightly higher than normal generally our measurements yield values higher than those previously determined these data together with those available for the variscan massifs of the northwestern mediterranean were used for constructing models of distribution of radiogenic heat production of the crust the lithologic composition was deduced from available p wave velocity data by taking into account the pressure and temperature effects depending on the rate of decrease with depth of the radiogenic heat the crustal contribution in terms of heat flux ranges from 26 to 39 mw m 2 and on average is 33 mw m 2 the mean heat production of the crust is 1 0 w m 3 both average crustal heat source and crustal heat contribution are quite similar to those estimated with the heat production seismic velocity relationship

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

a simple heat flow quality function and appraisal of heat flow measurements and heat flow estimates from the uk geothermal catalogue abstract a comprehensive database of temperature heat flow thermal conductivity and geochemistry is the basis of geothermal modelling the latest revision 1987 of the uk geothermal catalogue ukgc contains over 2600 temperatures at over 1150 sites and over 200 observations of heat flow about 93 of the temperature data are from depths less than 2000 m and about 50 are bottom hole temperatures bht heat flow density distribution models can be expanded to include estimates of heat flow derived from bht and thermal conductivity data contained in the ukgc a simple quantitative assessment of the quality of individual heat flow measurements has been devised based on the type and frequency of temperature and conductivity measurements and the borehole depth the dimensionless quality function hfq has been defined so that for a heat flow borehole with two equilibrium temperature measurements made across an interval with a mean depth of 1 km or greater with complementary thermal conductivity determinations made at intervals of 1 m across this zone the heat flow quality function is 1 0 over 50 of the uk heat flow dataset has a hfq function less than 0 10 the 4 highest quality observations have values above 1 0 the same function can be used to assess the quality of estimates of heat flow by assigning quality functions to various types of temperature and thermal conductivity observation schemes appraisal of the uk heat flow dataset indicates that some of the observational data have a similar quality rating to estimates of heat flow derived from convolution of temperature and thermal conductivity data for deep boreholes within the catalogue in eastern england the heat flow density pattern is significantly modified by incorporation of estimates of heat flow from deep boreholes which have hfq values comparable with early heat flow measurements made in this region

delineating fracture zones using surface tunnel surface seismic data p s and s p mode conversions a surface tunnel surface seismic experiment was conducted at the aspo hard rock laboratoryto study the seismic response of major fracture systems intersecting the tunnel a newly developedthree com

a multiscale methodology for the analysis of velocity anisotropy in organic rich shale abstractchanges in the sources of velocity anisotropy and their relative magnitude as maturation progresses in organic rich shale are still incompletely characterized in the rock physics literature as a result of the increasing importance of organic rich shale as unconventional reservoirs a more thorough understanding of the elastic behavior of shale is needed we have formulated a comprehensive multiphysics multiscale experimental methodology for the characterization of the intrinsic syn lithification and extrinsic postlithification factors contributing to velocity anisotropy application of this methodology to unsaturated samples also enabled the characterization of the shale frame for fluid substitution modeling the methodological framework was then tested on a set of five naturally matured organic rich shale samples in this experimental methodology we combined classical rock physics measurements e g ultrasonic velocity and emergent high resolution imaging techniques such as x ray diffra

velocity anisotropy of shales and depth estimation in the north sea basin it is known that in the north sea basin the depths to major reflectors as determined from surface seismic data are often larger than the well log depths from a study of data sets which tie 21 wells i found a strong correlation between the occurrence of the depth error and the presence of shales in the subsurface assuming that the error is caused by elliptical velocity anisotropy in shales i measured the anisotropy from a comparison of the well log sonic data and the interval velocity profile obtained from the surface seismic data and also from a comparison of the seismic depth and the well log depth it was found that the two methods of measurements agree with each other and also agree qualitatively with the previous laboratory measurements of anisotropy in shale samples the results strongly suggest that the depth anomaly in the north sea basin is caused by the velocity anisotropy of shales a simple method to correct the seismic depth is given

azimuthal velocity variations caused by borehole stress concentrations in laboratory experiments borehole stress concentrations caused by far field uniaxial stress produce measurable variations in compressional wave velocities near the borehole uniaxial stress was applied perpendicular to the axis of a borehole drilled through a sandstone block inside the fluid filled borehole refracted compressional waves were propagated in the rock parallel to the borehole axis at discrete azimuths producing a scan of velocity versus azimuth as uniaxial stress increased significant variations of compressional wave velocity with azimuth developed of the order of 10 variation the azimuth of velocity minima provides an excellent indicator of the direction of maximum far field uniaxial stress accurate to 5 the detailed variation of velocity with azimuth while approximately sinusoidal has sufficient character to provide new information about the rock one interpretation yields the curvature of the velocity versus stress curve of the rock

the saline waters of llandrindod and builth central wales saline or brackish mineral waters have been recorded at several locations in mid wales and the welsh borderlands the main groups are centered on llandrindod wells and builth wells where maximum salinities of 5340 and 16 380 mg l 1 respectively are found the total discharge from these springs is very low combined 2 l s 1 yet their flow remains almost constant residence times of several thousand years are derived using 14 c analysis and 18 o and 2 h results suggest that the waters at llandrindod although not at builth contain a component of late pleistocene water evidence from the br cl ratios and trace elements indicates that the origin of the salinity lies within the lower palaeozoic formations and has not been derived from evaporites the mineral waters have undergone complete reduction of sulphate which has led to high concentrations of ba maximum 53 2 mg l 1 at llangammarch wells the most likely origin of these waters is the deep circulation of meteoric water over a residence time of several thousand years which has risen slowly along minor fracture systems to the points of outlet the interconnected fracture storage of these waters implied from the various lines of evidence must be of the order 30 mm 3

heat flow heat production and crustal structure in peri atlantic regions abstract a linear relationship is commonly observed between heat flow and heat generation it provides information about the distribution of radioelements with depth over large regions the linear relationship is no more tenable but points still cluster within an elongated trend in which a regression analysis provides the bulk reduced heat flow and a gross estimate of the heat production distribution with depth over the whole considered region when geological provinces share an identical heat flow heat generation relation they form a geothermal province data measurements in western europe suggest that at least two provinces should be considered one can be related to the hercynian crust and the second to the older caledonian crust we suggest that the depth obtained from thermal data corresponds to the depth of the mafic granulite layer western france south and central england share identical geothermal parameters which can be correlated with the depth of the granulitic layer down to 17 18 km data from scotland do not fit the relationship of south and central u k and present a lower slope indicating that the radiogenic enriched layer is shallow 8 10 km this correlates with the seismic structure of the caledonian crust where the granulite layer is observed at this depth data from scotland can be compared to those from norway newfoundland new hampshire and eastern appalachian crust where the same crustal composition is observed

estimation of the anisotropy parameters of transversely isotropic shales with a tilted symmetry axis summary this paper reports a new approach for the estimation of thomsen anisotropy parameters and symmetry axis orientation from ultrasonic p wave traveltime measurements on transversely isotropic shale samples of arbitrary geometry this approach can be used for core samples cut in any direction with respect to the bedding plane because no a priori assumption regarding the symmetry axis orientation is made this orientation is rather part of the solution of the inverse problem together with the anisotropy parameters themselves very fast simulated reannealing is used to search for the best possible estimate of the model parameters the methodology is applied to spherical and cylindrical anisotropic shale samples

impact of fabric microcracks and stress field on shale anisotropy summary few data are available on shales in terms of seismic to ultrasonic properties and anisotropy although all are important with regards to imaging problems often encountered in such lithologies additionally mechanisms causing changes in these properties are not well documented due to the fine grain size of such materials and time required for testing under controlled pore pressure conditions the results presented here are derived from a set of experiments run on muderong shale with pore pressure control in order to evaluate the effect of stress magnitude and stress anisotropy on ultrasonic response this shale was noted to have a linear velocitymean effective stress response and extremely high anisotropy both likely the result of the presence of fluid filled cracks in a low permeability porous medium changes in velocity and vp vs ratios are dependent on both stress and smectite content s wave velocity is significantly affected by the presence of smectite in this and other shales and at low stress 20 mpa is less sensitive to stress change than p wave velocity vp vs ratios are noted to increase in this shale up to 20 mpa effective stress then decrease slightly due to stress induced loss of interlayer water in smectite intrinsic anisotropy comes from composition a strong compaction fabric and the presence of microfractures changes to ultrasonic anisotropy are the result of the magnitude of the stresses their orientation with respect to the fractures and the degree of stress anisotropy

a deep geothermal exploration well at eastgate weardale uk a novel exploration concept for low enthalpy resources the first deep geothermal exploration borehole 995 m to be drilled in the uk for over 20 years was completed at eastgate weardale co durham in december 2004 it penetrated 4 m of sandy till quaternary 267 5 m of lower carboniferous strata including the whin sill and 723 5 m of the weardale granite devonian with vein mineralization occurring to 913 m unlike previous geothermal investigations of uk radiothermal granites that focused on the hot dry rock concept the eastgate borehole was designed to intercept deep fracture hosted brines associated with the major geologically ancient hydrothermal vein systems abundant brine 46 c was encountered within natural fracture networks of very high permeability transmissivity c 2000 darcy m within granite evidence for the thermal history of the carboniferous rocks from phytoclast reflectance measurements shows very high values 3 3 indicating maximum temperatures of 130 c prior to intrusion of the whin sill geochemical analysis of cuttings samples from the eastgate borehole suggests radiothermal heat production rates for unaltered weardale granite averaging 4 1 w m 3 with a mean geothermal gradient of 38 c km 1 the eastgate borehole has significant exploitation potential for direct heat uses it demonstrates the potential for seeking hydrothermal vein systems within radiothermal granites as targets for geothermal resources

seismic anisotropy in sedimentary rocks part 2 laboratory data part one of this paper presents a method for measuring seismic velocities and transverse isotropy in rocks using a single core plug this method saves at least two thirds of the time for preparing core samples and measuring velocities in transversely isotropic ti rocks using this method we have measured velocity and anisotropy of many shale and reservoir rocks from oil and gas fields around the world we present some of the data in this paper which include seismic velocity and anisotropy in 17 brine saturated shale samples 1 gas and brine saturated coal sample 8 brine saturated sands 12 gas saturated sands 32 gas saturated carbonate samples and 25 brine saturated carbonate samples the results show that clays and fine layering in sedimentary rocks are the main causes of seismic anisotropy very little intrinsic anisotropy exists in unfractured reservoir rocks such as sands sandstones and carbonates under reservoir conditions in contrast all shales were found seismically anisotropic anisotr

sediment geochemical records of productivity and oxygen depletion along the margin of western north america during the past 60 000 years teleconnections with greenland ice and the cariaco basin abstract many sediment records from the margins of the californias alta and baja collected in water depths between 60 and 1200 m contain anoxic intervals laminated sediments that can be correlated with interstadial intervals as defined by the oxygen isotope composition of greenland ice dansgaard oeschger d o cycles these intervals include all or parts of oxygen isotope stage 3 ois3 60 24 cal ka the bolling allerod warm interval b a 15 13 cal ka and the holocene this study uses organic carbon corg and trace element proxies for anoxia and productivity namely elevated concentrations and accumulation rates of molybdenum and cadmium in these laminated sediments to suggest that productivity may be more important than ventilation in producing changes in bottom water oxygen bwo conditions on open highly productive continental margins the main conclusion from these proxies is that during the last glacial interval lgi 24 15 cal ka and the younger dryas cold interval yd 13 11 6 cal ka productivity was lower and bwo levels were higher than during ois3 the b a and the holocene on all margins of the californias the corg and trace element profiles in the lgi b a holocene transition in the cariaco basin on the margin of northern venezuela are remarkably similar to those in the transition on the northern california margin correlation between d o cycles in greenland ice with gray scale measurements in varved sediments in the cariaco basin also is well established synchronous climate driven changes as recorded in the sediments on the margins of the californias sediments from the cariaco basin and in the gisp 2 greenland ice core support the hypothesis that changes in atmospheric dynamics played a major role in abrupt climate change during the last 60 ka millennial scale cycles in productivity and oxygen depletion on the margins of the californias demonstrate that the california current system was poised at a threshold whereby perturbations of atmospheric circulation produced rapid changes in circulation in the eastern north pacific ocean it is likely that the pacific and atlantic oceans were linked through the atmosphere warmer air temperatures during interstadials would have strengthened hadley and walker circulations which in turn would have strengthened the subtropical high pressure systems in both the north pacific and the north atlantic producing increased rainfall over the cariaco basin and increased upwelling along the margins of the californias

electrical conductivity imaging of the philippine sea upper mantle using seafloor magnetotelluric data abstract we performed a three year seafloor electromagnetic survey in the philippine sea including the western edge of the pacific ocean to image electrical features of a deep mantle slab stagnating in the transition zone and the surrounding mantle in three dimensions 3 d the project iterated one year deployment of ocean bottom electromagnetometers obems using a total of 37 instruments installed at 18 sites the data obtained have been analyzed in the order of their recovery based on a magnetotelluric mt method in this study we attempt to obtain a one dimensional 1 d electrical conductivity model beneath the philippine sea and the pacific region separately that can be used as a reference model in the first step toward the 3 d analysis the resultant 1 d models show three main features 1 the conductivity in the shallower 200 km of the upper mantle depths of the two regions contrasts sharply which is qualitatively consistent with the large difference in lithospheric age 2 the conductivity at 200 300 km depth in both regions is more or less the same at approximately 0 3 s m 1 3 the conductivity just below 400 km depth is higher for the philippine sea mantle than for the pacific mantle the conductivity structure can be interpreted in terms of the thermal structure mantle hydration and existence of partial melt using experimental results for the conductivity of mantle minerals if the conductivity is interpreted simply as the effect of temperature the mantle beneath the philippine sea could be hotter than the dry solidus of mantle peridotite and thus partially molten however beneath the pacific region the present analysis suggests that the partial melting is not required under the assumed peridotitic composition even if we consider mantle hydration

tsunami signals from the 2006 and 2007 kuril earthquakes detected at a seafloor geomagnetic observatory 1 a seafloor geomagnetic observatory in the northwest pacific detected clear electromagnetic em variations associated with tsunami passage from two earthquakes that occurred along the kuril trench previous seismological analyses indicated that the m8 3 earthquake on 15 november 2006 was an underthrust type on the landward slope of the trench while the m8 1 earthquake on 13 january 2007 was a normal fault type on the seaward side the em measurements enabled precise monitoring of the tsunami propagation direction as well as particle motion of the seawater the estimated horizontal water velocity differs significantly for the 2006 and 2007 tsunamis in terms of initial motion and dispersive characters being consistent with the hydrodynamic simulation results of the tsunamis namely the tsunami induced horizontal geomagnetic components showed opposite signs for the rise and retreat waves as expected from the electric current wall hypothesis the dispersion effect is more remarkable in the 2007 event with a smaller source region of its tsunamigenic earthquake the 2007 tsunamis therefore tend to violate the long wave approximation the boussinesq approximation was required to reproduce the dispersive character of the 2007 event in our numerical simulation in terms of tsunami forecast an important advantage of em sensors over conventional tsunami sensors such as seafloor pressure gauges is their capability of vector measurements in addition to their ability to monitor particle motions the first peak of the downward magnetic component always precedes the tsunami peak suggesting a significant improvement in global tsunami warning systems if vector em sensors are integrated into the existing systems

highly varying radiogenic heat production in finland fennoscandian shield abstract radiogenic heat production in finland has been previously studied using airborne gamma ray surveys and glacial till measurements alike for the first time this paper presents a detailed survey on the spatial variation in radiogenic heat production determined using outcrop samples obtained from all important lithologies of the country the dataset of 6465 samples represents mostly mesoarchean about 2 7 ga paleoproterozoic ca 2 2 1 8 ga and mesoproterozoic ca 1 6 1 3 ga rocks nearly all data are from precambrian fennoscandian shield area but heat production appears to be highly variable and above global archean and proterozoic averages spot readings show an arithmetic average of 1 34 1 19 wm 3 and a range from 0 02 to 19 4 wm 3 the interpolated areal average of the whole area is 1 42 1 41 wm 3 the high standard deviation of data is related to the geochemical characteristics of uranium u thorium th and potassium k resulting in a skewed distribution of heat production mesoproterozoic anorogenic rapakivi granites and late paleoproterozoic svecofennian granitoids show the highest heat production values in the range of 3 5 wm 3 the results show no distinct dependencies of heat production with geological age metamorphic grade nor seismic p wave velocity but an increasing trend of heat production with sio2 content and decreasing trends of heat production with fe2o3 content and with rock density are evident surface heat flow 44 borehole data values correlates weakly with heat production r 0 35 the general heterogeneity of heat production calls for supporting information from other geophysical methods for better understanding of the thermal state of the lithosphere in finland and beyond

heat flow heat production relationships in the uk and the vertical distribution of heat production in granite batholiths recently the uk heat flow heat production data base has been expanded the linear correlation fonnerly recognised for southern britain is now in doubt and there seems no justification for recognising heat flow provinces with characteristic q and d in the uk interpretation of heat flow heat production data from two voluminous granite batholiths is consistent with geochemical evidence that depth distributions of heat production differ according to magma type

properties of electromagnetic fields generated by tsunami first arrivals classification based on the ocean depth tsunami flow coupled with the geomagnetic field generates electric currents and associated magnetic fields although electromagnetic em tsunami signals can be used for analysis and even forecasting tsunami propagation the dynamically self consistent effect of shoaling water depth on the fluid electrodynamics has not been adequately clarified in this study we classify tsunami em phenomena into three cases based on the ocean depth and find that the deeper ocean results in stronger self induction due to the increase in both tsunami phase velocity and ocean conductance in this deep ocean case the phase lead of the vertical magnetic variation relative to the sea surface elevation is smaller while an initial rise in the horizontal magnetic component becomes observable prior to tsunami arrival furthermore we confirm that the enhancement of tsunami height in shallower oceans shifts the ocean depth supplying maximum amplitudes of tsunami magnetic fields from approximately 2 0 km to 1 5 km

three dimensional simulation of the electromagnetic fields induced by the 2011 tohoku tsunami the motion of seawater induces electromotive force of significant intensity due to faraday s law and the resulting electromagnetic em field can be recorded by instruments installed on land or on the ocean bottom however few studies have successfully made a quantitative interpretation to obtain geophysical information from observations of tsunami induced em signals by an exact and accurate application of maxwell equations we built a scheme for three dimensional numerical simulation to calculate em fields due to ocean tidal flow and tested the system s accuracy by using the source currents in the ocean as expected from a tohoku tsunami simulation here we show examples of a comparison of data from one land observatory in the tohoku district one island observatory in the izu bonin arc and one seafloor station in the northwest pacific ocean the water motion that generates source current in the sea consists of both the primary poloidal and toroidal magnetic modes our numerical simulation shows that the field of the primary toroidal magnetic mode can be effective for seafloor observations but only when the seafloor is highly conductive we examined how the conductivity of the shallower part of the seabed composed of sediments can be constrained by the tsunami induced em field observations which is difficult in case of using ordinary seafloor magnetotelluric signals we also defined the motional impedance just as the case of ordinary magnetotellurics and showed that both modeled and observed impedances approximately indicate the phase velocity of the long wave as predicted by a simple theory

ultrasonic velocities in cretaceous shales from the williston basin compressional and shear wave velocities were measured in the laboratory from 1 bar to 4 kbar confining pressure for wet undrained samples of cretaceous shales from depths of 3200 and 5000 ft in the williston basin north dakota these shales behave as transversely isotropic elastic media the plane of circular symmetry coinciding with the bedding plane for compressional waves the velocity is higher for propagation in the bedding plane than at right angles to it and the anisotropy is greater for the 5000 ft shale for shear waves the sh wave perpendicular to bedding and the sv wave parallel to bedding propagate with the same speed which is about 25 percent lower than that for the sh wave parallel to bedding in general compressional and shear velocities are higher for the indurated 5000 ft shale than for the friable 3200 ft shale all velocities increase with in increasing confining pressure to 4 kbar the 3200 ft shale exhibits velocity hysteresis as a function of pressure whereas this effect is a

borehole stability analysis accounting for anisotropies in drilling to weak bedding planes abstract borehole instabilities pose significant challenges to drilling and completion operations particularly in regions with weak bedding planes and pre existing fractures where formations have strong anisotropies the bedding planes rock anisotropy and their impacts on horizontal stresses are considered in the proposed model to improve borehole stability modeling this improved model enables to calculate borehole failures and minimum mud weight along borehole trajectories with various drilling orientations versus bedding directions laboratory test data of rock compressive strengths are analyzed and a new correlation is developed to allow for predicting uniaxial compressive strengths in weak rocks from sonic velocities time dependent rock compressive strength is also examined to analyze the wellbore failure evolution with time the slip failure gradient in the weak planes is derived which can be used to model wellbore sliding shear failure in the planes of weakness the mud weight applied to prevent borehole shear failures in both intact rocks and ones with weak bedding planes can be obtained from the proposed model

the effect of anisotropy on the young s moduli and poisson s ratios of shales young s modulus and poisson s ratio are required for geomechanics applications such as hydraulic fracture design analysis of wellbore stability and rock failure determination of in situ stress and assessment of the response of reservoirs and surrounding rocks to changes in pore pressure and stress shales are usually anisotropic and models that neglect shale anisotropy may fail to describe geomechanical behaviour correctly anisotropy in shales results from a partial alignment of anisotropic clay particles kerogen inclusions microcracks low aspect ratio pores and layering for shales the young s modulus measured parallel to bedding e1 is usually greater than the young s modulus measured perpendicular to bedding e3 however the poisson s ratio 31 corresponding to stress applied perpendicular to bedding and strain measured parallel to bedding can be greater than equal to or less than the poisson s ratio 12 for stress applied parallel to bedding and strain measured parallel to bedding for transverse isotropy the elastic anisotropy resulting from a partial alignment of clay particles can be written in terms of the coefficients w200 and w400 which describe the impact of clay particle orientation on the anisotropy of shales disorder in the orientation of clay particles acts to reduce w400 faster than w200 since w400 is a higher order moment of the clay particle orientation distribution function than w200 this is confirmed by analysis of measured anisotropy parameters for shales a partial alignment of clay particles is consistent with the measured young s moduli for shales and with values of poisson s ratio 31 12 but not with values 31 12 these values can be explained if there exist kerogen inclusions microcracks or low aspect ratio pores aligned parallel to the bedding plane

gas hydrate saturation in the krishna godavari basin from p wave velocity and electrical resistivity logs abstract during the indian national gas hydrate program nghp expedition 01 a series of well logs were acquired at several sites across the krishna godavari kg basin electrical resistivity logs were used for gas hydrate saturation estimates using archie s method the measured in situ pore water salinity seafloor temperature and geothermal gradients were used to determine the baseline pore water resistivity in the absence of core data arp s law was used to estimate in situ pore water resistivity uncertainties in the archie s approach are related to the calibration of archie coefficient a cementation factor m and saturation exponent n values we also have estimated gas hydrate saturation from sonic p wave velocity logs considering the gas hydrate in frame effective medium rock physics model uncertainties in the effective medium modeling stem from the choice of mineral assemblage used in the model in both methods we assume that gas hydrate forms in sediment pore space combined observations from these analyses show that gas hydrate saturations are relatively low s h 15 20 in two zones between 168 and 198 mbsf site nghp 01 05 s h 35 38 in two discrete zone between 70 and 90 mbsf and site nghp 01 07 shows the gas hydrate saturation more than 25 in two zones between 75 and 155 mbsf a total of 10 drill sites and associated log data regional occurrences of bottom simulating reflectors from 2d and 3d seismic data and thermal modeling of the gas hydrate stability zone were used to estimate the total amount of gas hydrate within the kg basin average gas hydrate saturations for the entire gas hydrate stability zone seafloor to base of gas hydrate stability sediment porosities and statistically derived extreme values for these parameters were defined from the logs the total area considered based on the bsr seismic data covers 720 km 2 using the statistical ranges in all parameters involved in the calculation the total amount of gas from gas hydrate in the kg basin study area varies from a minimum of 5 7 trillion cubic feet tcf to 32 1 tcf

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

seismic anisotropy and its impact on imaging the shallow alpine fault an experimental and modeling perspective the transpressional alpine fault in new zealand has created a thick shear zone with associated highly anisotropic rocks low seismic velocity zones lvz and high seismic reflectivity are recorded in the alpine fault zone but no study has explored the underlying physical rock parameters of the shallow crust that control these observations protomylonites are the volumetrically dominant lithology of the fault zone here we combine experimental measurements of p wave speeds with numerical models of elastic wave anisotropy of protomylonite samples to explore how the fault zone can be seismically imaged numerical models that account for the porosity free real samples fabric elastic tensors from ebsd are calculated by mtex and a finite element model fem while microfractures are modeled with differential effective media dem theory at effective pressures representative of the alpine fault brittle zone experimental wave speeds are lower than those predicted by mtex fem a possible dem model suggests that a combination of random and aligned microfractures with aspect ratios increasing with pressure can explain the experimental wave speeds for pressures 70 mpa such micro porosity in the form of foliation and mica basal plane parallel microfractures and grain boundaries is validated with synchrotron x ray microtomography and tem images finally by modeling anisotropy of seismic reflection coefficients with angle of incidence we demonstrate that the high reflectivity and lvz observed at the alpine fault can only be explained if this microporosity is accounted for throughout the brittle fault zone even at depths of 7 10 km

the shear properties of oil shales a vast unexploited source of hydrocarbons is oil shales i e shales rich in kerogen the schlumberger oilfield glossary defines kerogen as the naturally occurring solid insoluble organic matter that occurs in source rocks and can yield oil upon heating the original organic constituents of kerogen are algae and woody plant material kerogens have a high molecular weight relative to bitumen or soluble organic matter bitumen forms from kerogen during petroleum generation estimates vary as to how much oil is contained in oil shale reserves the united states office of naval petroleum and oil shale reserves estimates some 1 6 trillion barrels of oil are contained in oil shales around the world with 60 70 of reserves 1 0 1 2 trillion barrels in the united states most u s oil shale is concentrated in the green river formation in wyoming utah and colorado covering 16 000 square miles

petrophysical implications of source rock microfracturing abstract hydrocarbon generation induced microfracturing in source rocks is important affecting both primary migration of hydrocarbons and unconventional shale plays in this study petrographic observations rock eval and total organic carbon content toc data and log derived physical properties were analyzed in order to evaluate eventual petrophysical implications of microfracturing induced by hydrocarbon generation petrographically evidences of microfracturing both normal and parallel to bedding have been found horizontal microfractures typically cross cut each other at an angle between 30 and 90 horizontal microfractures are readily imaged compared to vertical microfractures vertical microfractures were clearly observed only in rare cases in samples with a high degree of microfracturing in the case of moderate microfracturing the vertical component of microfractures may be too small to be detectable using conventional microscopy techniques longer vertical components of the microfractures may be facilitated by higher toc and particularly dense laminated organic matter fabric as well as higher thermal maturity levels clay minerals particularly smectites are also playing a role in reducing permeability and thereby increasing the local pressure generated by hydrocarbon generation eventually resulting in microfracturing log derived petrophysical properties particularly p wave velocity vp and formation resistivity can give information on microfracturing potential even though the techniques can t resolve the microfractures directly vp has been postulated to be sensitive to organic matter quantity and fabric whereas formation resistivity is largely governed by fluid content and clay minerals a reverse trend of increasing resistivity with decreasing vp was found and is linked to higher hydrocarbon saturation and toc and or dense laminated fabric of organic matter favoring microfractures the implications of the log derived petrophysical results are in agreement with the direct petrographic observations formation resistivities in the source rocks however are lower than those observed in non clay dominated hydrocarbon saturated intervals this indicate that low permeable organic rich source rocks with a high clay content particularly smectites may facilitate formation of the hydrocarbon filled vertical microfractures even at relatively low thermal maturities

3 d modelling the electric field due to ocean tidal flow and comparison with observations 1 the tidal motion of the ocean water through the ambient magnetic field generates secondary electric field this motionally induced electric field can be detected in the sea or inland and has a potential for electrical soundings of the earth a first goal of the paper is to gain an understanding of the global distribution of the electric signal due to tidal ocean flow we simulate the electric signals for two tidal constituents lunar semidiurnal m2 and diurnal o1 tides we assume a realistic earth s conductivity model with a surface thin shell and 1 d mantle underneath simulations demonstrate that in some coastal regions the amplitudes of the electric field can reach 100 mv km and 10 mv km for m2 and o1 tides respectively the changes of lithosphere resistance produce detectable changes in the tidal electric signals we show that our predictions are in a good agreement with observations

noncontacting benchtop measurements of the elastic properties of shales we evaluated a laser based noncontacting method to measure the elastic anisotropy of horizontal shale cores whereas conventional transducer data contained an ambiguity between phase and group velocity measurements small laser source and receiver footprints on typical core samples ensured group velocity information in our laboratory measurements with a single dense acquisition of group velocity versus group angle on a horizontal core we estimated the elastic constants c11 c33 and c55 directly from ultrasonic waveforms and c13 from a least squares fit of modeled to measured group velocities the observed significant p wave velocity and attenuation anisotropy in these dry shales were almost surely exaggerated by delamination of clay platelets and microfracturing but provided an illustration of the new laboratory measurement technique although challenges lay ahead to measure preserved shales at in situ conditions in the lab we evaluated the fundamental advantages of the proposed method over conventional transducer measurements

geothermal resources of the united kingdom geothermal prospects in the uk are represented by low enthalpy resources in deep sedimentary basins and 9hot dry rock9 hdr resources in radiothermal granites and possibly in deep basement rocks where they are overlain by thick low conductivity sediments the low enthalpy resources are in permo triassic sandstones at temperatures of more than 40 c four deep exploration wells have been drilled to investigate the potential of these sedimentary aquifers the main hdr resource potential is associated with major granite batholiths in southwest and northern england where temperatures are predicted to be 200 c at about 5 4 and 6 km respectively the hdr potential is being investigated by the camborne school of mines at their test site in cornwall where three boreholes have been drilled to depths of between 2 and 2 5 km the hot dry rock accessible resource base at temperatures of more than 100 c and depths of less than 7 km is 36 x 10 21 joules equivalent to 130 10 4 million tons of coal the low enthalpy geothermal resource of the permo triassic sandstones at temperatures of more than 40 c is 200 10 l8 joules equivalent to about 8000 million tons of coal if only a small fraction of these resources could be developed it would be significant in terms of the uk s energy balance

a simple formula for estimating the magnetic fields generated by tsunami flow 1 ocean flow is known to generate magnetic fields which reach land and satellite observatories with detectable amplitudes but because the expected signal to noise ratio is poor one must typically know in advance of the data analyses much about the expected behavior in order to identify these small oceanic contributions we show that in the case of ocean flow associated with tsunamis a very simple formula relating both amplitudes and phase allows the expected magnetic fields to be directly related to the sea surface displacement using sea surface data from jason 1 the formula gives maximum magnetic amplitudes of about 2 nt for the recent dec 26 2004 tsunami which occurred near the magnetic equator but near the magnetic poles the maximum amplitudes reach about 20 nt per meter sea surface displacement determining the feasibility for extraction of tsunami generated magnetic signals is of interest in designing early warning systems and for remotely tracking tsunami development

anisotropic elastic moduli of carbonates and evaporites from the weyburn midale reservoir and seal rocks assuming vertical transverse isotropy vti symmetry the elastic anisotropy as a function of confining pressure of four carbonates and one evaporite from the williston sedimentary basin in saskatchewan canada is investigated using the ultrasonic pulse transmission method ultrasonic p and s wave velocities are obtained from cylindrical plugs cut from a main sample along horizontal vertical and 45 orientations with respect to the sample s presumed vertical axis of symmetry the elastic constants were then calculated from the measured velocities and densities anisotropy was quantified by estimating thomsen parameters thomsen 1986 from elastic constants the results show that the samples are at the best weakly anisotropic the presence of microcracks and pores as well as the heterogeneity of the samples play an important role in defining the p and s wave velocities the weak anisotropy found in these samples suggests that intrinsic properties of these rocks negligibly contribute to the anisotropy observed at the seismic scale

the 2011 tohoku tsunami observed by an array of ocean bottom electromagnetometers a tsunami induces secondary electromagnetic em fields of significant intensity as a result of faraday s law and these em fields can be recorded by instruments on the seafloor such observations will provide parameters that are useful in understanding tsunami generation and propagation processes as such em sensors can be used as a type of tsunami sensor in the present study we report the observation of tsunami induced em signals by a small array of ocean bottom electromagnetometers consisting of four stations in the northwestern pacific ocean then several data analysis methods are used to estimate tsunami parameters referring to the theoretical relation the wave height is estimated from the observed magnetic and electric fields also the propagation direction of the 2011 tohoku tsunami is estimated by applying analysis methods for an array and a single station

magnetic signals at easter island during the 2010 and 2015 chilean tsunamis compared with numerical models tsunami flow across the geomagnetic field induces electric currents in both the ocean and the ionosphere these currents generate secondary magnetic fields observable at the seafloor and on land magnetic field disturbances during two chilean tsunamis 2010 and 2015 were recorded at easter island observatory these tsunamis were produced after the earthquakes in chile on february 27 2010 at 06 34 utc and september 16 2015 at 22 55 utc respectively differences between existing studies regarding the origin of the tsunamigenic disturbances and the lack of studies using a numerical model for both the water velocity and the induced magnetic field motivated us to compare magnetic records with computed magnetic fields for the two events modeled disturbances were calculated by applying the biot savart law to tsunami simulations our model can calculate tsunami induced perturbations in the vertical component of the geomagnetic field obtaining a good agreement with the observations we hypothesize that the magnetic measurements may be produced by a combination of oceanic and ionospheric electric currents our analysis further reveals that even a relatively small tsunami such as the one produced by the 2015 m text w 8 2 earthquake induces an observable magnetic perturbation due to the water movement future improvements to our model may allow us to identify situations in which magnetic variations precede the tsunami arrival thereby allowing early tsunami detection

lithospheric thermal regimes in europe abstract the heat flow pattern of europe derived from more than 8000 observations is dominated by a general northeast to southwest increase in geothermal activity which is the consequence of the tectonic evolution of the whole continent this paper reviews the history of the geothermal mapping of europe and describes the recently compiled set of geothermal maps of europe surface heat flow is correlated with the age of the last tectonothermal event with the near surface heat production and with the crustal thickness deep temperature distributions within the crust lithosphere are calculated for 1 d 2 d and simple 3 d models characteristic temperature depth curves are given for some of the major tectonic provinces and the results of various techniques are compared the value of the crustal heat contribution is assessed and a regional moho heat flow pattern is proposed the mohorovicic discontinuity is clearly not an isothermal surface neither is the heat flow from below the crust constant

heat flow heat production and thermo tectonic setting in mainland uk new heat flow data for the united kingdom together with additional heat flow and heat production determinations for caledonian age granites have led to a revision of the uk heat flow map and a re examination of the relationship between heat flow q 0 and heat production a 0 for granites and basement rocks previously recognized broad belts of above average heat flow are now resolved into separate zones which reflect to a greater extent the geological structure and tectonic history of the uk the zones of highest heat flow are spatially associated with voluminous high heat production granitoid batholiths in sw england northern england and the eastern highlands of scotland a single linear correlation between q 0 and a 0 is no longer tenable and an analysis in terms of broad heat flow provinces each with a characteristic upper crustal heat production distribution and deep heat flow contribution is also considered to be an oversimplification on the q 0 a 0 plot the data form four separate clusters three corresponding to the granite batholiths in sw england northern england and the eastern highlands of scotland and the fourth to the basement rocks of central england and wales an explanation of the q 0 a 0 data is proposed in terms of the crustal structure and thermo tectonic setting of each area in the case of the granite batholiths the data reflect the contrasting depth extent and radioelement depth functions of the intrusions these parameters in turn are related to the magmatic evolution and emplacement history of each batholith and the nature of the crust into which they were emplaced

radiogenic heat production in the continental crust abstract the thermal structure and evolution of continents depend strongly on the amount and distribution of radioactive heat sources in the crust determining the contribution of crustal rocks beneath a superficial layer is a major challenge because heat production depends weakly on major element composition and physical properties such as seismic wavespeed and density enriched granitic intrusives that lie at the current erosion level have a large impact on the surface heat flux but little influence on temperatures in the deep crust many lower crustal rocks that are poor in heat producing elements are restites from ancient orogenic events implying that enrichment of the upper crust was achieved at the expense of deeper crustal levels for the same total heat production concentrating heat sources in an upper layer acts to reduce temperatures in the lower crust thereby allowing stabilization of the crust the present day structure of the crust is a consequence of orogeny and should not be adopted for thermal models of the orogenic event itself this review summarizes information extracted from large data sets on heat flow and heat production and provides estimates of crustal stratification and heat production in several geological provinces analysis of global and regional data sets reveals the absence of a positive correlation between surface heat flow and crustal thickness showing that the average crustal heat production is not constant differences of heat flow between geological provinces are due in large part to changes of crustal structure and bulk composition collating values of the bulk crustal heat production in a few age intervals reveals a clear trend of decrease with increasing age this trend can be accounted for by radioactive decay indicating that thermal conditions at the time of crustal stabilization have not changed significantly for the average crustal thickness of 40 km moho temperatures are near solidus values at the time of stabilization suggesting an intrinsic thermal control on crustal thickness and heat production distribution crustal thickening by more than about 10 km above this mean value induces changes of gravitational potential energy that exceed the strength of the lithosphere for several provinces where strong constraints on heat production are available it is shown that prior to intracrustal fractionation only modest amounts of thickening were needed to generate the conditions of ultra high temperature metamorphism the tell tale signature of crustal heat production is anatectic and metamorphic events that lag the cessation of orogenic activity by several tens of million years crustal heat production is decreasing with time because it is due to the radioactive decay of uranium thorium and potassium its rundown is responsible for the secular cooling of lithospheric roots at a typical rate of about 100 k gy 1 implying complex thermal interactions with a convecting mantle that is not cooling at the same rate

dynamic and static moduli static and dynamic bulk moduli ks and kd are measured as continuous functions of pressure from zero to 2 3 kilobars for two sandstones a tuff limestone granite and oil shale results for the sandstones and granite are in good agreement with previously reported data with ks kd varying from about 0 5 at atmospheric pressure to close to unity at pressures 2 kilobars and above for rocks behaving elastically under static loading the ks kd ratio is inversely related to the microcrack density for the limestone time dependent deformation associated with pore collapse results in ks kd ratios approaching 0 1 at high pressure upon unloading while initially high 1 0 at high pressures ks kd becomes lower than values obtained during loading at low pressures 1 kilobar due to opening of microcracks generated during pore collapse for the oil shale in which few microcracks exist ks kd remains relatively constant with pressure at a value of about 0 7

transversely isotropic stiffness parameters and their measurement in colorado shale drained stress path triaxial tests and confined torsion tests were conducted on colorado shale core samples to investigate transversely isotropic stiffness parameters at small strain deformation nonlinear plastic behaviour occurred along the primary loading path even at strains less than 0 01 nonlinear hysteric behaviour was only observed during the loading unloading path however the shale material displayed transverse isotropy in deformation and very small or nondetectable poisson s ratios in vertical and horizontal directions this special response alludes to the postulate that the colorado shale could be approximated by a transversely isotropic elasticity model at small strain levels with negligible yielding key words anisotropy elasticity stiffness triaxial test torsion test shale

organic matter geochemistry and petrography of late cretaceous cenomanian turonian organic rich shales from the belle fourche and second white specks formations west central alberta canada abstract organic rich mudstones with up to 10 wt toc from the upper portion of the belle fourche formation and the lower part of the second white specks formation in the western canada sedimentary basin were evaluated as source rocks both geochemistry and organic petrography indicate an open marine paleoenvironment with deposition of type ii kerogen based on the predominance of marine alginite and amorphous organic matter om limited amounts of terrigenous vitrinite and inertinite macerals the presence of marine fossils and the low ratio of toc to total sulfur 1 26 the prevalence of short chain n alkanes n c13 to n c19 a predominance of c28 h 20s steranes and small concentrations of oleanane confirm the dominantly algal and planktonic origin of om alternating oxic to anoxic paleoenvironmental sedimentary conditions are proposed based on common bioturbation abundant inoceramid prisms and good organic richness biomarker distributions are consistent with intermittent anoxia without unequivocal evidence for water column stratification or hypersalinity the thermal maturity measured in seven sediment cores by different methods consistently indicates a westward increase in maturity according to vitrinite reflectance tmax and hopane and sterane biomarkers two cores are thermally immature 0 42 ro one is early mature 0 65 ro and four cores are within the oil window 0 78 to 0 89 ro all thermally mature cores retain good to very good hydrocarbon potential 248 mg hc g rock and are dominantly oil prone and minor gas prone based on their maceral compositions the upper belle fourche and lower second white specks formations represent potential targets for unconventional light shale oil production

3 d numerical modelling of the conductive heat flow of sw england summary the effect of 3 d geology on conductive heat flow was investigated using the finite element technique on two models from sw england one a regional model centred on the comubian batholith as a whole and the other a more detailed model centred on the cammenellis pluton only two rock types granite and country rock were used to represent the geology of the region and yet good agreement between modelled and observed data was obtained provided that the granite was assumed to be highly homogeneous with surface heat production values persisting throughout its depth and the base of the batholith was assumed to be flat at a depth of 15 km the results show that the surface heat flow pattern is dominated by the 3 d shape of the batholith which controls the relative importance of the two opposing effects that operate at its margins heat refraction due to conductivity contrasts enhancing heat flow in the granite and lateral flow of heat caused by heat production contrasts diminishing it the highest heat flows occur at the boundaries of outcrops facing the axis of the batholith where there is significant heat refraction but little lateral loss a high degree of correlation between mineralized zones and areas of very high heat flow in both granite and country rock is also noticeable the temperature field at any depth displays wide ranging lateral variations over relatively short distances the highest values occurring in areas of granite which are covered by insulating country rock and which lie towards the centre of the batholith regions of highest heat flow are not necessarily the regions where the highest sub surface temperatures are likely to be found and it is shown that the hot dry rock geothermal test project at rosemanowes is not optimally sited from temperature considerations when the constraints on the physical parameters of the model are sufficiently reliable as they are in sw england the heat flow and temperature predictions from 3 d numerical models can be of enormous value in the assessment of the geothermal potential of a region

satellite observations of magnetic fields due to ocean tidal flow the ocean is an electrically conducting fluid that generates secondary magnetic fields as it flows through earth s main magnetic field extracting ocean flow signals from remote observations has become possible with the current generation of satellites measuring earth s magnetic field here we consider the magnetic fields generated by the ocean lunar semidiurnal m2 tide and demonstrate that magnetic fields of oceanic origin can be clearly identified in satellite observations

hydrochemistry of the saline groundwaters of the lower mersey basin permo triassic sandstone aquifer uk saline groundwater occurs at depth in the triassic sandstones of the northern end of the cheshire basin in northwest england major and minor ion data suggest that the origin of the salinity is dissolution of evaporite deposits the salinity probably developed in an interval following the tertiary inversion of the basin which would have allowed faulted contact between the sandstones and the overlying evaporite sequence of the mercia mudstone group isotope evidence suggests the saline waters to have been considerably diluted by presumably dispersive mixing with a meteoric water recharged under cool and therefore quaternary climatic conditions comparison with other uk permo triassic basin brines suggests the merseyside waters are not unusual except in terms of the importance of exchange reactions and dilution by quaternary recharge waters these factors are due to the shallow maximum burial depth of the aquifer and the preservation of smectites and also to the geometry of the aquifer and its low permeability faults in the light of the water chemistry data it is suggested in a slight modification of the proposal of naylor et al q geol soc lond 146 685 699 1988 that the cheshire basin mineralization resulted from mixing of the relatively oxidized so4 rich evaporite brines with the reduced so4 poor metal rich barich coal measures brines which were expelled through faults from the coal measures during basin inversion some degree of oxyhydroxide stripping of the sandstones by the coal measures brines would have enhanced metal concentrations the water resulting from the mixing of brines would have been far from equilibrium and the barite and sulphide precipitation followed along the faults

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

hydrochemical and stable isotope evidence for the extent and nature of the effective chalk aquifer of north norfolk uk in eastern england the chalk aquifer is covered by extensive pleistocene deposits which influence the hydraulic conditions and hydrochemical nature of the underlying aquifer in this study the results of geophysical borehole logging of groundwater temperature and electrical conductivity and depth sampling for major ion concentrations and stable isotope compositions 18o and 2h are interpreted to reveal the extent and nature of the effective chalk aquifer of north norfolk it is found that the chalk aquifer can be divided into an upper region of fresh groundwater with a cl concentration of typically less than 100 mg l 1 and a lower region of increasingly saline water the transition between the two regions is approximately 50 m below sea level and results in an effective aquifer thickness of 50 60 m in the west of the area but less than 25 m where the eocene london clay boundary is met in the east of the area hydrochemical variations in the effective aquifer are related to different hydraulic conditions developed in the chalk where the chalk is confined by low permeability chalky boulder clay isotopically depleted groundwater 18o less than 7 5 is present in contrast to those areas of unconfined chalk where glacial deposits are thin or absent 18o about 7 0 the isotopically depleted groundwater is evidence for groundwater recharge during the late pleistocene under conditions when mean surface air temperatures are estimated to have been 4 5 c cooler than at the present day and suggests long groundwater residence times in the confined aquifer elevated molar mg ca ratios of more than 0 2 resulting from progressive rock water interaction in the confined aquifer also indicate long residence times a conceptual hydrochemical model for the present situation proposes that isotopically depleted groundwater occupying areas where confined groundwater dates from the late pleistocene is being slowly modified by both diffusion and downward infiltration of modem meteoric water and diffusive mixing from below with an old saline water body

velocity anisotropy in shales a petrophysical study using ultrasonic velocity and anisotropy measurements on a variety of shales with different clay and kerogen content clay mineralogy and porosity at a wide range of effective pressure we find that elastic anisotropy of shales increases substantially with compaction the effect is attributed to both porosity reduction and smectite to illite transformation with diagenesis a means of kerogen content mapping using velocity versus porosity crossplot for shales is shown matrix anisotropy of shales dramatically increases with kerogen reaching the maximum values of about 0 4 at total organic carbon toc 15 20 a strong chemical softening effect was found in shales containing even minor amounts of swelling smectite clay when saturated with aqueous solution this effect results in a significant p wave anisotropy reduction as compared to dry and oil saturated shales since mature black shales are normally oil wet this effect can only have a local significance restricted to the wellbore wall accurate measurements of phase velocities including velocities at a 45 direction to the bedding plane allow us to immediately calculate elastic stiffnesses and anisotropic parameters intrinsic high pressure properties of shales display an e 0 relation introduction of the bedding parallel microcracks in overpressured shales results in a decrease when fully fluid saturated and a increase when partially gas saturated with a characteristic effect on the shape of the p wave velocity surface at small angles of incidence filtering the contribution of the intrinsic anisotropy of shales it is possible to estimate the pore fluid phase microcrack density and aspect ratio parameters using seismic anisotropy measurements

a comparative study of the anisotropic dynamic and static elastic moduli of unconventional reservoir shales implication for geomechanical investigations abstractwe obtained the complete set of dynamic elastic stiffnesses for a suite of shales representative of unconventional reservoirs from simultaneously measured p and s wave speeds on single prisms specially machined from cores static linear compressibilities were concurrently obtained using strain gauges attached to the prism regardless of being from static or dynamic measurements the pressure sensitivity varies strongly with the direction of measurement furthermore the static and dynamic linear compressibilities measured parallel to the bedding are nearly the same whereas those perpendicular to the bedding can differ by as much as 100 compliant cracklike porosity seen in scanning electron microscope images controls the elastic properties measured perpendicular to the rock s bedding plane and results in highly nonlinear pressure sensitivity in contrast those properties measured parallel to the bedding are nearly insensitive to stress this anisotropy to the pressure dependency of the stra

anisotropy of elastic wave velocities in deformed shales part 1 experimental results elastic wave velocity measurements in the laboratory are used to assess the evolution of the microstructure of shales under triaxial stresses which are representative of in situ conditions microstructural parameters such as crack aperture are of primary importance when permeability is a concern the purpose of these experiments is to understand the micromechanical behavior of the callovo oxfordian shale in response to external perturbations the available experimental setup allows for the continuous simultaneous measurement of five independent elastic wave velocities and two directions of strain axial and circumferential performed on the same cylindrical rock sample during deformation in an axisymmetric triaxial cell the main results are 1 identification of the complete tensor of elastic moduli of the transversely isotropic shales using elastic wave velocity measurements 2 assessment of the evolution of these moduli under triaxial loading and 3 assessment of the evolution of the elastic ani

three dimensional simulation of tsunami generation and propagation application to intraplate events 1 a parallel finite difference numerical simulation program based on the navier stokes ns equations is developed for simulating 3 d tsunami generation and propagation we can simulate tsunami propagation over more than 1000 km using this program although such tsunami propagation over long distances has usually been conducted on the basis of on 2 d simulations some 2 d simulations have assumed that the initial tsunami distribution is identical to the sea bottom deformation caused by the earthquake the 3 d simulations however indicate that this assumption is inappropriate when the source width 2ax is less than 10 times the sea depth h 2ax 10h for a source process time of 20 s dispersion of tsunami appears when the source is of small size and the dispersion is more apparent in a direction perpendicular to the fault strike we also conduct tsunami simulations for two intraplate events the 2004 off kii peninsula m 7 4 and the 2007 off kuril islands m 8 1 events the 3 d tsunami simulation has successfully simulated the offshore tsunami and we obtained good agreement between the observations and the calculations for both events in particular for the 2004 off kii peninsula event although the 2 d linear long wave theory cannot simulate important characteristics in the record such as the arrival time of the peak amplitude and the dispersive tsunami the 3 d ns simulation is well able to model those characteristics

anisotropic approximations for mudrocks a seismic laboratory study an experimental technique for determining the in situ elastic properties of mudrocks with horizontal alignments in the microstructure is used to study the accuracy of a set of three nested scalar anisotropic approximations for transversely isotropic ti media each subsequent approximation adds one more velocity parameter and includes the previous as a special case these approximations are convenient and robust because of their close relationship to standard geophysical measurements there exists no good theory to predict the effects of an imposed stress on the elasticity of mudrocks in this study the tensor of elastic moduli of a single test specimen of mudrock subjected to an anisotropic stress field is determined from ultrasonic group velocity measurements involving pointlike transducers the mechanical characterization performed at constant pore pressure is accompanied by detailed microscopic observations and analysis the method was used to obtain accurate elastic constants for five well defi

geomagnetic field changes in response to the 2011 off the pacific coast of tohoku earthquake and tsunami abstract does the geomagnetic field change in association with earthquakes this question was first raised more than 100 years ago and since that time theoretical and observational researches have been conducted in order to obtain an answer to this question large earthquakes provide an opportunity to examine this problem because large signals are generally expected in association with large earthquakes we herein present a brief report on simultaneous measurements of the geomagnetic field in association with the 2011 tohoku earthquake m9 0 and tsunami by magnetometers at 14 stations operating in japan since the earthquake occurred during a geomagnetic storm we used time series after correcting the effect of external disturbances and induced fields a coseismic change of the geomagnetic field was observed at several stations located relatively close to the epicenter the magnitude of this coseismic change was only about 0 8 nt at one station and much smaller at other stations which prevented us from quantitatively comparing these observations with predictions based on piezomagnetic theory more distinct and rapid changes were observed during the hours following the main shock these changes are supposed to be caused either by motional induction of the tsunami or by ionospheric disturbance contrary to the significant observations of these coseismic and postseismic geomagnetic changes in response to the tohoku earthquake and tsunami we did not observe any clear precursors

experimental laboratory determination of the dynamic elastic properties of wet drained shales the ultrasonic anisotropic elastic properties of drained saturated shales were measured as a function of confining pressure two shales were characterized in this study a jurassic outcrop shale retrieved under the sea in a saturated state and a kimmeridge clay shale cut from a north sea borehole both shales were highly anisotropic both texturally as revealed by scanning electron microscopy analysis and elastically as measured ultrasonically in the laboratory the strongest anisotropy was seen in the kimmeridge clay shale where up to 38 compressional wave anisotropy thomsen s parameter e and up to 58 shear wave anisotropy thomsen s parameter were observed in addition for both shales e and were found to decrease as a function of increasing confining pressure with the pore pressure drained to atmosphere while the anellipticity deviation of the slowness surfaces from ellipses was found to be positive and decreased as a function of increasing confining pressure accompanying these changes in elastic properties was a decrease in porosity with increasing confining pressure from 10 5 to 8 5 for the jurassic shale the decrease in overall anisotropy of the shales with increasing confining pressure was found to be consistent with theoretical modeling of shale properties where the shale anisotropy and anellipticity were predicted to decrease as a function of decreasing fluid filled porosity

book reviewgeothermal energy the potential in the united kingdom r a downing and d a gray editors h m s o norwich 1986 xiii 187 pp stg 20 00 paperback