a subsurface lithostratigraphic division of the hauterivian to aptian furt informal and qishn formations yemen the mesozoic basins of yemen have a multiphase history of rift development sediments of the furt formation were deposited as a result of a second discrete phase of rift activity during the hauterivian to barremian and unconformably overlie older deposits a c ellis h m kerr c p cornwell and d o williams 1996 petroleum geoscience2 29 42 the name is taken from the suggested type well ai furt 1 where the unit reached its maximum drilled thickness to date in the jeza howarime basin the lithology in the type well predominantly comprises calcareous mudstones with subordinate carbonates in western yemen and more marginal settings the furt formation is dominated by arenaceous facies biostratigraphic analysis suggests that the upper and lower limits of the furt formation are bounded by stratigraphic breaks regional seismic lines suggest and biostratigraphy confirms the extension of the furt formation into basin margin areas and other rift basins supporting the case for regarding the furt section as a formation in its own right the qishn formation has been divided on a tripartite basis the oldest units are the clastic and lower carbonate members which are lateral facies and age equivalents the clastic member is found in the west of yemen while the lower carbonate member is best developed in the east the transition between the two is seen in the jeza howarime basin the middle unit the shale member is a regionally extensive mudstone facies thought to relate to a maximum flooding event the youngest unit the carbonate member comprises a limestone sequence the qishn formation is unconformably overlain bythe clastics of the harshiyat formation and in the extreme east of the yemen by the carbonates of the fartaq formation the qishn formation represents a transition from a rift to a post rift phase ellis et al 1996

a markov chain model for characterizing medium heterogeneity and sediment layering structure 1 by leveraging use of soft data e g initial moisture content qi this study applies the transition probability tp based markov chain mc model to sediment textural classes for characterizing the medium heterogeneity and sediment layering structure the tp mc method is evaluated by simulating the vadose zone moisture movement at a field site where the stratigraphy consists of imperfectly stratified soil layers soil heterogeneity is characterized via spatial variability of the geometry of soil textural classes when the qi measurements which carry signature about medium heterogeneity and stratigraphy are not included in the tp mc model it is not possible to identify the horizontal tp the qi measurements when transformed into soil classes are necessary in mapping the soil layering structure prevalent at the site the soil hydraulic parameters for each soil class are treated deterministically and are estimated on the basis of core samples to evaluate uncertainty in characterizing geometry of the soil classes multiple conditional realizations of the soil classes are generated a monte carlo simulation shows that the simulated mean moisture contents agree well with corresponding field observations the observed splitting of the moisture plume in a coarse sand layer that is sandwiched between two fine textured layers the southeastward movement of the plume during the redistribution period and the near zero fluid flux below the bottom fine layer are adequately simulated spatial variability of the field measured moisture content is sufficiently captured by the 95 confidence intervals calculated from the monte carlo simulations investigating the effect of data conditioning on the simulated results shows that a reduction of conditioning data does not necessarily deteriorate simulation results if other conditioning data exist within the mean length of the soil classes the tp mc method is flexible so that other types of site characterization data e g geophysical data can be incorporated as they become available

relating reactive solute transport to hierarchical and multiscale sedimentary architecture in a lagrangian based transport model 2 particle displacement variance this series of papers addresses the transport of sorbing solutes in groundwater in part 2 plume dispersion as quantified by the particle displacement variance x11r t is linked to hierarchical sedimentary architecture using a lagrangian based transport model this allows for a fundamental understanding of how dispersion arises from the hierarchical architecture of sedimentary facies and allows for a quantitative decomposition of dispersion into facies related contributions at different scales within the hierarchy as in part 1 the plume behavior is assumed to be controlled by linear equilibrium sorption and the heterogeneity in both the log permeability y ln k and the log distribution coefficient ln kd heterogeneity in y and arises from sedimentary processes and is structured by the consequent sedimentary architecture our goal is to understand the basic science of the dispersion process at this very fundamental level the spatial auto and cross covariances for the relevant attributes are linear sums of terms corresponding to the probability of transitioning across stratal facies types defined at different scales unlike previous studies that used empirical relationships for the spatial covariances here the model parameters are developed from independent measurements of physically quantifiable attributes of the stratal architecture i e proportions and lengths of facies types and univariate statistics for y and nothing is assumed about y point correlation it is allowed to differ by facies type however it is assumed that y and variance is small but meaningful and that pore scale dispersion is negligible the time dependent spreading rate is a function of the effective ranges of the cross transition probability structures i e the ranges of indicator correlation structures for each relevant scale of stratal hierarchy as in part 1 the well documented perchloroethene pce tracer test at the borden research site is used to illustrate the model the model was parameterized with univariate statistics for y of pce and proportions and lengths of lithologic facies types defined at two scales within a two level hierarchical classification as given by ritzi et al 2013 the model gives a viable explanation for the observed pce plume dispersion and thus x11r t can be explained by the process of linear equilibrium sorption and the heterogeneity in k and kd the results quantitatively show that the k kd cross correlation though small and varied by facies type can significantly impact the particle displacement variance furthermore by quantitatively decomposing the dispersion into facies related contributions we gain the fundamental insight that that the time dependent rate of spreading is mostly defined by the cross transition probability correlation structure imparted by the proportions and sizes of the larger scale facies types

mesozoic rift basins of yemen abstract this special issue is the first compilation and review of the stratigraphy and basin evolution of the mesozoic petroleum basins of yemen the volume arises from an international symposium on the sedimentation and tectonics of rift basins of the red sea gulf of aden area held at the university of sana a in september 1995 papers relating to the cenozoic rifting of the gulf of aden red sea and gulf of suez are to be published shortly b h purser and d w j bosence sedimentation and techtonics of rift basins the red sea gulf of aden chapman and hall london in press eight papers within this issue focus on basins within the interior of the country and the margins of the gulf of aden indian ocean the papers cover reviews of the developing stratigraphic concepts for these basins outcrop studies and subsurface studies of recently explored areas by geoscientists from the u k oil industry and from u k lebanese and yemeni universities

evaluation of single well injection withdrawal tests in swedish crystalline rock using the lagrangian travel time approach a series of 10 single well injection withdrawal swiw tests are evaluated with two tracers each uranine and cesium cs an evaluation tool for swiw tests in crystalline rock is presented on the

characterization and quantification of aquifer heterogeneity using outcrop analogs at the canadian forces base borden ontario canada accurate characterization of internal structures and geometries of aquifers is critical for evaluation of plume migration and dispersion of contaminants for this reason high resolution transport study field sites such as the waterloo groundwater research site at the canadian forces base borden ontario canada have been established however geological characterization at this site is based primarily on cores and shallow geophysical data outcrop analog studies offer detailed horizontal data that can help to build quantified models of aquifer heterogeneity we used a combination of ground based light detection and ranging lidar and high resolution photographs at a sand quarry cut into borden aquifer sediment to evaluate and quantify the distribution of lithofacies and hydrofacies that control flow properties in the borden aquifer we exposed sixteen 20 m 1 5 m outcrops lidar surveyed photographed and field mapped lithofacies at each exposure and segmented the lithofacies from photographs to produce maps of facies distributions we grouped different lithofacies into hydrofacies based on overall facies geometry and estimated hydraulic properties we used lidar scans and the segmented facies maps to produce a digital outcrop model dom of the site the resultant dom combines lithofacies and hydrofacies derived from field observations with high resolution 5 mm lidar data to reconstruct hydrofacies distributions in a three dimensional 3 d geomodel the dom offers a relatively complete horizontal correlation structure that was used in transition probability geostatistical modeling to create realizations of hydrofacies distributions in the aquifer at the study site

withdrawn petrographic and origin of authigenic carbonate minerals and the associated fluid evolution in the lacustrine carbonate siliciclastic mudrocks a case from the low cretaceous of the erennaoer sag erlian basin ne china

horizontal spatial correlation of hydraulic and reactive transport parameters as related to hierarchical sedimentary architecture at the borden research site 1 highly resolved data from the borden research site provide a unique opportunity to study the horizontal spatial bivariate correlation of hydraulic and reactive attributes affecting subsurface transport the data also allow quantitatively relating this correlation to the hierarchical sedimentary architecture of the aquifer the data include collocated samples of log permeability y the log of the perchloroethene sorption distribution coefficient and lithologic unit type the horizontal y and autosemivariograms and the y cross semivariogram have the same underlying correlation structure shape and range in the rise to a sill the common structure is not due to y point correlation or in unit spatial correlation the common structure is defined by how the proportion of lag transitions crossing different unit types i e the cross transition probability structure increases with increasing lag distance the common underlying cross transition structure contains two substructures with different correlation ranges corresponding to two scales of unit types within the sedimentary architecture for each substructure a large standard deviation in the length of units relative to the mean length gives rise to an exponential like shape and the proportions and mean length of units define the ranges the horizontal y spatial cross correlation is primarily defined by the larger scale substructure and the differences in mean and y between larger scale unit types

relationship between diagenesis and reservoir quality in sandstones of the garn formation haltenbanken mid norwegian continental shelf a quantitative model is proposed for the dependence of porosity and permeability on diagenesis in subarkosic arenites of the middle jurassic garn formation porosity variation is controlled by the combined effects of compaction and quartz cementation in general more porosity has been lost by compaction than by quartz cementation but compactional porosity loss appears to have occurred relatively early in the burial history before burial below 2 km below the sea floor thus progressive reduction of the total porosity with increasing burial below 2 km results mainly from quartz cementation permeability is a function of the abundance of intergranular macroporosity which is interpreted to be a measure of effective porosity at depths less than 3 5 km below the sea fl or intergranular macroporosity generally comprises more than 50 percent of the total porosity but at greater depth as total porosity decreases below about 16 percent the ratio of effective to ineffective porosity drops below one this depth corresponds to the onset of extensive illitization and grain dissolution which results in major reorganization of the pore system generation of secondary porosity by feldspar dissolution appears not to have been beneficial to reservoir quality in the garn formation but it is regarded as an intrinsic part of the overall process of porosity destruction with increasing diagenesis

transient dike propagation and arrest near the level of neutral buoyancy abstract we present a finite difference perturbation method to investigate transient dike propagation from a magma chamber 1 2 km below the level of neutral buoyancy in oceanic crust and explore the role of density gradation in dike propagation arrest the dike is modeled as a magma filled blade crack and the host rock is assumed to be a linear elastic medium with graded mass density an integral equation approach is used to obtain the dike propagation velocity and stress intensity factor at the propagating dike tip the finite difference perturbation method is applicable generally to mafic dikes with v less than 50 pa m where is the magma viscosity and v the dike propagation velocity numerical results show that dike propagation velocity initially increases with dike length reaches a peak value when the dike tip reaches a position well above the level of neutral buoyancy and then rapidly decreases to zero after the dike propagates further into the region above the level of neutral buoyancy which indicates that density gradation is an effective mechanism for dike arrest the effects of host rock fracture toughness and magma chamber depth relative to the level of neutral buoyancy are also discussed

source rock characterization and oil generating potential of the jurassic madbi formation onshore east shabowah oilfields republic of yemen abstract the hydrocarbon source rock potential of shales from the jurassic madbi formation was evaluated using organic geochemistry rock eval pyrolysis toc and bitumen extraction and organic petrology very good source rock potential is suggested by high values of total organic carbon content toc 2 0 wt and high extractable organic matter content and hydrocarbon yields 11 000 and 6000 ppm respectively the madbi formation samples have high hydrogen index hi and low oxygen index oi values most of the samples in the study area are thermally mature and contain oil prone type i and type ii kerogen vitrinite reflectance ro values for the madbi shale samples were measured from 0 74 to 0 89 tmax values range from 430 to 438 c which are in reasonably good agreement with vitrinite reflectance data reveal that the madbi shales are at the early to peak mature stage on the basis of biomarker maturity parameters these shales are thermally mature shales of the madbi formation contain abundant hydrogen rich kerogen liptinite up to 55 and therefore good oil generating potential is anticipated this is supported by high hydrogen indices hi of up to 400 mg hc g toc and early to peak mature oil window range

testing and parameterizing a conceptual model for solute transport in a fractured granite using multiple tracers in a forced gradient test 1 a cross hole tracer test involving the simultaneous injection of two nonsorbing solute tracers with different diffusion coefficients bromide and pentafluorobenzoate and a weakly sorbing solute tracer lithium ion was conducted in a fractured granite near an underground nuclear test cavity in central nevada the test was conducted to 1 test a conceptual radionuclide transport model for the site and 2 obtain transport parameter estimates for predictive modeling the differences between the responses of the two nonsorbing tracers when normalized to injection masses are consistent with a dual porosity transport system in which matrix diffusion is occurring the large concentration attenuation of the sorbing tracer relative to the nonsorbing tracers suggests that diffusion occurs primarily into matrix pores not simply into stagnant water within the fractures the relative responses of the tracers at late times suggest that the diffusion accessible matrix pore volume is possibly limited to only half the total volume of the flow system implying that the effective retardation factor due to matrix diffusion may be as small as 1 5 for nonsorbing solutes in the system the lower end of the range of possible sorption kd values deduced from the lithium response is greater than the upper 95 confidence bound of kd values measured in laboratory sorption tests using crushed granite from the site this result suggests that the practice of using laboratory sorption data in field scale transport predictions of cation exchanging radionuclides such as 137cs and 90sr should be conservative for the shoal site

biological markers and carbon isotope composition of organic matter in the upper cretaceous coals and carbonaceous shale succession jiza qamar basin yemen origin type and preservation abstract bituminous coals and carbonaceous shales located in the jiza qamar basin on the eastern yemen were analysed based on a combined investigation of organic geochemistry and petrology to define the palaeodepositional environment condition organic matter inputs and their thermal maturity carbon isotope compositions and various biomarkers were performed on coals and carbonaceous shales within the upper cretaceous mukalla formation in the jiza qamar basin the 13 c values range from 29 2 to 24 5 with average values around 26 7 whereas the organic carbon contents in most sediment samples are consistently high 3 indicating that the organic matter in the mukalla coal and carbonaceous shale sediments has a predominantly terrigenous origin with slightly marine influence during burial this has also been identified from kerogen microscopy which is characterized by dominance of vitrinite and liptinite organic matter the investigated biomarkers indicated that the mukalla coals and carbonaceous shales contain high contribution of land plants with a minor aquatic organic matter input that was deposited in a fluvial to deltaic environments and preserved under relatively oxic conditions this has been achieved from acyclic isoprenoids terpane and sterane biomarkers of a saturated hydrocarbon and dibenzothiophene alkylnaphthalene and methylphenanthrene biomarkers of an aromatic hydrocarbon based on the analysed biomarker thermal maturity indicators it may be deduced that the mukalla coals and carbonaceous shales in the jiza qamar basin have entered an early mature to mature stages for hydrocarbon generation this is also supported by vitrinite reflectance values of 0 63 0 83 ro indicative that these sediments have reached oil window maturity

sorbing tracer experiments in a crystalline rock fracture at aspo sweden 2 transport model and effective parameter estimation 1 transport and retention of sorbing tracers in a single altered crystalline rock fracture on a 5 m scale is investigated we evaluate the results of a comprehensive field study referred to as

petroleum source rock characterisation and hydrocarbon generation modeling of the cretaceous sediments in the jiza sub basin eastern yemen non source to good source rocks were identified in the studied cretaceous rocks oil and gas generation were expected from cretaceous source rocks biomarkers reflect marine and deltaic depositional environments for cretaceous source rocks oil generation from qishn formation was began in late cretaceous

hydrophobic organic contaminant transport property heterogeneity in the borden aquifer we determined that the spatial heterogeneity in aquifer properties governing the reactive transport of volatile organic contaminants is defined by the arrangement of lithofacies we measured permeability k and perchloroethene sorption distribution coefficient kd for lithofacies that we delineated for samples from the canadian forces base borden aquifer we compiled existing data and collected 57 new cores to characterize a 30 m section of the aquifer near the test location of mackay et al 1986 the k and kd were measured for samples taken at six elevations from all cores to create a data set consisting of nearly 400 colocated measurements through analysis of variance corrected for multiple comparisons we determined that the 12 originally mapped lithofacies could be grouped into five relatively distinct chemohydrofacies that capture the variability of both transport properties the mean of ln k by lithofacies was related to the grain size and the variance was relatively consistent in contrast both the mean and variance of ln kd were greater for more poorly sorted lithofacies which were also typically more coarse grained half of the aquifer sorption capacity occurred in the three highest sorbing lithofacies but comprised only 20 of its volume the model of the aquifer that emerged is that of discontinuous scour fill deposits of medium sand generally characterized by greater kd and k within laterally extensive fine grained to very fine grained sands of lower kd and k our findings demonstrate the importance of considering source rock composition transport and deposition processes when constructing conceptual models of chemohydrofacies

dilution enhancement in hierarchical and multiscale heterogeneous sediments abstract we quantify the dilution of solute clouds in geological formations displaying hierarchical and multiscale sedimentary architecture through the use of a lagrangian framework this allows for a fundamental understanding of how dilution arises from the hierarchical architecture of sedimentary facies and enables for a quantitative decomposition of dilution into facies related contributions at different scales within the hierarchy the new developed semi analytical solution that quantify the dilution index is based on hierarchical expressions of the spatial covariance of the log conductivity the spatial correlation structure in the covariance expression is defined by the probability of transitioning within and across facies types of different scales which are parameterized by independent and physically quantifiable attributes of sediments including geostatistical properties of the conductivity field and the proportions and lengths of facies types we illustrate the applicability of the model in the well documented tracer test at the borden research site canada we show how different scales of sedimentary architecture contribute to the dilution enhancement of the solute cloud at borden aquifer by quantitatively decomposing the dilution index into facies related contributions we gain fundamental insights on the key factors controlling the time dependent rate of dilution the results also illustrate that the probability of transitioning from one facies to another i e cross transitions at different scales defines the temporal scaling for enhanced dilution additionally we perform sensitivity analyses to investigate the effects of mean difference in conductivity volume proportion the statistical anisotropy ratio and the scale of heterogeneity on the overall solute dilution

brittle creep damage as the seismic signature of dyke propagations within basaltic volcanoes contemporary to nine dyke intrusions on piton de la fournaise etna and miyakejima volcanoes we recover stationary seismicity rate and energy release over time whether the dyke reaches the surface or not this generic seismicity pattern for the dyke propagation of low viscosity magma argues for the fluid driven crack propagation to be a scale independent stationary process this prevents any prediction of the time to eruption during the dyke propagation phase using seismicity rate alone the seismic signature of the volcano deformation triggered by dyke injections corresponds to brittle creep damage in a strain driven setting whether mechanical properties of host rock structure or geometrical effects influence this generic stationary response is not resolved by the seismic data because a few if any aftershocks are resolved contemporary to dyke intrusion the seismicity is purely driven by the dyke dynamics that is a proxy for the dyke volumetric growth

geostatistical analysis of the borden aquifer hydraulic conductivity field abstract a total of 11 vertical cores spaced 1 m apart along a single transect were extracted from the borden aquifer at a location 60 m north northeast from the site studied by sudicky previously examination of these cores shows the upper 1 5 2 0 m of the aquifer to be comprised of relatively unstructured fine to medium sands underlain by a 0 1 0 8 m thick peaty layer and a 0 1 m thick organic rich horizon between depths of 3 05 and 6 10 m the aquifer is comprised of clean horizontally bedded fine to medium sands similar to those examined by sudicky previously statistical analysis of 642 subsamples of 5 cm length from this interval suggests that the permeability data may follow a log normal distribution with a mean lntransformed permeability m 2 of 25 67 and a variance of 0 585 no consistent trend with depth was detected for ln k or for the mean and variance of ln k on a core by core basis exponential spherical and gaussian models all provided excellent fits to the vertical experimental variogram calculated using the classical estimator without the removal of outliers these fits produced correlation scales ranging from 0 16 to 0 23 m of the three theoretical models only the gaussian model produced a reasonable fit to the horizontal experimental variogram with a correlation scale of 4 8 m a linear model was also found to fit the experimental variogram data well in comparison with earlier results of sudicky and woodbury and sudicky it can be concluded that similar deposits were examined in this study particularly with respect to correlation structure on the basis of statistical tests however it cannot be concluded that the mean and variance of ln k are stationary over the 60 m distance between the cores examined in this study and those of sudicky the results of this study indicate that the borden hydraulic conductivity field is relatively uniform over the scale examined but that it cannot be characterized by a single spatially invariant statistical distribution

sedimentary and diagenetic controls on reservoir quality of low porosity and low permeability sandstone reservoirs in chang101 upper triassic yanchang formation in the shanbei area ordos basin china abstract there are many reservoirs with low porosity and low permeability in the world and many large oilfields have been found in these reservoirs unlike conventional reservoirs the genesis of low porosity and low permeability reservoirs and the controls of relatively high porosity and high permeability zones are still unclear this study takes the chang101 reservoir sandstones of the shanbei area in the ordos basin china a typical low porosity and low permeability as an example chang101 sandstones are fine grained to medium grained moderately to well sorted arkose and lithic arkose deposited in a delta plain environment it is a typical low porosity and low permeability reservoir with an average porosity of 10 21 and an average permeability of 2 88 md pore types mainly include primary intergranular pores and secondary dissolved pores the main controls on the reservoirs are the sedimentary environment and diagenesis the sedimentary environment determines the initial properties of the reservoir sandstones including the material composition and texture that determine the primary porosity and permeability diagenesis further transforms the reservoir quality to develop heterogeneity in the porosity and permeability the reservoir sandstones have undergone complex diagenetic processes and are currently in stage a of mesodiagenesis compaction accounts for the major reduction of the primary porosity of the sandstones different types of cementation have both positive and negative influences on reservoir quality carbonate cementation quartz overgrowths and some authigenic clay cementation i e i s and illite are major pore filling components that reduce the reservoir quality an appropriate amount of chlorite resists compaction and prevents quartz overgrowth but excessive chlorite coatings fill the pores and block the pore throats the laumontite cement is not only resistant to compaction but also easily dissolved to form a large number of effective secondary pores the dissolution of feldspar and rock fragments plays a role in contributing to connecting the isolated intergranular pores and increasing the secondary pores relatively high porosity and high permeability zones are deposited in high energy environment mainly delta plain distributary channel sandstones with more detrital quartz fewer rock fragments and coarser grains than other sandstones were deposited in high energy environment there is weaker compaction and less or no carbonate cement with the preservation of the primary pores by chlorite coatings and an increase in the pores by the dissolution of laumontite cement

a new method for analysis of variance of the hydraulic and reactive attributes of aquifers as linked to hierarchical and multiscaled sedimentary architecture this technical note presents a useful methodology for studying how the variance of hydraulic and or reactive attributes of an aquifer are linked to the multiscaled and hierarchical sedimentary architecture of the aquifer a new recursive equation is derived which quantitatively describes how the variance is related to sedimentary facies defined at all scales across an entire stratal hierarchy as compared to prior published equations that emphasize differences in means among facies populations within a hierarchical level it emphasizes differences across levels because of the hierarchical relationships among the terms of the equation we find it to be useful for conducting a holistic analysis of the relative contributions to the variance arising from all facies types defined across all scales the methodology is demonstrated using appropriate field data and is shown to be useful in defining parsimonious classification systems

diagenesis and reservoir quality in high resolution sandstone sequences an example from the middle jurassic ravenscar sandstones yorkshire coastuk abstract a section of the middle jurassic ravenscar sandstones exposed between cloughton wyke and burniston bay was studied to understand fine scale variation in reservoir quality that can affect flow properties at the reservoir scale the study has identified two 3rd order depositional sequences consisting of twelve 4th order high resolution sandstone sequences deposited mostly in a lower delta plain although these sandstones exhibit a narrow range in porosity values however a sharp disparity exists in their permeability which can have implications at the scale of reservoir development diagenetic studies have revealed that mechanical compaction produced the same effect for most of these sandstones however dissolution and cementation vary hence are mostly responsible for the sharp contrast in their reservoir quality the distributary channel sandstones developed during normal regression of the area in the fs9 sequence are considered the best reservoir sand bodies however these lst sandstones are compartmentalised by authigenic illite quartz and kaolin into two reservoir segments the upper portion lacks illite with resultant higher permeability values above 1100 md ave 2217 md and classified as reservoir group 4 in contrast the lower part contains illite with relatively lower permeability values in the range of 300 1100 md ave 879 md and classified as reservoir group 3 together with the transgressive crevasse channel sandstones in the fs11 sequence the presence of illite cement in these sandstones is linked to the occurrence of k feldspar hence facilitated illitization of kaolin in contrast to group 4 which lacks this mineral the other transgressive sandstones deposited in interdistributary bay crevasse delta back barrier lagoon lagoon and estuarine environments which form reservoir groups 1 and 2 have permeability values in the range of 0 50 md ave 6 md and 50 300 md ave 184 md respectively these sandstones have complex styles of diagenetic cement with variable higher volumes of total authigenic cement consisting of quartz kaolin illite chlorite and calcite than reservoir groups 3 and 4 hence have significantly reduced their reservoir potential therefore for effective reservoir development of these sandstone reservoirs in the north sea and elsewhere in the world with a similar geological setting detailed reservoir characterisation involving linking lithofacies sequence stratigraphy and diagenesis at high resolution are essential for understanding the distribution of reservoir flow properties

modelling petroleum generation of late cretaceous dabut formation in the jiza qamar basin eastern yemen abstract the jiza qamar basin in eastern yemen is still undergoing hydrocarbon exploration and hydrocarbon potential has not been assigned yet in this study subsurface samples from two onshore and offshore wells were collected to characterize the source rocks of dabut formation and to incorporate into basin modelling in order to know and determine the timing of petroleum generation and expulsion of the dabut source rocks based on organic geochemical analysis the dabut sediments have variable toc content in the range of 0 5 2 5 wt indicating fair to good source rock generative potential the organic matter of dabut source rock is dominated by type iii kerogen with minor mixed iii ii kerogen contributions and is thus considered to be mainly gas prone and some oil prone this is supported by hi values in the range of 50 212 mg hc g toc vitrinite reflectance in the range of 0 63 0 88 ro and pyrolysis tmax in the range of 427 454 c generally indicate that the dabut source rocks contain mature organic matter one dimensional basin modelling was performed to analyse the hydrocarbon generation and expulsion history of the dabut source rocks in the jiza qamar basin based on the reconstruction of the burial and thermal maturity histories in order to improve our understanding of the hydrocarbon generation potential calibration of the model with measured vitrinite reflectance ro and borehole temperature bht data indicates that the paleo heat flow was constant during the late cretaceous paleogene but increased during the late paleogene neogene and then decreased exponentially from neogene to present day the modelled maturity history predicts that the oil generation 0 5 ro in the dabut source rock began from about 56 ma to 42 ma and the peak hydrocarbon generation 0 86 ro occurred approximately from 14 ma to 13 ma these models also indicate that the main phase of oil generation was at 56 ma to 25 ma whereas the main phase of gas generation began from about 25 ma to 14 ma and still generated in the present day

a numerical model of dyke propagation in layered elastic media summary we develop a mathematical model describing dyke propagation in proximity of an elastic discontinuity of the embedding medium the dyke is modelled as a fluid filled crack in plane strain configuration employing the boundary element method the pressure gradient along the crack is assumed proportional to the difference between the densities of the host rock and the fluid mass conservation is imposed during propagation and fluid compressibility is taken into account the path followed by the crack is found by maximizing the total energy release given by the sum of the elastic and gravitational contributions the mathematical simulations provide a sort of refraction phenomenon that is a sudden change in the direction of propagation when the crack crosses the boundary separating different rigidities if the dyke enters a softer medium its path deviates towards the vertical if the dyke enters a harder medium its path deviates away from the vertical and may even become arrested as a horizontal sill along the interface if the rigidity contrast is large gravitational energy plays a major role during propagation in particular in proximity of layer boundaries this role is enhanced by the shift of the centre of mass due to changes of dyke shape mathematical results were validated by laboratory experiments performed injecting tilted air filled cracks through gelatin layers with different rigidities

pyrite chlorite and pyrite biotite relations in sandstones abstract authigenic euhedral pyrite in feldspathic sandstones of the visingso group upper proterozoic southern sweden is observed to be closely associated with authigenic fine crystalline interstitial chlorite and or sand sized chlorite or biotite microprobe analyses revealed that chlorites which are accompanied by relatively large amounts 3 vol of pyrite are characterized by a lower fe fe mg ratio than chlorites with lesser amounts 0 5 vol of associated pyrite the lower fe fe mg ratio of the former chlorites might have resulted from subsequent substitution of fe 2 by mg 2 in an initially fe rich chlorite the released fe 2 would then react with sulfide ions in an anoxic sulfidic environment to form pyrite another alternative is that the chlorites with lower fe fe mg ratio were crystallized from solutions characterized by a higher activity of mg 2 than chlorites with higher fe fe mg ratio iron from the biotite grains became available due to diagenetic illitization kaolinization and or chloritization

matrix diffusion rates in fractured volcanic rocks at the nevada test site evidence for a dominant influence of effective fracture apertures 1 solute matrix diffusion in saturated fractured volcanic rock at the nevada test site was evaluated from field tracer tests conducted at two different locations and from laboratory scale transport experiments using core samples from the two locations the laboratory tests included 15 separate tracer transport experiments conducted in 8 fractured cores 4 from each location and 17 diffusion cell experiments conducted in matrix material adjacent to the fractures all of the experiments featured two nonsorbing tracers with free diffusion coefficients differing by a factor of approximately 3 to allow the effects of diffusion to be distinguished from the effects of advection dispersion and source term tailing in the experiments when considering all the laboratory and field transport experiments collectively the lumped mass transfer parameter that characterizes matrix diffusion rates sec 1 2 where m is the matrix porosity b is the effective fracture half aperture and dm is the matrix diffusion coefficient appears to decrease as time and length scales of observation increase however these decreasing trends largely disappear when the laboratory and field data are considered separately and there is little difference in dm values measured at different timescales in laboratory experiments using the same rocks also the overall variability in m and dm in the laboratory experiments is not large enough to account for the order of magnitude smaller field scale values of compared to lab scale values we conclude that experimentally observed trends of versus time or distance scale in saturated fractured rocks at the nevada test site are dominated by differences in effective fracture apertures in the various experiments with a tendency toward larger apertures in the field experiments these results underscore the importance of acquiring a better understanding of the factors that control effective fracture apertures as a function of distance scale in fractured media if values of from laboratory and field tracer experiments are to be reliably extrapolated to time and distance scales in risk assessment models

synrift continental to marine depositional sequences tertiary gulf of aden yemen abstract tertiary synrift deposits along the northern margin of the gulf of aden republic of yemen provide new information on the controls on deposition and stratigraphic relationships during the transition from continental to marine rift sedimentation intracontinental rifting in the region commenced in the oligocene developing into a marine extensional margin in the miocene the outcropping part of a small subbasin at wadi hiru west of mukalla contains carbonate platform alluvial fan fan delta and raised beach deposits that record the development of the rift margin the spatial relationships between carbonate and clastic units their location adjacent to rift border faults and timing of sea level changes indicate that tectonics was the overriding control on relative sea level change accommodation space created by fault movement and the morphology of older sediment bodies dictated the three dimensional architecture of carbonate platforms and clastic fans fault movements are documented by changes in clast provenance in fanglomerates rift parallel and rift perpendicular faults formed a trap door configuration that controlled long lived pathways of terrigenous clastic supply throughout rifting five local depositional sequences bounded by erosion surfaces are recognized sequences have a distinct tectonic signature in the form of sequence boundaries overlain by thick fanglomerates followed by transgressive and highstand carbonates two of these sequences were dated using 87sr 86sr isotope dating the relative sea level curve derived from thi study bears little relationship to published eustatic curves

magma ascent and effusion from a tensile fracture propagating to the earth s surface summary an effusive volcanic eruption results from a sequence of different processes such as the pressurization of a magma chamber the propagation of a dyke and the flow of lava at the earth surface the aim of this paper is to establish relationships between the different quantities describing such processes we consider a spherical magma chamber filled with a low viscosity magma and included in a homogeneous and isotropic elastic half space we assume that as a result of the inflow of fresh magma or a phase transition the pressure in the chamber increases slowly during a finite time interval assuming that the pressure increase is linear in time we calculate the stress field generated in the surrounding medium considering the chamber as a centre of dilation we assume that a vertical tensile fracture originates at the top of the magma chamber after the rock strength is exceeded the fracture is assumed to propagate quasi statically along a vertical plane driven by the stress distribution both the cases of positive and negative buoyancy force are considered the problem is solved in two dimensions by considering the fracture as a tensile somigliana dislocation and expanding the associated stress release into chebyshev polynomials the fracture may reach the earth s surface or not depending on the depth and radius of the magma chamber the rate and duration of pressure increase the rock and magma densities and the rock strength when the fracture reaches the earth s surface we assume that it becomes a vertical conduit magma pours out from the vent driven by the pressure gradient in the conduit under the assumption of laminar flow of a newtonian fluid we evaluate the initial effusion rate as a function of the relevant model parameters the flow rate is found to be a non linear function of the density contrast we also establish a relationship between the flow rate in the conduit and the initial thickness of the ensuing lava flow in the case of effusion on a steep slope

key factors controlling hydrocarbon enrichment in a deep petroleum system in a terrestrial rift basin a case study of the uppermost member of the upper paleogene shahejie formation nanpu sag bohai bay basin ne china abstract mineralogical petrographical geochemical analyses and fluid inclusions petrography and microthermometry were combined to investigate the basic properties of the source rock organic matter content kerogen type and thermal maturity and sandstone reservoirs composition pore systems porosity and permeability the hydrocarbon origin and the formation mechanisms of the deep 3 5 km petroleum system in the upper paleogene es1 the uppermost member of the shahejie formation in the no 3 structural belt in the nanpu sag bohai bay basin the results indicate that the es1 source rock is primarily composed of dark gray mudstone and presents a set of high quality source rocks 500 m average total organic carbon toc 1 38 in a mature stage maximum pyrolysis yield of 430 c 460 c the es1 sandstone is composed of lithic arkose formed in a braided river delta and has low porosity average 13 4 but moderate high permeability average 184 9 md the hydrocarbons originated from the es1 source rocks in the caofeidian subsag during two charging periods 10 ma and 3 ma the key factors controlling the formation of the deep petroleum system are as follows a high quality hydrocarbon supply b medium high permeability reservoirs c a favorable configuration of the source rock and reservoirs self generated and self accumulated and d late hydrocarbon charging the second factor is the most important the medium high permeability reservoirs are attributed to a high energy depositional environment distributary channels of braid delta front a high content of rigid detrital grains mainly quartz and metamorphic rock fragments provided by the archean granite provenance and the secondary pores formed by feldspar dissolution this study provides a new example for revealing the formation mechanisms of deep 3 5 km petroleum systems in the terrestrial rift basin across the bohai bay basin

pore fluid evolution distribution and water rock interactions of carbonate cements in red bed sandstone reservoirs in the dongying depression china the compositions distribution and its interaction with rocks of the evolving pore fluids controls the distribution of carbonate cements and reservoir storage spaces the reservoir quality of the red bed sandstone reservoirs in the dongying depression was investigated by an integrated and systematic analysis including carbonate cement petrology mineralogy carbon and oxygen isotope ratios and fluid inclusions the investigation was also facilitated by probing the mineral origins precipitation mechanisms pore fluid evolution and distribution and water rock interaction of carbonate cements and their influences on reservoir quality diagenetic evolving fluids in the interbedded mudstones are the main source for the precipitation of calcite cements that completely fill the intergranular volume cfiv calcite with heavier oxygen and carbon isotopes the ferro carbonate cements in the reservoir sandstone are enriched in lighter carbon and oxygen isotopes in addition to the cations released by the conversion of clay minerals in reservoirs products of organic acid decarboxylation and the associated feldspar dissolution process provide important sources for such carbonate cementation the carbon isotopes of co2 and the oxygen isotopic composition of fluids equilibrated with the cfiv calcite ferro calcite dolomite and ankerite cements indicate that the pore in the red bed reservoirs experienced high salinity fluids which evolved from the early formed interbedded mudstones through organic acid input and to organic acid decarboxylation pore fluids from nearby mudstones migrated from the edge to the centre of sandbodies causing strong calcite cementation along the sandbody boundaries and forming tight cementation zones pore fluids associated with organic co2 and acids and organic acid decarboxylation are mainly distributed in the internal portion of sandbodies causing feldspar dissolution and precipitation of ferro carbonate cements the distribution of pore fluids caused the zonal distribution of carbonate cements in sandbodies during different periods this may be advantageous to preserve the porosity of reservoirs as exemplified by the distribution of high quality reservoirs in the red bed sandbodies

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

getting granite dikes out of the source region whether a dike can propagate far from a magma reservoir depends upon the competition between the rate at which propagation widens the dike and the rate at which freezing constricts the aperture available for magma flow various formulations are developed for a viscous fluid at temperature t sub m intruding a growing crack in an elastic solid the initial solid temperature equals t sub m at the source and decreases linearly with distance from the source if t sub m is the unique freezing temperature of the fluid dike growth is initially self similar and an essentially exact solution is obtained if t sub m is above the solidus temperature the solution is approximate but is designed to overestimate the distance the dike may propagate the ability of a dike to survive thermally depends primarily upon a single parameter that is a measure of the ratio of the dike frozen margin thickness to elastic thickness perhaps more intuitively one may define a minimum distance from the essentially solid reservoir wall to the point at which the host rock temperature drops below the solidus necessary for dikes to propagate far into subsolidus rock it is concluded that for reasonable material properties and source conditions most basalt dikes will have little difficulty leaving the source region but most rhyolite dikes will be halted by freezing soon after the magma encounters rock at temperatures below the magma solidus while these results can explain why granitic dikes are common near granitic plutons but rare elsewhere the potentially large variation in magmatic systems makes it premature to rule out the possibility that most granites are transported through the crust in dikes nonetheless these results highlight difficulties with such proposals and suggest that it may also be premature to rule out the possibility that most granite plutons ascend as more equidimensional bodies

a variable aperture fracture network model for flow and transport in fractured rocks a three dimensional variable aperture fracture network model for flow and transport in fractured rocks was developed the model generates both the network of fractures and the variable aperture distribution of individual fractures in the network before solving for the flow and transport of the whole network a library of single fracture permeabilities and particle transport residence time spectra is first established the spatially varying aperture field within an individual fracture plane is constructed by geostatistical methods then the flow pattern the fracture transmissivity and the residence times for transport of particles through each fracture are calculated the library of transmissivities and frequency distributions of residence times is used for all fractures in the network by a random selection procedure the solution of flow through the fracture network and the particle tracking calculation of solute transport for the whole network are derived from one side of the network to the other the model thus developed can handle flow and transport from the single fracture scale to the multiple fracture scale the single fracture part of the model is consistent with earlier laboratory tests and field observations the multiple fracture aspect of the model was verified in the constant aperture fracture limit with an earlier code the simulated breakthrough curves obtained from the model display dispersion on two different scales as has been reported from field experiments

diffusion controlled tracer retention in crystalline rock on the field scale 1 tracer retention is a key process for the barrier function of crystalline rock to any contaminant here we investigate the nature of retention mechanisms and their field scale parametrization using results of a comprehensive tracer transport experiment in crystalline rock on the field scale aspo hard rock laboratory sweden a method for identifying dominant retention mechanisms and inferring key parameters on the site scale is presented taking advantage of multiple tracer tests with a wide range of sorption affinities retention is shown to be diffusion controlled for the considered site robust features of tracer migration can be reasonably well predicted within a rock volume on at least 200 m scale by combining independent information with a simple model

an analysis of the influence of fracture geometry on mass transport in fractured media a stochastic modeling technique has been developed to investigate mass transport within a network of discrete fractures the fracture network is composed of two orthogonal fracture sets with fracture length location and aperture characterized by appropriate probability distributions emphasis is placed on understanding how fracture geometry influences mass transport within a network of discontinuous fractures the network is aligned in such a manner that one fracture set set one forms the dominant pathway for transport the primary role of the second fracture set is to provide connecting pathways between the discontinuous fractures of set one results suggest that mass transport can be described in terms of the directness of the connection between the upstream and downstream boundaries variations in fracture geometry which have the effect of increasing the probability that a relatively indirect or circuitous pathway exists through the network generally lead to an increase in both the mean and the standard deviation in the arrival time of various breakthrough fractions examples include a reduction in the number of fractures forming the set aligned with the direction of the hydraulic gradient or a decrease in the average length of fractures forming that set variations in fracture geometry which have the effect of increasing the probability that a relatively direct pathway will exist through the network have the opposite effect transport is sensitive to the variability in fracture aperture the connectivity of the fracture network is also shown to influence the magnitude of dispersive effects

petroleum generation modeling of the organic rich shales of late jurassic early cretaceous succession from mintaq 01 well in the wadi hajar sub basin yemen late jurassic early cretaceous shales of the naifa safer and madbi formations were studied to evaluate source rock characterization the results of the source rock were then incorporated into basin modeling to understand the timing of hydrocarbon hc generation and expulsion the late jurassic early cretaceous shales have low to high organic matter with total organic carbon toc values in the range of 0 50 28 01 indicating fair to excellent source rock potential main oil and gas are anticipated to be generated from the naifa safer and lam shale samples with types i and or ii and types ii iii kerogens in contrast the meem samples are dominated by type iii kerogen hydrogen index hi 200 mg hc g toc and are thus considered to be gas prone the late jurassic early cretaceous shale samples have temperatures of maximum pyrolysis yield tmax in the range of 337 515 c consistent with immature to post mature stages the tmax data also indicate that the safer and madbi shale samples h

characterizing the heterogeneity and correlation of perchloroethene sorption and hydraulic conductivity using a facies based approach a facies based approach was used to delineate both geochemical and physical aquifer property heterogeneity specifically the parameters considered were the sorption coefficient kd for a model organic contaminant and hydraulic conductivity k inferred from the particle size distribution subfacies sized samples were analyzed for both tetrachloroethene kd and k in a vertical core of the borden aquifer both parameters were correlated with the six sedimentary facies identified within the vertical core as a consequence of their relations to sedimentary facies significant positive correlations between ln k and ln kd which were different from the core scale correlation and different from each other were identified for some facies fades specific correlations generally resulted in improved statistics i e higher correlation coefficients and reduced confidence intervals compared to the core scale correlation the results suggest that a facies based approach can be useful in characterizing the heterogeneity of the transport properties of sedimentary aquifers

tracer tests in a fractured dolomite 2 analysis of mass transfer in single well injection withdrawal tests we investigated multiple rate diffusion as a possible explanation for observed behavior in a suite of single well injection withdrawal swiw tests conducted in a fractured dolomite we first investigated the ability of a conventional double porosity model and a multirate diffusion model to explain the data this revealed that the multirate diffusion hypothesis model is consistent with available data and is capable of matching all of the recovery curves second we studied the sensitivity of the swiw recovery curves to the distribution of diffusion rate coefficients and other parameters we concluded that the swiw test is very sensitive to the distribution of rate coefficients but is relatively insensitive to other flow and transport parameters such as advective porosity and dispersivity third we examined the significance of the constant double log late time slopes 2 1 to 2 8 which are present in several data sets the observed late time slopes are significantly different than would be predicted by either conventional double porosity or single porosity models and are believed to be a distinctive feature of multirate diffusion fourth we found that the estimated distributions of diffusion rate coefficients are very broad with the distributions spanning a range of up to 3 6 orders of magnitude fifth when both heterogeneity and solute drift are present late time behavior similar to multirate mass transfer can occur although it is clear that multirate diffusion occurs in the culebra the number of orders of magnitude of variability may be overestimated because of the combined effects of drift and heterogeneity

spatial moments analysis of kinetically sorbing solutes in aquifer with bimodal permeability distribution 1 we analyze the influence of the formation structure upon transport of nonreactive and kinetically sorbing solutes in heterogeneous porous formations formation structure is represented through a bimodal distribution of hydraulic conductivity with two scales of spatial variability which is a simplified yet realistic model of spatial variability kinetic sorption is modeled using a linear reversible rate expression we derive new closed form solutions of the second ergodic spatial moments of a kinetically sorbing solute although these solutions are obtained through a perturbation expansion in term of logconductivity variance they are not limited to any particular model of spatial variability we show that the formation structure as described by the bimodal model has a significant impact on plume moments of a non reactive tracer at moderate contrast between mean hydraulic conductivity of the two hydrofacies when the two scales of variability have comparable weight on the contrary the impact diminishes when bimodality weakens at both low and high contrast as expected the large time asymptotic longitudinal macrodispersion coefficient is influenced by the structure only through the variance and integral scale of log conductivity and thus the result for the bimodal model is identical to that of a unimodal gaussian field sharing the same second order statistics the impact of kinetic sorption depends upon the plume travel time since injection at early times sorption kinetics tends to accentuate the difference between the longitudinal macrodispersivity in bimodal and unimodal fields while at later times the difference is minimal because overall macrodispersivity is dominated by the spreading caused by nonequilibrium sorption in a bimodal formation transverse macrodispersivity peaks later and declines to zero slower than in a gaussian unimodal field with the same second order statistics these results demonstrate that even a very simplified facies model such as the bimodal model relying on a statistical distribution of high and low conductivity zones has important impacts upon global parameters describing the migration of nonreactive and reactive tracers consequently larger effects are expected for quantities such as early arrival times and btc tailing which are more directly influenced by the spatial patterns of high hydraulic conductivity than global parameters such as macrodispersivity furthermore these solutions contribute to bridge the gap between stochastic modeling and applications since bimodal fields can be obtained to honor soft data typically available in applications for example through conditional simulations using stratigraphic information from well logs

mechanics of two interacting magma driven fractures a numerical study to understand magma focusing from broad melting zones in the crust propagation in brittle rocks of two interacting dikes ascending from a single deep source has been modeled using a time dependent plane strain hydraulic fracturing model the source is assumed to generate a constant influx rate to feed the dike growth which is also aided by buoyancy effects in contrast to uncoupled model results the simultaneous parallel growth of two dikes to a certain distance is found to occur provided that the two dikes are initially of different heights which might be produced either by previous magma intrusion or during nucleation the shorter dike will chase the longer one and they can either progressively merge or continue subparallel growth at a reduced spacing depending on the deviator stress between the vertical and horizontal stresses and the initial lateral separation with parameters given in dimensionless forms numerical results reveal the mechanics for simultaneous ascents of two subparallel dikes in that dike interaction can produce a low stress field which is just above the tip of the shorter dike favorable to growth of the shorter dike the energy analysis indicates that the energy required for two subparallel dikes is less than that for a single dike during the late time buoyancy viscosity propagation stage where considerable ascent occurs this growth behavior might provide the mechanism for simultaneous instead of sequential growth of various dikes in a single set

effective matrix diffusion in kilometer scale transport in fractured crystalline rock concentrations of tritium 3h and dichlorodifluoromethane cfc 12 in water samples taken from glacial drift and fractured crystalline rock over 4 km2 in central new hampshire are interpreted to identify a conceptual model of matrix diffusion and the magnitude of the diffusion coefficient dispersion and mass transfer to and from fractures has affected the 3h concentration to the extent that the peak 3h concentration of the 1960s is no longer distinguishable because of heterogeneity in the bedrock the sparsely distributed chemical data do not warrant a three dimensional transport model instead a one dimensional model of cfc 12 and 3h migration along flow lines in the glacial drift and bedrock is used to place bounds on the processes affecting kilometer scale transport arid model parameters are varied to reproduce the measured relation between 3h and cfc 12 rather than their spatial distributions a model of mass exchange to and from fractures that is dependent on the time varying concentration gradient at fracture surfaces qualitatively reproduces the measured relation between 3h and cfc 12 with an upper bound for the fracture dispersivity approximately equal to 250 m and a lower bound for the effective matrix diffusion coefficient equal to 1 m2 yr 1 the diffusion coefficient at the kilometer scale is at least 3 orders of magnitude greater than laboratory estimates of diffusion in crystalline rock the large diffusion coefficient indicates that diffusion into an immobile fluid phase rock matrix is masked at the kilometer scale by advective mass exchange between fractures with large contrasts in trarismissivity the measured transmissivity of fractures in the study area varies over more than 6 orders of magnitude advective mass exchange from high permeability fractures to low permeability fractures results in short migration distances of a chemical constituent in low permeability fractures over an extended period of time before reentering high permeability fractures viewed at the kilometer scale this process is analogous to the chemical constituent diffusing into and out of an immobile fluid phase

contaminant tailing in highly heterogeneous porous formations sensitivity on model selection and material properties summary coupled impacts of slow advection diffusion and sorption were investigated using two heterogeneity models that differ in structure and in the mathematical framework that was used to simulate flow and transport and to quantify contaminant tailing both models were built using data from a highly heterogeneous exposure of the borden aquifer at a site located 2 km north west of the stanford waterloo experimental site at canadian forces base borden ontario canada the inclusions based model used a simplified representation of the different materials found at the site while the second model was based on transitional probability geostatistics of the formation these two models were used to investigate sensitivity of contaminant tailing on model selection and on geometric and material properties while simulations were based on data collected at borden models were exercised beyond the geometric and material properties that characterize the site various realizations have identified very low conductive silty clay found at volume fraction of 23 4 as the material with dominant influence on tailing and vertical diffusion in and out of low conductive units affected by sorption as the dominant transport mechanism causing tailing the two models yielded almost identical transport results when vertical correlation lengths of silty clay were matched several practical implications relevant for characterization of low conductive units were identified and briefly discussed

tide influenced sedimentation in a rift basin cretaceous qishn formation masila block yemen a billion barrel oil field the lower cretaceous qishn clastics member in masila block 14 hadhramaut region republic of yemen has estimated reserves of 1 1 billion bbl recoverable oil and has produced 600 million bbl of oil sedimentation took place in an elongate paleogulf of the say un al masila basin with open marine carbonates to the east the qishn clastics member unconformably overlies mixed carbonates and clastics of the sa af member lower qishn onlap resulted in deposition of brackish and tidal likely macrotidal estuarine to open bay or gulf deposits the middle portion of the lower qishn clastics member shows evidence of arid nonmarine sedimentation including debris flow deposits red beds and shale clast conglomerates in turn overlain by interfingering coastal and nonmarine deposits the lower qishn clastics member is truncated by a sequence boundary overlain by an extensive sandstone deposited in a low accommodation braid plain close to the shoreline a flooding surface is present at the top of the sandstone over which progradational tide influenced deltaic strata were deposited delta progradation culminated in shallow water clastic dolomitic deposits on the coastal plain with subsequent transgression a rising water table caused a nonmarine flooding surface with lakes and lacustrine deltas overlain by tidal flat deposits ongoing transgression resulted in wave ravinement overlain by shallow shelf clastics and then deposition of slightly deeper shelf carbonates the uppermost unit comprises bioturbated clastic shelf deposits related to a drop in relative sea level throughout much of the qishn clastics interval accommodation was moderate except for low accommodation associated with regional sheet sandstone at the base of the upper qishn clastics member virtually all marine and brackish deposits show evidence of tidal sedimentation climate was arid and seasonally wet

upscaling of reactive mass transport in fractured rocks with multimodal reactive mineral facies 1 this paper presents a methodology for upscaling matrix material transport parameters in fractured flow dominated systems with multimodal reactive mineral facies the upscaling method provides a theoretical and practical link between controlled experimental results at the laboratory bench scale and multikilometer field scales at which contaminant remediation and risk assessment are actually conducted as sorption reactions in matrix are in part determined by mineral properties a new conceptual model is developed to reflect the hierarchical structure of reactive mineral facies at the microform mesoform and macroform scales the conceptual model of hierarchical reactive matrix mineral facies is integrated with a dual porosity model for simulating diffusion of solutes out of fractures and sorption onto the matrix minerals by assuming that sorption reactions primarily occur in the rock matrix we develop a multimodal spatial random function for characterizing both the tortuosity physical heterogeneity and sorption coefficient chemical heterogeneity at different scales in the rock matrix the effective tortuosity at the field scale is derived by volume averaging of mass transfer coefficient for a conservative species subsequently using a sorbing species e g uranium we derive the equations for upscaling the sorption coefficients in a saturated fractured rock system for field scale simulations the effective field scale tortuosity and sorption coefficient are related to their mean variance integral scale and domain size along a pathway through a three dimensional flow field the upscaled values increase with the integral scale and are larger than their geometric mean simulations conducted with upscaled sorption coefficients and tortuousities are compared very well with high resolution monte carlo simulations capturing the parameter spatial variations results of this study can be extended to explore scaledependenceofotherimportant transportparametersforfractured rocksolutetransport citation deng h z dai a wolfsberg z lu m ye and p reimus 2010 upscaling of reactive mass transport in fractured rocks with multimodal reactive mineral facies water resour res 46 w06501 doi 10 1029 2009wr008363

effects of volcano loading on dike propagation in an elastic half space we use laboratory experiments and numerical models to examine the effects of volcano loading on the propagation of buoyant dikes in a two dimensional elastic half space in laboratory experiments we simulate the propagation of buoyant dikes in an isotropic regional stress field by injecting air into tanks of solidified gelatin a weight resting on the surface of the gelatin represents a volcanic load a numerical model is used to simulate these experiments both experiments and numerical simulations show that as a dike ascends it begins to curve toward the load in response to the local stress field imposed by the load the lateral distance over which dikes curve to the load increases with the ratio of average pressure at the base of the load to the dike driving pressure for realistic volcano and dike dimensions this pressure ratio is going to be large suggesting that dikes can converge to a volcano over lateral distances several times the load width numerical calculations involving an anisotropic regional stress field however predict that the lateral extent of dike attraction shrinks as the regional horizontal compressive stress decreases relative to the vertical compressive stress dike focusing will be substantial if the regional differential stresses are less than the average pressure at the base of the load if this is the case then our models predict a positive feedback between the size of volcanoes and the area of dike attraction this feedback may promote the development of large discrete volcanoes and also predicts a positive correlation between the spacing and sizes of adjacent volcanoes to test this prediction we examine nearest neighbor pairs of the 21 largest volcanoes in the cascade range the 14 pairs examined show a large range in volcano spacing 6 115 km and a statistically significant correlation between spacing and average volcano height this result is consistent with our model results and suggests that the local compressive stress induced by these volcanoes may be an important factor in controlling magma transport in the lithosphere

discrete dual porosity model for electric current flow in fractured rock the identification of fractures and the characterization of their properties are of critical importance in a wide variety of research fields and applications to this end geophysical methods are of significant interest as they can provide information regarding the spatial distribution of a number of subsurface physical properties in a rapid and noninvasive manner electrical resistivity surveying in particular has been shown in several previous investigations to exhibit sensitivity to the presence of fractures suggesting that geoelectrical experiments may contain important information regarding how fractures are distributed and connected in the subsurface however a lack of suitable numerical modeling tools for electric current flow in fractured media has prevented a detailed and systematic exploration of this concept to address this issue we present a novel discrete dual porosity modeling approach that is specifically tailored to the electrical resistivity problem with our approach an analytical formulation for fracture matrix current flow exchange at the fracture scale is integrated into a discrete fracture network model which is then combined with a block scale finite volume representation of the rock matrix our methodology allows for low cost and accurate simulation of electric current flow through both the fractures and matrix and is readily applicable to complex fracture networks at relatively large scales although formulated here in two dimensions this work represents an important first step toward investigating the effect of fracture network characteristics on bulk electrical properties as well as toward the simulation of geoelectrical survey data in realistic fractured rock environments

use of sedimentological information for geometric simulation of natural porous media structure a geometric simulation method was used to develop a three dimensional highly detailed synthetic representation of point bar sediments in the wabash river system geometric simulation methods in comparison to well known second order stochastic methods offer the advantage of being more closely related to depositional processes which are often similarly conceptualized i e described in terms of shapes of discrete bed forms trends in grain size and spatial relationships of defined geologic facies multiple scales of geometric variation were defined within a sedimentologically prescribed framework and shapes of discrete geometric elements were established at each scale the selected shapes were based on published field studies including sedimentological bed form studies and trench studies in active point bar sediments the parameterization of the shapes allowed for random variability of the shape descriptors discrete shapes were then generated and assimilated by computer hydraulic conductivity values were assigned to the discrete elements based on reports of observed variations in grain size and field measurements of hydraulic conductivity the synthetic model referred to as a numerical aquifer is being used as the basis for extensive numerical experimentation to study the relationship between natural spatial structure and subsurface flow and transport

propagation regimes of buoyancy driven hydraulic fractures with solidification this study investigates the propagation of a semi infinite buoyancy driven hydraulic fracture in situations when the fluid is able to solidify along the crack walls such problems occur when hot magma ascends from a chamber due to buoyancy forces and solidifies by interacting with colder rock in the model the solidification rate is calculated assuming a one dimensional heat transfer problem in which case it becomes mathematically equivalent to carter s leak off model which is commonly used to describe the fluid leak off from a hydraulic fracture into a porous rock formation in order to construct a mathematical model for a buoyancy driven hydraulic fracture with solidification the aforementioned thermal problem is combined with i linear plane strain elasticity to ensure equilibrium of the rock surrounding the fracture ii linear elastic fracture mechanics to determine the fracture propagation iii lubrication theory to capture the viscous fluid flow inside the crack and to account for the effect of buoyancy and iv volume balance of the magma to address the problem the governing equations are first rewritten in terms of one integral equation with a non singular kernel which significantly simplifies the analysis and the procedure for obtaining a numerical solution the latter solution is shown to obey a multiscale behaviour near the fracture tip that is fully resolved by the numerical scheme in order to understand the structure of the solution and to quantify the regimes of propagation and the associated transitions a thorough analysis of the problem has been performed finally the developments are applied to investigate the non steady propagation of a buoyancy driven fracture that is fed by a constant flux

a constant influx model for dike propagation implications for magma reservoir dynamics 1 most observations of seismicity rate during dike propagation on basaltic volcanoes show 1 rate stationarity despite possible variations of the dike tip velocity 2 frequent lack of clear and monotonic hypocenter migration following dike propagation and 3 event occurrences located backward with respect to the dike tip position on these bases the origin of the seismicity contemporary to dike intrusion within basaltic volcanoes cannot be solely related to the crack tip propagation seismicity rather appears to be the response of the edifice itself to the volumetric deformation induced by the magma intruding the solid matrix the volume change induced into the volcano edifice over time by the intruding magma is equal to the magma flux injected into the dike from the reservoir the consequence of this is that the stationary seismicity rate observed during the intrusion is a proxy for the magma flux withdrawn from the reservoir we consider a two phase dike propagation model including a first vertical propagation followed by a lateral migration along a lithological discontinuity we explore 1 under which geophysical conditions the vertical dike is fed at constant flow rate of magma and 2 dike propagation patterns implications entailed by constant volumetric flux on the piton de la fournaise volcano case study suggest a minimum size for the magma reservoir of about 1 km3 and a maximum value for the initial magma reservoir overpressure of about 2 2 mpa considering similar magma inflow rates during vertical and lateral dike propagation phases we reproduce independent estimates of propagation velocities rise times and injected volumes when applying the model to the august 2003 piton de la fournaise eruption

spatial distributions of perchloroethylene reactive transport parameters in the borden aquifer 1 we determined the descriptive statistical and spatial geostatistical properties of the perchloroethene ln kd and the ln k of a 1 5 m thick by 10 m horizontal transect of the borden aquifer near the location of the stanford waterloo sw tracer experiment the ln kd distribution is not normal and is right skewed because of a few high values that occur localized in two regions of the transect in contrast the ln k data can be characterized by a normal distribution a linear regression of ln kd on ln k yields a statistically significant positive correlation also shown at small lags in the cross correlogram no significant vertical or horizontal trend in the ln kd data was detected the semivariogram ranges of ln k and ln kd differ from one another in the vertical direction 0 33 0 06 m and 0 20 0 04 m respectively and are much less than the horizontal ranges a few meters despite significant effort the horizontal range of ln kd remains poorly characterized because of limitations of the sample locations many of the characteristics described above do not match those assumed in prior theoretical studies that examined the importance of various aquifer characteristics on sw tracer transport we suggest that there is knowledge to be gained by revisiting the conclusions of these prior studies in light of the new information presented here

subcritical dyke propagation in a host rock with temperature dependent viscoelastic properties summary in this paper we examine the effects of temperature dependent viscoelastic properties of the host rock on the subcritical growth of a dyke from a magma chamber a theoretical relationship between the velocity of subcritical dyke growth and dyke length is established using a perturbation solution of stress intensity factor at the dyke tip and a viscoelastic crack growth theory in which the temperature dependent creep properties are taken into account the temperature field around the dyke is calculated using an analytic solution the numerical results for a dyke subcritically propagating from a magma chamber indicate that while the general dyke growth characteristics are similar to those with constant creep properties the subcritical dyke growth velocity is increased by an order of magnitude by considering the temperature dependence of the creep properties hence the subcritical growth duration before the dyke reaches the unstable growth state is significantly shortened

tracer transport in fractured crystalline rock evidence of nondiffusive breakthrough tailing extended tailing of tracer breakthrough is often observed in pulse injection tracer tests conducted in fractured geologic media this behavior has been attributed to diffusive exchange of tracer between mobile fluids traveling through channels in fractures and relatively stagnant fluid between fluid channels along fracture walls or within the bulk matrix we present a field example where tracer breakthrough tailing apparently results from nondiffusive transport tracer tests were conducted in a fractured crystalline rock using both a convergent and weak dipole injection and pumping scheme deuterated water bromide and pentafluorobenzoic acid were selected as tracers for their wide range in molecular diffusivity the late time behavior of the normalized breakthrough curves were consistent for all tracers even when the pumping rate was changed the lack of separation between tracers of varying diffusivity indicates that strong breakthrough tailing in fractured geologic media may be caused by advective transport processes this finding has implications for the interpretation of tracer tests designed to measure matrix diffusion in situ and the prediction of contaminant transport in fractured rock

effects of mineral spatial distribution on reaction rates in porous media 1 this study examined the effects of variations in mineral spatial distributions on reaction rates in porous media pore scale network models were constructed to represent sandstones with anorthite and kaolinite present in various amounts and in different spatial patterns simulation conditions corresponded to geological sequestration of carbon dioxide to examine scaling effects arising from pore scale heterogeneities reaction rates from network models were compared to rates from continuum models that use uniform concentrations with small percentages of reactive minerals the scaling effects are large and the effect of spatial distribution is significant scaling effects are largest when reactive minerals are closely clustered and oriented parallel to flow conversely spatial distributions that enhance mass transport to and from reactive minerals such as small mineral clusters or elongated clusters oriented transverse to flow result in reaction rates that are well represented by the continuum model

diagenetic sequence related to structural history and petroleum accumulation spindle field colorado two upper cretaceous marine sandstones have produced 36 million bbl of oil and 164 bcf of gas at spindle field in the denver basin of colorado the sandstones are offshore bars enclosed in finer grained rocks of the middle pierre shale they were deposited in response to western interior sea level fluctuations that affected water depths energy levels and sediment distribution across structurally controlled sea floor topography during several intervals of cretaceous sedimentation some of the structures that influenced pierre deposition are believed to have controlled later emplacement of oil and gas preliminary petrographic analysis of the sandstones indicates that four phases of diagenesis have occurred early diagenetic events of compaction and formation of authigenic chlorite rims silica overgrowths and calcite cement within the sandstones phases i and ii largely destroyed initially good primary porosity and permeability in these well sorted sandstones these early events approximately coincide with the energy of formation dgr g f related paragenetic sequences in fine to medium grained well sorted marine rocks as reported by other workers however later diagenetic events phases iii and iv clearly record separate phases with no sequential relationship to earlier events later diagenetic events of calcite solution to form secondary porosity and partial occlusion of the secondary porosity by authigenic kaolinite and minor illite reflect a change in pore fluid chemistry believed to be related to vertical migration of acidic fluids from below acid water resulting from dissociation of the co2 gas produced during degradation of organic matter in the source rocks is considered a likely solvent for the calcite secondary porosity has created the reservoir at spindle field elsewhere thick originally well sorted sandstones are tight both the acidic fluids and the oil and gas are postulated to have migrated vertically under pressure related to petroleum generation into the reservoir along tensional faults and fractures related to a paleostru tural element at depth spindle field hydrocarbons represent a combination of stratigraphic and diagenetic trapping diagenetic sequences record aspects of the total burial history of a rock that may be combined with other geologic information to give a better understanding of the total burial history predictability of timing and mechanism of hydrocarbon emplacement may be enhanced by relating diagenetic sequences to the structural features and history of an area the diagenetic sequence observed in the sandstones at spindle field is recognized as a response to structural influence on fluid migration

review of diagenetic facies in tight sandstones diagenesis diagenetic minerals and prediction via well logs abstract the tight sandstones are characterized by low porosity low permeability complex pore structure and strong heterogeneity due to the extensive diagenetic modifications they experienced understanding of the impact of diagenetic alterations on reservoir quality is crucial to the hydrocarbon exploration and production in tight sandstones diagenetic facies which is the comprehensive description of the diagenesis and diagenetic minerals determines the formation and distribution of sweet spot by correlating the diagenetic facies to well log responses the subsurface distribution of porosity and permeability can be predicted however the prediction of diagenetic facies and reservoir quality via well logs in tight sandstones remains a challenging task this paper critically reviews the impact of diagenesis and diagenetic minerals on reservoir quality in tight sandstones and establishes a model for prediction of diagenetic facies via well logs as assessed from peer reviewed papers in the literature as well as from the authors personal experiences this review begins with reviewing the impacts of compaction cementation dissolution and various types of diagenetic minerals on reservoir quality evolution the definition and classification schemes of diagenetic facies are then discussed and the reservoir quality as well as diagenetic evolution sequence of various diagenetic facies is summarized the same diagenetic facies commonly display similar compositional and textural attributes matrix and cement as well as porosity systems the well log responses gr ac den cnl and rt of various diagenetic facies are summarized by the calibration of log values with cores and related thin sections by translating the diagenetic facies to conventional well logs a predictable model which can be used for subsurface reservoir quality prediction is established then the theory of ecs logs is reviewed and the application of ecs logs in diagenetic facies evaluation is discussed at last the quantitative characterization for various type and degree of diagenesis is reviewed and the subsurface diagenetic facies is predicted by quantitative calculation of the compactional porosity loss cementational porosity loss and dissolution porosity content via well logs correlating the diagenetic facies to well logs provides a powerful tool to predict the distribution of high quality reservoirs in tight sandstones this review will provide insights into the reservoir quality evaluation and sweet spot prediction via well logs in tight sandstones

diagenetic characteristics and reservoir quality of the lower cretaceous biyadh sandstones at kharir oilfield in the western central masila basin yemen the lower cretaceous biyadh formation in the masila basin is an important hydrocarbon reservoir however in spite of its importance as a reservoir published studies on the biyadh formation more specifically on the diagenesis and relate with reservoir quality are limited based on core samples from one well in the kharir oilfield western central masila basin this study reports the lithologic and diagenetic characteristics of this reservoir the biyadh sandstones are very fine to very coarse grained moderate to well sorted quartzarenite and quartzwacke the diagenetic processes recognized include mechanical compaction cementation carbonate clay minerals quartz overgrowths and a minor amount of pyrite and dissolution of the calcite cement and feldspar grains the widespread occurrences of early calcite cement suggest that the biyadh sandstones lost a significant amount of primary porosity at a very early stage of its diagenetic history based on the framework grain cement relationships precipitation of the early calcite cement was either accompanied or followed by the development of part of the pore lining and pore filling clay cements secondary porosity development occurred due to partial to complete dissolution of early calcite cement and feldspar grains in addition to calcite several different clay minerals including kaolinite and chlorite occur as pore filling and pore lining cements kaolinite largely occurs as vermiform and accelerated the minor porosity loss due to pore occlusion chlorite coating grains helps to retain primary porosity a by retarding the envelopment of quartz overgrowths porosity and permeability data exhibit good inverse correlation with cement thus reservoir quality is controlled by pore occluding cement diagenetic history of the biyadh sandstones as established here is expected to help better understanding and exploitation of this reservoir the relation between diagenesis and reservoir quality is as follows the initial porosity was decreased by compaction and cementation and then increased by dissolution of early calcite cement and feldspar grains the reservoir quality is also affected by depositional environment controls of grain size sorting and matrix thus best good quality reservoir rocks were deposited in braided river channels environment where no inhibited authigenic clays and high percentages of detrital quartz

solute transport through fractured rock radial diffusion into the rock matrix with several geological layers for an arbitrary length decay chain the paper presents a model development to derive a semi analytical solution to describe reactive solute transport through a single channel in a fracture with cylindrical geometry the model account

effect of advective flow in fractures and matrix diffusion on natural gas production although hydraulic fracturing has been used for natural gas production for the past couple of decades there are significant uncertainties about the underlying mechanisms behind the production curves that are seen in the field a discrete fracture network based reservoir scale work flow is used to identify the relative effect of flow of gas in fractures and matrix diffusion on the production curve with realistic three dimensional representations of fracture network geometry and aperture variability simulated production decline curves qualitatively resemble observed production decline curves the high initial peak of the production curve is controlled by advective fracture flow of free gas within the network and is sensitive to the fracture aperture variability matrix diffusion does not significantly affect the production decline curve in the first few years but contributes to production after approximately 10 years these results suggest that the initial flushing of gas filled background fractures combined with highly heterogeneous flow paths to the production well are sufficient to explain observed initial production decline lastly these results also suggest that matrix diffusion may support reduced production over longer time frames

numerical modeling of the geomechanical behavior of ghawar arab d carbonate petroleum reservoir undergoing co2 injection sedimentary porous rocks can be used for long term subsurface containment of co2 before injecting co2 to sedimentary reservoirs it is necessary to perform stability analysis of the reservoir and to estimate the maximum sustainable pore fluid pressures in order to avoid the reservoir damage during the co2 injection the effective stresses in the reservoir should be evaluated in this paper numerical modeling techniques are used for the evaluation of stresses and deformations in a naturally fractured carbonate sedimentary reservoir the developed numerical modeling scheme couples the behavior of the co2 injection and the change in the geomechanical behavior of the sedimentary carbonate reservoir for a case study from saudi arabia the present investigation extends the previous studies by considering the sorption based deformation during the injection of the compressed co2 fluid into the arab d naturally fractured carbonate reservoir the change in permeability during the injection of co2 is evaluated the adopted co2 injection scenario was shown to be within the safe maximum occupancy and that the increase in the pore pressure does not result in the reservoir failure

effects of reservoir size and boundary conditions on pore pressure buildup and fault reactivation during co 2 injection in deep geological reservoirs the excessive burning of the fossil fuels has caused severe global climatic changes such as increasing the global temperature causing initiation of the wild fire rising the sea level increasing the floods storms amount of rain and snow one of the effective global mitigation strategies is sequestration of huge quantity of co2 deep below the ground level for a long period of time an important issue is to ensure the permanency and safety of the sequestration process due to the associated pore pressure buildup it is necessary to have correct estimates of the pore pressure buildup ground uplift and re activation of any existing fault during the process of co2 injection and long term storage in this investigation the effects of reservoir size and boundary conditions are investigated by means of geomechanical modeling of the deep biyadh sandstone reservoir in saudi arabia currently carbon dioxide is not injected into the actual biyadh reservoir in this investigative modeling co2 is injected for an injection period of ten years using a single injection well at the center of the reservoir the developed modeling scheme for a single injection well has been extended further to include multiple injection wells for multiple injection wells the reservoir size and locations of injection wells are varied to evaluate their effect on the pore pressure buildup and ground uplift the reservoir stability analysis has been performed using mohr coulomb failure criterion for both small and large reservoir models with the same injection parameters the simulation results demonstrated that pressure buildup and ground uplift are relatively higher for reservoirs with small sizes and closed boundaries while in the case of large sizes and open boundaries the pore pressure buildup and ground uplift are relatively lower moreover the effect of the reservoir size and boundary conditions on the reactivation of faults during co2 injection has been evaluated the stability analysis performed in this study shows that injecting co2 into larger size reservoir is safer as compared to smaller size reservoir injecting co2 with multiple injection wells will cause pore pressure buildup of huge magnitudes the modeling results show that suggesting a representative volume for the reservoir during co2 injection can under estimate the pore pressure buildup and fault re activation that can cause the reservoir failure and leakage of the stored co2

an interdisciplinary approach to reservoir characterisation an example from the early to middle eocene kaimiro formation taranaki basin new zealand abstract the kaimiro formation is an early to middle eocene ne sw trending reservoir fairway in taranaki basin and comprises a range of coastal plain through to shallow marine facies a time of regional transgression is observed across the paleocene eocene transition which is linked to a general global warming trend and to regional thermal relaxation related subsidence in new zealand the earliest eocene transgressive deposits pass upwards into a series of cyclically stacked packages interpreted as 3rd and 4th order sequences maximum regression occurred within the early eocene and was followed by punctuated retrogradational stacking patterns associated with shoreline retreat and subsequent regional transgression in the middle eocene the kaimiro formation is considered a good reservoir target along most of the reservoir fairway which can largely be attributed to a consistently quartz rich lithic poor composition and reasonably coarse sand grain size correlations demonstrate that within the early eocene the main reservoir facies are channel fill sandstones overlying candidate sequence boundaries in paleoenvironmentally landward proximal settings and upper shoreface shoreline sandstones in relatively basinward distal settings middle eocene reservoir facies are not represented in distal wells due to overall transgression at this time yet they form a significant target in more proximal well locations particularly on the taranaki peninsula depositional facies is one of the principal controls on sandstone reservoir quality however while reservoir facies have been proven along the length of the reservoir fairway it is evident that diagenesis has significantly impacted sandstone quality relatively poor reservoir properties are predicted for deeply buried parts of the basin maximum burial 4 5 km due to severe compaction and relatively abundant authigenic quartz and illite in contrast good reservoir properties are locally represented in reservoir facies where present day burial depths are these results illustrate how an interdisciplinary approach to regional reservoir characterisation are used to help reduce risk during prospect evaluation assessment of both reservoir distribution and quality is necessary and can be undertaken through integrated studies of facies sequence stratigraphy burial modelling and petrography

analytical predictions for a natural spacing within dyke swarms dykes often grow next to other dykes evidenced by the widespread occurrence of dyke swarms that comprise many closely spaced dykes in giant dyke swarms dykes are observed to maintain a finite spacing from their neighbors that is tens to hundreds of times smaller than their length to date mechanical models have not been able to clarify whether there exists an optimum or natural spacing between the dykes and yet the existence of a natural spacing is at the heart of why dykes grow in swarms in the first place here we present and examine a mechanical model for the horizontal propagation of multiple closely spaced blade like dykes in order to find energetically optimal dyke spacings associated with both constant pressure and constant influx magma sources we show that the constant pressure source leads to an optimal spacing that is equal to the height of the blade like dykes we also show that the constant influx source leads to two candidates for an optimal spacing one which is expected to be around 0 3 times the dyke height and the other which is expected to be around 2 5 times the dyke height comparison with measurements from dyke swarms in iceland and canada lends initial support to our predictions and we conclude that dyke swarms are indeed expected to have a natural spacing between first generation dykes and that this spacing scales with and is on the order of the height of the blade like dykes that comprise the swarm

spatial correlation of permeability in cross stratified sediment with hierarchical architecture 1 cross stratified deposits can give rise to a hierarchy of permeability modes across scales corresponding to a hierarchy of sedimentary unit types the shape of the sample semivariogram for permeability can be largely controlled by the shape of the cross transition probabilities of unit types having the greatest contrast in permeability the shape of those cross transition probabilities can be in turn largely determined by the variance of the lengths of those unit types a sufficient condition for an exponential like semivariogram is the repeated occurrence of unit types having both a contrast in permeability and a large length variance these relationships are shown through writing the identities for spatial correlation of permeability in a hierarchical and multimodal form and as a function of the transition probabilities for the sedimentary unit types these relationships are also illustrated through analyzing data representing cross stratified sediments within a point bar deposit

channeling with diffusion into stagnant water and into a matrix in series numerous field observations show that most water flow in fractured rocks takes place in only a small part of the fractures we call these channels solutes in the flowing water can diffuse in and out of stagnant water in the porous rock matrix that the flowing water contacts via the so called flow wetted surface fws in addition the solutes can diffuse into stagnant water in the fractures themselves and from this water further into the rock matrix for narrow channels with small fws the transport via the stagnant water in the fracture can considerably add to the exchange of solutes between flowing water and matrix water for sorbing solutes that interact with the micropore surfaces in the matrix the effect can be very strong some models that account for these processes are developed and solved using laplace transforms some examples are presented that show the effects of first diffusion into stagnant waters in fractures with subsequent diffusion into the rock matrix effects of slit like and tube like channels are considered as well as the presence of intersecting fractures the solutions are especially useful to model solute transport in complex three dimensional channels networks where wide and narrow or even tube like channels with widely varying flow rates combine into a multitude of different paths

diagenetic sequences of continuously deposited tight sandstones in various environments a case study from upper paleozoic sandstones in the linxing area eastern ordos basin china an integrated analysis of the petrographic characteristics and types and distribution of diagenetic alteration in the upper paleozoic benxi taiyuan shanxi and xiashihezi formations provides insights into the controlling factors on variations in porosity and permeability in tight sandstones 85 of the sandstone samples display porosity values 10 and 90 of the samples exhibit permeability 1 md diagenetic alteration includes mesogenetic compaction cementation by dolomite ankerite and quartz dissolution of feldspar and illitization of smectite eodiagenesis includes compaction development of smectite cementation by pore filling quartz and disordered kaolinite and precipitation of calcite and fe calcite chlorite and quartz preserve primary pores against damage whereas kaolinite illite smectite i s mixed layer and illite significantly diminish reservoir quality via permeability reduction chlorite and i s content decrease abruptly as depth increases whereas the kaolinite content remains elevated at depth because of the complete destruction of k feldspar the transformation from smectite to illite provides silica ions for the widely distributed quartz overgrowths as the depositional environment transformed from fluvial xiashihezi to deltaic shanxi and to epicontinental taiyuan and benxi the dissolution effect increased monotonically feldspar dissolution is dominant in the shanxi formation whereas the benxi and taiyuan formations commonly contain quartz dissolution pores the taiyuan formation has markedly higher porosities than in the overlying and underlying formations caused by strong dissolution and high silica content the decrease in porosity in the benxi formation results from the extensive formation of clay minerals caused by high frequency transgressions in a transitional environment

improving permeability semivariograms with transition probability models of hierarchical sedimentary architecture derived from outcrop analog studies received 21 july 2004 revised 22 february 2005 accepted 23 march 2005 published 30 july 2005 1 as analogs for aquifers outcrops of sedimentary deposits allow sedimentary units to be mapped permeability to be measured with high resolution and sedimentary architecture to be related to the univariate and spatial bivariate statistics of permeability sedimentary deposits typically can be organized into hierarchies of unit types and associated permeability modes the types of units and the number of hierarchical levels defined on an outcrop might vary depending upon the focus of the study regardless of how the outcrop sediments are subdivided a composite bivariate statistic like the permeability semivariogram is a linear summation of the autosemivariograms and cross semivariograms for the unit types defined weighted by the proportions and transition probabilities associated with the unit types the composite sample semivariogram will not be representative unless data locations adequately define these transition probabilities data reflecting the stratal architecture can often be much more numerous than permeability measurements these lithologic data can be used to better define transition probabilities and thus improve the estimates of the composite permeability semivariogram in doing so bias created from the incomplete exposure of units can be reduced by a bayesian approach for estimating unit proportions and mean lengths we illustrate this

reactive transport modeling an essential tool and a new research approach for the earth sciences abstract reactive transport modeling is an essential tool for the analysis of coupled physical chemical and biological processes in earth systems and has additional potential to better integrate the results from focused fundamental research on earth materials appropriately designed models can describe the interactions of competing processes at a range of spatial and time scales and hence are critical for connecting the advancing capabilities for materials characterization at the atomic scale with the macroscopic behavior of complex earth systems reactive transport modeling has had a significant impact on the treatment of contaminant retardation in the subsurface the description of elemental and nutrient fluxes between major earth reservoirs and in the treatment of deep earth processes such as metamorphism and magma transport active topics of research include the development of pore scale and hybrid or multiple continua models to capture the scale dependence of coupled reactive transport processes frontier research questions that are only now being addressed include the effects of chemical microenvironments coupled thermal mechanical chemical processes controls on mineral fluid reaction rates in natural media and scaling of reactive transport processes from the microscopic to pore to field scale

sedimentology diagenesis and reservoir quality of the upper abu gabra formation sandstones in the fula sub basin muglad basin sudan abstract successful hydrocarbon exploration of the lower cretaceous abu gabra formation has established the need to understand the diagenesis and reservoir quality of the sandstones reservoirs in the area therefore this study contains a subsurface facies analysis based on description of three conventional cores from the moga21 2 well methods include wireline log analysis a petrographic study with both thin sections and scanning electron microscope investigations grain size x ray diffraction xrd and heavy minerals analysis of the abu gabra sandstone sedimentary composition and facies sequences of the well logs indicate a complex fluvial channel paleo environment grain size analysis revealed that the sandstone is a mixture of mainly sand size petrographically the sandstones are classified based on standard rock classification schemes into subfeldspathic arenites and feldspathic arenite lithofacies quartz grains are the most abundant detrital components in the samples both polycrystalline and monocrystalline followed by feldspars mainly k feldspar micas and detrital and authigenic clays with carbonatic detritus although lithic fragments iron oxides and heavy minerals occur in minor amounts presence of sillimanite epidote and hornblende compared to zircon tourmaline and rutile as well as the presence of chlorite the dominance of polycrystalline quartz and high crystallinity of kaolinite could be responsible for the low grade metamorphism kaolinite is an authigenic component while quartz overgrowths occur in variable quantity and carbonates calcite and siderite in a relatively minor amount pore types are basically primary and secondary interparticle with few secondary intraparticle pores due to the dissolution of feldspars although porosity ranges from 9 20 to 31 20 the presence of kaolinite carbonate and quartz overgrowth cement reduce the porosity of the samples analyzed samples are characterized by poor to very good pore interconnectivity despite the fact that most of the sandstones display point concavo convex and long contacts with poor to good compaction few sutured grain contacts which reflect a higher degree of compaction still exist xrd and sem analyses show that kaolinite chlorite illite smectite and illite smectite mixed layer clay are the common clay minerals in the studied samples the presence of vermiform morphology besides the sharp peak pattern of the kaolinite in most of the xrd pattern indicates that part of the kaolinite was authigenically formed

linking hierarchical stratal architecture to plume spreading in a lagrangian based transport model 2 evaluation using new data from the borden site 1 a new data set collected at the well documented borden research site was used in order to evaluate a newly published but as yet untested idea for stochastic modeling ramanathan et al 2008 the new data set reveals the stratal architecture of the borden aquifer and allowed us to determine how the stratal architecture at different scales controlled the macrodispersion observed in the original natural gradient tracer test the newly published idea for modeling uses a lagrangian based model for the particle displacement variance developed from independent physically based quantifiable univariate statistics including the proportions and mean length of the strata the method for defining model parameters avoids the often equivocal step of fitting sample bivariate permeability statistics the model parameters were developed from the new data from the borden site the new data included geologic data in much greater abundance than permeability data there are two scales of unit types delineated in a hierarchy of stratal architecture their shapes are complex not simple layers or lenses the method facilitated the direct use of both geologic and permeability data which need not be collocated the dispersion model developed from these data represents the field measured particle displacement variance that occurred in the natural gradient tracer test well the contributions to time dependent macrodispersion by strata at each scale were computed and analyzed independently this analysis revealed that macrodispersion at the borden site is primarily controlled by the proportions and the mean and variance in length of larger scale strata of medium sand m and strata of fine sand and silt fz with secondary contributions by smaller scale strata types occurring within the larger scale units when sampling the pattern in the longitudinal direction m and fz couplets repeat at 10 m intervals on average with a high length variance to reach a time constant macrodispersivity the stratal length variability must be fully sampled by the plume the macrodispersivity becomes asymptotic beyond an advective distance of about 60 m corresponding to about 12 longitudinal transitions between m and fz unit types

introduction to the revised mesozoic stratigraphy and nomenclature for yemen abstract until the early 1980s the mesozoic stratigraphy of yemen was based on measured surface sections exposed mainly in the faulted and dissected shoulders of the gulf of aden and red sea rifts or on the high yemen plateau on the basis of correlations between areas the broad facies belts palaeogeographies and tectonic frameworks for the mesozoic epochs were established the arealy extensive tertiary limestone tablel and and tertiary volcanics however masked more local underlying pre cenozoic major structural features extensive oil exploration drilling backed by regional and or detailed geophysical surveys increasingly based on seismic surveys from the late 1970s have gradually unraveled a complex mesozoic tectonic history which had given rise to the formation of a number of nw se and e w trending rift basins and depressions these were initiated mainly in the late jurassic and early cretaceous principally by rejuvenation of ancient basement controlled fractures during further gondwanan break up which led to the separation of india with eastern gondwana from afro arabia these basins exhibit considerably thicker and rapidly varying stratigraphic sequences which reflect successive phases of rifting subsidence and depositional settings in time with the type and provenance of basin fill helping to detail the developing palaeogeography for each stage the precise relationships of these varied intra and inter basin facies are not yet properly understood the discovery of commercial oil and gas in several of these mesozoic rift basins accelerated competitive exploration activity by a host of operating companies leading to the proliferation of informal locally applicable in house subsurface lithostratigraphic nomenclature schemes these in the extreme cases either ignore published surface nomenclature or else utilize existing surface defined formation names which then become over loaded with undifferentiated coeval but depositionally and environmentally different units without due regard to internationally accepted rules this confusion is further compounded by detailed local academic research from within and outside yemen with little or no access to subsurface data and by service companies utilizing limited client supplied data which is then extrapolated on a province wide or a regional basis proliferation takes place through data exchange between operators or through circulation of non exclusive reports or by means of localized publications a stratigraphic commission was appointed to address this problem and to carry out nomenclature clean up and simplification after intensive review of all utilised nomenclature and with full cooperation from the operating companies its principal findings are summarised in graphic form in figure 4 and figure 5 which include for example retention but revision correction and expansion of the formalised nomenclature in beydoun and greenwood 1968 which will apply to all of yemen one new formation previously unrecognised until recent subsurface and outcrop studies the saar formation has been added formalisation of several new members in the madbi formation previously informally assigned formation rank a new member to the qishn formation the sa af member previously informally called the furt formation correction to and reassignment of the nayfa formation type section to the ma abir member of the madbi formation the type nayfa provisionally now being at mintaq salt dome full descriptions of these and of all the revised mesozoic nomenclature together with that for the palaeozoic and cenozoic will be published later in international lexicon of stratigraphy format

solute transport in fractured rocks with stagnant water zone and rock matrix composed of different geological layers model development and simulations a model is developed to describe solute transport and retention in fractured rocks it accounts for the fact that solutes can not only diffuse directly from the flowing channel into the adjacent ro

hydrogeophysical characterization of transport processes in fractured rock by combining push pull and single hole ground penetrating radar experiments the in situ characterization of transport processes in fractured media is particularly challenging due to the considerable spatial uncertainty on tracer pathways and dominant controlling processes such as dispersion channeling trapping matrix diffusion ambient and density driven flows we attempted to reduce this uncertainty by coupling push pull tracer experiments with single hole ground penetrating radar gpr time lapse imaging the experiments involved different injection fractures chaser volumes and resting times and were performed at the fractured rock research site of ploemeur in france h network hplus ore fr en for the gpr acquisitions we used both fixed and moving antenna setups in a borehole that was isolated with a flexible liner during the fixedantenna experiment time varying gpr reflections allowed us to track the spatial and temporal dynamics of the tracer during the push pull experiment during the moving antenna experiments we clearly imaged the dominant fractures in which tracer transport took place fractures in which the tracer was trapped for longer time periods and the spatial extent of the tracer distribution up to 8 meters at different times this demonstrated the existence of strongly channelized flow in the first few meters and radial flow at greater distances by varying the resting time of a given experiment we identified regions affected by density driven and ambient flow these experiments open up new perspectives for coupled hydrogeophysical inversion aimed at understanding transport phenomena in fractured rock formations

stochastic simulation of radionuclide migration in discretely fractured rock near the aspo hard rock laboratory we study the migration of sorbing tracers through crystalline rock by combining relatively simple transport measures with particle tracking in a discrete fracture network the rock volume is on a 1

organic geochemistry characterization of the paleogene to neogene source rocks in the sayhut subbasin gulf of aden basin with emphasis on organic matter input and petroleum generation potential paleogene umm er radhuma and ghaydah and neogene sarar source rocks from sayhut subbasin in the gulf of aden basin were studied to provide information such as organic matter types paleoenvironmental conditions and petroleum generation potential this study is based on whole rock organic geochemical analyses and organic petrology the total organic carbon toc contents of the paleogene to neogene source rocks range from 0 43 to 6 11 with an average toc value of 1 00 indicating fair to very good source rock potential the paleogene ghaydah and umm er radhuma source rocks are relatively higher in genetic petroleum potential than neogene sarar source rocks mainly oil and gas are anticipated from the ghaydah and umm er radhuma source rocks with hydrogen index hi values ranging from 95 to 715 mg hydrocarbon hc g toc this is supported by the presence of significant amounts of liptinite macerals in the ghaydah and umm er radhuma source rocks the sarar source rocks are dominated by vitrinitic type iii kerogen hi 200 mg hc g toc and are thus considered to be gas source rocks the paleogene to neogene source rocks have vitrinite reflectance r o values in the range between 0 30 and 0 77 r o and pyrolysis maximum temperature values range from 412 c to 444 c 774 f to 831 f consistent with the immature to early mature oil window therefore the present day kerogen type in the paleogene to neogene source rocks is original and should not have been altered by thermal maturity the biomarker of organic matter suggests that the paleogene to neogene source rocks were deposited in a marine environment under suboxic to anoxic conditions the biomarkers also indicate that the paleogene to neogene source rocks contain a mixture of aquatic organic matter planktonic and bacterial and terrigenous organic matter with increasing terrigenous influence to sarar source rock samples highly hypersaline reducing conditions are also evidenced in ghaydah and umm er radhuma source rocks as indicated by the presence of the gammacerane biomarker low pristane to phytane ratios and homohopane distribution patterns

stochastic analysis of early tracer arrival in a segmented fracture pathway a stochastic model for transport and retention in fractured rock is proposed as an alternative to more elaborate numerical simulations contaminants are transported by advection through a series of n rock fractures the microscopic processes of matrix diffusion and sorption act together to retain contaminants in the host rock the transport pathway is characterized by large scale fluctuations in the advection velocity caused by spatial variability in the fracture attributes along the pathway the moments of the time of arrival of an initial solute pulse are related in a generic way to the joint distribution of fracture aperture and length these moments are controlled primarily by a dimensionless retention parameter that incorporates all the deterministic model parameters and by correlation between fracture length and aperture the results show that a systematic bias in the predicted contaminant transport can be introduced by neglecting spatial variability in fracture attributes the relative contributions of fracture to fracture variability and within fracture variability are also explored the proposed stochastic methodology can be merged with relatively simple numerical simulations to broaden the applicability

buoyancy driven crack propagation from an over pressured source the propagation of a liquid filled crack from an over pressured source into a semi infinite uniform elastic solid is studied the fluid is lighter than the solid and propagates due to its buoyancy and to the source over pressure the role of this over pressure at early and late times is considered and it is found that the combination of buoyancy and over pressure leads to significantly different behaviour from buoyancy or over pressure alone lubrication theory is used to describe the flow where the pressure in the fluid is determined by the elastic deformation of the solid due to the presence of the crack numerical results for the evolution of the crack shape and speed are obtained the crack grows exponentially at early times but at later times when buoyancy becomes important the crack growth accelerates towards a finite time blow up these results are explained by asymptotic similarity solutions for early and late times the predictions of these solutions are in close agreement with the full numerical results a different case of crack geometry is also considered in order to highlight connections with previous work the geological application to magma filled cracks in the earth s crust or dykes is discussed