prediction of lithofacies and reservoir quality using well logs late cretaceous williams fork formation mamm creek field piceance basin colorado understanding the controls and distribution of reservoir quality is important for the economic success of tight gas reservoirs in which diagenesis interacts with primary depositional variations in environment and texture to exert a strong control on pore networks rock mechanical properties and natural fractures in the upper cretaceous williams fork formation of the piceance basin framework grain composition is a major control on compaction and the occurrence of authigenic phases alteration of volcanic grains in the upper williams fork led to grain coating clay precipitation ferroan dolomite cement is found only in the deeper marine influenced intervals in which dolostone fragments are present this study shows that careful petrographic assessment of lithofacies heterogeneity can be upscaled by correlation with log properties to yield tools for field scale reservoir quality prediction twelve lithofacies are identified based on sand grain populations cement types and clay matrix content sandstones of the highest reservoir quality are those with grain coating clays that inhibit quartz cementation these sandstones can be identified based on high density porosity log values sandstones with the poorest reservoir qualities are tightly cemented with carbonate and quartz cement or are rich in clay matrix carbonate cemented intervals are identified by low density porosity clay matrix rich samples have high gamma ray and low density porosity values the presence of abundant potassium feldspar in the upper intervals results in high gamma ray readings even in the clean clay matrix free sandstone

convective momentum transport by rainbands within a madden julian oscillation in a global nonhydrostatic model with explicit deep convective processes part i methodology and general results abstractthe convective momentum transport cmt properties of 13 215 rainbands within a madden julian oscillation mjo event simulated by a global nonhydrostatic model are examined cmt vectors which represent horizontal accelerations to the mean winds due to momentum flux convergences of deviation winds are derived for each rainband the cmt vectors are composited according to their locations relative to the mjo center while a similar number of rainbands are detected in the eastern and western halves of the mjo convective envelope cmt vectors with large zonal components are most plentiful between 0 and 20 to the west of the mjo center the zonal components of the cmt vectors exhibit a coherent directionality and have a well organized three layer structure positive near the surface negative in the low to midtroposphere and positive in the upper troposphere in the low to midtroposphere where the longitudinal difference in the mean zonal wind across the mjo is 10 m s 1 on average the net acceler

a reaction transport mechanical approach to modeling the interrelationships among gas generation overpressuring and fracturing implications for the upper cretaceous natural gas reservoirs of the piceance basin colorado predicting reservoir characteristics in tight gas sandstone reservoirs such as those of the upper cretaceous units of the piceance basin is difficult due to the interactions of multiple processes acting on sediments during basin development to better understand the dynamics of these systems a forward numerical model which accounts for compaction fracturing hydrocarbon generation and multiphase flow basinrtm is used in a one dimensional simulation of the u s department of energy s multiwell experiment mwx site in the piceance basin of particular interest is the effect of gas generation on the dynamics of the system

origin and timing of dauphine twins in quartz cement in fractured sandstones from diagenetic environments insight from fluid inclusions abstract electron backscattered diffraction techniques ebsd show that dauphine twins in quartz are widespread in many tectonometamorphic environments our study documents that under diagenetic temperatures

a multiscale model for tropical intraseasonal oscillations the tropical intraseasonal 40 to 50 day oscillation tio is the dominant component of variability in the tropical atmosphere with remarkable planetary scale circulation generated as envelopes of complex multiscale processes a new multiscale model is developed here that clearly demonstrates the fashion in which planetary scale circulations sharing many features in common with the observational record for the tio are generated on intraseasonal time scales through the upscale transfer of kinetic and thermal energy generated by wave trains of organized synoptic scale circulations having features in common with observed superclusters the appeal of the multiscale models developed below is their firm mathematical underpinnings simplicity and analytic tractability while remaining self consistent with key features of the observational record the results below demonstrate in a transparent fashion the central role of organized vertically tilted synoptic scale circulations in generating a planetary circulation resembling the tio

parameterization of the vertical transport of momentum by cumulus clouds part i theory abstract a scheme is developed to parameterize the vertical transport of momentum by cumulus clouds in which the effect of a cloud induced pressure field is included in addition a new form for momentum exchange between clouds and their environment is used the scheme incorporates a simple cloud model which includes both updraft and downdraft and specifies the cloud dynamic fields to enable us to determine the mean pressure gradient force across the clouds it is shown that in a typical environment with vertical wind shear the pressure gradient force is along the direction of the wind shear the equation governing cloud mean momentum together with the diagnostic equation for cloud induced pressure field is solved by iteration to evaluate quantitatively the horizontal pressure gradient force across the cloud and determine the cloud mean momentum application of the parameterization scheme to gate convective events will be presented in part ii of this paper

propagation velocity of a natural hydraulic fracture in a poroelastic medium the propagation rate of a natural hydraulic fracture is limited by the rate that fluid flows from the saturated rock into the void space created by fracture growth unlike induced hydraulic fractures natural hydraulic fractures can not be modeled by specifying rates of fracture growth or fluid flow into the fracture as boundary conditions numerical solutions of the governing equations for natural hydraulic fracture growth in a poroelastic medium indicate that growth rates are primarily controlled by the hydraulic conductivity the storage sp and the initial flaw length 2 o computationally more efficient models which partially and completely decouple material stresses from fluid pressures give similar results results for several rock types indicate that although the rate of fracture propagation is limited by fluid flow fracture growth still accelerates results are generalized in dimensionless plots of fracture length versus time for various values of the dimensionless parameter 1 gsp where g is the shear modulus and is the drained poisson s ratio

a new multiscale model for the madden julian oscillation abstract a multiscale model of the mjo is developed here that accounts in a simplified fashion for both the upscale transfer from synoptic to planetary scales of momentum and temperature from wave trains of thermally driven equatorial synoptic scale circulations in a moving convective envelope as well as direct mean heating on planetary scales this model involves idealized thermally driven congestus synoptic scale fluctuations in the eastern part of the moving wave envelope and convective superclusters in the western part of the envelope the model self consistently reproduces qualitatively many of the detailed structural features of the planetary circulation in the observations of the mjo including the vertical structure in both the westerly onset region and the strong westerly wind burst region as well as the horizontal quadrupole planetary vortex structure the westerly midlevel inflow in the strong westerly region and the quadrupole vortex are largely produced in the model by the upscale transpor

geodynamic significance of s type granites in circum pacific orogens in phanerozoic circum pacific orogenic belts most post collisional s type granites and associated high temperature low pressure metamorphic complexes formed during early arc extension the granites are part of a tripartite association consisting of 1 inboard s type granite 2 outboard oceanic arc and 3 intervening turbidite filled backarc basin s type granites herald the formation of new outboard oceanic arc and extensional backarc systems but thickening of a preexisting sediment dominated back arc basin is a prerequisite for their generation in these environments s type plutonism is triggered by renewal of arc magmatism following thickening when hot basaltic magmas are intruded into the thickened backarc crust once slab retreat is reestablished with ongoing extension during retreat the crust becomes progressively thinned the sedimentary contribution is diminished and the granites lose their s type character such tripartite associations involving s type granite are probably diagnostic of repeated slab retreat episodes and the jurassic u s cordillera might be an example

momentum and mass transport by convective bands comparisons of highly idealized dynamical models to observations the importance of the vertical transport of horizontal momentum by convective clouds has been documented in studies of momentum budgets e g shapiro and stevens 1980 sui and yanai 1986 furthermore it is obvious that the boundary layer wind itself and hence surface heat moisture and momentum transports is affected by deep convection most of the airsea transfer in tropics is concentrated in regions with deep convection

relationship of p wave seismic attributes azimuthal anisotropy and commercial gas pay in 3 d p wave multiazimuth data rulison field piceance basin colorado this case history is one of three field projects funded by the us department of energy as part of its ongoing research effort aimed to expand current levels of drilling and production efficiency in naturally fractured tight gas reservoirs the original stated goal for the 3 d p wave seismic survey was to evaluate and map fracture azimuth and relative fracture density throughout a naturally fractured gas reservoir interval at rulison field this interval is the cretaceous mesaverde approximately 2500 ft 760 m of lenticular sands silts and shales three dimensional full azimuth p wave data were acquired for the evaluation of azimuthal anisotropy and the relationship of the anisotropy to commercial pay in the target interval the methodology is based on the evaluation of two restricted azimuth orthogonal source receiver azimuth 3 d p wave volumes aligned with the natural principal axes of the azimuthal anisotropy as estimated from velocity analysis of multiazimuth prestack gathers the dix interval

high temperature hydrothermal origin for fractured carbonate reservoirs in the blackburn oil field nevada geologic note 1 preliminary petrographic and fluid inclusion studies of drill cuttings and core from the blackburn oil field reveal that many of the oil saturated fractures veinlets and breccias in the dolomite reservoir rock may be of high temperature hydrothermal origin textures of the earliest formed fracture veinlet networks and breccias suggest development by explosive hydrothermal fracturing the veinlets themselves preserve evidence that high temperature fluids favorable for such natural hydrothermal rock rupture once circulated in these rocks primary fluid inclusion homogenization temperatures indicate that early vein dolomite precipitated from hydrothermal brines at temperatures exceeding 350 degrees c 662 degrees f younger quartz sphalerite galena veinlets developed from dilute aqueous solutions at temperature of more than 225 degrees c 437 degrees f the high paleotemperatures recorded by early vein dolomite in the now much cooler about 120 degrees c or 248 degrees f blackburn reservoir rock imply an ancient magmatic heat source in this case almost certainly a small granodiorite stock tertiary adjoining and possibly underlying the field other carbonate hosted petroleum reservoirs in eastern nevada are also intimately associated with felsic intrusives we propose that igneous related high temperature hydrothermal fracturing could have created reservoir porosity and permeability at some or all of these fields and that future petroleum exploration in the basin and range might profitably incorporate the search for concealed plutons

natural fractures in tight oil sandstones a case study of the upper triassic yanchang formation in the southwestern ordos basin china natural fractures are important storage spaces and fluid flow channels in tight oil sandstones intraformational open fractures are the major channels for fluid flow in tight oil sandstones small faults may provide fluid flow channels across different layers according to analogous outcrops cores and borehole image logs small faults and intraformational open fractures are developed in the tight oil sandstones of the upper triassic yanchang formation in the southwestern ordos basin china among them high dip angle intraformational open fractures are the most abundant northeast southwest trending fractures are the principal fractures for fluid flow because that is the present day maximum horizontal compressive stress direction combined with production data horizontal wells striking normal to or at a large angle relative to the major flow pathways are beneficial for tight oil production improvement fractures with high dip angles are the main factor that influences initial oil production linkage and tip damage zones are more favorable for oil production improvement than wall damage zones this study provides an example of natural fracture characterization and unravels fracture contributions to reservoir physical properties and oil production of tight oil sandstones which could provide a geological basis for oil exploration and development in tight sandstones

fracture parameter estimation from well log data we evaluated a method of deriving seismic fracture parameters from vertical well log data with the assumption that the fractured medium is transversely isotropic with a horizontal axis of symmetry hti one approximation we used is that the observed vertical p wave velocity is the same as the background isotropic p wave velocity of the hti medium another assumption was that the fractures and cracks are noninteractive and penny shaped using these approximations we generated the fracture compliance matrix for each layer fracture parameters were then derived by constructing the hti stiffness matrix for those layers we tested our method using vertical well log data from a tight sand reservoir in colorado usa thomsen style parameters were derived and gas filled fractures were identified on this log the identified gas filled fractures were compared to the production log data the fracture density was also obtained at the well location within the depth of interest we also found some problems and limitations caused by approximating vertical p wave velocity the same as the background isotropic p wave velocity

an mjo simulated by the nicam at 14 and 7 km resolutions this study discloses detailed madden julian oscillation mjo characteristics in the two 30 day integrations of the global cloud system resolving nonhydrostatic icosahedral atmospheric model nicam using the allseason real time multivariate mjo index of wheeler and hendon the model anomaly is derived by excluding the observed climatology because the simulation is sufficiently realistic results show that the mjo has a realistic evolution in amplitude pattern geographical locations eastward propagation and baroclinic and westwardtilted structures in the central indian ocean convection develops with the low level easterly wind anomaly then matures where the low level easterly and westerly anomalies meet anomalous moisture tilts slightly with height in contrast over the western pacific the convection grows with a low level westerly anomaly moisture fluctuations leading convection in eastward propagation tilt clearly westward with height the frictional moisture convergence mechanism operates to maintain the mjo such success can be attributed to the explicit representation of the interactions between convection and large scale circulations the simulated event however grows faster in phases 2 and 3 and peaks with 30 higher amplitude than that observed although the 7 km version shows slight improvement the fast growth phases are induced by the fast growing low level convergence in the indian ocean and the strongly biased itcz in the west pacific when the model undergoes a spinup the simulated olr has a substantial bias in the tropics possible solutions to the deficiencies are discussed

momentum transport processes in the stratiform regions of mesoscale convective systems over the western pacific warm pool summary momentum transport by the stratiform components of mesoscale convective systems mcss during the tropical ocean global atmosphere coupled ocean atmosphere response experiment in december 1992 is investigated using a cloud resolving model the mesoscale momentum transport by the stratiform regions of mcss is examined in two distinct large scale flow regimes associated with the intraseasonal oscillation over the western pacific warm pool model simulations for 14 december 1992 characterize the westerly onset period which has relatively weak low level westerlies with easterlies above simulations for 23 24 december represent the strong westerly regime when westerlies extend from the upper troposphere to the surface with a jet 2 3 km above the surface in the westerly onset simulation the extensive stratiform region of a mcs contained a broad region of descent that transported easterly momentum associated with the mid level easterly jet downward thus the stratiform regions acted as a negative feedback to decrease the large scale mean westerly momentum developing at low levels in the strong westerly regime the mesoscale downward air motion in the stratiform regions of large mcss transported westerly momentum downward and thus acted as a positive feedback strengthening the already strong westerly momentum at low levels momentum fluxes by the mesoscale stratiform region downdraughts are shown to have a systematic and measurable impact on the large scale momentum budget

fractures in the low porosity and ultra low permeability glutenite reservoirs a case study of the late eocene hetaoyuan formation in the anpeng oilfield nanxiang basin china the naxiang basin located within the qin and dabie mountains orogenic belt in central china is a small intermountain faulted basin in which the late eocene hetaoyuan formation in the anpeng oilfield is the low porosity and ultra low permeability glutenite reservoirs the large scale fractures are mainly developed in the thick bedded conglomerates and gravel bearing gritstones the small scale jointed fractures bounded by layer are mainly developed in the medium granular and fine sandstones between the conglomerates or gravel bearing gritstones there also developed three kinds of micro fractures namely intergranular fractures intragranular fractures and transgranular fractures in the tight glutenites the fractures in the glutenite reservoirs are of chiefly high dip angles they assume chiefly the e w strikes next are the ne sw and nw se strikes on the log curve fractures usually show such responses as a decrease of the deep and shallow lateral resistivities an increase of the acoustic time difference a reduction of the density an increase of the compensation neutrons an occurrence of middle and high gamma ray and an expansion of the calipers fractures make contributions to the low porosity and ultra low permeability glutenite reservoirs by improving the permeability and then porosity micro fractures are the important channels connecting intergranular and intragranular solution pores thereby making better the connectivity within the tight glutenite reservoirs the small and medium scale fractures serve as the flow channels within the layers of fine and medium granular sandstones while the large scale fractures serve as the main flow channels for the whole reservoir under the impact of the present day stress the ne sw fractures perpendicular to the minimum principal stress assume a tensile state and have good connectivity large apertures and high permeability and are the major direction for fluid flow thereby providing a major basis for a further development

a late cenozoic regional mesofracture system in southern england and northern france the upper cretaceous and palaeogene rocks of s england and n france are cut by a nw trending system of fractures characterized by swarms of vertical extension joints accompanied by conjugate sets of hybrid and shear joints and normal mesofaults many major photolineaments exhibit the same nw trend as the fractures and are particularly conspicuous in n france where they are coincident with rectilinear drainage channels suggesting a relationship between fracture orientation and physiography in s england this relationship is absent possibly because of the influence of additional fracture systems related to major flexures trending obliquely to the nw se direction these major e w trending flexures and associated fracture systems were formed during the oligocene to early miocene 9helvetic9 phase of deformation and are cross cut obliquely by fractures in the nw trending system the nw trending fractures and lineaments are parallel to neotectonic normal faults in the lower rhine embayment and become less well developed to the west with increasing distance from these major structures the lower rhine faults were reactivated and propagated into the quaternary cover as a consequence of ne sw regional tension generated during the late neogene to recent 9jura9 phase of nw se alpine convergence the nw trending extensional structures in s england and n france are considered to be of about the same age and related to the same stress regime as the neotectonic normal faults of the lower rhine embayment however because fractures of the nw system cutting palaeogene sediments in se england are truncated by the erosion surface beneath the plio pleistocene red crag deposits it is possible that in england fracture initiation did not continue into quaternary times

analysis of states of stress between provinces of constant stress recent studies have indicated the existence of crustal provinces or domains within which the state of stress shows little apparent horizontal variation between provinces the state of stress may undergo substantial changes often over remarkably short distances as analyzed here the transition in stress state between adjacent domains is caused by shear tractions acting on the base of the elastic brittle layer and is mediated by a stress field within a zone between the provinces that can be determined by solving the equations of force equilibrium and stress compatibility the component of horizontal stress oriented perpendicular to the provincial boundary changes smoothly across the transition zone from one province to the other whereas the horizontal stress oriented parallel to the boundary shows smaller but discontinuous changes the horizontal component of shear stress is unlikely to change from one province to another because of the implausible nature of the required basal traction thus in this regard states of stress in adjacent domains appear to be coupled the coincidence of a number of stress transition zones with boundaries defined by heat flow suggests that in many cases the basal tractions are the result of thermally induced mass transport below the elastic brittle layer in the direction of increasing horizontal compressive stress this analysis provides a quantitative relationship between changes in the stress field measured in the upper portion of the crust and shear stresses acting on the base of the elastic brittle layer

natural hydraulic fracturing of tight gas sandstone reservoirs piceance basin colorado natural fractures form preferred pathways for basinal fluid flow and associated heat and mass transport in gas sandstone reservoirs with low matrix permeability fractures provide flow pathways between organic rich source and reservoir layers during gas charge and between matrix pores hydraulic fractures and the well bore during production while the formation of natural fractures has previously been associated with gas generation and pore fluid pressure increase through a process referred to as natural hydraulic fracturing other driving mechanisms such as stress changes by tectonic or exhumation processes remained viable alternatives to test whether these mechanisms contributed to fracture development we investigated the spatial and temporal distribution of fracture formation and its relationship to gas generation migration and charge in sandstone of the cretaceous mesaverde group across the entire production interval on a basinwide scale using fluid inclusion microthermometry of crack seal fracture cement formed concurrently with fracture opening we observed temperature trends that when compared with temperature evolution models of the formation date fracture formation between 41 and 6 ma in the northern and between 39 and 6 ma in the southern piceance basin the onset of fracture formation 20 30 m y prior to maximum burial eliminates changes in stress state associated with exhumation as a mechanism for triggering the onset of fracture formation instead calculated paleo pore fluid pressures of 40 90 mpa 5800 13 000 psi during fracture opening and the presence of methane rich inclusions in fracture cement suggest that fracture formation was aided by high pore fluid pressures during gas generation in organic rich shales and coals and associated charging of adjacent and interlayered sandstone reservoirs a 10 20 m y age progression in the onset of fracture formation from deeper to shallower horizons of the mesaverde group is consistent with gas generation and onset of fracture formation activated by burial temperature with limited upward migration of gas at this stage of reservoir evolution this age progression with depth is inconsistent with fracture formation triggered by changes in stress conditions associated with tectonic or structural processes expected to affect the entire formation synchronously our observations are thus most consistent with fracture formation by natural hydraulic fracturing in response to gas generation in interbedded source layers and reservoir charge based on widespread observations of fractures with similar structural and diagenetic attributes we consider natural hydraulic fracture formation in response to thermocatalytic gas generation to be a fundamental mode of brittle failure in otherwise structurally quiescent basins

diverse fracture properties and their impact on performance in conventional and tight gas reservoirs saudi arabia the unayzah south haradh case study the upper permian carboniferous unayzah formation in south haradh saudi arabia includes two major mechanical and petrophysical layers that are separated by shale rich zones open tectonic fracture clusters are rare and not essential for fluid flow in the unayzah a zone which has high porosity and permeability however such fracture clusters are essential to and impact the production performance in the unayzah b c tight gas reservoir the occurrence of the tectonic fractures in the unayzah formation is linked to the rock mechanical properties which vary with porosity shale volume cement type and texture the b c unit is more fractured than the a unit but its layers vary in the degree of fracturing the variation in fracture development within the b c unit results in differences in fracture enhanced permeability based on production profiles where flow is restricted to preferentially fractured mechanical layers that lack effective vertical fluid communication with other layers we identify two tectonic fracture systems an older subordinate fully mineralized system and a younger primary mostly open system early extensional fractures including joints and faults developed parallel to the basement faults during the opening of the neotethys these are fully mineralized and have little or no function as fluid conduits the younger system includes open fracture clusters that are predominantly parallel or nearly parallel to the regional east northeast west southwest maximum horizontal stress of the zagros that has been active since the late cretaceous and is independent of local structures therefore these fractures are controlled by remote stresses instead of the basement rooted forced folds and faults in this article we demonstrate that in the unayzah b c natural fractures are essential to permeability and in some areas to porosity and thence to reservoir performance the results of this study are being implemented in well placement and completion design to optimize the intersection of open fracture clusters with positive preliminary results

effects of vertical wind shear on the cumulus transport of momentum observations and parameterization abstract dynamical effects of organized cumulus convection on its environment with vertical wind shear are studied analyses of the wind field and momentum budget residual for mesoscale convective systems observed during sesame and pre storm reveal systematic differences in the vertical transport of horizontal momentum between mesoscale convective complex mcc and squall line cases in the mcc a distinct minimum in wind speed appears over the area of intense convection and the momentum budget residual acts to decelerate the environmental wind and to reduce the upper level vertical shear therefore the inferred vertical transport of momentum in the mcc is downgradient in the upper layer on the other hand in the squall line there is no wind speed minimum and the upper level vertical shear of the line normall component of the environmental wind increases as convection develops thus the vertical transport of momentum normal to the squall line is upgradient in the upper layer although the transport of

the role of environmental shear and thermodynamic conditions in determining the structure and evolution of mesoscale convective systems during toga coare abstract a collection of case studies is used to elucidate the influence of environmental soundings on the structure and evolution of the convection in the mesoscale convective systems sampled by the turboprop aircraft in the tropical ocean global atmosphere toga coupled ocean atmosphere response experiment coare the soundings were constructed primarily from aircraft data below 5 6 km and primarily from radiosonde data at higher altitudes the well documented role of the vertical shear of the horizontal wind in determining the mesoscale structure of tropical convection is confirmed and extended as noted by earlier investigators nearly all convective bands occurring in environments with appreciable shear below a low level wind maximum are oriented nearly normal to the shear beneath the wind maximum and propagate in the direction of the low level shear at a speed close to the wind maximum when there is appreciable shear at middle levels 800 400 mb convective bands form parallel to the shear with

testing the basin centered gas accumulation model using fluid inclusion observations southern piceance basin colorado the upper cretaceous mesaverde group in the piceance basin colorado is considered a continuous basin centered gas accumulation in which gas charge of the low permeability sandstone occurs under high pore fluid pressure in response to gas generation high gas pressure favors formation of pervasive systems of opening mode fractures this view contrasts with thatofothermodelsoflow permeabilitygasreservoirsinwhich gas migrates by buoyant drive and accumulates in conventional traps with fractures an incidental attribute of these reservoirs we tested the aspects of the basin centered gas accumulation model as it applies to the piceance basin by determining the timing of fracturegrowth and associated temperature pressure and fluid composition conditions using microthermometry and raman microspectrometry of fluid inclusions trapped in fracture cement that formed during fracture growth trapping temperatures of methane saturated aqueous fluid inclusions record systematic temperature trends that increase from approximately 140 to 185 c and then decrease to approximately 158 c over time which indicates fracture growth during maximum burial conditions calculated pore fluid pressures for methanerich aqueous inclusions of 55 to 110 mpa 7977 15 954 psi indicate fracture growth under near lithostatic pressure conditions consistent with fracture growth during active gas maturation and charge lack of systematic pore fluid pressure trends

momentum budget of a squall line with trailing stratiform precipitation calculations with a high resolution numerical model abstract in this paper the authors investigate the momentum budget of a squall line with trailing stratiform precipitation by examining how the momentum balance varies with respect to the storm s internal structure in particular the authors determine differences between the momentum budgets of the convective and stratiform precipitation regions which are physically distinct parts of the storm the results from a high resolution nonhydrostatic numerical simulation of the two dimensional segment of the 10 11 june 1985 pre storm squall line are used the momentum equation is averaged over a 300 km wide large scale area for time periods of 1 h on the 1 h timescale the convective scale temporal variations of horizontal and vertical velocities are nearly uncorrelated and thus their contribution to the momentum flux is negligible the remaining standing eddy and mean flow circulations account for the momentum flux on this timescale the combination of the standing eddy and mean flow behave almost exactly

a madden julian oscillation event realistically simulated by a global cloud resolving model a madden julian oscillation mjo is a massive weather event consisting of deep convection coupled with atmospheric circulation moving slowly eastward over the indian and pacific oceans despite its enormous influence on many weather and climate systems worldwide it has proven very difficult to simulate an mjo because of assumptions about cumulus clouds in global meteorological models using a model that allows direct coupling of the atmospheric circulation and clouds we successfully simulated the slow eastward migration of an mjo event topography the zonal sea surface temperature gradient and interplay between eastward and westward propagating signals controlled the timing of the eastward transition of the convective center our results demonstrate the potential making of month long mjo predictions when global cloud resolving models with realistic initial conditions are used

regional fractures ii fracturing of mesaverde reservoirs in the piceance basin colorado 1 cretaceous strata in the east central piceance basin of northwestern colorado were subjected to several phases of stress due to horizontal tectonic compression burial and uplift these rocks contain a regional set of west northwest extension fractures observed in abundant vertical and deviated core from the u s department of energy s multiwell experiment and slant hole completion test wells time depth relationships fracture orientation and fluid inclusion analyses indicate that the fractures formed at about 36 40 ma during a phase of increased laramide west northwest compression and in a pressure temperature regime compatible with the geologically reconstructed maximum burial depths this regional fracturing is an example of load parallel extension fracturing and basinwide dilatancy at depth under conditions of high pore pressure and anisotropic tectonically created horizontal stress

experimental stretching of fluid inclusions in calcite implications for diagenetic studies homogenization temperatures of fluid inclusions trapped in calcite crystals may change with increased heating beyond the homogenization temperature fluid inclusions trapped in calcite during basin subsidence will tend to yield homogenization temperatures approaching maximum burial temperatures diagenetic studies that depend on these data will be biased coarse crystalline calcite containing saline fluid inclusions was used to examine the influence of increased temperatures and pressures on measured homogenization temperatures stepped heating experiments were conducted at 1 atm over a temperature range of 90 to 245 c along with hydrothermal experiments at confining pressures of 173 and 691 bar and temperatures of 160 250 and 350 c in all cases significant increases in the homogenization temperatures of the inclusion population were recorded presumably stresses generated during heating of the fluid inclusions exceeded the combined strength of the calcite crystal and the external pore pressure and thus caused fluid inclusion stretching size is a secondary factor that controls fluid inclusion reequilibration

late laramide thrust related and evaporite domed anticlines in the southern piceance basin northeastern colorado plateau new seismic and gravity data across the hydrocarbon producing divide creek and wolf creek anticlines in the southern piceance basin reveal contrasting styles of deformation within two widely separated time frames seismic data indicate that prebasin paleozoic deformation resulted in block faulting of the precambrian crystalline basement rocks and overlying cambrian through middle pennsylvanian strata movement along these block faults throughout much of pennsylvanian time during northeast southwest crustal extension likely influenced distribution of the middle pennsylvanian desmoinesian evaporite rich facies younger rocks including the thick succession of cenozoic basin strata then buried the paleozoic structures tectonic reconfiguration of the basin s eastern margin occurred during late laramide northeast southwest compression when a basement involved thrust block whose surface expression is the grand hogback monocline moved into the piceance basin a decollement developed in front of the thrust block within the mechanically weak desmoinesian evaporites and splayed out basinward as small scale imbricate thrusts in the upper cretaceous mancos shale the divide creek anticline formed above these splays as thrusting locally overthickened the shale and repeated the sandstone units between it and the evaporites the wolf creek anticline to the east however is due to both depositional and tectonic thickening of the evaporite section along the decollement gravity data confirm that excess mater al of relatively low density exists beneath the wolf creek structure whereas material of relatively higher density overthickened shale is found beneath the divide creek anticline thrust related basin margins and intrabasin folds structurally analogous to the divide creek and wolf creek anticlines may be more common than presently recognized in the rocky mountain foreland one well documented example is the pinedale anticline in the northern green river basin wyoming which like the divide creek anticline developed above a zone of splay faults from a decollement in front of a large thrust block

evidence for a petroleum subsystem in the frontier formation of the uinta piceance basin petroleum province anomalous carbonate horizons with intercrystalline hydrocarbon residue cone in cone structures and calcite beef veins in adjacent sandstone beds record potential evidence for hydrocarbon generation and seepage in the middle to upper turonian frontier formation from the uinta basin utah and colorado eight carbonate occurrences all encountered within distal delta front facies thin bedded sandstones and siltstones were sampled at outcrop locations from the southern and eastern margins of dinosaur national monument seven petrographic facies pf1 pf7 were identified using standard petrographic and cathodoluminescence microscopy pf1 large and small botryoids and fans pf2 yellow brown spherules pf3 microcrystalline spar cement pf4 blocky spar pf5 prismatic spar pf6 drusy mosaic spar and pf7 dolomite facies pf1 pf3 are synsedimentary phases comprising a large percentage of carbonate horizon volume whereas pf4 pf7 are late stage fabrics the 13c values of pf1 pf3 9 9 to 20 0 are consistent with contributions from biogenic methane seepage during deposition and early diagenesis brecciated pf1 fabrics and blowout depressions within sandstone horizons further indicate significant methane generation during deposition and early burial late stage fabrics contain 13c 8 0 to 17 3 and 18o 6 5 to 13 5 values consistent with progressive burial during which intercrystalline hydrocarbon residue cone in cone structures and calcite beef veins were formed by the thermal maturation of organic matter from enclosing distal delta front facies together these features reveal the potential for the thin bedded facies of the frontier formation distal delta front to serve as a potentially viable petroleum subsystem previously unrecognized in the uinta piceance petroleum province

sedimentological controls on the fracture distribution and network development in mesaverde group sandstone lithofacies uinta basin utah usa the mesaverde group uinta basin utah is the source of current significant natural gas production and contains several trillion cubic feet of undiscovered natural gas resources to evaluate and model the potential connectivity of hydraulically induced fractures to natural fractures in the subsurface the natural fracture network was examined using scanline sampling image and well logs core and microstructural analyses regional fracture sets include subvertical fractures with dominant orientations of north south 006 0158 ne 045 0598 nnw 326 3428 and a wnw 271 2868 sedimentologic and diagenetic characteristics of seven sandstone lithofacies control the fracture development and distribution in the group key sedimentologic and diagenetic influences on fracture distribution include bed thickness stratigraphic architecture the degree of cementation and the type of cement from these sedimentologic controls on the character of natural fractures lithofacies can potentially predict fracture distribution within the mesaverde group based on environments of deposition the presence of nw trending discontinuous sandstone reservoirs deposited in meandering fluvial environments that are highly fractured by a pervasive wnw striking fracture set helps to explain fairways of prolific natural gas production within

fractures in sandstone reservoirs with ultra low permeability a case study of the upper triassic yanchang formation in the ordos basin china the upper triassic yanchang formation in the ordos basin central china is a typical sandstone reservoir with an ultra low permeability high angle tectonic fractures and diagenetic fractures such as near horizontal bedding fractures intragranular fractures and grain boundary fractures are abundant fractures are major pathways and enhance fluid flow in sandstone reservoirs with ultra low permeability because of their weak lateral continuity and their small apertures under lithostatic pressure bedding fractures make a relatively small contribution to the overall permeability of reservoirs as they are both of small size and low permeability intragranular fractures and grain boundary fractures mainly improve the connectivity of reservoirs by connecting the matrix pores high angle tectonic fractures control the fluid movement in the ultra low permeability reservoirs under the effect of different successive tectonic stress fields four assemblages of high angle tectonic fractures developed in the sandstone reservoirs under the present day stress differently oriented fractures have different connectivities apertures and permeabilities the northeast southwest fractures parallel to the maximum principal stress have a good connectivity large apertures and a high permeability forming the dominant flow paths knowledge of these paths can be used for optimizing well placement because of their sensitivity to pressure fractures in different directions will show varying apertures as the formation pressure decreases therefore the permeability of the fractures of different orientations and its impact on reservoirs vary at different developmental stages

mapping permeable subsurface fracture networks a case study on the cooper basin australia abstract the spatial distribution of permeable fracture networks is constrained in the subsurface cooper basin australia through the integration of most positive curvature k analysis of five three dimensional 3d seismic surveys wellbore fracture data and geomechanical modelling the k provides the likely distribution of subsurface extensional fractures based on the stress redistribution along the outer arc of an anticline these results are reprocessed into the semblance similarity attribute to improve the signal noise ratio prior to being extracted along the gas rich and low permeability patchawarra formation the subsurface fracture distribution maps show the geometry and density of extensional fractures that have been shown to facilitate fluid migration in this province particularly those striking se nw and e w as these are properly oriented to undergo tensile reactivation the density of these permeable se nw and e w striking fracture sets is predicted to significantly increase along e w elongate anticlines and may contribute to improved hydrocarbon recovery in this low permeability stratigraphic interval we show that wellbore fracture data n 917 in the patchawarra formation presents a close relationship to k results and can be used to generate high density structural data in this basin with the methodology applicable to other subsurface and offshore provinces

deciphering fracturing and fluid migration histories in northern appalachian basin an integrated structural and geochemical analysis of mineralized faults and fractures revealed that the most widespread fracture systems in the northern appalachian basin resulted from two periods of post alleghenian deformation fluid inclusion homogenization measurements on calcite samples from pre syn and post kinematic structural settings bracketed the temperature ranges predominantly a function of depth of burial for each period of fracturing the first period of deformation produced northwest west northwest and east northeast fractures and related faults that experienced recurrent strike slip movements during a cooling event from 176 to 120 c 349 to 248 f this cooling episode was associated with the waning of an elevated thermal grad ent attained during dewatering caused by late paleozoic burial metamorphism at depths of 3 to 3 5 km 9 800 to 11 500 ft later normal faulting reopened the earlier strike slip fault zones during subsequent cooling of the system from 112 c 234 f to below 76 c 169 f this second cooling stage resulted from the 1 to 2 km 3 300 to 6 600 ft of uplift and erosion that occurred throughout the eastern united states during the cretaceous the ubiquitous occurrence of carbonate silicate and sulfide epigenetic mineralization in many environments allows for widespread application of the dating techniques demonstrated in this study basic to this approach is the analysis of mineral assemblages deposited during increases in hydrothermal circulation resulting from enhanc d permeability associated with periods of faulting and fracturing the presence of different mineral assemblages representing a range of ages and crystallization environments on various generations of brittle structures provides a means for developing detailed faulting and circulation histories and the determination of approximate as well as precise relative ages for each event

analogue simulation of natural orthogonal joint set formation in brittle varnish abstract two orthogonal joint sets are commonly observed in exposed sedimentary rocks with a wide variety of abutting and cross cutting relationships brittle varnish analogue models are carried out in conjunction with field studies in order to classify the different orthogonal fracture patterns and constrain the mechanical basis of orthogonal joint development the results suggest that the stress which creates the second joint set can result from i relaxation effects ii slight tension due to warping of the bands defined by the first parallel fractures and iii local and or regional reversals between 2 and 3 a ladder pattern formed by the combination of an initial set of long parallel joints and associated non cross cutting joints of the second set is obtained if the shear strength of the initial joints is low during the development of the second set a grid pattern where both sets mutually cross cut occurs when the shear strength of the initial joint set is high possibly the result of a high normal stress or healing and could result from two independent stress events an intermediate pattern comprising cross cutting and abutting orthogonal cross joints can form if the shear strength of the initial joints was intermediate and or variable during the development of the second set mutually abutting joint sets are observed within each pattern and could result from stress reversals or low differential stress during the final stages of joint development the classical presentation of joint data using rose diagrams cannot distinguish between the wide variety of orthogonal joint patterns maps of fracture intersections should compliment the orientation data we discuss methods to estimate the joint pattern where intersection data are absent

coal cleat domains and domain boundaries in the allegheny plateau of west virginia regional face cleats cutting pennsylvanian and permian coal seams in the allegheny plateau of west virginia can be divided into domains separated by boundaries that are sharply defined along most of their lengths domains and domain boundaries are established based on cleat trends number of regional cleat sets and relative chronology of cleat set development regional cleats of each set show a common trend and abutting relationships between multiple sets within a domain describe a progressive history of changing stress fields and cleat development boundaries dividing the in situ directions of horizontal principal stress are coincident with cleat domain boundaries suggesting a common and persistent controlling factor uniform trends of face cleats within domains and ab upt changes in cleat signature across domain boundaries can be spatially related to regional basement structures and a depositional hinge line within the coal bearing and underlying mississippian rocks in addition fold structures in coal and underlying sedimentary rocks across the allegheny plateau commonly terminate or change trend abruptly at joint domain boundaries in some cases regions of common fold trends in coal bearing rocks are contained within specific domains face cleat trends commonly differ from joint trends in rocks immediately bounding coal seams however one domain boundary in coal can be traced into mississippian rocks through the unconformity at the base of the pennsylvanian section in this case mississippian and pennsylvanian joint trends differ it follows tha joint domain boundaries can extend downward through rocks of different lithologies as well as coincide with conformable and unconformable stratigraphic boundaries

regional joint sets in the arabian platform as indicators of intraplate processes the eastern part of the saudi arabian craton is a platform underlain by gently tilted and horizontal mesozoic cenozoic sedimentary rocks everywhere more than 250 km distant from the zagros deformation front despite its tectonic simplicity the platform contains several laterally extensive but subdued structures and lineaments belonging to more than one system of fault zones and flexures new microtectonic observations of dominant sets of extension and conjugate hybrid joints permit regionally significant extension directions to be inferred and the origin of the macrostructures to be assessed the central arabian arch the e w crest of which coincides with an axis of mesozoic subsidence developed during the late cretaceous to eocene when the basin inverted as a consequence of the emplacement of ophiolite bearing nappes on the zagros and oman margins during arching there was strike parallel elongation of beds at the same time as the arch amplified the central arabian graben system evolved as a result of the northward displacement of an east arabian block or sheet that became detached across an arcuate separation zone which in the south is coincident with the crest of the arch an important neogene response in the arabian platform to ne sw shortening in the zagros ranges was the formation of a swarm of ne striking master joints and lineaments these structures reflect the diffuse and peripheral expansion of the foreland beyond the zagros deformation front

organized convective systems in the tropical western pacific as a process in general circulation models a toga coare case study we examine the large scale effects of organized convective systems in the tropical western pacific observed during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare in a case study approach we examine realizations of a supercluster associated with the onset of the december 1992 westerly wind burst in the t213 operational medium range weather forecasting model of the european centre for medium range weather forecasts ecmwf we idealize a supercluster as a hierarchy of three interacting scales namely organized cumulonimbus c 1 mesoscale convective systems c 2 and the supercluster component c 3 it is shown that the ecmwf model represents this hierarchy as a c 3 like surrogate whose influence dominates the effect of parametrized convection this causes over prediction of the model tendencies which in the case of zonal momentum is explained in elementary terms the structure of the resolved scale momentum flux is explained by moncrieff s 1992 archetypal theory of organized convection which has been verified against observations and cloud resolving model data sets the parametrization of subgrid scale convective momentum flux in the ecmwf model based on a momentum mixing concept produces subgrid scale tendencies that are physically different from transports associated with cumulonimbus convection in a shear flow we outline a strategy for parametrizing the momentum flux by the c 1 component based on the archetypal model the c 2 component which is part resolved and part parametrized is at odds with the assumptions of scale separation underpinning parametrization it is argued that this component should be represented as part of the prognostic treatment of convectively generated cirrus finally we suggest cloud resolving modelling studies to further quantify the structure and large scale impact of superclusters in a westerly wind burst environment ranging from idealized models to models having data assimilation capability

inferring paleostresses from natural fracture patterns a new method we introduce a method to infer the remote differential stress magnitude from the curvature of overlapping echelon fracture traces the curving paths of overlapping echelon cracks imply the predominance of local crack induced stresses over remote stresses during propagation nearly straight crack paths imply the controlling influence of a remote compressive crack parallel differential stress this method is used to interpret complex joint patterns mapped in sedimentary rock it is also applied to the problem of fracture pattern generation using computer models

simulation of the madden julian oscillation in the ncar ccm3 using a revised zhang mcfarlane convection parameterization scheme abstract this study presents the simulation of the madden julian oscillation mjo in the ncar ccm3 using a modified zhang mcfarlane convection parameterization scheme it is shown that with the modified scheme the intraseasonal 20 80 day variability in precipitation zonal wind and outgoing longwave radiation olr is enhanced substantially compared to the standard ccm3 simulation using a composite technique based on the empirical orthogonal function eof analysis the paper demonstrates that the simulated mjos are in better agreement with the observations than the standard model in many important aspects the amplitudes of the mjos in 850 mb zonal wind precipitation and olr are comparable to those of the observations and the mjos show clearly eastward propagation from the indian ocean to the pacific in contrast the simulated mjos in the standard ccm3 simulation are weak and have a tendency to propagate westward in the indian ocean nevertheless there remain several deficiencies that are yet

parametrization of momentum transport by convection ii tests in single column and general circulation models diagnostics derived from cloud resolving model simulations in part i of this study relating to the vertical transport of horizontal momentum by convection are used to develop a parametrization of convective momentum transports for deep convection based upon the mass flux convection scheme discussed by gregory and rowntree the importance of cloud pressure gradients to the flow within the cloud is emphasised and a simple method of representing their effect is suggested the scheme is able to reproduce the fluxes derived from the cloud resolving model studies where cloud organization by the flow is unimportant inclusion of the parametrization in a version of the meteorological office unified model demonstrates that convective momentum transports play a large role in the momentum balance of the atmosphere generally simulation of the mean atmospheric circulation by the unified model is improved by the inclusion of such transports

hydrocarbon generation as a mechanism for overpressuring in rocky mountain region overpressured reservoirs are present in the deeper parts of most basins in the rocky mountain region a variety of conditions can cause overpressuring however most high pressures in the region are caused by present day or recently active oil and gas generation or generation in the last few million years in low permeability rock successions that still contain organic matter capable of yielding thermally generated hydrocarbons rocks with above normal pressure range from devonian to tertiary and commonly are associated with low permeability tight reservoirs most of the overpressuring occurs in cretaceous and tertiary rocks overpressuring in rocks older than cretaceous is rare and where present only occurs in strata with very rich hydrocarbon source beds such as the d vonian mississippian bakken formation most organically lean pre cretaceous source beds are no longer capable of yielding enough hydrocarbons to maintain abnormal pressure nearly all overpressured reservoirs and source rocks have temperatures of approximately 200 f 93 c or higher in addition available data indicate that hydrocarbon related overpressuring does not generally occur if vitrinite reflectance ro values are less than 0 6 in oil prone strata or less than 0 7 in gas prone strata overpressured gas bearing strata generally have ro values of 0 8 or higher maximum reservoir pressures are about equal to the fracture gradient pressure in the reservoir rocks some vertical fractures in reservoir rocks are probably caused by rapid expulsion of hydrocarbons from the source beds high pressures in the rocky mountain region means that the rock succession is gas or oil saturated and discrete hydrocarbon water contacts are generally not present classical concepts of hydrodynamics do not appear to be applicable to these overpressured successions the optimum depths for exploration are generally the upper 1 000 2 000 ft 305 610 m of the overpressured succession

correlation between deformation lamellae microfractures macrofractures and in situ stress measurements white river uplift colorado dynamic analyses of quartz deformation lamellae and microfractures in lower paleozoic quartzites from the white river uplift record a northwest direction of compression which can be related to joint and fault orientations and in situ stress determinations crystallographic orientations of deformation lamellae resemble those formed in the subbasal i relatively nonselective domain microfractures in quartz grains form orthogonal sets of generally north northeast and west northwest trending fracutres which are approximately normal to bedding the strongest set of microfractures in most samples lies in the 2 plane deduced from deformation lamellae analyses suggesting that the microfractures are extensional features maxima of microfractures correspond to maxima of joints measured at adjacent locations the strikes of prominent west northwest sets of microfractures and joints are subparellel to the dominant northwest strike of faults on the uplift in situ stress measurements conducted in the piceance basin and rangely colorado areas indicate principal stress orientations similar to those determined from quartz deformation lamellae microfractures and joints which are pre uplift to early uplift late laramide fabric elements

analytic representation of the large scale organization of tropical convection the pivotal role of mesoscale organization on the large scale coherence of tropical convection is represented by a nonlinear dynamical model the general model consists of two interlocked systems a mesoscale parameterization of organized convection and a two layer model of large scale equatorial dynamics the lower layer dynamics is rossby gyre like whereas outflow from organized convection maintains the upper layer circulation the transports of zonal momentum in the vertical and meridional directions are key processes an archetype of the general model in spite of being brutally simplified represents the convective organization momentum transport and equatorial superrotation realized by the cloud resolving convection parameterization or superparameterization explicit approach developed by grabowski the mesoscale parameterization is an analytic equivalent of the cloud system resolving models used in this computational approach finally issues in parameterizing convective organization are discussed

simulations of the madden julian oscillation in four pairs of coupled and uncoupled global models the status of the numerical reproduction of the madden julian oscillation mjo by current global models was assessed through diagnoses of four pairs of coupled and uncoupled simulations slow eastward propagation of the mjo especially in low level zonal wind is realistic in all these simulations however the simulated mjo suffers from several common problems the mjo signal in precipitation is generally too weak and often eroded by an unrealistic split of an equatorial maximum of precipitation into a double itcz structure over the western pacific the mjo signal in low level zonal wind on the other hand is sometimes too strong over the eastern pacific but too weak over the indian ocean the observed phase relationship between pre cipitation and low level zonal wind associated with the mjo in the western pacific and their coherence in gen eral are not reproduced by the models the seasonal migration in latitude of mjo activity is missing in most simulations air sea coupling generally strengthens the simulated eastward propagating signal but its effects on the phase relationship and coherence between precipi tation and low level zonal wind and on their geographic distributions seasonal cycles and interannual variability are inconsistent among the simulations such inconsis tency cautions generalization of results from mjo sim ulations using a single model in comparison to observations biases in the simulated mjo appear to be related to biases in the background state of mean pre cipitation low level zonal wind and boundary layer moisture convergence this study concludes that while the realistic simulations of the eastward propagation of the mjo are encouraging reproducing other funda mental features of the mjo by current global models remains an unmet challenge

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

origin of fracture porosity example from altamont field utah the occurrence of natural fracture systems in subsurface rock can be predicted if careful evaluation is made of the geologic processes that affect sedimentary strata during their cycle of burial diagenesis uplift and erosional unloading variations in the state of stress within rock arise for example from changes in temperature pore pressure weight of overburden or tectonic loading hence geologic processes acting on a sedimentary unit should be analyzed for their several contributions to the state of stress and this information used to compute a stress history from this stress history predictions may be made as to when in the burial cycle to expect fracture joint formation what type of fractures extension or shear may occur and which geologic factors are most favorable to development of fractures a stress history is computed for strata of the naturally fractured altamont oil field in utah s uinta basin calculations suggest that fractures formed in extension that the well cemented rocks are those most likely to be fractured that fractures began to develop only after strata were buried to great depth and that the fracture system continued to develop as strata were uplifted and denuded of overburden geologic evidence on fracture genesis and development is in accord with the stress history prediction stress history can be useful in evaluating a sedimentary basin for naturally fractured reservoir exploration plays

aperture size scaling variations in a low strain opening mode fracture set cozzette sandstone colorado the aperture size distribution of a set of opening mode fractures in the cozzette sandstone is complex and cannot be described uniquely by a single equation this study of horizontal core includes aperture size data of macrofractures measured using a hand lens and microfractures measured using scanning electron microscope based cathodoluminescence sem cl macrofractures are poorly cemented and total fracture strain is an order of magnitude lower than the smallest strain values of most previously described vein sets macrofractures in this set therefore resemble typical joints as opposed to veins in most respects although intragranular microfractures compose about 98 of the microfracture population orientation fracture fill and fracture trace characteristics suggest that only transgranular microfractures can be shown to be genetically related to macrofractures aperture size data below 0 012 mm and above 1 mm follow a log normal distribution intermediate size data though relatively sparse suggest a power law aperture size distribution these results support the notion that this fracture set is an intermediate case between typical veins and joints the results also suggest that processes leading to size distributions commonly associated with veins i e power laws may be present in joint sets but over a more limited range bound at small size scales by grain scale effects and above by mechanical layering effects

moment tensor inversion of microseisms from the b sand propped hydrofracture m site colorado abstract we apply a moment tensor inversion algorithm to microseismic events generated by hydrofracturing our dataset consists of microseismic events associated with a hydraulic fracturing experiment conducted at the gri doe m site near rifle colorado the event recordings were from a vertical string of 3 component accelerometer pods that are cemented in a borehole the accelerograms clearly show p and s waves which can be rotated into the sh and sv components to invert the p and s amplitudes for moment tensors we use just the first two peaks after the first arrival using this amplitude information and the average pulse width we formed a symmetric stylized pulse for integration and we inverted for the moment tensor resolution tests revealed that with the source microseism to receiver geometry we have at the m site where all receivers are in one borehole and at the same azimuth from the source we can extract the five deviatoric components of the moment tensor using combinations of p sh and sv amplitudes for example a minimum data set of 3 p wave 2 sv wave and 1 sh wave amplitudes to obtain the sixth component which is the isotropic component requires amplitude information from receivers at another azimuth we studied seven high quality events in detail and tested their results against two alternative source geometries these microseismic events tend to have a major double couple nodal plane aligned parallel to the main hydrofracture plane rather than have their tension t axes aligned parallel to the regional minimum principal compressive stress direction the events have seismic moments m0 on the order of 10 5 nm and moment magnitudes mw of about 2 5

scaling relationships of joint and vein arrays from the burren co clare ireland abstract we present a study of the systematics of veins and joints in carboniferous limestones of the burren ireland scaling relationships were established for fracture arrays mapped from low elevation aerial photographs that image fractures on numerous limestone pavements for areas up to ca 1 km2 the veins and joints occur in the same sequence but have contrasting scaling properties the veins strike north south and cut many beds to form vertically persistent non stratabound arrays they are strongly clustered and have scale invariant geometric properties vein geometries suggest they grew sub critically under relatively high differential stresses during north south directed variscan compression the joints form stratabound arrays with regular spacings that scale with bed thickness they show greater strike variation than the veins and have lognormal length distributions the joints formed during uplift under low differential stress conditions the contrasting scaling properties of the joints and veins are attributed to different overburden stresses at the time of formation the veins formed at greater depths than the joints in conditions that favoured fracture propagation across mechanical discontinuities resulting in the development of non stratabound scaling properties

parametrization of momentum transport by convection i theory and cloud modelling results summary the theory of the mass flux approach to parametrization of convective momentum transport is presented a cloud resolving model is used to simulate momentum transport by ensembles of deep convective clouds in two very different regimes a mid latitude cold air outbreak and tropical convection forced by convergence idealized unidirectional wind profiles are used to simplify interpretation of the results diagnostics relevant to the parametrization problem are presented and it is shown that for both regimes the approximations inherent in the parametrization equations are reasonable the pressure gradients inside clouds play an important role in determining horizontal velocities in the clouds for the cold air outbreak with linear shear the results suggest that these pressure gradients are proportional to the shear and to the up downdraught mass fluxes sensitivity studies suggest that the results are not very sensitive to resolution or parametrization of subgrid scale processes giving some confidence that the results are reasonably accurate for the tropical case with a low level jet the pressure gradients change sign with the wind shear in part i1 of this paper these results will be used to develop and validate a mass flux parametrization of convective momentum transport which is tested in single column and global versions of the meteorological office unified model

regional fractures i a mechanism for the formation of regional fractures at depth in flat lying reservoirs 1 regional fractures may form slowly at depth in extension and parallel to regional horizontal tectonic compression such fracture sets can be common in reservoirs despite the absence of flexure of the strata and are commonly important contributors to reservoir permeability such fractures make good targets for deviated wells high formation pore pressure is crucial to creating low effective confining stresses and brittle rock properties in the reservoirs conditions conducive to fracturing despite deep burial but pore pressure does not exceed the least principal stress and does not cause tensile fracturing the mechanism of natural hydraulic fracturing is incompatible with the characteristics of most regional fracture sets rather many regional fractures form duri g far field compression initiate at locally induced tensile stresses caused by flaws in the rock and propagate in the plane of the maximum and intermediate compressive stresses the differential stress required for initiation and propagation of regional fractures is well below that necessary for shear failure in the presence of high pore pressure fractures can be held open at depth by a tectonic basinwide dilatancy of the strata and the open void space commonly becomes mineralized

coupling of convective momentum transport with convective heating in global climate simulations abstract the effects of convective momentum transport cmt on global climate simulations are examined in this study comparison between two sets of 20 yr 1979 98 integration using the ncar community climate model version 3 ccm3 illustrates that the inclusion of cmt in the convection scheme systematically modifies the climate mean state over the equatorial region the convective momentum tendencies slow down the equatorward flow at higher latitudes near the surface and weaken the equatorial convergence and convection this reduces the convective heating and drying around the equator and produces an improved meridional distribution within the upward branch of the hadley circulation the major heating peak during the boreal winter is moved to south of the equator at about 10 s which is closer to the heat budget residuals of the ecmwf reanalysis data the responses of meridional wind to the reduced heating result in the secondary meridional circulation within the intertropical convergence zone

laramide crustal thickening event in the rocky mountain foreland and great plains the rocky mountain foreland and great plains of the western united states were formerly part of a continental platform adjusted by erosion and deposition in cambrian through jurassic time to near mean sea level and therefore to a near uniform crustal thickness of approximately 33 km today the region stands at regional elevations up to 2 km isostatically supported by a crust exceeding 50 km in thickness reasonable estimates of tertiary sedimentation and laramide strain do not account for more than 15 of the implied thickening however from approximately 70 40 m y b p this region was underlain by a horizontally subducting slab of farallon plate lithosphere moving northeast this slab could have been the cause of the thickening finite difference thermal models with specified kinematics show only a temporary cooling of the base of the north american lithosphere by this slab the excess weight of the slab would have depressed the region plate bending calculations show a quantitative agreement of predicted depression with upper cretaceous isopachs since depression by this slab lasted until the eocene at least the latest cretaceous regression was probably caused by a laramide crustal thickening event the farallon slab might have caused crustal thickening in two ways its excess weight would have drawn in ductile lower crust from surrounding regions however calculations show that this effect is too slow too local and too reversible to explain most of the crustal thickening therefore it seems likely that ductile lower crust was transported from sw to ne by shear stresses which the farallon plate exerted on the base of the north american lithosphere a preliminary finite element calculation based on this hypothesis shows the correct general pattern of crustal thickening an unexpected but encouraging result is that predicted principal compression directions are orthogonal to many laramide basement uplifts

a joint satellite and global cloud resolving model analysis of a madden julian oscillation event model diagnosis 1 in this study a methodology to diagnose a global cloud resolving model gcrm is explored on the basis of a joint analysis with satellite measurements the madden julian oscillation experiment carried out with the nonhydrostatic icosahedral atmospheric model nicam is used as the test bed the nicam output is compared with tropical rainfall measuring mission trmm and cloudsat measurements in terms of composite analysis contoured frequency by altitude diagrams cfads and the joint histogram of cloud top and precipitation top heights it is found in the composite diagram that the gcrm reproduces a slow eastward migration of a convective envelope well comparable to the satellite measurement the gcrm cfad qualitatively reproduces trmm and cloudsat cfads except that the gcrm tends to overly produce snow in deep convection the joint histograms reveal that while the overproduction of snow is evident nicam simulated snow is incapable of producing 94 ghz radar echoes higher than 5 dbz this deficiency can be mitigated by a modification to microphysical parameterization in the way that a proportion of small particles is enhanced in the snow mass spectrum

systematic multiscale models for the tropics systematic multi scale perturbation theory is utilized to develop self consistent simplified model equations for the interaction across multiple spatial and or temporal scales in the tropics one of these models involves simplified equations for intraseasonal planetary equatorial synoptic scale dynamics ipesd this model includes the self consistent quasi linear interaction of synoptic scale generalized steady matsuno webster gill models with planetary scale dynamics of equatorial long waves these new models have the potential for providing self consistent prognostic and diagnostic models for the intraseasonal tropical oscillation other applications of the systematic approach reveal three different balanced weak temperature gradient wtg approximations for the tropics with different regimes of validity in space and time a synoptic equatorial scale wtg sewtg a mesoscale equatorial wtg mewtg which reduces to the classical models treated by others and a new seasonal planetary equatorial wtg spewtg both the spewtg and mewtg model equations have solutions with general vertical structure yet have the linearized dispersion relation of barotropic rossby waves thus these models can play an important role in theories for midlatitude connections with the tropics the models are derived both from the equatorial shallow water equations in a simplified context and also as distinguished limits from the compressible primitive equations in general

large scale organization of tropical convection in two dimensional explicit numerical simulations effects of interactive radiation we examine interactions among radiative processes water vapour clouds and the multi scale organization of tropical convection in two dimensional idealized cloud resolving simulations using planetary scale horizontal domains we extend our earlier study where radiative cooling was prescribed therein deep convection spontaneously organized into two primary scales westward travelling mesoscale convective systems on a scale of a few hundred kilometres and the eastward propagating envelopes of convection spanning thousands of kilometres these envelopes represented large scale convectively coupled gravity waves two dimensional non rotating analogues of equatorially trapped kelvin waves interactive radiation introduces a new mechanism of large scale convective organization weak overturning circulations steered by the mean wind and of a few thousand kilometres in scale gradually develop this overturning is a manifestation of the baroclinic response to horizontal gradients of radiative heating established between the moist and dry regions which causes a spontaneous positive feedback among large scale dynamics water vapour clouds and radiation the mechanism is as follows the convective systems maintain the humidity vapour and cloud in the ascending branch which in turn maintains the differential radiative heating conversely the large scale overturning provides the large scale dynamical forcing that maintains the deep convection this quantifies recent idealized studies that applied convective parametrizations the radiatively driven overturning and the deep convection are modulated by large scale convectively coupled gravity waves responsible for the large scale envelopes reported earlier a series of sensitivity tests including the effects of environmental shear demonstrate the robustness of these results copyright 2002 royal meteorological society

momentum transport by a line of cumulonimbus abstract the vertical transport of horizontal momentum normal to a line of cumulonimbus observed during gate on 14 september 1974 is against the vertical momentum gradient contrary to the predictions of mixing length theory data from repeated aircraft passes normal to the line s axis at heights from 0 15 to 5 5 km are used to document the flux and determine its source the flux is concentrated in roughly a 25 km wide active zone just behind the leading edge of the line in kilometer scale convective updrafts accelerated upward by buoyancy and toward the rear of the line by mesoscale pressure forces the fall in mesoscale pressure from the leading edge to the rear of the active zone is mainly hydrostatic resulting from relatively high virtual temperatures and the 60 degree tilt of the leading edge from the vertical with the clouds at the surface well ahead of those aloft evaluation of the terms in the momentum flux generation equation confirms that the above process reflected by the velocity buoyan