reservoir monitoring and characterization using satellite geodetic data interferometric synthetic aperture radar observations from the krechba field algeria deformation in the material overlying an active reservoir is used to monitor pressure change at depth a sequence of 11 field estimates allows us to construct a measure of diffusive traveltime throughout a reservoir the dense distribution of traveltime values means that we can construct an exactly linear inverse problem for reservoir flow properties application to interferometric synthetic aperture radar insar data gathered over a carbon dioxide c o2 injection site in algeria reveals pressure propagation along two northwest trending corridors an inversion of the traveltimes indicates the existence of two northwest trending high permeability zones the high permeability features trend in the same direction as the regional fault and fracture zones model parameter resolution estimates indicate the features are well resolved

finite difference calculation of traveltimes in three dimensions the traveltimes of first arriving seismic rays through most velocity structures can be computed rapidly on a three dimensional numerical grid by finite difference extrapolation head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 11 percent are found between the results of this technique and ray tracing for a complex but smooth model this scheme has proven useful for earthquake location and shows promise as an inexpensive well behaved substitute for ray tracing in forward modeling and kirchhoff inversion applications

physics and seismic modeling for monitoring co2 storage we present a new petro elastical and numerical simulation methodology to compute synthetic seismograms for reservoirs subject to co2 sequestration the petro elastical equations model the seismic properties of reservoir rocks saturated with co2 methane oil and brine the gas properties are obtained from the van der waals equation and we take into account the absorption of gas by oil and brine as a function of the in situ pore pressure and temperature the dry rock bulk and shear moduli can be obtained either by calibration from real data or by using rock physics models based on the hertz mindlin and hashin shtrikman theories mesoscopic attenuation due to fluids effects is quantified by using white s model of patchy saturation and the wet rock velocities are calculated with gassmann equations by using an effective fluid modulus to describe the velocities predicted by white s model the simulations are performed with a poro viscoelastic modeling code based on biot s theory where viscoelasticity is described by generalizing the solid fluid coupling modulus to a relaxation function using the pseudo spectral method which allows general material variability a complete and accurate characterization of the reservoir can be obtained a simulation that considers the utsira sand of the north sea illustrates the methodology

on the seasonality of the hadley cell abstract the annual march of the climatological mean meridional circulations mmcs in the ncep ncar reanalyses is dominated by two components of roughly comparable mean squared amplitude 1 a seasonally invariant pair of hadley cells with rising motion centered near and just to the north of the equator and subsidence in the subtropics and 2 a seasonally reversing sinusoidally varying solsticial cell with ascent in the outer tropics of the summer hemisphere and subsidence in the outer tropics of the winter hemisphere the meridional structure and seasonal evolution of the solsticial cell are suggestive of a close association with the monsoons these results are consistent with previous analyses of the mean meridional circulation based on radiosonde data

late miocene upward and outward growth of eastern tibet and decreasing monsoon rainfall over the northwestern indian subcontinent since 10 ma 1 many geologic observations suggest that the eastern portion of the tibetan plateau has expanded eastward and grown in height over the past 15 10 ma and other observations suggest that climate over the northwestern indian subcontinent nw india became more arid between 11 and 7 ma we suggest that they are linked higher terrain increased orographic precipitation over eastern tibet which diabatically heated the atmosphere there that heating then forced subsidence to the west via the mechanism proposed by rodwell and hoskins and subsidence suppressed rainfall simple gill model calculations for a heat source displaced from the equator show such subsidence and a regression of july august outgoing long wave radiation olr over southeastern tibet with rainfall shows a negative relationship between eastern tibet and nw india consistent with the proposed link between growth of eastern tibet and diminished south asian monsoon rainfall over the northwestern indian subcontinent

onset of the somali jet in the arabian sea during june 1997 the national aeronautics and space administration scatterometer surface wind vectors are used to describe the rapid onset of the somali jet throughout the arabian sea in june 1997 the time of somali jet onset varied over the arabian sea with june 17 18 the average time the somali jet appeared first in the western arabian sea expanded over 2 weeks to encompass the arabian sea and produced a threefold increase in surface wind convergence in the eastern arabian sea the onset time of the 12 m s 1 isotach preceded by 3 4 days the onset of monsoon rainfall in goa for somali jet wind speeds above 10 m s 1 the 2 day 1 1 sea surface temperature decreased 0 5 c per 1 m s 1 increase in collocated wind speed the somali jet created a north south distribution of ekman pumping and suction in the central arabian sea to enhance the eastward surface current by 0 1 m s 1 the somali jet doubled the southward ekman transport across the southern boundary of the arabian sea in june 1997 when the most intense el nino episode of the century was in its onset phase the southward ekman transport across the southern boundary of the arabian sea was one half that observed since 1992

a three dimensional planetary boundary layer model for the somali jet abstract this paper is an extension of an earlier study on the planetary boundary layer dynamics of the low level monsoonal flow over the arabian sea krishnamurti and wong 1979 where the long term steady state motion field for a boundary layer was determined using a zonally symmetric model with a prescribed pressure field in that study we examined the balance of forces in the surface layer and the planetary boundary layer for regions across the equator across and along the low level somali jet and across an intertropical convergence zone the important role of advective accelerations in the near equatorial balance of forces was demonstrated the important study is based on a three dimensional model that removes the restriction of zonal symmetry this mesoscale fine mesh model with a horizontal resolution of 55 km and a vertical resolution of 200 m is integrated to examine the evolution of three dimensional planetary boundary layer flows for prescribed three dimensional pressure patterns the obs

the mechanical impact of the tibetan plateau on the seasonal evolution of the south asian monsoon the impact of the tibetan plateau on the south asian monsoon is examined using a hierarchy of atmospheric general circulation models during the premonsoon season and monsoon onset april june when westerly winds over the southern tibetan plateau are still strong the tibetan plateau triggers early monsoon rainfalldownstream particularlyoverthebay ofbengalandsouth china the downstreammoist convection is accompanied by strong monsoonal low level winds in experiments where the tibetan plateau is removed monsoon onset occurs about a month later but the monsoon circulation becomes progressively stronger and reaches comparable strength during the mature phase during the mature and decaying phase of monsoon july september when westerly winds over the southern tibetan plateau almost disappear monsoon circulation strength is not much affected by the presence of the tibetan plateau a dry dynamical core with east west oriented narrow mountains in the subtropics consistently simulates downstream convergence with background zonal westerlies over the mountain in a moist atmosphere the mechanically driven downstream convergence is expected to be associated with significant moisture convergence the authors speculate that the mechanically driven downstream convergence in the presence of the

monsoons and the dynamics of deserts the existence of subtropical deserts such as the sahara has often been attributed to the annual mean zonal mean hadley circulation which shows strong descent in the subtropics however the zonal mean hadley circulation shows considerable evolution over the course of the year with very strong subtropical descent during winter but practically no zonal mean subtropical descent during summer when rainfall over the eastern sahara and the mediterranean is least charney 1975 proposed a biosphere albedo feedback mechanism whereby local anthropogenic effects related to over grazing could affect the radiative balance enhancing summertime diabatic descent and leading to desertification of the subtropics in general the present study which uses an idealized model suggests a monsoon desert mechanism for desertification whereby remote diabatic heating in the asian monsoon region can induce a rossby wave pattern to the west integral with the rossby wave solution is a warm thermal structure that interacts with air on the southern flank of the mid latitude westerlies causing it to descend this adiabatic descent is localized over the eastern sahara and mediterranean and over the kyzylkum desert to the south east of the aral sea by the mountains of north africa and south west asia trajectories indicate that the monsoon desert mechanism does not represent a simple walker type overturning cell instead the descending air is seen to be mainly of mid latitude origin it is speculated that the monsoon forced adiabatic descent may result in clear air and therefore a local diabatic enhancement which effectively doubles the strength of descent with this mechanism desertification can be forced by remote changes in monsoon strength rather than by local effects this conclusion is supported by the observed dramatic strengthening of descent over the mediterranean and east sahara during the onset of the asian monsoon and on the longer timescale by relating prehistoric lake levels to milankovitch monsoon forcing the latter may help to explain the perceived discrepancies between the palaeoclimate of the eastern sahara and the strength of a tropic wide monsoon the monsoon desert mechanism may not be confined to the asian monsoon alone and the existence of other monsoon climate regions over the globe may in a similar way explain the observed summertime strengthening of the oceanic sub tropical anticyclones and the existence of western continental deserts and mediterranean type climate regions

crosswell seismic imaging in a contaminated basalt aquifer multiple seismic crosswell surveys have been acquired and analyzed in a fractured basalt aquifer at idaho national engineering and environmental laboratory most of these surveys used a high frequency 1000 10 000 hz piezoelectric seismic source to obtain p wave velocity tomograms the p wave velocities range from less than 3200 m s to more than 5000 m s additionally a new type of borehole seismic source was deployed as part of the subsurface characterization program at this contaminated groundwater site this source known as an orbital vibrator allows simultaneous acquisition of p and s waves at frequencies of 100 to 400 hz and acquisition over larger distances the velocity tomograms show a relationship to contaminant transport in the groundwater zones of high contaminant concentration are coincident with zones of low velocity and high attenuation and are interpreted to be fracture zones at the boundaries between basalt flows the orbital vibrator data show high vp vs values from 1 8 to 2 8 in

modeling tropical convergence based on the moist static energy budget abstract the vertically integrated moist static energy equation provides a convenient starting point for the construction of simple models of the time mean low level convergence in the tropics a vertically integrated measure of the moist static stability the gross moist stability proves to be of central importance minima in this quantity mark the positions of the tropical convergence zones we argue that the positions of these minima are determined by the time mean moisture field which is in turn closely tied to the time mean surface temperature

on large scale circulations in convecting atmospheres the dominant thinking about the interaction between large scale atmospheric circulations and moist convection holds that convection acts as a heat source for the large scale circulations while the latter supply water vapour to the convection we show that this idea has led to fundamental misconceptions about this interaction and offer an alternative paradigm based on the idea that convection is nearly in statistical equilibrium with its environment according to the alternative paradigm the vertical temperature profile itself rather than the heating is controlled by the convection which ties the temperature directly to the subcloud layer entropy the understanding of large scale circulations in convecting atmospheres can therefore be regarded as a problem of understanding the distribution in space and time of the subcloud layer entropy we show that the subcloud layer entropy is controlled by the sea surface temperature the surface wind speed and the large scale vertical velocity in the convecting layer and demonstrate how the recognition of this control leads to a simple physically consistent view of large scale flows ranging from the hadley and walker circulations to the 30 50 day oscillation in particular we argue that the direct effect of convection on large scale circulations is to reduce by roughly an order of magnitude the effective static stability felt by such circulations and to damp all of them

quantitative analysis of time lapse seismic monitoring data at the sleipner co2 storage operation the co2 storage operation at sleipner in the norwegian north sea provides an excellent demonstration of the application of time lapse surface seismic methods to co2 plume monitoring under favorable conditions injection commenced at sleipner in 1996 with co2 separated from natural gas being injected into the utsira sand a major saline aquifer of late cenozoic age co2 injection is via a near horizontal well at a depth of about 1012 m below sea level bsl some 200 m below the reservoir top at a rate approaching 1 million tonnes mt per year with more than 11 mt currently stored

annual intensification of the somali jet in a quasi equilibrium framework observational composites the annual intensification of the somali jet which accompanies the onset of the indian summer monsoon is rapid compared to the evolution of the seasonal insolation forcing using observationally based data sets the dynamic and thermodynamic changes accompanying the onset of this jet are presented the abrupt component of jet onset is shown to occur over ocean about 1000 km east of the east african highlands and is accompanied by increases in both deep convection and baroclinic flow over the off equatorial arabian sea these abrupt changes are well separated from the core of the cross equatorial jet which is located over land adjacent to the east african highlands the onset of the somali jet and the associated monsoon are then examined in a convective quasi equilibrium framework such a framework is consistent with the mean summer state in that peak free tropospheric temperatures are nearly collocated with peak subcloud layer entropies over the northern bay of bengal and adjacent coastal regions jet onset is accompanied by a large o 100 w m 2 increase in surface enthalpy flux over the arabian sea that is nearly collocated with and linearly related to the concurrent increase in deep tropospheric ascent at the same time the highest subcloud entropies shift inland slightly from the bay of bengal and the region of warmest free tropospheric temperatures expands poleward the consistency of all of these changes with a wind evaporation feedback and several other hypothesized mechanisms of abrupt monsoon onset is discussed copyright c 2009 royal meteorological society

gravity monitoring of co2 movement during sequestration model studies sequestration enhanced oil recovery eor petroleum reservoirs have relatively thin injection intervals with multiplefluidcomponentsoil hydrocarbongas brine andcarbon dioxide or co2 whereas brine formations usually have much thicker injection intervals and only two components brine and co2 coal formations undergoing methane extractiontendtobethin3 10 mbutshallowcomparedtoeithereororbrineformations injectingco2intoanoilreservoir decreases the bulk density in the reservoir the spatial pattern of the change in the vertical component of gravity gz is correlated directly with the net change in reservoir density furthermore time lapse changes in the borehole gz clearlyidentifytheverticalsectionofthereservoirwherefluidsaturationsarechanging theco2 brinefront ontheorder of1 kmwithina20 m thickbrineformationat1900 mdepth with 30 co2 and 70 brine saturations respectively produceda 10 galsurfacegravityanomaly suchananomaly would be detectable in the field the amount of co2 in a coal bed methane scenario did not produce a large enough surface gravity response however we would expect that for an industrial size injection the surface gravity response wouldbemeasurable gravityinversionsinallthreescenarios illustrate that the general position of density changes causedbyco2canberecoveredbutnottheabsolutevalueof thechange analysisofthespatialresolutionanddetectability limits shows that gravity measurements could under certaincircumstances beusedasalower costalternativetoseismicmeasurements

ecmwf and ers 1 surface winds over the arabian sea during july 1995 abstract the european centre for medium range weather forecasts ecmwf and institut francais pour la recherche et l exploitation de la mer european remote sensing satellite named ifr2 surface wind velocity data products are compared during july 1995 over the arabian sea substantial differences were found the central positions of the maximum isotach were separated by 450 km and the ecmwf maximum isotach was 2 m s 1 higher than that of ifr2 ifr2 wind components contained about 10 times more variance than ecmwf winds for horizontal distances from 50 to 250 km along the 8 5 n southern boundary of the arabian sea ecmwf southward ekman transport was higher than that of ifr2 by an amount that could be observed with current measurements the ecmwf and ifr2 difference in upward transport of water into the ekman layer computed from wind stress curl was large enough to measure

global sensitivity analysis for crosswell seismic and neutron capture measurements in co2 storage projects abstractquantification of reservoir uncertainty is an essential part of a monitoring design a systematic approach that quantitatively links predicted uncertainties in a monitoring program to the underlying reservoir variability is however needed we developed a methodology for quantifying uncertainty in crosswell seismic monitoring combined with neutron capture logging and applied global sensitivity analysis gsa to compute and rank contributions of uncertain reservoir parameters to the predicted uncertainty of the measurements the workflow is illustrated by a numerical study using a simplified model of a co2 storage site where crosswell measurements have not actually been taken synthetic seismic responses are computed through the integration of multiphase flow a new thermodynamically consistent fluid substitution model and a fast marching eikonal solver we quantified uncertainty in first arrival times to illustrate the potential utility of crosswell seismic surveys and their limitation consiste

gravimetric monitoring of gas reservoir water influx a combined flow and gravity modeling approach knowledge of the magnitude and distribution of water influx can be essential for managing water drive gas fields geophysical fieldwide monitoring can give valuable information particularlyoffshorewherewellcontrolissparseand observationwellsareexpensive advancesintheaccuracyof seafloor time lapse gravimetry have made this method feasible it can quantify which areas are flooded providing information complementary to well monitoring production and 4d seismic data gravimetric monitoring may aid materialbalance calculations which are vital for assessing reservoirdrive mechanism and estimating initial and remaining gas volumes in addition it can constrain reservoir simulation models our goal is to produce better physical insight into typical density changes occurring in water drive gas fields andtheirassociatedsurface gravityresponse itisfeasibleto monitor displacement of gas by water in reservoirs that are only a few meters thick gravimetric monitoring can detect edgewater encroachment in early stages with current accuracy the method is applicable for gas reservoirs of modest size 210 8 m 3 in situ gas volume at medium depths 2k m

ocean atmosphere land feedbacks in an idealized monsoon summary an intermediate complexity atmospheric model coupled with a simple land surface model and a mixedlayer ocean model is used to investigate the processes involved in an idealized monsoon occumng on a single rectangular continent idealized divergences of ocean heat transports are specified as an annual average q flux in this simple coupled configuration the mechanisms that affect land ocean contrast and in turn the seasonal movement of the continental convergence zones are examined these include soil moisture feedbacks cooling of tropical oceans by ocean transport ventilation defined as the import into continental regions of low moist static energy air from ocean regions where heat storage opposes summer warming and the interactive rodwellhoskins mechanism in which rossby wave induced subsidence to the west of monsoon heating interacts with the convection zone the fixed ocean transports have a substantial impact on the continental convection if q flux is set to zero subtropical subsidence and ventilation tend to substantially limit the poleward movement of summer monsoon rainfall when land hydrology feedbacks are active the drying of subtropical continents disfavours continental convection even in the tropics when ocean transports are included tropical oceans are slightly disfavoured as regions for producing convection which by contrast favours continental convection the monsoon circulation then produces moisture transport from the ocean regions that allows substantial progression of convection into the subtropics over the eastern portion of the continent the western portion of the continent tends to have a dry region of characteristic shape this east west asymmetry is partly due to the interactive rodwell hoskins mechanism the ventilation is of at least equal importance in producing east west asymmetry and is the single most important process in limiting the poleward extent of the continental convection zone

time lapse crosswell seismic and vsp monitoring of injected co2 in a brine aquifer seismic surveys successfully imaged a small scale co2 injection 1 600 ton conducted in a brine aquifer of the frio formation near houston texas these time lapse borehole seismic surveys crosswell and vertical seismic profile vsp were acquired to monitor the co2 distribution using two boreholes the new injection well and a pre existing well used for monitoring which are 30 m apart at a depth of 1 500 m the crosswell survey provided a high resolution image of the co2 distribution between the wells via tomographic imaging of the p wave velocity decrease up to 500 m s the simultaneously acquired s wave tomography showed little change in s wave velocity as expected for fluid substitution a rock physics model was used to estimate co2 saturations of 10 20 from the p wave velocity change the vsp survey resolved a large 70 change in reflection amplitude for the frio horizon this co2 induced reflection amplitude change allowed estimation of the co2 extent beyond the monitor well and on three azimuths the vsp result is compared with numerical modeling of co2 saturations and is seismically modeled using the velocity change estimated in the crosswell survey

the influence of cross equatorial pressure gradients on the location of near equatorial convection tomas and webster note that in regions where there is a substantial cross equator surface pressure gradient there is locally anticyclonic absolute vorticity on the low pressure side of the equator and thus the flow in this region meets the parcel criterion for inertial instability they hypothesize that the atmospheric response to this absolute vorticity distribution is a convergence divergence doublet in the boundary layer the convergence centre results in strong convection and thus is very important in determining the strength and location of convection i e the intertropical convergence zones whereas the divergence centre results in suppressed convection in this work a zonally symmetric model of the boundary layer is developed to investigate this hypothesis further an analysis of a linearized version of the model indicates that although the observed flow in these regions meets the parcel criterion for instability it does not satisfy the linear stability criteria because of the stabilizing influence of dissipation and the finite vertical scale much greater shear than that observed is required for linear instability it is noted however that when the parcel criterion is met one of the nonlinear terms which was neglected in the linear analysis may have an important influence on the flow several experiments are performed integrating the full nonlinear model relaxing back to a pressure distribution having a cross equatorial gradient to test whether the observed vorticity wind and convergence distributions can be well simulated it is found that the simulations reach a steady state in which there is a region of locally anticyclonic absolute vorticity on the low pressure side of the equator this absolute vorticity distribution results in an anomalous acceleration of the meridional wind and a convergence divergence doublet similar to that observed by tomas and webster this response is explained as resulting from accelerations that act to bring the zonal flow out of geostrophic balance as it passes through the region of locally anticyclonic absolute vorticity the response of the meridional wind to the strength of the pressure gradient is quasi linear for small and somewhat larger values of forcing but between these values there is a range where the response is highly nonlinear i e large increases in the strength of the meridional wind result from small changes in the pressure gradient it is suggested that this nonlinear response may play a role in the observed sudden onset of the monsoon circulations the nonlinear model is also forced using pressure distributions taken from observations the resulting steady state simulated vorticity wind and convergence distributions closely match the observations for the cases of pressure distributions taken from the east pacific and east atlantic during july when forced using the pressure distribution from the indian ocean region during july the model produces an unrealistically strong meridional wind response some improvement is obtained by including the latitudinally dependent zonal pressure gradient force which is moderately strong in this region finally the model is forced using a pressure distribution taken from observations in the central pacific ocean during july in this case the cross equator pressure gradient is near zero

3d csem modeling and time lapse sensitivity analysis for subsurface co2 storage abstractmonitoring a time lapse geophysical anomaly due to variation in the pore fluid contents of a subsurface reservoir is critical for further development and management however it may be difficult to detect the changes in p wave responses beyond a certain level of saturation a comprehensive 3d finite difference time domain fdtd forward modeling based on idealized subsurface resistivity structures demonstrates the possibility of marine controlled source electromagnetic csem surveying to monitor the movement of subsurface co2 storage we focused on csem sensitivity studies with respect to variations in geometry and or saturation of co2 storage evaluation of the effects of reservoir depths and lithology and detection of co2 leakage from the main storage a 100 lateral expansion from the initial diameter 1500 m of a typical co2 plume with thickness and resistivity of 100 m and 80 m respectively at 850 m below seafloor results in 41 electric field e field magnitude increase at 2500 m s